Effector functions of human decidual NK cells in healthy early pregnancy are dependent on the specific engagement of natural cytotoxicity receptors

NK cell receptor profiling of endometrial and decidual NK cells reveals pregnancy-induced adaptations

Natural killer (NK) cells, with a unique NK cell receptor phenotype, are abundantly present in the non-pregnant (endometrium) and pregnant (decidua) humanuterine mucosa. It is hypothesized that NK cells in the endometrium are precursors for decidual NK cells present during pregnancy. Microenvironmental changes can alter the phenotype of NK cells, but it is unclear whether decidual NK cell precursors in the endometrium alter their NK cell receptor repertoire under the influence of pregnancy. To examine whether decidual NK cell precursors reveal phenotypic modifications upon pregnancy, we immunophenotyped the NK cell receptor repertoire of both endometrial and early-pregnancy decidual NK cells using flow cytometry. We showed that NK cells in pre-pregnancy endometrium have a different phenotypic composition compared to NK cells in early-pregnancy decidua. The frequency of killer-immunoglobulin-like receptor (KIR expressing NK cells, especially KIR2DS1, KIR2DL2L3S2, and KIR2DL2S2 was significantly lower in decidua, while the frequency of NK cells expressing activating receptors NKG2D, NKp30, NKp46, and CD244 was significantly higher compared to endometrium. Furthermore, co-expression patterns showed a lower frequency of NK cells co-expressing KIR3DL1S1 and KIR2DL2L3S2 in decidua. Our results provide new insights into the adaptations in NK cell receptor repertoire composition that NK cells in the uterine mucosa undergo upon pregnancy.

Toxoplasma gondii Causes Adverse Pregnancy Outcomes by Damaging Uterine Tissue-Resident NK Cells That Secrete Growth-Promoting Factors

Vertical transmission of the intracellular parasite, Toxoplasma gondii can lead to adverse pregnancy outcomes especially when infection occurs in early pregnancy. Decidual natural killer (dNK) cells accumulate at the maternal-fetal interface in large numbers during early pregnancy. Their nutritional roles during infection with T. gondii remain poorly defined. In the present study, we demonstrated that a functional deficiency of the uterine tissue-resident NK (trNK) cells, a subset of dNK cells, contributes to the adverse pregnancy outcomes induced by T. gondii in early pregnancy. Adverse pregnancy outcomes could be ameliorated by adoptive transfer of trNK cells. Moreover, fetal growth restriction could be improved after supplementation of growth-promoting factors. In addition to the widely recognized disturbance of the immune balance at the interface between the mother and the fetus, our study reveals a novel mechanism in T. gondii that contributes to the adverse pregnancy outcomes.

The use of immunomodulation therapy in women with recurrent implantation failure undergoing assisted conception: A multicentre cohort study

PROBLEM

Recurrent implantation failure (RIF) after multiple embryo transfers remains a vexing problem and immunomodulators have been used with conflicting results. This study aims to assess the effect of immunomodulation therapy on live birth rate (LBR) in women with RIF undergoing assisted reproduction treatment (ART).

METHOD OF STUDY DESIGN

This is a retrospective cohort study in multicentre network of private assisted conception units in the UK. The study included women who had at least two failed attempts of embryo transfers at CARE fertility network in the period from 1997 to 2018. Women in the treatment group had immunomodulator drugs in the form of corticosteroids, low molecular weight heparin (LMWH), and intravenous intralipid (IVIL) infusions, either separately or in combination, after immunological testing, in addition to standard ART whilst women in the control group had only ART without immunomodulators. The primary outcome was LBR per cycle. Secondary outcomes included the rates of clinical pregnancy (CPR), cumulative live birth (CLBR), and miscarriage.

RESULTS

A total of 27 163 ART cycles fulfilled the inclusion criteria, of which 5083 had immunomodulation treatment in addition to standard ART treatment, and 22 080 had standard ART treatment alone. Women in the treatment group were significantly older (mean age 38.5 vs. 37.1 years, p < .001), and had a higher number of previous failed ART cycles (mean 4.3 vs. 3.8, p < .01). There was a higher LBR in women who received immunomodulation therapy when compared with the control group (20.9% vs. 15.8%, odds ratio [OR] 1.4, 95% confidence interval [CI] 1.29-1.53, p < .001). Multivariate regression analysis showed that immunomodulation treatment was a significant independent predictor of live birth after adjusting for other confounders (adjusted OR [aOR] 1.33, 95% CI 1.15-1.54, p < .001). Survival analysis showed a higher CLBR in the treatment group (adjusted hazard ratio [aHR] 1.78, 95% CI 1.62-1.94, p < .001).

CONCLUSION(S)

This study provides evidence of a potential beneficial effect of immunomodulation therapy in women with RIF after immunological testing. There remains a need for high quality, adequately powered multicentre RCTs to robustly address the role of immunomodulation in women with RIF. There is also an urgent need for standardised screening tests for immune disorders that could preclude implantation.

The role of immune cells and mediators in preeclampsia

Preeclampsia is a hypertensive disorder of major concern in pregnancy than can lead to intrauterine growth restriction, placental abruption and stillbirth. The pathophysiology of preeclampsia is multifactorial, including not only kidney dysfunction but also endothelial dysfunction, as the maternal endothelium becomes exposed to placental factors that are released into the circulation and increase systemic levels of vasoconstrictors, oxidative stress, anti-angiogenic factors and inflammatory mediators. Importantly, inflammation can lead to insufficient placental perfusion and low birthweight in offspring. Various innate and adaptive immune cells and mediators have been implicated in the development of preeclampsia, in which oxidative stress is associated with activation of the maternal inflammatory response. Immune cells such as regulatory T cells, macrophages, natural killer cells, and neutrophils are known to have major causative roles in the pathology of preeclampsia, but the contributions of additional immune cells such as B cells, inflammatory cytokines and anti-angiotensin II type 1 receptor autoantibodies are also now recognized. Immunological interventions, therefore, have therapeutic potential in this disease. Here, we provide an overview of the immune responses that are involved in the pathogenesis of preeclampsia, including the role of innate and adaptive immune cells and mediators.

