Major histocompatibility complex–peptide complex (MHC–peptide complex (or pMHC))

The **major histocompatibility complex–peptide complex** refers to a molecular structure formed when an intracellularly derived short peptide binds within the groove of a major histocompatibility complex (MHC) molecule. This composite structure is then displayed on the surface of an antigen-presenting cell. The primary biological function is **to present processed antigens for recognition by T lymphocytes**, enabling discrimination between self and non-self peptides—a cornerstone event in adaptive immunity. There are two main classes: *Class I* MHC-peptide complexes present peptides from endogenous proteins primarily to CD8+ cytotoxic T lymphocytes, while *Class II* MHC-peptide complexes display exogenous peptides mainly to CD4+ helper T lymphocytes.[1][2] The specificity arises from both the sequence/structure diversity among individual’s MHC alleles and the nature of bound peptides.[3] Recognition by a matching **T cell receptor** triggers downstream immune responses including cytotoxicity or cytokine production.[5] These complexes play central roles not only in defense against pathogens but also in anti-tumor immunity,[4] transplant rejection, autoimmunity,[1] vaccine response prediction,[3] and are increasingly being targeted/exploited using advanced immunotherapies such as engineered antibodies (“TCR-like” Abs), adoptive cellular therapies like CAR-T/TCR-T,[6] as well as being used diagnostically for monitoring immune responses. Their extreme genetic polymorphism underlies both their effectiveness at population-level pathogen defense—and challenges for universal drug/vaccine development.[2] In summary, “Antigen-specific peptide-MHC complex” describes a fundamental molecular entity at the heart of adaptive immunity that serves both as a natural ligand for therapeutic targeting strategies and as an essential biomarker across many diseases.

Other names

peptide-MHC complexpMHCantigen–MHC complexMHC–antigen complexHLA–peptide complex (in humans)

Drugs or biologics targeting this molecule act by one of the following mechanisms: - Recognition and binding of specific peptide-MHC complexes by engineered antibodies or T cell receptors to mediate cytotoxicity against target cells presenting disease-associated antigens.