Immunopathology

EM Cabana, BSAH, DVSM, DipVSt, MVSt, PhD

Professor – Veterinary Pathology
Review of Immune System
Cellular Response
 PATHOGEN

INNATE immunity ADAPTIVE immunity

PHAGOCYTES B CELLS T CELLS

NK cells humoral cell-mediated
immunity immunity

Common Mechanisms for Pathogen Destruction

 Cells of the Immune System
 T lymphocytes and clones
 B lymphocytes and plasma cells
 Macrophages
 Dendritic and Langerhans’ cells
 Natural killer (NK) cells
 Cellular Immune Response
 Mediated by thymus-derived lymphocytes
(T lymphocytes).
 Initiated by the binding of the antigen with
an antigen receptor on the surface of the
sensitized T lymphocyte.
 T cell programming
 Developing T cells undergo two tests:
• They must be able to recognize “self” antigen
molecules, and
• Must not bind to both “self” and any of the body’s
own antigens.
 T cells that fail either of these tests die.
 T-cell Receptor (TCR)
 T cell receptors are analogous to
immunoglobulins in the humoral immune
response. However, TCR:
• Monovalent
• It exists only as a cell surface receptor and has no
counterpart to secreted antibody.
B-cell Receptor: Review
 T-cell Receptor (TCR)

Nature Reviews Immunology 5, 571-577 (July 2005)

 B cell receptor vs TCR
B Cell Receptor T Cell Receptor
• Immunoglobulin • Cell membrane protein
• Recognises: • Recognizes only protein (peptide
– Proteins segments)
– Nucleic acids • Receptor binding plus co-
– Polysaccharides stimulatory signal from antigen
– Some lipids presenting cells (APC) result to
– Small chemicals (haptens) positive cell signalling and
• Bound Ags are internalised and reactivity of the T-cell
processed during plasma cell
differentiation
 T Lymphocytes
 T cell subpopulations:
• Helper T cells – assist B cell transformation
• Suppressor T cells that regulate the intensity of the body's
immune response
• Reactive T cells – produce Lymphokines
• Cytotoxic T cells - contain granules that kills on contact;
requires antigen recognition
• Natural Killer cells – similar to Cytotoxic T cells but does
not require antigen recognition
T-helper Cells (CD4)
Natural Killer cells
Cytotoxic T-cells
 Cytotoxicity
 Effected by T-cytotoxic lymphocytes (CTL) and
Natural killer cells (NK)
 Effectors of cytotoxicity:
• Perforin – a cytolytic mediator produced by killer
cells partially homologous to MAC of complement
• Granzyme – serine protease inducing apoptosis
resulting to DNA collapse

Immunology and Cell Biology (1993) 71, 201–208

 Suppressor T-cells (CD8)

Science 299, p1057, 2003

 Lymphokines
 A mixed group of proteins mediators
produced by T cells
 Macrophages are probably the primary target
cells.
• Some lymphokines will aggregate macrophages at
the site of the infection,
• others activate macrophages, inducing them to
phagocytose and destroy foreign antigens more
vigorously.
 Lymphokines
 Attract neutrophils and monocytes to the site
of infection.
 The end result of their combined action is an
amplification of the local inflammatory
reaction with recruitment of circulating cells
of the immune system
 Lymphokines
 Contact between antigen and specific
sensitized T lymphocytes is necessary to cause
release of lymphokines.
 Once released the lymphokine action is not
antigen specific; for example, an immune
reaction to the tubercle bacillus may protect
an animal against simultaneous challenge by
brucella organisms.
 Important Lymphokines
 Interferon-gamma
 Interleukin-2
 Leukocyte Migration-Inhibitory Factors
 Lymphotoxin-alpha
 Macrophage-Activating Factors
 Macrophage Migration-Inhibitory Factors
 Neuroleukin
 Immunonologic Suppressor Factors
 Transfer Factor
Review of Immune System
Humoral Response
 Functions of Antibodies

