Mast cells and histamine: do they influence placental vascular network and development in preeclampsia?

Insight into the Potential Mechanisms of Endocrine Disruption by Dietary Phytoestrogens in the Context of the Etiopathogenesis of Endometriosis

Phytoestrogens (PEs) are estrogen-like nonsteroidal compounds derived from plants (e.g., nuts, seeds, fruits, and vegetables) and fungi that are structurally similar to 17β-estradiol. PEs bind to all types of estrogen receptors, including ERα and ERβ receptors, nuclear receptors, and a membrane-bound estrogen receptor known as the G protein-coupled estrogen receptor (GPER). As endocrine-disrupting chemicals (EDCs) with pro- or antiestrogenic properties, PEs can potentially disrupt the hormonal regulation of homeostasis, resulting in developmental and reproductive abnormalities. However, a lack of PEs in the diet does not result in the development of deficiency symptoms. To properly assess the benefits and risks associated with the use of a PE-rich diet, it is necessary to distinguish between endocrine disruption (endocrine-mediated adverse effects) and nonspecific effects on the endocrine system. Endometriosis is an estrogen-dependent disease of unknown etiopathogenesis, in which tissue similar to the lining of the uterus (the endometrium) grows outside of the uterus with subsequent complications being manifested as a result of local inflammatory reactions. Endometriosis affects 10-15% of women of reproductive age and is associated with chronic pelvic pain, dysmenorrhea, dyspareunia, and infertility. In this review, the endocrine-disruptive actions of PEs are reviewed in the context of endometriosis to determine whether a PE-rich diet has a positive or negative effect on the risk and course of endometriosis.

Female reproductive health impacts of Long COVID and associated illnesses including ME/CFS, POTS, and connective tissue disorders: a literature review

Long COVID disproportionately affects premenopausal women, but relatively few studies have examined Long COVID's impact on female reproductive health. We conduct a review of the literature documenting the female reproductive health impacts of Long COVID which may include disruptions to the menstrual cycle, gonadal function, ovarian sufficiency, menopause, and fertility, as well as symptom exacerbation around menstruation. Given limited research, we also review the reproductive health impacts of overlapping and associated illnesses including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), postural orthostatic tachycardia syndrome (POTS), connective tissue disorders like Ehlers-Danlos syndrome (EDS), and endometriosis, as these illnesses may help to elucidate reproductive health conditions in Long COVID. These associated illnesses, whose patients are 70%-80% women, have increased rates of dysmenorrhea, amenorrhea, oligomenorrhea, dyspareunia, endometriosis, infertility, vulvodynia, intermenstrual bleeding, ovarian cysts, uterine fibroids and bleeding, pelvic congestion syndrome, gynecological surgeries, and adverse pregnancy complications such as preeclampsia, maternal mortality, and premature birth. Additionally, in Long COVID and associated illnesses, symptoms can be impacted by the menstrual cycle, pregnancy, and menopause. We propose priorities for future research and reproductive healthcare in Long COVID based on a review of the literature. These include screening Long COVID patients for comorbid and associated conditions; studying the impacts of the menstrual cycle, pregnancy, and menopause on symptoms and illness progression; uncovering the role of sex differences and sex hormones in Long COVID and associated illnesses; and addressing historical research and healthcare inequities that have contributed to detrimental knowledge gaps for this patient population.

Use of antihistamines before or during pregnancy and risk of early-onset pre-eclampsia in allergic women: a population-based cohort study

OBJECTIVE

We have previously found that allergy is a risk factor for early-onset pre-eclampsia. The aim of this study was to assess the association between pregestational maternal use of antihistamines and early-onset pre-eclampsia.

DESIGN

A population-based cohort study.

SETTING AND PARTICIPANTS

All women giving birth in Norway 2004-2016, including 692 487 pregnancies. Data from the Medical Birth Registry of Norway were linked with data from the Norwegian Prescription Database. Prescriptions of antihistamines were divided into three groups: before pregnancy (<6 months), early pregnancy (<20 weeks) and late pregnancy (20-36 weeks). ORs with 95% CIs for pre-eclampsia <34 and <37 weeks by antihistamine use were estimated by logistic regression and stratified on multiple pregnancy and parity. Predicted proportions (%) with 95% CIs were estimated.

