Clinical significance of antibodies to TS1-RNA in patients with mixed connective tissue disease.

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.