Human uterine lymphocytes

Increased cytotoxic natural killer cells in the endometrium alone cannot be considered the immunological cause of recurrent miscarriage

OBJECTIVE

To study the distribution and gene expression of endometrial immune cell populations, especially natural killer (NK) subsets, between assisted reproductive technology patients and healthy donors and explore a possible relationship of these results with patients' killer cell immunoglobulin-like receptor (KIR) genotypes and KIR-human antigen leukocyte-C (HLA-C) binding.

DESIGN

Prospective observational cohort study.

SETTING

Clinic and university laboratories.

PATIENT(S)

Participants included 39 women with recurrent miscarriages who had undergone in vitro fertilization cycles with donated oocytes and 21 healthy oocyte donors with proven fertility.

INTERVENTION(S)

Endometrial biopsy samples were collected from both patients and donors, and the KIR genotypes of the assisted reproductive technology patients were analyzed.

MAIN OUTCOME MEASURE(S)

Endometrial gene expression (cluster of differentiation [CD] antigens and anti-inflammatory and proinflammatory interleukins) and the number and percentage of regulatory T and NK cell populations in patients and donors were determined. Subsequently, the results obtained were categorized in the group of patients by KIR genotype. Killer cell immunoglobulin-like receptor-HLA-C binding was also examined in patients, considering their KIRs.

RESULT(S)

A higher percentage of CD56dimCD16+ NK cells were observed in patients than those in healthy donors. Nevertheless, when categorizing patients by KIR genotype and comparing the KIR AA (35.9%), AB (43.6%), and BB (20.5%) groups, no statistically significant difference was observed in either endometrial gene expression or any of the immune cell populations analyzed. Finally, no differences in binding between KIR and HLA-C molecules were registered among these 3 sets of patients.

CONCLUSION(S)

The reported increase in the number of NK cells with a cytotoxic profile in the endometrium of women with a history of recurrent miscarriages cannot alone explain these events because no relationship is observed between such cellular increase and the KIR genotypes, which individually, and in combination with the different HLA-C alleles, have also been associated, by previous studies, with negative reproductive outcomes.

CLINICAL TRIAL REGISTRATION NUMBER

1405-MAD-025-JG.

Cytokines, NK cells and regulatory T cell functions in normal pregnancy and reproductive failures

PURPOSE OF THE REVIEW

Pregnancy brings about an intricate assortment of dynamic changes, which causes proper connection of genetically discordant maternal and foetal tissues. Uterine NK cells are immune cells populating the endometrium and play a major role in implantation and also regulate placentation. This review mainly aims explore the role of uterine NK cells in implantation and how it is affecting in adverse pregnancy outcomes.

RECENT FINDINGS

Though the functions of uterine NK (uNK) cells are not clearly understood, NK cell activity plays a vital role during immunomodulation which is the main step in implantation and sustaining the early pregnancy. Cytokines, cell surface receptors of NK cells and hormones such as progesterone modulate the NK cell activity in turn affect the implantation of the embryo. Altered NK cell activity (number and functionality) would be an important attributing factor in adverse pregnancy outcomes. Furthermore, T regulatory cells and cytokines also modulate the immune responses in the decidua which in turn contributes to successful implantation of embryos.

SUMMARY

Immunological responses and interactions in the Foetus-maternal interface is crucial in the successful implantation of allogenic foetus resulting in a healthy pregnancy. NK cells, Treg cells and cytokines play a major role in successful implantation which remains an enigma. Comprehending pregnancy-induced immunological changes at the foetus-maternal interface will allow newer therapeutic strategies to improve pregnancy outcomes.

Recurrent implantation failure: A comprehensive summary from etiology to treatment

Implantation is the first step in human reproduction. Successful implantation depends on the crosstalk between embryo and endometrium. Recurrent implantation failure (RIF) is a clinical phenomenon characterized by a lack of implantation after the transfer of several embryos and disturbs approximately 10% couples undergoing in vitro fertilization and embryo transfer. Despite increasing literature on RIF, there is still no widely accepted definition or standard protocol for the diagnosis and treatment of RIF. Progress in predicting and preventing RIF has been hampered by a lack of widely accepted definitions. Most couples with RIF can become pregnant after clinical intervention. The prognosis for couples with RIF is related to maternal age. RIF can be caused by immunology, thrombophilias, endometrial receptivity, microbiome, anatomical abnormalities, male factors, and embryo aneuploidy. It is important to determine the most possible etiologies, and individualized treatment aimed at the primary cause seems to be an effective method for increasing the implantation rate. Couples with RIF require psychological support and appropriate clinical intervention. Further studies are required to evaluate diagnostic method and he effectiveness of each therapy, and guide clinical treatment.

Emerging Concepts in Innate Lymphoid Cells, Memory, and Reproduction

Members of the innate immune system, innate lymphoid cells (ILCs), encompass five major populations (Natural Killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer cells) whose functions include defense against pathogens, surveillance of tumorigenesis, and regulation of tissue homeostasis and remodeling. ILCs are present in the uterine environment of humans and mice and are dynamically regulated during the reproductive cycle and pregnancy. These cells have been repurposed to support pregnancy promoting maternal immune tolerance and placental development. To accomplish their tasks, immune cells employ several cellular and molecular mechanisms. They have the capacity to remember a previously encountered antigen and mount a more effective response to succeeding events. Memory responses are not an exclusive feature of the adaptive immune system, but also occur in innate immune cells. Innate immune memory has already been demonstrated in monocytes/macrophages, neutrophils, dendritic cells, and ILCs. A population of decidual NK cells characterized by elevated expression of NKG2C and LILRB1 as well as a distinctive transcriptional and epigenetic profile was found to expand during subsequent pregnancies in humans. These cells secrete high amounts of interferon-γ and vascular endothelial growth factor likely favoring placentation. Similarly, uterine ILC1s in mice upregulate CXCR6 and expand in second pregnancies. These data provide evidence on the development of immunological memory of pregnancy. In this article, the characteristics, functions, and localization of ILCs are reviewed, emphasizing available data on the uterine environment. Following, the concept of innate immune memory and its mechanisms, which include epigenetic changes and metabolic rewiring, are presented. Finally, the emerging role of innate immune memory on reproduction is discussed. Advances in the comprehension of ILC functions and innate immune memory may contribute to uncovering the immunological mechanisms underlying female fertility/infertility, placental development, and distinct outcomes in second pregnancies related to higher birth weight and lower incidence of complications.

The role of endometrial B cells in normal endometrium and benign female reproductive pathologies: a systematic review

STUDY QUESTION

What are the similarities and differences in endometrial B cells in the normal human endometrium and benign reproductive pathologies?

SUMMARY ANSWER

Endometrial B cells typically constitute <5% of total endometrial CD45+ lymphocytes, and no more than 2% of total cells in the normal endometrium, and while their relative abundance and phenotypes vary in benign gynaecological conditions, current evidence is inconsistent.

