Background:Primary biliary cirrhosis( PBC ) is an autoimmune liver disease,the cause of the disease remain incompletely understood. In addition to genetic and environmental factors,autoantibodies,multiple immunocytes and cytokines are considered to be involved in the development of PBC. Recent studies indicated that interleukin-9(IL-9)had pleiotropic functions in inflammatory regulation in allergic and autoimmune diseases. Aims:To investigate the expression and clinical significance of IL-9 in patients with PBC. Methods:A total of 30 specimens of peripheral blood and 20 specimens of liver tissue from PBC patients were collected. Ten specimens of peripheral blood from healthy subjects and 4 specimens of normal liver tissue were served as controls. Level of serum IL-9 was determined by ELISA,and expression of IL-9 in liver tissue was detected by immunohistochemistry. Correlations between IL-9 and serum biochemical indicators, immune indicators and histologic stage of liver tissue were analyzed. Results:Level of serum IL-9 was significantly increased in PBC patients than in normal control group(P<0. 05),and was positively correlated with level of serum IgG (r=0. 681,P<0. 01). Amount of IL-9 positive cells in liver tissue was significantly increased in PBC patients than in normal control group(P <0. 01),and was positively correlated with histologic stage of liver tissue(rs =0. 465,P <0. 05). Conclusions:Expression of IL-9 is significantly increased in peripheral blood and liver tissue in patients with PBC and is positively correlated with level of serum IgG and histologic stage of liver tissue,which suggests an important role of IL-9 in the pathogenesis of PBC.