The products of MHC genes are antigen-presenting molecules (APMs) designed for antigen fragment (peptide) presentation to the T-cell receptor. In particular, MHC Class I molecules play a key role in the immune system by presenting endogenously synthesized peptides derived from the endoplasmic reticulum (ER) lumen to CD8+ T-lymphocytes, which are usually cytotoxic T-cells. MHC Class I antigens are heterodimers consisting of one 44kD highly polymorphic alpha chain non-covalently complexed with an invariant 11.5kD beta2-microglobulin subunit.
