Peptide FKA

T cell antigen receptors (TCR) recognize ligands displayed on classical Major Histocompatibility Complex (MHC), non-classical MHC and MHC-like proteins. Classical MHC proteins are the most polymorphic genes in humans. Within a population, MHC allele diversity greatly limits the ability of pathogens to escape immune responses. However, the diversity of MHC creates a unique problem for generating host-MHC restricted mature T cell repertoires. Prior to selection, TCR rearrangement has to generate a collection of TCRs which, in aggregate, have the ability to recognize any of the possible MHC classes and alleles present within a species. After selection, individual TCRs must be MHC class specific, allowing a division of labor between MHC class II-reactive helper T cells and MHC class I-reactive cytotoxic T cells.