Evidence for immune cell involvement in decidual spiral arteriole remodeling in early human pregnancy

Uterine Spiral Artery Remodeling: The Role of Uterine Natural Killer Cells and Extravillous Trophoblasts in Normal and High-Risk Human Pregnancies

The process of uterine spiral artery remodeling in the first trimester of human pregnancy is an essential part of establishing adequate blood perfusion of the placenta that will allow optimal nutrient/waste exchange to meet fetal demands during later development. Key regulators of spiral artery remodeling are the uterine natural killer cells and the invasive extravillous trophoblasts. The functions of these cells as well as regulation of their activation states and temporal regulation of their localization within the uterine tissue are beginning to be known. In this review, we discuss the roles of these two cell lineages in arterial remodeling events, their interaction/influence on one another and the outcomes of altered temporal, and spatial regulation of these cells in pregnancy complications.

M1/M2 macrophage polarity in normal and complicated pregnancy

Tissue macrophages play an important role in all stages of pregnancy, including uterine stromal remodeling (decidualization) before embryo implantation, parturition, and post-partum uterine involution. The activation state and function of utero-placental macrophages are largely dependent on the local tissue microenvironment. Thus, macrophages are involved in a variety of activities such as regulation of immune cell activities, placental cell invasion, angiogenesis, and tissue remodeling. Disruption of the uterine microenvironment, particularly during the early stages of pregnancy (decidualization, implantation, and placentation) can have profound effects on macrophage activity and subsequently impact pregnancy outcome. In this review, we will provide an overview of the temporal and spatial regulation of utero-placental macrophage activation during normal pregnancy in human beings and rodents with a focus on more recent findings. We will also discuss the role of M1/M2 dysregulation within the intrauterine environment during adverse pregnancy outcomes.

Ultrastructure alteration of decidual natural killer cells in women with unexplained recurrent miscarriage: a possible association with impaired decidual vascular remodelling

This study aimed to evaluate the extent of remodelling of intra-decidual segments of the spiral arteries in human deciduas between the 6th and 10th gestational weeks in women with unexplained recurrent miscarriages (RM) in comparison to gestational-matched controls. A possible association with the number, immunoexpressive behaviour and ultrastructural changes of decidual natural killer cells (dNKCs) was investigated. Decidual biopsies were obtained from RM cases (n = 40) and women with no history of spontaneous miscarriage and at least one live birth at term (n = 30). Staining was performed using PAS, anti-CD34 and anti-CD56 antibodies, using an avidin-biotin-peroxides technique. Analysis by means of light and transmission electron microscopy was employed. To determine the extent of remodelling of decidual vessels, a quantitative score was analysed using histological criteria of vascular transformation and then related to the number of CD56(+) dNKCs. In RM, dNKCs were distributed among decidual cells and around the vessels. They possessed numerous polyploidic protrusions on cell membranes crossing from one cell to another. The cells became more irregular and exhibited heterogeneous electron-dense granules in their cytoplasm compared to controls. The non-remodelling score and number of dNKCs were significantly increased in RM group (p < 0.001). The number of dNKCs was significantly correlated with the scores in both control (r = 0.491; p = 0.006) and RM (r = 0.852; p < 0.001) groups. It appears that dNKCs play a key role in impaired decidual artery remodelling that may be involved with early RM. This may be due to increased numbers of cells or impaired cellular interactions resulting from alterations to the ultrastructure.

Insights into the paracrine effects of uterine natural killer cells

Uterine natural killer (uNK) cells are recruited into the uterus during establishment of the implantation and placentation of the embryo, and are hypothesized to regulate uterine spiral artery remodeling and angiogenesis during the initial stages of pregnancy. Failures in uNK cell activation are linked to diseases associated with pregnancy. However, the manner in which these cells interact with the endometrium remain unknown. Therefore, this study investigated the paracrine effects of uNK cells on the gene expression profile of an endometrial epithelial and stromal cell co‑culture system in vitro, using a microarray analysis. Results from reverse transcription‑quantitative polymerase chain reaction and enzyme‑linked immunosorbent assay experiments showed that soluble factors from uNK cells significantly alter endometrial gene expression. In conclusion, this study suggests that paracrine effects of uNK cells guide uNK cell proliferation, trophoblast migration, endometrial decidualization and angiogenesis, and maintain non‑cytotoxicity of uNK cells.

Dynamic changes in maternal decidual leukocyte populations from first to second trimester gestation

INTRODUCTION

Decidual leukocytes are critical to the development of the fetomaternal interface, regulating tolerance to the semi-allogeneic fetus and vascular transformation of the uterine spiral arteries. Despite the continuation of these processes beyond the first trimester of pregnancy, the second trimester has largely been unstudied, with investigation focusing on early gestation and term tissues. We sought to characterize changes in decidual leukocyte populations from first to second trimester.

METHODS

Multicolor flow cytometry was performed on isolated decidual leukocytes from elective terminations of pregnancy between 6 and 20 weeks of gestation for study of first (6-12 weeks) and second trimesters (13-20 weeks). Specific subpopulations were identified by comparison to isotype and fluorescent-minus-one (FMO) controls.

RESULTS

Decidual natural killer cells (CD56(+)CD16(-)CD3(-)) did not change in number, although a population of dNK with decreased CD56 brightness was observed in second trimester decidua. CD14(+)HLA-DR(+) macrophage numbers declined from first to second trimester (p = 0.031), yet a CD163(+)CD206(+) subset designating alternatively activated M2-like macrophages increased during the same period (p = 0.015). Intermediate CD205(+) dendritic cells demonstrated significant decline (p = 0.022), but immature CD209(+) and mature CD83(+) dendritic cells did not differ between trimesters. Total CD3(+) and CD3(+)CD4(+) T lymphocytes increased (p = 0.0079, p = 0.0028); CD3(+)CD8(+) T cells trended towards increase but did not differ significantly.

CONCLUSION

Several changes in leukocyte subsets are observed in the second trimester that promote a tolerogenic and angiogenic decidual microenvironment through mid-gestation.

Elastin-derived peptides stimulate trophoblast migration and invasion: a positive feedback loop to enhance spiral artery remodelling

Elastin breakdown in the walls of uterine spiral arteries during early pregnancy facilitates their transformation into dilated, high-flow, low-resistance channels. Elastin-derived peptides (EDP) can influence cell migration, invasion and protease activity, and so we hypothesized that EDP released during elastolysis promote extravillous trophoblast (EVT) invasion and further elastin breakdown. Treatment of the trophoblast cell line SGHPL4 with the elastin-derived matrikine VGVAPG (1 μg/ml) significantly increased total elastase activity, promoted migration in a wound healing assay and increased invasion through Matrigel-coated transwells compared with vehicle control (0.1% DMSO) or the scrambled sequence VVGPGA. Furthermore, treatment of first-trimester placental villous explants with this EDP significantly increased both the area of trophoblast outgrowth and distance of migration away from the villous tips. Primary first-trimester cytotrophoblast exposed to VGVAPG (1 μg/ml) for 30 min showed increased phosphorylation of endothelial nitric oxide synthase and activation of the mitogen activated protein kinase pathway, events also associated with tumour cell migration and invasion. These in vitro observations suggest liberation of bioactive EDP during induction of elastolysis in the uterine spiral arteries may orchestrate a positive feedback loop that promotes EVT invasion and further elastin breakdown, contributing to the process of vascular remodelling.

Placental disease and the maternal syndrome of preeclampsia: missing links?

Preeclampsia remains a significant obstetric risk worldwide. The pathophysiology of preeclampsia is complex, with multiple stages involving maladaptations in both placental and maternal physiology. The placenta links the pre-clinical stage of impaired remodeling of the uterine vasculature, occurring in early pregnancy, to the later clinical stages characterised by the maternal syndrome of hypertension and proteinuria. This review focuses on some of the recent candidates for the missing links in this process.

