C3 and systemic sclerosis: Additionally, we searched for correlations between dcSSc-associated anti-DNA topoisomerase I (Scl-70) autoantibody, anti-citrate synthase (CS) natural autoantibody and complement component 3 (C3) levels and found a negative correlation between C3 and anti-CS autoantibody in dcSSc but not in HCs, supporting the hypothesis that natural autoantibodies could activate the complement system contributing to tissue injury in SSc.