Antibodies against mitochondrial dehydrogenase complexes in primary biliary cirrhosis

Antimitochondrial antibodies, serological hallmarks of primary biliary cirrhosis, recently were found to be directed against the E2 subunits of mitochondrial dehydrogenase complexes (pyruvate, branched-chain ketoacid, and alpha-ketoglutarate dehydrogenases). The objectives of this study were to extend these findings and to determine whether purified immunoglobulin from the sera of patients with primary biliary cirrhosis inhibit activity of these dehydrogenase complexes in vitro. Sera were examined from 14 patients with primary biliary cirrhosis (13 mitochondrial antibody positive), 23 with rheumatic diseases and 30 with chronic active hepatitis (all 53 positive for mitochondrial antibodies by indirect immunofluorescence), 10 with alcoholic liver disease, and 5 normal controls. Antibodies against pyruvate dehydrogenase, branched-chain alpha-ketoacid dehydrogenase and alpha-ketoglutarate dehydrogenase complexes were detected by immunoblot and quantified by enzyme-linked immunosorbent assay. Of the 14 serum samples obtained from patients with primary biliary cirrhosis, 13, 11, and 2 samples tested positive by immunoblot for the E2 subunits of pyruvate, branched-chain ketoacid, and alpha-ketoglutarate dehydrogenase, respectively. In contrast, samples from subjects with rheumatic diseases, chronic active hepatitis, and alcoholic liver disease and control subjects tested negative for these antibodies. Serum immunoglobulin G with high titers of mitochondrial antibodies showed concentration-dependent inhibition of activity of the dehydrogenase complexes, and close correlation (r = 0.917, n = 13) was observed between inhibitory activity against pyruvate dehydrogenase complex and the reciprocal titer of immunoglobulin against this complex. These data suggest that such autoantibodies, besides serving as diagnostic markers for primary biliary cirrhosis, may have a pathogenic role by their ability to inhibit important mitochondrial enzymes.