PRIMARY BILIARY-CIRRHOSIS (PBC) - CHARACTERIZATION OF A MONOCLONAL-ANTIBODY (PBC-MOAB) HAVING SPECIFICITY IDENTICAL WITH DISEASE-ASSOCIATED AUTOANTIBODIES

We have raised a monoclonal antibody (PBC-MoAb) directed against mitochondria which resembles patent anti-mitochondrial autoantibodies (AMA) (M2 type) in several respects. The reaction pattern of PBC-MoAb was characterized by western blot experiments, immunoaffinity purification and enzyme inhibition studies. PBC-MoAb reacts specifically with an epitope on the E2 subunit of pyruvate dehydrogenase (dihydrolipoamide acyltransferase) which is essential for enzymatic activity. This was shown as follows: (1) PBC-MoAb, like PBC-AMA, completely inhibited PDH enzyme activity and reacted weakly with OGDH; (2) PBC-MoAb bound strongly to the E2 subunit in western blots, with weaker binding to a doublet of about 56 kDa; and (3) in immunosorbent experiments, PBC-MoAb absorbed most (> 95%) of the AMA reactive material found in solubilized mitochondria. The present data together with earlier findings that the majority of PBC patient autoantibodies bind to epitopes defined by the PBC-MoAb, makes this antibody a valuable tool for characterizing the major PBC-associated epitope on PDH-E2 and localizing this epitope in liver tissue.