Innate and Adaptive Immunity
Curriculum: Phase 1/ Semester2/ TOB / Session 10
Lecturer: Dr. Ayam mohammed salih.
Degrees: phD of Microbiology .
Email: ms_ay20@yahoo.com
Learning outcomes
Having revised this lecture you should be able to:
• Briefly describe the cellular and humoral components
of the innate and adaptive immune systems
• Describe the main differences between the innate and
adaptive immune responses
• Give examples of the cooperation and interdependence of the
innate and adaptive immune systems
immune system
• The body’s defense against disease
causing organisms. The immune system
recognizes foreign bodies by structures
on their cell walls and responds with the
production of immune cells and proteins
Innate immunity
• is present before any exposure to pathogens
and is effective from the time of birth
• It involves nonspecific responses to
pathogens
• Innate immunity consists of external barriers
plus internal cellular and chemical defenses
The First Line of Defense
Skin
- The dead, outer layer of skin, known as
the epidermis, forms a shield against
invaders and secretes chemicals that kill
potential invaders
Mucus and Cilia
- Breathe in, foreign particles
and bacteria bump into
mucus throughout your
respiratory system and
become stuck
- Hair-like structures called
cilia sweep this mucus into
the throat for coughing or
swallowing
Saliva
• Saliva contains many chemicals that break down bacteria
• Stomach Acid
- Swallowed bacteria are broken down by
strong acids in the stomach that break down
your food
Cells Involved in Innate Immunity
Macrophage Phagocytosis
Monocyte Presentation to
lymphocytes
Neutrophil Phagocytic
PMN Anti-bacterial
Eosinophil Anti-parasite
Immunity - Allergy
Basophil Protection of
mucosal surfaces - Allergy
Mast cell Protection of
mucosal surfaces - Allergy
• Cellular innate defenses also involve natural killer
cells
• These circulate through the body and detect
abnormal cells
• They release chemicals leading to cell death,
inhibiting the spread of virally infected or
cancerous cells
Cellular Innate Defenses
White Blood Cells
- If invaders actually get within the body, then your
white blood cells (WBCs) begin their attack
- WBCs normally circulate throughout the blood,
but will enter the body’s tissues if invaders are
detected
- A white blood cell engulfs a microbe, then fuses
with a lysosome to destroy the microbe
White Blood Cells
Pathogen
Phagocytes
These white blood cells PHAGOCYTIC
are responsible for eating
CELL
foreign particles by
engulfing them Vacuole
Once engulfed, the
Lysosome
containing
phagocyte breaks the
enzymes
foreign particles apart in
organelles called
Lysosomes
• There are different types of phagocytic cells
– Neutrophils engulf and destroy pathogens
– Macrophages are found throughout the body
– Dendritic cells stimulate development of
adaptive immunity
– Eosinophils discharge destructive enzymes
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Antimicrobial Peptides and Proteins
• Peptides and proteins function in innate defense
by attacking pathogens or impeding their
reproduction
• Interferon proteins provide innate defense,
interfering with viruses and helping activate
macrophages
© 2011 Pearson Education, Inc.
Adaptive immunity
• Adaptive immunity, or acquired immunity, develops
after exposure to agents such as microbes, toxins, or
other foreign substances
• It involves a very specific response to pathogens
© 2011 Pearson Education, Inc.
Innate immunity
• Natural immunity present from birth
• Not specific for any particular microbial
substance
• Not enhanced by second exposure
• Has no memory
• Uses cellular and humoral components
• Is poorly effective without adaptive immunity
Adaptive immunity
• Immunity established to adapt to infection
• Learnt by experience
• Confers pathogen-specific immunity
• Enhanced by second exposure
• Has memory
• Uses cellular and humoral components
• Is poorly effective without innate immunity
Inflammatory Responses
• The inflammatory response, such as pain and
swelling, is brought about by molecules released
upon injury of infection
• Mast cells, a type of connective tissue, release
histamine, which triggers blood vessels to dilate
and become more permeable
• Activated macrophages and neutrophils release
cytokines, signaling molecules that enhance
the immune response
© 2011 Pearson Education, Inc.