 Enhancment of Phagocytosis by Opsonization

 Complement activation and MAC Cytolysis
 Antibody-dependent Cellular Cytotoxicity (ADCC) by
NK Cell
 Neutralization of Exotoxins
 Neutralization of Viruses
 Preventing Bacterial Adherence to Host Cells
 Agglutination of Microorganisms
 Immobilization of Bacteria and Protozoans.
 Dynamics of Antibody Production

 Antibody production
• Initial antibody produced in IgM
• Lasts 10-12 days
• Followed by production of IgG
• Lasts 4-5 days
• Without continued antigenic challenge antibody
levels drop off, although IgG may continue to be
produced.
 The Kinetics of the Antibody Response

Total IgM
Ab Ab
Ab Tite r

1o Ag

LAG

Days After Immunization

 5 Classes of Immunoglobulin or Isotypes

Class is based on differences in the heavy chain constant regions (blue)

• Length
• Distribution of carbohydrates
• Location of hinges

RECALL: Constant Region determines function

THEREFORE: each Ig isotype has a different function

© New Science Press Ltd. 2003
IgM – IgG Shift
Primary response to antigen :

1o Ag

IgM

IgG

Memory Cells
Secondary response to antigen :

Virgin B cell IgM

IgG

Memory Cells
Memory Pool

IgG

Memory Cells
Review of Immune System
Major Histocompatibility
Complex (MHC)
 MHC
 A set of molecules displayed on cell surfaces
that are responsible for lymphocyte
recognition and "antigen presentation“
 Controls immune function by recognition of
“self” from “non-self”
 Coded for by several specific gene segments
 MHC
 Classes:
• MHC I are expressed on the great majority of cells
and recognized by CD8+ (cytotoxic) T cells
• MHC II are expressed on B cells, macrophages,
dendritic cells and recognized by CD4+ T (T-helper)
cells
MHC II (Class II Molecule)
Major Histocompatibility Complex
Class I vs Class II
MHC restrictions of Ag Presentation
Cellular Immune Response: Cytotoxicity
Cellular Immune Response: Helper Activity
Immunopathology
Basic Concepts
 Immunopathology
“Immunitas”
Freedom from disease
Protective response against disease

Host tissue damage by immune response

“Pathos”
Suffering or disease
 Pathologies
 Hypersensitivity states
 Immunodeficiency states
 Autoimmune diseases
 Adverse drug reactions
 Tissue rejection
Hypersensitivity
States
 Hypersensitivity Reactions
 Gell and Coombs (1963) classification:
• Type I – IgE mediated (Anaphylaxis)
• Type II – Antibody/Complement-mediated
cytotoxicity
• Type III – Immune Complex Disease
• Type IV – Delayed-Type Hypersensitivity (DTH)
 Types I, II and III are “immediate”, Type IV
is delayed

Gell PGH, Coombs RRA, eds. Clinical Aspects of Immunology. 1st ed.
Oxford, England: Blackwell; 1963
 Type I Hypersensitivity
 Antigens are called “allergens”
 Reasons for allergies unknown, in humans, there
is a strong genetic predisposition (called atopy)
 Hallmark is inappropriate production of IgE
against allergens that cause mast cell
degranulation
 Normally IgE/mast cell activity should be
directed against parasitic infections
 Type I Hypersensitivity

 Mediators of Type I hypersensitivites

• Mast cell granule contents (early effects)
• Histamine and Heparin - ↑ vascular permeability,
smooth muscle contraction (intestines, bronchi),
mucus secretion
• Chemotactic factors – attract eosinophils and
neutrophils
• Proteases – mucus secretion, complement
activation, degradation of blood vessel basement
membrane
 Type I Hypersensitivity

 Mediators of Type I hypersensitivites

• Later Effects
• Leukotrienes and prostaglandins –
secreted after tissue disruption caused by
mast cell degranulation, effects are similar
to histamine
• Arrival of proinflammatory eosinophils and
neutrophils
 Type I Hypersensitivity in Animals