Identification of a novel neutrophil population: proangiogenic granulocytes in second-trimester human decidua

The maternal leukocytes of the first-trimester decidua play a fundamental role in implantation and early development of the fetus and placenta, yet little is known regarding the second-trimester decidual environment. Our multicolor flow cytometric analyses of human decidual leukocytes detected an elevation in tissue resident neutrophils in the second trimester. These cells in both human and murine samples were spatially restricted to decidua basalis. In comparison with peripheral blood neutrophils (PMNs), the decidual neutrophils expressed high levels of neutrophil activation markers and the angiogenesis-related proteins: vascular endothelial growth factor-A, Arginase-1, and CCL2, similarly shown in tumor-associated neutrophils. Functional in vitro assays showed that second-trimester human decidua conditioned medium stimulated transendothelial PMN invasion, upregulated VEGFA, ARG1, CCL2, and ICAM1 mRNA levels, and increased PMN-driven in vitro angiogenesis in a CXCL8-dependent manner. This study identified a novel neutrophil population with a physiological, angiogenic role in human decidua.

Leukocyte driven-decidual angiogenesis in early pregnancy

Successful pregnancy and long-term, post-natal maternal and offspring cardiac, vascular and metabolic health require key maternal cardiovascular adaptations over gestation. Within the pregnant decidualizing uterus, coordinated vascular, immunological and stromal cell changes occur. Considerable attention has been given to the roles of uterine natural killer (uNK) cells in initiating decidual spiral arterial remodeling, a process normally completed by mid-gestation in mice and in humans. However, leukocyte roles in much earlier, region specific, decidual vascular remodeling are now being defined. Interest in immune cell-promoted vascular remodeling is driven by vascular aberrations that are reported in human gestational complications such as infertility, recurrent spontaneous abortion, preeclampsia (PE) and fetal growth restriction. Appropriate maternal cardiovascular responses during pregnancy protect mothers and their children from later cardiovascular disease risk elevation. One of the earliest uterine responses to pregnancy in species with hemochorial placentation is stromal cell decidualization, which creates unique niches for angiogenesis and leukocyte recruitment. In early decidua basalis, the aspect of the implantation site that will cradle the developing placenta and provide the major blood vessels to support mature placental functions, leukocytes are greatly enriched and display specialized properties. UNK cells, the most abundant leukocyte subset in early decidua basalis, have angiogenic abilities and are essential for normal early decidual angiogenesis. The regulation of uNK cells and their roles in determining maternal and progeny cardiovascular health over pregnancy and postpartum are discussed.

Interferon-γ protects first-trimester decidual cells against aberrant matrix metalloproteinases 1, 3, and 9 expression in preeclampsia

Human extravillous trophoblast (EVT) invades the decidua via integrin receptors and subsequently degrades extracellular matrix proteins. In preeclampsia (PE), shallow EVT invasion elicits incomplete spiral artery remodeling, causing reduced uteroplacental blood flow. Previous studies show that preeclamptic decidual cells, but not interstitial EVTs, display higher levels of extracellular matrix-degrading matrix metalloproteinase (MMP)-9, but not MMP-2. Herein, we extend our previous PE-related assessment of MMP-2 and MMP-9 to include MMP-1, which preferentially degrades fibrillar collagens, and MMP-3, which can initiate a local proteolytic cascade. In human first-trimester decidual cells incubated with estradiol, tumor necrosis factor-α (TNF-α) significantly enhanced MMP-1, MMP-3, and MMP-9 mRNA and protein levels and activity measured by real-time quantitative RT-PCR, ELISA, immunoblotting, and zymography, respectively. In contrast, interferon γ (IFN-γ) reversed these effects and medroxyprogesterone acetate elicited further reversal. Immunoblotting revealed that p38 mitogen-activated protein kinase signaling mediated TNF-α enhancement of MMP-1, MMP-3, and MMP-9, whereas IFN-γ inhibited p38 mitogen-activated protein kinase phosphorylation. Unlike highly regulated MMP-1, MMP-3, and MMP-9, MMP-2 mRNA and protein expression was constitutive in decidual cells. Because inflammation underlies PE-associated shallow EVT invasion, these results suggest that excess macrophage-derived TNF-α augments expression of MMP-1, MMP-3, and MMP-9 in decidual cells to interfere with normal stepwise EVT invasion of the decidua. In contrast, decidual natural killer cell-derived IFN-γ reverses such TNF-α-induced MMPs to protect against PE.

Relationship between macrophages in mouse uteri and angiogenesis in endometrium during the peri-implantation period

The objective of this study is to examine the change in macrophage numbers, inducible form of NO synthase (iNOS), and vascular endothelial growth factor (VEGF) expression both before and after embryo implantation in the uterine tissue of mice. In order to explore the mechanism of macrophages in endometrial angiogenesis, 8-week-old female mice were divided into three groups: pregnant group, pseudopregnant group (mated to male mice that had been vasectomized), and estrous group (unmated). Individuals from these three groups were sacrificed at time intervals D1.5 to D6.5. Formalin-fixed paraffin-embedded tissue was used for immunocytochemical localization of Mφ, iNOS, and VEGF utilizing standard methodology. The proportion of macrophages in the peripheral blood was determined by flow cytometry, and the relationship between macrophage, iNOS, and VEGF expression was analyzed. The proportion of peripheral blood macrophages in the pregnancy group was significantly higher than that in the other groups. The results of immunohistochemistry determined that the macrophages exhibited changes in both numbers and distribution. The number of macrophages in the endometrium of the pregnancy and pseudopregnancy groups was significantly higher than that in the control (estrous) group. In the pregnancy group, macrophage numbers dramatically decreased and gradually transferred to the perimetrium on D4.5. Immunostaining revealed strong staining in the pregnancy group and weaker staining in the pseudopregnant and control groups for both iNOS and VEGF. There was strong, dense immunostaining at the implantation site for both iNOS and VEGF, whereas light immunostaining was seen in interimplantation tissues on D5.5 to D6.5. In the pregnant group, peripheral blood and uterine macrophage proportions were negatively correlated, whereas the amount of macrophages, iNOS, and VEGF expression in the endometrium were positively correlated. The expression of iNOS and VEGF in the endometrium also displayed a strong positive correlation. In conclusion, during embryo implantation, macrophages levels decreased in the uterus, whereas the number of peripheral macrophages increased, suggesting that macrophages may migrate into the peripheral blood and uterus to adapt for pregnancy. Additionally, an increase in the expression of iNOS and VEGF was observed during the implantation window, implying that iNOS and VEGF may play an important role in promoting embryo implantation. The positive correlation between macrophages, iNOS, and VEGF in the implanting uterus implied that macrophages might regulate iNOS and VEGF during the implantation process.

Monocytes and macrophages in pregnancy and pre-eclampsia

Preeclampsia is an important complication in pregnancy, characterized by hypertension and proteinuria in the second half of pregnancy. Generalized activation of the inflammatory response is thought to play a role in the pathogenesis of pre-eclampsia. Monocytes may play a central role in this inflammatory response. Monocytes are short lived cells that mature in the circulation and invade into tissues upon an inflammatory stimulus and develop into macrophages. Macrophages are abundantly present in the endometrium and play a role in implantation and placentation in normal pregnancy. In pre-eclampsia, these macrophages appear to be present in larger numbers and are also activated. In the present review, we focused on the role of monocytes and macrophages in the pathophysiology of pre-eclampsia.

