Evidence for participation of uterine natural killer cells in the mechanisms responsible for spontaneous preterm labor and delivery

The landscape of decidual immune cells at the maternal-fetal interface in parturition and preterm birth

BACKGROUND

Parturition is similar to an inflammatory response in which resident and infiltrating immune cells release cytokines and chemokines into the maternal-fetal interface, promoting expulsion of the fetus from the mother. The untimely activation of these inflammatory pathways can result in preterm labor. The maternal-fetal interface is composed mainly of decidual tissue and placental villous space.

OBJECTIVE

The objective of this review is to examine the role and mechanisms of decidual immune cells during parturition and preterm birth. A deeper understanding of decidual immune cells at the maternal-fetal interface could provide significant insight into parturition and preterm birth pathogenesis.

METHODS

We searched major databases (including PubMed, Web of Science, and Google Scholar etc.) for literature encompassing decidual immune cells, parturition and preterm birth up to July 2024 and combined with studies found in the reference lists of the included studies.

RESULTS

Decidual neutrophils release inflammatory mediators that facilitate parturition. The M1/M2 ratio of decidual macrophages increases among preterm birth population. Mast cells may cause uterine contractions. In parturition and preterm birth, there is an increase in CD56dimCD16+ natural killer cells and immature dendritic cells. The increase of Th1/Th2 and Th17/Treg cells leads to preterm birth. Women with preterm birth had a higher proportion of decidual B cells. ILC2 can help protect the steady-state environment at the maternal-fetal interface. The activation of invariant NKT cells plays an important role in inflammation-induced preterm birth. These decidual immune cells communicate with each other. The development of sequencing technology enables a more in-depth study of decidual immune cells.

CONCLUSION

The dynamic balance of the maternal-fetal immune microenvironment plays a crucial role in maintaining human pregnancy and in the initiation of delivery. A deep understanding of the mechanism of decidual immune dysfunction is crucial for understanding the pathogenesis of preterm birth.

Understanding the heterogeneity of natural killer cells at the maternal-fetal interface: implications for pregnancy health and disease

Natural killer (NK) cells are the most abundant leukocytes located at the maternal-fetal interface; they respond to pregnancy-related hormones and play a pivotal role in maintaining the homeostatic micro-environment during pregnancy. However, due to the high heterogeneity of NK cell subsets, their categorization has been controversial. Here, we review previous studies on uterine NK cell subsets, including the classic categorization based on surface markers, functional molecules, and developmental stages, as well as single-cell RNA sequencing-based clustering approaches. In addition, we summarize the potential pathways by which endometrial NK cells differentiate into decidual NK (dNK) cells, as well as the differentiation pathways of various dNK subsets. Finally, we compared the alterations in the NK cell subsets in various pregnancy-associated diseases, emphasizing the possible contribution of specific subsets to the development of the disease.

Interleukin-10: a novel metabolic inducer of macrophage differentiation and subsequently contributing to improved pregnancy outcomes of mice by orchestrating oxidative phosphorylation metabolism†

Metabolism regulates the phenotype and function of macrophages. After recruitment to local tissues, monocytes are influenced by the local microenvironment and differentiate into various macrophages depending on different metabolic pathways. However, the metabolic mechanisms underlying decidual macrophage differentiation remain unknown. Interleukin-10 (IL-10) is an important decidual macrophage inducer and promotes oxidative phosphorylation (OXPHOS) of bone marrow-derived macrophages. In this study, we mainly investigate the metabolic changes involved in IL-10-generated macrophages from monocytes using in vitro models. We demonstrate that exposure of monocytes (either peripheral or THP-1) to IL-10 altered the phenotype and function of resultant macrophages that are linked with OXPHOS changes. Interleukin-10 enhanced the mitochondrial complex I and III activity of THP-1 cell-differentiated macrophages and increased the mitochondrial membrane potential, intracellular adenosine triphosphate, and reactive oxygen species levels. Oxidative phosphorylation blockage with oligomycin changed the cell morphology of IL-10-generated macrophages and the expression levels of cytokines, such as transforming growth factor beta, tumor necrosis factor-alpha, interferon gamma, and IL-10, apart from changes in the expression level of the surface markers CD206, CD209, and CD163. Moreover, in vivo IL-10 administration reduced the lipopolysaccharide (LPS)-induced embryo resorption rate, and this effect was diminished when OXPHOS was inhibited, demonstrating that OXPHOS is important for the improved pregnancy outcomes of IL-10 in LPS-induced abortion-prone mice. Our findings provide deep insights into the roles of IL-10 in macrophage biology and pregnancy maintenance. Nevertheless, the direct evidence that OXPHOS is involved in decidual macrophage differentiation needs further investigations.

GBS hyaluronidase mediates immune suppression in a TLR2/4- and IL-10-dependent manner during pregnancy-associated infection

IMPORTANCE

Bacteria such as GBS can cause infections during pregnancy leading to preterm births, stillbirths, and neonatal infections. The interaction between host and bacterial factors during infections in the placenta is not fully understood. GBS secretes a hyaluronidase enzyme that is thought to digest host hyaluronan into immunosuppressive disaccharides that dampen TLR2/4 signaling, leading to increased bacterial dissemination and adverse outcomes. In this study, we show that GBS HylB mediates immune suppression and promotes bacterial infection during pregnancy that requires TLR2, TLR4, and IL-10. Understanding the interaction between host and bacterial factors can inform future therapeutic strategies to mitigate GBS infections.

Overexpression of lipocalin 2 in PBX1-deficient decidual NK cells promotes inflammation at the maternal-fetal interface

PROBLEM

Impairment of PBX1 expression in decidual natural killer (dNK) cells is associated with the pathogenesis of unexplained recurrent spontaneous abortion, which results in fetal growth restriction (FGR) by affecting the secretion of downstream growth factors. However, whether other mechanisms limit embryo growth in decidua containing PBX1-deficient natural killer (NK) cells is unknown.

METHOD OF STUDY

Pbx1^f/f ; Ncr1^Cre mice were employed to explore the underlying mechanisms by which PBX1^- NK cells affect embryonic development. To simulate the clinical testing of pregnant women, Doppler ultrasound imaging was used to detect embryo implantation and development. Differentially expressed genes (DEGs) in PBX1^- NK cells that may affect normal pregnancy were screened using RNA-sequencing and real-time PCR. Immune cell changes caused by DEGs were detected by flow cytometry. Finally, the mechanism of FGR was explored by injecting the protein LCN2, corresponding to the selected DEG, into mice.

RESULTS

We verified the embryonic dysplasia in pregnant Pbx1^f/f ; Ncr1^Cre mice by Doppler ultrasound imaging and found that LCN2 was upregulated in dNK cells. We also observed higher infiltration of neutrophils and macrophages in the decidua of Pbx1^f/f ; Ncr1^Cre mice. Finally, we found an increase in the number and activation of neutrophils at the maternal-fetal interface after injecting LCN2 into pregnant mice and observed that these mice showed signs of FGR.

CONCLUSION

Excessive LCN2 secreted by PBX1^- dNK cells at the maternal-fetal interface recruit neutrophils and causes an inflammatory response, which is related to FGR.

Cross-Generational Impact of Innate Immune Memory Following Pregnancy Complications

Pregnancy complications can have long-term negative effects on the health of the affected mothers and their children. In this review, we highlight the underlying inflammatory etiologies of common pregnancy complications and discuss how aberrant inflammation may lead to the acquisition of innate immune memory. The latter can be described as a functional epigenetic reprogramming of innate immune cells following an initial exposure to an inflammatory stimulus, ultimately resulting in an altered response following re-exposure to a similar inflammatory stimulus. We propose that aberrant maternal inflammation associated with complications of pregnancy increases the cross-generational risk of developing noncommunicable diseases (i.e., pregnancy complications, cardiovascular disease, and metabolic disease) through a process mediated by innate immune memory. Elucidating a role for innate immune memory in the cross-generational health consequences of pregnancy complications may lead to the development of novel strategies aimed at reducing the long-term risk of disease.

