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

Regional Analysis of the Immune Microenvironment in Human Endometrium

PROBLEM

Endometrial immune cells are essential for maintaining homeostasis and the endometrial receptivity to embryo implantation. Understanding regional variations in endometrial immune cell populations is crucial for comprehending normal endometrial function and the pathophysiology of endometrial disorders. Despite previous studies focusing on the overall immune cell composition and function in the endometrium, regional variations in premenopausal women remain unclear.

METHOD OF STUDY

Endometrial biopsies were obtained from four regions (anterior, posterior, left lateral, and right lateral) of premenopausal women undergoing hysteroscopy with no abnormalities. A 15-color human endometrial immune cell-focused flow cytometry panel was used for analysis. High-dimensional flow cytometry combined with a clustering algorithm was employed to unravel the complexity of endometrial immune cells. Additionally, multiplex immunofluorescent was performed for further validation.

RESULTS

Our findings revealed no significant variation in the distribution and abundance of immune cells across different regions under normal conditions during the proliferative phase. Each region harbored similar immune cell subtypes, indicating a consistent immune microenvironment. However, when comparing normal regions to areas with focal hemorrhage, significant differences were observed. An increase in CD8+ T cells highlights the impact of localized abnormalities on the immune microenvironment.

CONCLUSIONS

Our study demonstrates that the endometrial immune cell landscape is consistent across different anatomical regions during the proliferative phase in premenopausal women. This finding has important implications for understanding normal endometrial function and the pathophysiology of endometrial disorders.

Beyond Immune Balance: The Pivotal Role of Decidual Regulatory T Cells in Unexplained Recurrent Spontaneous Abortion

Recurrent spontaneous abortion (RSA) is defined as two or more consecutive pregnancy failures, which brings tremendous stress to women of childbearing age and seriously affects family well-being. However, the reason in about 50% of cases remains unknown and is defined as unexplained recurrent spontaneous abortion (URSA). The immunological perspective in URSA has attracted widespread attention in recent years. The embryo is regarded as a semi-allogeneic graft to the mother. A successful pregnancy requires transition to an immune environment conducive to embryo survival at the maternal-fetal interface. As an important member of regulatory immunity, regulatory T (Treg) cells play a key role in regulating immune tolerance at the maternal-fetal interface. This review will focus on the phenotypic plasticity and lineage stability of Treg cells to illustrate its relationship with URSA.

Uterine macrophages and NK cells exhibit population and gene-level changes after implantation but maintain pro-invasive properties

Introduction

Prior to pregnancy, hormonal changes lead to cellular adaptations in the endometrium allowing for embryo implantation. Critical for successful pregnancy establishment, innate immune cells constitute a significant proportion of uterine cells prior to arrival of the embryo and throughout the first trimester in humans and animal models. Abnormal uterine immune cell function during implantation is believed to play a role in multiple adverse pregnancy outcomes. Current work in humans has focused on uterine immune cells present after pregnancy establishment, and limited in vitro models exist to explore unique functions of these cells.

Methods

With single-cell RNA-sequencing (scRNAseq), we comprehensively compared the human uterine immune landscape of the endometrium during the window of implantation and the decidua during the first trimester of pregnancy.

Results

We uncovered global and cell-type-specific gene signatures for each timepoint. Immune cells in the endometrium prior to implantation expressed genes associated with immune metabolism, division, and activation. In contrast, we observed widespread interferon signaling during the first trimester of pregnancy. We also provide evidence of specific inflammatory pathways enriched in pre- and post-implantation macrophages and natural killer (NK) cells in the uterine lining. Using our novel implantation-on-a-chip (IOC) to model human implantation ex vivo, we demonstrate for the first time that uterine macrophages strongly promote invasion of extravillous trophoblasts (EVTs), a process essential for pregnancy establishment. Pre- and post-implantation uterine macrophages promoted EVT invasion to a similar degree as pre- and post-implantation NK cells on the IOC.

Conclusions

This work provides a foundation for further investigation of the individual roles of uterine immune cell subtypes present prior to embryo implantation and during early pregnancy, which will be critical for our understanding of pregnancy complications associated with abnormal trophoblast invasion and placentation.

Morphology of the immune cells in the wall of the human uterine tube and their possible impact on reproduction-uterine tube as a possible immune privileged organ

The uterine tube, as well as other parts of the upper female reproductive system, is immunologically unique in its requirements for tolerance to allogenic sperm and semi-allogenic embryos, yet responds to an array of sexually transmitted pathogens. To understand this dichotomy, there is a need to understand the functional morphology of immune cells in the wall of the uterine tube. Thus, we reviewed scientific literature regarding immune cells and the human uterine tube by using the scientific databases. The human uterine tube has a diverse population of immunocompetent cells representing both the innate and adaptive immune systems. We describe in detail the possible roles of cells of the mononuclear phagocyte system (macrophages and dendritic cells), T and B lymphocytes, natural killer cells, neutrophils and mast cells in association with the reproductive functions of uterine tubes. We are also discussing about the possible "immune privilege" of the uterine tube, as another mechanism to tolerate sperm and embryo without eliciting an inflammatory immune response. In uterine tube is not present an anatomical blood-tissue barrier between antigens and circulation. However, the immune cells of the uterine tube probably represent a type of "immunological barrier," which probably includes the uterine tube among the immunologically privileged organs. Understanding how immune cells in the female reproductive tract play roles in reproduction is essential to understand not only the mechanisms of gamete transport and fertilization as well as embryo transport through the uterine tube, but also in improving results from assisted reproduction.

Deciphering decidual leukocyte traffic with serial intravascular staining

The decidual immunome is dynamic, dramatically changing its composition across gestation. Early pregnancy is dominated by decidual NK cells, with a shift towards T cells later in pregnancy. However, the degree, timing, and subset-specific nature of leukocyte traffic between the decidua and systemic circulation during gestation remains poorly understood. Herein, we employed intravascular staining in pregnant C57BL/6J mice and cynomolgus macaques (Macaca fascicularis) to examine leukocyte traffic into the decidual basalis during pregnancy. Timed-mated or virgin mice were tail-vein injected with labelled αCD45 antibodies 24 hours and 5 minutes before sacrifice. Pregnant cynomolgus macaques (GD155) were infused with labelled αCD45 at 2 hours or 5 mins before necropsy. Decidual cells were isolated and resulting suspensions analyzed by flow cytometry. We found that the proportion of intravascular (IVAs)-negative leukocytes (cells labeled by the 24h infusion of αCD45 or unlabeled) decreased across murine gestation while recent immigrants (24h label only) increased in mid- to late-gestation. In the cynomolgus model our data confirmed differential labeling of decidual leukocytes by the infused antibody, with the 5 min infused animal having a higher proportion of IVAs+ cells compared to the 2hr infused animal. Decidual tissue sections from both macaques showed the presence of intravascularly labeled cells, either in proximity to blood vessels (5min infused animal) or deeper into decidual stroma (2hr infused animal). These results demonstrate the value of serial intravascular staining as a sensitive tool for defining decidual leukocyte traffic during pregnancy.

Downregulation of Salt-Inducible Kinase 3 Enhances CCL24 Activation in the Placental Environment with Preeclampsia

Preeclampsia (PE) remains one of the leading causes of maternal and perinatal morbidity and mortality. However, the exact pathophysiology of PE is still unclear. The recent widely accepted notion that successful pregnancy relies on maternal immunological adaptation is of utmost importance. Moreover, salt-inducible kinase 3 (SIK3) is an AMP-activated protein kinase-related kinase, and it has reported a novel regulator of energy and inflammation, and its expression related with some diseases. To explore whether SIK3 expression correlated with PE, we analyzed SIK3 gene expression and its association with PE through GEO datasets. We identified that SIK3 was significantly downregulated in PE across four datasets (p < 0.05), suggesting that SIK3 participated in the pathogenesis of PE. We initially demonstrated the significant downregulation of SIK3 in trophoblast cells of PE. SIK3 downregulation was positively correlated with the increased number of CD204(+) cells in in vivo and in vitro experiments. The increased number of CD204(+) cells could inhibit the migration and invasion of trophoblast cells. We then clarified the potential mechanism of PE with SIK3 downregulation: M2 skewing was triggered by trophoblast cells derived via the CCL24/CCR3 axis, leading to an increase in CD204(+) cells, a decrease in phagocytosis, and the production of IL-10 at the maternal-fetal interface of the placenta with PE. IL-10 further contributed to a reduction in the migration and invasion of trophoblast cells. It also established a feedback loop wherein trophoblast cells increased CCL24 production to maintain M2 dominance in the placental environments of PE.