INTERVENTIONS

Use of antihistamines in relation to pregnancy in allergic women.

MAIN OUTCOME MEASURES

Development of early-onset pre-eclampsia.

RESULTS

2997 (0.43%) and 5769 (0.83%) women had pre-eclampsia <34 and <37 weeks, respectively. Use of antihistamines before and in early pregnancy was associated with a risk of developing early-onset pre-eclampsia that was comparable to the background population (OR 1.0, 95% CI 0.8 to 1.2 and OR 0.9, 95% CI 0.7 to 1.1, respectively). Antihistamine use only in late pregnancy was not treated as exposure, but as an indicator of allergy, and was associated with an increased risk of early-onset pre-eclampsia (OR 1.8, 95% CI 1.5 to 2.2). Predicted proportions of pre-eclampsia <34 weeks were significantly lower in women using antihistamines before (0.41%, 95% CI 0.34 to 0.49) and in early pregnancy (0.37%, 95% CI 0.31 to 0.44), compared with women using antihistamines after placentation (0.69%, 95% CI 0.57 to 0.83). Results were similar for pre-eclampsia <37 weeks.

CONCLUSIONS

Antihistamine use before or during placentation was associated with reduced risk of developing early-onset pre-eclampsia in allergic women compared with women using antihistamines after placentation.

Research progress of placental vascular pathophysiological changes in pregnancy-induced hypertension and gestational diabetes mellitus

The placenta is a vital organ for fetal development, providing the fetus with nutrients, oxygen, and other important factors. Placenta is rich in blood vessels. Abnormal placental vascular function and blood circulation may lead to insufficient blood supply to the fetus in the uterus, leading to serious consequences such as pregnancy complications, fetal distress and even stillbirth. Pregnancy-induced hypertension (PIH) and gestational diabetes mellitus (GDM) are common complications of pregnancy. Recent studies report that pregnancy complications are often accompanied by changes in placental vascular structure and function. What are the physiological characteristics of human placental blood vessels? What are the pathological changes in the state of PIH and GDM? What are the relationships between these pathological changes and the occurrence of these pregnancy complications? Answers to these questions not only increase the understanding of placental vascular characteristics, but also provide important information for revealing the pathological mechanism of PIH and GDM. This article will summarize the research on the pathological changes of placental blood vessels in PIH and GDM, hoping to further unravel the physiological and pathological characteristics of placental blood vessels in the state of PIH and GDM, provide information for guiding clinical treatment for PIH and GDM.

Mast Cell Activation Syndrome in COVID-19 and Female Reproductive Function: Theoretical Background vs. Accumulating Clinical Evidence

Coronavirus disease 2019 (COVID-19), a pandemic disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, can affect almost all systems and organs of the human body, including those responsible for reproductive function in women. The multisystem inflammatory response in COVID-19 shows many analogies with mast cell activation syndrome (MCAS), and MCAS may be an important component in the course of COVID-19. Of note, the female sex hormones estradiol (E2) and progesterone (P4) significantly influence mast cell (MC) behavior. This review presents the importance of MCs and the mediators from their granules in the female reproductive system, including pregnancy, and discusses the mechanism of potential disorders related to MCAS. Then, the available data on COVID-19 in the context of hormonal disorders, the course of endometriosis, female fertility, and the course of pregnancy were compiled to verify intuitively predicted threats. Surprisingly, although COVID-19 hyperinflammation and post-COVID-19 illness may be rooted in MCAS, the available clinical data do not provide grounds for treating this mechanism as significantly increasing the risk of abnormal female reproductive function, including pregnancy. Further studies in the context of post COVID-19 condition (long COVID), where inflammation and a procoagulative state resemble many aspects of MCAS, are needed.

