Placental immune state shifts with gestational age.

Placental immunologic functions are implicated in both the maintenance of a healthy pregnancy and the pathogenesis of obstetric complications. Immune populations at the maternal-fetal interface are hypothesized to support fetomaternal tolerance, defend the fetus from infection, and contribute to labor initiation. Despite the many potential roles of placental immune cells in normal and abnormal pregnancy, little is known about placental immune population dynamics over gestation, particularly near parturition.A daily placental immune cell census was established in a murine model by flow cytometry from mid to late gestation and compared to the maternal systemic immune census. Shifts in the placental immune state were further characterized through cytokine ELISAs.The placental immune census is distinct from the maternal systemic immune census, although the cells are primarily maternal in origin. Near term parturition, the placenta contains fewer CD11c-positive myeloid cells and regulatory T cells, and there is a concurrent decrease in placental IL-9 and IL-35.The immune profile of the placenta demonstrates a decrease in both regulatory immune cell types and cytokines late in gestation. Establishing the placental immune population dynamics over a healthy pregnancy will allow future investigation of placental immune cells during abnormal pregnancy.