Placental extracellular vesicles-associated microRNA-519c mediates endotoxin adaptation in pregnancy

BACKGROUND

Pregnancy represents a unique challenge for the maternal-fetal immune interface, requiring a balance between immunosuppression, which is essential for the maintenance of a semiallogeneic fetus, and proinflammatory host defense to protect the maternal-fetal interface from invading organisms. Adaptation to repeated inflammatory stimuli (endotoxin tolerance) may be critical in preventing inflammation-induced preterm birth caused by exaggerated maternal inflammatory responses to mild or moderate infections that are common during pregnancy. However, the exact mechanisms contributing to the maintenance of tolerance to repeated infections are not completely understood. MicroRNAs play important roles in pregnancy with several microRNAs implicated in gestational tissue function and in pathologic pregnancy conditions. MicroRNA-519c, a member of the chromosome 19 microRNA cluster, is a human-specific microRNA mainly expressed in the placenta. However, its role in pregnancy is largely unknown.

OBJECTIVE

This study aimed to explore the role of "endotoxin tolerance" failure in the pathogenesis of an exaggerated inflammatory response often seen in inflammation-mediated preterm birth. In this study, we investigated the role of microRNA-519c, a placenta-specific microRNA, as a key regulator of endotoxin tolerance at the maternal-fetal interface.

STUDY DESIGN

Using a placental explant culture system, samples from term and second-trimester placentas were treated with lipopolysaccharide. After 24 hours, the conditioned media were collected for analysis, and the placental explants were re-exposed to repeated doses of lipopolysaccharide for 3 days. The supernatant was analyzed for inflammatory markers, the presence of extracellular vesicles, and microRNAs. To study the possible mechanism of action of the microRNAs, we evaluated the phosphodiesterase 3B pathway involved in tumor necrosis factor alpha production using a microRNA mimic and phosphodiesterase 3B small interfering RNA transfection. Finally, we analyzed human placental samples from different gestational ages and from women affected by inflammation-associated pregnancies.

RESULTS

Our data showed that repeated exposure of the human placenta to endotoxin challenges induced a tolerant phenotype characterized by decreased tumor necrosis factor alpha and up-regulated interleukin-10 levels. This reaction was mediated by the placenta-specific microRNA-519c packaged within placental extracellular vesicles. Lipopolysaccharide treatment increased the extracellular vesicles that were positive for the exosome tetraspanin markers, namely CD9, CD63, and CD81, and secreted primarily by trophoblasts. Primary human trophoblast cells transfected with a microRNA-519c mimic decreased phosphodiesterase 3B, whereas a lack of phosphodiesterase 3B, achieved by small interfering RNA transfection, led to decreased tumor necrosis factor alpha production. These data support the hypothesis that the anti-inflammatory action of microRNA-519c was mediated by a down-regulation of the phosphodiesterase 3B pathway, leading to inhibition of tumor necrosis factor alpha production. Furthermore, human placentas from normal and inflammation-associated pregnancies demonstrated that a decreased placental microRNA-519c level was linked to infection-induced inflammatory pathologies during pregnancy.

CONCLUSION

We identified microRNA-519c, a human placenta-specific microRNA, as a novel regulator of immune adaptation associated with infection-induced preterm birth at the maternal-fetal interface. Our study serves as a basis for future experiments to explore the potential use of microRNA-519c as a biomarker for infection-induced preterm birth.

Macrophages exert homeostatic actions in pregnancy to protect against preterm birth and fetal inflammatory injury

Macrophages are commonly thought to contribute to the pathophysiology of preterm labor by amplifying inflammation — but a protective role has not previously been considered to our knowledge. We hypothesized that given their antiinflammatory capability in early pregnancy, macrophages exert essential roles in maintenance of late gestation and that insufficient macrophages may predispose individuals to spontaneous preterm labor and adverse neonatal outcomes. Here, we showed that women with spontaneous preterm birth had reduced CD209⁺CD206⁺ expression in alternatively activated CD45⁺CD14⁺ICAM3^– macrophages and increased TNF expression in proinflammatory CD45⁺CD14⁺CD80⁺HLA-DR⁺ macrophages in the uterine decidua at the materno-fetal interface. In Cd11b^DTR/DTR mice, depletion of maternal CD11b⁺ myeloid cells caused preterm birth, neonatal death, and postnatal growth impairment, accompanied by uterine cytokine and leukocyte changes indicative of a proinflammatory response, while adoptive transfer of WT macrophages prevented preterm birth and partially rescued neonatal loss. In a model of intra-amniotic inflammation–induced preterm birth, macrophages polarized in vitro to an M2 phenotype showed superior capacity over nonpolarized macrophages to reduce uterine and fetal inflammation, prevent preterm birth, and improve neonatal survival. We conclude that macrophages exert a critical homeostatic regulatory role in late gestation and are implicated as a determinant of susceptibility to spontaneous preterm birth and fetal inflammatory injury.

Maternal natural killer cells at the intersection between reproduction and mucosal immunity

Many maternal immune cells populate the decidua, which is the mucosal lining of the uterus transformed during pregnancy. Here, abundant natural killer (NK) cells and macrophages help the uterine vasculature adapt to fetal demands for gas and nutrients, thereby supporting fetal growth. Fetal trophoblast cells budding off the forming placenta and invading deep into maternal tissues come into contact with these and other immune cells. Besides their homeostatic functions, decidual NK cells can respond to pathogens during infection, but in doing so, they may become conflicted between destroying the invader and sustaining fetoplacental growth. We review how maternal NK cells balance their double duty both in the local microenvironment of the uterus and systemically, during toxoplasmosis, influenza, cytomegalovirus, malaria and other infections that threat pregnancy. We also discuss recent developments in the understanding of NK-cell responses to SARS-Cov-2 infection and the possible dangers of COVID-19 during pregnancy.

Enhanced drug delivery to the reproductive tract using nanomedicine reveals therapeutic options for prevention of preterm birth

Inflammation contributes to nearly 4 million global premature births annually. Here, we used a mouse model of intrauterine inflammation to test clinically used formulations, as well as engineered nanoformulations, for the prevention of preterm birth (PTB). We observed that neither systemic 17a-hydroxyprogesterone caproate (Makena) nor vaginal progesterone gel (Crinone) was sufficient to prevent inflammation-induced PTB, consistent with recent clinical trial failures. However, we found that vaginal delivery of mucoinert nanosuspensions of histone deacetylase (HDAC) inhibitors, in some cases with the addition of progesterone, prevented PTB and resulted in delivery of live pups exhibiting neurotypical development. In human myometrial cells in vitro, the P4/HDAC inhibitor combination both inhibited cell contractility and promoted the anti-inflammatory action of P4 by increasing progesterone receptor B stability. Here, we demonstrate the use of vaginally delivered drugs to prevent intrauterine inflammation-induced PTB resulting in the birth of live offspring in a preclinical animal model.

