uNK Cell Function Research Articles

High concentration of estrogen resulted by COH may affect the secretion of pro-angiogenic factors in uNK cells by downregulating the expression of IL-11 in decidual stromal cells.

High serum estrogen concentrations after controlled ovarian hyperstimulation (COH) and fresh embryo transfers are associated with the increased risk of pregnancy complications resulting from aberrant placentation. Uterine natural killer (uNK) cells are important for establishment of pregnancy and normal placentation. It has been found that the proliferation and function of uNK cells are compromised by COH. However, the underlying role of high concentration of estrogen following COH in the abnormalities of uNK cells is poorly understood. Expression of cytokines and immunophenotype study of uNK was performed by flow cytometry analysis. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to quantify RNA expression; Western blot was performed to quantify protein levels. The secretion level of pro-angiogenic factors in uNK cells is significantly reduced by co-culture with decidual stromal cells (DSCs) induced by high estrogen. It was discovered that COH and supraphysiologic levels of estrogen downregulated IL-11 in decidual tissue of mice. Additionally, we found that the downregulation of IL-11 is a major factor contributing to the downregulation of VEGF and PLGF in uNK cells. Moreover, we found that uNK cells may acquire IL-11Rα sequentially during differentiation and that only a portion of uNK cells are IL-11Rα positive. Lastly, we discovered that IL-11 may regulate VEGF and PLGF secretion in uNK cells via the ERK signaling pathway. These results suggested the downregulation of IL-11 expression in DSCs caused by high estrogen levels affects the secretion of pro-angiogenic factors in uNK cells, which provided an explanation for the pregnancy complications caused by COH.

A New Look at Immunogenetics of Pregnancy: Maternal Major Histocompatibility Complex Class I Educates Uterine Natural Killer Cells.

Our incomplete knowledge of maternal-fetal interface (MFI) physiology impedes a better understanding of the pathological mechanisms leading to pregnancy complications, such as pre-eclampsia and fetal growth restriction. At the MFI, uterine natural killer (uNK) cells do not attack fetal cells but engage in crosstalk with both fetal and maternal cells to support feto-placental development. However, mother and fetus are genetically half-mismatched and certain combinations of variable immune genes-human leukocyte antigens (HLAs) and killer-cell immunoglobulin-like receptor (KIR), indeed, the most variable gene sets in the genome-associate with pregnancy outcomes, suggesting that these interactions regulate uNK cell function. How do these interactions influence the physiology and pathology at the MFI? Uterine NK cell function is regulated by both maternal and fetal Major Histocompatibility Complex (MHC); however, evidence for fetal cells educating uNK cells is lacking, and new evidence shows that maternal rather than fetal MHC class I molecules educate uNK cells. Furthermore, uNK cell education works through self-recognition by the ancient and conserved NKG2A receptor. Pregnant mice lacking this receptor produce normal litter sizes, but a significant portion of the offspring have low birthweight and abnormal brain development. Evidence from a genome-wide association study of over 150,000 human pregnancies validates the finding because women whose NKG2A receptor is genetically determined to engage their own MHC class I molecules are exposed to lower risk of developing pre-eclampsia, suggesting that maternal uNK cell education is a pre-requisite for a healthy pregnancy and, likely, for healthy offspring too.

P-447 Dynamic changes in uterine natural killer cell (uNK) function across menstrual phases: Implications for implantation

