Major Histocompatibility Complex Class I Molecule (MHC Class I)

Major histocompatibility complex (MHC) class I molecules are cell surface glycoproteins found on all nucleated cells and platelets in vertebrates. Their primary function is to present peptide fragments derived from intracellular proteins to cytotoxic T lymphocytes (CTLs), specifically CD8+ T cells, enabling the immune system to monitor cellular health and detect infected or abnormal cells. They are heterodimers composed of a polymorphic heavy α-chain (with three extracellular domains: α1, α2, and α3) and an invariant light chain called beta-2 microglobulin (β2m). The peptide-binding groove is formed by the α1 and α2 domains; it accommodates peptides typically 8–10 amino acids long. The α3 domain interacts with the CD8 co-receptor on cytotoxic T cells. β2-microglobulin stabilizes the structure but does not span the membrane. MHC class I genes correspond to HLA-A, HLA-B, and HLA-C loci within the human leukocyte antigen (HLA) complex. CTLs recognize foreign or abnormal peptides presented by MHC class I. If a CTL's receptor matches both peptide and MHC allele, it triggers apoptosis in target cells displaying non-self antigens such as viral or tumor-derived proteins. Normal expression of self-MHC class I inhibits natural killer (NK) cell activity; Loss or reduction of surface MHC-I can activate NK-mediated killing.

Other names

MHC-IHLA Class IHuman Leukocyte Antigen Class I

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