Network-Based Analysis Reveals Novel Biomarkers in Peripheral Blood of Patients With Preeclampsia

WGCNA is a potent systems biology approach that explains the connection of gene expression based on a microarray database, which facilitates the discovery of disease therapy targets or potential biomarkers. Preeclampsia is a kind of pregnancy-induced hypertension caused by complex factors. The disease’s pathophysiology, however, remains unknown. The focus of this research is to utilize WGCNA to identify susceptible modules and genes in the peripheral blood of preeclampsia patients. Obtain the whole gene expression data of GSE48424 preeclampsia patients and normal pregnant women from NCBI’s GEO database. WGCNA is used to construct a gene co-expression network by calculating correlation coefficients between modules and phenotypic traits, screening important modules, and filtering central genes. To identify hub genes, we performed functional enrichment analysis, pathway analysis, and protein-protein interaction (PPI) network construction on key genes in critical modules. Then, the genetic data file GSE149437 and clinical peripheral blood samples were used as a validation cohort to determine the diagnostic value of these key genes. Nine gene co-expression modules were constructed through WGCNA analysis. Among them, the blue module is significantly related to preeclampsia and is related to its clinical severity. Thirty genes have been discovered by using the intersection of the genes in the blue module and the DEGs genes as the hub genes. It was found that HDC, MS4A2, and SLC18A2 scored higher in the PPI network and were identified as hub genes. These three genes were also differentially expressed in peripheral blood validation samples. Based on the above three genes, we established the prediction model of peripheral blood markers of preeclampsia and drew the nomogram and calibration curve. The ROC curves were used in the training cohort GSE48424 and the validation cohort GSE149437 to verify the predictive value of the above model. Finally, it was confirmed in the collected clinical peripheral blood samples that MS4A2 was differentially expressed in the peripheral blood of early-onset and late-onset preeclampsia, which is of great significance. This study provides a new biomarker and prediction model for preeclampsia.

Interactions between Macrophages and Mast Cells in the Female Reproductive System

Mast cells (MCs) and macrophages (Mϕs) are innate immune cells that differentiate from early common myeloid precursors and reside in all body tissues. MCs have a unique capacity to neutralize/degrade toxic proteins, and they are hypothesized as being able to adopt two alternative polarization profiles, similar to Mϕs, with distinct or even opposite roles. Mϕs are very plastic phagocytic cells that are devoted to the elimination of senescent/anomalous endogenous entities (to maintain tissue homeostasis), and to the recognition and elimination of exogenous threats. They can adopt several functional phenotypes in response to microenvironmental cues, whose extreme profiles are the inflammatory/killing phenotype (M1) and the anti-inflammatory/healing phenotype (M2). The concomitant and abundant presence of these two cell types and the partial overlap of their defensive and homeostatic functions leads to the hypothesis that their crosstalk is necessary for the optimal coordination of their functions, both under physiological and pathological conditions. This review will examine the relationship between MCs and Mϕs in some situations of homeostatic regulation (menstrual cycle, embryo implantation), and in some inflammatory conditions in the same organs (endometriosis, preeclampsia), in order to appreciate the importance of their cross-regulation.

Insights into Early-Pregnancy Mechanisms: Mast Cells and Chymase CMA1 Shape the Phenotype and Modulate the Functionality of Human Trophoblast Cells, Vascular Smooth-Muscle Cells and Endothelial Cells

Spiral-artery (SA) remodeling is a fundamental process during pregnancy that involves the action of cells of the initial vessel, such as vascular smooth-muscle cells (VSMCs) and endothelial cells, but also maternal immune cells and fetal extravillous trophoblast cells (EVTs). Mast cells (MCs), and specifically chymase-expressing cells, have been identified as key to a sufficient SA-remodeling process in vivo. However, the mechanisms are still unclear. The purpose of this study is to evaluate the effects of the MC line HMC-1 and recombinant human chymase (rhuCMA1) on human primary uterine vascular smooth-muscle cells (HUtSMCs), a human trophoblast cell line (HTR8/SV-neo), and human umbilical-vein endothelial cells (HUVEC) in vitro. Both HMC-1 and rhuCMA1 stimulated migration, proliferation, and changed protein expression in HUtSMCs. HMC-1 increased proliferation, migration, and changed gene expression of HTR8/SVneo cells, while rhuCMA treatment led to increased migration and decreased expression of tissue inhibitors of matrix metalloproteinases. Additionally, rhuCMA1 enhanced endothelial-cell-tube formation. Collectively, we identified possible mechanisms by which MCs/rhuCMA1 promote SA remodeling. Our findings are relevant to the understanding of this crucial step in pregnancy and thus of the dysregulated pathways that can lead to pregnancy complications such as fetal growth restriction and preeclampsia.

