Primary biliary cirrhosis: current knowledge, perspectives, and future directions

These perspectives from the first International Symposium on Primary Biliary Cirrhosis review recent advances and single out some areas for further enquiry. The latter include frequency and type of associated autoimmune diseases, the existence of clinical subsets of PBC, immunohistochemical analysis of lymphoid infiltrates in the liver, effects of immunosuppressive and other treatment regimens, and models for predicting the optimal time for liver transplantation. The M2 autoantigens have been identified as mitochondrial 2-oxo-acid dehydrogenase enzymes. These include pyruvate dehydrogenase (70-74 kd antigen) and branched chain 2-oxo-acid dehydrogenase and 2-oxo-acid glutaric dehydrogenase (45-52 kd antigens). Each of these enzymes has three subunits, E1 to E3. For PDH, an autoepitope has been identified as a decapeptide containing the attachment site of lipoic acid, an essential cofactor for enzyme activity. Current questions include the degree to which antibodies to PDH, and related enzymes, account for the mitochondrial reactivity defined by immunofluorescence or other procedures, the cell-surface expression of M2 autoantigens, and the significance of the occurrence of nonmitochondrial (such as centromeric) autoantibodies in PBC. The unknown T lymphocyte contribution to the autoimmune response in PBC may involve inducer and effector components. A postulated T-cell autoepitope may be presented, in association with MHC class I or class II molecules, on the surface of biliary epithelial cells. T cell lines from PBC livers removed during transplantation could provide data on the T-lymphocyte contribution to the pathogenesis of PBC.