 Dogs - visceral pooling and portal hypertension

 Cat - broncho-constriction and pulmonary
oedema
 Ruminants - systemic hypotension and
pulmonary hypertension
 Horse - systemic and pulmonary hypertension
 Type I Hypersensitivity in Humans

 Hay Fever
 Asthma
 Atopic Dermatitis (allergic eczema)
• Often occurs in young children
• Red skin rash
• Strong hereditary predisposition
 Type II Hypersensitivity
 Antibody-mediated or Complement-mediated
Cytotoxic HS
• Antibodies (IgM or IgG) or Complement bind to
cell surface antigens. Antigen/antibody complex
may lead to:
• Complement activation  lysis
• ADCC
• Opsonization  phagocytosis
• These are normal reactions, but when they cause
unwarranted tissue damage, they are considered
a hypersensitivity.
Type II Hypersensitivity: Antibody
Mediated

IgG or Cytotoxic cell

IgM bind to Fc of
Antibody

Target cell
Type II Hypersensitivity: Complement
Mediated

Complement binds
IgG or
to Fc of antibody
IgM

Target cell
 Type II Hypersensitivity
 Examples of Type II HS:
• Transfusion reactions
• To ABO blood groups
• To other RBC blood groups
• Hemolytic disease of the newborn
(erythroblastosis fetalis)
• Drug-induced hemolytic anemia (penicillin)
 Type III Hypersensitivity

 Immune Complex Disease

• Antibody (IgG) / attaching to soluble antigen
leads to complex formation
• Immune complexes may deposit in:
• Blood vessel walls (vasculitis)
• Synovial joints (arthritis)
• Glomerular basement membrane
(glomerulonephritis)
• Choroid plexus
 Type III Hypersensitivity

 Damage occurs due to:

• Anaphylatoxin release due to complement activation
(C3a, C5a) which then attracts neutrophils, and causes
mast cell degranulation
• Neutrophils have trouble phagocytosing “stuck”
immune complexes so they release their granule
contents leading to more inflammation
• Platelet aggregation also results from complement
activation
 These effects are also known as the Arthus
reaction
 Type III Hypersensitivity
 Localized reactions
• edema and redness (erythema) and tissue
necrosis of the affected tissue
• Can occur in the skin following insect bites
• Can occur in the lungs
• E.g. “farmer’s lung” from inhaling particles from moldy
hay
 Type III Hypersenstivity
 Generalized reactions:
• Serum sickness (following treatment with
antiserum to a toxin)
• Autoimmune diseases
• SLE
• Rheumatoid arthritis
• Drug reactions (penicillin)
• Infectious diseases
• Meningitis, hepatitis, malaria, mono etc.
 Type III Hypersensitivity in Animals
 “blue eye” in CAV infection in dogs
 Equine infectious anaemia
 Glomerulopathy in Dirofilariasis
 Seen in most cases of pyometra, endocarditis,
distemper, lymphosarcoma, mastocytoma
Blue Eye: CAV-1 infection; Infectious Canine Hepatitis
Dirofilaria immitis: Canine heartworm
Dirofilaria immitis: Canine heartworm; Membrano-proliferative glomerulonephritis
Cutaneous Lupus, Dog
Cutaneous Lupus, Human
 Type IV Hypersensitivity

 Delayed type hypersensitivity (DTH)