First trimester screening can predict adverse pregnancy outcomes

There has been an increasing drive over the last two decades to push the detection of women at risk of adverse pregnancy outcomes into the first trimester. This has led to a plethora of techniques, risk assessments and biomarkers, both fascinating and bewildering in its breadth. Despite the vast amount of knowledge available, it is often difficult to determine what is practicable and valuable for clinical practice. This is especially true as earlier diagnosis does not necessarily equate to improved outcomes for mother and child. We suggest that, at least for preeclampsia, fetal growth restriction, spontaneous preterm birth and gestational diabetes, there are effective first trimester tests available to identify the women at risk of subsequently developing complications. Unfortunately, there are no currently reliable first trimester tests available for identifying women at risk of stillbirth. It is likely that this field will continue to develop over time, and we hope that new and better strategies will continue to emerge to target these clinically important pathologies.

Effect of factors produced by the placenta on cytokine secretion by THP-1 cells cultured on a 3D scaffold

We compared the effects of soluble products from the placenta obtained from women with normal pregnancy and pregnancy complicated by preeclampsia on cytokine secretion by THP-1 cells cultured on a 3D Matrigel scaffold. In the presence of soluble products from all placentas, the cells actively secreted IL-8, MCP-1, and soluble forms of CD14, TNFRI, and TNFRII receptors. Secretion of VEGF was below the spontaneous level. Secretion of IL-6 by THP-1 cells after incubation with soluble products of the placentas obtained during weeks 9-11 of physiological pregnancy and 38-39 of pregnancy complicated by preeclampsia surpassed the spontaneous level. In the presence of soluble factors of trimester I placentas, secretion of IL-6 and soluble form of TNFRI receptor was higher than in the presence of trimester III placental factors. Secretion of IL-6 by THP-1 cells was higher, while secretion of soluble TNFRII receptor was lower in the presence of placentas from women with preeclampsia in comparison with physiological pregnancy.

Major histocompatibility complex I mediates immunological tolerance of the trophoblast during pregnancy and may mediate rejection during parturition

During pregnancy in larger mammals, the maternal immune system must tolerate the fetus for months while resisting external infection. This tolerance is facilitated by immunological communication between the fetus and the mother, which is mediated by Major Histocompatibility Complex I (MHC I) proteins, by leukocytes, and by the cytokines secreted by the leukocytes. Fetal-maternal immunological communication also supports pregnancy by inducing physiological changes in the mother. If the mother “misunderstands” the signal sent by the fetus during pregnancy, the fetus will be miscarried or delivered preterm. Unlike any other maternal organ, the placenta can express paternal antigens. At parturition, paternal antigens are known to be expressed in cows and may be expressed in horses, possibly so that the maternal immune system will reject the placenta and help to expel it. This review compares fetal-maternal crosstalk that is mediated by the immune system in three species with pregnancies that last for nine months or longer: humans, cattle, and horses. It raises the possibility that immunological communication early in pregnancy may prepare the mother for successful expulsion of fetal membranes at parturition.

Innate and adaptive immune interactions at the fetal-maternal interface in healthy human pregnancy and pre-eclampsia

Maternal immune tolerance of the fetus is indispensable for a healthy pregnancy outcome. Nowhere is this immune tolerance more important than at the fetal–maternal interface – the decidua, the site of implantation, and placentation. Indeed, many lines of evidence suggest an immunological origin to the common pregnancy-related disorder, pre-eclampsia. Within the innate immune system, decidual NK cells and antigen presenting cells (including dendritic cells and macrophages) make up a large proportion of the decidual leukocyte population, and are thought to modulate vascular remodeling and trophoblast invasion. On the other hand, within the adaptive immune system, Foxp3⁺ regulatory T cells are crucial for ensuring immune tolerance toward the semi-allogeneic fetus. Additionally, another population of CD4⁺HLA-G⁺ suppressor T cells has also been identified as a potential player in the maintenance of immune tolerance. More recently, studies are beginning to unravel the potential interactions between the innate and the adaptive immune system within the decidua, that are required to maintain a healthy pregnancy. In this review, we discuss the recent advances exploring the complex crosstalk between the innate and the adaptive immune system during human pregnancy.

Decidual cell regulation of natural killer cell-recruiting chemokines: implications for the pathogenesis and prediction of preeclampsia

First trimester human decidua is composed of decidual cells, CD56(bright)CD16(-) decidual natural killer (dNK) cells, and macrophages. Decidual cells incubated with NK cell-derived IFN-γ and either macrophage-derived TNF-α or IL-1β synergistically enhanced mRNA and protein expression of IP-10 and I-TAC. Both chemokines recruit CXCR3-expressing NK cells. This synergy required IFN-γ receptor 1 and 2 mediation via JAK/STAT and NFκB signaling pathways. However, synergy was not observed on neutrophil, monocyte, and NK cell-recruiting chemokines. Immunostaining of first trimester decidua localized IP-10, I-TAC, IFN-γR1, and -R2 to vimentin-positive decidual cells versus cytokeratin-positive interstitial trophoblasts. Flow cytometry identified high CXCR3 levels on dNK cells and minority peripheral CD56(bright)CD16(-) pNK cells and intermediate CXCR3 levels on the majority of CD56(dim)CD16(+) pNK cells. Incubation of pNK cells with either IP-10 or I-TAC elicited concentration-dependent enhanced CXCR3 levels and migration of both pNK cell subsets that peaked at 10 ng/mL, whereas each chemokine at a concentration of 50 ng/mL inhibited CXCR3 expression and pNK cell migration. Deciduae from women with preeclampsia, a leading cause of maternal and fetal morbidity and mortality, displayed significantly lower dNK cell numbers and higher IP-10 and I-TAC levels versus gestational age-matched controls. Significantly elevated IP-10 levels in first trimester sera from women eventually developing preeclampsia compared with controls, identifying IP-10 as a novel, robust early predictor of preeclampsia.

Uterine artery impedance at very early clinical pregnancy

OBJECTIVE

The aim of the study was to construct gestational age-based reference ranges for the uterine artery (UtA) mean pulsatility (PI) and resistance (RI) indices from 6 to 10 weeks of pregnancy.

METHOD

A prospective, cross-sectional, observational study was carried out in 312 singleton pregnancies with gestational age ranging from 6 to 10 weeks. UtAs were examined transvaginally by color and pulsed Doppler imaging, and the mean of the right and left values of PI and RI, as well as the presence or absence of a bilateral protodiastolic notch, was recorded. UtA-PI and UtA-RI reference percentiles were derived through time-conditional quantile regression.

RESULTS

The authors derived the 10th, 50th, and 90th reference percentile curves and correspondent 95% confidence intervals, for the evolution of the UtA mean PI and RI from week 6 to week 10 of gestation. The prevalence of bilateral notching absence was 8.1% (6/74) at 6 weeks and 28.8% (15/52) at 10 weeks.

CONCLUSION

The authors present evidence of progressive reduction of uterine vascular impedance in a very early stage of pregnancy and provide new, averaged UtA-PI and UtA-RI charts between 6 and 10 weeks of gestation.

Increased angiogenic factor secretion by decidual natural killer cells from pregnancies with high uterine artery resistance alters trophoblast function

STUDY QUESTION

Are the concentrations of factors secreted by decidual natural killer (dNK) cells from pregnancies at high risk of poor spiral artery remodelling different to those secreted from pregnancies at low risk?

SUMMARY ANSWER

Expression levels of PLGF, sIL-2R, endostatin and angiogenin were significantly increased by dNK cells from high-risk pregnancies, and angiogenin and endostatin were found to alter trophoblast function.

WHAT IS KNOWN ALREADY

During early pregnancy, maternal uterine spiral arteries are remodelled from small diameter, low-flow, high-resistance vessels into larger diameter, higher flow vessels, with low-resistance. This change is essential for the developing fetus to obtain sufficient oxygen and nutrients. dNK cells have been implicated in this process.

