Major histocompatibility complex protein (MHC)

The Major Histocompatibility Complex (MHC) protein is an essential glycoprotein found on the cell surface of vertebrates, playing a fundamental role in the adaptive immune system by presenting peptide fragments to T cells. MHC molecules are primarily classified into Class I, expressed on almost all nucleated cells to present intracellular peptides to CD8+ cytotoxic T cells, and Class II, which are restricted to professional antigen-presenting cells to activate CD4+ helper T cells [1, 2, 8, 9]. This interaction is vital for self-recognition and the elimination of infected or malignant cells, as MHC-peptide complexes serve as the primary ligands for T-cell receptors [3, 4, 5]. In clinical medicine, MHC proteins are central to transplant compatibility (HLA matching) and are the primary mediators of graft rejection and graft-versus-host disease [5, 6, 7]. Furthermore, certain drugs like abacavir and carbamazepine can bind directly within the MHC peptide-binding groove, altering the repertoire of presented peptides and triggering severe hypersensitivity reactions in genetically predisposed individuals [10, 11]. Many cancers develop immune evasion strategies by downregulating MHC expression, making these proteins a significant focus for the development of TCR-based therapies and cancer vaccines [2, 12]. Due to their extreme genetic polymorphism, MHC proteins remain one of the most complex yet high-impact targets in personalized medicine and immunology [3, 7].

Other names

Human leukocyte antigenHLA complexMHC moleculeTissue-type antigenHistocompatibility antigen

Modulation of antigen presentation, competitive binding within the peptide-binding groove to alter T-cell recognition, and regulation of surface expression levels through cytokine induction or immunosuppressive signaling.