Populations of NK Cells and Regulatory T Cells in the Endometrium of Cycling Mares-A Preliminary Study

Endometrial immune cells are essential to support uterine functions across the estrous cycle and in preparation for pregnancy. It has been acknowledged that changes in phenotype and/or numbers of lymphocytes, such as regulatory T cells (Tregs) and NK cells, might result in lower fertility in women and mice. Little is known about equine endometrial immune cells across the estrous cycle. Here, we compared the populations of endometrial Tregs and NK cells in estrus and diestrus in mares. Endometrial biopsy and blood samples were taken in estrus and diestrus from 11 mares ages 4-12 years. Flow cytometry with anti-CD4, -CD25 and -FOXP3 and anti-NKp46 and -CD3 antibodies was used to determine the populations of Tregs and NK cells, respectively. The concentration of progesterone was measured with chemiluminescence immunoassay. The results were analyzed with paired Student t tests. The mean percentage of endometrial CD4⁺FOXP3⁺ Tregs was 13.7 ± 6.2% in diestrus and 14.5 ± 5.9% in estrus, while the mean percentage of endometrial CD4⁺FOXP3⁺CD25⁺ Tregs changed from 3.6 ± 2.1% in diestrus to 2 ± 2% in estrus (p = 0.0947). The mean proportion of CD3^-NKp46⁺ lymphocytes in the endometrium was not significantly different, with 6 ± 1% in estrus and 6.5 ± 1.4% in diestrus. There was a large variation in the percentage of NK cells between mares of 2.1-12.7%. This study showed, for the first time, the presence of CD4⁺FOXP3⁺CD25⁺ Tregs and CD3^-NKp46⁺ NK cells in the endometrium of non-pregnant cycling mares. The percentage of Tregs, and to a greater extent NK cells, showed large fluctuations between mares. Both Tregs and NK cells might be important for the preparation of the endometrium for semen deposition and pregnancy; however, further research is required.

The mechanisms underlying the immune control of Zika virus infection at the maternal-fetal interface

Unlike other Flaviviruses, Zika virus (ZIKV) infection during the first trimester of pregnancy causes severe pregnancy outcomes including the devastating microcephaly and diseases associated with placental dysfunctions. We have previously reported that the maternal decidua basalis, the major maternal-fetal interface, serves as a replication platform enabling virus amplification before dissemination to the fetal compartment. However, the rate of congenital infection is quite low, suggesting the presence of a natural barrier against viral infection. Using primary cells from first-trimester pregnancy samples, we investigated in this study how the maternal decidua can interfere with ZIKV infection. Our study reveals that whether through their interactions with dNK cells, the main immune cell population of the first-trimester decidua, or their production of proinflammatory cytokines, decidual stromal cells (DSCs) are the main regulators of ZIKV infection during pregnancy. We also validate the functional role of AXL as a crucial receptor for ZIKV entry in DSCs and demonstrate that targeted inhibition of ligand-receptor interaction at the early stage of the infection is effective in drastically reducing virus pathogenesis at the maternal-fetal interface. Collectively, our results provide insights into the mechanisms through which ZIKV infection and spreading can be limited. The strategy of circumventing viral entry at the maternal-fetus interface limits virus dissemination to fetal tissues, thereby preventing congenital abnormalities.

Prevention of intrauterine fetal growth restriction by administrating C1q/TNF-related protein 6, a specific inhibitor of the alternative complement pathway

PURPOSE

The latest treatments do not sufficiently prevent miscarriage and fetal growth restriction (FGR) in pregnant women. Here, we assessed the effects of a human protein, CTRP6, that specifically inhibits the activation of the alternative complement pathway on miscarriage, fetal and placental development.

METHODS

Pregnant CBA/J mice mated with DBA/2 male mice as a model of spontaneous abortion and FGR were randomly divided into the control and CTRP6 groups. In the CTRP6 group, the mice were intravenously administered CTRP6 on days 4.5 and 6.5 post-conception (dpc). The abortion rate and fetal and placental weights on 14.5 dpc were examined. Remodeling of the spiral artery was also assessed.

RESULTS

The abortion rate in the CTRP6 group (13%) was reduced compared to the control group (21%), but there was no statistical difference. The placental and fetal weights in the CTRP6 group were also heavier than those in the control (P < 0.05). Moreover, the thickness of the blood vessel wall in the CTRP6 group was significantly thinner than that in the control (P < 0.05) and comparable to that in the non-abortion model (CBA/J x BALB). The ratio of the inner-per-the-outer diameter of the spiral artery increased more in the CTRP6 group than that in the control (P < 0.05). As well, the Th1/Th2 cytokine ratio was significantly reduced by CTRP6 treatment.

CONCLUSIONS

Taken together, the supplementation with a protein that regulates the alternative complement pathway in vivo improves FGR and promotes spiral artery remodeling in a mouse model of miscarriage and FGR.

The Role of Different Lymphoid Cell Populations in Preeclampsia Pathophysiology

Preeclampsia (PE), new-onset hypertension during pregnancy, affects up to 10% of pregnancies worldwide. Despite being the leading cause of maternal and fetal morbidity and mortality, PE has no cure beyond the delivery of the fetal-placental unit. Although the exact pathogenesis of PE is unclear, there is a strong correlation between chronic immune activation; intrauterine growth restriction; uterine artery resistance; dysregulation of the renin-angiotensin system. Which contributes to renal dysfunction; and the resulting hypertension during pregnancy. The genesis of PE is thought to begin with insufficient trophoblast invasion leading to reduced spiral artery remodeling, resulting in decreased placental perfusion and thereby causing placental ischemia. The ischemic placenta releases factors that shower the endothelium and contribute to peripheral vasoconstriction and chronic immune activation and oxidative stress. Studies have shown imbalances in proinflammatory and anti-inflammatory cell types in women with PE and in animal models used to examine mediators of a PE phenotype during pregnancy. T cells, B cells, and natural killer cells have all emerged as potential mediators contributing to the production of vasoactive factors, renal and endothelial dysfunction, mitochondrial dysfunction, and hypertension during pregnancy. The chronic immune activation seen in PE leads to a higher risk for other diseases, such as cardiovascular disease, CKD, dementia during the postpartum period, and PE during a subsequent pregnancy. The purpose of this review is to highlight studies demonstrating the role that different lymphoid cell populations play in the pathophysiology of PE. Moreover, we will discuss treatments focused on restoring immune balance or targeting specific immune mediators that may be potential strategies to improve maternal and fetal outcomes associated with PE.

Number and function of uterine natural killer cells in recurrent miscarriage and implantation failure: a systematic review and meta-analysis

BACKGROUND

Uterine natural killer cells (uNK) are the most abundant lymphocytes found in the decidua during implantation and in first trimester pregnancy. They are important for early placental development, especially trophoblast invasion and transformation of the spiral arteries. However, inappropriate uNK function has been implicated in reproductive failure, such as recurrent miscarriage (RM) or recurrent implantation failure (RIF). Previous studies have mainly focussed on peripheral NK cells (pNK), despite the well-documented differences in pNK and uNK phenotype and function. In recent years, there has been an explosion of studies conducted on uNK, providing a more suitable representation of the immune environment at the maternal-foetal interface. Here, we summarize the evidence from studies published on uNK in women with RM/RIF compared with controls.

OBJECTIVE AND RATIONALE

The objectives of this systematic review and meta-analysis are to evaluate: differences in uNK level in women with RM/RIF compared with controls; pregnancy outcome in women with RM/RIF stratified by high and normal uNK levels; correlation between uNK and pNK in women with RM/RIF; and differences in uNK activity in women with RM/RIF compared with controls.

SEARCH METHODS

MEDLINE, EMBASE, Web of Science and Cochrane Trials Registry were searched from inception up to December 2020 and studies were selected in accordance with PRISMA guidelines. Meta-analyses were performed for uNK level, pregnancy outcome and uNK/pNK correlation. Narrative synthesis was conducted for uNK activity. Risk of bias was assessed by ROBINS-I and publication bias by Egger's test.

