Marianne J. van den Heuvel

Uterine natural killer cells: a specialized differentiation regulated by ovarian hormones

Summary:  In adult females of many species, a transient population of natural killer (NK) cells appears in cycles within the uterine endometrium (lining). Appearance of these lymphocytes coincides with specific phases of the ovarian hormone cycle and/or early pregnancy. Studies in rodents, women, and pigs dominate the literature and suggest the uterine (u)NK cells are an activated subset sharing many but not all features with circulating or lymphoid organ‐residing NK cells. During successful murine pregnancy, uNK cells appear to regulate initiation of structural changes in the feed arterial systems that support maternal endometrial tissue at sites of implantation and subsequent placental development. These changes, which reverse after pregnancy, create a higher volume arterial bed with flaccid vessels unresponsive to vasoactive compounds. These unique pregnancy‐associated arterial changes elevate the volume of low‐pressure, nutrient‐rich, maternal arterial blood available to conceptuses. Regulation of the differentiation, activation, and functions of uNK cells is only partially known, and there is lively debate regarding whether and how uNK cells participate in infertility or spontaneous abortion. This review highlights the biology of uNK cells during successful pregnancy.

Update on pathways regulating the activation of uterine Natural Killer cells, their interactions with decidual spiral arteries and homing of their precursors to the uterus

Virgin adult C57Bl/6J mouse uterus contains a population of small, non-granulated Natural Killer (NK) cells with balanced expression of NK cell activating and inhibiting LY49 receptors. Coincident with blastocyst implantation and decidualization, uterine (u)NK cells become activated. The surface glycoslyation of uNK changes, the cells proliferate and they induce production of interferon (IFN)gamma, perforin, serine esterases and other molecules, including angiogenic factors. Mouse strains genetically ablated in uNK cells fail to undergo modification of spiral artery segments that branch from the uterine artery and feed into the placenta and these mice do not sustain a robust decidualization response. IFN-gamma is thought, from bone marrow transplantation and therapeutic studies, to be the key uNK-cell derived mediator regulating gene expression in vascular and decidual tissues. Here, we review recent studies showing that IL-15 is the critical cytokine controlling uNK cell differentiation and that uNK cells are activated by either IL-12 or IL-18 and by other factors when both IL-12 and IL-18 are genetically absent from implantation sites. We address possible roles of the IFN-gamma regulated gene alpha2-macroglobulin (alpha2-M) in regulation of the position of fetal trophoblast within the walls of the spiral arteries, and we discuss approaches that have been successful in evaluating mechanisms involved in homing of mouse uNK cell precursors to the uterus. These approaches maybe applicable to studies in women. Our studies show that complex immuno-physiological events contribute to spiral artery modification by mid-gestation in mice.

Decline in Number of Elevated Blood CD3+ CD56+ NKT Cells in Response to Intravenous Immunoglobulin Treatment Correlates with Successful Pregnancy

Patients with elevated blood natural killer (NK) cells may be offered intravenous immunoglobulin (IVIG) treatment, but there is controversy about the utility of blood NK cell testing. Human CD56+ NK cells include several subpopulations that include the putatively cytotoxic CD56+ CD16+ subset. In mouse models of pregnant failure, NKT cells appear to be important. However, a mouse model may only be pertinent to a subset of patients, as recurrent pregnancy failure is a heterogenous group.

A Review of Trafficking and Activation of Uterine Natural Killer Cells

Enrichment of uterine natural killer (uNK) cells occurs during pregnancy in many species. However, functions of uNK cells and regulation of their uterine homing are not fully defined. In mice and women, uNK cells contribute to angiogenesis, a role reviewed here and now addressed in a mammal with an alternative placental type.

Trafficking of Circulating Pro-NK Cells to the Decidualizing Uterus: Regulatory Mechanisms in the Mouse and Human

Natural Killer (NK) lymphocytes, strongly expressing CD56, become abundant in the human uterus three to five days after the mid-menstrual cycle surge in pituitary-derived luteinizing hormone (LH). The primary functions of LH are to initiate final oocyte maturation/ovulation and to contribute to decidualization of the uterine stroma. Decidualization is the transformation of estrogen-primed uterine stromal fibroblasts into large hormone-producing cells under the influence of progesterone (P4). Decidual CD56bright (dNK) cells are a distinct, transient, tissue-specific NK cell subset that undergoes proliferation, terminal differentiation, and then death prior to menses. If pregnancy occurs, dNK cells increase during first trimester, then decline and are virtually absent in late pregnancy. In mouse models, pregnancy-associated uterine NK (uNK) cells appear coincident with onset of decidualization during embryonic implantation. Murine uNK cells traffic from the circulation to the anti-mesometrial side of the uterus and migrate to the mesometrial side of each implantation site. Here they proliferate and are implicated in regulation of mid-gestation structural changes to major arteries supplying the placenta, before dying in late gestation. Emerging data indicate that interactions between lymphocytes and endothelial cells within the uterine microenvironment are mediated by classical molecules associated with lymphocyte trafficking in immune surveillance and in response to inflammation. Here, we review factors influencing NK cell trafficking to decidualizing murine and human uteri and the differentiation and functions of these cells within the uterus.

