Upregulation of lymphotoxin β expression in liver progenitor (oval) cells in chronic hepatitis C

Background: Bipotent liver progenitor (oval) cells with the ability to differentiate into hepatocytes and biliary epithelium have recently been identified in human subjects with hepatitis C. Animal studies suggest that members of the tumour necrosis factor family, including lymphotoxin β (LT-β), regulate oval cell proliferation in liver disease, but its role in human liver disease is unclear. Aims: This study seeks to establish a role for LT-β in hepatitis C related liver injury and to provide evidence that its increased expression is related to the presence of oval cells. Methods: Liver biopsy specimens were obtained from patients with chronic hepatitis C virus (HCV) infection (n=20). Control liver samples (n=5) were obtained from liver resection or transplant surgery. LT-β expression in liver biopsy specimens was studied using quantitative real time polymerase chain reaction and immunohistochemistry. Results: LT-β mRNA levels were similar in control and HCV liver in the absence of fibrosis. In subjects with portal fibrosis, LT-β mRNA levels were elevated 2.2-fold over control liver levels (p=0.04). In subjects with bridging fibrosis, LT-β mRNA levels increased 4.4-fold over control liver levels (p=0.02). LT-β mRNA levels in subjects with established cirrhosis were increased 3.3-fold compared with controls and 2.6-fold compared with mild liver damage (p=0.02). Immunohistochemical analysis established that LT-β was expressed by oval cells, inflammatory cells, and small portal hepatocytes. Conclusions: In chronic HCV infection, LT-β expression is observed in multiple hepatic cell types, including oval cells. LT-β expression is significantly increased when fibrosis or cirrhosis is present, suggesting a role for LT-β in the pathogenesis of chronic hepatitis C and a possible role in oval cell mediated liver regeneration.