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Five different target mitochondrial autoantigens recognized by sera from patients with primary biliary cirrhosis (PBC) have been identified as subunits of the following 2-oxo acid dehydrogenase complexes: the pyruvate dehydrogenase complex (PDC), the branched chain 2-oxo acid dehydrogenase complex (BCOADC), and the 2-oxoglutarate dehydrogenase complex (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 sera but none of the 45 controls reacted with recombinant OGDC-E2. The recombinant OGDC-E2 was judged to express the immunodominant epitope, because when sera from patients with PBC were preabsorbed with the recombinant fusion protein, such sera were depleted of reactivity against 48 kD OGDC-E2 when probed on beef heart mitochondria (BHM) but retained reactivity 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 2-oxo acid dehydrogenase complex. Antimitochondrial autoantibodies (AMA) against OGDC-E2 included immunoglobulin (Ig)G2, IgG3 and IgM and the relative titers were as follows: IgG2 > IgG3 > IgM. Finally, using overlapping recombinant polypeptides, it was determined that a minimum of 81 amino acids (residues 67-147) corresponding to the lipoyl domain of OGDC-E2 are necessary for reactivity, suggesting that a conformational autoepitope is recognized by AMA. These data suggest that each of the 2-oxo acid dehydrogenase enzymes has distinct antigenicity despite their similarities in structure and function. The availability of recombinant OGDC-E2 autoantigen will allow the design of additional studies to further our understanding of the role of mitochondrial autoantigens in the pathogenesis of PBC.

AMAs are detectable by indirect immunofluorescence (IF)We examined the clinical usefulness of measurements on tissue substrates in 93% to 99% of patients with PBC, but of antimitochondrial autoantibodies (AMA) in prethis method also detects AMAs of differing specificities in dicting disease progression in patients with primary bilother diseases. The mitochondrial antigens recognized by iary cirrhosis (PBC). We determined the relationships AMAs in patients' sera have been classified numerically as between AMA levels measured by indirect immunofluo-M1 through M9, with the M2 antigen complex recognized by rescence (IF) and those measured by quantitative enAMAs in sera from 95% to 99% of PBC patients. M2 antigen is zyme immunoassays (EIAs) using recombinant 2-oxocomposed of enzyme proteins of the 2-oxo-acid dehydrogenase acid dehydrogenase complex (2-OADC) proteins and the complex (2-OADC) family that are located on inner mitochonMayo Risk Score, an established indicator of disease prodrial membranes. Included in this group of autoantigens are gression in primary biliary cirrhosis (PBC). Results of tests for AMA by either method correlated weakly (r Å pyruvate dehydrogenase complex (PDC), branched-chain 2-.24 to .30) with disease progression as indicated by Mayo oxo-acid dehydrogenase complex (BCOADC), and 2-oxo-gluRisk Scores. The levels of AMA to 2-OADC proteins var-tarate dehydrogenase complex (OGDC). The 2-OADC enied by more than 200-fold between patients but re-zymes are complex multimers composed of E1, E2, and E3 mained relatively constant over time in individual pa-subunits; the E2 subunits contribute immunodominant epitients. Despite being positively correlated with Mayo topes recognized by anti-M2 autoantibodies. 3 ImmunoreacRisk Score results, the levels of AMA to 2-OADC proteins tive epitopes of the E2 subunits of 2-OADC enzymes have were not useful for predicting disease progression in been cloned, and enzyme immunoassays (EIAs) that use reindividual patients with PBC. In addition, we found no combinant PDC-E2 and BCOADC-E2 proteins as capture ansignificant differences in the levels of autoantibodies to tigens detect autoantibodies in sera from more than 95% of 2-OADC proteins among patients with different histolog-patients with PBC. 4 Approximately 10% of sera from PBC ical stages of disease. Our results show that measure-patients contain autoantibodies to BCOADC-E2 but not PDCments of AMA by IF or by quantitative EIA methods with E2. Recently, Leung et al. 5 constructed a recombinant hybrid recombinant 2-OADC proteins are not useful parameters molecule that contains the immunodominant epitopes of both for predicting disease progression in patients with PBC. PDC-E2 and BCOADC-E2, and this hybrid molecule is recog-(HEPATOLOGY 1997;25:6-11.)nized by AMAs specific for either antigen. No study to date has reported on the levels of AMA to 2-OADC enzyme proteins in sera from a large number of PBC Primary biliary cirrhosis (PBC) is a progressive liver dispatients who have been followed up longitudinally throu...

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The aim of this study was to assess the diagnostic value of cholangiography in men with chronic cholestasis and positive antimitochondrial antibody (AMA) titers who were suspected of having primary biliary cirrhosis (PBC). The authors reviewed retrospectively the records of men who had positive AMA titers over a 16-month period to determine the results of cholangiography. They also reviewed the records of 102 patients with primary sclerosing cholangitis (PSC) from 1989 to 1995 who had undergone cholangiography and testing for AMA. Of 35 men with positive tests for serum AMA, 12 of these patients were referred for cholangiography (11 endoscopic and 1 transhepatic). All completed cholangiograms were normal. A diagnosis of PBC was made in nine patients and atypical autoimmune hepatitis in one. Conversely, only two PSC patients had positive AMA titers (1:20 and 1:80). Both of these patients had coexisting inflammatory bowel disease and cholangiograms diagnostic of PSC. Cholangiography was negative in the male patients with positive AMA titers who were suspected of having PBC. In men with cholestatic liver biochemistries and strongly positive AMA titers, especially in the absence of associated inflammatory bowel disease, routine cholangiography does not add to the diagnostic evaluation.