Notes 4/22

Antibodies (4.22)

I. Cell-mediated
a) Cell-mediated
-interaction between cells required
-ex: CD8+ T-cell killing virus-infected cell
b) Humoral
-“fluids”=humorsblood serum
-in the absence of cells, because from soluble antibodies in serum
II. Anitbody production-released by B-cells
a) B1 cells and marginal zone B-cells
-behave like innate immune cells
-produce low-affinity antibodies, independent of interaction with T-cells,
in absence of infection
-because antibodies are nonspecific, act more like collectins, other generic
opsonins than like traditional antibodies
b) Follicular zome B-cells
-acquired immunity
-found in follicles in secondary lymphoid tissue
-interact with activated, mature T-cells (CD4+)
-interaction with T-cellsclonal expansion and differentiation
*all follicular zone B-cells start making IgM-type antibody
i. Activated by T-cells in secondary lymphoid tissue
III. Functions of antibodies
a) Neutralizing
-antibodies stick to pathogen antigens, prevent pathogen from causing
problems
b) Opsonization
-Fc receptor on macrophages which interacts with the antibody Fc region,
phagocytosis
c) Complement activation
-C1 binds to Fc region of antibodycomplement cascade, creation of
MAC on microbe surface
d) Effector functions
-stimulating other cells to do other things
-IgE bound to parasite surfaceeosinophil degranulation
IV. Structure of antibodies-note similarity to TCRs
a) Heavy and light chains
-each antibody made of 2 heavy and 2 light chains
-antigen-binding region, made up of 1 heavy and 1 light chain, which
2 binding regions per antibody
-both binding domains code for the same antigen
b) Fc region
-conserved region of the antibody
-doesn’t vary by epitope, but has effector functions
-can vary some between classes of antibodies
c) Fab region
-contains antigen binding site
i. Variable domain
-variability in determined by the same mechanisms in T-cell
receptors
-VDJ recombination during mitosis
ii. antigen binding
-proteins, carbohydrates, some lipids
d) Hinge region
-links the Fab region and Fc region via chain of small amino acids
-makes antibodies very flexible, making it possible to bind to antigens
that are REALLY close together
Differences from TCRs: 1. Ab's have 2 binding areas, where the TCRs only have 1
2. Ab's can bind more than just proteins
Similarities: 1.Ab's are made of light and heavy chains, which is similar to alpha and beta constructing TCR's (although both alpha and beta are more like light chains than heavy chains)
2. The variable region is created in a way that similar to TCRs with the VDJ recombination