WHAT IS KNOWN ALREADY

B cells are vitally important in the mucosal immune environment and have been extensively characterized in secondary lymphoid organs and tertiary lymphoid structures (TLSs), with the associated microenvironment germinal centre. However, in the endometrium, B cells are largely overlooked, despite the crucial link between autoimmunity and reproductive pathologies and the fact that B cells are present in normal endometrium and benign female reproductive pathologies, scattered or in the form of lymphoid aggregates (LAs). A comprehensive summary of current data investigating B cells will facilitate our understanding of endometrial B cells in the endometrial mucosal immune environment.

STUDY DESIGN SIZE DURATION

This systematic review retrieved relevant studies from four databases (MEDLINE, EMBASE, Web of Science Core Collection and CINAHL) from database inception until November 2021.

PARTICIPANTS/MATERIALS SETTING METHODS

The search strategy combined the use of subject headings and relevant text words related to 'endometrium', 'B cells' and B-cell derivatives, such as 'antibody' and 'immunoglobulin'. Non-benign diseases were excluded using cancer-related free-text terms, and searches were limited to the English language and human subjects. Only peer-reviewed research papers were included. Each paper was graded as 'Good', 'Fair' or 'Poor' quality based on the NEWCASTLE-OTTAWA quality assessment scale. Only 'Good' quality papers were included.

MAIN RESULTS AND THE ROLE OF CHANCE

Twenty-seven studies met the selection criteria and were included in this review: 10 cross-sectional studies investigated B cells in the normal endometrium; and 17 case-control studies compared the characteristics of endometrial B cells in control and benign female reproductive pathologies including endometritis, endometriosis, infertility, abnormal uterine bleeding, endometrial polyps and uterine fibroids. In all studies, B cells were present in the endometrium, scattered or in the form of LAs. CD20+ B cells were more abundant in patients with endometritis, but the data were inconsistent as to whether B-cell numbers were increased in endometriosis and patients with reproductive pathologies.

LIMITATIONS REASONS FOR CAUTION

Although only 'good' quality papers were included in this systematic review, there were variations in patients' age, diagnostic criteria for different diseases and sample collection time among included studies. Additionally, a large number of the included studies only used immunohistochemistry as the identification method for endometrial B cells, which may fail to provide an accurate representation of the numbers of endometrial B cells.

WIDER IMPLICATIONS OF THE FINDINGS

Histological studies found that endometrial B cells are either scattered or surrounded by T cells in LAs: the latter structure seems to be under hormonal control throughout the menstrual cycle and resembles TLSs that have been observed in other tissues. Further characterization of endometrial B cells and LAs could offer insights to endometrial B-cell function, particularly in the context of autoimmune-associated pathologies, such as endometriosis. Additionally, clinicians should be aware of the limited value of diagnosing plasma cell infiltration using only CD138.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by Finox Biotech. The authors have no conflicts of interest to declare.

PROSPERO REGISTRATION NUMBER

This systematic review was registered in PROSPERO in January 2020 (PROSPERO ID: CRD42020152915).

HLA-G: An Important Mediator of Maternal-Fetal Immune-Tolerance

Maternal-fetal immune-tolerance occurs throughout the whole gestational trimester, thus a mother can accept a genetically distinct fetus without immunological aggressive behavior. HLA-G, one of the non-classical HLA class I molecules, is restricted-expression at extravillous trophoblast. It can concordantly interact with various kinds of receptors mounted on maternally immune cells residing in the uterus (e.g. CD4+ T cells, CD8+ T cells, natural killer cells, macrophages, and dendritic cells) for maintaining immune homeostasis of the maternal-fetus interface. HLA-G is widely regarded as the pivotal protective factor for successful pregnancies. In the past 20 years, researches associated with HLA-G have been continually published. Indeed, HLA-G plays a mysterious role in the mechanism of maternal-fetal immune-tolerance. It can also be ectopically expressed on tumor cells, infected sites and other pathologic microenvironments to confer a significant local tolerance. Understanding the characteristics of HLA-G in immunologic tolerance is not only beneficial for pathological pregnancy, but also helpful to the therapy of other immune-related diseases, such as organ transplant rejection, tumor migration, and autoimmune disease. In this review, we describe the biological properties of HLA-G, then summarize our understanding of the mechanisms of fetomaternal immunologic tolerance and the difference from transplant tolerance. Furthermore, we will discuss how HLA-G contributes to the tolerogenic microenvironment during pregnancy. Finally, we hope to find some new aspects of HLA-G in fundamental research or clinical application for the future.

Extracellular Vesicle-Mediated Secretion of HLA-E by Trophoblasts Maintains Pregnancy by Regulating the Metabolism of Decidual NK Cells

Extracellular vesicles derived from trophoblasts (T-EVs) play an important role in pregnancy, but the mechanism is not entirely clear. In this study, we found that HLA-E, which is mostly confined to the cytoplasm of trophoblast cells, was secreted by T-EVs. The level of HLA-E in T-EVs from unexplained recurrent spontaneous abortion (URSA) patients was lower than that in normal pregnancy (NP) and RSA patients who had an abnormal embryo karyotype (AK-RSA). T-EVs promoted secretion of IFN-γ and VEGFα by decidual NK (dNK) cells from URSA patients via HLA-E, VEGFα was necessary for angiogenesis and trophoblast growth, and IFN-γ inhibited Th17 induction. Glycolysis and oxidative phosphorylation (OxPhos) were involved in this process. Glycolysis but not OxPhos of dNK cells facilitated by T-EVs was dependent on mTORC1 activation. Inhibition of T-EV production in vivo increased the susceptibility of mice to embryo absorption, which was reversed by transferring exogenous T-EVs. T-EVs promoted secretion of IFN-γ and VEGFα by dNK cells to maintain pregnancy via Qa-1 in abortion-prone mouse models. This study reveals a new mechanism of pregnancy maintenance mediated by HLA-E via T-EVs.

Uterine natural killer cells: from foe to friend in reproduction

BACKGROUND

Recurrent miscarriage and pre-eclampsia are common reproductive disorders, but their causes are often unknown. Recent evidence has provided new insight into immune system influences in reproductive disorders. A subset of lymphocytes of the innate immune system known as uterine natural killer (uNK) cells are now recognized as fundamental to achieving embryo implantation and successful pregnancy, but were initially attributed a bad reputation. Indeed, immune therapies have been developed to treat the 'exaggerated' immune response from uNK cells. These treatments have been based on studies of peripheral blood natural killer (pbNK) cells. However, uNK cells and pbNK cells have different phenotypic and functional characteristics. The functions of uNK cells are closely related to their interactions with the extravillous trophoblast cells (EVTs) and spiral arteries, which underlie an essential role in regulating vascular function, controlling trophoblast invasion and promoting placental development. EVTs express MHC molecules of class I HLA-C/E/G/F, while uNK cells express, among other receptors, killer cell immunoglobulin-like receptors (KIRs) that bind to HLA-C or CD94/NKG2A inhibitory receptors, and then bind HLA-E. Associations of certain KIR/HLA-C combinations with recurrent miscarriage, pre-eclampsia, and foetal growth restriction and the interactions between uNK cells, trophoblasts and vascular cells have led to the hypothesis that uNK cells may play a role in embryo implantation.

