[The association between autoantibodies to enzyme and diseases--with special reference to antibodies to pyruvate...

A serological feature of primary biliary cirrhosis (PBC) is the presence of high-titer antimitochondrial autoantibodies (AMA) in patient sera. Five different target mitochondrial autoantigens recognized by sera from PBC patients have been identified as subunits of the 2-oxoacid dehydrogenase complex (2-OADC), of which pyruvate dehydrogenase complex-E2 (PDH-E2) is the most prominent antigenic component. Extensive molecular and immunological studies in PBC such as cloning of mitochondrial autoantigens, mapping of both T and B cell epitopes and immunohistochemical studies have provided valuable reagents in the understanding of immunopathogenesis of PBC. We mapped the epitope recognized by AMA specific to 2-oxoglutarate dehydrogenase complex-E2 (OGDC-E2) in patients with PBC using full-length rat OGDC-E2 cDNA and a series of expression clones spanning the entire molecule. It appears that the epitope is dependent on conformation and includes the lipoic acid-binding region. Furthermore we have taken advantage of the antigenic mapping studies of PDC-E2, OGDC-E2 and branched chain 2-oxoacid dehydrogenase complex-E2 (BCOADC-E2) subunits and designed a hybrid clone, pML-MIT3, that expressed three different immunodominant epitopes. Our results indicate that an immunoassay using recombinant, cloned autoantigen is a powerful and very specific method for detecting AMA in PBC.