Download Adaptive Immune Response

ADAPTIVE
IMMUNE RESPONSE
When the body is
exposed to an antigen
Innate Immunity
Adaptive Immunity
(Acquired)
Active immunity
•B cells encounter antigens and produce antibodies
• Active immunity can be naturally or artificially acquired
Passive Immunity
• Antibodies are obtained from someone else
• Conferred naturally from a mother to her fetus
• Conferred artificially from immune serum or
gamma globulin
• Immunological memory does not occur
• Protection provided by “borrowed antibodies”
Types of Adaptive Immune Response
1. Cell-mediated immune
response (CMIR) – T cells
2. Humoral immune response – B cells
Humoral Immune Response
B lymphocytes with specific receptors bind to a
specific antigen
 The binding event activates the lymphocyte to
undergo clonal selection
 A large number of clones are produced (primary
humoral response)
 Most B cells become plasma cells
Produce antibodies to destroy antigens
Activity lasts for four or five days
 Some B cells become long-lived memory cells
(secondary humoral response)
Activation of B cells
Recognition of antigen by B cells
• B cells recognize their cognate antigen in its native form.
• They recognize free antigens in the blood or lymph using their Bcell receptor (BCR) or membrane bound-immunoglobulin
• After antigen recognition, the B cell ingests the whole protein
antigen and processes it into peptides for presentation to
activated T cells.
Antibodies
 Proteins that recognize and bind to a particular
antigen with very high specificity.
 Made in response to exposure to the antigen.
 One virus or microbe may have several antigenic
determinant sites, to which different antibodies may
bind.
 Each antibody has at least two identical sites that
bind antigen: Antigen binding sites.
 Valence of an antibody: Number of antigen binding
sites. Most are bivalent.
 Belong to a group of serum proteins called
immunoglobulins (Igs).
Antibody Structure
 Monomer: A flexible Y-shaped molecule with four
polypeptide chains:
– 2 identical light chains
– 2 identical heavy chains
held together by disulphide
bridges
 Variable Regions:
Two sections at the end of Y’s arms.
 Contain the antigen binding sites (Fab).
Identical on the same antibody, but vary from one antibody
to another.
 Constant Regions:Stem of monomer and lower parts of Y
arms.
 Fc region: Important because they can bind to complement
or cells.
Antibody Structure
Hinge Region
The region at which the
arms of the antibody
molecule forms a Y is
called the hinge region
because there is some
flexibility in the molecule
at this point.
An antibody digested by papain
yields three fragments: two Fab
fragments and one Fc fragment
General Functions of Immunoglobulins
A. Antigen binding (primary function)
• Immunoglobulins bind specifically to one or more
antigenic determinant and can result in protection of
the host.
Valency:
Is the number of antigenic determinants that an
individual antibody molecule can bind. The valency of
all antibodies is at least two and in some instances
more.
B. Effector functions
Fixation of complement
lysis of cells, release of
biologically active molecules
Binding to various cells:
phagocytic cells, lymphocytes, mast cells, and
basophils have receptors that bind immunoglobulins
and thus get activated.
 Some immunoglobulins also bind to receptors on
placental trophoblasts, leading to transfer of the Igs
across the placenta (provide immunity to the fetus)
Immunoglobulin Classes
• IgG - Gamma (γ) heavy chains
Immunoglobulin
• IgM - Mu (µ) heavy chains
Light Chain Types:
• IgA - Alpha (α) heavy chains
Kappa (κ)
• IgD - Delta (δ) heavy chains
Lambda (λ)
• IgE - Epsilon (ε) heavy chains
Immunoglobulin Subclasses
• IgG Subclasses
– IgG1 - Gamma 1 (γ1) heavy chains
– IgG2 - Gamma 2 (γ2) heavy chains
– IgG3 - Gamma 3 (γ3) heavy chains
– IgG4 - Gamma 4 (γ4) heavy chains
• IgA subclasses
– IgA1 - Alpha 1 (α1) heavy chains
– IgA2 - Alpha 2 (α2) heavy chains
Different Immunoglobulins
Type
Number of Ag
binding sites
Site of action
Functions
IgG
2
•Blood
•Tissue fluid
•Can cross placenta
•Increase
macrophage activity
•Antitoxins
•Agglutination
IgM
10
•Blood
•Tissue fluid
Agglutination
IgA
2 or 4
•Secretions (saliva,
tears, small intestine,
vaginal, prostate,
nasal, breast milk)
•Stop bacteria
adhering to host
cells
•Prevents bacteria
forming colonies on
mucous membranes
IgE
2
Tissues
•Activate mast cells
 HISTAMINE
•Worm response
IgD
2
B-cell surfaces where it •B cell activation
functions as a receptor
for Ag.
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