Frequency of IgG, IgM, and IgA class autoantibodies against 2-oxo-acid dehydrogenase complex in 102 Japanese patients with primary biliary cirrhosis

Abstract

We investigated the proportion of serum samples containing IgG, IgM, and IgA class autoantibodies against 2-oxo-acid dehydrogenase complex (2-OADC) tested by sensitive immunoblotting with enhanced chemiluminescence in 102 Japanese patients with primary biliary cirrhosis (PBC). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in our assay condition were 99, 86, 89, 99 and 93%, respectively. Among these patients, 13 were seronegative for antimitochondrial antibodies (AMA) by indirect immunofluorescence (AMA-negative group). Of the 102 serum samples, 98 (96%), 85 (83%), and 72 (71%) contained IgG, IgM, or IgA class antibodies against at least one of the 2-OADC enzymes, respectively. All of the 13 AMA-negative sera contained IgG, IgM, or IgA class antibodies against at least one of the 2-OADC enzymes. In contrast, only one serum sample positive for AMA by immunofluorescence at a titer of 1:20 did not contain any IgG, IgM, or IgA class antibodies. Although the proportion of samples containing IgG class autoantibodies against E2 subunit of branched chain oxo-acid dehydrogenase complex (BCOADC-E2) (77%) was similar to that against E2 subunit of pyruvate dehydrogenase complex (PDC-E2) (74%), IgM and IgA class antibodies against BCOADC-E2 were not frequently detected compared with those against PDC-E2. Overall, our results indicated that IgG class antibodies against PDC-E2 and BCOADC-E2 showed the most dominant reactivities both in AMA-positive and -negative groups of PBC.