Notes April 22

April 22, 2008

I. Cell mediated vs. Humoral Immunity

a. Cell-mediated
*Interactions between cells required
*CD8+ - T-cell killing virus-infected cell

b. Humoral
*”Fluids”= humors (blood serum)
*Does not require cell because from soluble antibodies in serum

II. Antibody production

a. B1 cells and marginal zone B-cells
*Produce low-affinity antibodies, independent of interaction with T-cells in absence of infection
*Because antibodies nonspecific act more like collectins, other genetic opsonins than like traditional antibodies

b. Follicular zone B-cells
*Chad’s Favorite!
*Found in secondary lymphoid tissue follicles
*Interact with activated, mature T-cells (CD4+)
*Interaction with T-cells-> clonal expansion and differentiation
*All follicular B-cells start making IgM-type antibody

III. Functions of antibodies

a. Neutralizing
*Antibodies stick to pathogen antigen, prevent pathogen from causing problems

b. Opsonization
*Fc Receptor on macrophages that will interact with the Fc region of the antibody which will lead to phagocytosis

c. Complement activation
*C1 binds to Fc region of antibody causing complement cascade, creation of MAC on microbe surface

d. Effector functions
*They stimulate other cells to act
IV. Structure of antibodies- note similarity to TCRs
a. Heavy and light chains
*Each antibody made of 2 heavy and light chains
*Antigen-binding domain from both heavy and light chains
*Both antigen-binding sites on an antibody bind same antigen

b. Fc region- conserved
*Doesn’t vary by epitope, but has an effector functions
*Varies among antibody isotypes

c. Fab region
*Contains antigen binding site

i. Variable domain
*Variability in determined by same mechanisms as in T-cell receptors
*There is going to be V, D, J recombination because the variability

ii. Antigen binding
*Antigens for antibodies: proteins, carbohydrates and lipids

d. Hinge region
*Links the Fab and Fc via chain of small amino acid sequences
**Flexibility allows binding of antigens very close to each other.

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