Characterization of antimitochondrial antibodies in healthy adults

The detection of antimitochondrial antibodies (AMAs) is an important criterion for the diagnosis of primary biliary cirrhosis (PBC). During the last decade, the mitochondrial autoantigens have been cloned, sequenced, and identified as members of the 2‐oxo‐acid dehydrogenase pathway, including the E2 subunits of pyruvate dehydrogenase (PDC‐E2), branched‐chain 2‐oxo‐acid dehydrogenase (BCOADC‐E2), and 2‐oxo‐glutarate dehydrogenase (OGDC‐E2). We have developed a rapid and sensitive diagnostic test for use in PBC based on a triple hybrid recombinant molecule (r‐MIT3) that contains the autoepitopes of PDC‐E2, BCOADC‐E2, and OGDC‐E2. To help understand the frequency and antigen specificity of AMAs in an asymptomatic population and to identify patients with early disease, we investigated the prevalence of AMA, by enzyme‐linked immunosorbent assay (ELISA), in a cohort of 1,530 people from northern Italy. Positive sera were further analyzed for immunoglobulin (Ig) isotypes, subclasses, and epitopes of AMA by a combination of ELISA and immunoblotting. In this cohort of 1,530 people, 9 (0.5%) reacted to r‐MIT3 by ELISA. Of the 9 reactive sera, 2 recognized PDC‐E2, 2 of 9 recognized BCOADC‐E2, 1 of 9 recognized OGDC‐E2, 2 of 9 recognized both PDC‐E2 and BCOADC‐E2, and 1 of 9 recognized PDC‐E2 and OGDC‐E2. AMA reactivity was primarily IgM and IgA. Epitope mapping revealed an AMA pattern of reactivity to PDC‐E2 that differed from that found in patients with histologically proven PBC in most of the sera. However, 1 sera of a 72‐year‐old female with a normal alkaline phosphatase had an AMA profile identical to typical PBC. After a variable follow‐up period (8‐14 months), sera from 8 of 9 of these people were re‐obtained for AMA and relative epitope mapping. Interestingly, the reactivity had a wider AMA pattern than before.