Glucocorticoids and Their Receptor Isoforms: Roles in Female Reproduction, Pregnancy, and Foetal Development

Alterations in the hypothalamic-pituitary-adrenal (HPA) axis and associated changes in circulating levels of glucocorticoids are integral to an organism's response to stressful stimuli. Glucocorticoids acting via glucocorticoid receptors (GRs) play a role in fertility, reproduction, placental function, and foetal development. GRs are ubiquitously expressed throughout the female reproductive system and regulate normal reproductive function. Stress-induced glucocorticoids have been shown to inhibit reproduction and affect female gonadal function by suppressing the hypothalamic-pituitary-gonadal (HPG) axis at each level. Furthermore, during pregnancy, a mother's exposure to prenatal stress or external glucocorticoids can result in long-lasting alterations to the foetal HPA and neuroendocrine function. Several GR isoforms generated via alternative splicing or translation initiation from the GR gene have been identified in the mammalian ovary and uterus. The GR isoforms identified include the splice variants, GRα and GRβ, and GRγ and GR-P. Glucocorticoids can exert both stimulatory and inhibitory effects and both pro- and anti-inflammatory functions in the ovary, in vitro. In the placenta, thirteen GR isoforms have been identified in humans, guinea pigs, sheep, rats, and mice, indicating they are conserved across species and may be important in mediating a differential response to stress. Distinctive responses to glucocorticoids, differential birth outcomes in pregnancy complications, and sex-based variations in the response to stress could all potentially be dependent on a particular GR expression pattern. This comprehensive review provides an overview of the structure and function of the GR in relation to female fertility and reproduction and discusses the changes in the GR and glucocorticoid signalling during pregnancy. To generate this overview, an extensive non-systematic literature search was conducted across multiple databases, including PubMed, Web of Science, and Google Scholar, with a focus on original research articles, meta-analyses, and previous review papers addressing the subject. This review integrates the current understanding of GR variants and their roles in glucocorticoid signalling, reproduction, placental function, and foetal growth.

The Next Frontier in ART: Harnessing the Uterine Immune Profile for Improved Performance

Assisted reproduction techniques have improved considerably in recent decades, but despite these advances, success rates remain relatively low. Endometrial immune profiling involves the analysis of cytokine biomarkers in the endometrium during the mid-luteal phase. This profiling aims to provide insights into the immune environment of the uterus. The aim is to identify immune disturbances and thus guide the development of personalized therapeutic approaches. The first part of the review looks back at the emergence of innovative concepts, highlighting the specificity of the human uterine environment at the time of implantation. Based on this new knowledge, biomarkers have been selected for endometrial immune profiling. The second part details the results of clinical studies conducted over the last ten years. These clinical results suggest that this approach can increase the rate of live births in patients suffering from repeated implantation failures or repeated pregnancy loss. Uterine immune profiling represents a clinical innovation that can significantly improve the performance of medically assisted reproduction treatments through personalized strategies tailored to the local immune profile. Innovation in personalized medicine for assisted reproduction is crucial to improving the success rates of fertility treatments, while reducing the risks and costs associated with ineffective or unnecessary interventions.

Immunomodulation for unexplained recurrent implantation failure: where are we now?

In brief

Immune dysfunction may contribute to or cause recurrent implantation failure. This article summarizes normal and pathologic immune responses at implantation and critically appraises currently used immunomodulatory therapies.

Abstract

Recurrent implantation failure (RIF) may be defined as the absence of pregnancy despite the transfer of ≥3 good-quality blastocysts and is unexplained in up to 50% of cases. There are currently no effective treatments for patients with unexplained RIF. Since the maternal immune system is intricately involved in mediating endometrial receptivity and embryo implantation, both insufficient and excessive endometrial inflammatory responses during the window of implantation are proposed to lead to implantation failure. Recent strategies to improve conception rates in RIF patients have focused on modulating maternal immune responses at implantation, through either promoting or suppressing inflammation. Unfortunately, there are no validated, readily available diagnostic tests to confirm immune-mediated RIF. As such, immune therapies are often started empirically without robust evidence as to their efficacy. Like other chronic diseases, patient selection for immunomodulatory therapy is crucial, and personalized medicine for RIF patients is emerging. As the literature on the subject is heterogenous and rapidly evolving, we aim to summarize the potential efficacy, mechanisms of actions and side effects of select therapies for the practicing clinician.

Oxidative stress on vessels at the maternal-fetal interface for female reproductive system disorders: Update

Considerable evidence shows that oxidative stress exists in the pathophysiological process of female reproductive system diseases. At present, there have been many studies on oxidative stress of placenta during pregnancy, especially for preeclampsia. However, studies that directly focus on the effects of oxidative stress on blood vessels at the maternal-fetal interface and their associated possible outcomes are still incomplete and ambiguous. To provide an option for early clinical prediction and therapeutic application of oxidative stress in female reproductive system diseases, this paper briefly describes the composition of the maternal-fetal interface and the molecular mediators produced by oxidative stress, focuses on the sources of oxidative stress and the signaling pathways of oxidative stress at the maternal-fetal interface, expounds the adverse consequences of oxidative stress on blood vessels, and deeply discusses the relationship between oxidative stress and some pregnancy complications and other female reproductive system diseases.

Zooming in on the endometrial factor of recurrent implantation failure

Recurrent implantation failure (RIF) is a major limiting factor in the success rates of in-vitro fertilisation despite the remarkable clinical and technological advancement made at improving assisted reproductive technology. The primary purpose of the endometrium is to provide a receptive site for the implantation of the blastocyst and support its growth and subsequent development. Endometrial pathologies such as endometrial polyps, adenomyosis, Asherman's syndrome, chronic endometritis, and congenital Müllerian ducts defect negatively influence the integrity and receptivity of the endometrium, as well as the implantation of the embryo. This review highlights the implications of these endometrial pathologies and their association with RIF.

Pregnancy preparation: redistribution of CCR7-positive cells in the rat uterus

In brief

Changes in the endometrium prior to implantation may be critical in predicting pregnancy outcomes. This study shows that the endocrine system directs positional changes in CCR7+ cells before implantation, which may be critical for developing maternal tolerance.

Abstract

Suppression of the maternal immune system is vital for the implantation of the semi-allogeneic embryo. Although progress in understanding the dialogue between mother and embryo has been made, key interactions between maternal immune cells, hormones, and chemokines remain elusive. Uterine expression of the C-C chemokine receptor type 7 (CCR7) could recruit T regulatory cells and facilitate localized immune suppression. To test this concept, Ccr7 mRNA and protein were assessed in uterine tissue. Ccr7 mRNA expression peaked at day 4 in pregnant rat uteri and then declined at days 5 and 6. CCR7 protein showed similar quantitative changes. To test if female sex steroids affected the spatial distribution of CCR7-expressing cells, uteri from ovariectomized rats, progesterone-pretreated rats (2 mg daily), and progesterone-pretreated rats injected with estradiol (0.2 µg) were analyzed. Progesterone increased CCR7-positive (+) cells in the antimesometrial stroma. Progesterone and estradiol increased CCR7+ cells in the mesometrial stroma. Estradiol increased the density of cluster of differentiation 4 (CD4) positive cells in the mesometrial stromal region over progesterone alone. The density of cells expressing the T regulatory cell marker, forkhead box protein 3 (FOXP3), increased in the antimesometrial stroma in response to progesterone alone. Progesterone and estradiol increased FOXP3+ cells in the antimesometrial region of the stroma. Co-localization of CCR7, CD4, and FOXP3 in the stroma suggests CCR7+ cells are T regulatory cells. Polarization of CCR7+ cells in the endometrial stroma was an intrinsic response regulated by sex steroids and did not require the presence of an embryo.

