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.(ABSTRACT TRUNCATED AT 250 WORDS)