PROCESSING OF BACTERIAL-ANTIGENS FOR PRESENTATION TO CLASS-I AND CLASS-II MHC-RESTRICTED T-LYMPHOCYTES

Phagocytosis leads to the destruction of many bacteria and the proteol ytic degradation of bacterial antigens within phagolysosomes to produc e immunogenic peptides that bind to Class II major histocompatibility (MHC) molecules within vacuolar compartments. On the other hand, Class I MHC molecules bind cytosol-derived peptides, including peptides fro m bacteria that escape the vacuolar system and penetrate into the cyto sol. A recently described pathway may also allow the presentation of p eptides from intravacuolar organisms by Class I MHC molecules in some cases. T cell recognition of peptide-MHC complexes then provides the p rimary basis for specific immunity to protein antigens of bacteria. Th is article will review the subcellular compartments and mechanisms inv olved in generating immunogenic peptides, the subcellular localization of MHC molecules that bind these peptides, and bacterial parameters t hat affect antigen processing.