Anti-Ro/SSA antibodies in systemic sclerosis (SSc): determination of the fine specificity, clinical and laboratory correlations

Background

The frequency of anti-Ro/SSA in SSc varies from 3% to 11% with immunoprecipitation assays and from 12% to 37% with ELISA. Significant associations were reported between anti-Ro/SSA and Sjögren's syndrome, pulmonary involvement and myositis in patients with SSc.

Objective

To evaluate the frequency the association of anti-Ro/SSA antibodies and their fine specificity with clinical and immunological features in SSc.

Patients and methods

We studied 193 patients with SSc (58 diffuse, 129 limited and 6 overlap syndromes) attending our outpatient clinic. Antibodies to ENA were determined by counter-immunoelectrophoresis (CIE) using rabbit thymus (Peel-Freeze) and human spleen extract as substrates. ELISA assay with recombinant 52 and 60 kD Ro proteins (Pharmacia) was performed on 107 sera, cut-off values were determined testing 75 sera from routine: 50 ANA negative and 25 ANA positive-ENA negative.

Results

Anti-Ro was detected by CIE in 12/193 patients (6%) and by ELISA in 14/107 (13%). As a whole, CIE and/or ELISA detected the presence of anti-Ro in 20 patients (Ro+). It was significantly associated with photosensitivity (P = 0.02), xerophtalmia (P = 0.05), raised ESR (P = 0.02), hyperγ globulinemia (P = 0.002), anti-La (P = 0.004) and antinucleolar antibodies (P = 0.02). Anti-Scl70 antibodies tended to be specifically associated with anti-Ro60 as compared with anti-Ro52 antibodies (P = 0.06). Anti-Ro+ patients had higher incidence of interstitial lung disease and slight reduction of DLCO at the moment of first evaluation, as compared with patients Ro– (P = 0.06), particularly with the subset anticentromere positive (P = 0.001). However, decrease of DLCO during follow-up was more frequent in patients Ro– (P < 0.001). This observation might be partially related to a longer steroid treatment received by patients Ro+ (P < 0.03).

Conclusion

Antibodies to Ro/SSA are not infrequently detected in SSc. They are associated with a subset of disease characterized by clinical and serological features commonly associated with anti-Ro/SSA independently from the underlying disease. Anti-Ro+ SSc patients tended to have an earlier lung involvement apparently less evolving as compared to anti-Ro– patients.