Functional prominence of natural killer cells and natural killer T cells in pregnancy and infertility: A comprehensive review and update

During pregnancy, complicated connections are formed between a mother and a fetus. In a successful pregnancy, the maternal-fetal interface is affected by dynamic changes, and the fetus is protected against the mother's immune system. Natural killer (NK) cells are one of the immune system cells in the female reproductive system that play an essential role in the physiology of pregnancy. NK cells not only exist in peripheral blood (PB) but also can exist in the decidua. Studies have suggested multiple roles for these cells, including decidualization, control of trophoblast growth and invasion, embryo acceptance and maintenance by the mother, and facilitation of placental development during pregnancy. Natural killer T (NKT) cells are another group of NK cells that play a crucial role in the maintenance of pregnancy and regulation of the immune system during pregnancy. Studies show that NK and NKT cells are not only effective in maintaining pregnancy but also can be involved in infertility-related diseases. This review focuses on NK and NKT cells biology and provides a detailed description of the functions of these cells in implantation, placentation, and immune tolerance during pregnancy and their role in pregnancy complications.

Immune determinants of endometrial receptivity: a biological perspective

Immune cells are essential for endometrial receptivity to embryo implantation and early placental development. They exert tissue-remodeling and immune regulatory roles-acting to promote epithelial attachment competence, regulate the differentiation of decidual cells, remodel the uterine vasculature, control and resolve inflammatory activation, and suppress destructive immunity to paternally inherited alloantigens. From a biological perspective, the endometrial immune response exerts a form of "quality control"-it promotes implantation success when conditions are favorable but constrains receptivity when physiological circumstances are not ideal. Women with recurrent implantation failure and recurrent miscarriage may exhibit altered numbers or disturbed function of certain uterine immune cell populations-most notably uterine natural killer cells and regulatory T cells. Preclinical and animal studies indicate that deficiencies or aberrant activation states in these cells can be causal in the pathophysiological mechanisms of infertility. Immune cells are, therefore, targets for diagnostic evaluation and therapeutic intervention. However, current diagnostic tests are overly simplistic and have limited clinical utility. To be more informative, they need to account for the full complexity and reflect the range of perturbations that can occur in uterine immune cell phenotypes and networks. Moreover, safe and effective interventions to modulate these cells are in their infancy, and personalized approaches matched to specific diagnostic criteria will be needed. Here we summarize current biological understanding and identify knowledge gaps to be resolved before the promise of therapies to target the uterine immune response can be fully realized.

Multiomic analysis reveals decidual-specific transcriptional programing of MAIT cells

PROBLEM

Mucosal-Associated Invariant T (MAIT) cells have been recently identified at the maternal-fetal interface. However, transcriptional programming of decidual MAIT cells in pregnancy remains poorly understood.

METHOD OF STUDY

We employed a multiomic approach to address this question. Mononuclear cells from the decidua basalis and parietalis, and control PBMCs, were analyzed via flow cytometry to investigate MAIT cells in the decidua and assess their transcription factor expression. In a separate study, both decidual and matched peripheral MAIT cells were analyzed using Cellular Indexing of Transcriptomes and Epitopes by Sequencing (CITE-seq) coupled with gene expression analysis. Lastly, decidual MAIT cells were stimulated with E.coli and expression of MR1 by antigen presenting cells was measured to evaluate decidual MAIT cell function.

RESULTS

First, we identified MAIT cells in both the decidua basalis and parietalis. CITE-seq, coupled with scRNA-seq gene expression analysis, highlighted transcriptional programming differences between decidual and matched peripheral MAIT cells at a single cell resolution. Transcription factor expression analysis further highlighted transcriptional differences between decidual MAIT cells and non-matched peripheral MAIT cells. Functionally, MAIT cells are skewed towards IFNγ and TNFα production upon stimulation, with E.coli leading to IFNγ production. Lastly, we demonstrate that MR1, the antigen presenting molecule restricting MAIT cells, is expressed by decidual APCs.

CONCLUSION

MAIT cells are present in the decidua basalis and obtain a unique gene expression profile. The presence of MR1 on APCs coupled with in vitro activation by E.coli suggests that MAIT cells might be involved in tissue-repair mechanisms at the maternal-fetal interface.

Sildenafil Citrate Downregulates PDE5A mRNA Expression in Women with Recurrent Pregnancy Loss without Altering Angiogenic Factors-A Preliminary Study

In our previous study, we showed that sildenafil citrate (SC), a selective PDE5A blocker, modulated NK cell activity in patients with recurrent pregnancy loss, which correlated with positive pregnancy outcomes. It was found that NK cells had a pivotal role in decidualization, angiogenesis, spiral artery remodeling, and the regulation of trophoblast invasion. Thus, in the current study, we determined the effects of SC on angiogenic factor expression and production, as well as idNK cell activity in the presence of nitric synthase blocker L-NMMA. Methods: NK cells (CD56⁺) were isolated from the peripheral blood of 15 patients and 15 fertile women on MACS columns and cultured in transformation media containing IL-15, TGF-β, and AZA—a methylation agent—for 7 days in hypoxia (94% N₂, 1% O₂, 5% CO₂). Cultures were set up in four variants: (1) with SC, (2) without SC, (3) with NO, a synthase blocker, and (4) with SC and NO synthase blocker. NK cell activity was determined after 7 days of culturing as CD107a expression after an additional 4h of stimulation with K562 erythroleukemia cells. The expression of the PDE5A, VEGF-A, PIGF, IL-8, and RENBP genes was determined with quantitative real-time PCR (qRT-PCR) using TaqMan probes and ELISA was used to measure the concentrations of VEGF-A, PLGF, IL-8, Ang-I, Ang-II, IFN–γ proteins in culture supernatants after SC supplementation. Results: SC downregulated PDE5A expression and had no effect on other studied angiogenic factors. VEGF-A expression was increased in RPL patients compared with fertile women. Similarly, VEGF production was enhanced in RPL patients’ supernatants and SC increased the concentration of PIGF in culture supernatants. SC did not affect the expression or concentration of other studied factors, nor idNK cell activity, regardless of NO synthase blockade.

Effect of Intralipid infusion on peripheral blood T cells and plasma cytokines in women undergoing assisted reproduction treatment

Objectives

Intravenous infusion of Intralipid is an adjunct therapy in assisted reproduction treatment (ART) when immune‐associated infertility is suspected. Here, we evaluated the effect of Intralipid infusion on regulatory T cells (Treg cells), effector T cells and plasma cytokines in peripheral blood of women undertaking IVF.

Methods

This prospective, observational pilot study assessed Intralipid infusion in 14 women exhibiting recurrent implantation failure, a clinical sign of immune‐associated infertility. Peripheral blood was collected immediately prior to and 7 days after intravenous administration of Intralipid. Plasma cytokines were measured by Luminex, and T‐cell subsets were analysed by flow cytometry.

Results

A small increase in conventional CD8⁺ T cells occurred after Intralipid infusion, but no change was seen in CD4⁺ Treg cells, or naïve, memory or effector memory T cells. Proliferation marker Ki67, transcription factors Tbet and RORγt, and markers of suppressive capacity CTLA4 and HLA‐DR were unchanged. Dimensionality‐reduction analysis using the tSNE algorithm confirmed no phenotype shift within Treg cells or other T cells. Intralipid infusion increased plasma CCL2, CCL3, CXCL8, GM‐CSF, G‐CSF, IL‐6, IL‐21, TNF and VEGF.

Conclusion

Intralipid infusion elicited elevated pro‐inflammatory cytokines, and a minor increase in CD8⁺ T cells, but no change in pro‐tolerogenic Treg cells. Notwithstanding the limitation of no placebo control, the results do not support Intralipid as a candidate intervention to attenuate the Treg cell response in women undergoing ART. Future placebo‐controlled studies are needed to confirm the potential efficacy and clinical significance of Intralipid in attenuating cytokine induction and circulating CD8⁺ T cells.

NK-92 cells change their phenotype and function when cocultured with IL-15, IL-18 and trophoblast cells

NK cell development is affected by their cellular microenvironment and cytokines, including IL-15 and IL-18. NK cells can differentiate in secondary lymphoid organs, liver and within the uterus in close contact with trophoblast cells. The aim was to evaluate changes in the NK cell phenotype and function in the presence of IL-15, IL-18 and JEG-3, a trophoblast cell line. When cocultured with JEG-3 cells, IL-15 caused an increase in the number of NKG2D+ NK-92 cells and the intensity of CD127 expression. IL-18 stimulates an increase in the amount of NKp44+ NK-92 cells and in the intensity of NKp44 expression by pNK in the presence of trophoblast cells. NK-92 cell cytotoxic activity against JEG-3 cells increased only in presence of IL-18. Data on changes in the cytotoxic activity of NK-92 cells against JEG-3 cells in the presence of IL-15 and IL-18 indicate the modulation of NK cell function both by the cytokine microenvironment and directly by target cells. IL-15 and IL-18 were present in conditioned media (CM) from 1st and 3rd trimester placentas. In the presence of 1st trimester CM and JEG-3 cells, NK-92 cells showed an increase in the intensity of NKG2D expression. In the presence of 3rd trimester CM and JEG-3 cells, a decrease in the expression of NKG2D by NK-92 cells was observed. Thus, culturing of NK-92 cells with JEG-3 trophoblast cells stimulated a pronounced change in the NK cell phenotype, bringing it closer to the decidual NK cell-like phenotype.