Abstract Study question Does the function of uNK cells change from the proliferative stage of the menstrual cycle to the secretory phase in readiness for implantation? Summary answer During the secretory phase, uNK cells demonstrate an enhanced ability to produce cytokines indicating their importance for implantation. What is known already The abundance of uNK cells during implantation, and their secretion of trophoblast chemoattractant factors, suggests their pivotal role in placentation. uNK cells express Killer Immunoglobulin-like Receptors (KIR), which interact with Human Leukocyte Antigen-C (HLA-C) on trophoblasts, inducing cytokine production that aids trophoblast migration. It has recently been discovered that uNK cells consist of three distinct subsets, with different propensities to produce cytokines. However, the cytokine production abilities of each subset, and how this changes over the menstrual cycle, remains unexplored. Study design, size, duration A prospective cross-sectional study was conducted to compare uNK cell function between the proliferative and secretory phases of the menstrual cycle. The proliferative phase was defined as before day 14 of the menstrual cycle, and the secretory phase after this, in those with a regular 28-32 day menstrual cycle. The current data analysed is from 6 proliferative phase samples and 10 secretory phase samples however recruitment is ongoing. Participants/materials, setting, methods Endometrial samples were collected with a Pipelle biopsy from healthy fertile women attending the sexual health clinic for contraception. In the laboratory, endometrial lymphocytes were isolated and cultured with Anti-CD107a PerCP-eFlour710 (100ul/ml), Brefeldin (3ug/ml) and Monensin (2uM/ml). Cells were then stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin (2ul/ml) and incubated for 4 hours at 37 °C. Flow cytometry was employed to analyse the samples after staining with viability dye, cell surface antibodies, and intracellular markers. Main results and the role of chance In initial experiments, degranulation declined during the proliferative phase in both uNK2 and uNK3 compared to the other two phases of the menstrual cycle. There was a significant increase in the production of TNFa by uNK1 and IL-8 by uNK3 in the secretory phase compared to the proliferative phase. There were also increases in IFNg and GM-CSF production across all subsets although this did not reach significance (Statistical testing was done using Kruskal Wallis with a post-hoc Dunn test, p < 0.05). Current work explores the production of more recently identified trophoblast chemoattractants, including XCL1 and CSF1, which we would expect to increase in a similar manner. Limitations, reasons for caution Limitations include the cross-sectional nature of the study, limiting the ability to establish causation. However another study, tracking pregnancy outcomes in those with recurrent implantation failure aims to address this. Additionally, variations within menstrual phases may exist. The sample size is also a limitation which I am working to expand. Wider implications of the findings A comprehensive understanding of uNK throughout various menstrual phases holds profound implications for reproductive health. The heightened cytokine production observed during the secretory phase indicates their pivotal role in the process of implantation. This finding not only underscores their significance but also serves as a catalyst for further research. Trial registration number not applicable

Ovarian Stimulation in Mice Resulted in Abnormal Placentation through Its Effects on Proliferation and Cytokine Production of Uterine NK Cells.

Ovarian stimulation is associated with an increased incidence of abnormal placentation. Uterine natural killer (uNK) cells are the major subpopulation of decidual immune cells, which are crucial for placentation. In a previous study, we found that ovarian stimulation impairs uNK cell density on gestation day (GD) 8.5 in mice. However, it was not clear how ovarian stimulation led to a reduction in the density of uNK cells. In this study, we constructed two mouse models, an in vitro mouse embryo transfer model and an estrogen-stimulated mouse model. We used HE and PAS glycogen staining, immunohistochemical techniques, q-PCR, Western blot, and flow cytometry to analyze the mouse decidua and placenta, and the results showed that SO resulted in a fetal weight reduction, abnormal placental morphology, decreased placental vascular density, and abnormal density and function of uNK cells. Our results suggest that ovarian stimulation resulted in aberrant estrogen signaling and may contribute to the disorder of uNK cells caused by ovarian stimulation. Together, these results provide new insights into the mechanisms of aberrant maternal endocrine environments and abnormal placentation.

Uterine NK cell functions at maternal-fetal interface†.

During pregnancy, maternal decidual tissue interacts with fetal trophoblasts. They constitute the maternal-fetal interface responsible for supplying nutrition to the fetus. Uterine natural killer (uNK) cells are the most abundant immune cells at the maternal-fetal interface during early pregnancy and play critical roles throughout pregnancy. This review provides current knowledge about the functions of uNK cells. uNK cells have been shown to facilitate remodeling of the spiral artery, control the invasion of extravillous trophoblast (EVT) cells, contribute to the induction and maintenance of immune tolerance, protect against pathogen infection, and promote fetal development. Pregnancy-trained memory of uNK cells improves subsequent pregnancy outcomes. In addition, this review describes the distinct functions of three uNK cell subsets: CD27-CD11b-, CD27+, and CD27-CD11b+ uNK cells.

