MULTIPLE CHOICE QUESTIONS ON HOST DEFENCE MECHANISM (IMMUNOLOGY)

1) Based on the principles of the ............................................. theory, each individual lymphocyte possesses a
distinct membrane receptor tailored to a specific antigen. When the antigen binds to its corresponding
receptor, it triggers an immune response targeted specifically against that particular antigen.
a) Clonal selection theory
b) Instructional theory
c) Selective theory
d) Germ theory

2) Immunity is the defense mechanism of the body that protects against foreign pathogens. The immunity
can be classified into innate immunity and acquired immunity.
Which of the following statements is FALSE concerning innate immunity?
a) It exhibits a broad specificity against foreign antigens.
b) It is present before exposure to antigens.
c) It has memory cells.
d) None of the above.

3) Which type of immunity develops after exposure to specific antigens?

a) Acquired immunity
b) Innate immunity
c) Natural immunity
d) Passive immunity

4) Which of the following is not an example of innate immunity?

a) The epidermis (skin)
b) Immune Cells
c) Sebaceous Glands
d) Measles immunity

5) Lysozyme is an enzyme present in the tears and mucous secretion that cleaves
a) Lipopolysaccharides
b) Cellulose
c) Peptidoglycan
d) None of the above

6) Lipopolysaccharides located in the cell membrane of gram-negative bacteria are identified by

..................................., leading to the initiation of an inflammatory immune response.
a) Phagocytosis
b) Antibodies
c) Mucus lining
d) Toll-Like receptors (TLR-2)

7) The cardinal signs of inflammation are rubor (redness), tumor (swelling), calor (heat), and dolor (pain).
Which of the following is the characteristic feature of inflammation response?
a) Vasodilation
b) Increased capillary permeability
c) Recruitment of phagocytosis
d) All of the above

8) Humoral immunity involves the production of:

a) Antibodies by B cells
b) Cytokines by T cells
c) Histamines by neutrophils
d) Memory cells by macrophages

9) The antigen-presenting cells (APCs) play a crucial role in the antibody-mediated and cell-mediated
immune response.
Which of the following is not the characteristic feature of APCs?
a) APCs internalize and degrade antigens
b) APCs present antigens to the T-cells via MHC-II molecules
c) APCs provide a co-stimulatory signal for T-cell activation
d) Excess co-stimulatory signals from APCs lead to hyperactivation of an immune response.

10) Which of the following is not the class of T cells?

a) T-helper cells
b) T-activator cells
c) T-suppressor cells
d) T-cytotoxic cells

11) Which of the following cells produces antibodies?

a) T-cells
b) B cells
c) Plasma cells
d) Memory cells

12) Which of the following is expressed in T cells that interact with antigen epitope?
a) T-cell receptor
b) T-cell antibodies
c) B-cell receptor
d) B-cell antibodies

13) Antibody functions as the effector of the humoral response by antigen binding and neutralizing it. The
antigen can be eliminated by..............................................................................
a) Facilitating the antibodies update by phagocytes
b) Activating complements and inducing cell lysis
c) Preventing the binding and host cell attachment
d) All of the above

14) Which of the following immune cells are not derived from lymphoid progenitor cells?
a) B-cells
b) T-cells
c) Neutrophils
d)Natural Killer cells

15) The development of pluripotent hematopoietic stem cells into different cell types requires the expression
of a different set of genes for lineage determination at appropriate time and order. Various transcription
factor is required for the expression of these genes.
Which of the following statement is TRUE?
a) GATA-1 is required for myeloid lineage
b) Oct-2 is required for B cell differentiation to plasma cells
c) Ikaros is required for erythroid lineage
d) None of the above
16) The different lineage of the lymphocytes can be distinguished by characterizing the expression of their
membrane molecules called the cluster of differentiation (CD).
Which of the following CD is only found in B-cells?
a) CD-4
b) CD-8
c) CD-32
d) CD-45

17) Which of the following CD molecule is present in both cell types of T cells (Th and Tc) and acts as a
receptor for the co-stimulatory signal from APCs?
a) CD28
b) CD4
c) CD2
d) CD45

18) Which of the following CD molecule is a signaling transduction molecule present in lymphoid lineage
cells such as T-cells, B-cells, and NK?
a) CD2
b) CD4
c) CD28
d) CD45

19) Which of the following cell plays a crucial role in antibody-dependent cell cytotoxicity?
a) Macrophage
b) Natural Killer cells
c) B-cells
d) Dendritic cells

20) The tissue-specific macrophage-like tissues are essential for phagocytosis of the antigens.
Which of the following cells are present in the kidney?
a) Mesangial cells
b) Kuffer cells
c) Histiocytes
d) Alveolar macrophages

21) Immunogens are antigens that can evoke an immune response.

Which of the following is not an immunogen?
a) Protein
b) Lipopolysaccharides
c) Hapten
d) Polysaccharides

22) The degree of immunogenicity generally depends on the degree of foreignness.

Which of the following protein are highly conserved among species and have little immunogenicity when
injected into cross-species?
a) Thyroglobulin
b) Collagen
c) Insulin
d)Bovine Serum Albumin

23) Although the degree of immunogenicity generally depends on the degree of foreignness, certain
antigens/tissues are immunogenic against self-antigens.
Name the organ/tissue doing this type of function?
a) Kidney
b) Cornea
c) Heart
d) Collagen

24) Which of the properties of an antigen makes it poorly immunogenic?

a) Distant species origin
b) High molecular weight proteins
c) Heteropolymers
d) Homopolymers

25) B-cells have cell surface antibodies that serve as the recognition molecule, and T cell recognizes when
these antigens are presented via MHC molecules.
Some glycolipids are also recognized by T-cell when presented by a non-MHC molecule known
as..................................
a) CD1
b) CD2
c) CD4
d) CD8

26) The discrete sites that are recognized by antibodies or T cells are called epitopes.
Which of the following is TRUE regarding epitopes?
a) B cell and T cells recognize the same epitopes
b) B cell and T cells recognize different epitopes
c) Epitope contains only sequential amino acids.
d) Epitopes bind to the antibody with covalent bonding

27) The epitopes that are recognized by B-cells are known as B-cell epitopes.
Which of the following is a true statement regarding the B-cell epitope?
a) they are generally hydrophilic amino acids present on the surface
b) they contain both sequential and conformational epitopes
c) they tend to present in the flexible region of the antigens
d) All of the above

28) The epitopes that are recognized by T-cells are known as T-cell epitopes.
Which of the following is a true statement regarding the T-cell epitope?
a) the epitopes are recognized by T-cell as a trimeric complex of TCR, antigen, and MHC molecule.
b) antigen processing is required for its presentation by APC
c) amino acid sequences of T-cell epitopes are generally internal of a protein molecule
d) All of the above

29) Name the congenital defect of thymus development that can lead to T-cell deficiency
a) Graves disease
b) Anaphylaxis
c) DeGeorge's syndrome
d) All of the above

30) Severe Combined immunodeficiency disorder (SCID) is a genetic disorder caused by a defective enzyme
known as...................................................
a) Adenosine deaminase
b) Xanthine oxidase
c) Anaphyloticase
d) Lysozyme
Multiple Choice Questions Answer review
1- a)Clonal selection theory. According to the clonal selection theory, each lymphocyte has a unique
membrane receptor specific to a particular antigen. When the antigen binds to its corresponding receptor, it
initiates an immune response specifically directed against that antigen.
2- c)It has memory cells. Innate immunity is the body's first line of defense against infections and does not
involve memory cells. It provides a general, non-specific defense against a wide range of pathogens and is
present from birth, providing immediate protection without the need for prior exposure to specific antigens.
3-a) Acquired immunity. Also known as adaptive immunity, it is a type of immunity that develops in
response to exposure to specific antigens. Unlike innate immunity, acquired immunity is highly specific to
particular pathogens or antigens.
4-d) Measles immunity. It is an example of acquired immunity is when a person develops immunity to a
specific pathogen after being exposed to it or through vaccination.
5-c)Peptidoglycan
6-d)Toll-Like Receptors (TLR-2). These are a specific type of innate immune system receptor that plays a
crucial role in recognizing various microbial components, such as lipoproteins and lipopeptides from bacteria
and other pathogens.
7-d)All of the above
8-a) Antibodies by B cells
9-d)Excess co-stimulatory signals from APCs lead to hyperactivation of an immune response
10-b) T-activator cells
11-c) Plasma cells
12-a)T-cell receptor
13-d)All of the above
14-c)Neutrophils
15-b) Oct-2 is required for B cell differentiation to plasma cells
16)-c)CD-32
17)-a) CD28
18)-d)CD45
19-b)Natural Killer cells
20)-a) Mesangial cells
21)-c)Hapten
22)-b)Collagen
23)-c) Heart
24)-d)Homopolymers
25)-a)CD1
26)-b)B cell and T cells recognize different epitopes
27)-d)All of the above
28)-d)
29)-c)DeGeorge's syndrome
30)-a)Adenosine deaminase
IMMUNOLOGY: MCQS WITH ANSWERS (EXPLAINED) ON COMPLEMENT PATHWAY

The complement pathway, a cornerstone of immunology, encompasses distinct types, functions, and disease
implications that intricately shape our immune responses. Comprising three main pathways – classical,
lectin, and alternative – this system orchestrates a dynamic interplay of interactions to bolster our defenses
against infections. The classical pathway is triggered by antigen-antibody complexes, while the lectin
pathway responds to pathogen-specific carbohydrates. The alternative pathway, on the other hand, offers a
rapid, antibody-independent response. These pathways collectively contribute to opsonization, inflammation,
and the formation of membrane attack complexes that eliminate threats. Understanding the complement
pathway is pivotal, as deficiencies or dysregulations can lead to various diseases, such as Paroxysmal
Nocturnal Hemoglobinuria (PNH) and autoimmune disorders.

Multiple Choice Questions on Complement Pathway and Immune Response

1) Complements are the proteins that are involved in the clearance of antigens/bacteria.
Which of the following pathway is involved in the adaptive immune response?
a) Alternative Pathway
b) Classical Pathway
c) Lectin Binding Pathway
d) All of the above

2) In the classical pathway, the antibody activated the C1 complex consisting of the C1q, C1r & C1s
subunits.
Which of the following subunit binds to the antibody?
a) C1q
b) C1r
c) C1s
d) All of the above

3) Which of the following isotype antibody is a potent activator of the classical complement pathway?
a) IgM
b) IgA
c) IgE
d) IgG

4) Which of the following C1 subunit has the catalytic activity that cleaves C4 and C2 complement proteins?
a) C1q
b) C1r
c) C1s
d) None of the above

5) In the classical pathway, which of the following complement complex serve as C3 convertase
a) C4aC2a
b) C4bC2b
c) C4bC2a
d) C4aC2b

6) In the classical pathway, after the proteolysis of the C3 complement pathway.

Which component is cleaved by C4bC2aC3b and initiates the formation of membrane attack complex?
a) C5
b) C6
c) C7
d) C8
7) The alternative pathway is activated in response to antigens but does not require antibody interaction. The
following proteins are the component of the alternative pathway, except?
a) C3
b) Factor B
c) Factor D
d) Properdin

8) C3 undergo spontaneous hydrolysis to form C3a and C3b, but they have a short half before encountering
the carbohydrate bacterial antigens only.

Which of the following carbohydrate moieties are present in the mammalian cells to inactivate C3b?
a) Mannose-6-phosphate
b) Sialic acid
c) Sphingosine
d) None of the above

9) Which of the following process is required for the formation of a C3 convertase that amplifies
complement activation?
a) C3b must bind to foreign antigens
b) Factor B must bind to C3b for its proteolysis by Factor D
c) Properdin must bind to the C3bBb complex for stabilization
d) All of the above

10) Certain microorganisms such as Salmonella, Listeria, Neisseria, and Cryptococcus consist of specific
carbohydrate moieties on the surface antigen that activate
a) Alternative Pathway
b) Classical Pathway
c) Lectin Binding Pathway
d) All of the above

11) The membrane attack complex consists of five different complement proteins C5, C6, C7, C8, and C9.
Which of the following subunits bind to the surface and provide a binding site for a subsequent component?
a) C5a
b) C5b
c) C6a
d) None of the above

12) Which of the following complement proteins polymerizes to form a perforin-like structure that stabilizes
membrane attack complex?
a) C6
b) C7
c) C8
d) C9

13) Which of the following component of complement proteins enhances inflammation (anaphylatoxin)?
a) C3a
b) C5a
c) Both of the above
d) None of the above

14) Which of the following complement component facilitate opsonization and phagocytosis?
a) C3a
b) C3b
c) C5a
4) C5b

15) Which of the complement receptor activate phagocytosis by binding to C3b & C4b coated particles
a) CR1
b) CR2
c) CR3
d) CR4

16) Which of the following complement receptor activate a humoral response by promoting the trapping of
an antigen-antibody complex?
a) CR1
b) CR2
c) CR3
d) CR4

17) The deficiency of the complement proteins (C1q, C1q, C1s) or the complement receptors leads to the
accumulation of immune complexes resulting in SLE or vasculitis.
The deficiency affects which of the following complement pathway?
a) Alternative pathway
b) Lectin binding pathway
c) Classical pathway
d) None of the above

18) Lack of complement proteins; factor D and properdin leads to recurrent bacterial infection.
Which of the following pathways is affected in this condition?
a) Alternative pathway
b) Classical pathway
c) Lectin binding pathway
d) None of the above

19) Erythrocytes express the complement receptor help that transports and clear the immune complex from
circulation.
Which of the following complement receptors is expressed in the erythrocytes?
a) CR4
b) CR2
c) CR3
d) CR1

20) Paroxysmal Nocturnal Hemoglobinuria is the condition that manifests as increased fragility of
erythrocytes, leading to chronic hemolytic anemia, pancytopenia, and venous thrombosis.
Which of the following options is associated with PNH?
a) Deficiency of complement protein C9
b) Deficiency of Factor D
c) Deficiency of DAF
d) Deficiency of complement receptor

Multiple Choice Answer:

1- b) Classical Pathway. the classical pathway of the complement system is closely linked to the adaptive
immune response through the interaction between antibodies and antigens. Antibodies (IgM or IgG) bind to
antigens on the surface of pathogens or other foreign substances during the initiation of the classical
pathway.
2- a) C1q, The first component of the classical pathway is the C1 complex, which consists of three subunits:
C1q, C1r, and C1s. When antibodies bind to antigens, the Fc (constant) region of the antibody interacts with
the C1q component of the C1 complex, and C1r and C1s act as protease (enzyme).
3- a) IgM, is a crucial initiator of the classical pathway of the complement system.
4- c)C1s. C1s subunit cleaves complement protein C4 into C4a and C4b fragments and also cleaves C2 into
C2a and C2b fragments.
5- b)C4bC2b, enzyme complex C1s-C4b-C2b, known as the C3 convertase.
6- a)C5
7- a)C3. The alternative pathway can be spontaneously activated on pathogen surfaces without the need for
antibody-antigen complexes. It is initiated by the spontaneous hydrolysis (splitting) of complement protein
C3 within the bloodstream.
8- b)Sialic acid
The carbohydrate moieties present in mammalian cells to inactivate C3b are sialic acids. Sialic acids are
negatively charged carbohydrates that are found on the surface of mammalian cells and play a role in
preventing the uncontrolled activation of the complement system. They provide a mechanism for regulating
the complement cascade and preventing excessive inflammation and tissue damage. Sialic acids on
mammalian cell surfaces can help to inactivate C3b by binding to it and preventing its further activity, thus
protecting the body's own cells from complement-mediated damage.
9- d)All of the above
The formation of a C3 convertase that amplifies complement activation involves multiple steps and
components. Each of the processes mentioned in the options is required for the complete formation and
stabilization of the C3 convertase complex:
a) C3b must bind to foreign antigens: This is an important step in the complement cascade. When C3b binds
to foreign antigens or surfaces, it initiates the alternative pathway of complement activation.
b) Factor B must bind to C3b for its proteolysis by Factor D: This is a key step in the alternative pathway.
Factor B binds to the C3b molecule bound to a foreign surface, and then it is cleaved by Factor D, resulting
in the formation of the C3 convertase C3bBb.
c) Properdin must bind to the C3bBb complex for stabilization: Properdin is a plasma protein that stabilizes
the C3 convertase (C3bBb) complex, preventing its rapid decay and allowing continued activation of the
complement cascade.
All of these processes are essential for the formation and amplification of the C3 convertase, which is a
central component in the alternative pathway of complement activation.
10- c)Lectin Binding Pathway
Certain microorganisms such as Salmonella, Listeria, Neisseria, and Cryptococcus consist of specific
carbohydrate moieties on the surface antigens that activate the complement system. These carbohydrate
moieties can trigger complement activation through pathways such as the lectin pathway, leading to the
immune response against these pathogens. The complement system plays a crucial role in identifying and
eliminating these microorganisms through opsonization, inflammation, and other immune mechanisms
11- b)C5b
Among the options provided, the subunit that binds to the surface and provides a binding site for a
subsequent component in the formation of the membrane attack complex (MAC) is C5b. C5b serves as the
initial component that binds to the target cell membrane. Subsequent components, including C6, C7, C8, and
C9, then assemble onto this complex to form the complete MAC.
12- d)C9
C9 is the complement protein that polymerizes and forms a pore-like structure within the cell membrane
during the assembly of the membrane attack complex (MAC). This perforin-like structure allows ions and
water to enter the target cell, leading to cell lysis and destruction. C9 molecules assemble in a circular
pattern, creating a stable pore that disrupts the integrity of the cell membrane and contributes to the cytolytic
activity of the MAC.
13- c)Both of the above
C3a as an Anaphylatoxin
When the complement system is activated, C3 is cleaved into two fragments, C3a and C3b. C3a acts as an
anaphylatoxin by binding to receptors on mast cells and basophils, triggering the release of histamine and
other inflammatory mediators from these cells. Histamine causes vasodilation, increased vascular
permeability, and smooth muscle contraction. This leads to the characteristic symptoms of inflammation,
including redness, swelling, and increased blood flow to the affected area. C3a also attracts and activates
immune cells, such as neutrophils and eosinophils, to the site of inflammation.
C5a as an Anaphylatoxin:
C5a is generated when C5 is cleaved during the complement cascade. Like C3a, C5a functions as an
anaphylatoxin by binding to receptors on mast cells, basophils, and other immune cells. Binding of C5a to
these receptors triggers the release of histamine and other pro-inflammatory substances, intensifying the
inflammatory response. C5a attracts various immune cells to the site of inflammation, including neutrophils,
monocytes, and macrophages. This accumulation of immune cells helps combat pathogens and clear cellular
debris.
14- b)C3b. C3b fragments can covalently bind to the pathogen's surface or other nearby surfaces, promoting
opsonization and phagocytosis.
15- a)CR1
Complement Receptor 1 (CR1), also known as CD35, is a receptor found on various immune cells, including
phagocytes like macrophages and neutrophils. CR1 binds to complement-coated particles, such as those
opsonized with C3b and C4b. This binding enhances phagocytosis by facilitating the recognition and uptake
of these particles by phagocytic cells. CR1 plays a significant role in enhancing the clearance of opsonized
pathogens and immune complexes, thus contributing to the immune response against infections and other
immune challenges.
16- b)CR2
Complement Receptor 2 (CR2), also known as CD21, is primarily found on B cells and certain subsets of T
cells. CR2 plays a crucial role in the humoral immune response by promoting the trapping of antigen-
antibody complexes, especially those that are opsonized by complement fragments (C3d). When B cells
encounter an antigen-antibody complex, CR2 binds to the C3d portion of the complex. This interaction
enhances the activation of B cells, leading to stronger immune responses, including increased antibody
production and memory cell generation. CR2 is also involved in the germinal center reaction, where B cells
undergo affinity maturation and class switching to produce more effective antibodies.
17- c)Classical pathway
Deficiencies in components of the classical pathway of the complement system, such as C1q, C1r, or C1s,
can lead to impaired clearance of immune complexes. The classical pathway is initiated by antigen-antibody
complexes, and its activation helps to eliminate these complexes from circulation. In SLE and certain
vasculitis conditions, the immune complexes are not efficiently cleared, leading to their accumulation and
deposition in tissues, which contributes to inflammation and tissue damage. This accumulation of immune
complexes is a hallmark of these autoimmune diseases.
18- a)Alternative pathway
The alternative pathway of the complement system is primarily responsible for initiating the complement
cascade in the absence of specific antibody-antigen complexes. Properdin is a key stabilizing factor that
helps in the stabilization of the alternative pathway C3 convertase (C3bBb) complex, which is crucial for
amplifying the complement response. Factor D is involved in the activation of the alternative pathway by
cleaving factor B to its active form, allowing it to bind to C3b and initiate the formation of the C3
convertase.
Lack of factor D and properdin can impair the proper functioning of the alternative pathway, which is
essential for the innate immune response against bacterial infections. Without these components, the
alternative pathway's ability to efficiently recognize and eliminate bacterial pathogens is compromised,
leading to recurrent bacterial infections.

19- d)CR1
Complement Receptor 1 (CR1), also known as CD35, is found on various cell types, including erythrocytes.
CR1 plays a significant role in the immune response by binding to complement-coated particles, such as
immune complexes. In the context of erythrocytes, CR1 helps transport immune complexes from circulation
to the liver and spleen, where they can be cleared by phagocytic cells. This process contributes to the
removal of immune complexes and prevents their accumulation in circulation, which is important for
maintaining immune homeostasis and preventing autoimmune reactions.
20- c)Deficiency of DAF
Paroxysmal Nocturnal Hemoglobinuria (PNH) is a rare acquired disorder of the hematopoietic stem cells. It
is characterized by the absence or deficiency of certain cell surface proteins, particularly those that are
involved in regulating the complement system. One of the key features of PNH is the increased sensitivity of
erythrocytes to complement-mediated lysis, leading to chronic hemolytic anemia.
The condition is associated with the deficiency of complement regulatory proteins, particularly Decay-
Accelerating Factor (DAF, also known as CD55) and membrane inhibitor of reactive lysis (MIRL, also
known as CD59). These proteins help protect cells, including erythrocytes, from complement-mediated lysis
MULTIPLE CHOICE QUESTIONS ON ANTIGEN PROCESSING AND PRESENTATION

1) The cells that display peptides associated with class II MHC molecules to CD4+ Th cells are called
antigen presentation cells. Which of the following is not a professional antigen-presenting cells?
a) Dendritic cells
b) Macrophages
c) B cells
d) Fibroblast

2) The professional antigen-presenting cells have different antigen uptake, constitutive MHC expression, and
co-stimulatory activity. Which of the following statement is true?
a) Dendritic cells constitutively express a high level of class II MHC molecules and co-stimulatory activity,
they can activate naïve T cells.
b) Macrophage must be activated by phagocytosis of particular antigens before they express class II MHC
molecules or co-stimulatory B-47 membrane molecules
c) B cells constitutively express class II MHC molecules but must be activated before they express the co-
stimulatory signal
d) All of the Above

3) The antigenic peptide derived by class I are derived from the endogenous processing pathway.
The researcher performed exposure of different antigens and obtained the following results.
Emetine is a protein synthesis inhibitor and Chloroquine inhibits the endocytosis pathway.
Exposure condition MHC 1 restricted T-cell activation
Infectious Virus +
Inactivated Non-infectious virus -
Infectious virus + Emetine -
Infectious virus + Cholorquine +
Which of the following options is the correct answer?
a) MHC class I antigen presentation requires active infectious virus
b) The viral protein synthesis is required for MHC-Class I- peptide presentation
c) The endocytic pathway is not required for MHC-class I restricted activation
d) All of the above

4) The peptides for presentation on MHC-I are generated by a protease complex called the proteasome.
a) The peptides are targeted for proteolysis with the attachment of ubiquitin
b) Ubiquitin-protein conjugate are recognized and degraded by a complex called proteasome
c) The proteasome-mediated proteolysis is ATP dependent
d) All of the above

5) The antigenic peptide derived by class II is derived from the exogenous processing pathway.
The researcher performed exposure of different antigens and obtained the following results.
Emetine is a protein synthesis inhibitor and Chloroquine inhibits the endocytosis pathway.
Exposure Condition MHC II-restricted T-cell activation
Infectious Virus +
Inactivated Non-infectious virus +
Infectious virus + Emetine +
Infectious virus + Chloroquine -
Which of the following options is the correct answer?
a) MHC class II presentation does not require active virus
b) The endogenous viral protein synthesis is not required for MHC-II peptide presentation
c) Inhibition of endocytic pathway hinders MHC class II-restricted T cell activation
d) None of the above
6) Transporter associated with antigen processing (TAP) is involved in the transport of the antigenic peptide
from the cytosol to the endoplasmic reticulum.
Which of the following is the correct answer?
a) TAP 1 & TAP 2 are class of ABC binding cassette proteins required for transport of processed peptides
and they are highly polymorphic
b) TAP has the highest affinity for a peptide containing 8-10 amino acids and favors hydrophobic amino
acids
c) Define mutation of TAP proteins lead to immunodeficiency and autoimmunity
d) All of the above

7) The chaperone is associated with free class Iα chain facilitate its folding and release after binding to β2
macroglobulin is.........................................
a) Calnexin
b) Calreticulin
c) Tapasin
d) Ubiquitin

8) Which of the following chaperones are bound to MHC class Iα chain and β2 microglobulin and facilitate
the formation of MHC- class Iα, β2 microglobulin, and antigenic peptide trimers?
a) Calnexin & Calreticulin
b) Calreticulin & Tapasin
c) Calnexin & Tapasin
d) Calnexin & Ubiquitin

9) Which of the following mechanism is involved in the internalization of antigen by B cells?

a) Pinocytosis
b) Phagocytosis
c) Receptor-mediated endocytosis
d) All the above

10) Chloroquine is an inhibitor of endocytic processing which...........................................................

a) increases the pH of lysosome and inactivation of lysosomal proteases
b) allosterically inhibit lysosomal proteases
c) inhibits peptide uptake into cells
d) None of the above

11) Before loading an antigenic peptide, MHC molecules exist in.......................................................

a) monomers of α and β chain
b) dimers with an empty peptide-binding site
c) Trimers with peptide binding site with class II-associated invariant peptide
d) None of the above

12) Which of the following non-classical MHC molecule is required for the catalysis of exchange of CLIP
peptide with antigenic peptide?
a) HLA-DI
b) HLA- DM
c) HLA-DQ
d) HLA-DO

13) Which of the following non-classical MHC molecule impede the exchange of CLIP peptide with
antigenic peptide?
HLA-DI
HLA-DM
HLA-DQ
HLA-DO

14) Which of the following is not the characteristic feature of HLA DM?
a) The HLA-DM is widely conserved among mammalian species
b) HLA is not polymorphic
c) HLA DM is present in the endosome
d) HLA is present in the cell surface

15) In B cell, the receptor that mediates the endocytosis of antigen is called........................................
a) Membrane-bound antibody
b) MHC-II molecule
c) CD41 antigen
d) CD20 antigen

16) The fate of the B-cell receptor that mediates antigen endocytosis is known as........................................
a) The antigen is endocytosed and the receptor remains at the surface
b) Both antigen and receptor are endocytosed but the receptor is recycled to the cell surface
c) Both antigen and receptor, processed and degraded
d) None of the above

17) Which of the following is true for the antigenic peptide that is presented via MHC class I and MHC class
II?
a) They are non-covalently but stably bound to MHC
b) They are covalently bound to the MHC
c) The antigen peptide dissociate from MHC once it reaches the cell surface
d) The antigen can be replaced by other peptides on the cell membrane

18) The properties of CD1, a non-classical pathway for antigen presentation is

a) Similar to MHC class I, CD1 interacts with β2 microglobulin
b) The genes are located in chromosome 1
c) The antigen-binding site for CD1 is deeper and more voluminous
d) All of the above

19) CD1 is mainly involved in the presentation of ……………………...... and activation of T cells
a) Peptides
b) Lipopolysaccharides
c) Both
d) None

20) What is the characteristic feature of TAP deficiency?

a) Increased NK cells
b) Increased CD8+ T cells
c) Increased MHC class I expression cell surface
d) None of the above

Multiple Choice Answers Review:

1-d) Fibroblast
2-b) Macrophage must be activated by phagocytosis of particular antigens before they express class II MHC
molecules or co-stimulatory B-47 membrane molecules
3-c) The endocytic pathway is not required for MHC-class I restricted activation
4- d) All of the above
5- d) None of the above
6-d) All of the above
7-a) Calnexin
8-b) Calreticulin & Tapasin
9-c) Receptor-mediated endocytosis
10-a) increases the pH of lysosome and inactivation of lysosomal proteases
11-c) Trimers with peptide binding site with class II-associated invariant peptide
12-b) HLA- DM
13- c) HLA-DQ
14- d) HLA is present in the cell surface
15-a) Membrane-bound antibody
16-b) Both antigen and receptor are endocytosed but the receptor is recycled to the cell surface
17- a) They are non-covalently but stably bound to MHC
18-d) All of the above
19-b) Lipopolysaccharides
20-a) Increased NK cells
MULTIPLE CHOICE QUESTION ON CYTOKINES, INTERFERON & INTERLEUKINS

1) Cytokines regulate the intensity and duration of the immune response by activating or downregulating
both innate and adaptive immune responses.
The mode of action of the cytokine is the following, Except?
a) Autocrine
b) Paracrine
c) Endocrine
d) Cell-autonomous

2) The characteristic properties of cytokines are:

a) pleiotropy and redundancy
b) synergy and antagonism
c) cascade induction and amplification
d) All of the above

3) Which of the following class of cytokine receptors utilize G-protein coupled receptors for its downstream
function?
a) Chemokines receptor
b) Hematopoietic receptor
c) Interferon receptor
d) None of the above

4) Tumor necrosis factor (TNF) is an endogenous pyrogen that induces fever.

