Although functions of Tph cells in peripheral tissues were investigated in a limited number of autoimmune diseases such as UC and juvenile idiopathic arthritis (34, 38), circulating Tph (cTPh) cells with the definition of PD-1hiCXCR5- or PD-1+CXCR5- in peripheral blood may reflect the systemic status of Tph cells. This evidence concerns the gene TPH1 and autoimmune disease.