Uterine natural killer cells and recurrent spontaneous abortion.

Recurrent spontaneous abortion (RSA), termed as two or more consecutive pregnancy loss is a great problem for some women of childbearing age. A large number of evidence confirm that there may be an immune background of RSA. As a member of the innate immune system, uterine natural killer (uNK) cells account for about 70% of total lymphocytes during pregnancy and play a critical role in the establishment and maintenance of pregnancy. This review mainly introduces the phenotype, origin, receptor, and function of uNK cells to illuminate its relationship with RSA.

Interleukin‐15 Regulates Decidual Osteopontin Expression in Rats

Introduction Placenta accreta (PA) is a potentially life-threatening pregnancy complication in which the placenta invades too deeply into the uterus. The underlying causes of PA remain unknown, but abnormal function of uterine natural killer (uNK) cells may be involved. uNK cells are the most prevalent immune cells within the uterus during early pregnancy. They secrete cytokines and growth factors that are thought to control the depth of placental invasion, yet the function of uNK cells remains poorly characterized. We recently generated rats devoid of uNK cells using targeted genomic editing of the Interleukin-15 (IL15) locus. Il15 encodes a cytokine needed for uNK cell survival. During pregnancy, Il15-deficient dams do not have uNK cells, and they exhibit an over invasive placenta. We therefore hypothesize that uNK cells produce factors during early pregnancy that control the depth of placental invasion. Objective: The goal of this study isto profile gene expression differences in the decidua between wild-type (WT) and IL15-deficient (IL15Δ/Δ) rats during early pregnancy, in order to deduce which genes are expressed by rat uNK cells. Methods: Pregnant IL-15Δ/Δ and WT Sprague-Dawley Holtzman rats (n=3 dams/group) were sacrificed on gestational day (GD) 9.5, conceptuses dissected, mRNA isolated, and global transcriptional changes assessed using Clariom S gene expression array (n=3 conceptuses/dam). Expression of select transcripts was determined in a separate cohort of conceptuses (n=13) using quantitative RT-PCR. To determine localization of perforin (PRF) and osteopontin (OPN), GD 7.5, 9.5, and 11.5 conceptuses were sectioned, and immunohistochemistry (IHC) was performed. Data was analyzed using Student's t-test or Analysis of Variance and P≤0.05 was considered statistically significant, unless indicated otherwise. Results: On GD 9.5, 230 genes were differentially expressed between WT and IL-15Δ/Δ rats (P≤0.01). Gene ontology analysis revealed pathways associated with immune responses, cell migration, and cell adhesion to be significantly altered in IL-15Δ/Δ conceptuses. Notably, we detected a pronounced decrease in Prf, a uNK cell marker (p≤0.0001), and Spp1 (p=0.0031), which encodes OPN. IHC staining of GD 9.5 conceptuses showed intracellular OPN staining in the uterine glands, decidua, and primitive placenta of WT, but not IL-15Δ/Δ rats. OPN and PRF staining was co-localized, suggesting that OPN is produced by uNK cells. Conclusion: IL-15Δ/Δ rats exhibited impaired immune responses and cellular adhesion and migration pathways in the decidua during early pregnancy. OPN expression was significantly decreased in IL-15Δ/Δ rats at mRNA and protein levels. We believe that reduced OPN in the decidua of IL-15Δ/Δ rats may contribute to the increased placental invasion that is apparent in these rats. Significance: This study provides new insights into factors produced by uNK cells that may contribute to the regulation of placental invasion during pregnancy. We are currently determining whether OPN is directly involved in controlling the extent of placental cell adhesion and invasion. Our research will lead to a better understanding of the early events controlling decidualization and placentation, and may provide insight into the mechanisms of serious placental diseases like PA.

