Cytokeratin expression in cells of the rodent bile duct developing under normal and pathological conditions

A polyclonal anti-cytokeratin antibody has been used to examine the expression of this intermediate filament both during normal development in the rat and in a variety of pathological states in the rat and mouse. Bile duct proliferation induced by the administration of alpha-naphthylisothiocyanate (ANIT) as well as the oval cell proliferation induced by 3'-methyl-4-dimethylaminoazobenzene (3-MeDAB) have been used to examine the expression of the rodent cytokeratins in the proliferating cells regarded as being of bile duct origin. Examples of cholangiofibrosis and cholangiocarcinomas were also examined for evidence of cytokeratin expression using this antibody, as well as proliferations of a morphological intermediate type between epithelial and mesenchymal. In all cases we have been able to demonstrate continuity of phenotypic expression of the cytokeratins recognized by this antibody in cells which are recognized as bile duct in origin, even where their morphological appearance does not resemble an epithelial cell type. Because this antibody can be used on formalin-fixed, paraffin-processed tissues, after trypsin treatment, it is proposed that it can be used routinely in the toxicological evaluation (even retrospectively) of bile duct related proliferations and tumours.