Expression of HLA-DR antigens on interlobular bile ducts in primary biliary cirrhosis and other hepatobiliary diseases: an immunohistochemical study.

Using a monoclonal antibody to alpha chains of HLA-DR antigens, we found that damaged biliary epithelial cells in primary biliary cirrhosis (PBC) and, to a lesser degree and frequency, in other hepatobiliary diseases expressed HLA-DR antigens, while normal bile ducts did not. There was no correlation between biliary epithelial expression of HLA-DR antigens and intraepithelial migration of HLA-DR-positive cells. In PBC, HLA-DR antigens were strongly expressed on the damaged bile ducts surrounded by no or mild inflammatory cell infiltration (nonflorid duct lesion) and on those surrounded by intense lymphoid cells (florid duct lesion). Immunoelectron microscopy confirmed the presence of HLA-DR antigens on the cellular membranes of damaged biliary epithelial cells. Although expression of HLA-DR antigens on bile ducts may itself be a nonspecific epiphenomenon of damaged bile ducts, it seems possible in PBC that biliary epithelial cells are at first damaged in some way and express HLA-DR antigens (and probably self-antigens), and then fall victim to an autoimmune reaction characterized by marked lymphoid cell infiltration (florid duct lesions). The agent causing nonflorid duct lesions is unknown. The reasons why such expression does not lead to immunologic reactions in other hepatobiliary diseases are only speculative.