NK cells ride the uterine cycle

Natural Killer Cells Tissue-resident natural killer (NK) cells in the uterus promote successful pregnancies by regulating the depth of placental trophoblast invasion. Endometrial tissue is naturally subject to constant remodeling in response to hormonal fluctuations during the menstrual cycle, but how the changing uterine microenvironment influences the heterogeneity of uterine NK (uNK) cells is poorly understood. Strunz et al. used proteomic and transcriptomic techniques to profile human uNK cells recovered from different stages of the menstrual cycle and during pregnancy. This analysis identified sequentially expressed uNK cell surface markers that define a recurring cycle of differentiation in response to progesterone-regulated release of stromal interleukin-15. These findings pave the way for further studies on how uNK cell functions are modulated by the dynamic endometrial microenvironment. Sci. Immunol. 6 , eabb7800 (2021).

Uterine natural killer cells: from foe to friend in reproduction.

Recurrent miscarriage and pre-eclampsia are common reproductive disorders, but their causes are often unknown. Recent evidence has provided new insight into immune system influences in reproductive disorders. A subset of lymphocytes of the innate immune system known as uterine natural killer (uNK) cells are now recognized as fundamental to achieving embryo implantation and successful pregnancy, but were initially attributed a bad reputation. Indeed, immune therapies have been developed to treat the 'exaggerated' immune response from uNK cells. These treatments have been based on studies of peripheral blood natural killer (pbNK) cells. However, uNK cells and pbNK cells have different phenotypic and functional characteristics. The functions of uNK cells are closely related to their interactions with the extravillous trophoblast cells (EVTs) and spiral arteries, which underlie an essential role in regulating vascular function, controlling trophoblast invasion and promoting placental development. EVTs express MHC molecules of class I HLA-C/E/G/F, while uNK cells express, among other receptors, killer cell immunoglobulin-like receptors (KIRs) that bind to HLA-C or CD94/NKG2A inhibitory receptors, and then bind HLA-E. Associations of certain KIR/HLA-C combinations with recurrent miscarriage, pre-eclampsia, and foetal growth restriction and the interactions between uNK cells, trophoblasts and vascular cells have led to the hypothesis that uNK cells may play a role in embryo implantation. Our objective was to review the evolution of our understanding of uNK cells, their functions, and their increasingly relevant role in reproduction. Relevant literature through June 2020 was retrieved using Google Scholar and PubMed. Search terms comprised uNK cells, human pregnancy, reproductive failure, maternal KIR and HLA-C, HLA-E/G/F in EVT cells, angiogenic cytokines, CD56+ NK cells, spiral artery, oestrogen and progesterone receptors, KIR haplotype and paternal HLA-C2. This review provides key insights into the evolving conceptualization of uNK cells, from their not-so-promising beginnings to now, when they are considered allies in reproduction. We synthesized current knowledge about uNK cells, their involvement in reproduction and their main functions in placental vascular remodeling and trophoblast invasion. One of the issues that this review presents is the enormous complexity involved in studying the immune system in reproduction. The complexity in the immunology of the maternal-foetal interface lies in the great variety of participating molecules, the processes and interactions that occur at different levels (molecular, cellular, tissue, etc.) and the great diversity of genetic combinations that are translated into different types of responses. Insights into uNK cells could offer an important breakthrough for ART outcomes, since each patient could be assessed based on the combination of HLA and its receptors in their uNK cells, evaluating the critical interactions at the materno-foetal interface. However, owing to the technical challenges in studying uNK cells in vivo, there is still much knowledge to gain, particularly regarding their exact origin and functions. New studies using novel molecular and genetic approaches can facilitate the identification of mechanisms by which uNK cells interact with other cells at the materno-foetal interface, perhaps translating this knowledge into clinical applicability.

UL16-Binding Protein 1 Induced HTR-8/SVneo Autophagy via NF-κB Suppression Mediated by TNF-α Secreted through uNK Cells.

UL16-binding protein 1(ULBP1) has been reported to inhibit trophoblast invasion through the modification of secretion functions of uNK cells in the previous study, but its mechanisms remain unclear. In this study, we investigated the related mechanism by which upregulated ULBP1 expression impaired trophoblast invasion. We found that conditioned media with ULBP1 increased autophagy in HTR-8/SVneo, and anti-TNF-α-neutralizing antibody rescued the autophagy caused by the conditioned medium. We further found TNF-α induced autophagy in trophoblast cells in a dose-dependent way and accompanied by a decreased activity of nuclear factor-kappa B (NF-κB). Inhibition of NF-κB activation by chemical inhibitor augmented these autophagic responses to TNF-α in the cells. In addition, interruption NF-κB caused a significant decrease in HTR-8/SVneo invasion and enhanced the inhibition effect of TNF-α on HTR-8/SVneo invasion. Taken together, these findings suggest that TNF-α is able to regulate autophagic activity via suppressing NF-κB, which might be the mechanism related to ULBP1 in preeclampsia pathogenesis.