Protective role of IL33 signaling in negative pregnancy outcomes associated with lipopolysaccharide exposure

Interleukin 33 (IL33) signaling has been implicated in the establishment and maintenance of pregnancy and in pregnancy disorders. The goal of this project was to evaluate the role of IL33 signaling in rat pregnancy. The rat possesses hemochorial placentation with deep intrauterine trophoblast invasion; features also characteristic of human placentation. We generated and characterized a germline mutant rat model for IL33 using CRISPR/Cas9 genome editing. IL33 deficient rats exhibited deficits in lung responses to an inflammatory stimulus (Sephadex G-200) and to estrogen-induced uterine eosinophilia. Female rats deficient in IL33 were fertile and exhibited pregnancy outcomes (gestation length and litter size) similar to wild-type rats. Placental weight was adversely affected by the disruption of IL33 signaling. A difference in pregnancy-dependent adaptations to lipopolysaccharide (LPS) exposure was observed between wild-type and IL33 deficient pregnancies. Pregnancy in wild-type rats treated with LPS did not differ significantly from pregnancy in vehicle-treated wild-type rats. In contrast, LPS treatment decreased fetal survival rate, fetal and placental weights, and increased fetal growth restriction in IL33 deficient rats. In summary, a new rat model for investigating IL33 signaling has been established. IL33 signaling participates in the regulation of placental development and protection against LPS-induced fetal and placental growth restriction.

Analysis of Transcripts of Uncertain Coding Potential Using RNA Sequencing During the Preattachment Phase in Goat Endometrium

Transcripts of uncertain coding potential (TUCP) are part of long noncoding RNAs, which include short open reading frames and could be translated into small peptides. In recent years, a growing number of TUCPs has been implicated in multiple biological activities, such as embryogenesis and transcriptional regulation. However, the abundance of TUCPs and their roles in goat endometrium during pregnancy recognition (day 16) remain undocumented. In this study, bioinformatics analyses were conducted to identify the differentially expressed (DE) TUCPs between pregnant animals and corresponding nonpregnant controls. A total of 5551 TUCPs were identified; 114 TUCPs were DE in goat endometrium, of which 74 TUCPs were upregulated in pregnant endometrium, whereas 40 TUCPs were downregulated. The related genes of TUCP were predicted by using coexpression and colocalization methods. In summary, 419 genes were predicted by colocalization, and 9464 genes were predicted by coexpression. The kyoto encyclopedia of genes and genomes (KEGG) and gene ontology (GO) analysis showed that TUCPs, which are highly expressed in pregnant endometrium, were mainly associated with endometrial remodeling, nutrient synthesis, and transportation. However, TUCPs that were lowly expressed in pregnant endometrium were mainly associated with immune tolerance, which is necessary for the protection and development of the embryo in the uterus. These findings may be used for the comparative analysis of TUCP transcripts in endometrium and assist in the selection of applicable candidate genes associated with embryo implantation for further functional analyses.

Dysfunction of Decidual Macrophages Is a Potential Risk Factor in the Occurrence of Preeclampsia

Preeclampsia is a multi-factorial and multi-genetic disorder that affects more than eight million mother and baby pairs each year. Currently, most of the attention to the pathogenesis of preeclampsia has been focused on placenta, but recent progresses suggest that excellent decidualization lays foundation for placentation and growth. Moreover, preeclampsia is associated with an imbalance in immunoregulatory mechanisms, however, how the immune regulatory system in the decidua affects preeclampsia is still unclear. In our study, after intersecting the genes of differentially expressed between preeclampsia and the control gotten by conventional expression profile analysis and the genes contained in the ligand receptor network, we found eight differentially expressed genes in a ligand-receptor relationship, and the eight genes have a characteristic: most of them participate in the interaction between decidual macrophages and other decidual immune cells. The results of single-cell sequencing of decidual cells further demonstrated that decidual macrophages affect the functions of other immune cells through export. As a result, abnormal gene expression affects the export function of decidual macrophages, which in turn affects the interaction of decidual macrophages with other immune cells, thereby destroying the original immune regulation mechanism, and ultimately leading to the occurrence of preeclampsia.

Single-cell Immune Landscape of Human Recurrent Miscarriage

Successful pregnancy in placental mammals substantially depends on the establishment of maternal immune tolerance to the semi-allogenic fetus. Disorders in this process are tightly associated with adverse pregnancy outcomes including recurrent miscarriage (RM). However, an in-depth understanding of the systematic and decidual immune environment in RM remains largely lacking. In this study, we utilized single-cell RNA-sequencing (scRNA-seq) to comparably analyze the cellular and molecular signatures of decidual and peripheral leukocytes in normal and unexplained RM pregnancies at the early stage of gestation. Integrative analysis identifies 22 distinct cell clusters in total, and a dramatic difference in leukocyte subsets and molecular properties in RM cases is revealed. Specifically, the cytotoxic properties of CD8⁺ effector T cells, nature killer (NK), and mucosal-associated invariant T (MAIT) cells in peripheral blood indicates apparently enhanced pro-inflammatory status, and the population proportions and ligand–receptor interactions of the decidual leukocyte subsets demonstrate preferential immune activation in RM patients. The molecular features, spatial distribution, and the developmental trajectories of five decidual NK (dNK) subsets have been elaborately illustrated. In RM patients, a dNK subset that supports embryonic growth is diminished in proportion, while the ratio of another dNK subset with cytotoxic and immune-active signature is significantly increased. Notably, a unique pro-inflammatory CD56⁺CD16⁺ dNK subset substantially accumulates in RM decidua. These findings reveal a comprehensive cellular and molecular atlas of decidual and peripheral leukocytes in human early pregnancy and provide an in-depth insight into the immune pathogenesis for early pregnancy loss.

Identifying biomarkers for predicting successful embryo implantation: applying single to multi-OMICs to improve reproductive outcomes

BACKGROUND

Successful embryo implantation is a complex process that requires the coordination of a series of events, involving both the embryo and the maternal endometrium. Key to this process is the intricate cascade of molecular mechanisms regulated by endocrine, paracrine and autocrine modulators of embryonic and maternal origin. Despite significant progress in ART, implantation failure still affects numerous infertile couples worldwide and fewer than 10% of embryos successfully implant. Improved selection of both the viable embryos and the optimal endometrial phenotype for transfer remains crucial to enhancing implantation chances. However, both classical morphological embryo selection and new strategies incorporated into clinical practice, such as embryonic genetic analysis, morphokinetics or ultrasound endometrial dating, remain insufficient to predict successful implantation. Additionally, no techniques are widely applied to analyse molecular signals involved in the embryo-uterine interaction. More reliable biological markers to predict embryo and uterine reproductive competence are needed to improve pregnancy outcomes. Recent years have seen a trend towards 'omics' methods, which enable the assessment of complete endometrial and embryonic molecular profiles during implantation. Omics have advanced our knowledge of the implantation process, identifying potential but rarely implemented biomarkers of successful implantation.

OBJECTIVE AND RATIONALE

Differences between the findings of published omics studies, and perhaps because embryonic and endometrial molecular signatures were often not investigated jointly, have prevented firm conclusions being reached. A timely review summarizing omics studies on the molecular determinants of human implantation in both the embryo and the endometrium will help facilitate integrative and reliable omics approaches to enhance ART outcomes.

SEARCH METHODS

In order to provide a comprehensive review of the literature published up to September 2019, Medline databases were searched using keywords pertaining to omics, including 'transcriptome', 'proteome', 'secretome', 'metabolome' and 'expression profiles', combined with terms related to implantation, such as 'endometrial receptivity', 'embryo viability' and 'embryo implantation'. No language restrictions were imposed. References from articles were also used for additional literature.