Crosstalk Between Trophoblasts and Decidual Immune Cells: The Cornerstone of Maternal-Fetal Immunotolerance

The success of pregnancy relies on the fine adjustment of the maternal immune system to tolerate the allogeneic fetus. Trophoblasts carrying paternal antigens are the only fetal-derived cells that come into direct contact with the maternal immune cells at the maternal–fetal interface. The crosstalk between trophoblasts and decidual immune cells (DICs) via cell–cell direct interaction and soluble factors such as chemokines and cytokines is a core event contributing to the unique immunotolerant microenvironment. Abnormal trophoblasts–DICs crosstalk can lead to dysregulated immune situations, which is well known to be a potential cause of a series of pregnancy complications including recurrent spontaneous abortion (RSA), which is the most common one. Immunotherapy has been applied to RSA. However, its development has been far less rapid or mature than that of cancer immunotherapy. Elucidating the mechanism of maternal–fetal immune tolerance, the theoretical basis for RSA immunotherapy, not only helps to understand the establishment and maintenance of normal pregnancy but also provides new therapeutic strategies and promotes the progress of immunotherapy against pregnancy-related diseases caused by disrupted immunotolerance. In this review, we focus on recent progress in the maternal–fetal immune tolerance mediated by trophoblasts–DICs crosstalk and clinical application of immunotherapy in RSA. Advancement in this area will further accelerate the basic research and clinical transformation of reproductive immunity and tumor immunity.

Evolutionary transcriptomics implicates HAND2 in the origins of implantation and regulation of gestation length

The developmental origins and evolutionary histories of cell types, tissues, and organs contribute to the ways in which their dysfunction produces disease. In mammals, the nature, development and evolution of maternal-fetal interactions likely influence diseases of pregnancy. Here we show genes that evolved expression at the maternal-fetal interface in Eutherian mammals play essential roles in the evolution of pregnancy and are associated with immunological disorders and preterm birth. Among these genes is HAND2, a transcription factor that suppresses estrogen signaling, a Eutherian innovation allowing blastocyst implantation. We found dynamic HAND2 expression in the decidua throughout the menstrual cycle and pregnancy, gradually decreasing to a low at term. HAND2 regulates a distinct set of genes in endometrial stromal fibroblasts including IL15, a cytokine also exhibiting dynamic expression throughout the menstrual cycle and gestation, promoting migration of natural killer cells and extravillous cytotrophoblasts. We demonstrate that HAND2 promoter loops to an enhancer containing SNPs implicated in birth weight and gestation length regulation. Collectively, these data connect HAND2 expression at the maternal-fetal interface with evolution of implantation and gestational regulation, and preterm birth.

Exosomal delivery of NF-κB inhibitor delays LPS-induced preterm birth and modulates fetal immune cell profile in mouse models

Accumulation of immune cells and activation of the pro-inflammatory transcription factor NF-κB in feto-maternal uterine tissues is a key feature of preterm birth (PTB) pathophysiology. Reduction of the fetal inflammatory response and NF-κB activation are key strategies to minimize infection-associated PTB. Therefore, we engineered extracellular vesicles (exosomes) to contain an NF-κB inhibitor, termed super-repressor (SR) IκBα. Treatment with SR exosomes (1 × 1010 per intraperitoneal injection) after lipopolysaccharide (LPS) challenge on gestation day 15 (E15) prolonged gestation by over 24 hours (PTB ≤ E18.5) and reduced maternal inflammation (n ≥ 4). Furthermore, using a transgenic model in which fetal tissues express the red fluorescent protein tdTomato while maternal tissues do not, we report that LPS-induced PTB in mice is associated with influx of fetal innate immune cells, not maternal, into feto-maternal uterine tissues. SR packaged in exosomes provides a stable and specific intervention for reducing the inflammatory response associated with PTB.

Maternal regulation of inflammatory cues is required for induction of preterm birth

Infection-driven inflammation in pregnancy is a major cause of spontaneous preterm birth (PTB). Both systemic infection and bacterial ascension through the vagina/cervix to the amniotic cavity are strongly associated with PTB. However, the contribution of maternal or fetal inflammatory responses in the context of systemic or localized models of infection-driven PTB is not well defined. Here, using intraperitoneal or intraamniotic LPS challenge, we examined the necessity and sufficiency of maternal and fetal Toll-like receptor (TLR) 4 signaling in induction of inflammatory vigor and PTB. Both systemic and local LPS challenge promoted induction of inflammatory pathways in uteroplacental tissues and induced PTB. Restriction of TLR4 expression to the maternal compartment was sufficient for induction of LPS-driven PTB in either systemic or intraamniotic challenge models. In contrast, restriction of TLR4 expression to the fetal compartment failed to induce LPS-driven PTB. Vav1-Cre-mediated genetic deletion of TLR4 suggested a critical role for maternal immune cells in inflammation-driven PTB. Further, passive transfer of WT in vitro-derived macrophages and dendritic cells to TLR4-null gravid females was sufficient to induce an inflammatory response and drive PTB. Cumulatively, these findings highlight the critical role for maternal regulation of inflammatory cues in induction of inflammation-driven parturition.

Human chorionic gonadotropin-mediated modulation of pregnancy-compatible peripheral blood natural killer cells in frozen embryo transfer cycles

PROBLEM

To evaluate pregnancy-compatible phenotypic and functional changes in peripheral blood natural killer (pNK) cells during frozen embryo transfer (FET) cycles.

METHOD OF STUDY

Peripheral blood was collected from patients undergoing frozen embryo transfer cycles at three separate time points in the cycle. pNK cell phenotype was analyzed by flow cytometry. Impact of pregnancy status on pNK cell cytotoxicity was characterized by two methods: (1) a three-dimensional endovascular tube formation approach and (2) a NK cell-specific K562 cell kill assay.

RESULTS

A total of 35 patients were enrolled, 15 with clinical pregnancies and 20 with negative serum β-hCG levels. Overall percentage of CD45⁺ CD3^- CD56⁺ pNK cell did not change during the FET cycle. Pregnancy resulted in an increase in CD45⁺ CD3^- CD56⁺ pNK cell population on the day of serum β-hCG. pNK cells from non-pregnant patients caused significant tube disruption when compared to pregnant patients. Addition of serum from pregnant women reduced the tube disruption by pNK cells from non-pregnant patients. pNK cells from pregnant patients showed significantly lower cytotoxicity toward K562 cells in serum-free conditions. The addition of pregnancy serum decreased non-pregnant pNK cell cytotoxicity. Pregnancy status had no impact on VEGF-A and VEGF-C serum levels. Recombinant hCG added to non-pregnant serum resulted in a significant reduction in non-pregnant pNK cell-mediated K562 cell kill.

CONCLUSION

There was no difference in pNK cell populations based on timing of the FET cycle. However, pregnancy increased the percentage of CD45⁺ CD3^- CD56⁺ pNK cells. Additionally, pNK cells from pregnant women have reduced cytotoxicity and this is possibly mediated by hCG.

MicroRNAs isolated from peripheral blood in the first trimester predict spontaneous preterm birth

OBJECTIVE

To predict spontaneous preterm birth among pregnant women in an African American population using first trimester peripheral blood maternal immune cell microRNA.

STUDY DESIGN

This was a retrospective nested case-control study in pregnant patients enrolled between March 2006 and October 2016. For initial study inclusion, samples were selected that met the following criteria: 1) singleton pregnancy; 2) maternal body mass index (BMI) <30 kg/m2; 3) blood sample drawn between 6 weeks to 12 weeks 6 days gestation; 4) live born neonate with no detectable birth defects. Using these entry criteria, 486 samples were selected for study inclusion. After sample quality was confirmed, 139 term deliveries (38-42 weeks) and 18 spontaneous preterm deliveries (<35 weeks) were selected for analysis. Samples were divided into training and validation sets. Real time reverse transcription quantitative polymerase chain reaction (rt-qPCR) was performed on each sample for 45 microRNAs. MicroRNA Risk Scores were calculated on the training set and area-under-the-curve receiver-operating-characteristic (AUC-ROC) curves were derived from the validation set.