STUDY DESIGN, SIZE, DURATION

dNK cells were isolated from first trimester terminations of pregnancies (obtained with local ethical approval) screened for normal- or high-resistance index, indicative of cases least (<1%) and most (>21%) likely to have developed pre-eclampsia had the pregnancy not been terminated (n = 18 each group). Secreted factors and the effects of these on the trophoblast cell line, SGHPL-4, were assessed in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A multiplex assay was used to assess dNK cell-secreted factors. SGHPL-4 cell functions were assessed using time-lapse microscopy, 3D invasion assays, endothelial-like tube formation ability and western blot analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

The expression levels of PLGF (P < 0.01), sIL-2R (P < 0.01), endostatin (P < 0.05) and angiogenin (P < 0.05) were significantly increased by dNK cells from high-risk pregnancies. Endostatin significantly decreased SGHPL-4 invasion (P < 0.05), SGHPL-4 tube formation (P < 0.05) and SGHPL-4 Akt^ser473 phosphorylation (P < 0.05). Angiogenin significantly decreased SGHPL-4 invasion (P < 0.05), but increased SGHPL-4 tube formation (P < 0.01) and decreased SGHPL-4 Akt^ser473 phosphorylation (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

The culture of dNK cells and protein concentrations in vitro may not fully represent the in vivo situation. Although SGHPL-4 cells are extravillous trophoblast derived, further studies would be needed to confirm the roles of angiogenin and endostatin in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

The altered expression of secreted factors of dNK cells may contribute to pregnancy disorders associated with poor spiral artery remodelling.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Wellcome Trust (project reference 091550). R.F. was a recipient of a PhD studentship from the Division of Biomedical Sciences, St. George's, University of London. The authors have no conflict of interests.

Gene expression profiling of the paracrine effects of uterine natural killer cells on human endometrial epithelial cells

The endometrium contains a population of immune cells that undergo changes during implantation and pregnancy. The majority of these cells are uterine natural killer (uNK) cells; however, it is unclear how these cells interact with endometrial epithelial cells. Therefore, we investigated the paracrine effects of the uNK cell-secretion medium on the gene expression profile of endometrial epithelial cells in vitro through microarray analysis. Our results, which were verified by qRT-PCR and western blot, revealed that soluble factors from uNK cells alter the gene expression profiles of epithelial cells. The upregulated genes included interleukin-15 (IL-15) and interleukin-15 receptor alpha (IL-15RA), which result in a loop that stimulates uNK cell proliferation. In addition, vascular endothelial growth factor C (VEGF-C) and chemokine (C-X-C motif) ligand 10 (CXCL-10) were also determined to be upregulated in epithelial cells, which suggests that uNK cells work synergistically with epithelial cells to support implantation and pregnancy. In addition, oriental herbal medicines have been used to treat infertility since ancient times; however, we failed to find that Zi Dan Yin can regulate these endometrial paracrine effects.

Review: the ADAM metalloproteinases - novel regulators of trophoblast invasion?

During pregnancy, the extravillous trophoblast (EVT) invades the maternal decidua and remodels spiral arteries reaching as far as the inner third of the myometrium. This process is mandatory to a successful pregnancy since EVTs regulate spiral artery remodeling to achieve maximal vasodilation and thus an adequate nutrient supply to the embryo or communicate with maternal leukocyte populations to guarantee acceptance of the allogeneic conceptus. To achieve this, EVTs undergo a remarkable and unique differentiation process, which yields different phenotypes such as proliferative cell column trophoblasts or growth-arrested, invasive interstitial or endovascular cytotrophoblasts. Matrix metalloproteinases have long been seen as imperative to trophoblast invasion because of their ability to degrade extracellular matrix and therefore allow cellular movement in foreign tissues. However, global gene expression analysis reveals that EVTs also express various members of distintegrin and metalloproteinases (ADAMs). These proteases are associated with the process of proteolytic shedding and activation of surface proteins including growth factors, cytokines, receptors and their ligands rather than extracellular matrix breakdown. While ADAM12 has been associated with chromosomal abnormalities as well as preeclampsia or intrauterine fetal growth restriction, the function of ADAMs in trophoblasts remains elusive. In this article, we review the diverse invasive trophoblast phenotypes, EVT-associated protease systems and related open questions. In addition, we examine recent information about relevant ADAM members and their putative implications for EVT biology.

AGEs, contributors to placental bed vascular changes leading to preeclampsia

Glycation of proteins or other biomolecules and their further long-term degradation result in the formation of advanced glycation end products, AGEs. AGEs and other ligands interact with their receptors, RAGEs, localized to a variety of tissues, but mainly in endothelium and vascular wall cells. This interaction triggers diverse signaling pathways that converge on the activation of NF-κB and the initiation of a local inflammatory reaction that, when prolonged, results in dysfunctional features. Preeclampsia is a serious vascular disorder centred at the placenta-uterine interface, the placental bed, but the condition extends to the mother's circulation. RAGEs have notorious expression in the placental bed tissues along pregnancy but, in addition, RAGEs and their ligands are expressed in the fetal membranes and are found in the amniotic fluid and the mother's serum. Disorders complicating pregnancies and having an important vascular involvement, as preeclampsia and diabetes mellitus, have additional enhanced AGE/RAGE expression variation. This indicates that for their assessment, the assay of RAGEs or their ligands may become useful diagnostic or prognostic procedures.

Decidual natural killer cell interactions with trophoblasts are impaired in pregnancies at increased risk of preeclampsia

Transformation of the uterine spiral arteries (SAs) during pregnancy is critical to support the developing fetus, and is impaired in some pregnancy disorders, including preeclampsia. Decidual natural killer (dNK) cells play a role in SA remodeling, although their interactions with fetal trophoblast remain unclear. A uterine artery Doppler resistance index (RI) in the first trimester of pregnancy can be used as a proxy measure of the extent of SA remodeling; we have used this technique to characterize dNK cells from pregnancies with normal (normal RI) and impaired (high RI) SA remodeling, which display least and highest risk of developing preeclampsia, respectively. We examined the impact of dNK cell secreted factors on trophoblast motility, chemoattraction, and signaling pathways to determine the contribution of dNK cells to SA transformation. We demonstrated that the chemoattraction of the trophoblast by dNK cells is impaired in pregnancies with high RI, as is the ability to induce trophoblast outgrowth from placental villous explants. These processes are dependent on activation of the extracellular signal-regulated kinase 1/2 and phosphatidylinositol 3-kinase-Akt signaling pathways, which were altered in trophoblasts incubated with secreted factors from dNK cells from high RI pregnancies. Therefore, by characterizing pregnancies using uterine artery Doppler RI before dNK cell isolation, we have identified that impaired dNK-trophoblast interactions may lead to poor placentation. These findings have implications for pregnancy pathological conditions, such as preeclampsia.

Immune balance at the foeto-maternal interface as the fulcrum of reproductive success

Viviparity has many evolutionary advantages but brings with it the problem of the semi-allogeneic foetus having to coexist with the mother for the duration of pregnancy. In species with haemochorial placentation this problem is particularly evident as foetal trophoblast cells are extensively intermingled with maternal tissue and are directly exposed to maternal blood. Fascinating adaptations on both the foetal and maternal side have allowed for this interaction to be re-directed away from an immune rejection response not only towards immunotolerance, but in fact towards actively supporting reproductive success. Recent data have shown that some of these remarkable adaptations are conserved between mice and humans. Thus, a subset of trophoblast cells that is directly exposed to the maternal uterine environment shares the feature of expressing an unusual antigen repertoire on their surface. Paternal antigens can be recognized by maternal immune cells, in particular uterine natural killer cells that express cognate receptors, to regulate the extensive remodelling events that take place at the implantation site. Detailed genetic dissection experiments in the mouse have further demonstrated the direct impact of antigenic dissimilarity on foetal growth. With the availability of inbred strains, in vitro culture systems of trophoblast stem cells, and in-depth genetic, genomic and epigenomic data the mouse will be a valuable model system to study the intricate immune crosstalk at the foeto-maternal boundary. These insights will pave the way towards unravelling the mutual and synergistic interactions between trophoblast and its surrounding maternal environment, and in doing so help understand pregnancy pathologies.

