Human preterm and term parturition is associated with inflammatory cascades in the uteroplacental unit. Activation of the complement cascade releases potent proinflammatory mediators, including the anaphylatoxin C5a, which exerts its biological effects through its receptors, C5AR (also known as CD88) and C5L2, official symbol GPR77. To date, there are few data available on the role of C5a and CD88 in human pregnancy, so the aim of this study was to determine the effect of C5a and CD88 on some key inflammatory pathways involved in human parturition. Placental tissue samples were obtained from normal pregnancies at the time of Cesarean section. Human placental and fetal membranes were incubated in the absence (basal control) or presence of 0.5 μg/ml (~60 nM) human recombinant C5a for 24 h. Concentrations of proinflammatory cytokines, prostaglandins, and 8-isoprostane (a marker of oxidative stress) were quantified by ELISA and secretory matrix metalloproteinases (MMPs) activity by zymography. NFKB DNA binding activity and NFKBIA (IkappaB-alpha; inhibitor of NFKB) protein degradation were analyzed by ELISA and Western blotting, respectively. In the presence of C5a, proinflammatory cytokines (IL6 and IL8), cyclooxygenase (COX)-2; official symbol PTGS2) expression, and subsequent prostaglandin (PGE(2) and PGF(2alpha)), MMP9 enzyme production, and NFKB DNA activation were all significantly increased. The C5a-induced prolabor responses were significantly reduced by treatment with the selective CD88 antagonist PMX53 and the NFKB inhibitor BAY 11-7082. We conclude that C5a upregulates prolabor mediators in human gestational tissues via CD88-mediated NFKB activation.