Anti-mitochondrial antibodies and reactivity to N. aromaticivorans proteins in Icelandic patients with primary biliary cirrhosis and relatives

OBJECTIVES: Primary biliary cirrhosis (PBC) is a chronic, progressive cholestatic disease of unknown etiology characterized by serum antimitochondrial antibodies (AMA) directed against a functionally related family of mitochondrial enzymes. We recently suggested that N. aromaticivorans might be the trigger of autoimmunity in PBC. No data are available on the specificity and crossreactivity of AMA in a genetically homogenous group of patients, such as the Icelandic population. METHODS: To address these issues and to confirm previous findings in a unique population, we obtained sera from 14 PBC patients and 85 first-degree relatives, all of Icelandic descent. We analyzed such sera for AMA specificity using recombinant mitochondrial antigens and for reactivity against N. aromaticivorans proteins. RESULTS: Thirteen of the 14 Icelandic patients with PBC (93%) were found AMA positive. We found that 5/13 AMA positive sera (38%) reacted against PDC-E2 only; 5/13 (or 38%) reacted against BCOADC-E2; and 2/13 (15%) reacted against all three antigens. There was no reactivity against OGDC-E2. Reactivities of patients' sera against N. aromaticivorans were consistent with the AMA status. One serum among the 85 first-degree relatives (1.2%) was found to be AMA-positive, as well as reactive against N. aromaticivorans. CONCLUSIONS: Interestingly, despite the homogenous genetic background, the group of Icelandic patients with PBC was heterogeneous in their AMA reactive patterns and also reacted with N. aromaticivorans proteins.