OUTCOMES

Our initial search yielded 4636 articles, of which 60 articles were included in our systematic review. Meta-analysis of CD56+ uNK level in women with RM compared with controls showed significantly higher levels in women with RM in subgroup analysis of endometrial samples (standardized mean difference (SMD) 0.49, CI 0.08, 0.90; P = 0.02; I2 88%; 1100 women). Meta-analysis of CD56+ uNK level in endometrium of women with RIF compared with controls showed significantly higher levels in women with RIF (SMD 0.49, CI 0.01, 0.98; P = 0.046; I2 84%; 604 women). There was no difference in pregnancy outcome in women with RM/RIF stratified by uNK level, and no significant correlation between pNK and uNK levels in women with RM/RIF. There was wide variation in studies conducted on uNK activity, which can be broadly divided into regulation and receptors, uNK cytotoxicity, cytokine secretion and effect of uNK on angiogenesis. These studies were largely equivocal in their results on cytokine secretion, but most studies found lower expression of inhibitory receptors and increased expression of angiogenic factors in women with RM.

WIDER IMPLICATIONS

The observation of significantly increased uNK level in endometrium of women with RM and RIF may point to an underlying disturbance of the immune milieu culminating in implantation and/or placentation failure. Further research is warranted to elucidate the underlying pathophysiology. The evidence for measuring pNK as an indicator of uNK behaviour is sparse, and of limited clinical use. Measurement of uNK level/activity may be more useful as a diagnostic tool, however, a standardized reference range must be established before this can be of clinical use.

NK Cells Under Hypoxia: The Two Faces of Vascularization in Tumor and Pregnancy

Environmental conditions greatly shape the phenotype and function of immune cells. Specifically, hypoxic conditions that exist within tissues and organs have been reported to affect both the adaptive and the innate immune system. Natural killer (NK) cells belong to the innate immune system. They are among the first immune cells responding to infections and are involved in tumor surveillance. NK cells produce cytokines that shape other innate and adaptive immune cells, and they produce cytolytic molecules leading to target cell killing. Therefore, they are not only involved in steady state tissue homeostasis, but also in pathogen and tumor clearance. Hence, understanding the role of NK cells in pathological and physiological immune biology is an emerging field. To date, it remains incompletely understood how the tissue microenvironment shapes NK cell phenotype and function. In particular, the impact of low oxygen concentrations in tissues on NK cell reactivity has not been systematically dissected. Here, we present a comprehensive review focusing on two highly compelling hypoxic tissue environments, the tumor microenvironment (pathological) and the decidua (physiological) and compare their impact on NK cell reactivity.

Immunity at maternal-fetal interface: KIR/HLA (Allo)recognition

Both KIR and HLA are the most variable gene families in the human genome. The recognition of the semi-allogeneic embryo-derived trophoblasts by maternal decidual NK (dNK) cells is essential for the establishment of the functional placenta. This recognition is based on the KIR-HLA interactions and trophoblast expresses a specific HLA profile that constitutes classical polymorphic HLA-C and non-classical oligomorphic HLA-E, HLA-F, and HLA-G molecules. This review highlights some features of the KIR/HLA-C (allo)recognition by decidual NK (dNK) cells as a main immune cell population specifically enriched at maternal-fetal interface during human early pregnancy. How KIR/HLA-C axis operates in pregnancy disorders and in the context of transplacental infections is discussed as well. We summarized old and new data on dNK-cell functional plasticity, their selective expression of KIR and fetal maternal/paternal HLA-C haplotypes present. Results showed that KIR-HLA-C combinations and the corresponding axis operate differently in each pregnancy, determined by the variability of both maternal KIR haplotypes and fetus' maternal/paternal HLA-C allotype combinations. Moreover, the maturation of NK cells strongly depends on if or not HLA allotypes for certain KIR are present. We suggest that the unique KIR/HLA combinations reached in each pregnancy (normal and pathological) should be studied according to well-defined guidelines and unified methodologies to have comparable results ease to interpret and use in clinics.

Placental colonization by Fusobacterium nucleatum is mediated by binding of the Fap2 lectin to placentally displayed Gal-GalNAc

While the existence of an indigenous placental microbiota remains controversial, several pathogens are known to be involved in adverse pregnancy outcomes. Fusobacterium nucleatum is an oral bacterium that is one of several bacteria associated with preterm birth. Oral fusobacteria translocate to the placenta hematogenously; however, the mechanisms localizing them to the placenta remain unclear. Here, using peanut agglutinin, we demonstrate that the level of Gal-GalNAc (Galβ1-3GalNAc; Thomsen Friedenreich antigen) found on trophoblasts facing entering maternal blood rises during gestation and is recognized by the fusobacterial Fap2 Gal-GalNAc lectin. F. nucleatum binding to human and mouse placenta correlates with Gal-GalNAc levels and is reduced upon O-glycanase treatment or with soluble Gal-GalNAc. Fap2-inactivated F. nucleatum shows reduced binding to Gal-GalNAc-displaying placental sections. In a mouse model, intravenously injected Fap2-expressing F. nucleatum, but not a Fap2 mutant, reduces mouse fetal survival by 70%.

Killer Timing: The Temporal Uterine Natural Killer Cell Differentiation Pathway and Implications for Female Reproductive Health

Natural killer (NK) cells are the predominant maternal uterine immune cell component, and they densely populate uterine mucosa to promote key changes in the post-ovulatory endometrium and in early pregnancy. It is broadly accepted that (a) immature, inactive endometrial NK (eNK) cells in the pre-ovulatory endometrium become activated and transition into decidual NK (dNK) cells in the secretory stage, peri-implantation endometrium, and continue to mature into early pregnancy; and (b) that secretory-stage and early pregnancy dNK cells promote uterine vascular growth and mediate trophoblast invasion, but do not exert their killing function. However, this may be an overly simplistic view. Evidence of specific dNK functional killer roles, as well as opposing effects of dNK cells on the uterine vasculature before and after conception, indicates the presence of a transitory secretory-stage dNK cell (s-dNK) phenotype with a unique angiodevelopmental profile during the peri-implantation period, that is that is functionally distinct from the angiomodulatory dNK cells that promote vessel destabilisation and vascular cell apoptosis to facilitate uterine vascular changes in early pregnancy. It is possible that abnormal activation and differentiation into the proposed transitory s-dNK phenotype may have implications in uterine pathologies ranging from infertility to cancer, as well as downstream effects on dNK cell differentiation in early pregnancy. Further, dysregulated transition into the angiomodulatory dNK phenotype in early pregnancy will likely have potential repercussions for adverse pregnancy outcomes, since impaired dNK function is associated with several obstetric complications. A comprehensive understanding of the uterine NK cell temporal differentiation pathway may therefore have important translational potential due to likely NK phenotypic functional implications in a range of reproductive, obstetric, and gynaecological pathologies.

