NK cells and pre-eclampsia

Emerging role of C5aR2: novel insights into the regulation of uterine immune cells during pregnancy

Pregnancy is a fascinating immunological phenomenon because it allows allogeneic fetal and placental tissues to survive inside the mother. As a component of innate immunity with high inflammatory potential, the complement system must be tightly regulated during pregnancy. Dysregulation of the complement system plays a role in pregnancy complications including pre-eclampsia and intrauterine growth restriction. Complement components are also used as biomarkers for pregnancy complications. However, the mechanisms of detrimental role of complement in pregnancy is poorly understood. C5a is the most potent anaphylatoxin and generates multiple immune reactions via two transmembrane receptors, C5aR1 and C5aR2. C5aR1 is pro-inflammatory, but the role of C5aR2 remains largely elusive. Interestingly, murine NK cells have been shown to express C5aR2 without the usual co-expression of C5aR1. Furthermore, C5aR2 appears to regulate IFN-γ production by NK cells in vitro. As IFN-γ produced by uterine NK cells is one of the major factors for the successful development of a vital pregnancy, we investigated the role anaphylatoxin C5a and its receptors in the establishment of pregnancy and the regulation of uterine NK cells by examinations of murine C5ar2-/- pregnancies and human placental samples. C5ar2-/- mice have significantly reduced numbers of implantation sites and a maternal C5aR2 deficiency results in increased IL-12, IL-18 and IFN-γ mRNA expression as well as reduced uNK cell infiltration at the maternal-fetal interface. Human decidual leukocytes have similar C5a receptor expression patterns showing clinical relevance. In conclusion, this study identifies C5aR2 as a key contributor to dNK infiltration and pregnancy success.

The novel role of activating receptor KIR2DS5 in preeclampsia

Preeclampsia (PE) is a serious complication of pregnancy. Decidual natural killer (dNK) cells were reported to participate in the remodeling of spiral arteries through producing a group of cytokines, including granulocyte-macrophage colony stimulating factor (GM-CSF). KIR2DS5 is an activating receptor of NK cells that specifically recognizes HLA-C2 on trophoblasts. Currently, there are no reports regarding the precise mechanism of KIR2DS5 in PE. This study included 30 PE patients and 30 healthy pregnant women. We found that the expressions of KIR2DS5 were significantly lower in PE deciduae compared to those of healthy pregnancies. By transfecting knockdown and overexpression lentivirus vectors of KIR2DS5 into dNK cells isolated from deciduae of early pregnancy, we altered the KIR2DS5 expression level in dNK cells. Then, these dNK cells and trophoblast cell lines were co-cultured as trophoblast-dNK cells. In the trophoblast-dNK cells, we examined the influence of KIR2DS5 on the biological manifestations of trophoblasts. As anticipated, overexpression of KIR2DS5 could facilitate cell proliferation, migration, and invasion. Furthermore, increased expression of KIR2DS5 inhibited cell apoptosis and enhanced the progression of cells from theG1 to theS stage. Further mechanistic study demonstrated a positive relationship between KIR2DS5 and GM-CSF in trophoblast-dNK cells. Accordingly, our observations indicated that a decrease in KIR2DS5 could reduce the expression of GM-CSF via the JAK2/STAT5 pathway, resulting in the failure of the activated signal to be transmitted to dNK cells and ultimately leading to the occurrence of PE. KIR2DS5 may be a new contributor for the prediction and diagnosis of PE.

Maternal respiratory SARS-CoV-2 infection in pregnancy is associated with a robust inflammatory response at the maternal-fetal interface

BACKGROUND

Pregnant women are at increased risk for severe outcomes from coronavirus disease 2019 (COVID-19), but the pathophysiology underlying this increased morbidity and its potential effect on the developing fetus is not well understood.

METHODS

We assessed placental histology, ACE2 expression, and viral and immune dynamics at the term placenta in pregnant women with and without respiratory severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

FINDINGS

The majority (13 of 15) of placentas analyzed had no detectable viral RNA. ACE2 was detected by immunohistochemistry in syncytiotrophoblast cells of the normal placenta during early pregnancy but was rarely seen in healthy placentas at full term, suggesting that low ACE2 expression may protect the term placenta from viral infection. Using immortalized cell lines and primary isolated placental cells, we found that cytotrophoblasts, the trophoblast stem cells and precursors to syncytiotrophoblasts, rather than syncytiotrophoblasts or Hofbauer cells, are most vulnerable to SARS-CoV-2 infection in vitro. To better understand potential immune mechanisms shielding placental cells from infection in vivo, we performed bulk and single-cell transcriptomics analyses and found that the maternal-fetal interface of SARS-CoV-2-infected women exhibited robust immune responses, including increased activation of natural killer (NK) and T cells, increased expression of interferon-related genes, as well as markers associated with pregnancy complications such as preeclampsia.

