Figure 1.

Classical and alternative pathways for MHC class I presentation. Cells with deficiencies in components of the MHC class I processing pathway, such as TAP, can present a repertoire of peptides derived from alternative processing pathways. Different “housekeeping” cell functions such as signal peptide cleavage, protein maturation in the Golgi, and protein/organelle disposal via autophagy can provide peptide ligands for MHC class I loading.