T cell autoreactivity against a 28 kD biliary protein (B1-p28) in primary biliary cirrhosis

Background/Aims: Cellular immune responses against biliary epithelial cells are important in understanding the pathogenesis of primary biliary cirrhosis. We previously reported a biliary antigen B1 which stimulated peripheral T lymphocytes of primary biliary cirrhosis as a possible, non-mitochondrial target of biliary epithelial cells. Further characterization of B1 was performed. Methods: To confirm localization of B1 in biliary epithelial cells, a mouse monoclonal antibody was raised against B1. As B1 could be separated into two main components by SDS-PAGE under reducing condition, these components were individually cut out from Western blots and converted into antigen-bearing particles for a proliferation assay to detect the antigenic component responsible for stimulating lymphocytes. The relation of this proliferation to HLA DR antigens was also analyzed. Results: Immunohistochemically, B1 was shown to be specifically expressed on biliary epithelial cells of human liver tissue. Of two components from B1 under reducing condition, prominent proliferation against B1-p28, a 28 kD component of B1 was detected in primary biliary cirrhosis. The reactivities were significantly higher than chronic liver diseases (p<0.001) or normal controls (p<0.001). Furthermore, high responders to B1-p28 were observed frequently in primary biliary cirrhosis patients with HLA DR8 (p<0.02), which was susceptible to the development of primary biliary cirrhosis. Conclusions: These data suggest B1-p28 expressed on biliary epithelial cells is a candidate for the target antigen of primary biliary cirrhosis in addition to mitochondrial autoantigens. Further characterization of B1-p28 may provide new insight into the autoimmune mechanisms of primary biliary cirrhosis.