T-cell receptor and Major histocompatibility complex (TCR and MHC)

The **T-cell receptor (TCR)** is a membrane-bound heterodimeric receptor expressed on the surface of T lymphocytes that recognizes antigenic peptides presented by the **major histocompatibility complex (MHC)** on other cells[2][7][8][10]. The MHC (in humans, also called HLA) consists of highly polymorphic molecules, classified as Class I (present on all nucleated cells, present peptides to CD8+ cytotoxic T cells) and Class II (present on antigen-presenting cells, present peptides to CD4+ helper T cells)[4][2][7]. Activation of the T cell requires engagement of the TCR with a specific peptide–MHC complex (pMHC), initiating a signaling cascade that triggers cellular responses fundamental to adaptive immunity[2][3][10]. The TCR–MHC interaction is highly specific and forms the molecular basis for recognition of self versus non-self, with mechanisms evolved for both broad recognition (diversity via V(D)J recombination) and self-tolerance (thymic selection)[7]. This axis is therapeutically targetable in the context of immunotherapy, autoimmunity, infection, and transplantation biology, but remains challenging due to the vast diversity and specificity of TCR–MHC interactions. Notably, the entity "T-cell receptor and Major histocompatibility complex" describes a **functional molecular interaction** (the immune synapse) rather than a single defined molecule, so the canonical target should be specified as either "T-cell receptor" or "Major histocompatibility complex" depending on context[2][4][7].

Other names

TCR–MHC complexT-cell antigen receptor–MHCTCR–pMHCTCR–HLA complex

Modulation of T-cell activation (upregulation or blockade of immune response). Enhancement of antigen-specific cytotoxicity. Inhibition of signaling pathways downstream of TCR (e.g., calcineurin inhibition). Induction of immune tolerance.