title: Differing epitope selection of experimentally-induced and natural antibodies to a disease-specific autoantigen, the E2 subunit of pyruvate dehydrogenase complex (PDC-E2).
abstract: Naturally-occurring autoantibodies to a family of mitochondrial enzymes, the 2-oxoacid dehydrogenase complexes (2-OADC), characterize the human liver disease primary biliary cirrhosis. The immunodominant epitope for these autoantibodies is associated with the lipoyl-binding domain of the E2 subunit of the enzymes. The reactivity of these disease-associated autoantibodies was compared with that of antibodies raised in rats and rabbits, by immunization with various preparations derived from the 2-OADC enzymes, using immunization protocols that have successfully induced various organ-specific autoimmune diseases in animals. The immunogens included the intact pyruvate dehydrogenase complex (PDC) from bovine heart, human recombinant PDC-E2, and short synthetic peptides representing the immunodominant lipoic acid binding sequences of the 2-OADC enzymes. The techniques for antibody analysis included immunofluorescence, immunoblotting on mitochondrial extracts, ELISAs using entire PDC, PDC-E2, or synthetic peptides, epitope mapping by peptide scanning on overlapping octameric peptides representing the human PDC-E2 sequence, affinity purification on PDC-E2, and inhibition in vitro by sera of the catalytic function of PDC. Experimental immunization did not elicit any evidence of autoimmune disease. Moreover, the experimentally-induced antibodies in striking contrast to the natural autoantibodies showed preferential reactivity with PDC-E2 rather than with intact PDC, failed to inhibit in vitro the catalytic function of PDC, and, on peptide scanning, reacted with discrete epitopes, but at sites other than the lipoyl-binding region of PDC-E2. Our data indicate that 'multisystem' autoimmune diseases including primary biliary cirrhosis may not be elicitable experimentally because a critical disease-relevant autoepitope is not engaged by the immune system.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology*; D001327:Autoimmune Diseases / Q000276:immunology*; D000939:Epitopes / Q000276:immunology*; D006801:Humans; D007114:Immunization; D008105:Liver Cirrhosis, Biliary / Q000276:immunology*; D008928:Mitochondria / Q000201:enzymology / Q000276:immunology; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology; D011768:Pyruvate Dehydrogenase Complex / Q000276:immunology*; D011817:Rabbits; D051381:Rats
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D010446:Peptide Fragments; D011768:Pyruvate Dehydrogenase Complex