BACKGROUND: Anti-C1q autoantibodies (autoAbs) are associated with systemic lupus erythematosus (SLE) but their presence in other rheumatic diseases has not been adequately investigated.
OBJECTIVE: We aim to assessanti-C1q autoAbs and circulating immune complexes (CICs) in systemic sclerosis (SSc).
METHODS: One hundred twenty four patients with SSc (106 females; median age 59.4 years, range 25-81.4; 75(60.5%) with limited cutaneous SSc[lcSSc], and 49(39.5%) with diffuse cutaneous SSc[dcSSc]), were studied. Twenty-five patients with Sjögren\u27s syndrome (SjS), 29 with rheumatoid arthritis (RA), and 38 patients with systemic lupus erythematosus (SLE) and 53 healthy controls (NC) were also included. ELISAs with high and low salt buffers the former allowing IgGFc binding to C1q, the latter not allowing IgGFc binding and anti-C1q Ab binding to C1q were used to measure anti-C1q Abs and CICs.
RESULTS: Anti-C1q Abs were present in20/124 (16.1%) SSc patients [5 had high levels (\u3e80 RU/mL) and 10 patients (50%) had moderate levels (40-80 RU/mL)] compared to 1/25 (4%) SjS, 1/29 (3.4%) RA patients (p
CONCLUSIONS: Anti-C1q autoAbs were frequently detected in patients with SSc and their high levels predict the co-occurrence of pulmonary fibrosis or pulmonary arterial hypertension
