- MHC encoded by HLA genes. Present antigen fragments to T cells and bind T-cell receptors (TCRs).
MHC I MHC II LOCI HLA-A, HLA-B, HLA-C
MHC I loci have 1 letter
HLA-DP, HLA-DQ, HLA-DR
MHC II loci have 2 letters
BINDING TCR and CD8 TCR and CD4 STRUCTURE 1 long chain, 1 short chain 2 equal-length chains (2 α, 2 β) EXPRESSION All nucleated cells, APCs, platelets
Not on RBCs
APCs FUNCTION Present endogenously synthesized antigens (eg, viral or cytosolic proteins) to CD8+ cytotoxic T cells Present exogenously synthesized antigens (eg, bacterial proteins) to CD4+ helper T cells ANTIGEN LOADING Antigen peptides loaded onto MHC I in RER after delivery via TAP (transporter associated with antigen processing) Antigen loaded following release of invariant chain in an acidified endosome ASSOCIATED PROTEINS β2-microglobulin Invariant chain