OUTCOMES

Here we provide a complete summary of the major achievements in human implantation research supplied by omics approaches, highlighting their potential to improve reproductive outcomes while fully elucidating the implantation mechanism. The review highlights the existence of discrepancies among the postulated biomarkers from studies on embryo viability or endometrial receptivity, even using the same omic analysis.

WIDER IMPLICATIONS

Despite the huge amount of biomarker information provided by omics, we still do not have enough evidence to link data from all omics with an implantation outcome. However, in the foreseeable future, application of minimally or non-invasive omics tools, together with a more integrative interpretation of uniformly collected data, will help to overcome the difficulties for clinical implementation of omics tools. Omics assays of the embryo and endometrium are being proposed or already being used as diagnostic tools for personalised single-embryo transfer in the most favourable endometrial environment, avoiding the risk of multiple pregnancies and ensuring better pregnancy rates.

Immune cells in normal pregnancy and gestational trophoblastic diseases

A healthy pregnancy requires the development of maternal-fetal immune tolerance against the semi-allogeneic fetus. The interactions between the trophoblastic cells and the maternal immune cells (p.e., natural killer cells, T cells, macrophages, dendritic cells and B-cells) are important for the development of the maternal-fetal immune tolerance and the placental growth and function. These interactions are mediated by cell to cell contact and secreted molecules such as cytokines, chemokines, angiogenic factors and growth factors. The maternal immune cells are present in normal non-pregnant and pregnant endometrium and there are several lines of evidence based on immunohistochemical and RNA sequencing data that the decidual immune cells and immune-related pathways display alterations in GTD, which may have pathogenetic and clinical significance. The present review focuses on the usefulness of the immunohistochemical analysis which provides multiparametric in situ information regarding the numbers, the immunophenotypes and the immunotopographical distributions of the decidual immune cells in tissue sections from normal pregnancy and GTD. We also discuss the significance of the immunohistochemical information in order to gain insight in the putative mechanisms explaining the alterations of the decidual immune cells in GTD and the potential implications of these alterations in the pathogenesis and the clinical behavior of GTD.

Innate Lymphoid Cells at the Maternal-Fetal Interface in Human Pregnancy

Pregnancy constitutes a major challenge to the maternal immune system, which must tolerate fetal alloantigen encoded by paternal genes. In addition to their role in inducing maternal-fetal immune tolerance, accumulating evidence indicates that decidual immune cells are involved in several processes required for a successful pregnancy, including trophoblast invasion as well as tissue and spiral artery remodeling. Innate lymphoid cells (ILCs), an important branch of the innate immune system, which has expanded rapidly in recent years, are strong actors in mucosal immunity, tissue homeostasis and metabolism regulation. With the recent identification of ILCs in the human decidua, the role of ILCs at the maternal-fetal interface raises concern. Herein, we review the presence and characterization of ILCs in the human decidua, as well as their function in normal pregnancy and pathological pregnancy, including reproductive failure, preeclampsia and others.

Natural killer cells as modulators of alloimmune responses

PURPOSE OF REVIEW

Natural killer (NK) cells are effector cells of the innate immune system that can lyse target cells without prior sensitization and are important in host defense to virally infected and transformed cells. Although the concept of 'missing-self' would suggest NK cells could target foreign allografts, the prevailing dogma has been that NK cells are not active participants in the rejection of solid organ allografts. This review summarizes recent studies that challenge this conclusion and instead suggest NK cells are important in outcomes posttransplant.

RECENT FINDINGS

NK cells expressing specific cell surface receptors may promote graft damage and rejection. However, recent studies suggest some NK cell subsets have tolerogenic or immunoregulatory potential and promote graft stability, suggesting a dichotomous role for NK cells after transplant. Furthermore, NK cells respond to cells infected with cytomegalovirus and Epstein-Barr virus, and studies suggest some NK cells have immune memory.

SUMMARY

Our understanding of the role of NK cells posttransplant has evolved from 'no role' to the current idea that NK cells may have 'complex interactions' that impact graft outcomes. Additional studies, using cutting edge techniques to comprehensively analyze the phenotypic and functional subsets of NK cells in transplant recipients, are clearly necessary.

Hemochorial placentation: development, function, and adaptations

Placentation is a reproductive adaptation that permits fetal growth and development within the protected confines of the female reproductive tract. Through this important role, the placenta also determines postnatal health and susceptibility to disease. The hemochorial placenta is a prominent feature in primate and rodent development. This manuscript provides an overview of the basics of hemochorial placental development and function, provides perspectives on major discoveries that have shaped placental research, and thoughts on strategies for future investigation.

Placental Galectins Are Key Players in Regulating the Maternal Adaptive Immune Response

Galectins are potent immunomodulators that regulate maternal immune responses in pregnancy and prevent the rejection of the semi-allogeneic fetus that also occurs in miscarriages. We previously identified a gene cluster on Chromosome 19 that expresses a subfamily of galectins, including galectin-13 (Gal-13) and galectin-14 (Gal-14), which emerged in anthropoid primates. These galectins are expressed only by the placenta and induce the apoptosis of activated T lymphocytes, possibly contributing to a shifted maternal immune balance in pregnancy. The placental expression of Gal-13 and Gal-14 is decreased in preeclampsia, a life-threatening obstetrical syndrome partly attributed to maternal anti-fetal rejection. This study is aimed at revealing the effects of Gal-13 and Gal-14 on T cell functions and comparing the expression of these galectins in placentas from healthy pregnancies and miscarriages. First-trimester placentas were collected from miscarriages and elective termination of pregnancies, tissue microarrays were constructed, and then the expression of Gal-13 and Gal-14 was analyzed by immunohistochemistry and immunoscoring. Recombinant Gal-13 and Gal-14 were expressed and purified, and their effects were investigated on primary peripheral blood T cells. The binding of Gal-13 and Gal-14 to T cells and the effects of these galectins on apoptosis, activation marker (CD25, CD71, CD95, HLA-DR) expression and cytokine (IL-1β, IL-6, IL-8, IL-10, IFNγ) production of T cells were examined by flow cytometry. Gal-13 and Gal-14 are primarily expressed by the syncytiotrophoblast at the maternal-fetal interface in the first trimester, and their placental expression is decreased in miscarriages compared to first-trimester controls. Recombinant Gal-13 and Gal-14 bind to T cells in a population- and activation-dependent manner. Gal-13 and Gal-14 induce apoptosis of Th and Tc cell populations, regardless of their activation status. Out of the investigated activation markers, Gal-14 decreases the cell surface expression of CD71, Gal-13 increases the expression of CD25, and both galectins increase the expression of CD95 on T cells. Non-activated T cells produce larger amounts of IL-8 in the presence of Gal-13 or Gal-14. In conclusion, these results show that Gal-13 and Gal-14 already provide an immunoprivileged environment at the maternal-fetal interface during early pregnancy, and their reduced expression is related to miscarriages.

Therapeutic Potential of Regulatory T Cells in Preeclampsia-Opportunities and Challenges

Inflammation is a central feature and is implicated as a causal factor in preeclampsia and other hypertensive disorders of pregnancy. Inflammatory mediators and leukocytes, which are elevated in peripheral blood and gestational tissues, contribute to the uterine vascular anomalies and compromised placental function that characterize particularly the severe, early onset form of disease. Regulatory T (Treg) cells are central mediators of pregnancy tolerance and direct other immune cells to counteract inflammation and promote robust placentation. Treg cells are commonly perturbed in preeclampsia, and there is evidence Treg cell insufficiency predates onset of symptoms. A causal role is implied by mouse studies showing sufficient numbers of functionally competent Treg cells must be present in the uterus from conception, to support maternal vascular adaptation and prevent later placental inflammatory pathology. Treg cells may therefore provide a tractable target for both preventative strategies and treatment interventions in preeclampsia. Steps to boost Treg cell activity require investigation and could be incorporated into pregnancy planning and preconception care. Pharmacological interventions developed to target Treg cells in autoimmune conditions warrant consideration for evaluation, utilizing rigorous clinical trial methodology, and ensuring safety is paramount. Emerging cell therapy tools involving in vitro Treg cell generation and/or expansion may in time become relevant. The success of preventative and therapeutic approaches will depend on resolving several challenges including developing informative diagnostic tests for Treg cell activity applicable before conception or during early pregnancy, selection of relevant patient subgroups, and identification of appropriate windows of gestation for intervention.