CONCLUSIONS

SARS-CoV-2 infection in late pregnancy is associated with immune activation at the maternal-fetal interface even in the absence of detectable local viral invasion.

FUNDING

NIH (T32GM007205, F30HD093350, K23MH118999, R01AI157488, U01DA040588) and Fast Grant funding support from Emergent Ventures at the Mercatus Center.

The enrichment of neutrophil extracellular traps impair the placentas of systemic lupus erythematosus through accumulating decidual NK cells

Despite the advances made in the management of pregnancies in women with systemic lupus erythematosus (SLE), the rate of adverse pregnancy outcomes is still higher than that in the general population. In the last few years, neutrophil extracellular traps (NETs) were proven to be detrimental in both autoimmune diseases and placental injury. We investigated whether NETs could be detected in the placentas of pregnant individuals with SLE and explored the relationship between NETs and decidual natural killer cells (dNKs), which comprise the majority of immune cells at the maternal–fetal interface, using clinical samples and animal models. In this study, we found that the infiltration of NETs and dNKs, especially CD56⁺CD16⁺ NK cells, was significantly increased in pregnant individuals with SLE with placental insufficiency. In the murine models of SLE, the number of dNKs was significantly decreased due to the decreased formation of NETs affected by Ly6G. Moreover, the histopathological placental injury was reduced, with a remarkable increase in fetal birth weight. This study shows that NETs may contribute to immunological disorder in the placenta and the pathological changes in pregnancies with SLE, which provides a research basis for further explorations of the mechanism of SLE in placental impairment.

Disruption in the Regulation of Immune Responses in the Placental Subtype of Preeclampsia

Preeclampsia is a pregnancy-specific disorder, of which one of its major subtypes, the placental subtype is considered a response to an ischemic placental environment, impacting fetal growth and pregnancy outcome. Inflammatory immune responses have been linked to metabolic and inflammatory disorders as well as reproductive failures. In healthy pregnancy, immune regulatory mechanisms prevent excessive systemic inflammation. However, in preeclampsia, the regulation of immune responses is disrupted as a result of aberrant activation of innate immune cells and imbalanced differentiation of T-helper cell subsets creating a cytotoxic environment in utero. Recognition events that facilitate immune interaction between maternal decidual T cells, NK cells, and cytotrophoblasts are considered an indirect cause of the incomplete remodeling of spiral arteries in preeclampsia. The mechanisms involved include the activation of immune cells and the subsequent secretion of cytokines and placental growth factors affecting trophoblast invasion, angiogenesis, and eventually placentation. In this review, we focus on the role of excessive systemic inflammation as the result of a dysregulated immune system in the development of preeclampsia. These include insufficient control of inflammation, failure of tolerance toward paternal antigens at the fetal-maternal interface, and subsequent over- or insufficient activation of immune mediators. It is also possible that external stimuli, such as bacterial endotoxin, may contribute to the excessive systemic inflammation in preeclampsia by stimulating the release of pro-inflammatory cytokines. In conclusion, a disrupted immune system might be a predisposing factor or result of placental oxidative stress or excessive inflammation in preeclampsia. Preeclampsia can thus be considered a hyperinflammatory state associated with defective regulation of the immune system proposed as a key element in the pathological events of the placental subtype of this disorder.

Review on role of progestogen (dydrogesterone) in the prevention of gestational hypertension

INTRODUCTION

Gestational hypertension remains one of the main causes of maternal deaths all over the world. Attempts to reduce/prevent the incidence had failed due to lack of understanding of the disease's aetiology. One of the early roles of natural progesterone in the first trimester of pregnancy is to promote formation of wide-calibre spiral vessels that invade into the myometrial layer of the gravid uterus. Theoretically, this will prevent or reduce the incidence of gestational hypertension in the latter half of the pregnancy.

REVIEW

The progestogen, dydrogesterone, has similar molecular structure and properties to natural progesterone. A pilot study was undertaken on primigravidae, who have higher risk of developing gestational hypertension. They were supplemented with dydrogesterone in the first trimester (Study Group) and compared with a similar number of primigravidae (Control Group) without supplementation with the progestogen. The incidence of gestational hypertension was significantly lower in the Study Group as compared to the Control Group (1.7% vs. 12.9%, respectively, p<0.001). The incidence of foetal distress was also significantly lower in the Study Group compared to the Control Group (4.3% vs. 18.1%, respectively, p<0.001).

