Inflammatory cytokines seem to play a key role in mechanisms initiating labor. Since cytokine levels are higher in preterm than in term labor, it has been hypothesized that labor-inducing effects of cytokines are inhibited by an upregulated production of cytokine antagonists, such as soluble cytokine receptors, at early stages of gestation. In this study, TNF, IL-1, IL-6, IL-8 and soluble TNF receptors (sTNFRs) were measured in amniotic fluid samples from a) 39 women in premature labor, b) 25 women who where not in labor but delivered prematurely, and c) 33 women in term labor. Fifty-four of the placentas from premature deliveries were evaluated for presence of histological chorioamnionitis. Chorioamnionitis was associated with increased levels of TNF, IL-1 and IL-6, whereas elevated IL-1, IL-6 and IL-8 concentrations were found in premature parturition with no signs of infection. Concentrations of sTNFR were lower in preterm than in term deliveries. The present study confirms the participation of inflammatory cytokines in parturition. Multivariate analysis suggests a dominant, role of IL-1 in the presence of chorioamnionitis, whereas IL-6 seems to be more important during idiopathic premature labor. TNFR data do not support the hypothesis that production of cytokine antagonists is upregulated prematurely to prevent partirution.

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Several lines of evidence suggest that a number of immunoactive cytokines participate in early reproductive events such as implantation and placental development. Furthermore, cytokines may influence embryo growth and differentiation. In the present study, the production of tumour necrosis factor (TNF), interleukin-1 (IL1), interleukin-6 (IL6) and transforming growth factor-beta (TGF beta) during the first 48 h after oocyte retrieval during in-vitro fertilization was investigated. In addition, the question was raised whether soluble receptors may contribute to cytokine activity regulation in early reproduction, and concentrations of TNF and IL6 receptors in culture media were determined. Finally, an investigation of whether any association exists between cytokine concentrations and embryo morphology was performed. Media from 256 embryos were analysed. IL1, IL6 and TGF beta were produced during the 48 h culture period, whereas no TNF was detected. Levels of IL1 and IL6 were significantly higher in media from the first 24 h culture period than from the second period, whereas TGF beta concentrations in supernatants from the two observation periods did not differ. IL6 receptors were not detected, whereas TNF receptors (p75) appeared in media from the 24-48 h culture period. Granulosa, cumulus and sperm cells are potential sources of cytokine production, especially during the first 24 h period. The contribution of the embryo to cytokine/cytokine receptor production remains an open question. No significant correlation was observed between cytokine/cytokine receptor concentrations and embryo morphological score.

The present study suggests a role of IL-6 and p55 in normal labor. However, as women being studied already were in labor, the study does not allow any conclusions whether observed changes in IL-6 and p55 levels have a causal relation to the process of labor or if changes are secondary effects of the process itself.