• TH cells that have been “sensitized” by an antigen develop
a TH1 and (sometimes a TC response) leading to
macrophage recruitment and activation.
• First noticed with reaction to tuberculosis bacteria
(tuberculin reaction)
• Hallmarks of type IV is the large number of macrophages
at the reaction site, and that it takes an average of 24 hrs
to manifest after repeat exposure.
 Type IV Hypersensitivity in Animals
 Allergic contact dermatitis
 Atopic dermatitis/Flea allergy
 Viral and fungal infections
 Graft rejection
 Graft vs host reaction
Atopic dermatitis, dog
Allergic Contact Dermatitis, Dog
Flea allergy, Dog
Flea allergy, Human
Adverse Drug
Reactions
 ADR: Basic Concepts
 Hypersensitivity states caused by
administration/ingestion of
pharmacological preparations
 Implicated substances:
• Antibiotics (penicillin, chloramphenicols)
• Analgesics/Antipyretics (aspirins,
phenothiazine)
 Criteria for ADR
 Prior sensitization is required
 Reproducible in small amount
 The same drug may cause it
 Reaction is not a drug side-effect
 Symptoms are typical of hypersensitivity
state
 Predisposing Factors
 Host Factor
 Drug Factor (form hapten)
 Route of administration
• topical > iv > im > per os
 Dose and duration of exposure
 Examples of ADR

 Reyes Syndrome in infants dosed with

ASA (aspirin) - Type II reaction-
haemolytic anaemia, encephalopathy
and liver fatty change
 Type III reactions in penicillin
Autoimmune
States
 Autoimmunity
 Caused by autoantibodies or lymphocytes
that attack molecules, cells, or tissues of the
organism producing them
 Impediments to early recognition:
• Burnet’s Clonal Selection Theory
• Erlich’s Horror Autotoxicus
• Koch’s Postulate on Infectious Disease
Immunotolerance
 Mechanisms for AID
 Molecular mimicry
 T cell bypass
 Hidden antigen release
 Loss of suppressor T-cell
 Genetic susceptibility
Molecular mimicry
 B-cell Reaction to Self-Antigen

T-helper
cell
APC

B-cells Self-antigen

tolerance
B-cells
 T-cell Bypass in AID

APC
Alternate
Signal
B-cells Self-antigen

autoantibodies

Plasma cells
 Hidden Antigen Release

B-cells T-cells

Hidden
Self
antigen

Plasma cells Reactive T-cells

 T-cell regulation

Regulatory T-cells

Immune
reactivity Antibody
secretion
 Loss of Suppressor T-cell

Regulatory T-cells

Cell-mediated
tissue injury Autoantibody
secretion
 When to suspect AID
 Presence of Autoantibodies
 Amyloidosis in tissues
 Hypergammaglobulinaemia
 Vasculitis, serositis and glomerulonephritis
 Other disorders such as endocrine disease
associated with AID
Amyloidosis, Wallaby, H&E
Amyloidosis, Wallaby, Congo red, birefringence on polarised light,
 Comparison of Organ-specific and Non-organ specific AID
Organ specific Non-organ specific
Antigen localized to given organ Widespread distribution
Lesions confined to target organ or Multiple organs/tissue
tissue affected; immune complexes
deposit in joints, skin and
kidneys

Overlap with other organ specific overlap with other non-organ

antibodies and diseases specific antibodies and
diseases

Examples autoimmune thyroid disease systemic Lupus

myasthenia gravis rheumatoid arthritis
pernicious anaemia systemic sclerosis
diabetes mellitus systemic vasculitis
Immunodeficiency
States
 Categories

 Primary - failure of development of

immune cells/tissues
 Secondary (Acquired) - associated with
damage from other disease
 Basic Mechanisms
 Deficiency in lymphocyte production
 Deficiency in hormone or growth factors
 Deficiency of complement
 Deficiency in phagocytic cell function
 Failure of passive immunity in neonate
Nude mouse (Athymic mouse; lacks T-cells)
Pituitary dwarfism
Pituitary cyst
 Failure of Passive immunity

 Intestinal uptake of Colostrum occur

within 24-48 hours (4 days in sheep/goat)
 Pigs, horse, goat and sheep depend
largely on colostral transfer
 Agammaglobulinaemia is the primary
cause of neonatal and perinatal
infectious diarrhoea
 Deficiency in Phagocytic Function

 Chediak-Higashi Syndrome – autosomal

recessive trait, cause lysosomal trafficking
disorder leading to failure of phagolysosome
formation
END OF LECTURE