Smart antigen-presenting cells (APCs) use proteolysis with restraint, according to Lélia Delamarre, Ira Mellman, Sergio Trombetta, and colleagues (Yale University, New Haven, CT). Although perhaps contrary to prevailing assumptions, this less-is-more approach may prevent excessive or premature peptide processing.
“We've been led to believe that, since so many different antigens have to be made, APCs need a large, diverse set of [protease] activities,” says Mellman. But dendritic cells (DCs) and B cells are no more endowed with lysosomal proteases than is the average fibroblast, based on the new results. Of the APCs tested, only macrophages were particularly protease packed.