However, several studies have reported that Th9 cells and IL-9 play pathogenic roles in multiple sclerosis, SLE, experimental autoimmune encephalomyelitis, and other autoimmune diseases.166–168 Qin et al[169] explored the level of Th9 cells in liver fibrosis caused by HBV or chronic hepatitis B. In this study, the levels of Th9 cells and IL-9 were significantly increased in both patients and mice with liver fibrosis. Here, IL9 is linked to autoimmune disease.