Primary biliary cirrhosis (PBC) is a cholestatic autoimmune liver disease characterized by antimitochondrial autoantibodies (AMA) in serum, for which the reactants are E2 subunits of the three 2-oxoacid dehydrogenase (2-OAD) enzymes, particularly pyruvate dehydrogenase complex (PDC-E2). Some 70% of patients with PBC have a coexisting autoimmune disease including Sjögren's syndrome. We aimed to ascertain the frequency and isotype of AMA in saliva in PBC.
Serum and saliva from 12 patients with PBC were tested for AMA by immunoblotting on bovine heart mitochondria, and by an automated microassay based on inhibition of the enzymatic activity of PDC.
Autoantibodies of the immunoglobulin (Ig)G, IgM, and IgA immunoglobulin isotypes against the E2 subunits of 2-OAD enzymes were demonstrable in PBC in serum (12 of 12 cases) and saliva (nine of 12 cases). Salivary autoantibodies, like serum autoantibodies, were predominantly reactive with PDC and of the IgG isotype. Results for serum and saliva corresponded closely with regard to reactivity with individual enzymes of the 2-OAD enzyme family, and to the autoantibody isotype that was predominantly expressed, and also in the capacity to inhibit the enzymatic activity of PDC.
The presence of AMA in saliva to 2-OAD enzymes indicates that salivary glands could participate in the pathogenetic process of PBC. The detection of salivary AMA by a semi-automated enzyme inhibition assay offers possibilities for rapid population screening for detection of preclinical PBC among at-risk individuals, middle-aged to older women.