Which of the following statement is true regarding TNF, Except?
a) TNF induces IL-1 production for induction of fever
b) TNF induces the synthesis of prostaglandins
c) TNF induces the production of acute-phase proteins
d) TNF level is lower in septic shock

5) Interleukin-1 is an inflammatory cytokine that has the following function, Except?

a) Inflammation
b) Leukocyte adhesion
c) Production of acute phase reactant protein
d) All of the above

6) Chemokines are the structurally homologous cytokines family that regulate lymphocyte migration. Which
of the following is an incorrect statement regarding the cytokines?
a) Chemokines consist of characteristic N-terminal cysteine residues
b) Chemokines are produced by endothelial cells, epithelial cells, and fibroblasts
c) Chemokines are suppressed by microbes, TNF and IL-1
d) Chemokines bind to the heparan sulfate on the endothelial tissue that enables recruitment and trapping of
cells into infection sites

7) Interleukin 12 is a key inducer of the cell-mediated immunity in response to infection by intracellular

pathogens.
Interleukin activate cell-mediated immune response by increasing the synthesis of which of the following
cytokines?
a) TNF
b) Interferon-beta
c) Interferon-gamma
d) Interleukin 1
8) Interferon type I mediate the early innate immune response to viral.
Which of the following viral antigens activates the production of Type I interferon?
a) Capsid protein
b) Double-stranded RNA
c) Double-stranded DNA
d) None of the above

9) Which of the following cytokine antagonizes the function of IL-12 and the absence of specific cytokine in
mice develop inflammatory bowel disease?
a) IL-1
b) IL-2
c) IL-10
d) IFN-gamma

10) Which of the following cytokine is used for the treatment of the chronic granulomatous disease?
a) INF-alpha
b) INF-beta
c) INF-gamma
d) TNF

11) Which of the following cytokine is used for the treatment of viral hepatitis and multiple sclerosis?
a) INF-alpha
b) INF-beta
c) INF-gamma
d) TNF

12) Which of the following interleukin is responsible for T cell expansion after antigen recognition?
a) IL-1
b) IL-2
c) IL-4
d) IL-5

13) Which of the following interleukin stimulate differentiation of Th2 subset and production of IgE?
a) IL-1
b) IL-2
c) IL-4
d) IL-5

14) Which of the following interleukin activates eosinophil that consists of FcR for IgE?
a) a) IL-1
b) IL-2
c) IL-4
d) IL-5

15) Which of the following cytokines stimulate the production of IgA that is required for mucosal immunity?
a) Interferon-gamma
b) Tumor Necrosis Factor
c) Transforming growth factor-beta
d) All of the above

16) Cytokines recognize and engage with their receptors for biological action.
Which of the following is the correct sequence of high-affinity to low-affinity interactions?
a) Antibody> MHC > Cytokine
b) MHC> Antibody > Cytokine
c) Cytokine > Antibody > MHC
d) None of the above

Multiple Choice Question Answers:

1)- d) Cell-autonomous
2)- d) All of the above
3)- a) Chemokines receptor
4)- d) TNF level is lower in septic shock
5)- d) All of the above
6)- c) Chemokines are suppressed by microbes, TNF and IL-1
7)- c) Interferon-gamma
8)- b) Double-stranded RNA
9)- c) IL-10
10)- c) INF-gamma
11)- b) INF- beta
12)- b) IL-2
13)- c) IL-4
14)- d) IL-5
15)- c) Transforming growth factor-beta
16)- c) Cytokine > Antibody > MHC
IMMUNOGLOBULINS STRUCTURE AND FUNCTION

Immunoglobulins, also known as antibodies, are crucial components of the immune system that play a vital
role in defending the body against pathogens. Understanding the structure and function of immunoglobulins
is essential for comprehending their importance in immune responses.
Structure of Immunoglobulins:
Immunoglobulins belong to a larger family of proteins called globulins and are characterized by their Y-
shaped structure. Each immunoglobulin molecule consists of four protein chains: two identical heavy chains
(H chains) and two identical light chains (L chains).
The H chains are further divided into constant (C) and variable (V) regions. The V regions, located at the N-
terminal ends of both H and L chains, are highly diverse and form the antigen-binding site of the
immunoglobulin. The C regions, found in the middle and C-terminal portions of the H and L chains, are
relatively more conserved.
Immunoglobulin Function:
The primary function of immunoglobulins is to recognize and bind to specific foreign substances, known as
antigens. This binding specificity is attributed to the antigen-binding site formed by the variable regions of
the H and L chains.
Upon encountering an antigen, the immunoglobulin undergoes a conformational change that enhances its
ability to neutralize or eliminate the antigen. This can occur through various mechanisms, including:
Neutralization: Immunoglobulins can bind to toxins or viruses, preventing them from interacting with target
cells and neutralizing their harmful effects.
Opsonization: Immunoglobulins can coat bacteria or other pathogens, marking them for recognition and
phagocytosis by immune cells such as macrophages and neutrophils.
Complement Activation: Immunoglobulins can initiate the classical pathway of the complement system,
leading to the recruitment of complement proteins and subsequent destruction of the target.
Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC): Immunoglobulins can bind to target cells, such as
infected cells or cancer cells, and recruit immune cells, such as natural killer (NK) cells, to eliminate the
targeted cells.
The diverse functions of immunoglobulins are mediated by the different classes and subclasses of antibodies,
including IgG, IgM, IgA, IgE, and IgD. Each class has unique properties and effector functions that
contribute to the overall immune response.

Multiple Choice Question on Immunoglobulin Structure, Function

1) Immunoglobulin is the plasma protein that specifically binds to antigens. Identify the region of
electrophoresis that consists of these major immunoglobulins.

a) Alpha region
b) Beta region
c) Gamma region
d) None of the above

2) The five classes of immunoglobulin include the following, except?

a) IgA
b) IgD
c) IgE
d) IgH

3) Which of the following class of immunoglobulin is pentameric structure?

a) IgA
b) IgD
c) IgH
d) IgM

4) Which of the following class of immunoglobulin is dimeric structure?

a) IgA
b) IgD
c) IgH
d) IgM

5) The IgA and IgMs consist of which of the following chain can allow its polymerization?
a) H chain
b) L chain
c) J chain
d) V chain

6) The monomeric immunoglobulin consists of heterodimers of heavy (H) and light (L) chains bound
together by non-covalent interaction and disulfide bonds.
Which of the following is the antigen-binding site?
a) Fab
b) Fc
c) Hinge region
d) None of the above

7) The hinge region of the immunoglobulin consists of the disulfide bond that held the heterotetramer
together. Also, it contributes to the flexibility of the antibody chain.
Which of the following antibody class do not have a hinge region?
a) IgA
b) IgD
c) IgE
d) IgG

8) The hypervariable complementarity determining region (CDR) is responsible for which of the following
function?
a) binding to antigen
b) binding to FcR
c) binding to complement
d) None of the above

9) Identify the protease that results in two different fragments of antibodies namely Fab and Fc fragments as
shown in the figure below:

a) Pepsin
b) Trypsin
c) Papain
d) Fucin

10) Identify the protease that results in two different fragments of antibodies namely Fab and Fc fragments as
shown in the figure below:
a) Pepsin
b) Trypsin
c) Papain
d) Fucin
11) The variable heavy and light chain makes up the antigen recognition region which consists of six
complementarity determining regions (CDRs) (three from each heavy and light chain).
In addition, a stretch of amino acid sequence also known as the framework region...................................
a) assist in the recognition of antigen
b) act as a scaffold to support CDR
c) are highly variable
d) None of the above

12) The variable heavy and light chains make up the antigen recognition region.
Which of the following is mostly involved in antigen binding?
a) Variable light chain
b) Variable heavy chain
c) Both of the above
d) None of the above

13) The contact area of the antigen binding area may consist of a protrusion or depression that
complementarity matches the antigen.
This contact area span approximately ............................. based on well-studied Lysozyme/anti-Lysozyme
interaction.
a) 15-22 amino acids
b) 5-12 amino acids
c) 25-60 amino acids
d) None of the above

14) The antigen-antibody interactions are considered inducible which means

a) The antigen binding site has performed a site that exactly fits the antigen.
d) The antigen binding site is rigid
c) The antigen binding site undergoes conformation changes after contact with the antigen
d) None of the above

15) Which of the following antibody have four constant regions (CH1, CH2, CH3, CH4)?
a) IgA
b) IgD
c) IgG
d) IgM

16) The effector function of the antibody requires its Fc region. The Fc region binds to cells or proteins to
mediate its function.
Which of the following is the effector function of the antibody?
a) Antigen binding to antibodies promotes opsonization
b) Antigen binding to antibody activates complement
c) Antigen binding to antibody activates cell cytotoxicity
d) All of the above

17) Which of the following immunoglobulins are secretory and present in the milk?
a) IgG
b) IgM
c) IgA
d) IgE

18) The receptor that is responsible for the transport of IgAs across the epithelial barriers:
a) Poly Fc receptor
b) Poly Ig receptor
c) Poly Fab receptor
d) All of the above

19) Which of the following antibody is produced as a primary immune response and have higher valency to
remove clear antigens?
a) IgM
b) IgG
c) IgA
d) IgE

20) Which of the following is the passive immunity transferred from the mother to its offspring?
a) Transplacental transfer of IgGs
b) Transfer of IgAs in the milk
c) Both a & b
d) None of the above

21) Which of the following antigen-bound antibodies bind to the Fc receptor present on the basophils and
tissue mast cells, and release various pharmacoactive mediators involved in anaphylaxis?
a) IgA
b) IgD
c) IgM
d) IgE

22) The Fc receptor is a plasma membrane glycoprotein that binds to different immunoglobulin and triggers
effective functions.
Which of the following Fc receptor is involved in the transfer of IgG from mother to fetus?
a) Fc€R
b) FcRN
c) FcµR
d) FcγR

23) The immunoglobulin superfamily is the group of membrane proteins that possess one or more
homologous immunoglobulin domains.
Which of the following is NOT an immunoglobulin superfamily?
a) T cell receptor
b) beta2 microglobulin
c) Insulin receptor
d) Platelet-derived growth factor

24) B-cell receptors consist of membrane-bound immunoglobulin and a small heterodimer protein required
for signaling.
Which of the following is the heterodimer protein?
a) Igα & Igβ
b) Igµ & Igγ
c) Igα & Igγ
d) None of the Above

25) Multiple Myeloma is characterized by excessive production of immunoglobulin and the presence of a
light chain in urine.
Which of the following cells are responsible for the production of immunoglobulin?
a) T cells
b) Plasma cells
c) B-cells
d) Dendritic cells

26) Which of the following complement protein binding to IgG facilitates phagocytosis?
a) C2a
b) C2b
c) C3a
d) C3b

27) Which of the following subclass of IgG molecule is the most potent activator of the complement
pathway?
a) IgG1
b) IgG2
c) IgG3
d) IgG4

28) Which of the following subclass of IgG does not readily cross the placental barriers?
a) IgG1
b) IgG2
c) IgG3
d) IgG4

29) Which of the immunoglobulin isotype have the shortest half-life?

a) IgG
b) IgM
c) IgA
d) IgE

30) Which of the immunoglobulin isotype have the longest half-life?

a) IgG
b) IgM
c) IgA
d) IgE

Multiple Choice Answers:

1-c)Gamma region
Immunoglobulins are often referred to as gamma globulins because, during plasma protein electrophoresis,
they migrate and concentrate in the gamma region of the albumin/globulin separation pattern. This term,
"gamma globulin," reflects the localization of immunoglobulins in the specific region of the electrophoretic
pattern where they are observed.

