PIBF positive uterine NK cells in the mouse decidua

•Mouse decidual DBA+ NK cells contain PIBF in their cytoplasmic granules.•RU486-treatment of pregnant mice reduces the number of PIBF+ decidual NK cells.•RU486 treatment of pregnant mice increases the ratio of perforin positive cells within the PIBF+ decidual NK cell population.

Though uterine NK cells (u NK cells) contain cytotoxic granules, and selectively over- express the genes of perforin and granzymes, during normal pregnancy, they are not cytotoxic.Progesterone is indispensable for the establishment and maintenance of pregnancy both in humans and in mice. Mouse uterine NK cells do not express the classical progesterone receptor, yet progesterone affects the recruitment and function of uterine NK cells, the latter partly via the Progesterone-Induced Blocking Factor (PIBF). We demonstrated PIBF positive granulated cells in the mouse decidua. The aim of this study was to characterize these cells by lectin immunohistochemistry and anti-perforin reactivity.PIBF+ granulated cells were absent from the deciduae of alymphoid mice, but appeared in the decidua of those that had been reconstituted with bone marrow from male BALB/c mice. PIBF+ granulated cells bound the DBA lectin, suggesting their NK cell nature, and also contained perforin, which co-localized with PIBF in the cytoplasmic granules. In anti-progesterone treated mice all of the PIBF+ cells were perforin positive at g. d. 12.5, in contrast to the 54% perforin positivity of PIBF+ cells in untreated mice.ConclusionThe PIBF+ granulated cells in the decidua belong to the NK population, and PIPB co-localizes with perforin in the cytoplasmic granules.