Major histocompatibility complex–antigen complex on antigen-presenting cell (Usually referred to as MHC–peptide complex or pMHC. Specific abbreviations: MHC-I–peptide complex, MHC-II–peptide complex.)

The major histocompatibility complex–antigen complex on antigen-presenting cells consists of an MHC molecule (either Class I or Class II) bound to a specific antigen peptide, displayed on the surface of an APC. MHC class I molecules present intracellular-derived peptides primarily to cytotoxic CD8+ T cells (on all nucleated cells), while MHC class II presents peptides derived from extracellular sources to helper CD4+ T cells (on professional APCs). Recognition of these complexes by T cell receptors is the fundamental step for the initiation and regulation of the adaptive immune response, determining self–nonself discrimination and immune activation or tolerance. MHC–antigen complexes are involved in infectious disease defense, autoimmune conditions, cancer immunotherapy, transplantation rejection, and are the molecular basis for HLA typing and many immunological diagnostics[1][2][3][4][8]. If you need deconstructed versions (Class I or Class II) or human-specific (HLA, etc.), specify for more details.

Other names

MHC–peptide complexpMHC complexMHC–antigen complexpeptide–MHC complexHLA–antigen complex (in humans)

Blocking T cell activation by interfering with antigen presentation Enhancing antigen presentation to stimulate immune responses (vaccines/adjuvants) Inhibiting peptide loading (preventing effective presentation) Modulating MHC expression/cross-presentation