NKT cell costimulation: experimental progress and therapeutic promise

Invariant natural killer T (iNKT) cells are innate lymphocytes with unique specificity for glycolipid antigens and remarkable immunomodulatory properties. The role of costimulatory interactions in iNKT cell responses has recently come under scrutiny. Although iNKT cells and their prototype glycolipid agonist α-galactosylceramide (α-GalCer) have shown promise in several clinical trials conducted in patients with cancer or viral diseases, current iNKT cell-based therapies are far from effective. The concomitant targeting of T cell receptors (TCRs) and costimulatory molecules on iNKT cells represents an exciting new opportunity to optimize such therapeutic approaches. Here, we review recent advances in our understanding of iNKT cell costimulation and discuss potential treatment modalities based on the responsiveness of iNKT cells to disease-tailored glycolipids and select costimulatory ligands.

An analysis of the uterine lymphocyte-derived hybridoma cell line GWM 1-2 for expression of receptors for estrogen, progesterone and interleukin 2

Characterisation of murine hybridoma cell lines derived from the fusion of lymphocytes migrating from explant cultures of early, pregnancy-associated metrial glands (days 6-8 of gestation) to SP 2/0 cells, has been extended (van den Heuvel et al., J. Reprod. Immunol., 27 (1994) 13-36). These hybridomas have been grown in culture for over 2 years and are thought to represent the only immortalized lines of murine pregnancy-associated, uterine natural killer (uNK) cells. Previous studies had shown that these hybridomas, known as GWM cells, lack uNK cell surface markers, but share with uNK cells the expression of the lytic protein perforin and the ability to lyse YAC cells, a natural killer cell target (van den Heuvel et al., J. Reprod. Immunol., 27 (1994) 13-36). We report here, the evaluation of the transcription and expression of genes encoding the estrogen receptor (ER), the progesterone receptor (PR) and the interleukin 2 receptor complex (IL 2R alpha, beta and gamma) by uNK cells at day 8 of gestation and by GWM 1-2 cells and SP 2/0 cells. Our investigations indicate that expression of these genes divides day 8 uNK cells into subsets, with the predominant population being ER+, PR-, IL 2R alpha +, IL 2R beta + and IL 2R gamma +. Like day 8 uNK cells, most GWM 1-2 cells expressed all three chains of the IL 2R complex. In addition, GWM 1-2 cells expressed the ER but the PR was not detected on this cell line. Only the IL 2R alpha was detected on the SP 2/0 myeloma cell line. These studies further validate the use of GWM hybridomas as models for pregnancy-associated uNK cells.

Characterization of the cells that migrate from metrial glands of the pregnant mouse uterus during explant culture

Granulated metrial gland (GMG) cells are estrogen-receptor and Interleukin 2 (IL-2) receptor positive lymphocytes of the Natural Killer cell lineage found in the murine uterus during pregnancy. Functional studies of these cells, which are now more frequently called uterine NK (uNK) cells, have been limited due to technical difficulties. The cells are difficult to isolate and their proliferation and differentiation have not been achieved in culture. In 1988, Mukhtar and Stewart (Cell Tiss. Res., 253, 413-417) reported a method for explant culture of metrial glands isolated from pregnant rodents that yielded an almost pure population of uNK cells. This major technical advance has supported most of the subsequent functional and molecular studies of rodent uNK cells. However, the quality of the cells isolated by the explant culture procedure has not been established. A cytochemical approach was used to identify and quantify the cells migrating from metrial glands. At midpregnancy, almost all (> 90%) migrating nucleated cells were NK cells. Earlier in gestation, a significant proportion (25%) of cells having lymphoid morphology could not be assigned to the lineage. The viability of cells migrating from explants was assessed by DNA isolation and electrophoresis on days 6-16 of gestation. At all times evidence for apoptosis was found, even after culture intervals as brief as 4 h. Parallel analyses of histological sections of the metrial gland, using terminal deoxytransferase labelling to detect nuclear fragmentation, did not support significant levels of uNK cell death in situ prior to day 12 of gestation. Supplementation of the explant culture medium with estrogen, IL-2, various extracellular matrices, decidual cells or combinations of these did not lead to in vitro proliferation of uNK cells and usually did not extend the short term viability of these cells in serum supplemented or serum free media. Thus, the optimal culture conditions for uNK cells remain undefined.

