C4A and systemic lupus erythematosus: Interestingly, C4d did not correlate significantly with C3 (rs = –0.07, p = 0.76) and C4 (rs = –0.41, p = 0.057) in the 22 non-renal SLE patients, but only in the 71 LN patients [C3 (rs = –0.31, p = 0.014), C4 (rs = –0.26, p = 0.031)] (Figures 2A,B).