C3 and systemic lupus erythematosus: In addition, SLE patients with both depressed C3 and C4 had significantly higher serum IFNL3 (N = 14) than those without complement C3 plus C4 depression (N = 56) (IFNL3 concentration 8.288 ± 1.696 pg/ml vs 4.154 ± 0.4514 pg/ml; P = 0.0013).