Anti-U1RNP antibodies in patients with localized scieroderma

Antibodies to U1 ribonucleoproteins (RNP) have been detected in serum from patients with various autoimmune diseases. However, the presence of anti-U1RNP antibodies in patients with localized scleroderma has not been reported. In this study, we examined the frequency of anti-U1RNP antibodies using immunoprecipitation of U small nuclear RNAs and determined the antigen specificity by immunoblotting. Of 70 serum samples from patients with localized scleroderma, 2 (3%) immunoprecipitated U1 small nuclear RNA. Indirect immunofluorescence using HEp-2 cells as substrate showed coarse speckled nuclear fluorescence without nucleolar staining in both of the samples positive for anti-U1RNP antibodies. In addition, the presence of anti-U1RNP antibodies in each serum sample was confirmed by immunodiffusion against HeLa cell extracts. Immunoblotting analysis showed anti-70 kDa antibodies in each serum sample. This reaction against 70 kDa protein in the patients with localized scleroderma was analogous to that in patients with systemic sclerosis or mixed connective tissue disease. Both patients with positive serum were diagnosed as having linear scleroderma, but neither had evidence of Raynaud's phenomenon or sclerodactyly. These results indicate that the presence of anti-U1RNP antibodies is one of the serological abnormalities in localized scleroderma, and that the mechanism of induction of anti-U1RNP antibodies in patients with localized scleroderma might be similar to that in patients with systemic sclerosis and mixed connective tissue disease.