2-d)IgH
Five classes of immunoglobulins are IgG, IgG, IgE, IgD, IgA
IgG (Immunoglobulin G): IgG is the most abundant class of immunoglobulins in the blood and tissue fluids.
It plays a crucial role in immune defense against bacteria, viruses, and toxins. IgG can cross the placenta,
providing passive immunity to the fetus.
IgA (Immunoglobulin A): IgA is primarily found in secretions such as saliva, tears, breast milk, and mucous
membranes. It provides protection at mucosal surfaces, preventing pathogens from entering the body. IgA
exists in both monomeric form (found in blood) and dimeric form (found in secretions).
IgM (Immunoglobulin M): IgM is the first immunoglobulin produced during an initial immune response. It
is a pentamer (consisting of five monomers) and is efficient at clumping together pathogens. IgM is involved
in the early stages of neutralizing and eliminating microbes.
IgD (Immunoglobulin D): IgD is found in low concentrations in the blood and is primarily expressed on the
surface of B cells. Its exact function is not entirely clear, but it is thought to play a role in B cell activation
and differentiation.
IgE (Immunoglobulin E): IgE is involved in allergic reactions and immune responses against parasites. It is
present in low concentrations in the blood but has a high affinity for receptors on mast cells and basophils.
When IgE binds to an allergen, it triggers the release of inflammatory mediators, leading to allergic
symptoms.
3-d)IgM
IgM exists as a pentamer, which means it is made up of five individual antibody subunits joined together.
The subunits are connected by a J chain and held together by disulfide bonds. This pentameric structure
gives IgM its characteristic shape.
4-a)IgA
Two IgA Monomers: sIgA is composed of two IgA monomers, each consisting of two heavy (H) chains and
two light (L) chains. The heavy chains in IgA are denoted as α (alpha) chains, and the light chains can be
either kappa (κ) or lambda (λ) chains.
5-c)J chain
J Chain: The two IgA monomers in sIgA are connected by a polypeptide called the J chain. The J chain helps
stabilize the dimeric structure and is responsible for the binding of the secretory component (SC) to IgA.
The J chain is a polypeptide that is primarily associated with IgM antibodies. It plays a role in the
polymerization and structural stabilization of IgM molecules. The J chain helps connect the individual IgM
monomers, promoting the formation of pentameric IgM structures.
6-a)Fab
Each Fab region is composed of one complete light chain and the variable (V) and constant (C) regions of
one heavy chain of the antibody molecule. The V regions of both the heavy and light chains contribute to the
formation of the antigen-binding site. Fab region consists of the antigen-binding side that is variable and
confers diversity specificity and affinity of the antibody.
7-c) IgE
The hinge region of an antibody is a flexible segment that connects the Fab (antigen-binding fragment) and
Fc (crystallizable fragment) regions.
Location: The hinge region is located between the two Fab regions of an antibody molecule. It is found in the
"middle" of the antibody structure, connecting the arms of the Y-shaped antibody molecule.
Amino Acid Composition: The hinge region is composed of a relatively long stretch of amino acids that vary
in length and composition among different antibody classes. For example, IgG antibodies have a longer
hinge region compared to IgM antibodies.
Flexibility: The hinge region is highly flexible due to the presence of amino acids that lack secondary
structure, such as proline and glycine. This flexibility allows the Fab arms to move independently of each
other, increasing the range of motion and enabling the antibody to bind to antigens at different angles.
IgE does not have a flexible region between the Fab and Fc regions. Instead, IgE has a relatively short and
rigid linker region that connects the Fab and Fc portions
8-a) binding to antigen
CDRs are specific segments within the variable (V) domains of both the heavy and light chains of an
antibody molecule. There are three CDRs in each chain, designated as CDR1, CDR2, and CDR3. CDRs play
a crucial role in the binding of antibodies to antigens. They form the antigen-binding site within the variable
regions of the antibody, directly interacting with the target antigen.
9-c) Papain
Papain cleaves the antibody molecule at the hinge region, which is a flexible segment that connects the Fab
(antigen-binding fragment) and Fc (crystallizable fragment) regions. The cleavage occurs specifically at the
disulfide bonds present in the hinge region.
10-a)Pepsin
Pepsin digestion of an antibody produces F(ab')2 fragment.
11-b)act as a scaffold to support CDR
12-b) Variable heavy chain
The heavy chain and light chain of the antibody molecule work together to form the antigen-binding site.
The heavy chain contributes a larger portion to the antigen-binding site, while the light chain complements it.
13-a) 15-22 amino acids
The antigen contact area on an antibody involves the complementarity-determining regions (CDRs) within
the variable regions of both the heavy and light chains. These CDRs, particularly CDRs 1, 2, and 3, form
loops that protrude from the antibody structure and directly interact with the antigen. The CDRs contribute to
the specificity and affinity of the antibody-antigen interaction.
14-c) The antigen binding site undergoes conformation changes after contact with the antigen
15-d) IgM
Not all antibody isotypes have a distinct CH4 domain. For example, IgG and IgD antibodies have CH1, CH2,
and CH3 domains, while IgM antibodies have CH1, CH2, and CH3 domains followed by additional constant
domains known as CH4-like domains.
16-d) All of the above
Opsonization: The Fc region can bind to specific receptors on immune cells, such as phagocytes (e.g.,
macrophages and neutrophils), through a process called opsonization. This opsonization enhances the
phagocytosis of pathogens, promoting their clearance from the body.
Antibody-Dependent Cellular Cytotoxicity (ADCC): The Fc region can also interact with Fc receptors on
certain immune cells, such as natural killer (NK) cells. This interaction triggers ADCC, where the NK cells
recognize the antibody-coated target cells (e.g., infected or tumor cells) and induce their destruction.
Complement Activation: Some antibody isotypes, such as IgG and IgM, can activate the complement system
through their Fc regions. A complement system is a group of proteins that, when activated, leads to the
destruction of pathogens via various mechanisms, including direct lysis, opsonization, and inflammation.
Neonatal Fc Receptor (FcRn) Binding: The Fc region interacts with the neonatal Fc receptor (FcRn) in
specific tissues and cells. This interaction plays a critical role in the transport of antibodies across epithelial
barriers, such as the placenta (providing passive immunity to the fetus) and the intestinal mucosa (facilitating
the transfer of antibodies from breast milk to the infant).
Modulation of Immune Responses: The Fc region can influence the magnitude and quality of immune
responses. It can regulate the activation and function of immune cells, modulate inflammation, and
contribute to immune regulation and tolerance.
17-c) IgA
Secretory IgA (sIgA) is a specialized form of immunoglobulin A (IgA) antibody that is primarily found in
mucosal secretions, such as saliva, tears, colostrum (first milk produced by mammary glands after giving
birth), and mucosal surfaces of the respiratory, gastrointestinal, and genitourinary tracts.
18-b) Poly Ig receptor
The receptor responsible for the secretion of IgA antibodies across mucosal epithelial cells is called the
polymeric immunoglobulin receptor (pIgR). The pIgR is a transmembrane protein expressed on the
basolateral surface of epithelial cells lining mucosal tissues, such as the respiratory, gastrointestinal, and
genitourinary tracts.
The polymeric immunoglobulin receptor binds to the dimeric form of IgA antibodies, known as secretory
IgA (sIgA). This binding occurs in the lamina propria, which is the connective tissue underlying the mucosal
epithelium. The pIgR interacts with the J chain of sIgA, which stabilizes the dimeric structure, allowing it to
be transported across the epithelial layer.
After binding to sIgA, the pIgR undergoes internalization and is transported through the epithelial cell via
transcytosis. The pIgR-bound sIgA is transported within vesicles across the cell and is subsequently released
on the apical surface of the epithelial cell. During transcytosis, a portion of the pIgR, known as the secretory
component (SC), remains associated with the transported sIgA, forming the secretory IgA complex.
19-a)IgM
IgM is a pentameric structure with 10 antigen-binding sites.
20-b)Transfer of IgAs in the milk
21-d)IgE
IgE-mediated anaphylaxis is a severe and potentially life-threatening allergic reaction that occurs when the
immune system overreacts to an allergen in individuals sensitized to it. This type of anaphylaxis is primarily
mediated by the immunoglobulin E (IgE) antibody class.
Here's how IgE-mediated anaphylaxis occurs:
Sensitization: Initially, an individual is sensitized to a specific allergen through exposure. The immune
system recognizes the allergen as foreign and produces specific IgE antibodies against it.
Allergen re-exposure: Upon re-exposure to the same allergen, the allergen binds to the IgE antibodies
already present on the surface of mast cells and basophils, which are types of immune cells involved in
allergic responses.
Cross-linking and activation: When the allergen binds to multiple IgE antibodies on the mast cells or
basophils, it causes cross-linking of the IgE-receptor complexes. This cross-linking triggers the release of
inflammatory mediators, including histamine, leukotrienes, prostaglandins, and cytokines, from the mast
cells and basophils.
Systemic effects: The released inflammatory mediators cause a rapid and widespread allergic reaction
throughout the body. This leads to a range of symptoms that can include hives, swelling (angioedema),
difficulty breathing, wheezing, low blood pressure, gastrointestinal distress, and in severe cases, loss of
consciousness and cardiovascular collapse.
22)-a) FcRn
FcRn is responsible for the transfer of maternal IgG antibodies across the placenta to provide passive
immunity to the developing fetus. The FcRn receptor in the placenta binds to IgG antibodies and transports
them from the maternal circulation into fetal circulation.
23-c) Insulin receptor
The immunoglobulin superfamily (IgSF) includes several protein families and subgroups, some of which are:
Immunoglobulins (antibodies): The IgSF includes the immunoglobulin proteins, which are involved in
recognizing and binding to specific antigens in immune responses. Antibodies are composed of Ig domains
and are produced by B cells as part of the adaptive immune system.
Cell Adhesion Molecules (CAMs): CAMs are proteins involved in cell-cell and cell-extracellular matrix
interactions. They play critical roles in processes such as cell migration, tissue development, and immune
cell activation. Examples of CAMs in the IgSF include neural cell adhesion molecules (NCAMs) and
intercellular adhesion molecules (ICAMs).
Co-stimulatory Molecules: Certain proteins in the IgSF act as co-stimulatory molecules and modulate
immune cell activation. For example, CD28 and CTLA-4 are IgSF proteins expressed on T cells that regulate
T cell activation and immune responses.
Signaling Receptors: Many receptors involved in cell signaling belong to the IgSF. Examples include
receptors of the tumor necrosis factor (TNF) receptor superfamily, such as CD40 and CD95 (Fas), which
play roles in immune regulation and cell death signaling.
Neural Cell Recognition Molecules: The IgSF also includes molecules involved in neural development and
synaptic function. Examples include neural cell adhesion molecules (NCAM) and contactins, which mediate
interactions between neurons and contribute to neural circuit formation.
24-a)Igα & Igβ
Igα (CD79a) and Igβ (CD79b) are transmembrane proteins that help in signal transduction.
25-b)Plasma cells
Plasma cells are specialized cells derived from activated B lymphocytes (B cells) that play a crucial role in
the immune response. They are primarily responsible for the production and secretion of antibodies, also
known as immunoglobulins (Igs).
26-d)C3b
C3b can covalently bind to the surface of pathogens or immune complexes that are bound by IgG antibodies.
This process is called opsonization, where C3b acts as an opsonin, marking the target for recognition and
uptake by phagocytic cells, such as macrophages and neutrophils. The binding of C3b to the Fc region of
IgG-coated antigens enhances the efficiency of phagocytosis by promoting the interaction between the target
and the phagocyte's complement receptors.
27-c)IgG3
IgG3 antibodies have a longer hinge region, making them more flexible and capable of binding to multiple
antigenic sites simultaneously. They are potent activators of the complement system and are effective against
viral infections. IgG3 antibodies are also associated with autoimmune diseases.
28-b)IgG2
IgG2 antibodies have limited ability to cross the placental barrier compared to other IgG subclasses, such as
IgG1. The placental barrier serves as a protective barrier between the maternal and fetal bloodstreams,
allowing essential nutrients and oxygen to pass through while preventing the transfer of potentially harmful
substances.
The transport of IgG antibodies across the placenta occurs through a specialized transport mechanism called
neonatal Fc receptor (FcRn)-mediated transcytosis. FcRn is expressed on the syncytiotrophoblast cells of the
placenta, which are responsible for facilitating the transfer of maternal IgG antibodies to the developing
fetus.
29-d)IgE
The half-life of IgE antibodies, also known as immunoglobulin E, is relatively short compared to other
immunoglobulin classes, such as IgG. The exact half-life of IgE can vary among individuals and depends on
various factors, including physiological conditions and the presence of specific allergens.
30-a)IgG
IgG: IgG antibodies have the longest half-life among the immunoglobulin classes, ranging from about 21 to
28 days. This extended half-life allows IgG antibodies to provide sustained protection and long-term
immunity.
IgA: The half-life of IgA antibodies is relatively shorter compared to IgG. The estimated half-life of IgA in
the bloodstream is around 5 to 6 days. However, it's important to note that the half-life of secretory IgA,
which is found in mucosal secretions, can vary and may be shorter due to degradation in the mucosal
environment.
IgM: IgM antibodies have a relatively short half-life compared to IgG. The half-life of IgM is estimated to be
around 5 to 7 days. IgM antibodies are usually the first antibodies produced during an immune response and
serve as the initial defense against pathogens.
IgE: IgE antibodies have the shortest half-life among the immunoglobulin classes. The half-life of IgE is
relatively rapid, ranging from just a few hours to a couple of days. This short half-life helps regulate the
allergic response and prevents prolonged activation of mast cells and basophils.
MULTIPLE CHOICE QUESTION ON B CELL PROLIFERATION AND MATURATION

1) The lymphoid stem cells commit to B cell lineage and differentiate into pro-B cells in the bone marrow.
Which of the cell surface marker is expressed in pro-B cells?
a) CD25
b) CD25R
c) CD45
d) CD45R

2) Stromal cells present in the bone marrow are required for the proliferation and survival of B cells. Which
of the following is the function of stromal cells?
a) They interact with pro B cells via VCAM-1 ligand on the stromal cells.
b) Stromal cells secrete IL-7 that induces the pro-B cell to mature into pre-B cells.
c) Both of the above
d) None of the above

3) During the B cell maturation, which of the following stage expresses a surrogate light chain complexed
with the heavy chain?
a) Pro-B cell
b) Pre-B cell
c) Immature B cell
d) Mature B cell

4) Which of the following cell surface marker is not expressed throughout the B cell maturation process from
Pro B cell to Mature B cell?
a) CD19
b) Igα/Igβ
c) CD24
d) IgD/IgM

5) During the pre-B cell stage of the maturation process, the µ heavy chain rearrangement is followed by the
light chain.
All of the following statements are correct, EXCEPT
a) Once the heavy chain is synthesized surrogate light chain forms complex
b) The surrogate light chain/heavy chain complex formation signals are required for light chain
rearrangement
c) The surrogate light chain/heavy chain complex signals prevent rearrangement of other heavy chains and
enable the allelic exclusion
d) The surrogate light chain remains complex with a heavy chain until B cell maturation

6) B1 B cells are self-renewing B cell subsets.

Which of the following is true regarding B1 B cells?
a) B1 B cells compose 95% of the total B cell population
b) B1 B cells express numerous IgD molecules in their cell surface
c) CD5 is an indispensable component of the B1 lineage
d) B1 population responds poorly to carbohydrate antigens

7) Thymus-independent antigens activate B cells without the help of T-helper cells.

These molecules include;
a) Lipids
b) Lipopolysaccharides
c) Polysaccharides
d) Proteins

8) Which of the following is correct regarding the activation of B cells by thymus-independent antigens (TI)?
a) Exposure to TI antigen leads to a weaker response than thymus-dependent (TD) antigens.
b) The activation of B cell results in the secretion of IgMs
c) TI antigens may serve as mitogens for B cell proliferation
d) All of the above

9) Which of the following is not true regarding thymus-dependent (TD) antigens?

a) Induce isotype switching
b) Induce affinity maturation
c) Possess immunological memory
d) Always induce polyclonal activation of B cells

10) In addition to the primary signal generated for antigen binding to the B cell receptor, the thymus-
dependent B cell activation requires a secondary signal.
The second signal is provided by..............................................
a) Igα/Igβ
b) B cell CD40 interaction with T cell CD40L
c) CD 8 interaction with MHC molecule
d) None of the above

11) The B cell receptors interact with the B cell co-receptors for effective signaling.
What is the component of the B cell coreceptor complex?
a) CD19, CD 21 (CR 2) & CD81
b) CD19, CD45 & CTLA-4
c) CD10, CD22 & CD81
d) None of the above

12) Which of the following cell surface marker constitutively expressed on B cells deliver a negative signal
for B cell activations?
a) CD22
b) CD40
c) Igα
d) Igβ

13) A patient presented with a history of recurrent respiratory tract infection and exhibited a reduced
concentration of all classes of immunoglobulins. The genetic testing shows a mutation of the RAG1 &
RAG2 genes.
What is the function of RAG1 and RAG2 proteins?
a) Signal B cell activation
b) Rearrange heavy chains of immunoglobulins
c) Inducing Affinity maturation
d) Induce Isotype switching

14) Omenn syndrome is characterized by the presence of pruritic skin, fever, lymphadenopathy, anemia, and
eosinophilia.
Which of the following condition may present as Omenn syndrome?
a) RAG gene deficiency
b) X-linked CD40 ligand deficiency
c) CD40 deficiency
d) None of the above
15) A patient visited a hospital with recurrent sinopulmonary infection. The laboratory evaluation showed a
marked deficiency of circulating B lymphocytes and decreased immunoglobulin levels.
The genetic testing showed the mutation of brk (breast tumor kinase)gene.
What is the function of brk gene?
a) Brk is involved in isotype class switching
b) Brk is a tyrosine kinase that functions BCR signaling pathway
c) Brk is involved in affinity maturation
d) All of the above

Multiple Choice Question Answers

1- d) CD45R
2- c) Both of the above
3- b) Pre-B cell
4- d) IgD/IgM
5- d) The surrogate light chain remains complex with a heavy chain until B cell maturation
6- c) CD5 is an indispensable component of the B1 lineage
7- d) Proteins
8- d) All of the above
9)- d) Always induce polyclonal activation of B cells
10)- b) B cell CD40 interaction with T cell CD40L
11)- a) CD19, CD 21 (CR 2) & CD81
12)- a) CD22
13)- b) Rearrange heavy chains of immunoglobulins
14)- a) RAG gene deficiency
15)- b) Brk is a tyrosine kinase that functions BCR signaling pathway
MULTIPLE CHOICE QUESTION ON T CELL DEVELOPMENT, DIFFERENTIATION, AND
ACTIVATION