Patients with idiopathic recurrent miscarriage have abnormally high TGFß+ blood NK, NKT and T cells in the presence of abnormally low TGFß plasma levels

Background

Previously, we demonstrated up-regulated activated CD4+ and CD8+ T lymphocytes as well as up-regulated cytotoxic NK cells in the blood of patients with idiopathic recurrent miscarriage. In the present study, we tried to identify deficiencies in counter-regulating immune mechanisms of these patients.

Method

Cytokines were determined in NK cells and in plasma samples of 35 healthy controls, 33 patients with idiopathic recurrent miscarriage, 34 patients with end stage renal disease, 10 transplant patients early and 37 transplant patients late post-transplant using flow-cytometry and luminex. In addition, cytokines were studied in supernatants of cell cultures with peripheral blood mononuclear cells stimulated in-vitro with tumor cell line K562.

Results

Patients with idiopathic recurrent miscarriage exhibited the highest absolute cell counts of circulating TGFß1+ NK, NKT and T lymphocytes and the lowest TGFß1 plasma levels of all study groups (for all p < 0.050). In-vitro, peripheral blood mononuclear cells of patients with idiopathic recurrent miscarriage showed high spontaneous TGFß1 production that could not be further increased by stimulation with K562, indicating increased consumption of TGFß1 by activated cells in the cell culture. Moreover, patients with idiopathic recurrent miscarriage had abnormally high IL4+ as well as abnormally high IFNy+ NK cells (p < 0.010) but similar IL10+ NK cell numbers as female healthy controls and showed the lowest plasma levels of IL10, TGFß3, IL1RA, IL1ß, IL5, IL6, IL8, IL17, TNFα, GM-CSF, TPO and VEGF and the highest plasma levels of G-CSF, FGF-basic, CCL3 and CXCL5 as compared to female HC and female transplant recipients (for all p < 0.050).

Conclusions

Patients with idiopathic recurrent miscarriage show an activated immune system that can hardly be stimulated further and cannot be efficiently down-regulated by up-regulated TGFß1+ and IL4+ NK, NKT and T lymphocytes which are present concomitantly in these patients. The strongly decreased TGFß and IL10 plasma levels indicate deficient down-regulation and reflect a dysbalance of the immune system in patients with idiopathic recurrent miscarriage. These findings may be relevant for explaining the pathogenesis of idiopathic recurrent miscarriage.

Electronic supplementary material

The online version of this article (10.1186/s12865-019-0290-3) contains supplementary material, which is available to authorized users.

NK and trophoblast cells interaction: cytotoxic activity on recurrent pregnancy loss

The trial objective was to determine the peripheral blood NK cells cytotoxic activity effect on trophoblast cells at recurrent pregnancy loss (RPL). The investigation involved non-pregnant women with PRL in proliferating and secretory menstrual cycle phases (PMCPh and SMCPh, respectively); women of 6-7 weeks pregnancy with RPL in past medical history; healthy fertile non-pregnant women in PMCPh and SMCPh, women of 6-7 weeks physiological pregnancy, nulliparity healthy women with regular menstrual function in PMCPh and SMCPh. NK cells cytotoxic activity was determined using peripheral blood mononuclear cells. The target cells were JEG-3 line trophoblasts. It has been established that NK cells cytotoxic activity effect on trophoblasts is lower in SMCPh than in PMCPh in non-pregnant fertile women. The NK cells cytotoxic activity was higher in SMCPh than in PMCPh in non-pregnant women with PRL and also higher than the same value in SMCPh in non-pregnant fertile women. The increased NK cells cytotoxic activity values in SMCPh in women with RPL may be the reason for miscarriage.

Fetal human leukocyte antigen-C and maternal killer-cell immunoglobulin-like receptors in cases of severe preeclampsia

INTRODUCTION

The pathogenesis of preeclampsia may involve inadequate trophoblast invasion caused by excessive inhibition of uterine natural killer cells (uNK) by extravillous trophoblast cells (EVT). This may be the result of a combination of maternal killer-cell immunoglobin-like receptor (KIR) AA genotype and fetal human leukocyte antigen-C2 (HLA-C2) genotype. A few studies have reported a significantly increased frequency of the maternal KIR AA/fetal HLA-C2 combination in cases of preeclampsia compared to controls.

METHODS

Study subjects were 259 cases of severe preeclampsia/eclampsia and 259 matched pregnant women without preeclampsia or eclampsia. All pregnancies were singleton pregnancies, and mothers were preferentially primigravidae. Blood samples from women and their newborns were obtained from the Danish National Birth Cohort (DNBC) and the Danish Neonatal Screening Biobank. Significant differences in the frequencies of KIR AA and HLA-C2 between cases and controls were investigated.

RESULTS

No significant difference was observed between cases and controls in the frequency of maternal KIR AA (OR = 0.86, 95%CI = 0.60-1.23, P = 0.41), neither when the fetus carried an HLA-C2 allele (OR = 0.85, 95%CI = 0.52-1.38, P = 0.51), nor when the fetus carried an HLA-C2 allele more than its mother (OR = 0.75, 95%CI = 0.34-1.64, P = 0.47).

CONCLUSION

The Results show no influence of HLA-C/KIR genetic variation on the risk of severe preeclampsia, contrary to what some previous studies have observed. An explanation could be that severe preeclampsia represents a separate pathological entity compared to mild preeclampsia.

Comparison of The Therapeutic Effect of Syngeneic, Allogeneic, and Xenogeneic Adipose Tissue-Derived Mesenchymal Stem Cells on Abortion Rates in A Mouse Model

Objective

Mesenchymal stem cells (MSCs), due to their immunomodulatory functions, are an ideal candidate for the treatment of immune-related diseases. Recurrent spontaneous abortion (RSA) is one of the most common complications of pregnancy which in many cases is related to the immune system disorders. Our previous study has shown that the abortion rate was decreased following the syngeneic MSCs therapy in abortion-prone mice. In this study, the therapeutic effect of syngeneic, allogeneic, and xenogeneic MSCs was compared in a mouse model of RSA.

Materials and Methods

In this experimental study, MSCs were isolated from adipose tissue (ASCs) of CBA/J and BALB/c mice and human. After characterization, ASCs were injected (IP) at day 4 of gestation to female CBA/J mice following their mating with DBA/2 male mice. In the control group, phosphate-buffered saline (PBS) was injected and CBA/J×BALB/c mating was also used as the normal pregnancy control. On day 14.5 of pregnancy, embryo resorption rate was determined.

Results

The abortion rate significantly decreased following the ASCs therapy from syngeneic (6.31%), allogeneic (6.54%), and xenogeneic group (12.36%) compared to ASCs non-treated group (34.4%). There was no statistical difference between ASCs treated groups, however syngeneic and allogeneic ASCs reduced the abortion rate more efficiently than xenogeneic ASC.

Conclusion

The abortion rate was significantly decreased following the intraperitoneal administration of ASCs from various donated sources in abortion-prone mice. These results indicated that the immunogenicity of allogeneic and xenogeneic ASCs is not a contradictory problem for their therapeutic effects on RSA.

Effect of miR-30e regulating NK cell activities on immune tolerance of maternal-fetal interface by targeting PRF1

AIM

Natural killer (NK) cells, as key regulatory cells, accumulate at the maternal-fetal interface in large numbers. This study explored the effect of miR-30e on regulating the activity and function of peripheral blood NK cells (PB-NK cells) and decidua NK cells (D-NK cells) by targeting PRF1 in immune tolerance of maternal-fetal interface.

METHODS

Expressions of miR-30e in PB and decidua tissues from 49 patients with recurrent spontaneous abortion and 52 normal pregnant women were measured using PCR. NK cells were isolated from PB and decidua tissues and identified by flow cytometry (FCM). In PB-NK cells and D-NK cells activated by IFN-α, expressions of miR-30e and PRF1 were determined by PCR and Western blot. Negative controls of miR-30e mimics/inhibitors and siRNA against PRF1 were transfected in PB-NK cells and D-NK cells. Expressions of miR-30e and PRF1 were determined and their relationship was verified. Expressions of KIR2DL1, NKp44, IFN-γ, TNF-α, IL-4 and IL-10 were determined by FCM. Cytotoxicity kit was used to identify the cytotoxicity of NK cells. PCR and ELISA were employed to measure expression of VEGF, Ang-2 and PGF in D-NK cells.

