The transfer of interleukin-8 across the human placenta perfused in vitro

Objective: To assess the placental transfer of interleukin (IL)-8 in vitro. Methods: Eighteen placentas obtained immediately after delivery were perfused with a mixture of I-125-labeled IL-8 (IL-8*) and unlabeled IL-8 in two different concentrations. Antipyrine was coinfused in all experiments as a reference compound. Fetal-to-maternal and maternal-to-fetal perfusions were performed. Radioactivity was measured in a gamma counter at the end of each perfusion experiment. In four experiments, unlabeled IL-8 was analyzed in addition to labeled IL-8 to exclude a change in the IL-8/IL8* ratio resulting from membrane transfer. Results: Two of the 18 experiments had to be discarded because of poor transfer of antipyrine. There was only faint accumulation of radioactivity in the transplacental compartment, regardless of whether the test substance was added maternally or fetally. Because measurement of unlabeled IL-8 yielded negative results, the radioactivity is clearly attributable to free iodine 125, which is generated during IL radiolabeling or which disassociates from IL-8 in small amounts after radiolabeling. Conclusion: Interleukin-8 does not appear to cross the placenta by simple diffusion, regardless of the concentration or the perfusion rate. The impermeability of the placenta to the diffusion of IL-8 might explain why there is insufficient correlation between serum and amniotic fluid cytokine concentrations of pregnant women and the presence of the amnion infection syndrome.