CTSS-deficient mice exhibit defective invariant chain (Ii) processing in dendritic cells and B cells, including the impairment of antigenic peptide presentation, suggesting that CTSS is essential for antigen presentation and further that inhibition of CTSS may be useful for treatment autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus (SLE), and multiple sclerosis12–14. Here, CTSS is linked to autoimmune disease.