The interleukin-1 system and human implantation.

PROBLEM: Cytokines and growth factors are increasingly implicated in embryonic implantation. In the present study, we focus on the interleukin-1 system as an example of local regulator in human implantation. METHOD: Three different approaches are considered. First, we present evidence demonstrating its presence, regulation, and relevance on the human endometrium. Second, we demonstrate the presence of IL-1 system in the human embryo and the selective IL-1 release only when embryos were co-cultured with human endometrial epithelial cells (EEC) or EEC-conditioned media, indicating an obligate role of the endometrium in the regulation of the embryonic IL-1 system. Finally, we show data regarding the presence, hormonal regulation, and endometrial origin of IL-1 alpha, IL-beta, and IL-1ra levels in the endometrial fluid inside the endometrial cavity. Specifically, we present the IL-1 intracavitary microenvironment surrounding the human embryo at the apposition phase. RESULTS: This work suggests that the IL-1 system seems to be relevant for human endometrial and embryonic physiology. Furthermore, this family of molecules must be considered as a relevant paracrine language displayed by both partners that may be important to endometrial and embryonic crosstalk during embryonic implantation.