Immunopathology of primary biliary cirrhosis.

A major advance in the study of primary biliary cirrhosis was identification of the major B-cell auto-antigen as the mitochondrial enzyme pyruvate dehydrogenase dihydrolipoamide acetyltransferase (PDC-E2). Subsequent studies revealed that PDC-E2 also contained epitopes recognized by patients' T cells. Furthermore, aberrant expression of MHC class II, intercellular adhesion molecules, lymphocyte co-stimulatory molecules and B-cell epitopes of PDC-E2 was observed on patients' biliary epithelium, supporting the concept that biliary epithelial cells are the target of a focused autoimmune reaction. Changes in distribution of auto-antigen on biliary epithelium and the presence of auto-antibody in patient's serum have both been shown to occur very early in the natural history of primary biliary cirrhosis, suggesting an intimate role for these molecules in immunopathogenetic mechanisms.