Synchronous regulation of the determinants of endometrial receptivity to interleukin 1 at key stages of early embryo implantation in vivo

ObjectiveTo investigate the expression kinetics of interleukin-1 receptors (IL-1R), receptor antagonist (IL-1RN), and monocyte chemotactic protein 1 (MCP-1) throughout early gestation in mice.DesignAssessment of IL-1R, IL-1RN, and MCP-1 throughout early pregnancy.SettingReproduction laboratory.Animal(s)B6C3F1 female mice bred with fertile males of the same strain.Intervention(s)Collection of endometrial tissue at necropsy from nonimplanted and implanted sites.Main Outcome Measure(s)IL-1R, IL-1RN, and MCP-1 mRNA expression by quantitative reverse-transcription polymerase chain reaction and protein expression by enzyme-linked immunosorbent assay and immunohistochemistry.Result(s)The expression of the signaling IL-1R1 significantly increased in the first 2 days of gestation, which corresponded to the inflammatory-like period triggered by the seminal fluid, before increasing again at the implantation window and lasting throughout embryo implantation. The expression of inhibitory IL-1R2 and IL-1RN concomitantly increased during gestational days 1–2 but remained low, particularly within the embryo implantation sites and throughout the implantation period. The expression of MCP-1 significantly increased only at the embryo implantation sites and showed a significant positive correlation with IL-1R1 expression.Conclusion(s)Our data identified for the first time synchronous changes in endometrial IL-1R throughout early gestation in vivo and point to a deep modulation of endometrial receptivity to IL-1 by embryo-driven signals. This may play a key role in the creation of a receptive phenotype in the maternal endometrium and represent a key mechanism underlying embryo implantation.