Effects of Microvesicles Derived from NK Cells Stimulated with IL-1β on the Phenotype and Functional Activity of Endothelial Cells

Microvesicles (MVs) are plasma extracellular vesicles ranging from 100 (150) to 1000 nm in diameter. These are generally produced by different cells through their vital activity and are a source of various protein and non-protein molecules. It is assumed that MVs can mediate intercellular communication and modulate cell functions. The interaction between natural killer cells (NK cells) and endothelial cells underlies multiple pathological conditions. The ability of MVs derived from NK cells to influence the functional state of endothelial cells in inflammatory conditions has yet to be studied well. In this regard, we aimed to study the effects of MVs derived from NK cells of the NK-92 cell line stimulated with IL-1β on the phenotype, caspase activity, proliferation and migration of endothelial cells of the EA.hy926 cell line. Endothelial cells were cultured with MVs derived from cells of the NK-92 cell line after their stimulation with IL-1β. Using flow cytometry, we evaluated changes in the expression of endothelial cell surface molecules and endothelial cell death. We evaluated the effect of MVs derived from stimulated NK cells on the proliferative and migratory activity of endothelial cells, as well as the activation of caspase-3 and caspase-9 therein. It was established that the incubation of endothelial cells with MVs derived from cells of the NK-92 cell line stimulated with IL-1β and with MVs derived from unstimulated NK cells, leads to the decrease in the proliferative activity of endothelial cells, appearance of the pan leukocyte marker CD45 on them, caspase-3 activation and partial endothelial cell death, and reduced CD105 expression. However, compared with MVs derived from unstimulated NK cells, a more pronounced effect of MVs derived from cells of the NK-92 cell line stimulated with IL-1β was found in relation to the decrease in the endothelial cell migratory activity and the intensity of the CD54 molecule expression on them. The functional activity of MVs is therefore mediated by the conditions they are produced under, as well as their internal contents.

Significance of inhibitory maternal killer-cell immunoglobulin-like receptor (KIR) and fetal KIR ligand genotype combinations in placenta related obstetric complications

Some maternal killer-cell immunoglobulin-like receptor (KIR) and fetal KIR ligand genotypes are associated with obstetric complications, such as recurrent miscarriage, fetal growth restriction, preeclampsia, and preterm birth. However, how KIR/KIR ligand genotypes affect these placenta-related obstetric complications has not been fully understood. We aimed to demonstrate the association of maternal KIR-fetal KIR ligand genotype combinations with immunological/metabolic risk factor associated placenta-related obstetric complications. This study consisted of three groups of pregnant women: 1) Miscarriage group (n = 30), 2) Complicated Pregnancy (CP) group (n = 30), and 3) Control group (n = 30). The observed maternal genotype frequencies of all inhibitory and activating KIRs were similar in all groups (p > 0.05). However, inhibitory 2DL3 was quite frequent in the miscarriage group (p = 0.052). There was no difference between groups in terms of centromeric and telomeric maternal haplotypes (p > 0.05). The fetal group 1 HLA-C genotype was frequently detected in the miscarriage and CP groups with rates of 83.3 % and 93.3 % respectively, while the observed frequency was 70 % in the control group. The fetal group 2 HLA-C genotype was the same in all groups. The results demonstrated significantly less fetal group 2 HLA-C homozygosity in the CP groups when compared to the control group (p = 0.020). The fetal HLA-Bw4 genotype was detected more frequently in the miscarriage and CP groups (p = 0.028 and p = 0.001, respectively). The inhibitory KIR/KIR ligand genotype combinations of 2DL3-C1 and 3DL1-Bw4 were more frequent in the miscarriage and CP groups (p = 0.045 and p = 0.002, respectively). Enhanced NK cell inhibition may be one of the mechanisms underlying placenta-related obstetric complications.

Innate Immune Response to Viral Infections at the Maternal-Fetal Interface in Human Pregnancy

The placenta, the first and largest organ to develop after conception, not only nurtures and promotes the development of the conceptus, but, it also functions as a barrier against invading pathogens. Early phases of pregnancy are associated with expansion of specific subsets of Natural Killer cells (dNK) and macrophages (dMφ) at the maternal uterine mucosa, the basal decidua. In concert with cells of fetal origin, dNK cells, and dMφ orchestrate all steps of placenta and fetus development, and provide the first line of defense to limit vertical transmission. However, some pathogens that infect the mother can overcome this protective barrier and jeopardize the fetus health. In this review, we will discuss how members of the classical TORCH family (Toxoplasma, Other, Rubella, Cytomegalovirus, and Herpes simplex virus) and some emerging viruses (Hepatitis E virus, Zika virus, and SARS-CoV2) can afford access to the placental fortress. We will also discuss how changes in the intrauterine environment as a consequence of maternal immune cell activation contribute to placental diseases and devastating pregnancy outcomes.

Differences in the Expression of KIR, ILT Inhibitory Receptors, and VEGF Production in the Induced Decidual NK Cell Cultures of Fertile and RPL Women

RESULTS

KIR2DL1 and ILT-2 expression on idNK cells was higher in healthy women than in RPL patients. Sildenafil enhanced NKG2A expression in RPL patients. VEGF concentration was higher in fertile woman idNK cell cultures. idNK cells were more sensitive for necrosis in RPL than in fertile women. SC did not influence VEGF production or idNK cell apoptosis.

CONCLUSIONS

A combination of hypoxia, IL-15, and AZA promotes the conversion of pbNK into idNK cells CD56+CD16--expressing KIR receptors and produces VEGF. Alterations in KIR2DL1 and ILT-2 expression as well as impaired VEGF production were associated with RPL. SC affects NKG2A expression on RPL idNK cells. SC had no effect on VEGF release or idNK cell apoptosis.

The Role of Tim-3 on dNK Cells Dysfunction During Abnormal Pregnancy With Toxoplasma gondii Infection

Vertical transmission of Toxoplasma gondii (T. gondii) infection during gestation can result in severe complications such as abortion, congenital malformation, fetal teratogenesis, etc. Immune inhibitory molecule Tim-3 was discovered to be expressed on some decidual immune cells and participates in the maintenance of maternal-fetal tolerance. Dysregulation of Tim-3 expression on decidual NK (dNK) cells was observed in several cases of pregnancy complications, whereas the role of Tim-3 on dNK cells during T. gondii infection remains unclear. In the present study, T. gondii infected Tim-3^-/- pregnant mice, and anti-Tim-3 neutralizing antibody treated and infected human dNK cells were successfully established to explore the role of Tim-3 in dysfunction of dNK cells during abnormal pregnancy. Our results illustrated that Tim-3^-/- pregnant mice displayed more worse pregnancy outcomes with T. gondii infection compared to infected WT pregnant mice. Also, it demonstrated that Tim-3 expression on dNK cells was significantly down-regulated following T. gondii infection. Data suggested a remarkable activation of dNK cells in Tim-3^-/- mice and anti-Tim-3 neutralizing antibody treated and infected groups, with higher ratios of activating receptor NKG2D to inhibitory receptor NKG2A or KIR2DL4, IFN-γ/IL-10, and increased granule production compared with that of the infected group. Mechanism analysis proved that T. gondii-induced Tim-3 down-regulation significantly activated the phosphatidylinositol-3-kinase (PI3K)-AKT and JAK-STAT signaling pathway, by which the GranzymeB, Perforin, IFN-γ, and IL-10 production were further up-regulated. Our research demonstrated that the decrease of Tim-3 on dNK cells caused by T. gondii infection further led to dNK cells function disorder, which finally contributed to the development of abnormal pregnancy outcomes.

