The interleukin-1 system and human implantation

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.

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.

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.