AIM: An increase in bile ductular structures is observed in diverse human liver diseases, especially in primary biliary cirrhosis (PBC). These structures harbor the progenitor cell component of the liver. Caveolins are cholesterol-binding proteins involved in the regulation of several intracellular processes including cholesterol transport. This study aims to examine the role of caveolin in PBC.METHODS: Immunohistochemical and West blottingstudies were performed on human liver specimens obtained from patients with PBC and normal liver samples. The expression of caveolin (CAV)-1 and -2 was determined using specific antibodies.RESULTS: In normal liver, scanty immunostaining for CAV1 and -2 was observed in bile ductules. In PBC liver samples, the expression levels of CAV-1 and -2 were increased on proliferating bile ductules especially in stage 3 cases, but was sparse on interlobular bile duct in stage 1 specimens. Especially, the regenerating bile ductules at the interface of portal tracts and necrotic areas were immunostained intensely for CAV-1 and -2. These phenomena were confirmed by West blot.CONCLUSION: The present results demonstrate increased expression of caveolins in proliferating bile ductules in PBC, which may be related to the homeostasis of cholesterol transport in regenerating bile ductules in PBC liver.