1) T cells (T lymphocytes) are crucial in the recognition of antigens presented by self-MHC. The T cell
progenitors undergo proliferation and differentiation in the thymus and form a mature T cell.
Which of the following organ is the origin of T cell progenitors?
a) Thymus
b) Hepatocytes
c) Bone marrow
d) None of the above

2) What is the characteristic feature of progenitor T cells that have migrated to the thymus?
a) They express T cell receptor/CD3 complex
b) They express CD28 cell adhesion molecule
c) They express CD4 or CD8 co-receptor
d) None of the above

3) Which of the following cell adhesion molecule is present in the T cell progenitors required for homing
these cells into the thymus?
a)CD25
b) CD44
c) IL-2
d) CTLA-4

4) Pre- T cell receptor complex consists of the β chain of TCR & CD3 molecules that are formed during the
proliferation of T cells.
The function of the pre-TCR complex includes all of the following, except?
a) signal productive rearrangement of TCR β for further proliferation
b) suppress further rearrangement of β chain (allelic exclusion)
c) prepare cells for rearrangement of α chain
d) commit T cells for CD4 or CD8 positive T cells

5) Which of the following is the process for T cell development and maturation?
a) Rearrangement of T cell receptor and expression of coreceptors
b) Positive selection of thymocytes bearing receptors that are capable of binding to self-MHC molecules
(MHC restriction)
c) Negative selection ensures the affinity receptor self MHC or MHC antigen complex is eliminated (self-
tolerance)
d) All of the above

6) During the differentiation of T lymphocytes, the double-positive cells are directed to become CD4 + T
cells & CD8+ T cells which are MHC II & MHC I restricted respectively.
Which of the following process might be the correct for T cell differentiation?
a) Intrinsic model- multiple interactions of MHC with double-positive (CD4+ & CD8+) instruct the cell to
differentiate
b) Stochastic model- CD4 or CD8 expression in switched of randomly
c) Both A and B
d) None of the above

7) The activation of T cell requires the interaction of MHC/peptide of TCR/CD3 complex activation requires
the expression of.................................................
a) Transcription factors such as c-Fos, c-Myc, c-Jun, etc.
b) Interleukins such as IL-2, IL-3, and IL-6
c) Adhesion molecules such as CD28, CTLA-4
d) All of the above

8) Which of the following cytoplasmic tail of CD4 or CD8 coreceptors are required for phosphorylation of
ITAM present in CD3 molecules?
a) Lck
b) ZAP70
c) LAD
d) None of the above

9) The cell surface proteins on T cell bind to B7 on the antigen-presenting cells and serve as a secondary
signal.
Which of the following statement is true regarding the secondary signal?
a) CD28 is a protein that binds to B7 on APC that acts as costimulatory signals for T cell activation
b) CTLA-4 is a protein that binds to B7 on APC that acts as a suppressor signal for T cell activation
c) Both
d) None

10) Which of the cytokines function in an autocrine manner and induce T cell proliferation after engagement
of TCR with antigens interaction and presence of secondary signal?
a) IL-1
b) IL-2
c) IL-3
d) IL-4

11) Cytokines such as IL-2, IFN-γ, and TNF-β, play an important role in cell-mediated cytotoxicity, and
delayed hypersensitivity.
Which of the following subset of T helper cells are involved in the process?
a) T helper 1 CD4+
b) T helper 2 CD4+
c) T helper 1 CD8+
d) T helper 2 CD8+

12) Cytokines such as IL-4, IL-5, IL-6 & IL-10 play an important role in B cell activation and humoral
immune response
a) T helper 1 CD4+
b) T helper 2 CD4+
c) T helper 1 CD8+
d) T helper 2 CD8+

13) The regulatory or suppressor T cells express the specific cell surface marker for its function. It is
a) CD4+ CD25+
b) CD4+ CD25-
c) CD4 - CD8 - CD25 +
d) CD4 + CD8 + CD25 +

14) The activated T cells undergo activation-induced cell death (AICD).

Which of the following is the effector molecule that is a response for AICD?
a) IL-2
b) Fas/Fas ligand
c) IL-4
d) INF-γ
15) T-cell receptor engagement with antigenic peptide MHC may induce T cell activation or the clonal
anergy.
Which of the following interaction favors T cell activation?
a) Fas/Fas ligand
b) B-7 & CTLA-4 interaction
c) B-7 & CD28 interaction
d) B-7 & CD 8 interaction

Multiple Choice Answers with Explanation:

1-c) Bone marrow
The origin of T cell progenitors is the bone marrow. However, these progenitor cells migrate to the thymus
where they undergo proliferation and differentiation to form mature T cells.

2-d) None of the above

Progenitor T cells that have migrated to the thymus do not express any of the markers listed in the answer
choices. These cells are called double-negative thymocytes because they do not express either CD4 or CD8
co-receptors, which are required for T cell activation. These cells undergo further differentiation in the
thymus, and some of them develop into T cells that express either CD4 or CD8 co-receptor, which are
involved in the recognition of antigen presented by MHC class II or MHC class I molecules, respectively.
The expression of T cell receptor/CD3 complex is a characteristic feature of all T cells, including progenitor
T cells that have migrated to the thymus. CD28 cell adhesion molecule is expressed on T cells after
activation and is involved in T cell activation and co-stimulation.
3-b) CD44
CD44 is a cell adhesion molecule that is expressed on the surface of T cell progenitors and is required for
homing these cells into the thymus. CD25 is the alpha chain of the IL-2 receptor and is expressed on
activated T cells. IL-2 is a cytokine that is produced by activated T cells and is important for the proliferation
and survival of T cells. CTLA-4 is a protein receptor that is expressed on activated T cells and regulates T
cell activation by competing with CD28 for binding to CD80 and CD86 on antigen-presenting cells.
4-d) commit T cells for CD4 or CD8 positive T cells
The pre-TCR complex plays an essential role in T cell development. It consists of the TCR β chain and CD3
molecules, and its function includes the following:
a) Signal productive rearrangement of TCR β for further proliferation b) Suppress further rearrangement of β
chain (allelic exclusion) c) Prepare cells for rearrangement of α chain
However, the pre-TCR complex does not commit T cells for CD4 or CD8 positive T cells. The commitment
of T cells to the CD4 or CD8 lineage occurs after successful rearrangement of the α chain and positive
selection in the thymus.5-d) All of the above
6-c) Both A and B
The activation of T cells requires a complex series of interactions and signaling events. The primary signal
for T cell activation is the interaction of the T cell receptor (TCR) with a peptide antigen presented by major
histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APCs). This
interaction activates the TCR/CD3 complex, which in turn triggers a series of intracellular signaling events.
One of the earliest events is the activation of transcription factors such as c-Fos, c-Myc, and c-Jun, which
help to initiate T cell proliferation and differentiation. Additionally, the activation of T cells requires the
presence of certain cytokines, such as interleukins like IL-2, IL-3, and IL-6, which play important roles in
promoting T cell growth and differentiation. Finally, adhesion molecules such as CD28 and CTLA-4 are also
involved in T cell activation, as they facilitate the interactions between T cells and APCs that are necessary
for proper T cell function.
7-d) All of the above
The phosphorylation of ITAMs (Immunoreceptor Tyrosine-based Activation Motifs) present in the CD3
complex is critical for T cell activation. CD4 and CD8 coreceptors do not directly phosphorylate the ITAMs
but instead play a role in enhancing T cell receptor (TCR) signaling.
The cytoplasmic tail of CD4 and CD8 coreceptors binds to the non-catalytic region of Lck, a Src family
tyrosine kinase that is constitutively associated with the cytoplasmic tails of the CD4 and CD8 molecules.
Upon TCR engagement, the Lck kinase activity is activated, leading to the phosphorylation of ITAMs
present in the CD3 complex.
Once phosphorylated, the ITAMs serve as docking sites for the recruitment and activation of ZAP70 (Zeta-
chain-associated protein kinase 70), another tyrosine kinase that propagates downstream signaling events
leading to T cell activation.
8-a) Lck
The cytoplasmic tail of CD4 and CD8 coreceptors do not directly phosphorylate the ITAMs
(Immunoreceptor Tyrosine-based Activation Motifs) present in the CD3 complex. Instead, the
phosphorylation of ITAMs is carried out by the Lck kinase, which is constitutively associated with the
cytoplasmic tails of CD4 and CD8 coreceptors.
Upon engagement of the T cell receptor (TCR) with its antigen, Lck is activated and phosphorylates the
ITAMs present in the CD3 complex. Once phosphorylated, the ITAMs act as docking sites for ZAP70 (Zeta-
chain-associated protein kinase 70), which is recruited and activated by the phosphorylated ITAMs.
ZAP70 then phosphorylates downstream signaling molecules, ultimately leading to T cell activation.
Therefore, the correct answer to the question is (a) Lck, as it is the kinase responsible for the initial
phosphorylation of ITAMs present in the CD3 complex.
9-c) Both
Both CD28 and CTLA-4 can bind to B7 on antigen-presenting cells (APCs) and modulate T cell activation in
different ways.
CD28 is a costimulatory receptor on T cells that binds to B7 molecules (CD80 or CD86) on APCs. This
interaction provides a crucial "second signal" that is necessary for full T cell activation and promotes the
proliferation, survival, and cytokine production of activated T cells. Without this costimulatory signal, T cell
activation can be aborted, leading to tolerance and immune suppression.
On the other hand, CTLA-4 (cytotoxic T-lymphocyte antigen 4) is another receptor on T cells that also binds
to B7 molecules on APCs. However, CTLA-4 has a higher affinity for B7 molecules than CD28 and acts as a
negative regulator of T cell activation. When CTLA-4 is engaged by B7 molecules, it inhibits T cell
activation, leading to T cell anergy (inactivation) or apoptosis (cell death).
Therefore, both CD28 and CTLA-4 can bind to B7 on APCs and modulate T cell activation in different
ways: CD28 acts as a costimulatory signal for T cell activation, while CTLA-4 acts as a suppressor signal for
T cell activation.
10-b) IL-2
IL-2 (Interleukin-2) is a cytokine that is produced by activated T cells and plays a critical role in T cell
proliferation and differentiation. After the engagement of TCR with antigens and the presence of a secondary
signal (e.g., CD28-B7 interaction), activated T cells upregulate the expression of IL-2 and its receptor (IL-
2R) on their surface.
IL-2 binds to the IL-2R on the surface of the same T cell (autocrine signaling) and induces a signaling
cascade that leads to T cell proliferation, survival, and differentiation into effector T cells. The autocrine
production of IL-2 is critical for the expansion and maintenance of antigen-specific T cells during an
immune response.
11- a) T helper 1 CD4+
T helper 1 (Th1) CD4+ cells are a subset of helper T cells that secrete cytokines such as IL-2, IFN-γ, and
TNF-β. These cytokines promote cell-mediated immunity, including the activation and differentiation of
cytotoxic T lymphocytes (CTLs) and the induction of delayed-type hypersensitivity (DTH) reactions.
IL-2, produced by Th1 cells, is critical for the expansion and differentiation of both CD4+ and CD8+ T cells
during cell-mediated immunity. IFN-γ and TNF-β, also produced by Th1 cells, enhance the cytotoxic activity
of CTLs and macrophages, leading to the destruction of infected or cancerous cells.
In contrast, T helper 2 (Th2) CD4+ cells primarily secrete cytokines such as IL-4, IL-5, and IL-13, which
promote humoral immunity and eosinophil-mediated responses. Therefore, Th2 cells are not involved in cell-
mediated cytotoxicity and delayed hypersensitivity.
T helper 1 CD8+ cells and T helper 2 CD8+ cells do not exist as distinct subsets. CD8+ T cells, also known
as cytotoxic T lymphocytes (CTLs), directly mediate cell-mediated immunity and cytotoxicity, but do not
produce cytokines in the same way that CD4+ helper T cells do.
12-b) T helper 2 CD4+
T helper 2 (Th2) CD4+ cells are a subset of helper T cells that secrete cytokines such as IL-4, IL-5, IL-6, and
IL-10. These cytokines play a critical role in the activation and differentiation of B cells, leading to the
production of antibodies and the promotion of humoral immunity.
IL-4, produced by Th2 cells, stimulates B cell proliferation, class switching to IgE and IgG1, and
differentiation into plasma cells. IL-5, also produced by Th2 cells, promotes the survival, proliferation, and
activation of eosinophils and plays a critical role in the defense against helminthic parasites.
IL-6, produced by both Th2 and Th1 cells, stimulates the differentiation of B cells into antibody-secreting
plasma cells and the production of acute-phase proteins by hepatocytes. IL-10, produced by Th2 cells,
inhibits the activation of macrophages and dendritic cells, leading to a decrease in pro-inflammatory cytokine
production.
In contrast, T helper 1 (Th1) CD4+ cells primarily secrete cytokines such as IFN-γ, TNF-β, and IL-2, which
promote cell-mediated immunity and the activation of macrophages and cytotoxic T cells.
T helper 1 CD8+ cells and T helper 2 CD8+ cells do not exist as distinct subsets. CD8+ T cells, also known
as cytotoxic T lymphocytes (CTLs), directly mediate cell-mediated immunity and cytotoxicity, but do not
produce cytokines in the same way that CD4+ helper T cells do.
13- a) CD4+ CD25+
The specific cell surface marker expressed by regulatory or suppressor T cells is (a) CD4+ CD25+.
Regulatory T cells (Tregs) are a subset of CD4+ T cells that play a crucial role in maintaining immune
tolerance and preventing autoimmune diseases. They express high levels of CD25, the alpha chain of the
interleukin-2 receptor (IL-2Rα), which is required for their development and function.
CD25 is also expressed by other activated T cells, but Tregs express it constitutively at high levels, allowing
them to compete for limited amounts of IL-2 and thereby suppress the activation and proliferation of other T
cells.
14-b) Fas/Fas ligand
The effector molecule that is responsible for activation-induced cell death (AICD) in activated T cells is
Fas/Fas ligand.
Fas (also known as CD95) is a cell surface receptor that belongs to the tumor necrosis factor (TNF) receptor
superfamily. Its ligand, Fas ligand (FasL), is expressed on activated T cells, natural killer (NK) cells, and
some other cell types.
When FasL binds to Fas on the surface of a target cell, it triggers a signaling cascade that leads to caspase
activation and apoptosis (programmed cell death). This process is important for regulating the immune
response and preventing the proliferation of autoreactive T cells that could cause autoimmune disease.
15-b) B-7 & CTLA-4 interaction
B7 molecules (B7-1 and B7-2) are expressed on the surface of antigen-presenting cells (APCs) and bind to
CD28 on the surface of T cells. This interaction provides the second signal required for T cell activation,
which is necessary in addition to the first signal provided by T cell receptor engagement with antigenic
peptide MHC.
CD28 is a costimulatory receptor that enhances T cell proliferation and survival by inducing the production
of cytokines such as IL-2. In contrast, CTLA-4 (cytotoxic T-lymphocyte-associated protein 4) is another
receptor on T cells that binds to B7 molecules, but it has an inhibitory effect on T cell activation by
competing with CD28 for binding to B7 and signaling for T cell anergy.
MCQS ON IMMUNOLOGY OF T CELL RECEPTORS (TCR GENE STRUCTURE AND T CELL
FUNCTIONS):

T cell receptors (TCRs) are cell surface proteins expressed on the surface of T cells, a type of white blood
cell involved in immune responses. TCRs play a crucial role in recognizing and binding to antigens, which
are foreign substances that activate the immune system.
The structure of TCRs consists of two protein chains, known as alpha (α) and beta (β) chains, which are
linked together and form a heterodimer. Each TCR has a unique combination of α and β chains that
determine its antigen specificity. The diversity of TCRs is generated through genetic recombination during T
cell development, allowing T cells to recognize a wide range of antigens.
When a TCR encounters an antigen presented on the surface of an antigen-presenting cell (APC), such as a
dendritic cell or macrophage, it binds to the antigen with high specificity. This binding interaction between
the TCR and antigen is critical for initiating an immune response. The TCR signaling cascade is then
activated, leading to T cell activation, proliferation, and differentiation into effector T cells that carry out
specific immune functions.