CONCLUSION

Supplementation of the progestogen, dydrogesterone, in the first trimester to primigravidae has shown great potential in reducing or preventing the incidence of gestational hypertension.

Placental Regulation of Inflammation and Hypoxia after TNF-α Infusion in Mice

PROBLEM

Increased levels of inflammatory cytokines are demonstrated in the serum of women with pre-eclampsia. TNF-α infusion in animal models induces proteinuric hypertension similar to human pre-eclampsia. The effect of TNF-α on regulation of the immune and hypoxic pathways in the developing placenta and their relationship with experimental pre-eclampsia remains unexamined.

METHOD OF STUDY

TNF-α was infused into pregnant mice, and the effects on maternal hypertension, proteinuria, circulating levels of sFlt-1 and corresponding placental changes in molecules responding to inflammation (TLR-3 and TLR-4) and hypoxia (HIF-1α) were examined.

RESULTS

TNF-α infusion resulted in maternal hypertension and proteinuria. Molecular changes in the placenta involved upregulation of TLR-3, TLR-4 and HIF-1α. Serum levels of sFlt-1 were high in pregnant animals, but not further upregulated by TNF-α infusion.

CONCLUSION

A role for maladaptive regulation of TLR and HIF-1α induced by an imbalance in inflammatory cytokines is implicated in the pathogenesis of pre-eclampsia.

The potential perinatal origin of placentation disorders in the young primigravida

The fetus is exposed to high plasma concentrations of unbound estrogens and progesterone throughout pregnancy. However, secretory or decidual changes in the fetal uterus occur relatively infrequently before birth, suggesting a variable endometrial progesterone response at the time of birth. Arguably, partial progesterone resistance that persists into adolescent years may compromise the physiological transformation of the spiral arteries and predispose for defective placentation in the case of pregnancy. Decidualization of the endometrial stromal compartment and junctional zone myometrium precedes trophoblast invasion. It represents the first step in the process of spiral artery remodeling needed to establish effective uteroplacental blood flow by midpregnancy. The major obstetric syndromes caused by impaired placental bed spiral artery remodeling are prevalent in teenage pregnancies, including preeclampsia, fetal growth restriction, and spontaneous preterm labor. Preconditioning of the uterus in response to cyclic menstruation during adolescence may be critical to achieve full uterine responsiveness to hormonal cues. Understanding the mechanisms of functional maturation of the uterus during the early reproductive years may yield novel insights into the major obstetric syndromes.

A pilot study to determine whether progestogen supplementation using dydrogesterone during the first trimester will reduce the incidence of gestational hypertension in primigravidae

BACKGROUND

Gestational hypertension (GH) remains one of the main causes of high maternal and perinatal morbidity and mortality worldwide with the highest incidence among primigravidae of about 10%-15%. However, it was noted that the incidence of GH in primigravidae who conceived following assisted reproductive technique (ART) or intrauterine insemination (IUI) supplemented with dydrogesterone during the first trimester was low.

AIM

To determine whether dydrogesterone supplementation during the first trimester can reduce the incidence of GH among primigravidae.

METHOD

A prospective cross-sectional comparative study was undertaken in 2010 on 116 primigravidae (study group) who conceived following ART or IUI and supplemented with dydrogesterone up to 16 weeks gestation. They were matched for age and race at 16 weeks gestation with a control patient from the early pregnancy clinic who were primigravidae (n = 116) who conceived spontaneously without dydrogesterone supplementation.

FINDINGS

The incidence of GH in the study group was significantly lower than the control group (1.7% versus 12.9%, p = 0.001). The incidence of fetal distress was also significantly lower in the study group compared to the control group (4.3% versus 18.1%, p = 0.001).

INTERPRETATION

Dydrogesterone supplementation during the first trimester significantly reduced the incidence of GH and fetal distress in primigravidae.

HLA-G regulates the invasive properties of JEG-3 choriocarcinoma cells by controlling STAT3 activation

The expression of human leucocyte antigen-G (HLA-G) in trophoblasts plays a crucial role in successful embryonic implantation, and reduced HLA-G expression might contribute to adverse obstetric outcomes. In this study, we silenced HLA-G expression using RNA interference in JEG-3 cells, resulting in a notably attenuated invasion capacity of the cells in a Transwell assay; however, no alterations in cell proliferation or apoptosis were observed. The down-regulation of HLA-G dampened the activation of signal transducer and activator of transcription 3 (STAT3), whereas the up-regulation of HLA-G promoted STAT3 activation and invasion in JEG-3 cells treated with human galectin-1. Most importantly, interleukin-6 (IL-6), but not galectin-1, was shown to rescue invasion deficiency in a dose-dependent manner. Thus, we demonstrate that HLA-G is able to regulate JEG-3 cell invasion by influencing STAT3 activation, which may underlie the implantation defects accompanying HLA-G hypo-expression in pre-eclampsia.

