Major histocompatibility complex class I molecule–viral peptide complex (MHC-I–peptide complex (no standard abbreviated form, but MHC-I is common for the class I molecule))

Major histocompatibility complex class I molecules (MHC-I) are cell surface glycoproteins responsible for presenting short peptide fragments, typically 8–10 amino acids, derived from intracellular proteins—including those from viral pathogens—to CD8+ cytotoxic T cells[1][3][4][2]. The complex of a viral peptide bound to MHC-I forms after the peptide is generated by proteasomal degradation in the cytosol, then transported into the endoplasmic reticulum, loaded onto the MHC-I protein (with the help of molecular chaperones such as tapasin, calreticulin, and the transporter associated with antigen processing—TAP), and finally trafficked to the cell surface[1][4][3]. There, the viral peptide–MHC-I complex is recognized by the T cell receptor (TCR) on CD8+ T lymphocytes, triggering targeted cell death and contributing to the adaptive immune response to infection[4][5][2]. These complexes are highly polymorphic due to the diversity of MHC alleles (especially HLA variants in humans), allowing broad coverage of pathogen epitopes across the population[2]. Structural studies show that the MHC-I molecule binds peptides in a groove formed by its α1 and α2 domains; both viral and non-viral peptides can be accommodated due to the flexible binding site[5][1]. Because MHC-I–peptide complexes directly determine whether a cell is recognized as infected or abnormal, they are central to immunity against viruses and cancers, and abnormalities in their presentation can contribute to immune escape, immune deficiencies, or autoimmunity[2][4]. There are currently no marketed drugs directly targeting the peptide–MHC complex, but immunotherapies such as checkpoint inhibitors and peptide vaccines function by enhancing or modulating responses to cells displaying these complexes.

Other names

MHC class I–viral peptide complexPeptide–MHC class I complexpMHC-I complexViral antigen–MHC class I complex

Presentation of viral (or tumor) peptides triggers recognition by cytotoxic T lymphocytes (CTLs) via their T cell receptor (TCR), leading to cell-mediated immunity and killing of infected or malignant cells[3][4]. Some viral proteins inhibit MHC-I processing/transport to evade immunity[4].