MOUSE GRANULATED METRIAL GLAND-CELLS ORIGINATE BY LOCAL ACTIVATION OF UTERINE NATURAL-KILLER LYMPHOCYTES

Natural killer (NK) lymphocytes were identified in the mouse uterus by immunostaining their surface membrane marker, LGL-1. The cells were present in large numbers from before mating through Day 14 of pregnancy. Double immunostaining indicated that uterine NK cells began to contain the pore-forming protein, perforin, on Day 6 of pregnancy in mesometrial decidua. Perforin is a probable mediator of cellular cytotoxicity found in lymphokine-activated NK and cytotoxic T lymphocytes. Activation of NK cells to produce perforin continued in mesometrial decidua on Days 8 and 10 of pregnancy and in the peripheral portion of metrial glands (MGs) on Days 12 and 14 of pregnancy, where cells at 3 stages of activation were simultaneously present: small cells with bright surface membrane staining of LGL-1 but no perforin (nonactivated), larger cells with intermediate staining of both markers (partially activated), and large cells with bright staining of perforin but no LGL-1 (fully activated). These observations indicate that activation of uterine NK cells involves loss of membrane LGL-1 as perforin accumulates in the cytoplasm, that the zone of activation shifts from mesometrial decidua to the MG on about Day 11 of pregnancy, and that nonactivated NK cells probably enter activation zones continuously during this period. Resting NK cells may enter activation zones by proliferation and/or migration from other regions of the uterus, rather than from blood, because depletion of circulating NK cells during pregnancy by treatment with NK-1.1 or asialo GM1 antibodies had no effect or only a small effect on the numbers of LGL-1-or perforin-positive cells seen in the uterus later in pregnancy. Uterine NK cells are probably not activated by interleukin-2 (IL-2) since few T lymphocytes were present in the uterus, nor were interferons detected in the uterus at this time. NK cells outside the mesometrial decidua on Day 6 and between implantation sites on Day 8 did not contain perforin, indicating that activation involves local factors produced at implantation sites. Since perforin has previously been shown to be present in mouse granulated metrial gland (GMG) cells, our observations indicate that GMG cells originate by local activation of uterine NK cells and that GMG cells can be identified as activated NK cells.