Indoleamine 2,3-dioxygenase expression and activity in patients with hepatitis C virus-induced liver cirrhosis

Indoleamine 2,3-dioxygenase (IDO) is an immunoregulatory enzyme. It plays a key role in various malignancies, infection and autoimmune diseases. IDO induces immunosuppression through the depletion of tryptophan and its downstream metabolites. Hepatitis C virus (HCV) has infected more than 12 million individuals in Pakistan. The aim of the present study was to assess the expression and activity of IDO in HCV-infected patients. The functional enzymatic activity of IDO was measured by colorimetric assay. Serum samples from 100 HCV-infected patients were taken to examine IDO activity and samples from 100 healthy volunteers were used as controls. Liver sections from patients with HCV (n=35) and healthy controls (n=5) were used for immunohistochemical studies. Immunohistochemical analysis revealed that IDO was overexpressed in 28 of 35 (80%) cirrhotic liver samples, whereas 5 of 35 (14.2%) cases presented moderate and 2 of 35 (5.7%) cases presented mild expression of IDO. The enzymatic activity of IDO was significantly higher in the serum samples of HCV-infected patients as compared with those in the control. These data indicate that the expression of IDO correlated with the pathogenesis of disease. In summary, it is suggested that the high expression of IDO in the progressively cirrhotic livers of HCV-infected patients might contribute to the development of hepatocellular carcinoma. IDO may characterize a novel therapeutic target against HCV.