Cell Bio Lect 37 Notes p1228-1238 TCR and MHC

Alpha-beta heterodimer has 2 domains. N-terminal domain that binds to foreign antigen displayed on target cell's surface. Invariant proteins associated with TCR send signal into T cell.

VDJ/C "minigenes" randomly assorted just like antibodies, but no somatic hypermutation, so, no affinity maturation (is high affinity as important here?)

T_H1-activate macrophages. T_H2-stimulate B cells. T_C kill infected cells (hopefully before virus proliferation). DHEA (European old men, French babies infant formula) deflects toward T_H1

Class I MHC(on all nucleated cells) present Ag to CD8⁺ T_C cells. Class II MHC present Ag to CD4⁺ T_H cells.

Class I molecule has 3 extracellular domains, 2 of which create Ag-binding "cradle".Beta-2 microglobulin doesn't recognize Ag, is not MHC encoded, but is essential.

Class II alpha and beta chains each have a domain that contributes to Ag binding.

Class I crable recognizes 8-10 a.a. in protein backbone, not a.a. "R" groups, so, many polypeptides bind. Allelic forms recognize various "groups" of Ags.

Class II recognize longer (15-24 a.a.), more heterogeneous peptides. Does this make sense?

Fewer than 20 different Class II, but present almost unlimited variety of foreign Ag.

CD4 (on helper T cell) binds to class II MHC molecule. CD8+ (on cytotoxic T) binds to Class I MHC molecule. (Both accessory receptors). Tail of each helps activate T cells.

MHC restriction: target must have same Class I MHC molecules for Tc to recognize.

Proteins inside cell pumped into E.R., put onto Class I, taken to surface(interferon amplifies).

TC killing involves perforin, or, signaled apoptosis. Some cancers thought to involve failure in apoptosis.