RESULTS

After activation by IFN-α, D-NK cells and PB-NK cells showed decreased miR-30e expression and increased PRF1 expression in normal non-pregnant women. PRF1 is a target gene of miR-30e and miR-30e negatively regulated PRF1 expression. The treatment of miR-30e mimics elevated KIR2DL1 expression and decreased NKp44 expression in PB-NK or D-NK cells. Moreover, up-regulation of miR-30e expression suppressed cytotoxicity, corresponding to increased expression of IL-4and IL-10 and reduced expression of IFN-γ and TNF-α in PB-NK and D-NK cells, as well as enhanced expression of VEGF, Ang-2 and PGF in D-NK cells. Transfection of miR-30e inhibitors could reverse the tendencies.

CONCLUSION

Up-regulated miR-30e can reduce the cytotoxicity of PB-NK cells and D-NK cells by targeting PRF1, whereby inhibiting Th1 tolerance phenotype and inducing Th2 immunodominance. miR-30e may be contributive to creating a micro-immune tolerance environment of maternal-fetal interface.

Regulatory T cells in embryo implantation and the immune response to pregnancy

At implantation, the embryo expresses paternally derived alloantigens and evokes inflammation that can threaten reproductive success. To ensure a robust placenta and sustainable pregnancy, an active state of maternal immune tolerance mediated by CD4+ regulatory T cells (Tregs) is essential. Tregs operate to inhibit effector immunity, contain inflammation, and support maternal vascular adaptations, thereby facilitating trophoblast invasion and placental access to the maternal blood supply. Insufficient Treg numbers or inadequate functional competence are implicated in idiopathic infertility and recurrent miscarriage as well as later-onset pregnancy complications stemming from placental insufficiency, including preeclampsia and fetal growth restriction. In this Review, we summarize the mechanisms acting in the conception environment to drive the Treg response and discuss prospects for targeting the T cell compartment to alleviate immune-based reproductive disorders.

B Regulatory Cells: Players in Pregnancy and Early Life

Pregnancy and early infancy represent two very particular immunological states. During pregnancy, the haploidentical fetus and the pregnant women develop tolerance mechanisms to avoid rejection; then, just after birth, the neonatal immune system must modulate the transition from the virtually sterile but haploidentical uterus to a world full of antigens and the rapid microbial colonization of the mucosa. B regulatory (Breg) cells are a recently discovered B cell subset thought to play a pivotal role in different conditions such as chronic infections, autoimmunity, cancer, and transplantation among others in addition to pregnancy. This review focuses on the role of Breg cells in pregnancy and early infancy, two special stages of life in which recent studies have positioned Breg cells as important players.

Innate lymphoid cells at the human maternal-fetal interface in spontaneous preterm labor

PROBLEM

Pathological inflammation is causally linked to preterm labor and birth, the leading cause of neonatal morbidity and mortality worldwide. Our aims were to investigate whether (i) the newly described family of innate lymphoid cells (ILCs) was present at the human maternal-fetal interface and (ii) ILC inflammatory subsets were associated with the pathological process of preterm labor.

METHODS OF STUDY

Decidual leukocytes were isolated from women with preterm or term labor as well as from gestational age-matched non-labor controls. ILCs (CD15- CD14- CD3- CD19- CD56- CD11b- CD127+ cells) and their subsets (ILC1, T-bet+ ILCs; ILC2, GATA3+ ILCs; and ILC3, RORγt+ ILCs) and cytokine expression were identified in the decidual tissues using immunophenotyping.

RESULTS

(i) The proportion of total ILCs was increased in the decidua parietalis of women with preterm labor; (ii) ILC1s were a minor subset of decidual ILCs during preterm and term gestations; (iii) ILC2s were the most abundant ILC subset in the decidua during preterm and term gestations; (iv) the proportion of ILC2s was increased in the decidua basalis of women with preterm labor; (v) the proportion of ILC3s was increased in the decidua parietalis of women with preterm labor; and (vi) during preterm labor, ILC3s had higher expression of IL-22, IL-17A, IL-13, and IFN-γ compared to ILC2s in the decidua.

CONCLUSION

ILC2s were the most abundant ILC subset at the human maternal-fetal interface during preterm and term gestations. Yet, during preterm labor, an increase in ILC2s and ILC3s was observed in the decidua basalis and decidua parietalis, respectively. These findings provide evidence demonstrating a role for ILCs at the maternal-fetal interface during the pathological process of preterm labor.

Increased natural killer cell subsets with inhibitory cytokines and inhibitory surface receptors in patients with recurrent miscarriage and decreased or normal subsets in kidney transplant recipients late post-transplant

Patients with recurrent miscarriage (RM) show up-regulated cytotoxic natural killer (NK) cells that are suspected to play a causal role in abortion. In the present study, we investigated counter-regulating inhibitory mechanisms and compared the results in RM patients with those of healthy controls (HC), patients with end-stage renal disease (ESRD) and kidney transplant recipients late post-transplant (TX). NK, NK T and T cell subsets were analysed in the peripheral blood of 31 RM, 14 female ESRD and nine female TX patients as well as 21 female HC using eight-colour fluorescence flow cytometry. Compared with HC, RM patients showed significantly higher absolute numbers of CD56⁺ NK cells co-expressing the phenotype interferon (IFN)-γR⁺ , IL-4⁺ , transforming growth factor (TGF)-β⁺ , IL-4⁺ human leucocyte antigen D-related (HLA-DR)⁺ , TGF-β⁺ HLA-DR⁺ , IL-4⁺ TGF-β⁺ , IL-4⁺ TGF-β^- , IFN-γ⁺ and/or IL-10^- IFN-γ⁺ (all P ≤ 0·01), more IL-17⁺ CD56^bright (P = 0·028) NK cells and more CD56^dim CD16⁺ NK cells co-expressing IFN-γR, IFN-γ, IL-4 and/or TGF-β (all P ≤ 0·01). When the same cell subsets were analysed in ESRD or TX patients, cytokine-producing NK cell subsets were not significantly different from those of HC. RM patients showed significantly higher absolute numbers of CD158a⁺ , CD158b⁺ , CD158a^- CD158e⁺ (all P < 0·05), NKG2D⁺ NKG2A⁺ , NKG2D ⁺ NKG2A^- , NKG2D⁺ and/or NKG2A⁺ (all P ≤ 0·01) CD56⁺ NK cells and higher CD158a⁺ , CD158b⁺ (all P < 0·05), NKG2D⁺ and/or NKG2A⁺ (all P < 0·01) CD56^dim+ CD16⁺ NK cells than HC. In contrast, ESRD patients had normal and TX recipients had lower CD158a⁺ and NKG2D⁺ NKG2A^- CD56⁺ NK cells and lower CD158a⁺ CD56^dim+ CD16⁺ NK cells (all P < 0·05) than HC. RM patients have abnormally high circulating NK cells expressing inhibitory cytokines and inhibitory surface receptors which might contribute to the pathogenesis of RM.

Granulysin-mediated apoptosis of trophoblasts in blighted ovum and missed abortion

PROBLEM

Granulysin (GNLY) is a cytotoxic molecule mostly present in decidual natural killer (NK) cells. Blighted ovum (BO) and missed abortion (MA) represent the early pathological pregnancies with hindered development of the embryoblast or a dead embryo. We investigated the GNLY-mediated apoptotic mechanism potentially responsible for delayed termination of pregnancy.

METHOD OF STUDY

We performed immunohistological and immunofluorescence labeling of decidual tissues (GNLY, Apaf-1, NF-κB). NKG2A expression was analyzed by flow cytometry and GNLY mRNA by RT-qPCR.

RESULTS

The GNLY labeling intensity (H score) was lower in the nuclei of trophoblast cells in BO and MA. GNLY gene levels were inversely detected in BO and MA. A decreased decidual NK cell percentage was found in MA. NK cells from pathological pregnancies expressed lower NKG2A levels. The highest frequency of Apaf-1 was found in trophoblast cells of MA. NF-kB was highly expressed in decidual cells of BO.

CONCLUSION

The reduced activation of GNLY-mediated killing might be implicated in the slower rejection of trophoblast cells in BO and MA. A decreased authentic decidual NK cell number could be responsible for low cytotoxicity against trophoblast cells in MA. In BO, trophoblast cells have a higher survival potential due to increased NF-kB expression.

