Cholestasis induces major histocompatibility complex class I expression in hepatocytes

The hepatic expression of major histocompatibility complex (MHC) antigens is normally limited. However, aberrant expression occurs in cholestatic diseases such as primary biliary cirrhosis. The aim of this work was to assess the effect of cholestasis itself on hepatocyte MHC expression and to determine if immunosuppressive drugs might modulate this expression. Liver fragments taken from six patients with extrahepatic cholestasis and eight control patients were analyzed for MHC expression by direct immunofluorescence. MHC class I expression by hepatocytes was present in six of six cholestatic patients and zero of eight control subjects. Hepatocytes did not express MHC class II in either group. In further studies, cholestasis was induced in rats by ligation-section of the bile duct. Five groups of rats were studied: control, 3-day cholestasis, 5-day cholestasis, 5-day cholestasis plus cyclosporine, and 5-day cholestasis plus corticosteroids. Hepatocyte MHC class I expression was detected by immunofluorescence in bile duct-ligated rats but not in control animals. Flow-cytofluorimetric analysis of isolated hepatocytes showed that the percentage of hepatocytes expressing MHC class I increased from day 0 (9.9%) to days 3 (50.2%) and 5 (82.9%); this hyperexpression was not modified by cyclosporine (79.7%) or corticosteroids (77.9%). The percentage of hepatocytes spontaneously expressing MHC class II was low (0.05%) and was not significantly modified by cholestasis or immunosuppressive drugs. Thus, a nonimmunological factor such as cholestasis is able to modulate MHC expression. The liver may become more vulnerable to immune destruction in the presence of cholestasis, and immunosuppressive treatment has no effect on this phenomenon.