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 CD56bright+, 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 CD56bright+ uterine leukocytes
represent a distinctive, hormonally regulated subset possibly adapted to control human
placentation.Peer Reviewe