The cell biology of MHC class I antigen presentation

MHC class I antigen presentation refers to the co-ordinated activities of many intracellular pathways that promote the cell surface appearance of MHC class I/beta(2)m heterodimers loaded with a spectrum of self or foreign peptides. These MHC class I peptide complexes form ligands for CD8 positive T MHC class I heterodimers are loaded within the endoplasmic cells and NK cells reticulum (ER) with peptides derived from intracellular proteins. Alternatively, MHC class I molecules may be loaded with peptides derived from extracellular proteins in a process called NHC class I cross presentation. This pathway is less well defined but can overlap those pathways operating in classical MHC class I presentation and has recently been reviewed elsewhere (1). This review will address the current concepts regarding the intracellular assembly of MHC class I molecules with their peptide cargo within the ER and their subsequent progress to the cell surface.