1) T cells express a transmembrane protein that recognizes the peptide-loaded MHC (pMHC) to activate T
cell-mediated immune response.
The T-cell receptor is a...........................................................
a) protein of immunoglobulin superfamily
b) seven-transmembrane G protein family
c) tyrosine kinase receptor superfamily
d) None of the above

2) T cell receptor is a heterodimer consisting of...........................................

a) alpha and beta chain
b) gamma and delta chain
c) Both of the above
d) None of the above

3) Which of the following statement is FALSE regarding the T-cell receptor?

a) The alpha and beta chains of TCR are proteins of the immunoglobulin superfamily
b) Both alpha and beta chains consist of one variable domain and one constant domain
c) The TCR resemble Fab fragment of an immunoglobulin
d) The variable region is present in the C terminal region of the TCR

4) Which of the following is NOT the characteristic feature of T cell receptor

a) T-cell lineage Exclusivity
b) Affinity Maturation
c) The combinatorial joining of VDJ
d) Somatic hypermutation

5) Gamma/delta T cell receptors are present in a subset of T-cells and play role in the unconventional
recognition of antigens.
All of the following statements are correct, EXCEPT
a) The gamma/delta T-cell receptors are co-expressed with alpha/beta T-cell receptors
b) The gamma/delta T cell receptors undergo allelic exclusion when alpha/beta are expressed and vice versa
c) The gamma/delta T cell receptors recognize the phospholipid antigens
d) All of the above

6) Which of the following statement is true regarding the TCR gene organization and rearrangement?
a) The alpha & gamma genes consist of multiple variables (V), joining (J), and one constant gene
b) The beta & delta genes consist of multiple variables (V), diversity (D), joining (J) genes, and one constant
gene.
c) Both of the above
d) None of the above

7) Which of the following process contribute to the diversity of TCR?

a) Somatic hypermutation
b) Junctional flexibility
c) Genetic recombination
d) None of the above

8) Once the TCR binds to the pMHC, the signal transduction mediates the T cell activation via CD3
molecules. The CD3 molecules consist of..................................................
a) Delta & Epsilon heterodimer
b) Gamma and Epsilon heterodimer
c) Zeta homodimer
d) All of the above

9) The alpha/beta chain of TCR has three complementarity determinant regions CDR1, CDR2, and CDR3.
Which of the following CDR binds to the antigen peptide?
a) CDR1
b) CDR2
c) CDR3
d) All of the above

10) Which of the following is NOT the function of the T-cell receptor?
a) Antigen Recognition
b) Facilitate binding of co-receptor
c) Serve as the signal transducer
d) Induce signal transduction via a CD3 protein complex

11) Which of the following CD3 molecule is required for assembly of TCR-CD3 complex into the plasma
membrane?
a) Gamma
b) Delta
c) Epsilon
d) Zeta

12) Which of the following protein of the TCR/CD3 complex do not consist of the ITAM domain required
for signal transduction?
a) alpha/ beta chain of TCR
b) gamma/epsilon heterodimer of the CD3 complex
c) delta/epsilon heterodimer of the CD3 complex
d) Zeta homodimer of the CD3 complex

13) Which of the following subunits have three ITAM domains?

a) Gamma
b) Delta
c) Epsilon
d) Zeta

14) In addition to the TCR-CD3 complex, the T cell activation requires the engagement of co-receptors with
the MHC of the antigen-presenting cells. Which of the following co-receptor binds to MHC-I APC
a) CD4
b) CD8
c) CD20
d) None of the above

15) In addition to the TCR-CD3 complex, the T cell activation requires the engagement of co-receptors with
the MHC of the antigen-presenting cells. Which of the following co-receptor binds to MHC-II APC
a) CD4
b) CD8
c) CD20
d) None of the above

Multiple Choice Answers Review:

1-a) protein of immunoglobulin superfamily
2-c) Both of the above
3-d) The variable region is present in the C terminal region of the TCR
4-d) Somatic hypermutation
5-a) The gamma/delta T-cell receptors are co-expressed with alpha/beta T-cell receptors
6-c) Both of the above
7-b) Junctional flexibility
8-d) All of the above
9-c) CDR3
10-c) Serve as the signal transducer
11-d) Zeta
12- a) alpha/ beta chain of TCR
13-d) Zeta
14-b) CD8
15-a) CD4
MCQ ON IMMUNODEFICIENCY DISEASES/IMMUNODEFICIENCY DISORDERS

It refers to the disorders characterized by a weakened or impaired immune system. These disorders leads an
individual more susceptible to infections and other diseases because their immune system is unable to
adequately defend against microbial infections.

1. Which of the following is a rare and severe form of immunodeficiency where individuals lack T cells and
B cells?
a) DiGeorge Syndrome
b) Wiskott-Aldrich Syndrome (WAS)
c) Severe Combined Immunodeficiency (SCID)
d) Common Variable Immunodeficiency (CVID)

2. Wiskott-Aldrich Syndrome (WAS, an X-linked disorder) is associated with which of the following
condition?
a) Hypertension
b) Asthma
c) Diabetes mellitus
d) Eczema

3. Which of the following is not a primary immunodeficiency disorder?

a) Acquired Immunodeficiency Syndrome (AIDS)
b) Common Variable Immunodeficiency (CVID)
c) DiGeorge syndrome (thymic hypoplasia)
d) Wiskott-Aldrich Syndrome (WAS)

4. All of the following are the humoral immunodeficiencies, except

a) Immunodeficiencies with hyper IgM
b) X-Linked Agammaglobulinemia (XLA)
c) DiGeorge syndrome (thymic hypoplasia)
d) Selective immunoglobulin deficiencies (IgM, IgG, IgA)

5. Which of the following immunodeficiency is only seen in infant males leading to recurrent pyogenic
bacterial infection?
a) Severe Combined Immunodeficiency (SCID)
b) Multiple sclerosis
c) X-Linked Agammaglobulinemia (XLA)
d) Diabetes mellitus

6. Which of the following best describes the Shwachman-Diamond syndrome/disorder?

a) The genetic disorder in which phagocytes are unable to kill certain bacteria and fungi (chronic
granulomatous syndrome)
b) The disorder of pancreas and bone marrow
c) A rare immunodeficiency where individuals lack T cells and B cells (combined immunodeficiency)
d) A rare disorder with recurrent skin staphylococcal infections and pulmonary infections (elevated IgE
levels in childhood)

7. Chronic mucocutaneous candidiasis is caused by which of the following type of

immunodeficiency/disorder?
a) Cellular immunodeficiency
b) Humoral or B cell deficiency
c) Phagocytosis disorder
d) Complement component (C3, C6, C7, C80 disorder
8. Which of the following is the correct statement regarding the Nezelof's syndrome (combined
immunodeficiency with immunoglobulin) ?
a) The disorder of pancreas and bone marrow
b) Abnormal immunological response to Candida albicans
c) Disorder with pigmentation of skin, hair and eyes is decreased with recurrent pyogenic infections
d) T cell and B cell deficiency with recurrent bacterial, viral, fungal and protozoal infections

9. Which of the following gram positive bacteria are the common bacteria responsible for eczema and
pneumonia in individuals with Hyper- IgE syndrome (high IgE level) ?
a) Bacillus cereus and Clostridium perfringens
b) Actinomyces israelii and Nocardia asteroides
c) Staphylococcus aureus and Streptococcus pyogenes
d) None of the above

10. What are the possible factors for secondary immunodeficiency?

a) Cytotoxic drugs
b) Metabolic disorders
c) Malnutrition
d) All of the above

Answers:
1. c) Severe Combined Immunodeficiency (SCID)
2. d) Eczema, it is a skin disorder
3. a) Acquired Immunodeficiency Syndrome (AIDS), it is a secondary immunodeficiency because the
immune system is impaired or weakened by other disease or treatment.
4. c) DiGeorge syndrome (thymic hypoplasia), it is a cellular immunodeficiency that results in
Underdevelopment of the thymus and parathyroid glands due to a chromosomal disorder where 22
chromosome is missing.
5. c) X-Linked Agammaglobulinemia (XLA)
6. b) The disorder of pancreas and bone marrow
7. a) Cellular immunodeficiency, cell mediated immunity to Candida albicans is deficient
8. d) T cell and B cell deficiency with recurrent bacterial, viral, fungal and protozoal infections
9. c) Staphylococcus aureus and Streptococcus pyogenes
10. d) All of the above
MCQS ON IMMEDIATE AND DELAYED HYPERSENSITIVITY

Immediate and delayed hypersensitivity reactions are two distinct immune responses that occur in response
to specific triggers, such as allergens or antigens. Immediate hypersensitivity, also known as Type I
hypersensitivity, results in an immediate and rapid reaction upon exposure to the trigger. This type of
hypersensitivity involves the release of histamine and other mediators, leading to symptoms like itching,
swelling, and wheezing. It is crucial to identify and avoid allergens that trigger immediate hypersensitivity
reactions to manage symptoms effectively.

Delayed hypersensitivity, on the other hand, is characterized by a delayed onset, typically occurring within
24 to 72 hours after exposure. This type of hypersensitivity involves the activation of T cells and the release
of cytokines, leading to inflammation and tissue damage. Delayed hypersensitivity reactions are commonly
seen in conditions like contact dermatitis and certain autoimmune disorders.
1) Hypersensitivity reactions are broadly classified into four different types.

Which of the following hypersensitivity occurs via IgE antibody?

a) Type I hypersensitivity
b) Type II hypersensitivity
c) Type III hypersensitivity
d) Type IV hypersensitivity

2) The T helper 1 cell releases cytokines to activate macrophage or T cells and cause direct cellular damage.
Which of the following hypersensitivity reactions are mediated by sensitized T helper-1 cells?
a) Type I hypersensitivity
b) Type II hypersensitivity
c) Type III hypersensitivity
d) Type IV hypersensitivity

3) Which of the following hypersensitivity reactions is a result of massive deposition of immune complex in
various tissues, and can induce complement activation and inflammation responses?
a) Type I hypersensitivity
b) Type II hypersensitivity
c) Type III hypersensitivity
d) Type IV hypersensitivity

4) Which of the following hypersensitivity reactions involve antibody-directed complement activation and
antibody-dependent cell cytotoxicity?
a) Type I hypersensitivity
b) Type II hypersensitivity
c) Type III hypersensitivity
d) Type IV hypersensitivity

5) When allergen crosslinks with IgE bound to the Fc receptor on the mast cells, the allergen induces the
release of mediators.
Which of the following receptor have a high affinity towards IgE?
a) FcεRI
b) FcεRII
c) Both of the above
d) None of the above

6) A hereditary predisposition of the development of immediate hypersensitivity reaction against common

environmental antigens are called.........................
a) Atrophy
b) Atopy
c) Anergy
d) Synergy

7) Which of the following domain present in the Fc region of IgE molecule enables the binding of
glycoprotein receptors on the surface of the basophils and mast cells?
a)CH1
b)CH2
c) CH3
d) CH4

8) The high-affinity FcεRI receptor functions in signal transduction, activation, and degranulation of
chemical mediators such as histamine, leukotrienes, and prostaglandins for the mast cells.
Which of the following intracellular messenger serves this function?
a) Ca++
b) cAMP
c) cGMP
d) None of the above

9) The persistent level of which of the following second messenger inhibits the degranulation of the mast
cells and release of the mediators of anaphylaxis?
a) Ca++
b) cAMP
c) cGMP
d) None of the above

10) Which of the following is not an example of Type I hypersensitivity reaction?

a) Asthma
b) Allergic Rhinitis
c) Systemic Lupus Erythematosus
d) Atopic Dermatitis

11) The type I early response occurs within minutes of allergic response.
Which of the following is the early mediator of type I hypersensitivity reaction?
a) Histamine
b) Leukotrienes
c) Prostaglandins
d) All of the above

12) The type I late response occurs hours later and involves the following mediators.
a) IL4
b) IL-5
c) TNF-α
d) All of the above

13) All of the following drugs are involved in increased production or maintenance of cAMP level to prevent
anaphylaxis, EXCEPT:
a) Theophylline
b) Epinephrine
c) Cromolyn sodium
d) Cortisone
14) During a blood transfusion, ABO incompatibilities lead to the recognition of A or B antigens present on
the RBC resulting in complement-mediated cell lysis.
Which of the following antibody isotype is primarily involved in this type II hypersensitivity reaction?
a) IgG
b) IgM
c) IgE
d) IgA

15) Erythroblastosis fetalis is a severe form of hemolytic disease developed when Rh+ fetus expresses Rh
antigen on its blood that the mother does not express.
Which of the following condition is true regarding this condition?
a) During the first pregnancy, the exposure of Rh antigen leads to the generation of memory cells and the
IgG response that is harmful during the subsequent pregnancy
b) The condition may be prevented by infusing Rh IgG and reducing exposure to Rh antigen within 24-48
hours of pregnancy
c) Plasmapheresis may be used to remove the antibodies from the circulation
d) All of the above

16) Which of the following drugs can induce all four types of hypersensitive reactions?
a) Penicillin
b) Sulfonamides
c) Local anesthetics
d) Salicylates

17) Which of the following the disease is not the example of type III hypersensitivity reaction?
a) Systemic Lupus Erythematosus
b) Rheumatoid Arthritis
c) Good Pasture’s syndrome
d) Down Syndrome

18) All of the following statement regarding Type III hypersensitivity reaction is true, EXCEPT:
a) Antigen-antibody forms a large complex and is deposited in the nearby tissue
b) Immune complex activate the complement system and anaphylatoxins
b) The anaphylatoxin such as C3a, C3b recruits neutrophils at the site of immune complex deposition
c) Neutrophils and macrophages clear the immune complexes and tissue damage

19) Which of the following statement is not true regarding the sensitization phase of delayed-type
hypersensitivity (DTH)?
a) The sensitization phase begins 1-2 weeks after the primary contact with antigens
b) T cell undergo activation and clonal expansion after interacting with antigen-MHC complex
c) CD8+ T Helper-1 cells are primarily activated after exposure to antigen
d) CD4+ T Helper-1 cells are primarily activated after exposure to antigen

20) Which of the following statement is not true regarding the effector phase of delayed-type
hypersensitivity (DTH)?
a) The response generally peaks at 48-72 hours after a second exposure to the antigen
b) T Helper 2 cells secrete antibodies and activate antibody-dependent cell cytotoxicity
c) T Helper 2 cells secrete a variety of cytokines that recruit and activate macrophages
d) DTH response becomes self-destructive to the intense response that is visible as the granulomatous
reaction.