The Placental Innate Immune System Is Altered in Early-Onset Preeclampsia, but Not in Late-Onset Preeclampsia

Preeclampsia is a severe placenta-related pregnancy disorder that is generally divided into two subtypes named early-onset preeclampsia (onset <34 weeks of gestation), and late-onset preeclampsia (onset ≥34 weeks of gestation), with distinct pathophysiological origins. Both forms of preeclampsia have been associated with maternal systemic inflammation. However, alterations in the placental immune system have been less well characterized. Here, we studied immunological alterations in early- and late-onset preeclampsia placentas using a targeted expression profile approach. RNA was extracted from snap-frozen placenta samples (healthy n=13, early-onset preeclampsia n=13, and late-onset preeclampsia n=6). The expression of 730 immune-related genes from the Pan Cancer Immune Profiling Panel was measured, and the data were analyzed in the advanced analysis module of nSolver software (NanoString Technology). The results showed that early-onset preeclampsia placentas displayed reduced expression of complement, and toll-like receptor (TLR) associated genes, specifically TLR1 and TLR4. Mast cells and M2 macrophages were also decreased in early-onset preeclampsia compared to healthy placentas. The findings were confirmed by an immunohistochemistry approach using 20 healthy, 19 early-onset preeclampsia, and 10 late-onset preeclampsia placentas. We conclude that the placental innate immune system is altered in early-onset preeclampsia compared to uncomplicated pregnancies. The absence of these alterations in late-onset preeclampsia placentas indicates dissimilar immunological profiles. The study revealed distinct pathophysiological processes in early-onset and late-onset preeclampsia placentas and imply that a tailored treatment to each subtype is desirable.

Cellular immune responses in the pathophysiology of preeclampsia

Preeclampsia, defined as new-onset hypertension accompanied by proteinuria occurring at 20 weeks of gestation or later, is a leading cause of perinatal morbidity and mortality worldwide. The pathophysiology of this major multi-systemic syndrome includes defective deep placentation, oxidative stress, endothelial dysfunction, the presence of an anti-angiogenic state, and intravascular inflammation, among others. In this review, we provide a comprehensive overview of the cellular immune responses involved in the pathogenesis of preeclampsia. Specifically, we summarize the role of innate and adaptive immune cells in the maternal circulation, reproductive tissues, and at the maternal-fetal interface of women affected by this pregnancy complication. The major cellular subsets involved in the pathogenesis of preeclampsia are regulatory T cells, effector T cells, NK cells, monocytes, macrophages, and neutrophils. We also summarize the literature on those immune cells that have been less characterized in this clinical condition, such as γδ T cells, invariant natural killer T cells, dendritic cells, mast cells, and B cells. Moreover, we discuss in vivo studies utilizing a variety of animal models of preeclampsia to further support the role of immune cells in this disease. Finally, we highlight the existing gaps in knowledge of the immunobiology of preeclampsia that require further investigation. The goal of this review is to promote translational research leading to clinically relevant strategies that can improve adverse perinatal outcomes resulting from the obstetrical syndrome of preeclampsia.

