Protein Plasticity and Peptide Editing in the MHC I Antigen Processing Pathway

Cytotoxic T lymphocytes (CTL) of the vertebrate immune system can eliminate pathogeninfected or malignantly transformed cells offering protection from infectious and noninfectious diseases. This protection is afforded by receptors expressed on the cell surface of CTLs, with each T cell receptor recognising a specific complex of an MHC I molecule bound to a particular peptide. In humans six MHC I allotypes can be expressed, each of which may bind a variety of peptides. Thus, thousands of different pMHC complexes are present on antigen presenting cells, where they are scanned by CTL, which may be activated if a cognate ligand is encountered.