1. ADAPTIVE IMMUNE RESPONSE
When the body is
exposed to an antigen
Innate Immunity
Adaptive Immunity
(Acquired)

3. Active immunity Passive 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”

4. Types of Adaptive Immune Response 1
Types of Adaptive Immune Response 1. Cell-mediated immune response (CMIR) – T cells 2. Humoral immune response – B cells

5. 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)

8. 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 B-cell 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.

10. 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).

11. held together by disulphide bridges
Antibody Structure
Monomer: A flexible Y-shaped molecule with four polypeptide chains:
2 identical light chains
2 identical heavy chains
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.
held together by disulphide bridges

12. Antibody Structure

13. 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.

14. An antibody digested by papain yields three fragments: two Fab fragments and one Fc fragment

15. General Functions of Immunoglobulins
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.

16. 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)

17. Immunoglobulin Classes
IgG - Gamma (γ) heavy chains
IgM - Mu (µ) heavy chains
IgA - Alpha (α) heavy chains
IgD - Delta (δ) heavy chains
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
Immunoglobulin Light Chain Types:
Kappa (κ)
Lambda (λ)

18. Different Immunoglobulins

19. Number of Ag binding sites
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
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
Tissues
Activate mast cells
 HISTAMINE
Worm response
IgD
B-cell surfaces where it functions as a receptor for Ag.
B cell activation
Cε4