Profiling the expression and function of oestrogen receptor isoform ER46 in human endometrial tissues and uterine natural killer cells.

STUDY QUESTIONDoes the oestrogen receptor isoform, ER46, contribute to regulation of endometrial function?SUMMARY ANSWERER46 is expressed in endometrial tissues, is the predominant ER isoform in first trimester decidua and is localised to the cell membrane of uterine natural killer (uNK) cells where activation of ER46 increases cell motility.WHAT IS KNOWN ALREADYOestrogens acting via their cognate receptors are essential regulators of endometrial function and play key roles in establishment of pregnancy. ER46 is a 46-kDa truncated isoform of full length ERα (ER66, encoded by ESR1) that contains both ligand- and DNA-binding domains. Expression of ER46 in the human endometrium has not been investigated previously. ER46 is located at the cell membrane of peripheral blood leukocytes and mediates rapid responses to oestrogens. uNK cells are a phenotypically distinct (CD56brightCD16−) population of tissue-resident immune cells that regulate vascular remodelling within the endometrium and decidua. We have shown that oestrogens stimulate rapid increases in uNK cell motility. Previous characterisation of uNK cells suggests they are ER66-negative, but expression of ER46 has not been characterised. We hypothesise that uNK cells express ER46 and that rapid responses to oestrogens are mediated via this receptor.STUDY DESIGN, SIZE, DURATIONThis laboratory-based study used primary human endometrial (n = 24) and decidual tissue biopsies (n = 30) as well as uNK cells which were freshly isolated from first trimester human decidua (n = 18).PARTICIPANTS/MATERIALS, SETTING, METHODSPrimary human endometrial and first trimester decidual tissue biopsies were collected using methods approved by the local institutional ethics committee (LREC/05/51104/12 and LREC/10/51402/59). The expression of ERs (ER66, ER46 and ERβ) was assessed by quantitative PCR, western blot and immunohistochemistry. uNK cells were isolated from first-trimester human decidua by magnetic bead sorting. Cell motility of uNK cells was measured by live cell imaging: cells were treated with 17β-oestradiol conjugated to bovine serum albumin (E2-BSA, 10 nM equivalent), the ERβ-selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; 10 nM) or dimethylsulphoxide vehicle control.MAIN RESULTS AND THE ROLE OF CHANCEER46 was detected in proliferative and secretory phase tissues by western blot and was the predominant ER isoform in first-trimester decidua samples. Immunohistochemistry revealed that ER46 was co-localised with ER66 in cell nuclei during the proliferative phase but detected in both the cytoplasm and cell membrane of stromal cells in the secretory phase and in decidua. Triple immunofluorescence staining of decidua tissues identified expression of ER46 in the cell membrane of CD56-positive uNK cells which were otherwise ER66-negative. Profiling of isolated uNK cells confirmed expression of ER46 by quantitative PCR and western blot and localised ER46 protein to the cell membrane by immunocytochemistry. Functional analysis of isolated uNK cells using live cell imaging demonstrated that activation of ER46 with E2-BSA significantly increased uNK cell motility.LARGE SCALE DATAN/A.LIMITATIONS, REASONS FOR CAUTIONExpression pattern in endometrial tissue was only determined using samples from proliferative and secretory phases. Assessment of first trimester decidua samples was from a range of gestational ages, which may have precluded insights into gestation-specific changes in these tissues. Our results are based on in vitro responses of primary human cells and we cannot be certain that similar mechanisms occur in situ.WIDER IMPLICATIONS OF THE FINDINGSE2 is an essential regulator of reproductive competence. This study provides the first evidence for expression of ER46 in the human endometrium and decidua of early pregnancy. We describe a mechanism for regulating the function of human uNK cells via expression of ER46 and demonstrate that selective targeting with E2-BSA regulates uNK cell motility. These novel findings identify a role for ER46 in the human endometrium and provide unique insight into the importance of membrane-initiated signalling in modulating the impact of E2 on uNK cell function in women. Given the importance of uNK cells to regulating vascular remodelling in early pregnancy and the potential for selective targeting of ER46, this may be an attractive future therapeutic target in the treatment of reproductive disorders.STUDY FUNDING/COMPETING INTEREST(S)These studies were supported by Medical Research Council (MRC) Programme Grants G1100356/1 and MR/N024524/1 to PTKS. H.O.D.C. was supported by MRC grant G1002033. The authors declare no competing interests related to the published work.

