MDSCs in pregnancy: Critical players for a balanced immune system at the feto-maternal interface.

• MDSCs are a broad and heterogeneous population with myeloid origin and mostly contribute to immunosuppressive conditions. • MDSCs, especially PMN-MDSCs are highly abundant at feto-maternal interface and in peripheral blood of pregnant women. • Several factors such as sex hormones, trophoblasts, HLA-G, hypoxia, and cytokines play critical roles in MDSCs expansion and activation at feto-maternal interface. • MDSCs are also abundant in fetuses and neonates and contribute to the balance of immune system. Myeloid-derived suppressor cells (MDSCs) have emerged as a new immune regulator at the feto-maternal interface. Although the phenotypes and functions of these cells were primarily studied in pathological conditions such as cancers and infections, new evidence has underscored their beneficial roles in homeostasis and physiological circumstances such as normal pregnancy. In this regard, studies have shown an increased number of MDSCs, particularly granulocytic MDSCs, at the feto-maternal interface. These cells participate in maintaining immunological tolerance between mother and semi-allograft fetus through various mechanisms. They further seem to play critical roles in placentation and fetus growth process. The absence or dysregulation of MDSCs during pregnancy have been reported in several pregnancy complications. These cells are also abundant in the cord blood of neonates so as to balance the immune responses and prevent aggressive inflammatory responses. The current review summarizes and organizes detailed data on MDSCs and their roles during pregnancy. [ABSTRACT FROM AUTHOR]