Major histocompatibility complex class I molecule, major histocompatibility complex class II molecule, and T-cell receptor complex (MHC class I/II–TCR complex)

The **major histocompatibility complex (MHC) class I and class II molecules** are cell-surface proteins that present peptide antigens to T cells as part of the immune surveillance process. MHC class I molecules present degraded intracellular peptides to **CD8+ cytotoxic T cells**, while MHC class II molecules present extracellular peptide fragments to **CD4+ helper T cells**[1][2][4][7]. The **T-cell receptor (TCR)** is a membrane-bound heterodimer expressed on the surface of T cells that specifically recognizes antigens bound within the grooves of MHC class I or II molecules on antigen-presenting cells or infected cells[2][3][5][6]. Structural studies show the TCR binds diagonally over the peptide/MHC (pMHC) complex, engaging both the presented peptide and MHC molecule, a binding mode essential for T-cell specificity and activation[3][6]. The engagement of the complex, often with co-receptors such as CD4 or CD8, initiates T-cell signaling, which is the central event in adaptive immune responses. **IMPORTANT NOTE:** This "target" as defined (MHC Class I/II and T-cell Receptor complex) is not a *single biomolecule*, but a **supramolecular complex** formed transiently at the immunological synapse between two cells. Each of its components (MHC class I molecule, MHC class II molecule, and T-cell receptor) is a recognized immune target, but the complex itself is not conventionally drugged as a discrete pharmacological entity[3][6]. Instead, most interventions modulate its assembly or downstream signaling. Therefore, **is_incorrect = true** since the entry refers to a functional interaction rather than to a distinct canonical biomacromolecule. For structured data purposes, you should represent them as separate targets unless the purpose is to study inter-molecular recognition or signaling.

Other names

MHC–TCR complexPeptide–MHC–TCR complexpMHC–TCR complex

Modulation of immune response by blocking co-receptors or downstream signaling after TCR–pMHC engagement; Enhancement or suppression of T-cell activation; Induction of immune tolerance or breaking immune tolerance via pMHC presentation