Role of Uterine Natural Killer Cells and Interferon γ in Placental Development

Large granular lymphocytes migrate in large numbers to the pregnant uteri of a wide variety of mammalian species 1. These cells, also known as granulated metrial gland cells in rodents and endometrial granulocytes in primates, will for the purposes of this review all be referred to as uterine (u)NK cells. uNK cells are bone marrow–derived leukocytes, but their immediate precursors may migrate from the spleen. Cells expressing a similar panel of activation antigens are found in the spleens of pregnant but not nonpregnant mice, and only splenocytes derived from pregnant donors can populate the uteri of uNK-deficient recipients during pregnancy 1,2. The signals that regulate migration of uNK to the uterus are not known. Homing precedes implantation in rodents and primates, so it is unlikely that the fetus plays a direct role. Circumstantial evidence implicates...