Recent research found that less secretion of C3 appears to inhibit the activation of the High-Mobility Group Box 1 (HMGB1)-TLR4-p65 pathway signal pathway and the production of transforming growth factor-β (TGF-β1), thereby alleviating renal fibrosis in unilateral ureteral obstruction (UUO) mice [11]. Here, TLR4 is linked to renal fibrosis.