Figure 43.8-3
Pathogen Splinter
Macro- Movement
Signaling
phage of fluid
Mast molecules
cell
Capillary Phagocytosis
Red Neutrophil
blood cells
Cells of the Adaptive Immune Response
T and B lymphocytes
respond to antigen (molecules that elicit a
specific immune response when introduced
into the tissues of an animal).
© 2011 Pearson Education, Inc.
Lymphocyte antigen receptors
Until the 1960’s, lymphocytes had no known function.
Lyc T and B cells are essentially inactive until they
encounter antigen.
T and B cells express ANTIGEN RECEPTORS
B
The B cell antigen receptor is a membrane-bound antibody
SURFACE IMMUNOGLOBULIN
T
The T cell antigen receptor IS NOT membrane bound
antibody but a distinct molecule
T CELL ANTIGEN RECEPTOR
Figure 43.UN01
Antigen
receptors
Mature B cell Mature T cell
• Antigens: are substances that can elicit a response
from a B or T cell
• Exposure to the pathogen activates B and T cells
with antigen receptors specific for parts of that
pathogen
• The small accessible part of an antigen that binds to
an antigen receptor is called an epitope
• Antibody
– Y-shaped antigen receptor (protein), made only by B
cells, that binds only to the antigen that prompted its
synthesis
– Facilitates phagocytosis, or neutralizes pathogens or
toxins
Antigen
Figure 43.10
receptor Antibody
B cell
Antigen Epitope
Pathogen
(a) B cell antigen receptors and antibodies
Antibody C
Antibody A
Antibody B
Antigen
(b) Antigen receptor specificity
Antigen- Antigen-
Figure 43.9
binding binding site
site
Disulfide
bridge
Variable
regions
B cell Constant
antigen C C
regions
receptor Light
chain
Transmembrane
region
Heavy Plasma
chains membrane
B cell Cytoplasm of B cell
Antigen Recognition by B Cells and
Antibodies
• Each B cell antigen receptor is a Y-shaped
molecule with two identical heavy chains and
two identical light chains
• The constant regions of the chains vary little
among B cells, whereas the variable regions
differ greatly
• The variable regions provide antigen
specificity
• Binding of a B cell antigen receptor to an antigen
is an early step in B cell activation
• This gives rise to cells that secrete a soluble
form of the protein called an antibody or
immunoglobulin (Ig)
• Secreted antibodies are similar to B cell
receptors but lack transmembrane regions that
anchor receptors in the plasma membrane
© 2011 Pearson Education, Inc.
Antigen Recognition by T Cells
• Each T cell receptor consists of two different
polypeptide chains (called and )
• The tips of the chain form a variable (V) region;
the rest is a constant (C) region
• T cell and B cell antigen receptors are
functionally different
© 2011 Pearson Education, Inc.
Antigen-
Figure 43.11
binding
site
T cell Variable
antigen V V regions
receptor
C C Constant
regions
Disulfide Transmembrane
bridge region
chain chain
Plasma
membrane
T cell Cytoplasm of T cell
Figure 43.2
Pathogens
(such as bacteria,
fungi, and viruses)
INNATE IMMUNITY Barrier defenses:
Skin
• Recognition of traits shared Mucous membranes
by broad ranges of Secretions
pathogens, using a small Internal defenses:
set of receptors Phagocytic cells
• Rapid response Natural killer cells
Antimicrobial proteins
Inflammatory response
ADAPTIVE IMMUNITY Humoral response:
Antibodies defend against
• Recognition of traits infection in body fluids.
specific to particular
pathogens, using a vast Cell-mediated response:
array of receptors Cytotoxic cells defend
against infection in body cells.
• Slower response
