Association of anti-DFS70 positivity with disease activity in systemic lupus erythematosus, Sjögren's syndrome, and systemic sclerosis: a cross sectional study

Objective Anti-DFS70 antibodies have been proposed as a potential marker of lower disease activity in systemic autoimmune diseases, but evidence remains conflicting. This study aimed to investigate the association between anti-DFS70 positivity and disease activity in three systemic autoimmune diseases: systemic lupus erythematosus (SLE), primary Sjögren's syndrome (pSS), and systemic sclerosis (SSc). Methods This cross-sectional study included 246 patients (59 SLE, 102 pSS, 85 SSc). Anti-DFS70 positivity was determined by immunoblot method. Disease activity was assessed using SLEDAI-2 K (SLE), ESSDAI (pSS), and EUSTAR activity index (SSc). Multivariate linear regression models were constructed for each disease cohort, adjusting for age, sex, disease-specific autoantibodies, glucocorticoid use, and interstitial lung disease (for SSc). Results Anti-DFS70 positivity was observed in 14 (23.3%) SLE, 23 (22.5%) pSS, and 12 (14.1%) SSc patients. In univariate analyses, anti-DFS70-positive SLE patients had significantly lower SLEDAI-2 K scores (median 3 vs 4, p = 0.001), lower anti-dsDNA positivity (6.7% vs 40.0%, p = 0.014), and less frequent glucocorticoid use (13.3% vs 46.6%, p = 0.02). However, in multivariate regression models, anti-DFS70 positivity was not independently associated with disease activity in any of the three diseases (SLE: β = −1.197, p = 0.191; pSS: β = −0.181, p = 0.394; SSc: β = −0.578, p = 0.187). Correlation analysis revealed a significant negative correlation between anti-DFS70 titre and SLEDAI-2 K in SLE (ρ = −0.440, q < 0.001), which was lost after multivariate adjustment, confounded by anti-dsDNA positivity and glucocorticoid use. Conclusion No independent association was demonstrated with Anti-DFS70 positivity and low disease activity in SLE, Sjögren's syndrome, or systemic sclerosis.