A deficiency in haem oxygenase-1 induces foetal growth restriction by placental vasculature defects

Haem oxygenase-1 (HO-1), the rate-limiting enzyme in haem degradation, plays a role in angiogenesis and vasculogenesis and is highly expressed in the placenta. Deficiencies in HO-1 are associated with several pregnancy disorders, such as recurrent miscarriages and pre-eclampsia. The unique combination of tissue protective, smooth muscle relaxing and angiogenesis regulatory properties makes HO-1 a key player in the maintenance of a healthy pregnancy through a direct effect on placental structural and vascular development, thus affecting foetal development.

CONCLUSION

  Therefore, we conclude that HO-1 plays an important role in placental vasculature development and a deficiency in HO-1 may contribute to pregnancy complications, such as pre-eclampsia, spontaneous abortions and premature births.

The prevalence and risk factors of infantile haemangiomas: a case-control study in the Dutch population

Haemangiomas are considered to be the most common tumours of infancy. However, despite their frequent occurrence the aetiological determinants of their development remain unknown. Identifying these factors may provide insight on their pathogenesis. We performed cross-sectional screening for haemangiomas in newborns (0-16 months of age) in the general Dutch population. Haemangioma-specific and pregnancy-related data were collected in children with a haemangioma. These data were compared in a case-control design using multivariable logistic regression analysis. Among 2204 newborns, 219 (9.9%) had a haemangioma. The male-to-female ratio was 1:2. The majority of haemangiomas were located on the trunk (37%). The general practitioners or medical specialists were consulted in only a minority of cases (<7%). Amniocentesis [odds ratio (OR) 3.6, 95% confidence interval (CI) 1.11, 11.42], breech presentation [OR 2.3, 95% CI 1.14, 4.44], being first-born [OR 1.55, 95% CI 1.03, 2.33] and a birthweight ≤2500 g [OR 4.95, 95% CI 1.63, 15.05] were independent factors associated with the development of a haemangioma. Duration of pregnancy did not differ between study groups. Our study showed that the prevalence of a haemangioma is 9.9% in the general (Dutch) population. Four factors appear relevant in the development of haemangiomas. These factors may provide clues to its pathogenesis.

Maternal heme oxygenase 1 regulates placental vasculature development via angiogenic factors in mice

The placental vasculature is critical for nutrient, gas, and waste exchange between the maternal and fetal systems. Its development depends on the proper expression and interaction of angiogenesis and associated growth factors. Heme oxygenase (HMOX), the enzyme for heme degradation, plays a role in angiogenesis and is highly expressed in the placenta. To evaluate the role of maternal HMOX1, the inducible HMOX isozyme, on placental vasculature formation, mice with a partial deficiency in Hmox1 (Hmox1(+/-)) were used. Three-dimensional images of placental vasculatures as well as spiral arteries from Hmox1(+/+) or Hmox1(+/-) placentas were created by vascular corrosion casting technique and imaged by micro-computerized tomography (microCT). The structures and morphologies of fetomaternal interfaces were observed by histological staining and the ultrastructure of uterine natural killer (uNK) cells, a major regulator in spiral artery remodeling, was analyzed by transmission electron microscopy. A group of growth factors and angiogenic factors from the decidua/mesometrial lymphoid aggregate of pregnancy (MLAp) as well as labyrinth regions were quantified using an angiogenesis PCR array kit and compared between Hmox1(+/+) or Hmox1(+/-) placentas. In conclusion, a partial deficiency of maternal Hmox1 resulted in the malformation of fetomaternal interface, insufficiency of spiral artery remodeling, and alteration of uNK cell differentiation and maturation. These changes were independent of the fetal genotype, but relied on the maternal HMOX1 level, which determined the balance of expression levels of pro- and antiangiogenic factors in the decidua/MLAp region. These results implied that Hmox1 polymorphisms among the human population might contribute to some unexplained cases of pregnancy disorders, such as fetal growth retardation and preeclampsia.

Preeclampsia--a placenta developmental biology perspective

There are abundant theories in the scientific literature that propose a range of pathophysiological pathways for preeclampsia. In this review we discuss some of the contributions made to this field from the perspective of a placental developmental biology laboratory. We discuss an underlying immune component of preeclampsia associated with expression of HLA-G and also a beneficial function of decidual NK cells. We conclude by summarizing newer findings regarding the anti-angiogenic expression of soluble fms-like tyrosine kinase (sFlt-1) and its role in the development of preeclampsia.