Detection of autoantibodies to nucleolar transcription factor NOR 90/hubf in sera of patients with rheumatic diseases, by recombinant autoantigen–based assays

Abstract

Objective. 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. Methods. 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. Results. 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, I 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. Conclusion. 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.