Distribution of interleukin-6 in maternal and embryonic tissues during the first trimester.

Interleukin-6 (IL-6) distribution was investigated in coelomic fluid, amniotic fluid, maternal serum, decidua and placental villous tissue collected from 16 normal pregnancies between 7 and 12 weeks of gestation. IL-6 levels in fluids and tissues were measured by an immunoenzymatic assay and mouse monoclonal antibodies specific for IL-6 were used to localize immunohistochemically IL-6 in decidual and placental tissue. IL-6 was detected in all samples of coelomic and amniotic fluids and in most extracts of placental and decidual tissues. IL-6 concentration was significantly (P < 0.005) higher in the coelomic fluid than in amniotic fluid and was positively correlated with gestational age. Immunostaining for IL-6 was present in both syncytiotrophoblast and extra-villous trophoblast. IL-6 was in significantly (P < 0.001) higher concentration in decidual than in placental tissues. These data indicate that IL-6 is normally present in coelomic and amniotic fluids of early pregnancy and that IL-6 concentrations mainly result from the accumulation of trophoblastic-derived IL-6. During the first trimester IL-6 could play a role in tissue remodelling associated with placentation but also in the haematopoiesis function of the secondary yolk sac and in the generation of new vessels in placental villous tissue.