Cysteine protease cathepsin S as a key step in antigen presentation

Cathepsin S is a cysteine protease in the papain super-family. Studies have shown that it is highly expressed in antigen-presenting cells. Along with other lysosomal proteases, cathepsin S plays an important role in the major histocompatibility complex class II-restricted antigen presentation, especially in the degradation of the invariant chain, a chaperone peptide bound to the class II complex. Compared with other lysosomal cysteine proteases, cathepsin S has displayed some unique characteristics. As a result, cathepsin S has been implicated as a potential target in the treatment of various disorders ranging from autoimmune diseases to atherosclerosis. Furthermore, a number of small-molecule cathepsin S inhibitors have demonstrated efficacy in disease-relevant models.