In order to implant and grow, the trophoblast cells from the allograft fetus need to invade the mother tissues and inevitably bring certain inflammatory reaction. How to control these inflammations and maintain tissue homeostasis is the key problem of embryo tolerance. Researchers have found that large numbers of unique NK cells accumulated at the maternal-fetal interface. Such decidual NK cells showed low cytotoxicity but produce much IFN-γ. In addition, researchers have verified that normal decidual NK cells can inhibit TH17 cells by IFN-γ and maintain immune balance at maternal-fetal interface. If the pregnant women encountered pathogens such as virus infection, the regulatory function of decidual NK cells is disrupted, which leads to a prominent TH17 response and increased inflammation, resulting in fetal loss or spontaneous abortion(Figure 1).The work "Natural killer cells promote immune tolerance by regulating inflammatory TH17 cells at the human maternal–fetal interface"was published on Jan 15th in PNAS(PNAS. 2013 Jan 15; 110 (3): E231-40) .

NK cells maintain embryonic immune tolerance

Why dose the decidual NK cells dispaly low cytotoxicity and become the guardians of maintaining the maternal-fetal immune tolerance? By using the microRNA array analysis, the researchers found that decidual NK cells showed much higher miR-483-3p expression when compared to peripheral blood NK cells, leading to decreased IGF-1 production, low cytotoxic activity and the best ability to secrete IFN-γ, which contribute to the immune balance at maternal-fetal interface. The work was published on Feb 12th in Nature Communications (Nat. Commun. 2013 Feb 12; 4:1479) entitled "IGF-1 promotes the development and cytotoxic activity of human NK cells".