PeptideMHCcomplex

PeptideMHCcomplex refers to the molecular assembly formed when a peptide antigen binds to a major histocompatibility complex (MHC) molecule on the surface of an antigen-presenting cell. The two main classes of MHC molecules, class I and class II, present peptides to different subsets of T cells and differ in the origin, length, and processing of the bound peptides.

MHC class I peptides are typically derived from intracellular proteins and are generated by the proteasome. These peptides are transported into the endoplasmic reticulum by the transporter associated with antigen processing (TAP) and loaded onto MHC class I molecules with the help of the peptide-loading complex, including chaperones such as calnexin, calreticulin, and ERp57. Peptides bound to MHC class I are usually 8 to 11 amino acids long and are recognized by CD8+ T cells. The peptide sits in a groove formed by the MHC heavy chain and beta-2 microglobulin, with specific anchor residues that influence binding and T cell recognition.

MHC class II peptides are generally derived from exogenous proteins that are endocytosed and degraded in endosomes/lysosomes. Loading occurs in specialized compartments with the help of auxiliary molecules such as HLA-DM. These peptides are typically longer, about 13 to 25 amino acids, and are presented to CD4+ T cells. The peptide binds in a groove formed by the alpha and beta chains of the MHC II molecule.

PeptideMHCcomplexes are central to antigen presentation, immune surveillance, and the initiation of adaptive immune responses. They are also used in research and clinical contexts, for example as pMHC tetramers or dextramers to detect antigen-specific T cells.