C3 and systemic lupus erythematosus: Serum CXCL13 levels in SLE patients were positively correlated with SLEDAI (r = 0.55, P < 0.001) (Figure 2(b)) and negatively correlated with C3 (r = −0.39, P < 0.001) (Figure 2(c)), and there was no significant correlation with the anti-dsDNA antibody titer (r = 0.037, P = 0.72).