immunohistochemical analysis of beta 1integrin receptors displayed by murine uterine natural killer cells over the course of successful pregnancy granulated metrial gland gmg cells are a natural killer nk celllike population present in large numbers in the pregnant rodent uterus by day 8 of gestation gmg cells are large and granulated and localized to the mesometrial side of each implantation site gmg cells appear to be highly migratory both in vivo and in vitro however little is known regarding their functions using indirect fluorescence immunohistochemistry murine uteri and implantation sites were studied on successive days of gestation to characterize the extracellular matrix receptors of the vlaintegrin family displayed by gmg cells on days 3 and 6 of gestation double immunostaining using the monoclonal antibody lgl1 was employed to recognize gmg cells because their morphology early in pregnancy resembles that of other lymphocytes between days 815 of gestation gmg cells can be recognized by their unique morphology the day 3 and day 6 lgl1 cells were positive for all antigens examined that is beta 1 plus alpha 1 alpha 3 alpha 4 alpha 5 and alpha 6 from days 815 of gestation gmg cells were beta 1 alpha 4 alpha 5 but alpha 1 alpha 3 alpha 6 thus between days 68 of gestation major changes occur in the uterine nkgmg cell population which include the loss of the surface molecules vla alpha 1 alpha 3 and alpha 6 or the rapid expansion of nk cells not expressing these proteins it is postulated that major changes in the functions of uterine nk cells are likely to be associated with these alterations in cell surface phenotype and that functional studies of uterine nk cells should focus upon this relatively early gestational time point