OBJECTIVE AND RATIONALE

Our objective was to review the evolution of our understanding of uNK cells, their functions, and their increasingly relevant role in reproduction.

SEARCH METHODS

Relevant literature through June 2020 was retrieved using Google Scholar and PubMed. Search terms comprised uNK cells, human pregnancy, reproductive failure, maternal KIR and HLA-C, HLA-E/G/F in EVT cells, angiogenic cytokines, CD56+ NK cells, spiral artery, oestrogen and progesterone receptors, KIR haplotype and paternal HLA-C2.

OUTCOMES

This review provides key insights into the evolving conceptualization of uNK cells, from their not-so-promising beginnings to now, when they are considered allies in reproduction. We synthesized current knowledge about uNK cells, their involvement in reproduction and their main functions in placental vascular remodeling and trophoblast invasion. One of the issues that this review presents is the enormous complexity involved in studying the immune system in reproduction. The complexity in the immunology of the maternal-foetal interface lies in the great variety of participating molecules, the processes and interactions that occur at different levels (molecular, cellular, tissue, etc.) and the great diversity of genetic combinations that are translated into different types of responses.

WIDER IMPLICATIONS

Insights into uNK cells could offer an important breakthrough for ART outcomes, since each patient could be assessed based on the combination of HLA and its receptors in their uNK cells, evaluating the critical interactions at the materno-foetal interface. However, owing to the technical challenges in studying uNK cells in vivo, there is still much knowledge to gain, particularly regarding their exact origin and functions. New studies using novel molecular and genetic approaches can facilitate the identification of mechanisms by which uNK cells interact with other cells at the materno-foetal interface, perhaps translating this knowledge into clinical applicability.

Localization of Indoleamine 2,3-Dioxygenase-1 and Indoleamine 2,3-Dioxygenase-2 at the Human Maternal-Fetal Interface

Immunohistochemical localization of indoleamine 2,3-dioxygenase-1 and indoleamine 2,3-dioxygenase-2, the first and rate-limiting enzyme in tryptophan metabolism along the kynurenine pathway, has been studied in order to better understand the physiological significance of these enzymes at the maternal-fetal interface of human pregnancy with a gestational age of 7 weeks (n = 1) and term placentas (37-40 weeks of gestation, n = 5). Indoleamine 2,3-dioxygenase-1 protein immunoreactivity was found in glandular epithelium of the decidua and the endothelium of the fetal blood vessels in the villous stroma with some additional positive cells in the villous core and in the decidua. The syncytiotrophoblast stained strongly for indoleamine 2,3-dioxygenase-2. Immunoreactivity of kynurenine, the immediate downstream product of indoleamine 2,3-dioxygenase-mediated tryptophan metabolism, showed the same localization as that of indoleamine 2,3-dioxygenase-1 and indoleamine 2,3-dioxygenase-2, suggesting these are functional enzymes. Interferon-γ added to placental villous explant culture markedly stimulated expression level of both mRNA and immunoreactivity of indoleamine 2,3-dioxygenase-1. The different cellular expression and interferon-γ sensitivity of these enzymes at the maternal-fetal interface suggests distinct physiological roles for each enzyme in normal human viviparity.

Human Term Pregnancy Decidual NK Cells Generate Distinct Cytotoxic Responses

Decidual NK cells (dNK) are the main lymphocyte population in early pregnancy decidual mucosa. Although dNK decrease during pregnancy, they remain present in decidual tissues at term. First trimester dNK facilitate trophoblast invasion, provide protection against infections, and were shown to have many differences in their expression of NKRs, cytokines, and cytolytic capacity compared with peripheral blood NK cells (pNK). However, only limited data are available on the phenotype and function of term pregnancy dNK. In this study, dNK from human term pregnancy decidua basalis and decidua parietalis tissues were compared with pNK and first trimester dNK. Profound differences were found, including: 1) term pregnancy dNK have an increased degranulation response to K562 and PMA/ionomycin but lower capacity to respond to human CMV-infected cells; 2) term pregnancy dNK are not skewed toward recognition of HLA-C, as was previously shown for first trimester dNK; and 3) protein and gene expression profiles identified multiple differences between pNK, first trimester, and term pregnancy dNK, suggesting term pregnancy dNK are a distinct type of NK cells. Understanding the role of dNK throughout pregnancy is of high clinical relevance for studies aiming to prevent placental inflammatory disorders as well as maternal-to-fetal transmission of pathogens.

Indoleamine 2,3-dioxygenase and trophoblast invasion in caesarean scar pregnancy: Implications for the aetiopathogenesis of placenta accreta spectrum

Immunohistochemical localisation of indoleamine 2,3-dioxygenase was studied in order to better understand the pathophysiology of placenta accreta spectrum. In the decidua staining for indoleamine 2,3-dioxygenase was found in the glandular epithelium with some additional positive cells. Extravillous cytotrophoblast invasion was present in the myometrium which was not covered by the decidual tissue whereas myometrial invasion of cytotrophoblasts was absent where this tissue lay deep to decidua. These results suggest that indoleamine 2,3-dioxygenase expression in the decidua may normally control trophoblast invasion and absence of its expression where decidua is absent may be involved in the pathogenesis of the over-invaded placenta.

The phenotype of decidual CD56+ lymphocytes is influenced by secreted factors from decidual stromal cells but not macrophages in the first trimester of pregnancy

During the first trimester of pregnancy the decidua is comprised of decidual stromal cells (DSC), invading fetal trophoblast cells and maternal leukocytes, including decidual natural killer (dNK) cells and macrophages. dNK cells are distinct from peripheral blood NK cells and have a role in regulating trophoblast invasion and spiral artery remodelling. The unique phenotype of dNK cells results from the decidual environment in which they reside, however the interaction and influence of other cells in the decidua on dNK phenotype is unknown. We isolated first trimester DSC and decidual macrophages and investigated the effect that DSC and decidual macrophage secreted factors have on CD56+ decidual lymphocyte receptor expression and cytokine secretion (including dNK cells). We report that DSC secreted factors induce the secretion of the cytokines IL-8 and IL-6 from first trimester CD56+ cells. However, neither DSC nor decidual macrophage secreted factors changed CD56+ cell receptor expression. These results suggest that secreted factors from DSC influence CD56+ decidual lymphocytes during the first trimester of pregnancy and therefore may play a role in regulating the unique phenotype and function of dNK cells during placentation.

