EPITOPE MAPPING AND REACTIVITY OF AUTOANTIBODIES TO THE E2 COMPONENT OF 2-OXOGLUTARATE DEHYDROGENASE COMPLEX IN PRIMARY BILIARY-CIRRHOSIS USING RECOMBINANT 2-OXOGLUTARATE DEHYDROGENASE COMPLEX

Five different target mitochondrial autoantigens recognized by sera fr om patients with primary biliary cirrhosis (PBC) have been identified as subunits of the following 2-oxo acid dehydrogenase complexes: the p yruvate dehydrogenase complex (PDC), the branched chain 2-oxo acid deh ydrogenase complex (BCOADC), and the a oxoglutarate dehydrogenase comp lex (OGDC), Unlike the E2 subunits of PDC (PDC-E2) and BCOADC (BCOADC- E2), the E2 subunits of OGDC (OGDC-E2) reactivity of PBC sera and the reactive epitope of OGDC-D2 have not hitherto been studied in detail. In this report, we took advantage of a recombinant fusion protein for OGDC-E2 to address these issues, Eighty of 268 (29.9%) PBC patient ser a but none of 45 controls reacted with recombinant OGDC-E2, The recomb inant OGDC-E2 was judged to express the immunodominant epitope, becaus e when sera from patients with PBC were preabsorbed with the recombina nt fusion protein, such sera were depleted of reactivity against 48 kD OGDC-E2 when probed on beef heart mitochondria (BHM) but retained rea ctivity toward PDC-E2 and/or BCOADC-E2, Furthermore, affinity-purified PBC sera against recombinant OGDC-E2 reacted only with native OGDC-E2 and not with any other enzyme components of the a-ore acid dehydrogen ase complex, Antimitochondrial autoantibodies (AMA) against OGDC-E2 in cluded immunoglobulin (Ig) G2, IgG3 and IgM and the relative titers we re as follows: IgG2 > IgG3 > IgM, Finally, using overlapping recombina nt polypeptides, it was determined that a minimum of 81 amino acids (r esidues 67-147) corresponding to the lipoyl domain of OGDC-E2 are nece ssary for reactivity, suggesting that a conformational autoepitope is recognized by AMA These data suggest that each of the 2-oxo acid dehyd rogenase enzymes has distinct antigenicity despite their similarities in structure and function, The availability of recombinant OGDC-E2 aut oantigen will allow the design of additional studies to further our un derstanding of the role of mitochondrial autoantigens in the pathogene sis of PBC.