Sphingosine signalling regulates decidual NK cell angiogenic phenotype and trophoblast migration

STUDY QUESTION

Is sphingosine-1-phosphate (S1P) signalling involved in the regulation of the angiogenic function of decidual (d)NK cells during human pregnancy?

SUMMARY ANSWER

Human dNK cells, characterized by S1P receptor 5 (S1PR5) expression, are reactive to microenvironmental S1P to modify their VEGF expression and to regulate trophoblast migration and endothelial angiogenesis.

WHAT IS KNOWN ALREADY

S1P signalling can modulate peripheral (p)NK cells migration and function. As a unique NK population, human dNK can produce multiple cytokines and angiogenic growth factors to mediate extravillous trophoblast (EVT) invasion and spiral artery remodelling during pregnancy.

STUDY DESIGN, SIZE, DURATION

The study was designed to examine S1PR expression and function by freshly isolated human dNK cells in response to different S1P scenarios, created by FTY720, an S1P analogue and S1PR modulator. Ex vivo and in vitro experiments were performed to evaluate the functions of dNK cells. The study was performed between September 2011 and June 2013.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human peripheral blood and decidual samples were collected and the S1PR expression by the decidual leukocytes population was examined. FTY720-induced dNK phenotypic and functional changes (including VEGF and IL-8 expression) were evaluated by multi-colour flow cytometric assays and transwell migration studies. Human placental explant culture and wound healing assays were performed to investigate whether S1P-activated dNK mediated trophoblast migration while angiogenesis was assessed by human umbilical vein endothelial cells (HUVEC) tube formation assays. Both first and second trimester dNK cells were studied to compare the difference in S1PR expression over time at the fetal-maternal interface.

MAIN RESULTS AND THE ROLE OF CHANCE

Freshly isolated NK cells (CD45(+)CD56(+)CD16(-)) from blood (pNK) and decidua (dNK) had low S1PR1 reactivity while S1PR5 was prominently expressed by dNK (40%) and, to a lesser extent, by pNK (18%; P < 0.05) cells. S1PR5 expression by dNK was significantly down-regulated by FTY720 treatment, which also impaired decidual leukocyte mobility and cellular contact with invasive EVT. FTY720 significantly reduced VEGF expression by dNK, both in the numbers of VEGF(+) cells and in fluorescence intensity (P < 0.05). IL-8 expression by dNK was not changed by FTY720 and remained low at 8% positivity. Trophoblast migration and HUVEC tube formation were stimulated by control leukocytes, enriched CD56(+) dNK or their conditioned medium, respectively, but this effect was markedly abrogated once they were pretreated with FTY720 (P < 0.05). There was a significant decrease in S1PR5 expression in second trimester dNK cells, compared with those from first trimester (P < 0.05). No significant differences in the levels of angiogenic factors (VEGF or IL-8) were detected between first and second trimester dNK cells.

LIMITATIONS, REASONS FOR CAUTION

Our ex vivo and in vitro experimental samples were from healthy women undergoing elective pregnancy termination. FTY720 is a chemical ligand for the S1PRs; little is known regarding the levels or actions of the naturally occurring ligand S1P in human gestational tissues. The in vivo function of S1PR5(+) dNK may be further investigated by using a genetically modified animal model.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to investigate the role of S1PR and S1P interaction on dNK cell physiology and their downstream effects on trophoblast migration. We suggest that S1PR5 may represent a potential target for cellular targeted treatments for gestational diseases such as pre-eclampsia and intrauterine growth restriction that are characterized by inadequate dNK/trophoblast-coordinated uterine spiral artery transformation.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by Canadian Institutes of Health Research (CIHR), MOP82811 to Dr S.J.L.

A review of the mechanism for poor placentation in early-onset preeclampsia: the role of autophagy in trophoblast invasion and vascular remodeling

Shallow trophoblast invasion and impaired vascular remodeling of spiral arteries have been recognized in early-onset preeclampsia. Placentation and vascular remodeling are multistep processes, and hypoxia, placental oxidative stress, excessive or atypical maternal immune response to trophoblasts, exaggerated inflammation, and increased production of anti-angiogenic factors such as the soluble form of the vascular endothelial growth factor (VEGF) receptor (sFlt-1) and soluble endoglin (sENG) may play a role in poor placentation in preeclampsia. Recent findings suggest that autophagy plays an important role in extravillous trophoblast (EVT) invasion and vascular remodeling under hypoxia, and sENG inhibits EVT invasion and vascular remodeling by the inhibition of autophagy under hypoxic conditions. In this review, we discuss the relationship between inadequate autophagy and poor placentation in preeclampsia.

Altered expression of interleukin-6, interleukin-8 and their receptors in decidua of women with sporadic miscarriage

STUDY QUESTION

Are alterations in decidual expression of interleukin (IL)-6 and IL-8 associated with sporadic miscarriage?

SUMMARY ANSWER

IL-6 and IL-8 secretion from decidual uterine natural killer (uNK) cells and macrophages isolated from women with spontaneous miscarriage was reduced compared with normal controls.

WHAT IS KNOWN ALREADY

Miscarriage is a common gynaecological problem with huge financial and personal implications. Eleven to twenty per cent of all clinically recognized pregnancies are lost before the 20th week of gestation, with miscarriages often being divided into early (≤ 12 completed weeks from last menstrual period) and late (≥ 13 weeks). Spiral artery remodelling is a key feature of early pregnancy; failure of this process has been implicated in sporadic miscarriage. The molecular triggers that initiate spiral artery remodelling are not clear, although cytokines such as IL-6 and IL-8 may play a role.

STUDY DESIGN, SIZE, DURATION

This was a laboratory-based study using decidual and placental bed biopsy samples from women with sporadic miscarriage (n = 30) and termination of pregnancy controls (n = 30).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Total adherent decidual cells, CD10(+) stromal cells, CD14(+) macrophages and CD56(+) uNK cells were isolated from decidua from apparently normal pregnancies that were terminated at either 8-10 or 12-14 weeks' gestation. In addition, CD14(+) macrophages and CD56(+) uNK cells were isolated from decidua from sporadic miscarriage at 8-10 weeks' gestation. Secreted IL-8 was measured in all isolated cell populations, while IL-6 was measured in CD14(+) macrophages and CD56(+) uNK cells from both sporadic miscarriage and normal controls. Placental bed biopsies were taken from women after sporadic miscarriage or termination of pregnancy at ≤ 12 completed weeks' or >13 weeks' gestational age, formalin-fixed, paraffin-embedded and immunostained for IL-6, IL-6Rα, GP130, IL-8, CXCR1, CXCR2 and CD13 (aminopeptidase N). Staining intensity for each factor was assessed in extravillous trophoblast cell populations, myometrial and decidual stroma, myometrial and decidual spiral arteries and decidual glandular epithelium. A CPA model was used to assess the potential role of IL-6 and IL-8 in spiral artery remodelling.

