Immunization of experimental animals with dihydrolipoamide acetyltransferase, as a purified recombinant polypeptide, generates mitochondrial antibodies but not primary biliary cirrhosis

Abstract

The availability of recombinant mitochondrial autoantigens may permit the experimental study of the pathophysiology of primary biliary cirrhosis. Previously, we demonstrated that high-titer antibodies to the 74 kD mitochondrial autoantigen dihydrolipoamide acetyltransferase could be generated when BALB/c mice were immunized with purified recombinant protein. Based on these data, we attempted an 8-month study to induce antibodies and liver dysfunction by immunizing AKR/J, C3H/J and CBA/HeJ mice as well as rats, guinea pigs, rabbits and rhesus monkeys with purified recombinant human dihydrolipoamide acetyltransferase. Antibodies to dihydrolipoamide acetyltransferase were readily induced and detected in all species of experimental animals with species and strain differences in the titer of the responses. Of particular interest, rabbits and guinea pigs produced antibodies which were specifically reactive with the functional site of dihydrolipoamide acetyltransferase, whereas the other strains and species produced antibodies to other epitopes on the molecule. Finally, similar to data on humans with primary biliary cirrhosis, the pyruvate dehydrogenase enzyme pathway was inhibited in the presence of immunized animal sera. These data imply that features other than simply an antibody response to mitochondrial enzymes are required for the development of primary biliary cirrhosis. Further studies will be necessary to determine the mechanisms by which mitochondrial proteins elicit an immune response.

Recurrent primary biliary cirrhosis

“…AMAs do not appear themselves to be pathogenetic because induction of AMA in laboratory animals does not lead to bile duct damage. 31 Similarly, neither the presence nor titer of AMA and the other PBC-specific autoantibodies (gp210 and the multiple nuclear dots antibodies) correlate with the histologic features of PBC recurrence. 32 Biliary epithelial cells from the native livers of patients with PBC but not with other conditions have plasma membrane expression of the antigen recognised by AMA (the E2 component of the dihydrolipoamide acetyl transferase).…”

Autoimmune Overlap Syndromes

“…Although this possibility must be qualified by the possibility that AMA may indeed be detectable in such cases if more sensitive laboratory techniques are used, it is supported by the lack of correlation of disease activity with AMA titer, and uncertain association of AMA with disease in animal models of PBC. 79,80 However, given that B-and T-cell epitopes of PDC-E2 overlap, 81 it is unclear why the association of AMA and PBC is not absolute: it remains to be seen whether T cells from patients with AMA-negative PBC react to the same epitope or derived peptides as those from patients with AMA, or whether lack of AMA positivity in PBC is conferred by different class II HLA loci. The introduction of HLA-antigen tetramer technology in probing T-cell receptor specificity may be of particular value in this setting.…”

Pbc and Ama—What Is the Connection?

“…In an initial study, Krams et al 32 found that immunization of a variety of laboratory animals with recombinant E2 resulted in the generation of circulating AMA, but granulomatous cholangitis was not detectable. These observations suggested that the AMA do not directly induce an immune response to normal biliary epithelial cells.…”