Pathogenesis of uteroplacental acute atherosis: An update on current research

Uteroplacental acute atherosis is a type of arterial vascular disease that affects the placenta during pregnancy and predominates in the maternal spiral arteries in the decidua basalis layer of the pregnant uterus. This condition is characterized by fibrin-like necrosis of the blood vessel walls, the accumulation of macrophages containing fat (foam cells), and the infiltration of macrophages around blood vessels. Uteroplacental acute atherosis is rare in normal pregnancy but occurs more frequently in patients with pregnancy complications, including preeclampsia, spontaneous preterm labor, preterm prelabor rupture of membranes, mid-trimester spontaneous abortion, fetal death, and small-for-gestational age. It is believed that the mechanisms underlying the development of uteroplacental acute atherosis are related to the incomplete physiological transformation of spiral arteries, placental inflammation, abnormal lipid metabolism, and oxidative stress. In this review, we describe the pathogenesis of uteroplacental acute atherosis to provide reference guidelines for the future prevention and treatment of uteroplacental acute atherosclerotic disease.

Association between rs1049174 NKG2D gene polymorphism and idiopathic recurrent spontaneous abortion in Iranian women: a case-control study

Natural killer group 2, member D (NKG2D) is one of the best known activating receptors of NK cells, which recognises its ligand on altered or stressed cells and activates NK cells to kill them. In this study, the single nucleotide polymorphism of the NKG2D gene for rs1049174 mutation was compared in 140 women with recurrent spontaneous abortion (RSA) and 175 control women with at least one successful pregnancy and without any known pregnancy loss. The findings just revealed that GG genotype and G allele were significantly higher in the case group compared with the control group (p < .001). Our results regarding decreased risk of RSA in C allele (OR = 0.438; 95%CI = 0.310-0.619; p < .001), and GC genotype (OR = 0.492; 95%CI = 0.214-0.574; p < .001) compared with G allele and GG genotype respectively. This study demonstrated a significant association between NKG2D gene polymorphism (rs1049174 G/C) and the risk of RSA in Iranian women.Impact statementWhat is already known on this subject? According to previous investigations, maternal immune responses may affect the foetus, causing recurrent spontaneous abortion (RSA). The main cause of RSA has not yet been detected in nearly 50% of the cases.What do the results of this study add? The results showed that the frequency of G allele and C allele were significantly different in the case group and control group.What are the implications of these findings for clinical practice and/or further research? The results suggest a protective function of C allele because it significantly decreased the risk of RSA compared to G allele. It improves inhibition of NK cells and probably participates in maintaining pregnancy in fertile controls; whereas, G allele is related to a slight inhibition of NK cells, probably leading to increase effectiveness of NK activation and undesirable inflammation, which consequently causes foetal rejection.

Distinct mRNA and long non-coding RNA expression profiles of decidual natural killer cells in patients with early missed abortion

Early non-chromosome-related missed abortion (MA) is commonly associated with an altered immunological environment during pregnancy. Human decidual natural killer (dNK) cells, the most abundant lymphocyte population within the first-trimester maternal-fetal interface, are vital maternal regulators of immune tolerance mediating successful embryo implantation and placentation. Previous studies have shown that dNK cells may play a role in MA. However, the gene expression status and specific altered manifestations of dNK cells in patients with early MA remain largely unknown. Here, we show that MA dNK cells have distinct mRNA and lncRNA expression profiles through RNA sequencing, with a total of 276 mRNAs and 67 lncRNAs being differentially expressed compared with controls. Protein-protein interaction analysis of differentially expressed mRNAs was performed to identify hub genes and key modules. An lncRNA-mRNA regulatory network characterized by the small-world property was constructed to reveal the regulation of mRNA transcription by differential hub lncRNAs. Functional annotation of differentially expressed mRNAs and lncRNAs was performed to disclose their potential roles in MA pathogenesis. Our data highlight several enriched biological processes (immune response, inflammatory response, cell adhesion, and extracellular matrix [ECM] organization) and signaling pathways (cytokine-cytokine receptor interaction, ECM-receptor interaction, Toll-like receptor signaling pathway, and phosphatidylinositol signaling system) that may influence MA. This study is the first to demonstrate the involvement of altered mRNA and lncRNA expression profiles in the dNK cell pathogenesis of early MA, facilitating a better understanding of the underlying molecular mechanisms and the development of novel MA therapeutic strategies targeting key mRNAs and lncRNAs.

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.

Learning from experience: cellular and molecular bases for improved outcome in subsequent pregnancies

The frequencies of preeclampsia, fetal growth restriction, fetal demise, and low birthweight are lower in subsequent pregnancies. Enhanced maternal cardiovascular adaptation, shorter first and second stages of labor, and more robust lactation also have been observed in subsequent as compared with first pregnancies. We sought to investigate the cellular and molecular bases for better outcomes in subsequent pregnancies. Based on the knowledge that specialized immune cells at the maternal-fetal interface, decidual natural killer cells, promote development of the placental bed and conversion of the spiral arteries by secreting a myriad of angiogenic and growth factors, we asked whether decidual natural killer cells differ in subsequent as compared with first pregnancies. This idea stemmed from recent studies suggesting that natural killer cells, although part of the innate immune system, possess some features of adaptive immunity, including a certain type of immune cell memory, termed trained immunity. We found that decidual natural killer cells from parous women "remember pregnancy" and differ from decidual natural killer cells of primigravidae. Compared with the decidual natural killer cells of first pregnancy, these cells, that we termed pregnancy-trained decidual natural killer cells, express greater levels of the natural killer receptors NKG2C and leukocyte immunoglobulin-like receptor B1, which interact with ligands expressed on invasive trophoblasts. Furthermore, they secrete greater levels of several growth factors, including vascular endothelial growth factor α as well as interferon-γ, augmenting remodeling of the placental bed. We propose that this pregnancy-trained memory dwells in the epigenome, where memory of stimuli is known to persist even when the stimulus is no longer present. This epigenetic memory apparently resides in endometrial natural killer cells between pregnancies. We suggest that this trained memory, which we coined pregnancy-trained decidual natural killer cells, may be the missing link in the immune basis for enhanced subsequent pregnancy. Epigenetic memory (chromatin modification) also may afford a global explanation for additional findings of enhanced maternal cardiovascular adaptation, shorter first and second stages of labor, and more robust lactation. Understanding the molecular and cellular bases of improved outcomes of subsequent pregnancy may lead to the development of treatment modalities designed for women at high risk for pregnancy disorders originating at the maternal-fetal interface.