Maternal exposure to CeO2NPs during early pregnancy impairs pregnancy by inducing placental abnormalities

Cerium dioxide nanoparticles (CeO2NPs) has been widely used in many fields, and also recommended as a promising carrier for cancer targeted drugs in human medicine for its excellent properties. However, its biological safety to human health remains controversial. In this study, we propose a mouse model exposed to CeO2NPs during early pregnancy, to clarify the effect of maternal CeO2NPs exposure and related molecular mechanism. Pregnant mice are injected intravenously with CeO2NPs by once a day on D5, D6, and D7. The effects of CeO2NPs exposure on pregnancy outcomes are observed on D8, D9, D10 and D12. The results show that CeO2NPs exposure during early pregnancy would lead to poor pregnancy outcomes. Further study find that low-quality decidualization, including the imbalance of trophoblast invasion regulators secreted by decidual cells and abnormal recruitment and differentiation of uNK cells, leads to subsequent biological negative “ripple effects”, including placental dysfunction, fetal loss or growth restriction. This study broadens the understanding of the biological safety of CeO2NPs, and provide clues for the prevention of its negative biological effects. Improving the function of uNK cells can be used as one of the therapeutic targets to prevent negative effects of CeO2NPs on pregnancy.

Innate immune cells in the placental bed in healthy pregnancy and preeclampsia

Immune cells in the placental bed are important for adequate development of the placental bed. The most prominent immune cells in the placental bed early in pregnancy are uterine natural killer cells (uNK) cells and macrophages. Also dendritic cells and mast cells can be found in the early placental bed. These cells not only have an immune regulatory function, but are also involved in the regulation of trophoblast invasion, angiogenesis and spiral artery remodeling. In preeclampsia, one of the major complications of pregnancy, decreased trophoblast invasion and spiral artery remodeling has been found. This is associated with decreased numbers of uNK cells, increased numbers of macrophages around the spiral arteries and similar or increased numbers of dendritic cells in the placental bed. In this review, we discuss the current insights in the functions of uNK cells, macrophages, dendritic cells and mast cells in the placental bed in humans during healthy pregnancy and during preeclampsia. As animal models are instrumental in understanding the role of immune cells in the placental bed, we also review studies on the function and phenotype of these innate immune cells in experimental preeclampsia. A better understanding of the dynamics and functional changes of these immune cells in the placental bed may eventually lead to new therapeutic targets for preeclampsia.

Angiogenic responses in the pregnant mouse uterus under uNK cell deletion and hypoxia

Inadequate uterine vascular remodeling is associated with pregnancy complication. Pregnancy specific uterine Natural Killer (uNK) cells produce angiogenic factors such as vascular endothelial growth factor (VEGF), nitric oxide (NO) and interferon- (IFNγ), but hypoxic effects of uNK cell functions are unknown. Here, we investigated the effects of hypoxia on murine uNK cell driven vascular remodeling and on pregnancy outcome. At gestational day (gd) 7.5, normal CD1 mice and genetically-modified IL-15-/- mice that lack uNK cells were exposed to 48 h of 420 Torr hypoxia. Pregnancies were then assessed at gestation day (gd) 9.5 for decidual gene and protein expression, histopathology or litter size at birth. Hypoxia delayed CD1 fetal development, but term deliveries occurred, with the exception in IL-15-/- uNK deficient mice. VEGF protein and gene expressions were down-regulated, but not abrogate in the uNK deficient mice, suggesting an alternative source of this angiogenic factor independent of uNK cell. High eNOS/iNOS expression seems to be uterine compensatory response in the uNK deficient mice and it is probably by increasing NO release to stimulate local angiogenesis. The reduced successful pregnancy outcome is not related to uNK cell cytotoxic activity. Otherwise, the high incidence of pregnancy failure of IL-15-/- animals confirmed the benefit of uNK cells in the homeostasis of pregnant uteri.