MAIN RESULTS AND THE ROLE OF CHANCE

IL-8 was secreted by total adherent decidual cells, CD10(+) stromal cells and CD14(+) macrophages at both 8-10 and 12-14 weeks' gestation, with CD14(+) cells secreting the highest levels. Both CD14(+) and CD56(+) cells isolated from decidua of early sporadic miscarriage produced lower IL-6 (P = 0.04, P = 0.01, respectively) and IL-8 levels (P = 0.0007, P = 0.002, respectively) compared with normal cases. In addition, altered expression of IL-6, IL-8 and their receptors was observed in various cell types in placental bed (myometrial stroma, glandular epithelium, interstitial extravillous trophoblast cells, vascular smooth muscle cells and endothelial cells) in sporadic miscarriage, particularly from later gestational ages. IL-6 and IL-8 disrupted vascular smooth muscle morphology and organization in an in vitro model of spiral artery remodelling.

LIMITATIONS, REASONS FOR CAUTION

By the nature of sampling at the time of miscarriage, it was not possible to ascertain the cause or effect in the observed alterations of levels of IL-6 and IL-8 in sporadic miscarriage.

WIDER IMPLICATIONS OF THE FINDINGS

Alterations in the expression of IL-6, IL-8 and their receptors may be associated with the aetiology of sporadic miscarriage, especially given the potential role of these cytokines in the regulation of trophoblast invasion and spiral artery remodelling.

STUDY FUNDING/COMPETING INTEREST(S)

This project was supported by funding from Wellbeing of Women (RG1000). The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

Not applicable.

Mononuclear leukocyte infiltrate in extraplacental membranes and preterm delivery

Large numbers of polymorphonuclear leukocytes in the amnion and chorion define histological chorioamnionitis (HCA), a condition linked to spontaneous preterm delivery (PTD). Less is known about placental patterns of mononuclear leukocyte (MNL) density and PTD. In this prospective study (1998-2004), women were sampled from 52 clinics in 5 Michigan communities and enrolled at 16-27 weeks' gestation. HCA and MNL distributions in delivered placentas were evaluated microscopically in a subcohort (290 preterm, 823 term). Midpregnancy biomarkers from maternal blood (i.e., C-reactive protein (CRP), corticotropin-releasing hormone, and cytokines) were compared among term and PTD subjects grouped by presence/absence of HCA and high MNL density. A density of more than 10 MNLs per high-power field in the chorion of the membrane roll, referred to as MNL-CMR, was associated with medically indicated PTD (odds ratio = 2.2, 95% confidence interval: 1.3, 3.6) and spontaneous PTD (odds ratio = 2.5, 95% confidence interval: 1.7, 3.7). Associations persisted after removal of women with HCA-positive placentas, abruption, hypertensive disorders, or obesity. HCA-associated PTD showed higher CRP and cytokine levels. MNL-CMR-associated PTD showed higher CRP and corticotropin-releasing hormone levels. These data suggest that an MNL infiltrate in the chorion of the membrane roll marks PTD pathways that are distinct from HCA and not entirely explained by pregnancy complications.

Fetal-derived adrenomedullin mediates the innate immune milieu of the placenta

The remodeling of maternal uterine spiral arteries (SAs) is an essential process for ensuring low-resistance, high-capacitance blood flow to the growing fetus. Failure of SAs to remodel is causally associated with preeclampsia, a common and life-threatening complication of pregnancy that is harmful to both mother and fetus. Here, using both loss-of-function and gain-of-function genetic mouse models, we show that expression of the pregnancy-related peptide adrenomedullin (AM) by fetal trophoblast cells is necessary and sufficient to promote appropriate recruitment and activation of maternal uterine NK (uNK) cells to the placenta and ultimately facilitate remodeling of maternal SAs. Placentas that lacked either AM or its receptor exhibited reduced fetal vessel branching in the labyrinth, failed SA remodeling and reendothelialization, and markedly reduced numbers of maternal uNK cells. In contrast, overexpression of AM caused a reversal of these phenotypes with a concomitant increase in uNK cell content in vivo. Moreover, AM dose-dependently stimulated the secretion of numerous chemokines, cytokines, and MMPs from uNK cells, which in turn induced VSMC apoptosis. These data identify an essential function for fetal-derived factors in the maternal vascular adaptation to pregnancy and underscore the importance of exploring AM as a biomarker and therapeutic agent for preeclampsia.

The Placenta in Toxicology. Part II

During pregnancy, the maternal immune system is challenged by the semiallogeneic fetus, which must be tolerated without compromising fetal or maternal health. This review updates the systemic and local immune changes taking place during human pregnancy, including some examples in rodents. Systemic changes are induced by contact of maternal blood with placental factors and include enhanced innate immunity with increased activation of granulocytes and nonclassical monocytes. Although a bias toward T helper (Th2) and regulatory T cell (Treg) immunity has been associated with healthy pregnancy, the relationship between different circulating Th cell subsets is not straightforward. Instead, these adaptations appear most evidently at the fetal–maternal interface, where for instance Tregs are enriched and promote fetal tolerance. Also innate immune cells, that is, natural killer cells and macrophages, are enriched, constituting the majority of decidual leukocytes. These cells not only contribute to immune regulation but also aid in establishing the placenta by promoting trophoblast recruitment and angiogenesis. Thus, proper interaction between leukocytes and placental trophoblasts is necessary for normal placentation and immune adaptation. Consequently, spontaneous maladaptation or interference of the immune system with toxic substances may be important contributing factors for the development of pregnancy complications such as preeclampsia, preterm labor, and recurrent miscarriages.

Does malaria affect placental development? Evidence from in vitro models

Background

Malaria in early pregnancy is difficult to study but has recently been associated with fetal growth restriction (FGR). The pathogenic mechanisms underlying malarial FGR are poorly characterized, but may include impaired placental development. We used in vitro methods that model migration and invasion of placental trophoblast into the uterine wall to investigate whether soluble factors released into maternal blood in malaria infection might impair placental development. Because trophoblast invasion is enhanced by a number of hormones and chemokines, and is inhibited by pro-inflammatory cytokines, many of which are dysregulated in malaria in pregnancy, we further compared concentrations of these factors in blood between malaria-infected and uninfected pregnancies.

Methodology/Principal Findings

We measured trophoblast invasion, migration and viability in response to treatment with serum or plasma from two independent cohorts of Papua New Guinean women infected with Plasmodium falciparum or Plasmodium vivax in early pregnancy. Compared to uninfected women, serum and plasma from women with P. falciparum reduced trophoblast invasion (P = .06) and migration (P = .004). P. vivax infection did not alter trophoblast migration (P = .64). The P. falciparum-specific negative effect on placental development was independent of trophoblast viability, but associated with high-density infections. Serum from P. falciparum infected women tended to have lower levels of trophoblast invasion promoting hormones and factors and higher levels of invasion-inhibitory inflammatory factors.

Conclusion/Significance

We demonstrate that in vitro models of placental development can be adapted to indirectly study the impact of malaria in early pregnancy. These infections could result in impaired trophoblast invasion with reduced transformation of maternal spiral arteries due to maternal hormonal and inflammatory disturbances, which may contribute to FGR by limiting the delivery of maternal blood to the placenta. Future prevention strategies for malaria in pregnancy should include protection in the first half of pregnancy.

LAIR2-expressing extravillous trophoblasts associate with maternal spiral arterioles undergoing physiologic conversion

Leukocyte-associated immunoglobulin-like receptor 2 (LAIR2) was identified on a global gene expression microarray analysis of surplus chorionic villus sampling (CVS) tissues as down-regulated in the first trimester of preeclampsia pregnancies. LAIR2 is the soluble receptor counterpart to LAIR1, an inhibitory receptor found on multiple immune cell subsets. In situ and immunohistochemical studies have previously shown that placental expression of LAIR2 expression is highly restricted, confined to the more distal portions of extravillous trophoblast (EVT) cell columns. This study examines LAIR2 expression in deeper layers of trophoblasts in the placental implantation site, maternal decidua and maternal spiral arterioles. Immunohistochemical staining detected LAIR2 expression on a subset of EVT within the implantation site. This trophoblast included the invasive EVT infiltrating the maternal decidual vessels and the EVT forming the endovascular trophoblastic plugs. More specifically, LAIR2-positive EVT showed a striking predilection for maternal decidual arterioles and the immediately surrounding decidua. Moreover, the appearance of EVT expressing LAIR2 in these areas was contemporaneous with the process of spiral arteriole remodeling. Based on these findings, we suggest that LAIR2-expressing EVT may play an important role in the remodeling of maternal spiral arterioles.