Bonus Question:
Which of the following cytokines are important for DTH and also used for the diagnosis of Mycobacterium
tuberculosis?
a) TNF-α
b) TNF-β
c) IFN-α
d) IFN-γ

Overview of Hypersensitivity
Type I hypersensitivity: This is also known as immediate hypersensitivity, and it is mediated by IgE
antibodies. In this type of reaction, the body's immune system produces IgE antibodies in response to an
allergen, such as pollen or certain foods. When the person is exposed to the allergen again, the allergen binds
to the IgE antibodies on mast cells and basophils, triggering the release of histamine and other inflammatory
mediators. This can cause symptoms ranging from mild itching and hives to severe anaphylaxis.
Type II hypersensitivity: This is also known as cytotoxic hypersensitivity, and it is mediated by IgG or IgM
antibodies that recognize and bind to specific antigens on the surface of cells or tissues, leading to their
destruction. This type of reaction is involved in autoimmune diseases such as autoimmune hemolytic anemia
and some drug-induced immune reactions.
Type III hypersensitivity: This is also known as immune complex hypersensitivity, and it is mediated by
the formation of immune complexes that deposit in various tissues, leading to inflammation and tissue
damage. This type of reaction is involved in autoimmune diseases such as systemic lupus erythematosus and
certain infections.
Type IV hypersensitivity: This is also known as delayed-type hypersensitivity, and it is mediated by T cells.
In this type of reaction, T cells that are sensitized to a specific antigen recognize and respond to the antigen
upon subsequent exposure, leading to an inflammatory reaction. This type of reaction is involved in contact
dermatitis, certain infections, and some autoimmune diseases.

Multiple Choice Answers:

1- a) Type I hypersensitivity
Type I hypersensitivity occur via IgE antibody. In Type I hypersensitivity, an individual's immune system
overreacts allergen, and produces a large amount of IgE antibodies specific to that allergen. When the
individual is exposed to the allergen again, the allergen binds to the IgE antibodies, causing the release of
histamine and other inflammatory mediators from mast cells and basophils, leading to an allergic reaction.
Examples of Type I hypersensitivity reactions include allergic rhinitis (hay fever), asthma, and anaphylaxis
2- d) Type IV hypersensitivity
Type IV hypersensitivity reactions, which are also known as delayed-type hypersensitivity reactions, are
primarily mediated by sensitized Th1 cells. In this type of reaction, antigen-specific Th1 cells are activated
upon re-exposure to the antigen, leading to the recruitment of macrophages and other immune cells to the
site of inflammation. This type of reaction is involved in contact dermatitis, tuberculin reactions, and certain
autoimmune diseases.
3- c) Type III hypersensitivity
Type III hypersensitivity occurs when there is an excessive formation and deposition of immune complexes
in various tissues and organs, leading to activation of the complement system and triggering an inflammatory
response.
Immune complexes are formed when antigens, such as pathogens or foreign substances, bind to antibodies
produced by the immune system. These immune complexes can then accumulate in various tissues and
organs, such as the kidneys, skin, and joints, leading to damage and inflammation.
The complement system, a part of the innate immune system, can be activated by these immune complexes
and trigger an inflammatory response by attracting immune cells, such as neutrophils and macrophages, to
the site of deposition. This can lead to tissue damage and contribute to the development of various
autoimmune and inflammatory diseases, such as systemic lupus erythematosus (SLE) and rheumatoid
arthritis.
4- b) Type II hypersensitivity
Type II hypersensitivity reactions involve the binding of antibodies, typically IgG or IgM, to antigens on the
surface of cells or tissues, resulting in activation of the complement system and destruction of the target
cells. This process is known as antibody-directed complement activation. Examples of Type II
hypersensitivity reactions include autoimmune hemolytic anemia and transfusion reactions.
5- a) FcεRI
The receptor that has a high affinity towards IgE antibodies is called the high-affinity IgE receptor, or FcεRI.
This receptor is expressed on the surface of certain immune cells, such as mast cells, basophils, and
eosinophils, as well as some dendritic cells.
When IgE antibodies bind to their specific antigens, such as allergens, they can also bind to FcεRI on the
surface of mast cells and basophils. This binding leads to cross-linking of the FcεRI receptors and activation
of the immune cells, which can release inflammatory mediators such as histamine, leukotrienes, and
cytokines.
6- b) Atopy
The hereditary predisposition of the development of immediate hypersensitivity reactions against common
environmental antigens is called atopy. Individuals with atopy have an increased likelihood of developing
allergies, such as allergic rhinitis (hay fever), asthma, and atopic dermatitis (eczema), when exposed to
certain environmental triggers, such as pollen, dust mites, or animal dander. Atopy is thought to result from a
complex interplay between genetic and environmental factors.
7- d) CH3
The CH3 domain present in the Fc region of the IgE molecule enables the binding of glycoprotein receptors
on the surface of basophils and mast cells. These receptors, known as FcεRI (Fc epsilon receptor I), bind to
the CH3 domain of IgE and trigger a signaling cascade that leads to the release of histamine and other
inflammatory mediators from the basophils and mast cells. This process is important in the pathophysiology
of allergic reactions, including allergic rhinitis, asthma, and anaphylaxis.
8- a) Ca++
When IgE molecules bind to the FcεRI receptors on the surface of mast cells and basophils, the receptors
cluster together and become phosphorylated on their intracellular domains by the enzyme Lyn. This
phosphorylation recruits and activates downstream signaling molecules, including Syk and the adapter
protein LAT, which then activate various enzymes and transcription factors.
These signaling pathways ultimately lead to the activation of phospholipase C, which cleaves
phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol triphosphate (IP3) and diacylglycerol (DAG). IP3
causes the release of calcium ions from intracellular stores, which then trigger the exocytosis of pre-formed
granules containing inflammatory mediators, such as histamine. DAG, on the other hand, activates protein
kinase C, which can lead to the production of additional inflammatory mediators, such as leukotrienes and
cytokines.
9- b) cAMP
The persistent level of a second messenger called cyclic AMP (cAMP) can inhibit the degranulation of mast
cells and the release of mediators of anaphylaxis such as histamine, leukotrienes, and prostaglandins. This
occurs because cAMP activates protein kinase A (PKA), which in turn inhibits the activity of several key
enzymes involved in the degranulation process.
10- c) Systemic Lupus Erythematosus
Allergic rhinitis: Also known as hay fever, this is a type I hypersensitive reaction to airborne allergens such
as pollen, dust mites, and animal dander.
Asthma: Asthma a type I hypersensitivity reaction that can be triggered by allergens, exercise, cold air, or
other factors. It causes inflammation and constriction of the airways, leading to wheezing, coughing, and
difficulty breathing.
Atopic dermatitis, also known as eczema, is a chronic inflammatory skin condition that is often associated
with Type I hypersensitivity reactions. In atopic dermatitis, the immune system reacts to environmental
triggers such as pollen, dust mites, and certain foods, leading to inflammation and itching of the skin.
11- d) All of the above
The early mediators of Type I hypersensitivity reactions are released within minutes to hours after exposure
to an allergen and include:
Histamine: Histamine is one of the most well-known and important early mediators. It is stored in mast cells
and basophils and is released rapidly in response to an allergen. Histamine can cause a variety of symptoms,
including itching, hives, flushing, and bronchoconstriction.
Prostaglandins and leukotrienes: These are lipid mediators that are released from mast cells and other
inflammatory cells. They contribute to inflammation, bronchoconstriction, and vascular permeability.
12- d) All of the above
IL-4 is a cytokine that is released early in the allergic response and plays a key role in the development and
maintenance of Th2 cells, which are important for the production of IgE antibodies. IL-4 also contributes to
the recruitment and activation of eosinophils and other inflammatory cells.
IL-5 is a cytokine that is released by Th2 cells and is important for the development, activation, and survival
of eosinophils. Eosinophils play a key role in the pathogenesis of allergic diseases, including asthma and
allergic rhinitis.
TNF-alpha is a pro-inflammatory cytokine that is released by mast cells and other inflammatory cells. It
contributes to the recruitment and activation of other immune cells, including eosinophils, neutrophils, and T
cells. TNF-alpha also plays a role in the development and maintenance of chronic inflammation in allergic
diseases.
13)- c) Cromolyn sodium
Beta-agonists: Beta-agonists such as albuterol and salmeterol can stimulate the production of cAMP in
airway smooth muscle cells and inhibit mast cell degranulation. These drugs are commonly used to treat
asthma and can be used to prevent anaphylaxis in patients with known allergies.
Methylxanthines: Methylxanthines such as theophylline can increase the production of cAMP in a variety of
cells, including mast cells and basophils. These drugs are less commonly used for the prevention of
anaphylaxis due to their potential side effects and interactions with other drugs.
Cromolyn sodium: Cromolyn sodium is a mast cell stabilizer that inhibits the release of histamine and other
mediators from mast cells by increasing the levels of cAMP. It is often used to prevent asthma attacks and
can also be used to prevent anaphylaxis in patients with allergies.
Epinephrine: Epinephrine is a hormone that can stimulate the production of cAMP in a variety of cells,
including mast cells and basophils. It is the first-line treatment for anaphylaxis and can be administered as an
injection in cases of severe allergic reactions.
14- b) IgM
The antibody isotype that is primarily involved in ABO incompatibility reactions during blood transfusion is
IgM. IgM antibodies are naturally occurring antibodies that are produced against A and B antigens early in
life, regardless of whether an individual has been exposed to these antigens. When a person receives a blood
transfusion with ABO-incompatible blood, the pre-existing IgM antibodies in the recipient's serum bind to
the A or B antigens on the transfused red blood cells, leading to complement activation and subsequent
hemolysis. In addition to IgM, IgG antibodies may also be produced in response to ABO-incompatible blood
transfusion, but IgM is the primary antibody involved in this type II hypersensitivity reaction.
15- d) All of the above
The exposure of Rh antigen leads to the generation of memory cells and the IgG response that is harmful
during the subsequent pregnancy.
Erythroblastosis fetalis is a severe form of hemolytic disease that can occur when a Rh-negative mother is
pregnant with a Rh-positive fetus. During delivery or any other event causing mixing of the fetal and
maternal blood, Rh antigens from the fetal RBCs can enter the maternal circulation, leading to the production
of Rh-specific antibodies by the mother's immune system. These antibodies can then cross the placenta and
cause hemolysis of fetal RBCs, leading to anemia, jaundice, and other complications.
During the first pregnancy, the mother is exposed to Rh antigens for the first time, leading to the generation
of memory B cells and the production of IgG antibodies against Rh antigens. These memory B cells can
persist for years and lead to a rapid and robust IgG response in subsequent pregnancies with Rh-positive
fetuses, leading to severe hemolytic disease.
16- a) Penicillin
Penicillin is a drug that can induce all four types of hypersensitivity reactions.
Type I hypersensitivity reactions are the most common and immediate, and can lead to anaphylaxis. Type II,
III, and IV hypersensitivity reactions can be delayed and are less common.
Penicillin can cause a type I hypersensitivity reaction by binding to serum proteins to form a hapten-carrier
complex, which can trigger the production of IgE antibodies. It can also cause type II hypersensitivity
reactions by binding to cell surface proteins and triggering complement-mediated lysis or antibody-
dependent cell-mediated cytotoxicity. Penicillin can cause type III hypersensitivity reactions by forming
immune complexes with penicillin and self-antigens that deposit in tissues and trigger complement activation
and inflammation. Finally, penicillin can cause type IV hypersensitivity reactions by inducing a delayed T-
cell-mediated response.
MULTIPLE CHOICE QUESTIONS AND ANSWERS WITH EXPLANATION ON MHC
STRUCTURE, GENE ARRANGEMENT & FUNCTION

1) Polymorphisms in the Major histocompatibility Complex (MHC) genes are linked to an elevated
vulnerability to specific diseases, with one such allele being B47, which is correlated with susceptibility
to..................................
a) Ankylosis spondylitis
b) Reactive arthritis
c) Reiter’s syndrome
d) All of the above

2) Hereditary hemochromatosis is a disorder characterized by iron overload liver and other tissues. Which of
the MHC allele is associated with the highest relative risk for hereditary hemochromatosis?
a) A13/B14 co-incidence
b) B12/A3 co-incidence
c) A3/B14 co-incidence
d) None of the above

3) Narcolepsy is a chronic neurological disorder that affects the brain's ability to control the sleep-wake
cycle.
Which of the following MHC allele is associated with it?
a) Human leukocyte antigen (HLA) DR1
b) Human leukocyte antigen (HLA) DR2
c) Human leukocyte antigen (HLA) DR3
d) Human leukocyte antigen (HLA) DR4

4) Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by persistent and

widespread inflammation resulting from the immune system's failure to tolerate nuclear autoantigens. This
susceptibility is linked to specific alleles within the Major Histocompatibility Complex (MHC),
including...........................
a) DP beta 1
b) DQ beta 1 gene
c) DR beta 1 gene
d) None of the above

5) Major Histocompatibility Complex (MHC-I) molecules are the cell surface proteins that activate T cells
and mediate effector T-cell function.
Which of the following class of MHC molecules activate cytotoxic T cells?
a) MHC class I
b) MHC class II
c) MHC class III
d) All of the above

6) The MHC molecules are encoded by specific genes.

