Major histocompatibility complex–peptide:T cell receptor complex (MHC–peptide:TCR complex)

The major histocompatibility complex–peptide:T cell receptor complex (MHC–peptide:TCR complex), also referred to as the pMHC:TCR complex, is a supramolecular assembly central to adaptive immunity. It forms when a T cell receptor (TCR) on the surface of a T lymphocyte binds to a specific peptide antigen presented by a major histocompatibility complex (MHC) molecule (called human leukocyte antigen, HLA, in humans) on an antigen-presenting cell or target cell. MHC molecules are highly polymorphic and are classified as MHC class I (found on most nucleated cells, present peptides to CD8+ T cells) and MHC class II (expressed on professional antigen-presenting cells, present peptides to CD4+ T cells). The peptide in the complex is typically a short fragment derived from endogenous (in the case of MHC I) or exogenous (MHC II) proteins. The recognition of this peptide–MHC (pMHC) complex by a TCR is the first and essential step in triggering T cell activation, leading to downstream immune responses including cytotoxicity, cytokine release, and proliferation. Dysregulation or altered recognition in this axis can result in autoimmunity, ineffective immune response to infections or cancer, or excessive immune activation. Therapeutic targeting of the MHC–peptide:TCR complex includes immune checkpoint inhibitors, engineered T cell therapies, and selective blockade or enhancement of antigen recognition.

Other names

peptide–MHC–TCR complexpMHC:TCR complexTCR:pMHC complexpeptide–MHC–T cell receptor complex

Modulation of T cell activation by interfering with or enhancing TCR–pMHC interaction; Blocking downstream immune signaling (checkpoint inhibition); Redirecting specificity via engineered TCRs or mimetics