Placental bed research: II. Functional and immunological investigations of the placental bed

Research on the placenta as the interface between the mother and the fetus has been undertaken for some 150 years, and in 2 subsequent reviews, we attempted to summarize the situation. In the first part, we described the discovery of unique physiological modifications of the uteroplacental spiral arteries, enabling them to cope with a major increase in blood flow necessary to ensure proper growth of the fetus. These consist of an invasion of the arterial walls by trophoblast and a progressive disappearance of its normal structure. Researchers then turned to the pathophysiology of the placental bed and in particular to its maternal vascular tree. This yielded vital information for a better understanding of the so-called great obstetrical syndromes (preeclampsia, fetal growth restriction, premature labor and delivery, placenta accreta). Systematic morphological investigations of the uteroplacental vasculature showed that preeclampsia is associated with decreased or failed transformation of spiral arteries and the persistence of endothelial and smooth muscle cells in segments of their myometrial portion. Here we report on recent functional investigations of the placental bed, including in situ biophysical studies of uteroplacental blood flow and vascular resistance, and manipulation of uteroplacental perfusion. These new methodologies have provided a novel way of identifying pregnancies in which remodeling is impaired. In animals it is now possible to manipulate uteroplacental blood flow, leading to an enhancement of fetal growth; this opens the way to trials in abnormal human pregnancies. In this second part, we explored a new, extremely important area of research that deals with the role of specific subsets of leukocytes and macrophages in the placental bed. The human first-trimester decidua is rich in leukocytes called uterine natural killer cells. Both macrophages and uterine natural killer cells increase in number from the secretory endometrium to early pregnancy and play a critical role in mediating the process of spiral artery transformation by inducing initial structural changes. It seems therefore that vascular remodeling of spiral arteries is initiated independently of trophoblast invasion. Dysregulation of the immune system may lead to reproductive failure or pregnancy complications, and in this respect, recent studies have advanced our understanding of the mechanisms regulating immunological tolerance during pregnancy, with several mechanisms being proposed for the development of tolerance to the semiallogeneic fetus. In particular, these include several strategies by which the trophoblast avoids maternal recognition. Finally, an important new dimension is being explored: the likelihood that pregnancy syndromes and impaired uteroplacental vascular remodeling may be linked to future maternal and even the child's cardiovascular disease risk. The functional evidence underlying these observations will be discussed.

Progestogens and immunology

Fifty percent of fetal antigens are of paternal origin. These are recognized by the maternal immune system, thereby resulting in lymphocyte activation and the induction of progesterone receptors (PRs) in immune cells. Upon binding of progesterone to PRs on lymphocytes, a downstream mediator called progesterone-induced blocking factor (PIBF) is produced. The full-length PIBF is a 90 kDa protein; however, because of alternative splicing, several smaller isoforms are also produced. While the 90 kDa molecule plays a role in cell cycle regulation, the small isoforms are localized in the cytoplasm, and after secretion, they bind to their receptors on other cells and act in a cytokine-like manner. The communication between the embryo and the maternal immune system is established through PIBF-containing extracellular vesicles. PIBF induces an increased production of Th2 cytokines and inhibits degranulation of NK cells, and by regulating the maternal immune response, it contributes to successful implantation and maintenance of pregnancy.

uNK cell-derived TGF-β1 regulates the long noncoding RNA MEG3 to control vascular smooth muscle cell migration and apoptosis in spiral artery remodeling

Successful pregnancy depends on correct spiral artery (SpA) remodeling, and thus, on normal patterns of the vascular smooth muscle cell (VSMC) apoptosis and migration. Uterine natural killer (uNK) cells-derived transforming growth factor β1 (TGF-β1) is known to mediate the separation of VSMC layers via as yet unknown mechanisms. Likewise, the long noncoding RNA maternally expressed gene 3 (MEG3) is a tumor suppressor that has been shown to regulate cancer cell apoptosis and migration; however, its role in VSMC loss is unclear. Thus, the aim of the present study was to assess the effects of uNK-derived TGF-β1 and MEG3 on VSMC function during SpA. Analyses were conducted to assess the effects of downregulating MEG3 expression, and/or administering treatments to increase or block TGF-β1 signaling on VSMC survival and behavior. The results of these analyses showed that treating the VSMC with uNK cell-derived supernatant or recombinant human TGF-β1 promoted MEG3 and matrix metalloprotease 2 expression and VSMC apoptosis and migration, and suppressed VSMC proliferation. Conversely, MEG3 silencing promoted VSMC proliferation and inhibited VSMC apoptosis and migration. Notably, TGF-β1 signaling induction had no significant effect on the proliferation, apoptosis, nor migration of the MEG3-silenced VSMC. Together, these findings suggest that MEG3 is regulated by uNK-derived TGF-β1, and itself mediates VSMC apoptosis and migration; thus, it may be an important positive regulator of VSMCs separation during maternal SpA remodeling.

Pre-eclampsia: the role of highly active antiretroviral therapy and immune markers

PURPOSE OF THE REVIEW

This review highlights the role immune cells and markers such as natural killer (NK) cells, cytokines and human leukocyte antigen (HLA-G) play in predisposing HIV-infected women who are on HAART to develop PE, thus contributing to a better understanding and early diagnosis of PE with a subsequent reduction in maternal foetal and neonatal deaths.

RECENT FINDINGS

Pregnant women infected with the Human Immunodeficiency Virus (HIV) have a 25% risk of mother to child transmission. This risk, however, decreases to 2% if the women is on treatment. Highly active antiretroviral therapy (HAART) is the recommended treatment for both pregnant and non-pregnant women infected with HIV. Treatment with HAART is reported to potentiate predisposition to the development of hypertensive disorders of pregnancy such as pre-eclampsia (PE). Pre-eclampsia accounts for 7-10% of abnormal pregnancies worldwide. Studies demonstrate that pregnant women with HIV have PE at lower frequencies than uninfected women, however, the converse is observed upon HAART initiation. HIV-infected women on HAART exhibit a greater tendency to develop PE, emanating from immune reconstitution induced by HAART. There is paucity of information as to the pathogenesis of PE upon HAART initiation and there are, therefore, controversial data as to whether HAART predisposes women to a lower, equal or higher risk of PE development compared to the general population, further investigations on the impact of HIV infection and HAART on the immune response and rate of PE development in HIV infected pregnant women are urgently needed.

Evaluating Stress during Pregnancy: Do We Have the Right Conceptions and the Correct Tools to Assess It?

Gestational stress is believed to increase the risk of pregnancy failure and perinatal and adult morbidity and mortality in both the mother and her child or children. However, some contradictions might arise from methodological issues or even from differences in the philosophical grounds that guide the studies on gestational stress. Biased perspectives could lead us to use and/or design inadequate/incomplete panels of biochemical determinations and/or psychological instruments to diagnose it accurately during pregnancy, a psychoneuroimmune-endocrine state in which allostatic loads may be significant. Here, we review these notions and propose a model to evaluate and diagnose stress during pregnancy.

The Role of Progesterone in Feto-Maternal Immunological Cross Talk

This review aims to provide a brief historical overview of the feto-maternal immunological relationship, which profoundly influences the outcome of pregnancy. The initial question posed in the 1950s by Medawar [Symp Soc Exp Biol. 1953; 7: 320-338] was based on the assumption that the maternal immune system recognizes the fetus as an allograft. Indeed, based on the association between HLA-matching and spontaneous miscarriage, it became obvious that immunological recognition of pregnancy is required for a successful gestation. The restricted expression of polymorphic HLA antigens on the trophoblast, together with the presence of nonpolymorphic MHC products, excludes recognition by both T and NK cells of trophoblast-presented antigens; however, γδ T cells, which constitute the majority of decidual T cells, are likely candidates. Indeed, a high number of activated, progesterone receptor-expressing γδ T cells are present in the peripheral blood of healthy pregnant women and, in the presence of progesterone, these cells secrete an immunomodulatory protein called progesterone-induced blocking factor (PIBF). As early as in the peri-implantation period, the embryo communicates with the maternal immune system via PIBF containing extracellular vesicles. PIBF contributes to the dominance of Th2-type reactivity which characterizes normal pregnancy by inducing increased production of Th2 cytokines. The high expression of this molecule in the decidua might be one of the reasons for the low cytotoxic activity of decidual NK cells.

