Processing of bacterial antigens for peptide presentation on MHC class I molecules.

Professional antigen-presenting cells (pAPC) can process and present exogenous antigens on major histocompatibility complex class I (MHC-I) molecules. This unusual pathway for antigen presentation may represent a physiologically important step in the course of priming and tolerance induction of CD8+ T cells. In addition, it may play an important role in immunological surveillance for pathogens that survive in vacuolar compartments in APC. The goal of the present review is to discuss recent studies on the processing of bacterial-derived antigens for presentation on MHC-I molecules. The antigen presentation emphasized will include bacteria that remain confined in vacuolar compartments. This is in contrast to antigens derived from bacteria that have intrinsic properties allowing translocation across membranes and access into the classical MHC-I presentation pathway. In particular, presentation of bacterial antigens by dendritic cells (DC) will be emphasized, and MHC-I presentation of antigens derived from apoptotic cells, particularly cells induced to undergo apoptosis by microbial infection, will be presented. Finally, some special aspects of the interaction between bacteria and DC will be discussed as it relates to DC maturation, antigen presentation and T-cell stimulation.