Bile duct cells in primary biliary cirrhosis are 'primed' for apoptosis

OBJECTIVE: Primary biliary cirrhosis (PBC) is characterized by progressive, immune-mediated destruction of bile ducts (<75 microm diameter) and secondary changes related to cholestasis which may involve apoptosis. In this study we sought to examine the protein expression of genes involved in apoptosis in biliary epithelium of PBC cases.

DESIGN: In order to investigate the susceptibility of biliary epithelial cells to apoptosis and their ability to proliferate, we examined the expression of a number of apoptosis related proteins in early and late stage PBC and histologically normal liver control tissue using immunohistochemistry.

METHODS: Liver biopsies from 15 early (stages I and II) and 14 late (stages III and IV) cases of PBC and 15 normal cases were examined immunohistochemically for expression of p53, CD95/Fas, bax, bcl-x, bcl-2 and the proliferation marker Ki-67.

RESULTS: CD95/Fas, bax and bcl-x were identified in biliary epithelium in 8/15, 11/15 and 8/15 normal biopsies. Weak expression of bcl-2 was found, but p53 was not identified. In cases of PBC surviving bile ducts showed strong bax and bcl-x expression. Inflammatory infiltrates were strongly bcl-2 positive. In cases showing a marked ductular reaction there was increased reactivity for bax and bcl-x in ductules. No change in CD95/Fas or p53 expression was seen. An increase in Ki-67 positive biliary epithelial cells was seen in PBC cases, indicating cell cycle activity.

CONCLUSIONS: Bile duct epithelium constitutively expresses several genes involved in the execution of apoptosis but these cells also retain the ability to proliferate.