The Natural Cytotoxicity Receptors in Health and Disease

The Natural Cytotoxicity Receptors (NCRs), NKp46, NKp44, and NKp30, were some of the first human activating Natural Killer (NK) cell receptors involved in the non-MHC-restricted recognition of tumor cells to be cloned over 20 years ago. Since this time many host- and pathogen-encoded ligands have been proposed to bind the NCRs and regulate the cytotoxic and cytokine-secreting functions of tissue NK cells. This diverse set of NCR ligands can manifest on the surface of tumor or virus-infected cells or can be secreted extracellularly, suggesting a remarkable NCR polyfunctionality that regulates the activity of NK cells in different tissue compartments during steady state or inflammation. Moreover, the NCRs can also be expressed by other innate and adaptive immune cell subsets under certain tissue conditions potentially conferring NK recognition programs to these cells. Here we review NCR biology in health and disease with particular reference to how this important class of receptors regulates the functions of tissue NK cells as well as confer NK cell recognition patterns to other innate and adaptive lymphocyte subsets. Finally, we highlight how NCR biology is being harnessed for novel therapeutic interventions particularly for enhanced tumor surveillance.

A unified (but in fact not fully testable) model of preeclampsia triggering

In this summary of my presentation in the last Reunion workshop I discuss a few assertions on preeclampsia, then turn on a (not fully testable) model where an embryonic defect in expression of embryo/ placental regulatory proteins results in complement activation, itself responsible for a down regulation of the T regs activity, resulting in a very early lack of complete down regulation of the preimplantation decidual inflammation, causing in the post implantation stage a low grade but chronic inflammatory state.

Tacrolimus treatment for infertility related to maternal-fetal immune interactions

Many approaches have been used to achieve successful pregnancies in patients with infertility, though existing treatments remain unsatisfactory in patients with infertility caused by abnormal maternal-fetal immunity. However, our understanding of the immunological aspects of infertility has steadily progressed, aided by recent research into organ transplantation and cancer. The results of these recent analyses have led to the development and evaluation of several candidate immunological treatments, but the use of immunological treatments remains a novel approach. The current paper presents the hypothesis that tacrolimus may have potential as a candidate agent for the treatment of maternal-fetal immunity-related infertility.

Trained Memory of Human Uterine NK Cells Enhances Their Function in Subsequent Pregnancies

Natural killer cells (NKs) are abundant in the human decidua, regulating trophoblast invasion and angiogenesis. Several diseases of poor placental development are associated with first pregnancies, so we thus looked to characterize differences in decidual NKs (dNKs) in first versus repeated pregnancies. We discovered a population found in repeated pregnancies, which has a unique transcriptome and epigenetic signature, and is characterized by high expression of the receptors NKG2C and LILRB1. We named these cells Pregnancy Trained decidual NK cells (PTdNKs). PTdNKs have open chromatin around the enhancers of IFNG and VEGFA. Activation of PTdNKs led to increased production and secretion of IFN-γ and VEGFα, with the latter supporting vascular sprouting and tumor growth. The precursors of PTdNKs seem to be found in the endometrium. Because repeated pregnancies are associated with improved placentation, we propose that PTdNKs, which are present primarily in repeated pregnancies, might be involved in proper placentation.

Lectin histochemical analysis of uterine natural killer cells in normal, hydatidiform molar and invasive molar pregnancy

Uterine natural killer (uNK) cells have been hypothesized to serve a role in controlling trophoblast invasion and proliferation. The aim of the present study was to identify the distribution and number of uNK cells in normal pregnancy (NP), partial mole (PM), complete mole (CM) and invasive mole (IM). uNK cells were detected using dolichos biflorus agglutinin lectin immunohistochemistry in decidual and villous tissues from early NP (n=15), late NP (n=15), PM (n=22), CM (n=20) and IM (n=10). A scaled eye piece was used for cell counting to obtain semi-quantitative results. It was revealed that uNK cells were mainly located in the uterine deciduas of early NP. As pregnancy progressed, the number of decidual uNK cells significantly decreased. Decidual uNK cells of PM, CM and IM were located near blood vessel endothelial cells. No significant differences were detected with respect to the numbers of decidual uNK between early NP and PM. However, the number of decidual uNK cells was significantly reduced in CM and IM compared with early NP. The populations of decidual uNK cells were not significantly different between CM and IM. No uNK cells were detected in the villi of PM, CM or IM. The decrease of decidual uNK cells in late NP, CP and IM, compared with early NP, suggested that uNK cells served an important role in controlling trophoblast invasion and proliferation.

Progress in the understanding of the etiology and predictability of fetal growth restriction

Fetal growth restriction (FGR) is defined as the failure of fetus to reach its growth potential for various reasons, leading to multiple perinatal complications and adult diseases of fetal origins. Shallow extravillous trophoblast (EVT) invasion-induced placental insufficiency and placental dysfunction are considered the main reasons for idiopathic FGR. In this review, first we discuss the major characteristics of anti-angiogenic state and the pro-inflammatory bias in FGR. We then elaborate major abnormalities in placental insufficiency at molecular levels, including the interaction between decidual leukocytes and EVT, alteration of miRNA expression and imprinted gene expression pattern in FGR. Finally, we review current animal models used in FGR, an experimental intervention based on animal models and the progress of predictive biomarker studies in FGR.Free Chinese abstract: A Chinese translation of this abstract is freely available at http://www.reproduction-online.org/content/153/6/R215/suppl/DC1.

Porphyromonas gingivalis and adverse pregnancy outcome

Porphyromonas gingivalis is a Gram-negative, anaerobic bacterium considered to be an important pathogen of periodontal disease that is also implicated in adverse pregnancy outcome (APO). Until recently, our understanding of the role of P. gingivalis in APO has been limited and sometimes contradictory. The purpose of this review is to provide an overview of past and current research on P. gingivalis that addresses some of the controversies concerning the role of this organism in the pathogenesis of APO.

Expression of natural cytotoxicity receptors and cytokine production on endometrial natural killer cells in women with recurrent pregnancy loss or implantation failure, and the expression of natural cytotoxicity receptors on peripheral blood natural killer cells in pregnant women with a history of recurrent pregnancy loss

AIM

Natural cytotoxicity receptors (NCR) are unique markers that regulate natural killer (NK) cell cytotoxicity and cytokine production. In this study, we investigated the expression of NCR (NKp46, NKp44, and NKp30) and cytokine production in NK cells derived from the uterine endometrium of women with recurrent pregnancy loss (RPL). We also investigated the expression of NCR in peripheral blood NK cells in pregnant women with and without a history of RPL.