Which of the following is an incorrect statement regarding MHC genes?
a) MHC class I proteins are encoded by B, C & A genes
b) MHC class II proteins are encoded by DP, DQ, and DR genes
c) Both MHC class I and MHC class II genes are present in the same region of chromosome
d) MHC class I and MHC class II are encoded by genes located in the different regions of chromosomes

7) The MHC proteins are highly polymorphic. The following factors contribute to the polymorphism,
EXCEPT
a) MHC proteins are present in haplotypes
b) MHC is co-dominantly expressed
c) MHC genes are highly conserved
d) None of the above

8) Which of the following statement is FALSE regarding MHC proteins?

a) MHC class I is a dimer consisting of two chains: one alpha chain (three subunits) and a b2 microglobulin
chain expressed outside the cell membrane
b) MHC class I is a dimer consisting of two chains: an alpha and a beta-chain each consisting of two subunits
expressed outside the cell membrane
c) Both of the above
d) None of the above

9) Beta2 microglobulin/β2 microglobulin/ B2M is a highly conserved subunit essential for the expression of
class I on the cell surface.
Identify the correct statement regarding the Beta2 microglobulin gene
a) It is located on the same chromosome as MHC Class I Genes (A, B, C)
b) It is located in a different chromosomal location than MHC Class I Genes (A, B, C)
c) It is a part of the MHC I gene cluster
d) None of the above

10) Which of the following is the characteristic feature of the peptide binding cleft in MHC class I
molecules?
a) It is a critical component on the α1 and α2 domains of the MHC class I molecule
b) The pocket can bind to 8-10 amino acid peptides and presented to Tcells
c) It plays crucial role in antigen presentation in adaptive immunity
d) All of the above

11) Anchor residues, which predominantly exist at the peptide's C-terminal end, interact with specific amino
acid residues within the binding groove of the peptide-binding cleft.
The anchor residues are............................................
a) Acidic amino acid
b) Basic amino acids
c) Hydrophobic amino acids
d) None of the Above
12) The CD8 cell surface protein of T cells interacts with ……………............ MHC class I molecules.
a) alpha-1 subunit
b) alpha-2 subunit
c) alpha-3 subunit
d) beta2- microglobulin

13) Interferon-gamma (IFN-γ) is a cytokine that regulates the expression of............................

a) MHC class I
b) MHC class II
c) Both of the Above
d) None of the Above

14) The MHC expression is decreased (downregulated) by some pathogenic viruses namely
a) Human Cytomegalovirus
b) Hepatitis Virus
c) Adenovirus 12
d) All of the above
15) Many viruses and other microbes produce a class of protein known as immunoevasins that are designed
to interfere with antigen presentation by MHC class I molecules.
The immunoevasin interferes with MHC presentation by..............................................
a) Block peptide transport to TAP
b) Inhibiting E3 ubiquitin ligase activity
c) Block tapasin function
d) All of the above

16) The requirement for antigen presentation by MHC molecules for T cell activation is also known
as.................................
a) MHC-recognition
b) MHC-restriction
c) MHC-processing
d) MHC-signaling

17) Which of the following gene is not the part of MHC class I gene cluster?
a) Transporter Associated with Antigen Processing (TAP) genes
b) Tapasin gene
c) Proteasome LMP gene
d) Tumor Necrosis Factor (TNF) genes

18) MHC molecules are necessary for T cell response.

Which of the following function is mediated by MHC-T cell interaction?
a) Immune Tolerance
b) Cytotoxicity
c) B-cell activation
d) All of the above

19) MHC class II molecules are primarily involved in presenting antigens to which type of immune cells?
a) Cytotoxic T cells (CD8+ T cells)
b) Helper T cells (CD4+ T cells)
c) Natural killer (NK) cells
d) B cells

20) The CD4 protein of T helper cells binds and stabilizes the MHC class II/peptide structure. The subunit
that interacts with CD4 cell surface protein is.............................................
a) alpha1 and beta1 subunit
b) alpha2 and beta2 subunits
c) alpha1 and alpha2 subunits
d) beta1 and beta2 subunits

21) Bare lymphocytes are a genetic disorder caused by a lack of class II molecules on the cell surface. This is
associated with................................................................
a) Mutation of the gene encoding MHC class II proteins
b) The mutation that leads to MHC folding
c) Mutation of transcription factor protein (CIITA) required for expression of MHC class II proteins
d) None of the above

22) Bare Lymphocyte Syndrome (BLS) is characterized by deficiencies in:

a) MHC class I molecules
b) MHC class II molecules
c) MHC class III molecules
d) TAP proteins
23) MHC class I molecules are typically associated with the presentation of:
a) Exogenous antigens
b) Intracellular antigens
c) Bacterial antigens
d) Extracellular antigens

24) Which MHC class is responsible for presenting antigens derived from extracellular pathogens?
a) MHC class I
b) MHC class II
c) MHC class III
d) MHC class IV

Multiple Choice Answers with explanation:

1-d) All of the above
2-c) A3/B14 co-incidence. The A3/B14 coincidence refers to a specific combination of major
histocompatibility complex (MHC) alleles found in individuals. These alleles can play a role in determining
an individual's immune response and susceptibility to certain diseases such as, Hereditary hemochromatosis.
3-b)HLA-DR2. Certain subtypes of narcolepsy, a sleep disorder characterized by excessive daytime
sleepiness and disruptions in sleep-wake cycles, are associated with HLA-DR2, particularly the DRB1*15:01
allele.
4-c) DR beta 1 gene. DR beta 1 gene, also known as HLA-DRB1 (Human Leukocyte Antigen-DRB1), is a
part of the major histocompatibility complex (MHC) in the human genome. HLA-DRB1 gene, such as
specific DRB1 alleles, have been associated with an increased susceptibility to SLE. This means that
individuals carrying these particular DRB1 alleles are more likely to develop SLE compared to those without
these alleles.
5-a) MHC class I. MHC class I molecules are found on the surface of nearly all nucleated cells in the body.
One of the key function of MHC class I molecule is immune surveillance, cytotoxic T cells continually scan
the body for cells displaying abnormal or foreign antigens on their MHC class I molecules. When they
encounter such cells, cytotoxic T cells can recognize and eliminate them, helping to control infections and
prevent the spread of cancer.
6-c) Both MHC class I and MHC class II genes are present in the same region of chromosome
7-c) MHC genes are highly conserved
8-d) None of the above
9-b) It is located in a different chromosomal location than B, C, and A genes. Beta-2 microglobulin or
β2 microglobulin/ B2M, is a small protein that is a component of the major histocompatibility complex class
I (MHC-I) molecules. It is encoded by a separate gene located on chromosome 15 in humans. Unlike the
MHC class I genes, it is not part of the MHC region.
MHC Class I Genes (A, B, C) are found within the MHC region on chromosome 6 in humans.
10-d) All of the above. It is located on the MHC class I molecule, specifically on the α1 and α2 domains of
the MHC class I heavy chain.The primary function of the peptide binding cleft is to bind and display
antigenic peptides to cytotoxic T cells (CD8+ T cells).
11-c) Hydrophobic amino acids
12-c) alpha-3 subunit
13-c) Both of Above. The expression of MHC class I and MHC class II molecules can be regulated by
cytokine known as interferon-gamma (IFN-γ), which can upregulate their expression in response to infection
or immune activation.
14-d) All of the above. The expression of Major Histocompatibility Complex (MHC) molecules can be
influenced by various factors, including infection. MHC expression can indeed sometimes appear to
decrease. Many viruses have evolved mechanisms to evade the host immune system, and one common
strategy is to downregulate the expression of MHC molecules on infected cells. By reducing MHC
expression, infected cells make themselves less visible to cytotoxic T cells.
15-d) All of the above.
16-b) MHC-restriction. T cell can only recognize and respond to antigens when they are presented by a
specific MHC molecule that matches the T cell's TCR.
17- d) Tumor Necrosis Factor genes (TNF). These genes are found within the Major Histocompatibility
Complex class III (MHC III) region and are vital for the immune system's ability to detect and respond to
intracellular pathogens, particularly viruses. The MHC III region is distinct from both MHC class I and
MHC class II regions.
18-d) All of the above
19-b) Helper T cells (CD4+ T cells)
20- d) beta1 and beta2 subunits
21- c) Mutation of transcription factor protein (CIITA) required for expression of MHC class II proteins
22- a) MHC class I molecules
23- b) Intracellular antigens. Antigens from extracellular pathogens through processes phagocytosis or
endocytosis, antigens are broken down into smaller peptides.These peptides are loaded onto MHC class II
molecules within endosomal compartment and transported to the cell surface for presentation to CD4+ T
cells.
MULTIPLE CHOICE QUESTIONS ON IMMUNE TOLERANCE & AUTOIMMUNITY

1) Which of the following options is the mechanism for induction of immune tolerance?
a) Central Anergy
b) Peripheral Anergy
c) Clonal Anergy
d) All of the above

2) The central tolerance occurs in the thymus and bone marrow.

Which of the following statements is true regarding central tolerance?
a) The positive selection occurs in the cortex before maturing and entering the circulation.
b) The negative selection occurs in the medulla.
c) The negative selection removes cells that have high affinities for self-antigen
d) All of the above

3) After exiting the thymus, mature T cells are subjected to the secondary selection where most self-reactive
T cells are deleted or rendered anergic.
The process is known as............................................?
a) Central Anergy
b) Peripheral Anergy
c) Clonal Anergy
d) All of the above

4) Certain autoimmune disorders are monogenic-caused by a mutation in a single gene.

The following are the monogenic autoimmune diseases, Except?
a) Autoimmune lymphoproliferative syndrome
b) Autoimmune polyadenopathy
c) Immunodysregulation polyendocrinopathy (X-linked)
d) Systemic Lupus Erythematosus

5) The autoimmune thyroid disorder with the presence of anti-TSH receptor antibodies is suggestive of:
a) Hashimoto thyroiditis
b) Grave's disease
c) Goodpasture syndrome
d) None of the above

6) Which of the following is the multifactorial autoimmune disorder?

a) Multiple Sclerosis
b) Rheumatic fever
c) Autoimmune hepatitis
d) Lymphoproliferative syndrome

7) The antibody generated against the intrinsic factor in the gastric tissue leads to which of the following
conditions?
a) Goodpasture syndrome
b) Pernicious anemia
c) Celiac disease
d) None of the above

8) The autoimmune disorder with an elevated anti-thyroglobulin antibody is known

as....................................?
a) Hashimoto thyroiditis
b) Grave's disease
c) Goodpasture syndrome
d) None of the above

9) The presence of anti-glutamic acid decarboxylase antibodies increased the susceptibility to which of the
following disorders?
a) Type 1 Diabetes mellitus
b) Celiac disease
c) Grave's disease
d) Pernicious anemia

10) The following antibodies are not associated with Systemic Lupus Erythematosus, EXCEPT?
a) Anti-ANA antibody
b) Anti-cardiolipin antibody
c) Anti-dsDNA
d) None of the above

11) In 'Rheumatic fever ', the cross-reactivity between the bacterial M protein and human lysoganglioside
leads to the development of cardiac T cells.
M protein is a cell wall component of........................................?
a) Staphylococcus aureus
b) Streptococcus pyogenes
c) Hemophilus influenza
d) Neisseria gonorrhea

12) The generation of reactive cells against HHV-6 encoded U24 cross-reactive with myelin basic protein
resulting in autoimmune disease
a) Myasthenia gravis
b) Multiple sclerosis
c) Grave's disease
d) Systemic Lupus Erythematosus

13) 'Myasthenia Gravis' is caused by the production of autoantibodies against the..................................?

a) Myelin basic proteins
b) TSH receptor
c) Acetylcholine receptor
d) None of the above

14) Which of the following MHC allelic forms is protective against ulcerative colitis?
a) HLA class II DR2
b) HLA class II DR4
c) HLA class II DR15
d) HLA class II DR9

15) The B27 HLA allele is associated with which of the following conditions?
a) Ankylosing spondylitis
b) Psoriasis
c) Inflammatory bowel disease
d) All of the above

Multiple Choice Answers with Explanation:

1-d) All of the above
Central Tolerance occurs during T cell development in the thymus, where self-reactive T cells are eliminated
to prevent autoimmunity.
Peripheral Tolerance: Tolerance mechanisms that operate outside the thymus, including anergy (inactivation
of self-reactive T cells), suppression by regulatory T cells (Tregs), and deletion of self-reactive B cells.
Clonal anergy" refers to a state in which a lymphocyte (such as a T cell or B cell) becomes functionally
unresponsive or inactive when exposed to its specific antigen. This state of unresponsiveness occurs when
the lymphocyte encounters its antigen without the appropriate co-stimulatory signals, typically required for
full activation
2-d) All of the above
Positive selection occurs in the cortex of the thymus. During positive selection, immature T cells are
screened for their ability to recognize self-major histocompatibility complex (MHC) molecules. T cells that
can weakly bind to self-MHC molecules receive a survival signal and move on to mature and enter the
circulation.
Negative selection occurs in the medulla of the thymus. In the medulla, self-reactive T cells are tested for
their ability to bind strongly to self-antigens presented by thymic epithelial cells. T cells that react too
strongly with self-antigens are eliminated through negative selection to prevent autoimmunity.
Negative selection removes T cells that have high affinities for self-antigens. This process helps ensure that
only T cells with a moderate affinity for self-antigens, which are less likely to cause autoimmune reactions,
are allowed to mature and circulate in the body.
3-b) Peripheral Anergy
Peripheral Tolerance: Tolerance mechanisms that operate outside the thymus, including anergy (inactivation
of self-reactive T cells), suppression by regulatory T cells (Tregs), and deletion of self-reactive B cells.
4-d) Systemic Lupus Erythematosus
Systemic Lupus Erythematosus (SLE), often referred to as lupus, is a complex autoimmune disease with a
strong genetic component. While the exact cause of SLE is not fully understood, there are various genetic
factors that play a role in its development and susceptibility.
5-b) Grave's disease
An autoimmune thyroid disorder characterized by the presence of anti-thyroid-stimulating hormone (TSH)
receptor antibodies is typically referred to as Graves' disease. Graves' disease is the most common cause of
hyperthyroidism and is characterized by the overproduction of thyroid hormones (thyroxine or T4 and
triiodothyronine or T3) due to the activation of TSH receptors by these autoantibodies.
6-d) Lymphoproliferative syndrome
Lymphoproliferative syndrome (LPS) is a group of rare and diverse disorders characterized by an abnormal
proliferation of lymphocytes, a type of white blood cell. This uncontrolled growth of lymphocytes can lead
to various clinical manifestations and complications. There are several different forms of lymphoproliferative
syndrome, each with its distinct genetic, clinical, and immunological features.
7-b) Pernicious anemia
Antibodies generated against intrinsic factor in gastric tissue can lead to a condition known as pernicious
anemia. Intrinsic factor is a protein produced in the stomach that is essential for the absorption of vitamin
B12 (cobalamin) in the small intestine. When antibodies target and interfere with intrinsic factor, it can result
in pernicious anemia, which is characterized by a deficiency of vitamin B12.
8-a) Hashimoto thyroiditis
Anti-thyroglobulin antibodies are one of the hallmark autoantibodies found in Hashimoto's thyroiditis.
Thyroglobulin is a protein produced by the thyroid gland, and these antibodies target it. The presence of anti-
thyroglobulin antibodies is a key diagnostic feature of Hashimoto's thyroiditis.
9-a) Type 1 Diabetes mellitus
10-d) None of the above
In Systemic Lupus Erythematosus (SLE), a complex autoimmune disease, various antibodies are associated
with the condition. Some of the key antibodies and autoantibodies commonly found in SLE include:
Antinuclear Antibodies (ANAs), Anti-double-stranded DNA (anti-dsDNA) Antibodiesnti-Smith (anti-Sm)
Antibodies, Anti-Phospholipid Antibodies, Anti-Ro (SSA) and Anti-La (SSB) Antibodies, Antibodies to
Ribosomal P Proteins, Complement-Fixing Antibodies
11-b) Streptococcus pyogenes
12-b) Multiple sclerosis
The immune system generates T cells or antibodies against HHV-6-encoded U24 that cross-react with MBP,
it can result in an autoimmune attack on the myelin sheath in the nervous system. MBP is a major component
of the myelin sheath, which insulates nerve fibers. Autoimmune attacks against myelin can lead to
demyelination and are associated with diseases like multiple sclerosis (MS).
13-c) Acetylcholine receptor
Myasthenia Gravis (MG) is an autoimmune disorder primarily caused by the production of autoantibodies
against a specific target in the body, which is the acetylcholine receptor (AChR) located on the surface of
muscle cells.
14-b) HLA class II DR4
15-d) All of the above