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BIOL 2050U (48)


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BIOL 2050U
Peter Cheung

T-CELL ANTIGEN RECOGNITION B and T cells are morphologically identical Claman studies – BOTH T and B cells are necessary for antibody response to antigen T cells obey CLONAL SELECTION also T cells don’t secrete antibodies once activated; they just proliferate sole function of THYMUS is to make T cells UNIQUE ANTIGEN RECOGNITION MECHANISM T cells recognize short linear aa stretches (approx. 10 aa’s)  no CONF. DET. only recognize proteins (no CHO’s) antigens must be PRESENTED on APC (antigen presenting cell) DENDRITIC cells Macrophages, to an extent MHC RESTRICTION – T cells only respond to host APC’s indicates there must be a genetic link  link is the major histocompatability complex lots of polymorphism in the MHC between individuals MHC: (HLA in humans) encodes cell surface proteins recognized by T cells 3 classes of genes (I, II, III) class human mouse Comp I A, B, C genes K,D,L HC, β2 II DP, DQ, DR IA, IE α, β Class I – expressed everywhere except RBC, neural tiss. Class II – B Cells, macrophages, dendridic cells **these genes are highly polymorphic**  “balanced polymorphism” no “wild-type” exists ***a T cell recognizes ONE of the several expressed MHC on an APC*** T CELL ANTIGEN RECEPTORS receptors behave as a unit that SIMULTANEOUSLY identifies Ag and MHC αβ heterodimer held together by disulfide bonds rearrangement within these units same as in B-Cells however: no class switching no somatic hypermutation CD3 – unique to T-cells; play no role in specific recognition involved in TCR surface expression and signal transduction can target CD3 to deplete T cells AG PROCESSING protein must first bind to MHC in APC before T-cell is even involved MHC is highly polymorphic  some APC’s will bind certain antigens in certain individuals; others won’t (most humans respond to most antigens) certain HLA genotypes predispose individuals to autoimmune diseases ANTIGEN-MHC BINDING CLASS I – at most 6 different types peptide binds tightly in groove between 2 alpha helices pocket not specific for ALL 10 aa’s, just at ANCHOR po
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