Peptide WIY

Unlike B cells that binds many different types of antigens, T cells bearing αβ antigen receptors (TCRs) usually react only with peptides from foreign antigens bound in the grooves of major histocompatibility complex proteins (MHC). Recent evidence suggests that this bias toward MHC presented antigens is caused by two phenomena: 1) the sequences of TCR variable regions themselves, which appear to have been selected during evolution to have some intrinsic affinity for MHC and 2) positive and negative selection in the thymus, which allows the maturation of only those thymocytes that bear TCRs that react weakly with self MHC⁺ self peptides.