Major histocompatibility complex class I molecule; Major histocompatibility complex class II molecule (MHC-I; MHC-II)

Major histocompatibility complex (MHC) class I and II molecules are cell surface glycoproteins critical for antigen presentation in the adaptive immune system[1][2][4][5][6][7].\n- MHC-I molecules are found on almost all nucleated cells and present endogenous peptide antigens (typically from viruses or abnormal proteins) to CD8+ cytotoxic T lymphocytes.\n- MHC-II molecules are primarily on antigen-presenting cells (such as dendritic cells, macrophages, B cells) and present exogenous antigens (from extracellular pathogens) to CD4+ helper T cells.\nBoth MHC classes are highly polymorphic, ensuring broad immune recognition, but also conferring increased risk for transplant rejection and some autoimmune diseases. MHC molecules are essential for T cell activation: their peptide-binding grooves display short peptides (8–10 aa for MHC-I; 13–25 aa for MHC-II) for surveillance by T cell receptors[1][4][5][6][7].

Other names

MHC class IMHC class IIHLA class I (in humans: HLA-A, HLA-B, HLA-C)HLA class II (in humans: HLA-DR, HLA-DP, HLA-DQ)

Promote recognition and killing of infected or cancerous cells via antigen presentation\n Drugs may increase antigen loading, enhance T cell activation, or inhibit immune responses to prevent rejection/allergy