Role of Circulating Blood Cells in Maternal Tissue Remodeling and Embryo-Maternal Cross Talk

Abstract

In humans, progesterone production of the corpus luteum during pregnancy is maintained by human chorionic gonadotropin (HCG) secreted by the implanting embryo. In addition to this endocrine system, accumulating evidence suggests that circulating immune cells play an important role in the embryo-maternal cross talk through blood circulation. Peripheral blood mononuclear cells (PBMC) derived from women in early pregnancy enhanced progesterone production by human luteal cells and trophoblast invasion in vitro. Spleen cells derived from mice during early pregnancy induced endometrial differentiation and embryo implantation in vivo. Furthermore, recombinant HCG stimulated human PBMC to produce chemokines through lectin-glycan interaction, promoting trophoblast invasion. Consequently, we proposed that the maternal immune system undergoes functional changes by recognizing developing embryos from the early stage of pregnancy and assists embryo implantation in cooperation with the endocrine system. On the other hand, chemokines secreted from the locally deposited platelets induced neovascularization during corpus luteum formation and promoted extravillous trophoblast invasion during placental formation, reconstructing maternal endometrial spiral arteries. These findings suggest that circulating blood cells including PBMC and platelets positively contribute to embryo-maternal cross talk and maternal tissue remodeling around the implantation period.