Meconium-stained amniotic fluid exhibits chemotactic activity for polymorphonuclear leukocytes in vitro

We have studied whether meconium-stained, turbid amniotic fluid (turbid AF) obtained during term pregnancy possesses chemotactic activity for polymorphonuclear leukocytes (PMNs) in the absence of clinically apparent infection. Eight samples of turbid AF were obtained from eight women who underwent a cesarean section (four emergency and four elective cesarean sections) in the absence of signs of clinical infection or fetal distress. Samples of clear AF obtained from nine women during an elective cesarean section served as a control. We used also a negative control (medium only) and a positive control containing 10 nM N-formyl-methionyl-leucyl-phenylalanine. The control or turbid AF specimen was placed in the lower compartment of a blind well chamber, and the PMN suspension was placed in the upper compartment. Following incubation, the number of PMNs that had migrated and passed through the filter to the AF was counted. The number of control PMNs that migrated to the turbid AF (200+/-59) was comparable to that of the positive (162+/-24) but significantly exceeded that of the clear AF (17+/-11; P < 0.0001) and of the negative control (25+/-9; P < 0.0001). Checkerboard assay indicated that the turbid AF exhibited a dose-dependent chemotactic activity for PMNs. The turbid AF contained higher levels of TNFalpha, IL-1beta and IL-8 than the clear AF. The concentration of IL-8 in the AF was correlated positively with the chemotactic activity of the AF (r = 0.733, P = 0.0005). Anti-human IL-8 antibody added in the turbid AF dose-dependently abolished the chemotactic activity of the turbid AF. It is concluded that meconium-stained AF is a chemoattractant for PMNs and that cytokines such as an IL-8 may be involved in this phenomenon.