C3 and systemic lupus erythematosus: Correlation analysis showed that in treatment-naive SLE patients, the NK count showed weak positive correlations with the levels of complement C3 (r = 0.193, P = 0.017) (Fig. 1C) and PLT (r = 0.258, P = 0.001) (Fig. 1D) and a negative correlation with SLEDAI score (r =  − 0.211, P = 0.008) (Fig. 1E).