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

Background Target of the immune response in chronic autoimmune cholestasis, is the bile duct epithelium. Lymphocytic infiltration and apoptosis have b oth been suggested to mediate the destruction of hepatocytes and biliary ep ithelium in primary biliary cirrhosis. Aims. To further address this issue in two cholestatic liver diseases chara cterized by an autoimmune pathogenesis and, furthermore, evaluate the relat ionship between apoptosis and both tumour necrosis factor alpha and cell pr oliferation. Methods. Liver tissue specimens from 16 patients with primary biliary cirrh osis, 15 with primary sclerosing cholangitis, and 16 with chronic hepatitis C (controls) were evaluated. DNA-fragmentation of apoptotic cells was asce rtained by the TdT-mediated deoxyuridine triphosphate nick-end labelling me thod. Tumour necrosis factor alpha expression and cell proliferation (Ki-67 antigen) were assayed by immunohistochemistry. Results. Hepatocytes with DNA fragmentation were observed in 75% of patient s with primary biliary cirrhosis, in 66.6% with primary sclerosing cholangi tis, and in 43.7% with chronic hepatitis C. Biliocytes showed apoptosis in only 3 cases of primary biliary cirrhosis. Biliocytes showed a strong cytop lasmic expression in 4 cases (1 primary biliary cirrhosis, 2 primary sclero sing 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 p rimary sclerosing cholangitis, and 56.2% with hepatitis C virus chronic hep atitis. The amount of intraportal mononuclear cells expressing Ki-67 antige n was significantly higher in primary biliary cirrhosis specimens than in p rimary sclerosing cholangitis (p<0.001) or hepatitis C virus-related chroni c hepatitis (p<0.03). No correlation was found within the 3 groups of patie nts between the Ki-67 histological scope and the severity of liver disease. Moreover, no relationship was found between TdT-mediated deoxyuridine trip hosphate nick-end labelling and either tumour necrosis factor alpha or Ki-6 7 staining. Conclusions. Apoptosis is a phenomenon which frequently involves hepatocyte s in chronic autoimmune cholestasis. This process is apparently parallel, b ut unrelated to cell proliferation. Cell proliferation mainly involves mono nuclear cells in portal tracts of primary biliary cirrhosis specimens. The finding of tumour necrosis factor alpha expression in biliocytes deserves f urther study to establish whether this cytokine is involved in triggering b ile duct lesions.