Maternal natural killer cell immunoglobulin receptor genes and human leukocyte antigen-C ligands influence recurrent spontaneous abortion in the Han Chinese population

The underlying mechanism of recurrent spontaneous abortion (RSA) has remained elusive for many years. Several previous studies have suggested that the killer cell immunoglobulin receptor (KIR) gene family is associated with RSA, however, it is not clear exactly how. The present study detected KIR and human leukocyte antigen-C (HLA-C) genes in 110 Han Chinese women with unexplained RSA and 105 Han Chinese healthy females. The aim of the present study was to determine if certain genotypes were more susceptible to the occurrence of miscarriage. The frequency of KIR genes and different KIR haplotypes in the 2 groups demonstrated no statistical differences. However, in women who had miscarried ≥3 times, the frequency of KIR3DL1 was significantly reduced and the BB haplotype frequency was significantly higher compared with the control group. HLA-C2C2 was significantly increased in the KIR AB and KIR BB groups in the RSA groups compared with the control group. The women in the RSA group who had a homozygous HLA-C2C2 had a significantly higher frequency of the 2DS1 gene compared with the control group. The reduction of inhibitory gene and increased activation combinations may induce the activation of uterine natural killer cells, which may reduce the probability of fetal survival. To the best of our knowledge, the present study is the first report demonstrating the association between maternal KIR and HLA-C genes and RSA in women of a Han Chinese ethnicity. The present study revealed that females who miscarry ≥3 times may be used as selection criteria for RSA and so may exhibit higher research value.

Physiological and pathological angiogenesis in endometrium at the time of embryo implantation

Embryo establishes contact with the endometrium during implantation. Proper endometrial vascular development and maintenance at the time of embryo implantation is crucial for successful pregnancy. Vascular development at the maternal-embryo interface can be regulated by various cell types, of which uterine natural killer (uNK) cells play an important role. Abnormal angiogenesis and uNK cell number/function may lead to reproductive failure, particularly in women with recurrent miscarriage (RM) and women with recurrent implantation failure (RIF) after IVF-ET treatment, which are the important clinical hurdles in reproductive medicine to overcome. In this review, we aim to discuss the current knowledge of physiological angiogenic processes and the pathological angiogenesis at the time of implantation, as well as the possible mechanism and potential treatment.

Pre-Pregnancy Levels of Peripheral Natural Killer Cells as Markers for Immunomodulatory Treatment in Patients with Recurrent Miscarriage

Immunological risk factors in patients with recurrent miscarriage (RM) are discussed controversially. Abnormalities of natural killer cells (NK) have been described in RM patients. Lipid infusions are known to modulate lymphocyte subsets. The aim of this study was to identify immune parameters that predict success of treatment with lipid infusions in RM patients with elevated NK. In sum, n = 341 couples with RM were screened for established risk factors and peripheral lymphocyte subpopulations as well as uterine NK cells. We identified n = 136 patients with ≥ 2 consecutive RM and elevated NK. So far, n = 40 RM patients with NK disorders were treated with lipid infusions starting at positive pregnancy test, every 2 weeks until 12 + 0 weeks of gestation (GW) or miscarriage. The pre-pregnancy immune diagnostics in idiopathic RM (iRM) patients with ongoing pregnancy were compared to the group with miscarriages and healthy controls (n = 15). Pre-pregnancy immune diagnostics differed significantly between the groups, with significant higher levels of peripheral NK (% and /µL) in iRM patients who miscarried again compared to controls (p = 0.0035 and p = 0.0019). Furthermore, iRM patients show lower percentages of CD3⁺ lymphocytes than healthy controls (p = 0.0049). In n = 22/40 (55%) patients, pregnancy is ongoing >12 + 0 GW. RM patients with very high pre-pregnancy peripheral NK (pNK) lymphocytes might not benefit from lipid infusions. Pre-pregnancy immunomodulatory treatment in RM patients might be helpful to lower pNK levels and establish an immune environment which is supportive for fetal development.

Immune regulatory network in successful pregnancy and reproductive failures

Maternal immune system must tolerate semiallogenic fetus to establish and maintain a successful pregnancy. Despite the existence of several strategies of trophoblast to avoid recognition by maternal leukocytes, maternal immune system may react against paternal alloantigenes. Leukocytes are important components in decidua. Not only T helper (Th)1/Th2 balance, but also regulatory T (Treg) cells play an important role in pregnancy. Although the frequency of Tregs is elevated during normal pregnancies, their frequency and function are reduced in reproductive defects such as recurrent miscarriage and preeclampsia. Tregs are not the sole population of suppressive cells in the decidua. It has recently been shown that regulatory B10 (Breg) cells participate in pregnancy through secretion of IL-10 cytokine. Myeloid derived suppressor cells (MDSCs) are immature developing precursors of innate myeloid cells that are increased in pregnant women, implying their possible function in pregnancy. Natural killer T (NKT) cells are also detected in mouse and human decidua. They can also affect the fetomaternal tolerance. In this review, we will discuss on the role of different immune regulatory cells including Treg, γd T cell, Breg, MDSC, and NKT cells in pregnancy outcome.

PIBF positive uterine NK cells in the mouse decidua

Though uterine NK cells (u NK cells) contain cytotoxic granules, and selectively over- express the genes of perforin and granzymes, during normal pregnancy, they are not cytotoxic. Progesterone is indispensable for the establishment and maintenance of pregnancy both in humans and in mice. Mouse uterine NK cells do not express the classical progesterone receptor, yet progesterone affects the recruitment and function of uterine NK cells, the latter partly via the Progesterone-Induced Blocking Factor (PIBF). We demonstrated PIBF positive granulated cells in the mouse decidua. The aim of this study was to characterize these cells by lectin immunohistochemistry and anti-perforin reactivity. PIBF+ granulated cells were absent from the deciduae of alymphoid mice, but appeared in the decidua of those that had been reconstituted with bone marrow from male BALB/c mice. PIBF+ granulated cells bound the DBA lectin, suggesting their NK cell nature, and also contained perforin, which co-localized with PIBF in the cytoplasmic granules. In anti-progesterone treated mice all of the PIBF+ cells were perforin positive at g. d. 12.5, in contrast to the 54% perforin positivity of PIBF+ cells in untreated mice.

