In Vivo Infusion of Interleukin-1b and Chorionic Gonadotropin Induces Endometrial Changes that Mimic Early Pregnancy Events in the Baboon

Both human chorionic gonadotropin (hCG) and IL-1b induce changes in the endometrium that are associated with the establishment of pregnancy. We investigated the synergistic effect of these two embryonic signals on endometrial function using a baboon model of simulated pregnancy. Recombinant hCG (30 IU/d) was infused between d 6 and 10 post ovulation (PO) to mimic blastocyst transit. On the expected day of implantation (d 10 PO), IL-1b (12 ng/d) or IL-1 receptor antagonist (IL-1Ra; 12 ng/d) was infused for an additional 5 d. Endometria were harvested on d 15 PO. Both hCG and hCG plus IL-1b induced marked differences in the distribution of a-smooth muscle actin, proliferation marker Ki67, decidualization marker IGF-binding protein-1, and cyclooxygenase-1. The most marked effect of IL-1b was the induction of IGF-binding protein-1 protein in stromal cells close to the apical surface, whereas cyclooxygenase-1 was down-regulated in the glandular epithelium. Protein arrays of uterine flushings showed significant suppression of death receptors, Fas and TNF receptor 1, in the hCG- with or without IL-1b-treated groups, suggesting an inhibition of apoptosis. Additionally, cytotoxic T lymphocyte antigen-4, matrix metalloproteinase-3, and IL-4 were suppressed in treated animals compared with controls. However, no differences were observed in cytokine profile between hCG-treated and hCG- plus IL-1b-treated baboons. This study confirms that in preparation for pregnancy, the primate endometrium undergoes both morphological and functional changes, which are modulated by hCG and IL-1b, that lead to the inhibition of apoptosis and the development of an immunotolerant environment. These changes suggest that infusion of IL-1b at the time of implantation into the nonpregnant baboon treated with hCG synergizes with hCG and mimics the early endometrial events associated with the presence of an embryo.