We attempted to clarify the clinical characteristics of Japanese patients with autoantibodies to nucleolar transcription factor NOR 90/hUBF (anti-NOR 90) and to analyze the autoantigenic epitopes recognized by anti-NOR 90.
Ninety-one patient sera containing anti-nucleolar antibodies (ANoA) by indirect immunofluorescence were collected. Immunoblottings were performed using recombinant fusion proteins expressed from several cloned complementary DNA (cDNA) encoding the NOR 90/hUBF autoantigen.
Anti-NOR 90 were detected in sera from 9 (9.9%) of 91 patients with ANoA. Seven of these patients were diagnosed as having Sjögren's syndrome, 4 had concomitant rheumatoid arthritis, 1 had concomitant systemic sclerosis (SSc), and 2 had SSc alone. All 9 sera were reactive with more than 2 recombinant fusion proteins from cDNA encoding separate regions on the hUBF polypeptide.
The results suggest that while anti-NOR 90 antibodies are rare, they are associated with Sjögren's syndrome in Japanese patients, and that autoimmunity is targeted toward at least 2 separate regions (amino acids 89-310 and 310-633) of the hUBF polypeptide.