We studied the expression of major histocompatibility complex (MHC) class II antigens in liver biopsies taken from ten patients with clinical and biochemical evidence of liver damage after bone marrow transplantation. In all six patients who had histologically confirmed graft-versus-host disease, MHC class II antigens were detected on intrahepatic bile ducts. In four patients with no histological features of graft-versus-host disease, MHC class II antigens were not detected. In controls, a positive reaction for bile duct MHC class II antigens was only detected in the patients with primary biliary cirrhosis. Characterisation of the lymphocytes surrounding the bile ducts showed a prevalence of Leu 3+ cells in graft-versus-host disease and primary biliary cirrhosis. We propose that the aberrant expression of class II antigens on bile duct epithelium cells may play a role in the pathogenesis of graft-versus-host disease. A similar pattern in primary biliary cirrhosis may suggest a common pathogenetic mechanism.
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