Tissue-resident natural killer cells derived from conventional natural killer cells are regulated by progesterone in the uterus.

The murine uterus contains three subsets of innate lymphoid cells (ILCs). Innate lymphoid cell type 1 (ILC1) and conventional natural killer (cNK) cells seed the uterus before puberty. Tissue-resident NK (trNK) cells emerge at puberty and vary in number during the estrous cycle. Here, we addressed the origin of uterine trNK cells and the influence of ovarian hormones on their local activation and differentiation in vivo. We used parabiosed mice in combination with intravascular fluorescent antibody labeling and flow cytometry to distinguish tissue-resident from circulating immune cells. Additionally, we used C57BL/6J ovariectomized (OVX) and non-OVX mice supplemented with ovarian hormones to assess their effects on uterine trNK cell function. Strikingly, mice OVX at three weeks of age and analyzed as adults lacked uterine trNK cells unless progesterone was administered. Our parabiosis studies confirmed that the progesterone-responsive trNK cells are derived from peripheral cNK cells. Moreover, medroxyprogesterone 17-acetate-induced expansion of cNK-derived trNK cells was abolished by a progesterone receptor antagonist. These data reveal a novel, uterine-specific differentiation pathway of trNK cells that is tightly regulated by progesterone.