RESULTS

The AUC-ROC for the validation set delivering preterm was 0.80 (95% CI: 0.69 to 0.88; p = 0.0001), sensitivity 0.89, specificity of 0.71 and a mean gestational age of 10.0 ±1.8 weeks (range: 6.6-12.9 weeks). When the validation population was divided by gestational age at the time of venipuncture into early first trimester (mean 8.4 ±1.0 weeks; range 6.6-9.7 weeks) and late first trimester (mean 11.5±0.8 weeks; range 10.0-12.9 weeks), the AUC-ROC scores for early and late first trimester were 0.79 (95% CI: 0.63 to 0.91) and 0.81 (95% CI: 0.66 to 0.92), respectively.

CONCLUSION

Quantification of first trimester peripheral blood MicroRNA identifies risk of spontaneous preterm birth in samples obtained early and late first trimester of pregnancy in an African American population.

Insight Into TLR4-Mediated Immunomodulation in Normal Pregnancy and Related Disorders

Unlike organ transplants where an immunosuppressive environment is required, a successful pregnancy involves an extremely robust, dynamic, and responsive maternal immune system to maintain the development of the fetus. A specific set of hormones and cytokines are associated with a particular stage of pregnancy. Any disturbance that alters this fine balance could compromise the development and function of the placenta. Although there are numerous underlying causes of pregnancy-related complications, untimely activation of Toll-like receptors (TLR), primarily TLR4, by intrauterine microbes poses the greatest risk. TLR4 is an important Pattern Recognition Receptor (PRR), which activates both innate and adaptive immune cells. TLR4 activation by LPS or DAMPs leads to the production of pro-inflammatory cytokines via the MyD88 dependent or independent pathway. Immune cells modulate the materno–fetal interface by TLR4-mediated cytokine production, which changes at different stages of pregnancy. In most pregnancy disorders, such as PTB, PE, or placental malaria, the TLR4 expression is upregulated in immune cells or in maternal derived cells, leading to the aberrant production of pro-inflammatory cytokines at the materno–fetal interface. Lack of functional TLR4 in mice has reduced the pro-inflammatory responses, leading to an improved pregnancy, which further strengthens the fact that abnormal TLR4 activation creates a hostile environment for the developing fetus. A recent study proposed that endothelial and perivascular stromal cells should interact with each other in order to maintain a homeostatic balance during TLR4-mediated inflammation. It has been reported that depleting immune cells or supplying anti-inflammatory cytokines can prevent PTB, PE, or fetal death. Blocking TLR4 signaling or its downstream molecule by inhibitors or antagonists has proven to improve pregnancy-related complications to some extent in clinical and animal models. To date, there has been a lack of knowledge regarding whether TLR4 accessories such as CD14 and MD-2 are important in pregnancy and whether these accessory molecules could be promising drug targets for combinatorial treatment of various pregnancy disorders. This review mainly focuses on the activation of TLR4 during pregnancy, its immunomodulatory functions, and the upcoming advancement in this field regarding the improvement of pregnancy-related issues by various therapeutic approaches.

Characterization of Endocannabinoid System and Interleukin Profiles in Ovine AEC: Cannabinoid Receptors Type-1 and Type-2 as Key Effectors of Pro-Inflammatory Response

Amniotic epithelial cells (AEC) have been proposed as promising clinical candidates for regenerative medicine therapies due to their immunomodulatory capacity. In this context, the endocannabinoid system (ECS) has been identified as mediating the immune-stem cell dialogue, even if no information on AEC is available to date. Therefore, this study was designed to assess whether ECS is involved in tuning the constitutive and lipopolysaccharide (LPS)-induced ovine AEC anti-inflammatory and pro-inflammatory interleukin (IL-10, IL-4, and IL-12) profiles. Firstly, interleukins and ECS expressions were studied at different stages of gestation. Then, the role of cannabinoid receptors 1 and 2 (CB1 and CB2) on interleukin expression and release was investigated in middle stage AEC using selective agonists and antagonists. AEC displayed a degradative more than a synthetic endocannabinoid metabolism during the early and middle stages of gestation. At the middle stage, cannabinoid receptors mediated the balance between pro-inflammatory (IL-12) and anti-inflammatory (IL-4 and IL-10) interleukins. The activation of both receptors mediated an overall pro-inflammatory shift-CB1 reduced the anti-inflammatory and CB2 increased the pro-inflammatory interleukin release, particularly after LPS stimulation. Altogether, these data pave the way for the comprehension of AEC mechanisms tuning immune-modulation, crucial for the development of new AEC-based therapy protocols.

Targeting Toll-like receptor-4 to tackle preterm birth and fetal inflammatory injury

Every year, 15 million pregnancies end prematurely, resulting in more than 1 million infant deaths and long-term health consequences for many children. The physiological processes of labour and birth involve essential roles for immune cells and pro-inflammatory cytokines in gestational tissues. There is compelling evidence that the mechanisms underlying spontaneous preterm birth are initiated when a premature and excessive inflammatory response is triggered by infection or other causes. Exposure to pro-inflammatory mediators is emerging as a major factor in the 'fetal inflammatory response syndrome' that often accompanies preterm birth, where unscheduled effects in fetal tissues interfere with normal development and predispose to neonatal morbidity. Toll-like receptors (TLRs) are critical upstream gatekeepers of inflammatory activation. TLR4 is prominently involved through its ability to sense and integrate signals from a range of microbial and endogenous triggers to provoke and perpetuate inflammation. Preclinical studies have identified TLR4 as an attractive pharmacological target to promote uterine quiescence and protect the fetus from inflammatory injury. Novel small-molecule inhibitors of TLR4 signalling, specifically the non-opioid receptor antagonists (+)-naloxone and (+)-naltrexone, are proving highly effective in animal models for preventing preterm birth induced by bacterial mimetic LPS, heat-killed Escherichia coli, or the TLR4-dependent pro-inflammatory lipid, platelet-activating factor (PAF). Here, we summarise the rationale for targeting TLR4 as a master regulator of inflammation in fetal and gestational tissues, and the potential utility of TLR4 antagonists as candidates for preventative and therapeutic application in preterm delivery and fetal inflammatory injury.

Toll-Like Receptor-4 Antagonist (+)-Naltrexone Protects Against Carbamyl-Platelet Activating Factor (cPAF)-Induced Preterm Labor in Mice

Spontaneous preterm labor is frequently caused by an inflammatory response in the gestational tissues elicited by either infectious or sterile agents. In sterile preterm labor, the key regulators of inflammation are not identified, but platelet-activating factor (PAF) is implicated as a potential rate-limiting effector agent. Since Toll-like receptor (TLR)-4 can amplify PAF signaling, we evaluated whether TLR4 contributes to inflammation and fetal loss in a mouse model of PAF-induced sterile preterm labor, and whether a small-molecule TLR4 inhibitor, (+)-naltrexone, can mitigate adverse PAF-induced effects. The administration of carbamyl (c)-PAF caused preterm labor and fetal loss in wild-type mice but not in TLR4-deficient mice. Treatment with (+)-naltrexone prevented preterm delivery and alleviated fetal demise in utero elicited after cPAF administered by i.p. or intrauterine routes. Pups born after cPAF and (+)-naltrexone treatment exhibited comparable rates of postnatal survival and growth to carrier-treated controls. (+)-Naltrexone suppressed the cPAF-induced expression of inflammatory cytokine genes Il1b, Il6, and Il10 in the decidua; Il6, Il12b, and Il10 in the myometrium; and Il1b and Il6 in the placenta. These data demonstrate that the TLR4 antagonist (+)-naltrexone inhibits the inflammatory cascade induced by cPAF, preventing preterm birth and perinatal death. The inhibition of TLR4 signaling warrants further investigation as a candidate strategy for fetal protection and delay of preterm birth elicited by sterile stimuli.

