Figure 2

Schematic summary of the role of endosomal proteases in antigen presentation. Both endoproteases (a) and exopeptidases (b, c) contribute to terminal degradation of internalized protein. The figure emphasizes that the progressive fragmentation of an internalized antigen (depicted in gray) is regulated by two separate processes: the presence of antibody and the ability of mature MHC class II to complex with free peptides. Antibodies greatly enhance the efficiency of antigen uptake and alter antigen processing [55]. Mature MHC class II molecules bind peptides and direct these complexes to the cell surface [59].