Maternal obesity alters uterine NK activity through a functional KIR2DL1/S1 imbalance

In pregnancy, uterine natural killer cells (uNK) play essential roles in coordinating uterine angiogenesis, blood vessel remodeling and promoting maternal tolerance to fetal tissue. Deviances from a normal uterine microenvironment are thought to modify uNK function(s) by limiting their ability to establish a healthy pregnancy. While maternal obesity has become a major health concern due to associations with adverse effects on fetal and maternal health, our understanding into how obesity contributes to poor pregnancy disorders is unknown. Given the importance of uNK in pregnancy, this study examines the impact of obesity on uNK function in women in early pregnancy. We identify that uNK from obese women show a greater propensity for cellular activation, but this difference does not translate into increased effector killing potential. Instead, uNK from obese women express an altered repertoire of natural killer receptors, including an imbalance in inhibitory KIR2DL1 and activating KIR2DS1 receptors that favors HLA-C2-directed uNK activation. Notably, we show that obesity-related KIR2DS1 skewing potentiates TNFα production upon receptor crosslinking. Together, these findings suggest that maternal obesity modifies uNK activity by altering the response toward HLA-C2 antigen and KIR2DL1/2DS1-controlled TNFα release. Furthermore, this work identifies alterations in uNK function resulting from maternal obesity that may impact early developmental processes important in pregnancy health.

MicroRNAs: crucial regulators of placental development

MicroRNAs (miRNAs) are small non-coding single-stranded RNAs that are integral to a wide range of cellular processes mainly through the regulation of translation and mRNA stability of their target genes. The placenta is a transient organ that exists throughout gestation in mammals, facilitating nutrient and gas exchange and waste removal between the mother and the fetus. miRNAs are expressed in the placenta, and many studies have shown that miRNAs play an important role in regulating trophoblast differentiation, migration, invasion, proliferation, apoptosis, vasculogenesis/angiogenesis and cellular metabolism. In this review, we provide a brief overview of canonical and non-canonical pathways of miRNA biogenesis and mechanisms of miRNA actions. We highlight the current knowledge of the role of miRNAs in placental development. Finally, we point out several limitations of the current research and suggest future directions.

Embryo Implantation: War in Times of Love

Contrary to widespread belief, the implantation of an embryo for the initiation of pregnancy is like a battle, in that the embryo uses a variety of coercive tactics to force its acceptance by the endometrium. We propose that embryo implantation involves a three-step process: (1) identification of a receptive endometrium; (2) superimposition of a blastocyst-derived signature onto the receptive endometrium before implantation; and finally (3) breaching by the embryo and trophoblast invasion, culminating in decidualization and placentation. We review here the story that is beginning to emerge, focusing primarily on the cells that are in "combat" during this process.

Immunological Tolerance, Pregnancy, and Preeclampsia: The Roles of Semen Microbes and the Father

Although it is widely considered, in many cases, to involve two separable stages (poor placentation followed by oxidative stress/inflammation), the precise originating causes of preeclampsia (PE) remain elusive. We have previously brought together some of the considerable evidence that a (dormant) microbial component is commonly a significant part of its etiology. However, apart from recognizing, consistent with this view, that the many inflammatory markers of PE are also increased in infection, we had little to say about immunity, whether innate or adaptive. In addition, we focused on the gut, oral and female urinary tract microbiomes as the main sources of the infection. We here marshall further evidence for an infectious component in PE, focusing on the immunological tolerance characteristic of pregnancy, and the well-established fact that increased exposure to the father's semen assists this immunological tolerance. As well as these benefits, however, semen is not sterile, microbial tolerance mechanisms may exist, and we also review the evidence that semen may be responsible for inoculating the developing conceptus (and maybe the placenta) with microbes, not all of which are benign. It is suggested that when they are not, this may be a significant cause of PE. A variety of epidemiological and other evidence is entirely consistent with this, not least correlations between semen infection, infertility and PE. Our view also leads to a series of other, testable predictions. Overall, we argue for a significant paternal role in the development of PE through microbial infection of the mother via insemination.

Two Distinct Myeloid Subsets at the Term Human Fetal-Maternal Interface

During pregnancy, immune cells infiltrate the placenta at different stages of fetal development. NK cells and macrophages are the most predominant cell types. These immune cells play pleiotropic roles, as they control spiral artery remodeling to ensure appropriate blood supply and maintain long-term tolerance to a true allograft; yet, they must be able to mount appropriate immune defenses to pathogens that may threaten the fetus. Whether the same cell type accomplishes all these tasks or if there are dedicated subsets remains controversial. Here, we identify and characterize two distinct subsets of myeloid cells that differ in their pro-inflammatory/regulatory capacity. While one subset predominantly produces the immune-modulating cytokine IL-10, the second subset has superior capacity to secrete pro-inflammatory mediators, such as IL-1β and IL-6. The putative regulatory myeloid cells also express high levels of inhibitory receptors and their ligands, including programmed cell death 1 (PD1) ligands. Importantly, a large fraction of CD8 and CD4 cells in normal term human placenta are PD1 positive, suggesting that the PD1/PD1 ligands axis might be critical to maintain tolerance during pregnancy.

Decreased NK cell immunity in kidney transplant recipients late post-transplant and increased NK-cell immunity in patients with recurrent miscarriage

BACKGROUND

There is evidence that NK-cell reactivity might affect graft outcome in transplant recipients and pregnancy in women.

METHOD

NK-cell subsets were determined in whole blood using eight-colour-fluorescence flow cytometry in patients before and after renal transplantation, patients with recurrent miscarriage (RM) and healthy controls (HC).

RESULTS

Patients late post-transplant (late-Tx) with functioning renal transplants showed abnormally low CD56dimCD16+ NK-cells containing both perforin and granzyme (vs HC p = 0.021) whereas RM patients exhibited abnormally high numbers of these cells (vs HC p = 0.043). CD56dimCD16+perforin+granzyme+ NK-cell counts were strikingly different between the two patient groups (p<0.001). In addition, recipients late-Tx showed abnormally low CD8+ NK-cells (vs HC p<0.001) in contrast to RM patients who showed an abnormal increase (vs HC p = 0.008). CD8+ NK-cell counts were strongly different between the two patient groups (p<0.001). Higher perforin+granzyme+CD56dimCD16+ and CD8+ NK-cells were associated with impaired graft function (p = 0.044, p = 0.032). After in-vitro stimulation, CD56dimCD16+ and CD56brightCD16dim/- NK-cells showed strong upregulation of CD107a and IFNy, whereas the content of perforin decreased dramatically as a consequence of perforin release. Recipients late post-Tx showed less in-vitro perforin release (= less cytotoxicity) than HC (p = 0.037) and lower perforin release was associated with good graft function (r = 0.738, p = 0.037). Notably, we observed strong in-vitro perforin release in 2 of 6 investigated RM patients. When circulating IL10+CD56bright NK-cells were analyzed, female recipients late post-Tx (n = 9) showed significantly higher relative and absolute cell numbers than RM patients (p = 0.002 and p = 0.018, respectively); and high relative and absolute IL10+CD56bright NK-cell numbers in transplant recipients were associated with low serum creatinine (p = 0.004 and p = 0.012) and high glomerular filtration rate (p = 0.011 and p = 0.002, respectively). Female recipients late post-Tx exhibited similar absolute but higher relative numbers of IL10+IFNy- NK-cells than RM patients (p>0.05 and p = 0.016, respectively).

CONCLUSION

NK-cells with lower cytotoxicity and immunoregulatory function might contribute to good long-term graft outcome, whereas circulating NK-cells with normal or even increased cytotoxicity and less immunoregulatory capacity are observed in patients with RM.

Glucocorticoids and Reproduction: Traffic Control on the Road to Reproduction

Glucocorticoids are steroid hormones that regulate diverse cellular functions and are essential to facilitate normal physiology. However, stress-induced levels of glucocorticoids result in several pathologies including profound reproductive dysfunction. Compelling new evidence indicates that glucocorticoids are crucial to the establishment and maintenance of reproductive function. The fertility-promoting or -inhibiting activity of glucocorticoids depends on timing, dose, and glucocorticoid responsiveness within a given tissue, which is mediated by the glucocorticoid receptor (GR). The GR gene and protein are subject to cellular processing, contributing to signaling diversity and providing a mechanism by which both physiological and stress-induced levels of glucocorticoids function in a cell-specific manner. Understanding how glucocorticoids regulate fertility and infertility may lead to novel approaches to the regulation of reproductive function.