CONCLUSION

The PIBF+ granulated cells in the decidua belong to the NK population, and PIPB co-localizes with perforin in the cytoplasmic granules.

dNK derived IFN-γ mediates VSMC migration and apoptosis via the induction of LncRNA MEG3: A role in uterovascular transformation

INTRODUCTION

Appropriate spiral artery remodeling is critical for successful fetal development and pregnancy outcomes. The vascular smooth muscle cell (VSMC) loss and separation, involving cell apoptosis and migration, plays an important role in this process. Decidual natural killer cells (dNK)-derived interferon gamma (IFN-γ), a key regulator of uterine arterial remodeling, can facilitate separation of VSMC layers, however, the specific mechanisms of it action are unknown. Long non-coding RNA MEG3 functions as tumor suppressor by regulating apoptosis and migration. Moreover, IFN-γ has been shown to influence cell vitality through regulating MEG3 expression. However, the functional role of dNK derived IFN-γ and MEG3 on VSMC viability, as well as the relationship between IFN-γ and MEG3 in VSMCs, has not been completely elaborated.

METHODS

The up-regulation strategies and reagent treatment were employed to detect the effects of MEG3 and dNK/IFN-γ on VSMC proliferation, apoptosis and migration. At the same time, MEG3, p53 and matrix metalloproteinase 2 (MMP-2) expressions were investigated.

RESULTS

dNK/IFN-γ treatment led to up-regulation of MEG3 expression in VSMCs. Both MEG3 over-expression and dNK/IFN-γ treatment inhibited VSMC proliferation, stimulated VSMC migration and resulted in a small but significant induction of VSMC apoptosis, as well as promoted p53 and MMP-2 expression in VSMCs.

DISCUSSION

MEG3 is regulated by dNK-derived IFN-γ and regulates VSMC migration and apoptosis. Therefore, it may be an important positive regulator in VSMC loss from the maternal uterine spiral arteries during vascular transformation.

The decidua-the maternal bed embracing the embryo-maintains the pregnancy

The decidua has been known as maternal uterine tissue, which plays essential roles in protecting the embryo from being attacked by maternal immune cells and provides nutritional support for the developing embryo prior to placenta formation. However, there are questions that still remain to be answered: (1) How does the decidua supply nutrition and provide a physical scaffold for the growing embryo, before placental vascular connection is established? (2) How is the balance between preventing an anti-embryo immune response and protecting both embryo and mother from infections established? To understand basic personas in decidual tissues, we review the structure of the decidua composed of terminally differentiated uterine stromal cells, blood vessels, and a number of repertoire of uterine local immune cells, including the well-known uterine natural killer (uNK) cells and recently discovered innate lymphoid cells (ILCs). Decidual macrophages and uterine dendritic cells (DCs) are supposed to modulate adaptive immunity via balancing cytokines and promoting generation of regulatory T (Treg) cells. During decidualization, vascular and tissue remodeling in the uterus provide nutritional and physical support for the developing embryo. Secretion of various cytokines and chemokines from both the embryo and the decidual cells activates multiple signaling network between the mother and the embryo upon implantation. Defects in the decidual development during early pregnancy result in loss of pregnancy or complications in later gestational stage.

The role of decidual NK cells in pregnancies with impaired vascular remodelling

The pathologies of the dangerous pregnancy complications pre-eclampsia (PE) and fetal growth restriction (FGR) are established in the first trimester of human pregnancy yet we know little of how this happens. Finely tuned interactions between maternal and placental cells are essential for pregnancy to progress without complications; however, the precise nature of this cross-talk and how it can go wrong are crucial questions that remain to be answered. This review summarises recent studies examining the role played by natural killer cells in regulating normal placentation and remodelling. Their involvement when it is impaired in PE/FGR pregnancies will additionally be discussed.

An In Vitro Coculture Model to Study Cytokine Profiles of Natural Killer Cells During Maternal Immune Cell-Trophoblast Interactions

OBJECTIVES

The cytokine milieu at the implantation site plays a role in human pregnancy. Th2 cytokines, such as interleukin (IL)-4 and IL-10, stimulate growth and development of placenta, whereas Th1 cytokines, such as tumor necrosis factor-alpha (TNF-alpha), are associated with pregnancy complications. Natural killer (NK) cells predominate at the implantation site. The aim of the present study is to investigate cytokine expression in NK cells when they are in close contact with JEG-3 trophoblast-like cells using an in vitro coculture model.

METHODS

Female peripheral blood mononuclear cells (PBMCs) were cocultured with JEG-3 cells for 24 hours. PBMCs were harvested from the cocultures and stimulated with 25 ng/mL phorbol myristate acetate and 1 micromol/mL ionomycin in the presence of 2 micromol/mL monensin. NK cells were analyzed by flow cytometry for intracellular TNF-alpha, interferon-gamma (IFN-gamma), and IL-4 and IL-10 cytokines. Controls were PBMCs cultured without JEG-3 cells.

RESULTS

The proportion of CD56+/TNF-alpha(+) NK cells was significantly decreased when they were in coculture with JEG-3 cells (26.1%) as compared to without JEG-3 cell coculture (40.8%) (P < .05). There was no difference in the proportion of CD56(+) NK cells expressing intracellular IFN-gamma, IL-4, and IL-10. Down-regulation of CD56+/TNF-alpha(+) NK cell levels was dependent on direct cell-to-cell contact between NK cells and JEG-3 cells. The expression of human leukocyte antigen (HLA)-G on trophoblast cell lines did not affect CD56+/TNF-alpha(+) NK cell levels under these experimental conditions.

CONCLUSION

We report that JEG-3 cells induce down-regulation of intracellular CD56+/TNF-alpha(+) NK cell levels. It is speculated that trophoblasts may secure themselves from NK cell cytotoxicity via this mechanism.

Evaluation of endometrial natural killer cell expression of CD4, CD103, and CD16 cells in women with unexplained infertility

OBJECTIVE

To determine whether natural killer cell (NK) concentrations in the mid-secretory endometrial tissue of women with unexplained infertility differ from those in the mid-secretory endometrial tissue of fertile women.

METHODS

This study was conducted with 22 patients with unexplained infertility caused by unsuccessful ovulation induced with gonadotrophins and 12 healthy fertile women, who formed a control group. Mid-secretory endometrial tissue samples were obtained with a Pipelle catheter, and the endometrial NK cell phenotypes were determined by flow cytometry.

RESULTS

The median number of CD4+ cells in the endometrium was significantly lower in women with unexplained infertility compared with in the fertile controls (3.31 vs. 5.81; p=0.02). The CD4(+)/CD8(+) cell ratio in the unexplained-infertility group was significantly lower than that in the control group (0.42 vs. 0.76, p=0.01). The median number of CD103(+) cells in the endometrium of the infertile group was significantly lower than that in the endometrium of the control group (4.40 vs. 6.73, p=0.02). The median number of CD16(+) cells was significantly higher in infertile women than in control women (0.12 vs. 0.001, p=0.01).

CONCLUSIONS

Significant reductions in the numbers of CD4(+) and CD103(+) cells as well as in the CD4(+)/CD8(+) ratio but an increased number of CD16(+) cells in the endometrium of infertile women suggest that disordered NK cell activity may be a contributor to the etiology of unexplained infertility.