Uterine Natural Killer Cells: Functional Distinctions and Influence on Pregnancy in Humans and Mice.

Our understanding of development and function of natural killer (NK) cells has progressed significantly in recent years. However, exactly how uterine NK (uNK) cells develop and function is still unclear. To help investigators that are beginning to study tissue NK cells, we summarize in this review our current knowledge of the development and function of uNK cells, and what is yet to be elucidated. We compare and contrast the biology of human and mouse uNK cells in the broader context of the biology of innate lymphoid cells and with reference to peripheral NK cells. We also review how uNK cells may regulate trophoblast invasion and uterine spiral arterial remodeling in human and murine pregnancy.

Uterine NK cells and macrophages in pregnancy

The presence of immune cells in the placental bed is important for both mother and child. Although various immune cells can be found in the placental bed, such as regulatory T cells and dendritic cells, uterine NK cells and macrophages are the most prominent immune cells in the placental bed in early pregnancy. uNK cell and macrophage numbers in the placental bed decrease in the third trimester. These cells seem to be specifically adapted for their function and environment. uNK cells do not show cytotoxic activity, but are producers of cytokines, growth factors and many other factors. uNK cell function is regulated by inhibitory and activating receptors binding to HLA class I on trophoblast cells. uNK cells are also involved in regulating trophoblast invasion. Macrophages mainly show an M2-like phenotype and also produce cytokines and various other factors. They are important in phagocytosis of various cells and cell debris in the placental bed. Both cell types are also involved in angiogenesis and spiral artery remodeling in the placental bed. In this review we will elaborate on the most important functions of uNK cells and macrophages in the placental bed in humans. We will also discuss animal models, since they may provide clues for function of uNK cells and macrophages in humans.

Activation of Blood CD3+CD56+CD8+ T Cells during Pregnancy and Multiple Sclerosis

A striking common feature of most autoimmune diseases is their female predominance, with at least twice as common among women than men in relapsing–remitting multiple sclerosis (MS), the prevailing MS clinical form with onset at childbearing age. This fact, together with the protective effect on disease activity during pregnancy, when there are many biological changes including high levels of estrogens and progesterone, puts sex hormones under the spotlight. The role of natural killer (NK) and NKT cells in MS disease beginning and course is still to be elucidated. The uterine NK (uNK) cells are the most predominant immune population in early pregnancy, and the number and function of uNK cells infiltrating the endometrium are sex-hormones’ dependent. However, there is controversy on the role of estrogen or progesterone on circulating NK (CD56dim and CD56bright) and NKT cells’ subsets. Here, we show a significantly increased activation of CD3+CD56+CD8+ cells in pregnant MS women (MSP) compared with non-pregnant MS women (NPMS) (p < 0.001) and even with respect to healthy pregnant women (HP, p < 0.001), remaining increased even after delivery. The dynamics of expression of early activation marker CD69 on CD3+CD56+CD8+ cells showed a progressive statistically significant increase along the gestation trimesters (T) and at postpartum (PP) with respect to NPMS (1T: p = 0.018; 2T: p = 0.004; 3T: p < 0.001; PP: p = 0.001). In addition, early activation expression of CD69 on CD3+CD56+CD8+ cells was higher in MSP than HP in the first two trimesters of gestation (p = 0.004 and p = 0.015, respectively). NPMS showed significantly increased cytotoxic/regulatory NK ratio compared with healthy controls (p < 0.001). On the other hand, gender studies showed no differences between MS women and men in NK and CD3+CD56+CD8+ cells’ subsets. Our findings may add on the understanding of the regulatory axis in MS during pregnancy. Further studies on specific CD8+ NKT cells function and their role in pregnancy beneficial effects on MS are warranted to move forward more effective MS treatments.

