Anti-mitochondrial antibodies (anti-M7) in heart diseases recognize epitopes on bacterial and mammalian sarcosine dehydrogenase.

The anti-mitochondrial antibody (AMA) anti-M7 has been shown to occur exclusively in sera from patients with acute and chronic myocarditis. Applying different enzymes of the inner mitochondrial membrane to ELISA, anti-M7-positive sera reacted only with sarcosine dehydrogenase (SD) from Pseudomonas aeruginosa. Testing these sera in the Western blot against a commercially available SD as well as against SD prepared from rat liver mitochondria, a determinant at 42 kD and 90 kD, respectively, was visualized. Using submitochondrial particles (SMP) from bovine heart and rat liver another major determinant at 64 kD could be observed with both antigen fractions. Liver SMP also expressed the SD-related, 90-kD epitope. Sera from patients with other AMA-positive and AMA-negative autoimmune diseases were negative with these different determinants. The identity of the 64-kD epitope on heart and liver SMP as well as the 42-kD polypeptide of bacterial SD and the 90-kD epitope on mammalian SD was proven by absorption studies and by elution of antibodies from the antigen bound to the immobilon sheets after immunoblotting. The SD enzyme activity was not affected by anti-64-kD and anti-42-kD antibodies in vitro. It is concluded that anti-M7 antibodies may be stimulated by an antigen expressed on cardiocytes during an infection which shares epitopes with SD, an evolutionary highly conserved protein. SD-sensitized B cell clones could therefore be triggered by the M7-antigen which shows homology to SD.