Background Anti-C1q autoantibodies are associated with systemic lupus erythematosus (SLE) but their presence in other rheumatic diseases has not been investigated in great detail.

Objectives We aim to assess the clinical significance of anti-C1q autoantibodies in systemic sclerosis (SSc).

Methods Seventy five patients with SSc (median age 59 years; females, 61; diffuse cutaneous SSc 35, limited cutaneous SSc, 40) were studied. Thirty eight patients with SLE, 25 patients with Sjögren's syndrome (SjS), 19 with rheumatoid arthritis (RA), and 31 healthy individuals (NC) were also included. IgG anti-C1q antibodies were tested by ELISA. Anti-nuclear antibodies (ANA), and SSc-specific autoantibodies were also tested.

Results A receiver operator characteristic curve (ROC) confirmed that the cut off at 20 RU/mL for the anti-C1q test (specificity, 0.94, 95% CI, 0.79 to 0.99, LR: 5.0) was appropriate. Anti-C1q antibodies were present in 32.0% of SSc patients compared to 16.0% SS, 10.5% RA patients (p<0.05, for all) and in 6.5% NC (p<0.01). The frequent presence of anti-C1q antibodies in SLE was confirmed (13/38, 34.2%). Amongst the 24 anti-C1q (+) SSc patients, 15 had high/moderate levels (>40 RU/mL). There was no association between anti-C1q antibodies and anti-topoisomerase I, anti-centromere, or anti-RNA polymerase III antibodies. Anti-C1q antibodies were associated with male sex (p=0.04) and lung fibrosis (LF) (p=0.008), and co-occurrence of LF and skin ulcers (p=0.006). Ulcers were more prevalent in anti-C1q(+) than anti-C1q(−) patients (64% vs 44%), but the difference did not reach statistical significance (p=0.1).

Conclusions Anti-C1q antibodies were frequently detected in SSc, were associated with PF and co-occurrence of PF and skin ulcers and may contribute to the autoimmune process in SSc.

Acknowledgement Fianancial support by ELKE, University of Thessaly

Disclosure of Interest None declared