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

Abstract

Systemic sclerosis (SSc) is a generalized connective tissue disease which is characterized by the presence of several autoantibodies. To determine the prevalence and antigen specificity of anti-U1RNP antibodies (anti-U1RNP) in 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 indirect immunofluorescent analysis (IIF), double immunodiffusion, and immunoblotting 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. The frequency of anti-U1RNP positivity in limited cutaneous SSc (14%) was significantly higher than that in those with diffuse cutaneous SSc (3%). Anti-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. Immunoblotting demonstrated that anti-70-kD antibodies were detected more often in patients with SSc positive for anti-U1RNP and in those with MCTD than in those with SLE. Furthermore, anti-U1RNP was closely correlated with pulmonary fibrosis and joint involvement in patients with SSc. These results suggest that anti-70-kD antibodies are useful in the classification of patients with anti-U1RNP.

Fig. 1

Immunoblot analysis of sera from patients with systemic sclerosis (SSc) (a), those with mixed connective tissue disease (MCTD) (b), and those with systemic lupus erythematosus (SLE) (c). Sera from healthy control subjects were also included (lane 19 (a); lane 19 (b); lane 29 (c)). The nitrocellulose blot strips contained HeLa nuclear extracts transferred after separation on 15% SDS–polyacrylamide gels. Each strip was incubated with patient serum at 1:50 dilution and bound antibodies were detected with alkaline phosphatase-conjugated goat anti-human IgG antibody, and colour was developed with nitroblue tetrazolium and 5-bromo-4-chloro-3-indolyl phosphatase.