Major histocompatibility complex class I–viral peptide complex (MHC class I–viral peptide complex (no widely used unique abbreviation beyond “MHC I–peptide complex” or “pMHC I”))

The **major histocompatibility complex class I–viral peptide complex** is a molecular assembly found on the surface of virtually all nucleated cells that have been infected by viruses or contain abnormal intracellular proteins. The complex is formed when viral peptides, generated through proteasomal degradation of viral proteins, are translocated into the endoplasmic reticulum and loaded onto MHC class I molecules, composed of a highly polymorphic α chain and an invariant β2-microglobulin subunit. The resulting peptide–MHC class I complex is presented at the cell surface, where it is recognized by the T-cell receptor (TCR) on cytotoxic CD8+ T lymphocytes, triggering targeted cell death of the infected cell[1][2][6]. This process is central to adaptive immunity, enabling surveillance for and elimination of virally infected or cancerous cells[4][5]. The specificity of the immune response is determined by the particular viral peptide of 8–10 amino acids bound within the MHC class I cleft and the TCR repertoire[7]. Pathogens and tumors may develop mechanisms to evade detection, such as downregulating MHC class I molecules or interfering with peptide loading[2][6]. While no classical drugs directly target the peptide–MHC complex itself, therapeutic modalities, including TCR-mimic antibodies, engineered T-cell therapies, and vaccines, exploit this axis for the treatment of infection and cancer. Monitoring the composition and expression of viral peptide–MHC complexes serves as a biomarker for immune engagement, efficacy, and disease progression. Safety challenges include potential for autoimmunity and immune escape by reduced complex expression[6].

Other names

Peptide–MHC class I complexViral peptide–MHC complexPeptide–HLA class I complexpMHC class IAntigen–MHC class I complex

Presentation of viral peptides to cytotoxic T lymphocytes (CTLs) via the T-cell receptor; Activation of targeted immune destruction of infected cells; Evasion mechanisms by pathogens may involve downregulation or masking of MHC class I complexes