C4A and systemic lupus erythematosus: The IgG autoantibody titers also correlated with the SLE disease activity index (SLEDAI; r = 0.65, p = 0.0001) (Fig. 2A), erythrocyte sedimentation rate (ESR; r = 0.43, p = 0.02) (Fig. 2B), complement C3 and C4 consumption (r = − 0.55, p = 0.002 and r = − 0.51, p = 0.006, respectively) (Fig. 2C, D), and anti-dsDNA antibodies (r = 0.49, p = 0.03) (Fig. 2E).