tained reactivity toward PDC-E2 and/or BCOADC-E2. Five different target mitochondrial autoantigens rec-Furthermore, affinity-purified PBC sera against recomognized by sera from patients with primary biliary cirbinant OGDC-E2 reacted only with native OGDC-E2 and rhosis (PBC) have been identified as subunits of the folnot with any other enzyme components of the 2-oxo acid lowing 2-oxo acid dehydrogenase complexes: the dehydrogenase complex. Antimitochondrial autoantipyruvate dehydrogenase complex (PDC), the branched bodies (AMA) against OGDC-E2 included immunoglobuchain 2-oxo acid dehydrogenase complex (BCOADC), lin (Ig) G2, IgG3 and IgM and the relative titers were as and the 2-oxoglutarate dehydrogenase complex (OGDC).
follows: IgG2 úIgG3 úIgM. Finally, using overlapping Unlike the E2 subunits of PDC (PDC-E2) and BCOADC recombinant polypeptides, it was determined that a min-(BCOADC-E2), the E2 subunits of OGDC (OGDC-E2) reimum of 81 amino acids (residues 67-147) corresponding activity of PBC sera and the reactive epitope of OGDCto the lipoyl domain of OGDC-E2 are necessary for reac-D2 have not hitherto been studied in detail. In this retivity, suggesting that a conformational autoepitope is port, we took advantage of a recombinant fusion protein recognized by AMA. These data suggest that each of the for OGDC-E2 to address these issues. Eighty of 268 2-oxo acid dehydrogenase enzymes has distinct antige-(29.9%) PBC patient sera but none of 45 controls reacted nicity despite their similarities in structure and funcwith recombinant OGDC-E2. The recombinant OGDCtion. The availability of recombinant OGDC-E2 autoanti-E2 was judged to express the immunodominant epitope, gen will allow the design of additional studies to further because when sera from patients with PBC were preabour understanding of the role of mitochondrial autoantisorbed with the recombinant fusion protein, such sera gens in the pathogenesis of PBC. (HEPATOLOGY 1996;23: were depleted of reactivity against 48 kD OGDC-E2 436-444.) when probed on beef heart mitochondria (BHM) but re-
Primary biliary cirrhosis (PBC) is an autoimmune
Abbreviations: PBC, primary biliary cirrhosis; AMA, antimitochondrial auliver disease characterized histologically by chronic intoantibodies; PDC-E2, E2 subunit of pyruvate dehydrogenase complex; flammatory destruction and obliteration of septal and BCOADC-E2, E2 subunit of branched chain 2-oxo acid dehydrogenase complex; OGDC-E2, E2 subunit of oxoglutarate dehydrogenase complex; cDNA, comple-intrahepatic bile ducts, and an infiltration of plasma mentary DNA; BHM, beef heart mitochondria; PCR, polymerase chain reac-cells and lymphocytes in the portal tracts. 1 The typical tion; IPIG, isopropyl b-D-thiogalactopyranoside; SDS, sodium dodecyl sulfate; serologic feature observed in patients with PBC is the PBS, phosphate-buffered saline; Ig, immunoglobulin; PAGE, polyacrylamide presence of high titer of antimitochondrial antibodies gel electrophoresis.