The developmental role of natural killer cells at the fetal-maternal interface.

Natural killer (NK) cells have been extensively studied in their traditional roles in host defense against tumor or virally infected cells. Uterine NK cells are of 2 distinct subsets: endometrial NK (eNK) cells, found in the uterus during the menstrual cycle, and decidual NK (dNK) cells, found in the decidua during pregnancy. This review will explore the immunosurveillance and cytotoxicity profiles of NK cells, the inert nature of eNK cells, and the role of dNK cells as builders at the maternal-fetal interface that create a pregnancy-favorable environment by inducing angiogenesis, trophoblast invasion, and vascular remodeling.