Mechanisms of Key Innate Immune Cells in Early- and Late-Onset Preeclampsia

Preeclampsia is a complex cardiovascular disorder of pregnancy with underlying multifactorial pathogeneses; however, its etiology is not fully understood. It is characterized by the new onset of maternal hypertension after 20 weeks of gestation, accompanied by proteinuria, maternal organ damage, and/or uteroplacental dysfunction. Preeclampsia can be subdivided into early- and late-onset phenotypes (EOPE and LOPE), diagnosed before 34 weeks or from 34 weeks of gestation, respectively. Impaired placental development in early pregnancy and subsequent growth restriction is often associated with EOPE, while LOPE is associated with maternal endothelial dysfunction. The innate immune system plays an essential role in normal progression of physiological pregnancy and fetal development. However, inappropriate or excessive activation of this system can lead to placental dysfunction or poor maternal vascular adaptation and contribute to the development of preeclampsia. This review aims to comprehensively outline the mechanisms of key innate immune cells including macrophages, neutrophils, natural killer (NK) cells, and innate B1 cells, in normal physiological pregnancy, EOPE and LOPE. The roles of the complement system, syncytiotrophoblast extracellular vesicles and mesenchymal stem cells (MSCs) are also discussed in the context of innate immune system regulation and preeclampsia. The outlined molecular mechanisms, which represent potential therapeutic targets, and associated emerging treatments, are evaluated as treatments for preeclampsia. Therefore, by addressing the current understanding of innate immunity in the pathogenesis of EOPE and LOPE, this review will contribute to the body of research that could lead to the development of better diagnosis, prevention, and treatment strategies. Importantly, it will delineate the differences in the mechanisms of the innate immune system in two different types of preeclampsia, which is necessary for a more personalized approach to the monitoring and treatment of affected women.

Human Placental Vascular Reactivity in Health and Disease: Implications for the Treatment of Pre-eclampsia

Adequate development of the placenta is essential for optimal pregnancy outcome. Pre-eclampsia (PE) is increasingly recognized to be a consequence of placental dysfunction and can cause serious maternal and fetal complications during pregnancy. Furthermore, PE increases the risk of neonatal problems and has been shown to be a risk factor for cardiovascular disease of the mother later in life. Currently, there is no adequate treatment for PE, mainly because its multifactorial pathophysiology remains incompletely understood. It originates in early pregnancy with abnormal placentation and involves a cascade of dysregulated systems in the placental vasculature. To investigate therapeutic strategies it is essential to understand the regulation of vascular reactivity and remodeling of blood vessels in the placenta. Techniques using human tissue such as the ex vivo placental perfusion model provide insight in the vasoactive profile of the placenta, and are essential to study the effects of drugs on the fetal vasculature. This approach highlights the different pathways that are involved in the vascular regulation of the human placenta, changes that occur during PE and the importance of focusing on restoring these dysfunctional systems when studying treatment strategies for PE.

Immune Cells in the Uterine Remodeling: Are They the Target of Endocrine Disrupting Chemicals?

Sufficient uterine remodeling is essential for fetal survival and development. Pathologies related to poor remodeling have a negative impact on maternal and fetal health even years after birth. Research of the last decades yielded excellent studies demonstrating the key role of immune cells in the remodeling processes. This review summarizes the current knowledge about the relevance of immune cells for uterine remodeling during pregnancy and further discusses immunomodulatory effects of man-made endocrine disrupting chemicals on immune cells.

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.

What is precise pathophysiology in development of hypertension in pregnancy? Precision medicine requires precise physiology and pathophysiology

It is widely accepted that placental ischemia is central in the evolution of hypertension in pregnancy. Many studies and reviews have targeted placental ischemia to explain mechanisms for initiating pregnancy hypertension. The placenta is rich in blood vessels, which are the basis for developing placental ischemia. However, is the physiology of placental vessels the same as that of nonplacental vessels? What is the pathophysiology of placental vessels in development of pregnancy hypertension? This review aims to provide a comprehensive summary of special features of placental vascular regulations and the pathophysiological changes linked to preeclamptic conditions. Interestingly, some popular theories or accepted concepts could be based on our limited knowledge and evidence regarding placental vascular physiology, pharmacology and pathophysiology. New views raised could offer interesting ideas for future investigation of mechanisms as well as targets for pregnancy hypertension.

Significance of mast cell distribution in placental tissue and membranes in spontaneous preterm birth

Background

Preterm birth is a common cause of adverse neonatal and childhood outcomes, in both the short and long term. Preterm labor is commonly associated with inflammation at the maternal–fetal interface. There is some indirect evidence that mast cells (MCs) might represent a link between hormonal influences and local reactions leading to the onset of labor.

