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OBJECTIVE: To investigate the clinical significance of anti-TS1-RNA antibodies in patients with mixed connective tissue disease (MCTD). METHODS: Anti-TS1-RNA antibodies were detected by immunoprecipitation using 32P-UTP labeled TS1-RNA as the antigen source. In total, 104 patients with MCTD, 30 with Sjögren's syndrome, 30 with systemic lupus erythematosus (SLE), 25 with systemic sclerosis, 23 with polymyositis or dermatomyositis, and 10 with rheumatoid arthritis were examined. Specificity of anti-TS1-RNA antibodies was analyzed by immunoprecipitation using HeLa cell extracts. RESULTS: The frequency of anti-TS1-RNA antibodies was 31.7% in patients with MCTD, significantly higher than in SLE (p < 0.05). In anti-TS1-RNA positive patients, the incidence of hypertension and proteinuria and the frequency of anti-Sm and anti-dsDNA antibodies associated with SLE were higher than those of anti-TS1-RNA negative patients. Clinical features of SS such as sicca complex, the serum level of IgA, and anti-SSA antibodies were also elevated. The frequency of anti-TS1-RNA antibodies was significantly higher in SLE patients with anti-U1-RNP antibodies (p < 0.01); however, anti-TS1-RNA positive sera did not precipitate the specific RNA including U1 RNA in immunoprecipitation using HeLa cell extracts. In longitudinal studies, the level of anti-TS1-RNA antibodies changed in parallel with disease activity. CONCLUSION: We found that the level of anti-TS1-RNA antibodies was possibly correlated with the disease activity of lupus-like clinical features in patients with MCTD.

OBJECTIVE: To define a novel RNA epitope recognized by serum from a patient with Sjögren's syndrome (SS) from a randomized RNA epitope library and investigate the epitope reactivity of the anti-RNA antibodies in patients with various connective tissue diseases. METHODS: Serum from a patient with SS was used to select ligands from a library of RNA oligomers with a central region of 25 degenerate nucleotides. Bound RNA was recovered by reverse transcription, PCR amplification, and subcloning. The relationship between the antibodies to the selected RNA and disease specificity was studied using immunoprecipitation. RESULTS: From the random RNA library, several unique RNA sequences were obtained. Sera from 32 of 61 patients with SS (52.5%) precipitated with one of the selected RNA (TS1-RNA), whereas sera from 8 of 41 patients with systemic lupus erythematosus (19.5%) and 3 of 25 patients with rheumatoid arthritis (12.0%) precipitated. Although the frequency of reactivity to the TS1-RNA was higher in anti-SSA/Ro positive sera, the presence of either native or recombinant SSA/Ro antigen showed no detectable competition, and no apparent sequence homology was found between the TS1-RNA and hY RNA. CONCLUSION: These data suggest that anti-TS1-RNA is a novel antibody against sequence-specific RNA in many patients with SS.