Microbial supernatants from Mobiluncus mulieris, a bacteria strongly associated with spontaneous preterm birth, disrupts the cervical epithelial barrier through inflammatory and miRNA mediated mechanisms

Recent human clinical studies have identified Mobiluncus mulieris, a fastidious strict anaerobic bacterium present in the cervicovaginal (CV) space, as being strongly associated with spontaneous preterm birth (sPTB). However, the molecular mechanisms that underlie this association remain unknown. As disruption of the cervical epithelial barrier has been shown to contribute to the premature cervical remodeling that precedes sPTB, we hypothesize that M. mulieris, a microbe strongly associated with sPTB in humans, has the ability to alter cervical epithelial function. We investigated if bacteria-free supernatants of M. mulieris were able to disrupt the cervical epithelial barrier through immunological and epigenetic based mechanisms in an in vitro model system. Ectocervical cells were treated with supernatant from cultured M. mulieris and epithelial cell permeability, immune cytokines and microRNAs (miRNAs) were investigated. M. mulieris supernatant significantly increased cell permeability and the expression of two inflammatory mediators associated with cervical epithelial breakdown, IL-6 and IL-8. Moreover, treatment of the ectocervical cells with the M. mulieris supernatant also increased the expression of miRNAs that have been associated with either sPTB or a shorter gestational length in humans. Collectively, these results suggest that M. mulieris induces molecular and functional changes in the cervical epithelial barrier thought to contribute to the pathogenesis of sPTB, which allows us to hypothesize that targeting CV bacteria such as M. mulieris could provide a therapeutic opportunity to reduce sPTB rates.

Repeated lipopolysaccharide exposure leads to placental endotoxin tolerance

PROBLEM

Placental infection induces increased levels of pro-inflammatory cytokines, which have been implicated in the pathogenesis of pre-term labor. Endotoxin tolerance is a phenomenon in which exposure to a dose of endotoxin makes tissue less responsive to subsequent exposures. The objective of our study was to determine whether repeated exposure to endotoxin will induce a tolerant phenotype in normal human second-trimester placental tissue.

METHODS OF STUDY

Human second-trimester placental explants from elective termination of pregnancy were cultured and exposed to endotoxin (LPS). After 24 hours, the media was collected for analysis, and the explants were re-exposed to LPS after adding fresh media for another 24 hours. This process was repeated for a total of 4 LPS doses. The media was collected from each day and analyzed for cytokine levels.

RESULTS

The first LPS treatment stimulated the secretion of the pro-inflammatory cytokines IL-1β and TNF-α. However, their production was significantly diminished with repeated LPS doses. Production of the anti-inflammatory cytokines, IL-1ra and IL-10, was also stimulated by the first LPS treatment, but secretion was more gradually and moderately decreased with repeated LPS doses compared to the pro-inflammatory cytokines. The ratios of the anti-inflammatory/pro-inflammatory mediators (IL-1ra/IL-1β and IL-10/TNF-α) indicate a progressively more anti-inflammatory milieu with repeated LPS doses.

CONCLUSION

Repeated LPS exposure of human second-trimester placental tissues induced endotoxin tolerance. We speculate that endotoxin tolerance at the maternal-fetal interface will protect the fetus from exaggerated inflammatory responses after repeated infectious exposure.

Renal natural killer cell activation and mitochondrial oxidative stress; new mechanisms in AT1-AA mediated hypertensive pregnancy

Women with preeclampsia (PE) have increased mean arterial pressure (MAP), natural killer (NK) cells, reactive oxygen species (ROS), and agonistic autoantibodies to the angiotensin II type 1 receptor (AT1-AA). AT1-AA's administered to pregnant rodents produces a well-accepted model of PE. However, the role of NK cells and mitochondrial reactive oxygen species (mtROS) in AT1-AA mediated hypertension during pregnancy is unknown. We hypothesize that AT1-AA induced model of PE will exhibit elevated MAP, NK cells, and mtROS; while inhibition of the AT1-AA binding to the AT1R would be preventative. Pregnant rats were divided into 4 groups: normal pregnant (NP) (n = 5), NP + AT1-AA inhibitory peptide (NP +'n7AAc') (n = 3), NP + AT1-AA infused (NP + AT1-AA) (n = 10), and NP + AT1-AA +'n7AAc' (n = 8). Day 13, rats were surgically implanted with mini-pumps infusing either AT1-AA or AT1-AA +'n7AAc'. Day 19, tissue and blood was collected. MAP was elevated in AT1-AA vs. NP (119 ± 1 vs. 102 ± 2 mmHg, p < 0.05) and this was prevented by 'n7AAc' (108 ± 3). There was a 6 fold increase in renal activated NK cells in AT1-AA vs NP (1.2 ± 0.4 vs. 0.2 ± 0.1% Gated, p = 0.05) which returned to NP levels in AT1-AA +'n7AAc' (0.1 ± 0.1% Gated). Renal mtROS (317 ± 49 vs. 101 ± 13% Fold, p < 0.05) was elevated with AT1-AA vs NP and was decreased in AT1-AA +'n7AAc' (128 ± 16, p < 0.05). In conclusion, AT1-AA's increased MAP, NK cells, and mtROS which were attenuated by AT1-AA inhibition, thus highlighting new mechanisms of AT1-AA and the importance of drug therapy targeted to AT1-AAs in hypertensive pregnancies.

Prevention of lipopolysaccharide-induced preterm labor by the lack of CX3CL1-CX3CR1 interaction in mice

Preterm labor (PTL) is the most common cause of neonatal death and long-term adverse outcome. The pharmacological agents for PTL prevention are palliative and frequently fail to prevent PTL and improve neonatal outcome. It is essential to fully understand the molecular mechanisms of PTL in order to develop novel therapeutic methods against PTL. Several lines of evidence indicate some chemokines are expressed in gestational tissues during labor or PTL. To reveal the pathophysiological roles of the CX3CL1-CX3CR1 axis in PTL, we performed present study using LPS-induced PTL mice model in CX3CR1-deficient (Cx3cr1-/-) mice. We indicated that PTL was suppressed in Cx3cr1-/- mice and immunoneutralization of CX3CL1 in WT mice. From immunohistochemical and the gene expression analyses, the CX3CL1-CX3CR1 axis has detrimental roles in PTL through intrauterine recruitment of macrophages and the enhancement of macrophage-derived inflammatory mediators. Thus, the CX3CL1-CX3CR1 axis may be a good molecular target for preventing PTL.

Maternal-fetal cross talk through cell-free fetal DNA, telomere shortening, microchimerism, and inflammation

There exists a strong correlation between unscheduled inflammation at the maternal-fetal interface and the continuum of pregnancy complications. In normal pregnancy, immunological tolerance is established to protect the semi-allogeneic fetus. There has been extensive research on how the immunity, endovascular trophoblast migration, and hormonal nexus are orchestrated during pregnancy at the maternal-fetal interface to program a normal pregnancy outcome. It is not clear what contributes to the plasticity of uterine immune tolerance, fetal survial, and long-term post-partum health of the mother and the offspring. Old and new concepts have reemerged and emerged that include cell-free fetal DNA (cffDNA), telomere shortening, microchimerism involving bidirectional migration of maternal and fetal cells, and pregnancy as a stress factor. The question is how these pathways converge in a gestational age-dependent manner to contribute to the health of the mother and the offspring later in life and respond to an array of inflammatory challenges. In this Review, we provide pertinent discussion on maternal-fetal cross talk through cffDNA, telomere shortening, and microchimerism in the context of inflammatory and anti-inflammatory settings, particularly how these pathways lead to normal and adverse pregnancy outcomes.

