CTSS is a lysosomal cysteine protease which is highly expressed in macrophages [33], has specific roles in MHC class II antigen presentation [34], toll-like receptor signaling [35] and is implicated in the pathology of multiple immune disorders, including rheumatoid arthritis, emphysema and atherosclerosis [36–39]. The gene discussed is CTSB; the disease is rheumatoid arthritis.