Relationship between apoptosis, tumour necrosis factor, and cell proliferation in chronic cholestasis

Target of the immune response in chronic autoimmune cholestasis, is the bile duct epithelium. Lymphocytic infiltration and apoptosis have both been suggested to mediate the destruction of hepatocytes and biliary epithelium in primary biliary cirrhosis.

To further address this issue in two cholestatic liver diseases characterized by an autoimmune pathogenesis and, furthermore, evaluate the relationship between apoptosis and both tumour necrosis factor alpha and cell proliferation.

Liver tissue specimens from 16 patients with primary biliary cirrhosis, 15 with primary sclerosing cholangitis, and 16 with chronic hepatitis C (controls) were evaluated. DNA-fragmentation of apoptotic cells was ascertained by the TdT-mediated deoxyuridine triphosphate nick-end labelling method. Tumour necrosis factor alpha expression and cell proliferation (Ki-67 antigen) were assayed by immunohistochemistry.

Hepatocytes with DNA fragmentation were observed in 75% of patients with primary biliary cirrhosis, in 66.6% with primary sclerosing cholangitis, and in 43.7% with chronic hepatitis C. Biliocytes showed apoptosis in only 3 cases of primary biliary cirrhosis. Biliocytes showed a strong cytoplasmic expression in 4 cases (1 primary biliary cirrhosis, 2 primary sclerosing cholangitis and 1 chronic hepatitis C). A few intralobular and portal inflammatory mononuclear cells expressing tumour necrosis factor alpha were observed in 62.5% of patients with primary biliary cirrhosis, 46.1% with primary sclerosing cholangitis, and 56.2% with hepatitis C virus chronic hepatitis. The amount of intraportal mononuclear cells expressing Ki-67 antigen was significantly higher in primary biliary cirrhosis specimens than in primary sclerosing cholangitis (p<0.001) or hepatitis C virus-related chronic hepatitis (p<0.03). No correlation was found within the 3 groups of patients between the Ki-67 histological score and the severity of liver disease. Moreover, no relationship was found between TdT-mediated deoxyuridine triphosphate nick-end labelling and either tumour necrosis factor alpha or Ki-67 staining.

Apoptosis is a phenomenon which frequently involves hepatocytes in chronic autoimmune cholestasis. This process is apparently parallel, but unrelated to cell proliferation. Cell proliferation mainly involves mononuclear cells in portal tracts of primary biliary cirrhosis specimens. The finding of tumour necrosis factor alpha expression in biliocytes deserves further study to establish whether this cytokine is involved in triggering bile duct lesions.