Maternal obesity alters uterine NK activity through a functional KIR2DL1/S1 imbalance

In pregnancy, uterine natural killer cells (uNK) play essential roles in coordinating uterine angiogenesis, blood vessel remodeling and promoting maternal tolerance to fetal tissue. Deviances from a normal uterine microenvironment are thought to modify uNK function(s) by limiting their ability to establish a healthy pregnancy. While maternal obesity has become a major health concern due to associations with adverse effects on fetal and maternal health, our understanding into how obesity contributes to poor pregnancy disorders is unknown. Given the importance of uNK in pregnancy, this study examines the impact of obesity on uNK function in women in early pregnancy. We identify that uNK from obese women show a greater propensity for cellular activation, but this difference does not translate into increased effector killing potential. Instead, uNK from obese women express an altered repertoire of natural killer receptors, including an imbalance in inhibitory KIR2DL1 and activating KIR2DS1 receptors that favors HLA-C2-directed uNK activation. Notably, we show that obesity-related KIR2DS1 skewing potentiates TNFα production upon receptor crosslinking. Together, these findings suggest that maternal obesity modifies uNK activity by altering the response toward HLA-C2 antigen and KIR2DL1/2DS1-controlled TNFα release. Furthermore, this work identifies alterations in uNK function resulting from maternal obesity that may impact early developmental processes important in pregnancy health.

Interleukin 22 prevents lipopolysaccharide- induced preterm labor in mice

Preterm birth is widespread and causes 35% of all neonatal deaths. Infants who survive face potential long-term complications. A major contributing factor of preterm birth is infection. We investigated the role of interleukin 22 (IL22) as a potential clinically relevant cytokine during gestational infection. IL22 is an effector molecule secreted by immune cells. While the expression of IL22 was reported in normal nonpregnant endometrium and early pregnancy decidua, little is known about uterine IL22 expression during mid or late gestational stages of pregnancy. Since IL22 has been shown to be an essential mediator in epithelial regeneration and wound repair, we investigated the potential role of IL22 during defense against an inflammatory response at the maternal-fetal interface. We used a well-established model to study infection and infection-associated inflammation during preterm birth in the mouse. We have shown that IL22 is upregulated to respond to an intrauterine lipopolysaccharide administration and plays an important role in controlling the risk of inflammation-induced preterm birth. This paper proposes IL22 as a treatment method to combat infection and prevent preterm birth in susceptible patients.

Natural killer-cell deficiency alters placental development in rats

Natural killer (NK) cells are the most prevalent leukocyte population in the uterus during early pregnancy. Natural killer cells contribute to uterine vascular (spiral artery) remodeling in preparation for the increased demand on these vessels later in pregnancy. A second wave of spiral artery modification is directed by invasive trophoblast cells. The significance of the initial wave of NK-cell-mediated vascular remodeling in species exhibiting deep trophoblast invasion such as humans and rats is not known. The purpose of this study was to generate a genetic model of NK-cell deficiency in rats, and determine the consequences of NK-cell deficiency on spiral artery remodeling and reproductive outcomes. To accomplish this task, we utilized zinc finger nuclease-mediated genome editing of the rat interleukin-15 (Il15) gene. Il15 encodes a cytokine required for NK-cell lineage development. Using this strategy, a founder rat was generated containing a frameshift deletion in Il15. Uteri of females harboring a homozygous mutation at the Il15 locus contained no detectable NK cells. NK-cell deficiency did not impact fetal growth or viability. However, NK-cell deficiency caused major structural changes to the placenta, including expansion of the junctional zone and robust, early-onset activation of invasive trophoblast-guided spiral artery remodeling. In summary, we successfully generated an NK-cell-deficient rat and showed, using this model, that NK cells dampen the extent of trophoblast invasion and delay trophoblast-directed spiral artery remodeling. This study furthers our understanding of the role of NK cells on uterine vascular remodeling, trophoblast invasion, and placental development.

Regulatory T cells decrease invariant natural killer T cell-mediated pregnancy loss in mice

Pregnancy loss is the commonest complication of pregnancy. The causes of pregnancy loss are poorly understood. It has been reported that stimulation of invariant natural killer T (iNKT) cells using α-galactosylceramide (αGC) induces pregnancy loss in mice. Here we investigated the mechanisms, especially the role of regulatory T (Treg) cells, in iNKT cell-mediated pregnancy loss. We found that injection of αGC rapidly induced fetal resorption, activated decidual iNKT cells, decreased the percentage of decidual Treg cells and their interleukin (IL)-10 and transforming growth factor (TGF)-β production, and upregulated the levels of interferon (IFN)-γ, tumor necrosis factor-α, IL-4, and IL-10 in serum. Adoptive transfer of iNKT cells from wild-type (WT) and IL-4^-/- mice but not IFN-γ^-/- mice into αGC-treated iNKT cell-deficient Jα18^-/- mice restored αGC-induced pregnancy loss. Adoptive transfer of Treg cells downregulated α-GC-induced pregnancy loss in WT mice. Finally, co-culture with αGC-stimulated decidual iNKT cells decreased the production of IL-10 and TGF-β in decidual Treg cells and inhibited their suppressive activity. These findings suggest that activation of iNKT cells induces pregnancy loss in mice in an IFN-γ-dependent manner. In addition, inhibition of the function of decidual Treg cells has an important role in iNKT cell-mediated pregnancy loss.

Lower Serum Vitamin D Metabolite Levels in Relation to Circulating Cytokines/Chemokines and Metabolic Hormones in Pregnant Women with Hypertensive Disorders

The aim of this study was to investigate whether lower serum vitamin D metabolite levels were associated with altered cytokine/chemokine and metabolic hormone levels in three different hypertensive disorders in pregnancy (HDP). Healthy pregnancy (n = 30) and hypertensive disorders in pregnancy (HDP) (n = 30), i.e., gestational hypertension (GH), preeclampsia (PE), and eclampsia (EC) subjects were enrolled. Vitamin D metabolites were measured by UPLC/APCI/HRMS method. Circulatory 27 cytokines/chemokines and 10 metabolic hormones were measured. Significantly decreased 25(OH)D and 1,25(OH)₂D levels were observed in HDP. The levels of 25(OH)D were significantly lower in PE and EC, whereas the serum levels of 1,25(OH)₂D significantly decreased only in EC subjects. Serum 25(OH)D and 1,25(OH)₂D levels were negatively correlated with systolic- and diastolic blood pressure, creatinine, and uric acid levels. Serum interleukin (IL)-6 and IL-13 decreased, and GIP levels were increased in gestational hypertensive subjects. Platelet-derived growth factor-BB and IL-8 levels were increased and macrophage inflammatory protein-1beta levels were decreased in EC subjects. IL-8 and IL-10 increased, and rantes and GIP levels decreased in the EC group as compared with the GH group. Multivariate logistic regression analysis showed that eotaxin, monocyte chemotactic protein-1, 25(OH)D, and 1,25(OH)₂D were predictors of HDP. Our analyses suggest that lower vitamin D metabolites are associated with altered cytokines/chemokines and metabolic hormones in HDP.

Polychlorinated biphenyls target Notch/Dll and VEGF R2 in the mouse placenta and human trophoblast cell lines for their anti-angiogenic effects

The intrauterine environment is particularly vulnerable to environmental exposures. We previously established a mouse model that provided evidence for pregnancy complications and placental anti-angiogenesis in response to Aroclor 1254 (A-1254), a mixture of polychlorinated biphenyls (PCBs). Importantly, these effects were observed in IL-10^-/-, but not wild type, mice, suggesting that IL-10 deficiency predisposes to pregnancy disruptive effects of environmental toxicants. However, the mechanisms by which PCBs cause anti-angiogenic effects are unclear. Here, we evaluated PCB-mediated anti-angiogenic effects by diverse but complementary approaches, including HUVEC-mediated trophoblast invasion in nude mice, in vitro three-dimensional capillary tube formation involving HUVEC and/or HTR8 trophoblasts, and aortic ring endothelial cell outgrowth/sprouting. Taken together, our data suggest that PCBs act as potent anti-angiogenic agents. Importantly, we show that treatment of pregnant IL-10^-/- mice with A-1254 resulted in placental activation of the Notch/Delta-like ligand (Dll) pathway, a master regulator of cell-cell interaction and vascular patterning. Similar results were obtained with HUVEC and HTR8 trophoblasts. Rescue of A-1254-induced disruption of HUVEC-based tube formation by γ-secretase inhibitor L1790 confirmed the critical role of the Notch/Dll pathway. Our data suggest that PCBs impart pregnancy disruptive functions by activating the Notch/Dll pathway and by inducing anti-angiogenic effects at the maternal-fetal interface.