METHODS

The expression of NCR (NKp46, NKp44, and NKp30) in NK cells (CD56^dim and CD56^bright ) in the uterine endometrium was analyzed using 3-color flow cytometry. Cytokine (tumor necrosis factor-α and interferon-γ) production was also analyzed. NK cells from the mid-secretory endometrium of 28 women with RPL, 34 women with implantation failure, and 74 controls were collected and mechanically dispersed using a tissue grinder. The expression of NCR in peripheral blood NK cells from pregnant women with (n = 17) and without (n = 91) a history of RPL was analyzed.

RESULTS

The percentages of NKp46⁺ NK cells were significantly lower in both women with RPL and pregnant women with a history of RPL. The percentages of tumor necrosis factor-α- and/or interferon-γ-producing uterine endometrial NK cells were significantly lower in women with RPL compared with controls.

CONCLUSION

The changes in NCR expression and cytokine production, especially decreased NKp46 expression in endometrial NK cells, suggests the presence of abnormal NK cell regulation in women with reproductive failures.

10 workshops on Immunology of preeclampsia

For the 10th issue of the « island workshops », now the Reunion Workshops, organised by Pierre Yves Robillard since the first one in Tahiti challenging the "vascular disease only" theory of pre eclampsia and introducing the primipaternity concept, we examined the reasons for considering an Immunological approach to the disease. This (brief) overview thus examines several important topics in an Immunological framework. I have chosen to present here the evolution of the main themes rather than a purely chronological vision.

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.

Immune Mechanisms Linking Obesity and Preeclampsia

Preeclampsia (PE) is characterized by hypertension occurring after the twentieth week of pregnancy. It is a significant contributor to maternal and perinatal morbidity and mortality in developing countries and its pervasiveness is increasing within developed countries including the USA. However, the mechanisms mediating the pathogenesis of this maternal disorder and its rising prevalence are far from clear. A major theory with strong experimental evidence is that placental ischemia, resulting from inappropriate remodeling and widening of the maternal spiral arteries, stimulates the release of soluble factors from the ischemic placenta causing maternal endothelial dysfunction and hypertension. Aberrant maternal immune responses and inflammation have been implicated in each of these stages in the cascade leading to PE. Regarding the increased prevalence of this disease, it is becoming increasingly evident from epidemiological data that obesity, which is a state of chronic inflammation in itself, increases the risk for PE. Although the specific mechanisms whereby obesity increases the rate of PE are unclear, there are strong candidates including activated macrophages and natural killer cells within the uterus and placenta and activation in the periphery of T helper cells producing cytokines including TNF-α, IL-6 and IL-17 and the anti-angiogenic factor sFlt-1 and B cells producing the agonistic autoantibodies to the angiotensin type 1 receptor (AT1-aa). This review will focus on the immune mechanisms that have been implicated in the pathogenesis of hypertension in PE with an emphasis on the potential importance of inflammatory factors in the increased risk of developing PE in obese pregnancies.

Overlap Chronic Placental Inflammation Is Associated with a Unique Gene Expression Pattern

Breakdown of the balance between maternal pro- and anti-inflammatory pathways is thought to allow an anti-fetal maternal immune response that underlies development of chronic placental inflammation. Chronic placental inflammation is manifested by the influx of maternal inflammatory cells, including lymphocytes, histiocytes, and plasma cells, into the placental membranes, villi, and decidua. These infiltrates are recognized pathologically as chronic chorioamnionitis, chronic villitis of unknown etiology, and chronic deciduitis. Each of these histological entities is associated with adverse fetal outcomes including intrauterine growth restriction and preterm birth. Studying the gene expression patterns in chronically inflamed placenta, particularly when overlapping histologies are present, may lead to a better understanding of the underlying mechanism(s). Therefore, this study compared tissue with and without chronic placental inflammation, manifested as overlapping chronic chorioamnionitis, chronic villitis of unknown etiology, and chronic deciduitis. RNA expression profiling was conducted on formalin fixed, paraffin embedded placental tissue using Illumina microarrays. IGJ was the most significant differentially expressed gene identified and had increased expression in the inflamed tissue. In addition, IGLL1, CXCL13, CD27, CXCL9, ICOS, and KLRC1 had increased expression in the inflamed placental samples. These differentially expressed genes are associated with T follicular helper cells, natural killer cells, and B cells. Furthermore, these genes differ from those typically associated with the individual components of chronic placental inflammation, such as chronic villitis, suggesting that the inflammatory infiltrate associated with overlapping chronic chorioamnionitis, chronic villitis of unknown etiology, and chronic deciduitis differs is unique. To further explore and validate gene expression findings, we conducted immunohistochemical assessment of protein level expression and demonstrate that IgJ expression was largely attributable to the presence of plasma cells as part of chronic deciduitis and that IgA positive plasma cells are associated with chronic deciduitis occurring in combination with chronic chorioamnionitis and chronic villitis of unknown etiology but not with isolated chronic deciduitis.

Decidual natural killer cell receptor expression is altered in pregnancies with impaired vascular remodeling and a higher risk of pre-eclampsia

HLA-interacting cell surface receptors are altered on decidual natural killer cells in pregnancy, potentially altering interactions with fetal cells via chemokine expression.

During pregnancy, a specialized type of NK cell accumulates in the lining of the uterus (decidua) and interacts with semiallogeneic fetal trophoblast cells. dNK cells are functionally and phenotypically distinct from PB NK and are implicated in regulation of trophoblast transformation of the uterine spiral arteries, which if inadequately performed, can result in pregnancy disorders. Here, we have used uterine artery Doppler RI in the first trimester of pregnancy as a proxy measure of the extent of transformation of the spiral arteries to identify pregnancies with a high RI, indicative of impaired spiral artery remodeling. We have used flow cytometry to examine dNK cells isolated from these pregnancies compared with those from pregnancies with a normal RI. We report a reduction in the proportion of dNK cells from high RI pregnancies expressing KIR2DL/S1,3,5 and LILRB1, receptors for HLA-C and HLA-G on trophoblast. Decreased LILRB1 expression in the decidua was examined by receptor blocking in trophoblast coculture and altered dNK expression of the cytokines CXCL10 and TNF-α, which regulate trophoblast behavior. These results indicate that dNK cells from high RI pregnancies may display altered interactions with trophoblast via decreased expression of HLA-binding cell-surface receptors, impacting on successful transformation of the uterus for pregnancy.

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.

Characterization of uterine NK cells in women with infertility or recurrent pregnancy loss and associated endometriosis

PROBLEM

Uterine natural killer cells (uNK) have been thought to play a key role in endometriosis and infertility. We investigated the expression of CD56, CD16, and NKp46 in endometrial tissues from 61 women with unexplained recurrent pregnancy loss (uRPL) or infertility (UI) and correlated this with the presence or absence of endometriosis. The results from the patients with subfertility were compared with those from 10 fertile patients.

METHOD OF STUDY

Mid-secretory phase endometrial biopsies were obtained, and the endometrial expression of CD56, CD16, or NKp46 was identified by immunohistochemistry and quantified (ImageJ Software).

