Studies of gene-knockout mice or specific inhibitors for cathepsins have demonstrated that the emzymatic activities of cathepsins play key roles in the pathogensesis of autoimmune diseases such as autoimmune myasthenia gravis, rheumatoid arthritis, Sjogren's syndrome, and autoimmune Type-1 diabetes (T1D) [6]–[9]. Here, CTSS is linked to rheumatoid arthritis.