A shift in the balance of T17 and Treg cells in menstrual blood of women with unexplained recurrent spontaneous abortion

To determine usefulness of menstrual blood for assessment of differential frequency of T cell subsets, peripheral blood (PB) and menstrual blood (MB) from healthy fertile (n=15), unexplained recurrent spontaneous abortion (URSA) women (n=15) and unexplained infertile women (n=8) were collected in the second day of menstrual bleeding. Frequency of T cell subsets was measured by flow cytometry. URSA and unexplained infertile patients had higher frequency of TCRαβ(+)CD3(+)CD56(-) and CD45RO(+) T cells as well as CD45RO(+)/CD45RO(-) ratio in PB as compared to MB. Frequency of CD3(+)TCRγδ(+) cells in PB of unexplained infertile and MB of URSA patients were significantly lower than that in fertile group. In all groups MB contained higher percentage of CD4(+)CD25(+)Foxp3(+) regulatory and lower percentages of CD16(+) T cells compared to PB. T17 cells (CD3(+)CD56(-)IL-17(+)) was found to be significantly higher in MB of only fertile and unexplained infertile subjects and not URSA patients in comparison with PB. Compared to PB, only fertile women had higher T17:Treg ratio in their MB. URSA women had significantly lower MB T17 cells and T17:Treg ratio compared to those in fertile and unexplained infertile women. Based on the findings presented here, we speculate that MB has its own unique immune milieu which is not solely continuation of the immune environment of secretory endometrium. Indeed, immunophenotyping of MB immune cells could potentially be a useful tool for investigation of immunological disturbances in pregnancy-related disorders.

Menstrual cycle distribution of uterine natural killer cells is altered in heavy menstrual bleeding

Heavy menstrual bleeding (HMB) affects 30% of women of reproductive age and significantly interferes with quality of life. Altered endometrial vascular maturation has been reported in HMB and recurrent miscarriage, the latter associated with increased uterine natural killer (uNK) cell numbers. This study compared endometrial leukocyte populations in controls and women with HMB. Formalin-fixed paraffin-embedded endometrial biopsies from controls (without endometrial pathology) and HMB were immunostained for CD14 (macrophages), CD56 (uNK cells), CD83 (dendritic cells), FOXP3 (regulatory T cells/Tregs), CD3 and CD8 (T cells). Leukocyte numbers were analysed as a percentage of total stromal cells in five randomly selected fields of view in the stratum functionalis of each sample. In control women across the menstrual cycle, 2-8% of total stromal cells were CD3(+) cells, 2-4% were CD8(+) T cells and 6-8% were CD14(+) macrophages. Compared with controls, CD3(+) cells were reduced during the mid-secretory phase (4%, P<0.01) and increased in the late secretory phase (12%, P=0.01) in HMB. CD83(+) dendritic cells and FOXP3(+) Tregs were scarce throughout the menstrual cycle in both groups. In controls, 2% of stromal cells in proliferative endometrium were CD56(+) uNK cells, increasing to 17% during the late secretory phase. In HMB, CD56(+) uNK cells were increased in the proliferative (5%, P<0.01) and early secretory (4%, P<0.02) phases, but reduced (10%, P<0.01) in the late secretory phase. This study demonstrates dysregulation of uNK cells in HMB, the functional consequence of which may have an impact on endometrial vascular development and/or endometrial preparation for menstruation.

Human dNK cell function is differentially regulated by extrinsic cellular engagement and intrinsic activating receptors in first and second trimester pregnancy

Decidual natural killer (dNK) cells express an array of activation receptors to regulate placental immunity and development during early pregnancy. We investigated the functional character of human dNK cells during the first and second trimester of gestation and the interaction between dNK and trophoblast cells. Although the frequency of CD56⁺CD16^- dNK among the total CD45⁺ leukocytes did not change over this period, the expression of the activating receptors, NKp80 and NKG2D, was greatly upregulated. We observed a significantly higher number of extravillous trophoblast cells in proximity to the dNK cells in the first trimester in comparison with the second trimester decidua. NKG2D expression by first trimester dNK cells was decreased when co-cultured with the HTR-8 trophoblast cell line. In the second trimester, functional markers of dNK activation, i.e., angiogenic factor production (e.g., vascular endothelial growth factor, interleukin-8, interferon-gamma), remained stable despite an increase in NKp80 or NKG2D surface expression. Furthermore, the degranulation capacity of dNK cells, as assessed by CD107a, was decreased in the second trimester. We suggest that in the first trimester, trophoblast-dNK interactions generate a population of dNK cells with a suppressed activating phenotype. In the second trimester, the loss of trophoblast-dNK interactions led to the inhibition of dNK cell function, although their activating receptor expression was increased. We speculate that during pregnancy, two mechanisms operate to modulate the dNK cell activation:suppression of activating receptor levels in the first trimester by trophoblasts and disengagement of receptor-ligand coupling in the second trimester.

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.

Oxygen modulates human decidual natural killer cell surface receptor expression and interactions with trophoblasts

Decidual natural killer (dNK) cells have been shown to both promote and inhibit trophoblast behavior important for decidual remodeling in pregnancy and have a distinct phenotype compared to peripheral blood NK cells. We investigated whether different levels of oxygen tension, mimicking the physiological conditions of the decidua in early pregnancy, altered cell surface receptor expression and activity of dNK cells and their interactions with trophoblast. dNK cells were isolated from terminated first-trimester pregnancies and cultured in oxygen tensions of 3%, 10%, and 21% for 24 h. Cell surface receptor expression was examined by flow cytometry, and the effects of secreted factors in conditioned medium (CM) on the trophoblast cell line SGHPL-4 were assessed in vitro. SGHPL-4 cells treated with dNK cell CM incubated in oxygen tensions of 10% were significantly more invasive (P < 0.05) and formed endothelial-like networks to a greater extent (P < 0.05) than SGHPL-4 cells treated with dNK cell CM incubated in oxygen tensions of 3% or 21%. After 24 h, a lower percentage of dNK cells expressed CD56 at 21% oxygen (P < 0.05), and an increased percentage of dNK cells expressed NKG2D at 10% oxygen (P < 0.05) compared to other oxygen tensions, with large patient variation. This study demonstrates dNK cell phenotype and secreted factors are modulated by oxygen tension, which induces changes in trophoblast invasion and endovascular-like differentiation. Alterations in dNK cell surface receptor expression and secreted factors at different oxygen tensions may represent regulation of function within the decidua during the first trimester of pregnancy.

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.

Effects of Acupuncture on CCL2 and CXCL8 Expression and the Subset of uNK Cells in Rats with Embryo Implantation Failure

The present study was designed to investigate the efficacy and mechanism of acupuncture treatment on embryo implantation failure in rats. The pregnant rats were randomized into normal group (N), implantation failure group (M), acupuncture treatment group (A), and progestin treatment group (W). The embryo implantation failure model was established by mifepristone. Efficacy of acupuncture treatment was evaluated by the number of implanted embryos. The expression of CCL2 and CXCL8 and the subset of uterine natural killer cells in the endometrium were detected. We demonstrated that the number of implanted embryos was dramatically reduced after mifepristone (M group) treatment, while the acupuncture (A group) and progestin (W group) treatments significantly rescued impaired embryo implantation. The protein and mRNA expressions of CCL2 and CXCL8 were significantly reduced by mifepristone treatment, but the attenuated expression of CCL2 and CXCL8 was markedly reversed by acupuncture or progestin treatment. More importantly, acupuncture and progestin could markedly increase the subset of uNK cells in rats with embryo implantation failure. These evidences suggest that acupuncture is able to modulate the endometrial immune microenvironment and thus improve embryo implantation in pregnant rats, which provides solid experimental evidence for the curative effect of acupuncture treatment on infertility.