Myometrial cytokines and their role in the onset of labour

Human labour is an inflammatory event, physiologically driven by an interaction between hormonal and mechanical factors and pathologically associated with infection, bleeding and excessive uterine stretch. The initiation and communicators of inflammation is still not completely understood; however, a key role for cytokines has been implicated. We summarise the current understanding of the nature and role of cytokines, chemokines and hormones and their involvement in signalling within the myometrium particularly during labour.

Uterine natural killer cells dysregulation in idiopathic human preterm birth: a pilot study

OBJECTIVE

To compare between uterine natural killer (uNK) cells in the placental samples of preterm birth and term labor.

STUDY DESIGN

Two-arm case-control study. This study included 60 participants divided into two groups. The first group included 30 cases of idiopathic spontaneous preterm labor and the other group included 30 women who delivered by a spontaneous term vaginal delivery and with no history of previous preterm labor.

RESULT(S)

There were no CD16^- CD56^bright uNK cells in either groups; CD16⁺ CD56^dim uNK cells were present in only 1 case out of 30 term delivery placentae (3.3%), whereas they were found in 21 cases out of 30 (70%) preterm placental samples with a significant statistical difference (p < 0.0001) and OR 67.667, 95% CI (7.95-575.69). CD16⁺CD56^dim uNK cells were found to be invading both the villi and the decidua in 11 cases (70%), whereas those cells were found invading only the villi in 10 cases (33.3%).

CONCLUSION

CD16⁺CD56^dim cells are expressed in both the decidua and the villi of patients with idiopathic preterm labor suggesting an association between uNK cells dysregulation and idiopathic human preterm labor.

Preeclampsia and health risks later in life: an immunological link

Pregnancy represents a period of physiological stress, and although this stress is experienced for a very modest portion of life, it is now recognized as a window to women's future health, often by unmasking predispositions to conditions that only become symptomatic later in life. In normal pregnancy, the mother experiences mild metabolic syndrome-like condition through week 20 of gestation. A pronounced phenotype of metabolic syndrome may program pregnancy complications such as preeclampsia. Preeclampsia is a serious complication with a myriad of manifestations for mother and offspring. This pregnancy syndrome is a polygenic disease and has been now linked to higher incidence of cardiovascular disease, diabetes, and several other disorders associated with vulnerable organs. Furthermore, the offspring born to preeclamptic mothers also exhibit an elevated risk of cardiovascular disease, stroke, and mental disorders during adulthood. This suggests that preeclampsia not only exposes the mother and the fetus to complications during pregnancy but also programs chronic diseases in later life. The etiology of preeclampsia is thought to be primarily associated with poor placentation and entails excessive maternal inflammation and endothelial dysfunction. It is well established now that the maternal immune system and the placenta are involved in a highly choreographed cross-talk that underlies adequate spiral artery remodeling required for uteroplacental perfusion and free flow of nutrients to the fetus. Since normal pregnancy is associated with a sequence of events represented by temporal events of inflammation (implantation), anti-inflammation (gestation), and inflammation (parturition), it is quite possible that unscheduled alterations in these regulatory responses may lead to pathologic consequences. Although it is not clear whether immunological alterations occur early in pregnancy, it is proposed that dysregulated systemic and placental immunity contribute to impaired angiogenesis and the onset of preeclampsia. This review will focus on important aspects of the immune system that coordinate with placental dysfunction to program preeclampsia and influence health in later life.

alpha-actin down regulation and perforin loss in uterine natural killer cells from LPS-treated pregnant mice

One of the most abundant immunologic cell types in early decidua is the uterine natural killer (UNK) cell that despite the presence of cytoplasmic granules rich in perforin and granzymes does not degranulate in normal pregnancy. UNK cells are important producers of angiogenic factors that permit normal dilation of uterine arteries to provide increased blood flow for the growing feto-placental unit. Gram-negative bacteria lipopolysaccharide (LPS) administration can trigger an imbalance of pro-inflammatory and anti-inflammatory cytokines impairing the normal immune cells activity as well as uterine homeostasis. The present study aimed to evaluate by immunohistochemistry the reactivity of perforin and alpha-actin on UNK cell from LPS-treated pregnant mice. For the first time, we demonstrate that LPS injection in pregnant mice causes alpha-actin down regulation, concomitantly with perforin loss in UNK cells. This suggests that LPS alters UNK cell migration and activates cytotoxic granule release.

Endogenous TWEAK is critical for regulating the function of mouse uterine natural killer cells in an immunological model of pregnancy loss

Uterine natural killer (uNK) cells are the most abundant lymphocyte population in the feto-maternal interface during early gestation, and uNK cells play a significant role in the establishment and maintenance of pregnancy-related vascularization, as well as in tolerance to the fetus. Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible molecule (Fn14), are involved in preventing local cytotoxicity and counterbalancing the cytotoxic function of uNK cells. Here, we studied the regulation of TWEAK/Fn14-mediated innate immunity in the uterus using a lipopolysaccharide (LPS)-induced model of abortion in pregnant mice. Specifically, we detected the expression of TWEAK and Fn14 in the uterus and in uNK cells following LPS treatment. Our results revealed that TWEAK and Fn14 are expressed by uNK cells in pregnant mice; in particular, it appears that the cytokine TWEAK is primarily derived from uNK cells. Interestingly, the down-regulation of TWEAK in uNK cells and the up-regulation of the Fn14 receptor in the uterus in LPS-treated mice may contribute to the disruption of decidual homeostasis by altering uNK cell cytotoxicity - ultimately leading to fetal rejection. In conclusion, the present study strongly suggests that the TWEAK-Fn14 axis in uNK cells is involved in maintaining the tolerance necessary for successful pregnancy.

Maternal and fetal roles in bacterially induced preterm labor in the mouse

BACKGROUND

The relative roles of the mother and fetus in signaling for labor remain poorly understood.

OBJECTIVE

We previously demonstrated using gene knockout (KO) mice that Escherichia coli-induced preterm delivery is completely dependent on MyD88, a toll-like receptor adaptor protein. Here we leveraged this finding to conduct a genetic experiment testing whether the mother, the fetus, or both signal for parturition in bacterially induced labor.

STUDY DESIGN

Six different maternal/fetal genotype combinations for MyD88 were studied: wild-type (WT) dams carrying one of the following: (1) WT or (2) MyD88 heterozygous (het) fetuses (generated by mating WT females with WT or MyD88-knockout [KO] males, respectively); (3) WT dams carrying MyD88-KO fetuses (generated by replacing the ovaries of WT females with MyD88-KO ovaries, followed by mating with MyD88-KO males); a similar strategy was used to generate MyD88-KO dams carrying (4) MyD88-KO, (5) MyD88 het, or (6) WT fetuses. On day 14.5 of gestation, mice received intrauterine injections of either 1 × 10(9) killed E coli or sterile medium. Delivery of ≥ 1 fetus within 48 hours was considered preterm. A separate group of similarly treated pregnant mice was euthanized 5 hours after surgery for gene expression and tissue analysis.

