We studied the distribution of class 1 and class 2 major histocompatibility complex (MHC) antigens on bile duct epithelial cells in liver from patients with primary biliary cirrhosis (PBC) by an immunohistochemical method using monoclonal antibodies to HLA-ABC products and HLA-D subregion products (HLA-DR, -DP, -DQ). By light microscopy, the expression of MHC class 1 antigens (HLA-ABC antigens) was enhanced in PBC compared with controls. While negligible staining of MHC class 2 antigens was detected on the bile duct in controls, de novo expression of MHC class 2 antigens, as well as the coexpression of HLA-DR, HLA-DQ, and HLA-DP antigens on the bile duct epithelial cells, was observed in PBC. By electron microscopy, HLA-ABC and HLA-DR antigens were present preferentially along the basolateral domain of the cell surface of the bile duct epithelial cells and on the membrane of the endoplasmic reticulum in the cytoplasm, suggesting that these MHC antigens are synthesized by the bile duct epithelial cells in PBC. The distribution of these MHC antigens on the basolateral surface of the bile duct epithelial cells, where they are easily accessible to immunocytes, supports the idea that MHC-restricted cytotoxic T lymphocytes are involved in the bile duct injury in PBC.
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