Combination assays for IgG class and IgM class anti-pyruvate dehydrogenase complex(PDC)-E2 by ELISA using recombinant autoantigen to diagnose primary biliary cirrhosis

Abstract

IgG and IgM class anti-pyruvate dehydrogenase complex (PDC)-E2 were studied in sera from anti-M2-positive 84 patients with PBC by enzyme-linked immunosorbent assay (ELISA) to assess the usefulness of combination assays. We used recombinant antigen coding the autoantigenic epitopes of PDC-E2 comprising the lipoic acid binding sites. Antigen specificity of this ELISA was confirmed by inhibition test with pre-incubation of recombinant antigen with tested sera. Neither IgG class nor IgM class anti-PDC-E2 could be detected in sera from healthy controls and patients with chronic liver diseases other than PBC. In 84 sera from patients with PBC, the positive rate of IgG class anti-PDC-E2 (66.7%) was almost the same as that of IgM class anti-PDC-E2 (65.5%). Seven sera were positive for IgG class anti-PDC-E2 but negative for IgM class anti-PDC-E2. In contrast, six sera were positive for IgM class anti-PDC-E2 but negative for IgG class anti-PDC-E2. In total, 62 (73.8%) of 84 sera were positive for IgG class and/or IgM class anti-PDC-E2. This rate was higher than with assay of IgG class anti-PDC-E2 or IgM class anti-PDC-E2 alone. The positive rate of IgG class and IgM class anti-PDC-E2s in sera with high AMA titers was higher than that in sera with low AMA titers. The sensitivity of ELISA matched that of immunoblotting in 67 sera (79.7%). We conclude that the combination ELISAs for IgG class and IgM class anti-PDC-E2 are useful for diagnosing PBC.