Expression of chemokine decoy receptors and their ligands at the porcine maternal-fetal interface

Successful pregnancy requires coordinated maternal–fetal cross‐talk to establish vascular connections that support conceptus growth. In pigs, two waves of spontaneous fetal loss occur and 30–40% of conceptuses are lost before parturition. Previous studies associated these losses with decreased angiogenic and increased inflammatory cytokines. Chemokines, a sub‐category of cytokines, and decoy receptors control leukocyte trafficking, angiogenesis and development. The availability of chemokines is regulated by three non‐signalling decoy receptors: chemokine decoy receptor (D6), Duffy antigen receptor for chemokines (DARC) and Chemocentryx decoy receptor (CCX CKR). We hypothesized that the expression of these receptors and their chemokine ligands regulate the porcine pregnancy success or failure. Here, we describe for the first time the transcription and translation of all three decoy receptors and several chemokine ligands in endometrium and trophoblast associated with healthy and arresting conceptuses at gestation day (gd) 20 and gd50. Among decoy receptors, transcripts for DARC were significantly reduced in endometrium, whereas that for CCX CKR were significantly increased in endometrium and trophoblast at gd50 arresting compared with healthy sites. However, western blot analysis revealed no differences in decoy receptor expression between healthy and arresting tissues. Transcripts for decoy receptor ligands CCL2, CCL3, CCL4, CCL5, CCL11, CCL19, CCL21, CXCL2 and CXCL8 were stable between healthy and arresting littermates. Quantification by SearchLight chemiluminescent protein array confirmed ligand expression at the protein level. These data indicate that decoy receptors and ligands are expressed at the porcine maternal–fetal interface and dysregulation of decoy receptor (DARC and CCX CKR) transcripts occurs at sites of fetal arrest.

Expression of angiogenic basic fibroblast growth factor, platelet derived growth factor, thrombospondin-1 and their receptors at the porcine maternal-fetal interface

BackgroundCommercial swine breeds in North America undergo two waves of spontaneous fetal loss; one during peri-attachment and another during mid-gestation. Although an exact mechanism for this loss is not known, deficits in vasculature at the attachment sites appear to be a major cause. We hypothesized that a balance between pro-angiogenic and anti-angiogenic factors is needed at the maternal-fetal interface for successful conceptus development. Six selected members of the pro-angiogenic fibroblast growth factor (FGF) and platelet derived growth factor (PDGF) families and anti-angiogenic factor thrombospondin-1 (TSP-1) and its receptor CD36 were quantified and localized at the porcine maternal-fetal interface at early and midgestation time points.MethodsMesometrial endometrium was collected from non-pregnant gilts (n = 8). Endometrial and chorioallantoic membrane samples were collected from healthy and arresting conceptus attachment sites at gestation day (gd) 20 (n = 8) and gd 50 (n = 8). At gd20 arresting conceptus attachment sites were distinguished by decreased vasculature of the placental membranes and decreased conceptus size. At gd50 arresting conceptuses attachment sites were identified by smaller conceptus length and weight measurements. Quantitative real time PCR was used to determine relative transcript levels of genes of interest, and cellular localization was determined by immunohistochemistry in paraffin embedded endometrial sections.ResultsAt gd20, endometrial samples from arresting conceptuses had elevated transcripts for bFGF, and PDGF-bb than healthy sites (p < 0.05). At gd50, bFGF, FGFR2, and CD36 were more abundant at arresting than at healthy conceptus attachment sites (p < 0.05). Chorioallantoic membrane from arresting conceptus attachment sites at gd20 had elevated transcripts for bFGF, FGFR1, FGFR2 and CD36 compared with healthy sites (p < 0.05). FGFR2 transcripts were more abundant in chorioallantoic membrane from arresting conceptuses at gd 50 (p < 0.05). Immunohistochemical localization of selected pro- and anti-angiogenic factors and receptors revealed their abundance in the luminal epithelium, uterine glands and perivascular areas of endometrium at gd20 and gd50.ConclusionsWe provide comprehensive analysis of pro and anti-angiogenic factors at the porcine maternal fetal interface during early and mid-pregnancy. At mRNA levels, the majority of pro-angiogenic factors investigated were elevated at the sites of fetal arrest. These observations contrast with our previous findings of decreased Vascular Endothelial Growth Factor (VEGF) family members at arresting sites, and suggest that the bFGF family functions as a compensatory survival mechanism when major angiogenic proteins are decreasing at the sites of fetal arrest.