Adaptive Immunity Flashcards
components of adaptive (acquired) immunity
- humoral branch: B cells and antibodies
- cell-mediated branch: T cells
lymphocytes
- T and B cells
- antigen-specific
randomly generated - T cells have T cell receptor
- B cells have B cell receptor
- have memory
antigen
- a substance that the body sees as foreign or non-self, to which it mounts an immune response
- most antigens are proteins
- some are polysaccharies, glycoproteins, nucleoproteins, etc.
- antigens are found on the surface of viruses and all cells (bacteria, human, parasites, etc.)
epitopes: proteins have epitopes, or short amino acid sequences on antigens that are recognized by antibodies and T cells
describe the primary and secondary immune response
- 1st exposure to an antigen: body has to make antibody for the first time (primary immune response, peaks at about 15 days, falls off quickly)
- 2nd exposure to the same antigen: much higher peak, takes less time to detect the antibody
what is happening during the primary response lag period?
naive B cells and T cells - clonal selection must occur for a specific cell to divide into identical cells (effectors) that make antibodies
naive cell
hasn’t seen it’s epitope
effector cell
has seen it’s epitope, now is activated
which cells become what?
B cell –> plasma cells
CD4T –> T helper
CD8T –> CTL
clonal selection of CD4T cells
- CD4T cells become T-helpers when they 1) see their epitope and 2) receive cytokine signals
- once activated, they help B and CD8T cells get activated
professional antigen-presenting cells (APC’s)
- express class II MHC
- MHC II has epitope on it, presents epitope to naive cell
- macrophages, dendritic cells, B cells are APC’s
- when a pathogen is inside a phagosome, its epitopes will enter the class II MHC pathway
describe clonal selection of T-helper cells
- T-helper cells are selected from CD4-T cells
- professional APC cells phagocytose antigen and present epitopes on cell surface on MHC II. they show this to naive CD4-T cells
- the APC also gives cytokines to the naive CD4 cell telling it to divide. seeing it’s epitope on MHC II AND receiving cytokines are the steps needed to create identical T-helper cells, which will be specific for the same epitope on that antigen!
what are T-helper cells needed for?
to activate B cells (which make antibodies) and CD8-T cells!
how do T-helper cells exert their protective role?
they secrete cytokines to tell:
- B cells to make antibody
- macrophages to become more hostile
- CD8-T cells to become CTL’s (kill target cells)
describe clonal selection of CD8-T cells
- naive CD8-T cells must see their specific epitope presented on MHC I, which is found on any nucleated cell
- they also must receive cytokines from T-helper cells
- with these two things, they can differentiate into cytotoxic T lymphocytes (CTL’s)
- most CTL’s die, but some CD8-T cells will live on as memory cells
differentiate MHC II vs. MHC I
- MHC II: macrophage phagocytoses an antigen, sends it to lysosome, which chops it up, and then one of those pieces is displayed on MHC II (only on APC’s, must present to naive CD4-T cells)
- MHC I: any infected cell shows part of the antigen (an eptitope) that infected it on its surface on MHC I (can be on any nucleated cell, must present to naive CD8-T cells
