AUTOANTIBODIES TO M2 MITOCHONDRIAL AUTOANTIGENS IN NORMAL HUMAN SERA BY IMMUNOFLUORESCENCE AND NOVEL ASSAYS

Primary biliary cirrhosis (PBC) is characterized by the presence of an timitochondrial antibodies (anti-M2), directed against the E2 subunits of the 2-oxo-acid dehydrogenase complexes (2-OADC), chiefly pyruvate dehydrogenase complex (PDC-E2). We present here a detailed study, base d on a large panel of normal Sera, of the specificity of tests for ant i-M2 by immunofluorescence and for anti-PDC by other assays for the di agnosis of PBC. The assays for anti-PDC included immunoblotting with b ovine heart mitochondria, ELISA using recombinant PDC-E2 and an enzyme inhibition assay using purified porcine PDC. The positivity rates for normal sera were 0 (0/170), 2 (4/201), 1.5 (3/198) and 0% (0/186) for immunofluorescence, immunoblotting, ELISA and the enzyme inhibition a ssay, respectively. The seven positive reactions detected either by im munoblotting (n = 4) or ELISA (n = 3) were negative by the other three assays and in no instance did biochemical indices give any indication of chronic liver disease. Thus, as judged by reactivity with normal s era, the specificity of a positive test for the antibody to the major M2 autoantigen (PDC-E2) is 100% for immunofluorescence and the enzyme inhibition assay, 98% for immunoblotting and 98.5% for ELISA.