Clinical Significance of Positive Immunoblotting but Negative Immunofluorescence for Antimitochondrial Antibodies in Patients with Liver Diseases Other than Primary Biliary Cirrhosis

The serum reaction to anti-2-oxo-acid dehydrogenase complex (2-OADC) enzymes, the antigens recognized by antimitochondrial antibodies (AMA), can be detected by immunoblotting in patients with liver diseases other than primary biliary cirrhosis (PBC), who are negative for AMA by conventional indirect immunofluorescence. Whether the presence of anti-2-OADC is related to PBC or represents preclinical PBC in such patients is obscure at present. We examined the immunoreactivity of AMA by immunofluorescense, immunoblotting, and enzyme inhibition assay in serum samples from 59 patients with liver diseases other than PBC and 71 healthy subjects. We also examined the clinical course of the patients in whom a positive result was obtained to elucidate whether such reaction was a "true" or "false" phenomenon. None of the 130 sera was positive for AMA by indirect immunofluorescence or for anti-pyruvate dehydrogenase complex (PDC) by enzyme inhibition assay. However, seven of 71 (10%) sera from healthy subjects contained weak IgG class antibody to PDC-E2 (four sera) or E2 subunit of branched-chain oxo-acid dehydrogenase complex (BCOADC-E2) (three sera). Of the 59 sera from patients with liver diseases other than PBC, four (7%) reacted against 2-OADC by immunoblotting. Of these, three sera were from patients with chronic hepatitis C virus (HCV) infection, and contained IgG class autoantibody to BCOADC-E2. The serum reactivity to BCOADC-E2 detected by immunoblotting in these three patients diminished after absorption with recombinant BCOADC-E2 fusion protein. During the 3-5 year follow-up period, AMA by immunofluorescence and anti-PDC activity by enzyme inhibition assay were always negative in these three patients. The other one serum was from patient with alcoholic cirrhosis, and contained IgM class autoantibody to E3 binding protein (E3-BP). This patient did not develop PBC during the following 2 years. Our results showed that anti-2-OADC antibodies could be detected in some patients with liver diseases other than PBC, and even in healthy individuals. The clinical significance of the presence of these serum reactions is obscure at this stage, but the production of anti-BCOADC-E2 may be linked to the presence of HCV in certain patients, Further prospective studies of larger population should clarify whether anti-2-OADC reaction can precede the clinical development of PBC.