Autoreactive responses to pyruvate dehydrogenase complex in the pathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a cholestatic liver disease characterised by immune-mediated destruction of the biliary epithelial cells (BEC) lining the intrahepatic bile ducts (non-suppurative destructive cholangitis (NSDC)). Autoantibody and autoreactive T-cell responses specific for the self-antigen pyruvate dehydrogenase complex (PDC) are almost ubiquitous in PBC patients, leading to the view that the disease has an autoimmune aetiology. Autoreactive responses in PBC appear to be directed at the E2 and at the E3-binding protein (E3BP) (protein X) components of PDC, with the dominant B-cell and T-cell epitopes in E2 (fewer data are available for E3BP) spanning the inner (of two) lipoic acid-binding domains. The causal link between the breakdown of self-tolerance to PDC (particularly at the T-cell level) and the development of NSDC has been emphasised by the demonstration, in a murine model (experimental autoimmune cholangitis), that sensitisation with PDC of mammalian origin results in a breakdown of both B-cell and T-cell tolerance to murine PDC accompanied by the development of NSDC. An increasing understanding of the role played by PDC-specific autoreactive T cells in the pathogenesis of PBC has led us to examine the role played by the target cells in PBC (BEC) in both the inducer and effector mechanisms responsible for PBC.