Recently the main targets of antimitochondrial
antibodies (AMA) of
primary biliary cirrhosis have been identified as parts of three related mitochondrial
multienzyme complexes, namely
pyruvate dehydrogenase (PDH), branched chain alpha-ketoacid
dehydrogenase (BKDH) and
alpha-ketoglutarate dehydrogenase (alpha-KGDH). Usually AMA-positive PBC serum samples show reactivity to more than one of these, raising the question whether they are exclusively different
antibodies or are, at least in part, the result of cross-reactive specificities. With Western immunoblotting, four
antigens with molecular masses of 74, 52, 51 and 43 kDa, are recognized by PBC sera. In this study, using affinity purified
antibodies from
mitochondrial proteins immobilized on
nitrocellulose blots, we demonstrate the presence of
peptide-specific and cross-reactive
epitopes in some targets. In particular, at least three different
epitopes present in the 74-kDa
protein (presumed to by PDH-E2) are also present in the 51-kDa
protein (probably PDH-X), and two in the 52-kDa
peptide (possibly BCKDH-E2). Moreover, the 43-kDa
mitochondrial protein (the identity of which is more problematic) has three
epitopes. One of these is also present in the 74-, 52- and 51-kDa
proteins, a second in the 74- and 51-kDa, and a third seems to be
peptide-specific. These results show that different sera with the same immunoblotting pattern of reactivity can have
antibodies with different antigenic specificities and, conversely, that the same specificity can be responsible for more than one band.