Natural killer cells in human autoimmune disorders

Natural killer (NK) cells are innate lymphocytes that play a critical role in early host defense against viruses. Through their cytolytic capacity and generation of cytokines and chemokines, NK cells modulate the activity of other components of the innate and adaptive immune systems and have been implicated in the initiation or maintenance of autoimmune responses. This review focuses on recent research elucidating a potential immunoregulatory role for NK cells in T-cell and B-cell-mediated autoimmune disorders in humans, with a particular focus on multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematous. A better understanding of the contributions of NK cells to the development of autoimmunity may lead to novel therapeutic targets in these diseases.

Interaction between natural killer cells and regulatory T cells: perspectives for immunotherapy

Regulatory T (Treg) cells and natural killer (NK) cells are key players in the immune system. The interaction between these two cell types has been reported to be beneficial in healthy conditions such as pregnancy. However, in the case of certain pathologies such as autoimmune diseases and cancer this interaction can become detrimental, as Treg cells have been described to suppress NK cells and in particular to impair NK cell effector functions. This review aims to discuss the recent information on the interaction between Treg cells and NK cells under healthy and pathologic conditions, to describe the specific conditions in which this interaction takes place, the effect of Treg cells on hematopoietic stem cell differentiation and the consequences of this interaction on the optimization of immunotherapeutic protocols.

Complete and unidirectional conversion of human embryonic stem cells to trophoblast by BMP4

Human ES cells (hESC) exposed to bone morphogenic protein 4 (BMP4) in the absence of FGF2 have become widely used for studying trophoblast development, but the soundness of this model has been challenged by others, who concluded that differentiation was primarily toward mesoderm rather than trophoblast. Here we confirm that hESC grown under the standard conditions on a medium conditioned by mouse embryonic fibroblasts in the presence of BMP4 and absence of FGF2 on a Matrigel substratum rapidly convert to an epithelium that is largely KRT7(+) within 48 h, with minimal expression of mesoderm markers, including T (Brachyury). Instead, they begin to express a series of trophoblast markers, including HLA-G, demonstrate invasive properties that are independent of the continued presence of BMP4 in the medium, and, over time, produce extensive amounts of human chorionic gonadotropin, progesterone, placental growth factor, and placental lactogen. This process of differentiation is not dependent on conditioning of the medium by mouse embryonic fibroblasts and is accelerated in the presence of inhibitors of Activin and FGF2 signaling, which at day 2 provide colonies that are entirely KRT7(+) and in which the majority of cells are transiently CDX2(+). Colonies grown on two chemically defined media, including the one in which BMP4 was reported to drive mesoderm formation, also differentiate at least partially to trophoblast in response to BMP4. The experiments demonstrate that the in vitro BMP4/hESC model is valid for studying the emergence and differentiation of trophoblasts.

Manifestations of immune tolerance in the human female reproductive tract

Like other mucosal surfaces (e.g., the gastrointestinal tract, the respiratory tract), the human female reproductive tract acts as an initial barrier to foreign antigens. In this role, the epithelial surface and subepithelial immune cells must balance protection against pathogenic insults against harmful inflammatory reactions and acceptance of particular foreign antigens. Two common examples of these acceptable foreign antigens are the fetal allograft and human semen/sperm. Both are purposely deposited into the female genital tract and appropriate immunologic response to these non-self antigens is essential to the survival of the species. In light of the weight of this task, it is not surprising that multiple, redundant and overlapping mechanisms are involved. For instance, cells at the immunologic interface between self (female reproductive tract epithelium) and non-self (placental trophoblast cells or human sperm) express glycosylation patterns that mimic those on many metastatic cancer cells and successful pathogens. The cytokine/chemokine milieu at this interface is altered through endocrine and immunologic mechanisms to favor tolerance of non-self. The “foreign” cells themselves also play an integral role in their own immunologic acceptance, since sperm and placental trophoblast cells are unusual and unique in their antigen presenting molecule expression patterns. Here, we will discuss these and other mechanisms that allow the human female reproductive tract to perform this delicate and indispensible balancing act.

Evaluation of KIR genes in recurrent miscarriage

PURPOSE

Natural killer (NK) cells express killer immunoglobulin-like receptors (KIRs) which recognize HLA class I molecules on trophoblasts. KIRs could either activate NK cells or inhibit them to produce soluble factors necessary for the maintenance of pregnancy, thus they are suspected of being involved in the causes of recurrent miscarriage. The aim of this study was to evaluate whether there is any possible association between KIR genes, genotypes and recurrent miscarriage.

METHODS

The present study was carried out on 40 women who had unexplained recurrent miscarriage and 90 controls. Sequence-specific oligonucleotide probes analysis were used to investigate 16 KIR genes. All data were statistically analyzed by Fisher Exact Test.

RESULTS

The rate of Bx genotypes that consists elevated number of activating KIR genes was significantly higher (p = 0.014) in women with recurrent miscarriage when compared with the control group. Additionally, the frequency of AA genotype (AA1) of the subjects in the study group was significantly lower than the frequency of the subjects in the control group (p = 0,014). Furthermore, there were no statistically significant differences in the frequencies of the individual KIR genes between women with recurrent miscarriage and the control group.

CONCLUSIONS

Inclined balance of KIRs toward an activating state in NK cells may contribute to recurrent miscarriage.

Extravillous trophoblast and decidual natural killer cells: a remodelling partnership

BACKGROUND

During pregnancy, maternal uterine spiral arteries (SAs) are remodelled from minimal-flow, high-resistance vessels into larger diameter vessels with low resistance and high flow. Fetal extravillous trophoblasts (EVT) have important roles in this process. Decidual natural killer cells (dNK cells) are the major maternal immune component of the decidua and accumulate around SAs before trophoblast invasion. A role for dNK cells in vessel remodelling is beginning to be elucidated. This review examines the overlapping and dissimilar mechanisms used by EVT and dNK cells in this process and how this may mirror another example of tissue remodelling, namely cancer development.

METHODS

The published literature was searched using Pubmed focusing on EVT, dNK cells and SA remodelling. Additional papers discussing cancer development are also included.

RESULTS

Similarities exist between actions carried out by dNK cells and EVT. Both interact with vascular cells lining the SA, as well as with each other, to promote transformation of the SA. EVT differentiation has previously been likened to the epithelial-mesenchymal transition in cancer cells, and we discuss how dNK-EVT interactions at the maternal-fetal interface can also be compared with the roles of immune cells in cancer.

CONCLUSIONS

The combined role that dNK cells and EVT play in SA remodelling suggests that these interactions could be described as a partnership. The investigation of pregnancy as a multicellular system involving both fetal and maternal components, as well as comparisons to similar examples of tissue remodelling, will further identify the key mechanisms in SA remodelling that are required for a successful pregnancy.