Patients and methods

The placentas and membranes of 51 uncomplicated spontaneous term births were compared to those from 50 spontaneous preterm births. Immunohistochemical staining for MC tryptase was undertaken allowing MC concentration, location, and degranulation status to be determined. Regression modeling was used to compare results.

Results

There were no significant differences in the demographic characteristics of the two cohorts. There were significantly more MCs in the decidua for term births than preterm births (P=0.03). The presence of histological chorioamnionitis did not affect MC concentrations.

Conclusion

Despite evidence suggesting a possible role for MCs in spontaneous preterm birth, this study found that the concentration of decidual MCs was in fact significantly lower in preterm compared to term birth.

Preeclampsia and future cardiovascular risk: A point of view from the clearance of plasma vasoactive amines

OBJECTIVE

To summarize the reported evidence on the relationship between vasoactive amines and preeclampsia.

METHODS

A literature search was conducted in MEDLINE/PubMed and EMBASE.

RESULTS

The summarized results are as follows: (1) Menstruation can effectively eliminate vasoactive amines norepinephrine, serotonin and histamine. (2) Pregnancy increases norepinephrine production due to fetal brain development and decreases vasoactive-amine elimination due to amenorrhea. (3) Preeclampsia is associated with a low renal and/or sweating capacity, or in rare cases, with increased norepinephrine production due to maternal pheochromocytoma and fetal neuroblastoma.

CONCLUSION

Preeclampsia is mainly due to decreased excretion of norepinephrine and other vasoactive amines.

Genetic recapitulation of human pre-eclampsia risk during convergent evolution of reduced placental invasiveness in eutherian mammals

The relationship between phenotypic variation arising through individual development and phenotypic variation arising through diversification of species has long been a central question in evolutionary biology. Among humans, reduced placental invasion into endometrial tissues is associated with diseases of pregnancy, especially pre-eclampsia, and reduced placental invasiveness has also evolved, convergently, in at least 10 lineages of eutherian mammals. We tested the hypothesis that a common genetic basis underlies both reduced placental invasion arising through a developmental process in human placental disease and reduced placental invasion found as a derived trait in the diversification of Euarchontoglires (rodents, lagomorphs, tree shrews, colugos and primates). Based on whole-genome analyses across 18 taxa, we identified 1254 genes as having evolved adaptively across all three lineages exhibiting independent evolutionary transitions towards reduced placental invasion. These genes showed strong evidence of enrichment for associations with pre-eclampsia, based on genetic-association studies, gene-expression analyses and gene ontology. We further used in silico prediction to identify a subset of 199 genes that are likely targets of natural selection during transitions in placental invasiveness and which are predicted to also underlie human placental disorders. Our results indicate that abnormal ontogenies can recapitulate major phylogenetic shifts in mammalian evolution, identify new candidate genes for involvement in pre-eclampsia, imply that study of species with less-invasive placentation will provide useful insights into the regulation of placental invasion and pre-eclampsia, and recommend a novel comparative functional-evolutionary approach to the study of genetically based human disease and mammalian diversification.

Transfer of regulatory T cells into abortion-prone mice promotes the expansion of uterine mast cells and normalizes early pregnancy angiogenesis

Implantation of the fertilized egg depends on the coordinated interplay of cells and molecules that prepare the uterus for this important event. In particular, regulatory T cells (Tregs) are key regulators as their ablation hinders implantation by rendering the uterus hostile for the embryo. In addition, the adoptive transfer of Tregs can avoid early abortion in mouse models. However, it is still not defined which mechanisms underlie Treg function during this early period. Cells of the innate immune system have been reported to support implantation, in part by promoting angiogenesis. In particular, uterine mast cells (uMCs) emerge as novel players at the fetal-maternal interface. Here, we studied whether the positive action of Tregs is based on the expansion of uMCs and the promotion of angiogenesis. We observed that abortion-prone mice have insufficient numbers of uMCs that could be corrected by the adoptive transfer of Tregs. This in turn positively influenced the remodeling of spiral arteries and placenta development as well as the levels of soluble fms-like tyrosine kinase 1 (sFlt-1). Our data suggest an interplay between Tregs and uMCs that is relevant for the changes required at the feto-maternal interface for the normal development of pregnancy.