Immunology of the maternal-fetal interface

The immune cells that reside at the interface between the placenta and uterus are thought to play many important roles in pregnancy. Recent work has revealed that the composition and function of these cells are locally controlled by the specialized uterine stroma (the decidua) that surrounds the implanted conceptus. Here, I discuss how key immune cell types (natural killer cells, macrophages, dendritic cells, and T cells) are either enriched or excluded from the decidua, how their function is regulated within the decidua, and how they variously contribute to pregnancy success or failure. The discussion emphasizes the relationship between human and mouse studies. Deeper understanding of the immunology of the maternal-fetal interface promises to yield significant insight into the pathogenesis of many human pregnancy complications, including preeclampsia, intrauterine growth restriction, spontaneous abortion, preterm birth, and congenital infection.

Trophoblast-induced changes in C-x-C motif chemokine 10 expression contribute to vascular smooth muscle cell dedifferentiation during spiral artery remodeling

OBJECTIVE

During pregnancy, fetal trophoblast disrupt endothelial cell and vascular smooth muscle cell (VSMC) interactions in spiral arteries of the maternal decidua to enable increased nutritional and oxygen delivery to the fetus. Little is known regarding this transformation because of difficulties of studying human pregnancy in vivo. This study investigated how trophoblast-secreted factors affect the interactions of vascular cells and the differentiation status of VSMC during spiral arteries remodeling using 3-dimensional vascular spheroid coculture.

METHODS AND RESULTS

Endothelial cell and VSMC were cocultured in hanging droplets to form spheroids representing an inverted vessel lumen. Control or conditioned media from an extravillous trophoblast (EVT) cell line was incubated with vascular spheroids for 24 hours. Spheroid RNA was then analyzed by Illumina Sentrix BeadChip array. Spheroids incubated with EVT conditioned medium showed significant up/downregulation of 101 genes (>1.5-fold; P<0.05), including an upregulation of C-X-C motif chemokine 10 (IP-10). C-X-C motif chemokine 10 expression was confirmed by qualitative real-time PCR and Western blot analysis of spheroids, and immunohistochemistry of first trimester decidua and ex vivo dissected nonplacental bed spiral arteries. EVT conditioned medium reduced VSMC expression of differentiation markers, and both EVT conditioned medium and C-X-C motif chemokine 10 increased motility of VSMC indicating dedifferentiation of VSMC.

CONCLUSIONS

EVT-induced C-X-C motif chemokine 10 expression may contribute to spiral arteries remodeling during pregnancy by altering the motility and differentiation status of the VSMC in the vessel.

Pregnancy and preeclampsia affect monocyte subsets in humans and rats

INTRODUCTION

Both nonclassical and intermediate monocytes have been implicated in different inflammatory conditions. We hypothesized that these monocytes would increase during pregnancy, a condition associated with generalized activation of inflammatory responses and that they would increase even more during preeclampsia, in which inflammatory responses are further stimulated. In the present study we investigated changes in monocyte subsets during healthy pregnancy and preeclampsia in humans and rats.

METHODS

Blood monocyte subsets of nonpregnant, preeclamptic and healthy pregnant women were identified with CD14 and CD16. In nonpregnant and pregnant rats, blood monocytes were identified with CD172a and CD43, as well as in rats infused with adenosine triphosphate (ATP), a pro-inflammatory stimulus known to induce preeclampsia-like symptoms. Total and CD206-positive macrophages were quantified in placentas of these animals.

RESULTS

Lower percentages of classical monocytes were found in pregnant women (91%-[83-98%]) compared to nonpregnant women (94%-[90-98%]) and even less in preeclamptic patients (90%-[61-92%]). In contrast, the percentage of combined nonclassical/intermediate monocytes was higher in pregnant women (8.5%-[2.3-16.6%] vs. 5.6%-[1.9-9.5%]) and even higher in preeclamptic patients (9.9%-[7.8-38.7%]), which was caused by a selective increase of intermediate monocytes. In rats, we also found lower percentages of classical monocytes and higher percentages of nonclassical monocytes in pregnant versus nonpregnant rats. ATP infusion increased the percentage of nonclassical monocytes in pregnant rats even further but not in nonpregnant rats. These nonclassical monocytes showed a more activated phenotype in pregnant ATP-infused rats only. Mesometrial triangles of ATP-infused rats had less CD206-positive macrophages as compared to those of saline-infused rats.

CONCLUSION

The higher percentage of nonclassical/intermediate monocytes found in pregnancy and preeclampsia confirms their association with inflammatory responses. The observation that ATP stimulated numbers/activation of nonclassical monocytes in pregnant rats only, suggests that nonclassical monocytes are specifically altered in pregnancy and may play a role in the pathophysiology of preeclampsia.

Glycodelin-A stimulates interleukin-6 secretion by human monocytes and macrophages through L-selectin and the extracellular signal-regulated kinase pathway

Macrophages represent the second major type of decidual leukocytes at the fetomaternal interface. Changes in macrophage number and activity are associated with fetal loss and pregnancy complications. Glycodelin-A (GdA) is an abundant glycoprotein in the first-trimester decidua. It is involved in fetomaternal defense and early placental development through its regulatory activities in various immune cells. The N-glycosylation of GdA mediates the binding and therefore the activities of the molecule. In this study, we studied the biological activities of GdA in the functions of human monocytes/macrophages. GdA was purified from amniotic fluid by affinity chromatography. GdA treatment did not affect the viability, cell death, or phagocytic activity of the monocytes/macrophages. GdA, but not recombinant glycodelin without glycosylation, induced IL-6 production as demonstrated by cytokine array, intracellular staining, and ELISA. GdA also induced phosphorylation of ERK in monocytes/macrophages. The involvement of ERKs in IL-6 induction was confirmed using pharmacological inhibitors. Co-immunoprecipitation showed that L-selectin on the monocytes/macrophages was the binding protein of GdA. Treatment with anti-L-selectin antibody reduced GdA binding and GdA-induced IL-6 production. GdA-treated macrophages suppressed IFN-γ expression by co-cultured T-helper cells in an IL-6-dependent manner. These results show that GdA interacts with L-selectin to induce IL-6 production in monocytes/macrophages by activating the ERK signaling pathway. In turn, the increased IL-6 production suppresses IFN-γ expression in T-helper cells, which may play an important role in inducing a Th-2-polarized cytokine environment that flavors the immunotolerance of the fetoplacental unit.

Uterine natural killer cells initiate spiral artery remodeling in human pregnancy

Uterine spiral artery remodeling is required for successful human pregnancy; impaired remodeling is associated with pregnancy complications, including late miscarriage, preeclampsia, and fetal growth restriction. The molecular triggers of remodeling are not known, but it is now clear that there are "trophoblast-independent" and "trophoblast-dependent" stages. Uterine natural killer (uNK) cells are abundant in decidualized endometrium in early pregnancy; they surround spiral arteries and secrete a range of angiogenic growth factors. We hypothesized that uNK cells mediate the initial stages of spiral artery remodeling. uNK cells and extravillous trophoblast (EVT) cells were isolated from early pregnancy decidua and placenta. Chorionic plate arteries from full-term placentas and spiral arteries from nonpregnant myometrium were cultured with angiogenic growth factors or conditioned medium (CM) from uNK cells or EVT or uNK cell/EVT cocultures. In both vessel models, uNK cell CM induced disruption of vascular smooth muscle cells (VSMCs) and breakdown of extracellular matrix components. Angiopoietin (Ang)-1, Ang-2, interferon-γ, and VEGF-C also disrupted VSMC integrity with an Ang-2 inhibitor abrogating the effect of uNK cell CM. These results provide compelling evidence that uNK cells contribute to the early stages of spiral artery remodeling; failure of this process could contribute to pregnancy pathology.

