Distribution and antigen specificity of anti-U1RNP antibodies in patients with systemic sclerosis

Systemic sclerosis (SSc) is a generalized connective tissue disease which i s characterized by the presence of several autoantibodies. To determine the prevalence and antigen specificity of anti-U1RNP antibodies (anti-U1RNP) i n patients with SSc, serum samples from 223 patients with SSc, 117 patients with systemic lupus erythematosus (SLE), 18 patients with mixed connective tissue disease (MCTD) and 40 healthy control subjects were examined by ind irect immunofluorescent analysis (IIF), double immunodiffusion, and immunob lotting using nuclear extract of HeLa cells. Eighteen of the 223 (8%) serum samples from patients with SSc were shown to be positive for anti-U1RNP. T he frequency of anti-U1RhTP positivity in limited cutaneous SSc (14%) was s ignificantly higher than that in those with diffuse cutaneous SSc (3%). Ant i-Sm antibodies were detected in patients with SLE positive for anti-U1RNP, but not in those with SSc positive for anti-U1RNP or those with MCTD. Immu noblotting demonstrated that anti-70-kD antibodies were detected more often in patients with SSc positive for anti-U1RNP and in those with MCTD than i n those with SLE. Furthermore, anti-U1RNP was closely correlated with pulmo nary fibrosis and joint involvement in patients with SSc. These results sug gest that anti-70-kD antibodies are useful in the classification of patient s with anti-U1RNP.