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***