Upregulated unique long 16 binding protein 1 detected in preeclamptic placenta affects human extravillous trophoblast cell line (HTR-8/SVneo) invasion by modulating the function of uterine natural killer cells.

Well-controlled trophoblast invasion at the maternal-fetal interface is crucial for normal placentation and successful pregnancy, otherwise pathological conditions of pregnancy occur, such as preeclampsia. In previous studies, it has been demonstrated that unique long 16 binding protein (ULBP)1, a ligand for the natural-killer group (NKG)2D receptor on uterine natural killer (uNK) cells, is upregulated in the placenta in patients with preeclampsia. As they are present on the majority of the decidua, uNK have an important role in pregnancy. The aim of the present study was to determine the role of ULBP1 in trophoblast cell invasion, which is closely associated with the occurrence of preeclampsia. In the present study, ULBP1 expression levels in placentas collected after cesarean section from women with preeclampsia and normal pregnant women were determined by immunohistochemistry, reverse transcription-quantitative polymerase chain reaction and western blotting. The effects of ULBP1 on extravillous trophoblast cell line (HTR-8/SVneo) invasion mediated via uNK cells and the underlying mechanisms were investigated. mRNA and protein expression levels of ULBP1 were significantly upregulated (P<0.05) in preeclamptic placentas compared with normal controls. ULBP1 inhibited HTR-8/SVneo cells via the regulation of biological functions of uNK cells, including the downregulation of NKG2D expression on uNK cells and the stimulation of production of cytokines and chemokines that affect extravillous cytotrophoblast invasion by uNK cells. ULBP1 may have an important role in the pathophysiology of preeclampsia through the modification of biological functions of uNK cells, which may affect trophoblast invasion.

Endogenous TWEAK is critical for regulating the function of mouse uterine natural killer cells in an immunological model of pregnancy loss.

Uterine natural killer (uNK) cells are the most abundant lymphocyte population in the feto-maternal interface during early gestation, and uNK cells play a significant role in the establishment and maintenance of pregnancy-related vascularization, as well as in tolerance to the fetus. Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible molecule (Fn14), are involved in preventing local cytotoxicity and counterbalancing the cytotoxic function of uNK cells. Here, we studied the regulation of TWEAK/Fn14-mediated innate immunity in the uterus using a lipopolysaccharide (LPS)-induced model of abortion in pregnant mice. Specifically, we detected the expression of TWEAK and Fn14 in the uterus and in uNK cells following LPS treatment. Our results revealed that TWEAK and Fn14 are expressed by uNK cells in pregnant mice; in particular, it appears that the cytokine TWEAK is primarily derived from uNK cells. Interestingly, the down-regulation of TWEAK in uNK cells and the up-regulation of the Fn14 receptor in the uterus in LPS-treated mice may contribute to the disruption of decidual homeostasis by altering uNK cell cytotoxicity - ultimately leading to fetal rejection. In conclusion, the present study strongly suggests that the TWEAK-Fn14 axis in uNK cells is involved in maintaining the tolerance necessary for successful pregnancy.

To serve and to protect: the role of decidual innate immune cells on human pregnancy.

The maternal-fetal interface undergoes dynamic changes that promote successful development of the embryo/fetal allograft during pregnancy. This immune privilege of the conceptus is mediated through local and systemic cellular responses. In species in which endometrial decidualization accompanies pregnancy, unique immune cell niches are found. Many studies have addressed the enigmatic roles of uterine (u)NK cells as killers and helpers because they are frequently found in the uterine lining and decidua of normal and pathological pregnancies. Accumulating evidence indicates that uNK cells are induced and transformed by sensing signals within their microenvironment to both protect the mother from the fetal allograft and support the fetus during its development. Here, we review the mechanisms that modulate these functions of uNK cells during pregnancy. We suggest that uNK cells must be tightly regulated in order to serve these two roles and support a healthy pregnancy.