CD3(-) Leukocytes Present in the Human Uterus During Early Placentation: Phenotypic and Morphologic Characterization of the CD56(++) Population

In this study, the CD3- LGL/NK cells present in the pregnant human uterus have been characterized. Phenotypic and morphologic analyses of decidual LGL revealed many similarities to the minor CD56(bright+), CD16(-) subset in peripheral blood, but there were some important differences. The relative surface density of CD56(+) is greatly increased on decidual LGL to 22 x that found on the majority of CD56 peripheral blood NK cells. The CD56bright cells in decidua show LGL morphology, whereas in peripheral blood, they are .mainly agranular. Proliferation of CD56(+) cells occurs predominantly during the nonpregnant secretory (luteal) phase, indicating these CD56(+) uterine LGL do not migrate as terminally differentiated cells. The appearance of CD56 cells was examined at the ultrastructural level using immunoelectron microscopy. Cells with phenotypic characteristics of decidual LGL occur in a higher percentage (1.11%) in the peripheral blood of women of reproductive age than in men (0.66%). On the basis of these results, it is proposed that the CD56(bright+) uterine leukocytes represent a distinctive, hormonally regulated subset possibly adapted to control human placentation.