Studies also suggested the importance of TL1A signaling in the pathogenesis of autoimmune or inflammatory diseases such as rheumatoid arthritis (8, 12, 13, 23, –, 26), psoriasis (27, 28), primary biliary cirrhosis (29, 30), ankylosing spondylitis (31, 32), and allergic lung inflammation (33, 34), however, the disease mechanisms involving TL1A and its receptor DR3 especially in humans remain elusive. Here, TNFSF15 is linked to rheumatoid arthritis.