[Immunological aspect of pregnancy]

Pregnancy is a temporary semi-allograft that survives for nine months. The importance of this event for the survival of the species justifies several tolerance mechanisms that are put into place at the beginning of pregnancy, some of which occur even at the time of implantation. The presence of multiple tolerance mechanisms and the richness of the means employed underline the central importance of the trophoblast. Understanding these mechanisms, and in particular, their integration into an overall scheme, enables the anomalies encountered in certain pathologies of pregnancy to be placed into context. Understanding these mechanisms and their interruption at the end of pregnancy should improve our understanding of disappointing results from current immunological treatments facilitate the implementation of new prophylactic and therapeutic strategies.

Impaired natural killer cell phenotype and function in idiopathic and heritable pulmonary arterial hypertension

BACKGROUND

Beyond their role as innate immune effectors, natural killer (NK) cells are emerging as important regulators of angiogenesis and vascular remodeling. Pulmonary arterial hypertension (PAH) is characterized by severe pulmonary vascular remodeling and has long been associated with immune dysfunction. Despite this association, a role for NK cells in disease pathology has not yet been described.

METHODS AND RESULTS

Analysis of whole blood lymphocytes and isolated NK cells from PAH patients revealed an expansion of the functionally defective CD56(-)/CD16(+) NK subset that was not observed in patients with chronic thromboembolic pulmonary hypertension. NK cells from PAH patients also displayed decreased levels of the activating receptor NKp46 and the killer immunoglobulin-like receptors 2DL1/S1 and 3DL1, reduced secretion of the cytokine macrophage inflammatory protein-1β, and a significant impairment in cytolytic function associated with decreased killer immunoglobulin-like receptor 3DL1 expression. Genotyping patients (n=222) and controls (n=191) for killer immunoglobulin-like receptor gene polymorphisms did not explain these observations. Rather, we show that NK cells from PAH patients exhibit increased responsiveness to transforming growth factor-β, which specifically downregulates disease-associated killer immunoglobulin-like receptors. NK cell number and cytotoxicity were similarly decreased in the monocrotaline rat and chronic hypoxia mouse models of PAH, accompanied by reduced production of interferon-γ in NK cells from hypoxic mice. NK cells from PAH patients also produced elevated quantities of matrix metalloproteinase 9, consistent with a capacity to influence vascular remodeling.

CONCLUSIONS

Our work is the first to identify an impairment of NK cells in PAH and suggests a novel and substantive role for innate immunity in the pathobiology of this disease.

Innate immunity, decidual cells, and preeclampsia

Preeclampsia (PE) manifested by hypertension and proteinuria complicates 3% to 8% of pregnancies and is a leading cause of fetal-maternal morbidity and mortality worldwide. It may lead to intrauterine growth restriction, preterm delivery, and long-term sequelae in women and fetuses, and consequently cause socioeconomic burden to the affected families and society as a whole. Balanced immune responses are required for the maintenance of successful pregnancy. Although not a focus of most studies, decidual cells, the major resident cell type at the fetal-maternal interface, have been shown to modulate the local immune balance by interacting with other cell types, such as bone marrow derived-immune cells, endothelial cells, and invading extravillous trophoblasts. Accumulating evidence suggests that an imbalanced innate immunity, facilitated by decidual cells, plays an important role in the pathogenesis of PE. Thus, this review will discuss the role of innate immunity and the potential contribution of decidual cells in the pathogenesis of PE.

Impaired decidual natural killer cell regulation of vascular remodelling in early human pregnancies with high uterine artery resistance

During human pregnancy, natural killer (NK) cells accumulate in the maternal decidua, but their specific roles remain to be determined. Decidual NK (dNK) cells are present during trophoblast invasion and uterine spiral artery remodelling. These events are crucial for successful placentation and the provision of an adequate blood supply to the developing fetus. Remodelling of spiral arteries is impaired in the dangerous pregnancy complication pre-eclampsia. We studied dNK cells isolated from pregnancies at 9–14 weeks' gestation, screened by uterine artery Doppler ultrasound to determine resistance indices which relate to the extent of spiral artery remodelling. dNK cells were able to promote the invasive behaviour of fetal trophoblast cells, partly through HGF. Cells isolated from pregnancies with higher resistance indices were less able to do this and secreted fewer pro-invasive factors. dNK cells from pregnancies with normal resistance indices could induce apoptotic changes in vascular smooth muscle and endothelial cells in vitro, events of importance in vessel remodelling, partly through Fas signalling. dNK cells isolated from high resistance index pregnancies failed to induce vascular apoptosis and secreted fewer pro-apoptotic factors. We have modelled the cellular interactions at the maternal-fetal interface and provide the first demonstration of a functional role for dNK cells in influencing vascular cells. A potential mechanism contributing to impaired vessel remodelling in pregnancies with a higher uterine artery resistance is presented. These findings may be informative in determining the cellular interactions contributing to the pathology of pregnancy disorders where remodelling is impaired, such as pre-eclampsia.

Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Aberrant expression of corticotropin-releasing hormone in pre-eclampsia induces expression of FasL in maternal macrophages and extravillous trophoblast apoptosis

Corticotropin-releasing hormone (CRH) and its receptors are expressed in human placenta. Recently, the impaired function of this system has been associated with a number of complications of pregnancy, including pre-eclampsia. The aim of the study was to test the hypothesis that CRH participates in the pathophysiology of pre-eclampsia through the induction of macrophage-mediated apoptosis of extravillous trophoblasts (EVTs). We found that the expression of CRH was increased in the EVT of the placental bed biopsy specimens from pre-eclamptic pregnancies (1.8-fold increase; P < 0.05). In addition, significantly larger numbers of apoptotic EVT were detected in pre-eclamptic placentas compared with normal ones (P < 0.05), and only in pre-eclamptic placentas, decidual macrophages were found to be Fas ligand (FasL)-positive. In vitro studies on the effect of CRH on human macrophages suggested that CRH induced the expression of the FasL protein in human macrophages and potentiated their ability to induce the apoptosis of a Fas-expressing EVT-based hybridoma cell line in co-cultures. These findings demonstrate a possible mechanism by which the aberrant expression of CRH in pre-eclampsia may activate the FasL-positive decidual macrophages, impair the physiological turnover of EVT and eventually disturb placentation.

The pathophysiology of preeclampsia in view of the two-stage model

Preeclampsia is a common and severe disease in pregnancy, a major cause of maternal and fetal morbidity and mortality. The main features of the disease are de novo hypertension after the 20th gestational week and proteinuria, and it is frequently accompanied by edema and other subjective symptoms. The origin of the disease is the placenta, but its sequelae affect multiple organ systems. According to the two-stage model of preeclampsia, the abnormal and hypoperfused placenta (stage 1) releases factors to the bloodstream, which are responsible for the maternal symptoms (stage 2). Oxidative stress, impaired function of nitric-oxide synthase, cellular and humoral immunological factors play an important role in the pathophysiology of the placenta. Endothelial dysfunction is the common denominator of the clinical symptoms. The theory explains the origins of hypertension, proteinuria, edema and other symptoms as well. Orv. Hetil., 2012, 153, 1167–1176.