Figure 2.

Potential roles of NADPH oxidase in antigen presentation. MHC-I and MHC-II are both present in phagosomes and endosomes of antigen presenting cells. For simplicity, MHC-I has been shown in a phagosome, while MHC-II has been shown in an endosome. During crosspresentation, exogenous antigens can be processed within these compartments by proteases, prior to loading onto MHC-I. NADPH oxidase has been shown to regulate antigen processing and MHC-I crosspresentation in DC; however, whether NADPH oxidase regulates this process by modulating the phagosomal pH or redox microenvironment is currently debated. During classical MHC-II presentation, exogenous antigens are processed within vesicular compartments by proteases and GILT. Following the removal of CLIP by HLA-DM, processed peptides are loaded onto MHC-II. NADPH oxidase can also regulate MHC-II presentation in B cells by altering the peptide repertoire displayed by MHC-II, possibly in favor of self antigens. However, the mechanism underlying this phenomenon is still unclear. Whether or not NADPH oxidase, MHC-I and -II, and the antigen processing machinery co-localize within the same vesicular compartment also remains to be elucidated.