RESULTS

The percentage of CD16(+) cells was higher in women with uRPL (7.9 ± 3.2) and UI (9.0 ± 5.5), even when these conditions were associated with endometriosis (8.9 ± 5.3), compared with fertile patients (5.6 ± 2.4, P < 0.05). Likewise, the ratio of NKp46(+) :CD56(+) cells was higher in women with uRPL (0.28 ± 0.25) and UI (0.21 ± 0.2), even when these conditions were associated with endometriosis (0.19 ± 0.14), compared with fertile patients (0.1 ± 0.1, P < 0.05). No differences were observed when comparing CD56.

CONCLUSIONS

Women, with or without endometriosis, who have larger populations of cytotoxic CD16(+) uNK cells and/or higher populations of NKp46(+) CD56(+) cells may be at greater risk of infertility disorders resulting from an inflammatory environment occurring during implantation or later during decidualization.

The up side of decidual natural killer cells: new developments in immunology of pregnancy

Early phases of human pregnancy are associated with the accumulation of a unique subset of natural killer (NK) cells in the maternal decidua. Decidual NK (dNK) cells that are devoid of cytotoxicity play a pivotal role in successful pregnancy. By secreting large amounts of cytokines/chemokines and angiogenic factors, dNK cells participate in all steps of placentation including trophoblast invasion into the maternal endometrium and vascular remodelling. In this review, we summarize some of dNK cell features and discuss more recent exciting data that challenge the conventional view of these cells. Our new data demonstrate that dNK cells undergo fine tuning or even subvert their classical inhibitory machinery and turn into a real defence force in order to prevent the spread of viruses to fetal tissue. Today it is not clear how these phenotypic and functional adaptations impact cellular cross-talk at the fetal-maternal interface and tissue homeostasis. Ultimately, precise understanding of the molecular mechanisms that govern dNK cell plasticity during congenital human cytomegalovirus infection should lead to the design of more robust strategies to reverse immune escape during viral infection and cancer.

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.

Human decidual NK cells: unique and tightly regulated effector functions in healthy and pathogen-infected pregnancies

NK cells present in the peripheral blood (PB) respond rapidly to pathogens or pathogen-infected cells by various means including cytotoxicity and release of cytokines and chemokines. In addition they modulate adaptive immunity via the interaction with dendritic cells. Decidual NK cells (dNK) are poorly cytotoxic in healthy pregnancy, both in humans and rodents, when compared to their PB counterparts. We will discuss recent findings that may contribute to answer the following questions: (i) Do dNK possess functional killing machinery in normal healthy pregnancy? (ii) If so, what are the regulatory mechanisms that negatively control this effector function? (iii) Have dNK from early pregnant uterus the intrinsic ability to kill pathogen-infected autologous maternal uterine cells and/or produce soluble factors that stimulate the anti-pathogen adaptive immune response? (iv) Do dNK undergo a receptor repertoire profile shift when they are in contact with pathogen-infected uterine cells? (v) Which pathogen-mediated signal(s) and molecular interactions subvert the inhibition of dNK cytolytic activity?

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.

Novel interaction between proliferating cell nuclear antigen and HLA I on the surface of tumor cells inhibits NK cell function through NKp44

NK cell function is closely regulated by numerous inhibitory and activating receptors binding corresponding ligands on the surface of target cells, providing vital first line defenses against infections and cancer. NKp44, originally discovered as an activating NK cell receptor, was recently found to elicit inhibitory effects on NK cell effector function through recognition of cell surface PCNA. Other reports have pointed to potential associations between NKp44 and HLA I molecules, as well as HLA I and Damage Associated Molecular Pattern molecules (DAMPs) on the surface of tumor cells. In this report, we have identified novel interaction between HLA I and PCNA on the surface of human tumor cells by confocal microscopy and immunoprecipitation. In addition to previous reports, we show PCNA on the cell surface where novel association with HLA I does not require the presence of NKp44 expressing NK cells and occurs with endogenous PCNA. The association of HLA I and PCNA forms the inhibitory ligand for NKp44, resulting in inhibition of NK cell cytotoxicity. We further postulate NCR ligands are composed of DAMP molecules localized to the cell surface, colocalizing with HLA I, and potentially heparin sulfate proteoglycans.

The multiple faces of the decidual natural killer cell

The decidual NK (dNK) cell is called on to support placental growth by providing an array of growth factors that directly transform the spiral artery and direct trophoblast invasion. Successful transformation is dependent upon adequate stimulation paradoxically stimulating the cell for placental support rather than cytotoxicity. With the identification of its supportive role, the presence of an intact cytotoxic mechanism has been confusing. Investigators have found that the cell remains fully capable of cytotoxic responses particularly in response to pathogen-specific signals. We postulate a dual threshold model where moderate stimulation results in release of stimulatory factors supporting placentation while intense stimulation, particularly triggered through pathogen-specific receptors, restores the cell to its protective, cytotoxic, role. Individual dNK cells mature attaining the capacity to respond to the delivery of cognate signals. The process, known as 'licensing' tunes responsiveness to the degree to which stochastically selected inhibitory receptors block cytotoxic response to self. A changing licensing milieu within the decidua may result in altered and unsuitable receptor expression. We postulate that a heterogeneous population of dNK cells where cells inappropriately licensed for the milieu contributes to pathology.

Role of NKp46 expression in cytokine production by CD56-positive NK cells in the peripheral blood and the uterine endometrium

PROBLEM

To investigate the role of natural cytotoxicity receptor, NKp46 expression in cytokine-producing NK cells.

METHOD OF STUDY

CD56(+) /NKp46(+) NK cells from the peripheral blood and the uterine endometrium were magnetically separated. IFN-γ, TNF-α, IL-4, IL-10, and TGF-β(1) expressions on NK cells were investigated using multicolor flow cytometry.

RESULTS

Peripheral blood and uterine endometrial NK cells were grouped into 4 subpopulations based upon the degree of CD56 and NKp46 expressions. NKp46 expression was associated with higher frequency of cytokine-producing NK cells, including CD56(dim) NK cells. The percentage of TNF-α(+) and IL-10(+) NK cells per total CD56(+) /NKp46(+) NK cells in the uterine endometrium showed a significant correlation with those of the peripheral blood in all subpopulations, but that of IFN-γ(+) , IL-4(+,) and TGF-β(1) (+) NK cells showed partial correlation.

CONCLUSION

Expression of NKp46 is involved in cytokine production of CD56(+) NK cells in the peripheral blood and the uterine endometrium.

[Innate and adaptative immunity of the female genital tract]

Most of molecules and cells involved in both types, innate and adaptive immunity are present within the feminine genital tract. This article attempts to list some of the various actors involved in these immunities, essentially at the vaginal level and to illustrate their implications in the most frequent pathologies. Among these molecules: defensins, collectins lysozyme, lactoferrin, calprotectin, SLP1, HSP and many others as well as Toll receptors and immunoglobulins (IgG and IgA) play a major role. Epithelial cells, antigen presenting cells, lymphocytes T, B, NK also contribute efficiently to the defenses in a coordinated way partially under the influence of sex hormones. The therapeutic perspectives, of which vaccines are briefly mentioned.