TIGIT and systemic lupus erythematosus: To confirm in detail whether TIGIT-expressing cells are involved in the pathogenesis of autoimmune diseases, we first checked TIGIT expression in T cells in patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and Sjögren’s syndrome (SjS), where TIGIT expression is known to be changed in peripheral T cells21–23.