CYP27A1 and autoimmune disease: IL17-producing Th17 cells are often present at sites of chronic tissue inflammation in multiple autoimmune diseases.37 Th17 cells are critical drivers of inflammation in autoimmune diseases, and are likely to be induced by specific components of gut microbiota.38 The role of bile acids in directly mediating host immunity by controlling Th17 response has been shown to be associated with Th17 expansion and IL17 production.39 We found significant upregulation of CYP27A1 expression in PSC-IBD compared with UC.