RESULTS

E coli-induced preterm delivery is dependent on maternal and not fetal genotype: > 95% of WT and < 5% of MyD88-KO dams deliver prematurely, regardless of fetal genotype (P = .0001). In contrast, fetal survival in utero is influenced by fetal genotype: in MyD88-KO dams, in which premature birth rarely occurs, only 81% of WT and 86% of MyD88-heterozygous fetuses were alive 48 hours after surgery compared with 100% of MyD88-KO fetuses (P < .01). Messenger ribonucleic acids for the inflammatory mediators interleukin-1β, tumor necrosis factor, interleukin-6, and cyclooxygenase-2 were elevated in uterine tissues only in WT mothers treated with E coli and were low or undetectable in the uteri of KO mothers or in animals treated with saline. Serum progesterone levels were lower in KO mothers with WT ovaries than in WT mothers with KO ovaries, but bacterial exposure did not have an impact on these levels.

CONCLUSION

In the murine E coli-induced labor model, preterm delivery and uterine expression of inflammatory mediators is determined by the mother and not the fetus and is not attributable to a decline in serum progesterone.

Invariant NKT Cell Activation Induces Late Preterm Birth That Is Attenuated by Rosiglitazone

Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality worldwide. Although intra-amniotic infection is a recognized cause of spontaneous preterm labor, the noninfection-related etiologies are poorly understood. In this article, we demonstrated that the expansion of activated CD1d-restricted invariant NKT (iNKT) cells in the third trimester by administration of α-galactosylceramide (α-GalCer) induced late PTB and neonatal mortality. In vivo imaging revealed that fetuses from mice that underwent α-GalCer-induced late PTB had bradycardia and died shortly after delivery. Yet, administration of α-GalCer in the second trimester did not cause pregnancy loss. Peroxisome proliferator-activated receptor (PPAR)γ activation, through rosiglitazone treatment, reduced the rate of α-GalCer-induced late PTB and improved neonatal survival. Administration of α-GalCer in the third trimester suppressed PPARγ activation, as shown by the downregulation of Fabp4 and Fatp4 in myometrial and decidual tissues, respectively; this suppression was rescued by rosiglitazone treatment. Administration of α-GalCer in the third trimester induced an increase in the activation of conventional CD4(+) T cells in myometrial tissues and the infiltration of activated macrophages, neutrophils, and mature dendritic cells to myometrial and/or decidual tissues. All of these effects were blunted after rosiglitazone treatment. Administration of α-GalCer also upregulated the expression of inflammatory genes at the maternal-fetal interface and systemically, and rosiglitazone treatment partially attenuated these responses. Finally, an increased infiltration of activated iNKT-like cells in human decidual tissues is associated with noninfection-related preterm labor/birth. Collectively, these results demonstrate that iNKT cell activation in vivo leads to late PTB by initiating innate and adaptive immune responses and suggest that the PPARγ pathway has potential as a target for prevention of this syndrome.

Tim-3 Is Upregulated in NK Cells during Early Pregnancy and Inhibits NK Cytotoxicity toward Trophoblast in Galectin-9 Dependent Pathway

NK cells accumulate at the maternal-fetal interface (MFI) and play essential roles in maintaining immune tolerance during pregnancy. The mechanisms that facilitate NK cells tolerance to fetal tissue are largely unknown. T cell Ig and mucin domain-containing protein 3 (Tim-3) is a newly defined molecule with essential immunological function in many physiological and pathological processes. Recent study showed that Tim-3 was involved in the regulation of immune tolerance at MFI. However, whether Tim-3 regulates NK cells cytotoxicity toward trophoblasts is unclear. Here, we showed Tim-3 was mainly expressed by decidual NK cells (dNK) and Tim-3 level in dNK was higher than peripheral NK cells (pNK). Tim-3⁺ dNK expressed more levels of mature markers CD94 and CD69 than Tim-3^- dNK cells and blocking Tim-3 significantly inhibited dNK IFN-γ and TNF-α secretion. Furthermore, we found TGF-β1 may contribute to such up-regulation of Tim-3 in NK cells. Interestingly, blocking Tim-3 enhanced NK cytotoxicity toward trophoblast cell line HTR-8 but not K562. We found HTR-8 expressed Tim-3 ligand Galectin-9, in contrast K562 did not. Small interfering RNA-mediated silencing of Galectin-9 expression enhanced NK cytotoxicity toward HTR-8. We further showed Tim-3/Galecin-9 inhibited NK cytotoxicity toward trophoblast partially via impairing the degranulation process. In addition, clinical data showed that abnormal Tim-3 level on pNK might be associated with recurrent spontaneous abortion (RSA). Thus, our data demonstrate Tim-3/Galectin-9 pathway maintains local tolerance by suppressing NK cytotoxicity toward trophoblasts which may represent a new immunologic tolerance mechanism at MFI.

Is parturition-timing machinery related to the number of inhibitor CD94/NKG2A positive uterine natural killer cells?

PURPOSE

Prematurity is the most common cause of infant mortality and morbidity. To prevent this, the timing of parturition and its mechanisms should be understood. It is likely that inhibitor CD94/NKG2A positive decidual natural killer cells (uNK) provide for the continuation of pregnancy. Here, we aimed to evaluate whether CD94/NKG2A positive uNK cells are highest in elective cesarian section (C/S) (suggesting ongoing gestation), moderate in normal full-term birth, and lowest in pre-eclamptic parturition.

METHODS

Of 48 pregnant women, 21 C/S, 16 normal, and 11 pre-eclamptic deliveries were included in this study. Five placentas in each group were assigned randomly. After staining, the volumetric analysis of the placental villi and villous blood vessels was performed via the Cavalieri principle. The CD94/NKG2A positive uNK cells were counted using the physical disector method.

RESULTS

The gestation periods and birth weights of the pre-eclamptic deliveries were lower than those of the other two groups. Additionally, the villi and villous vascular volumes were lowest in the pre-eclamptic placentas. As proposed in our hypothesis, the inhibitor CD94/NKG2A positive uNK cells were the highest in the C/S, moderate in the normal, and lowest in the pre-eclamptic placentas.

CONCLUSIONS

These data suggest that CD94/NKG2A positive uNK cells are related with the continuation of pregnancy, and that our human model could be used to search for parturition-timing machinery. We believe that CD94/NKG2A positive uNK cells are also related to the timing of birth.

Depletion of polymorphonuclear leukocytes has no effect on preterm delivery in a mouse model of Escherichia coli-induced labor

OBJECTIVE

The objective of the study was to investigate the role of polymorphonuclear leukocytes (PMNs) in a mouse model of Escherichia coli-induced labor.

STUDY DESIGN

Intraperitoneal injection of rabbit antimouse PMN antiserum or control was performed in CD-1 mice 29 hours and 5 hours prior to laparotomy and intrauterine injection of either killed E coli or phosphate-buffered saline on day 14.5 of pregnancy. Preterm delivery was defined as delivery of at least 1 pup within 48 hours. Circulating leukocyte counts were determined manually or by flow cytometry at the time of surgery and 8, 24, and 48 hours afterward. Maternal and fetal tissues were analyzed in a separate group of animals 8 hours after surgery.

RESULTS

Pretreatment with anti-PMN antiserum significantly decreased the numbers of circulating leukocytes and the proportion of neutrophils among all leukocytes by 70-80% at surgery and at least 8 hours thereafter. Neutrophil depletion significantly reduced 2 markers of neutrophil activation in the uterus and placenta (neutrophil elastase and myeloperoxidase activity) and neutrophil infiltration into gestational tissues in bacterially treated animals to baseline (control) levels but did not affect preterm birth rates. The large E coli-induced increases in uterine inflammatory markers (interleukin-1β, tumor necrosis factor, chemokine ligand-5, cyclooxygenase-2) were not affected or were only minimally affected by neutrophil depletion.

CONCLUSION

Although PMN antiserum reduces both neutrophil number and activity, it does not diminish sensitivity to bacterially induced delivery or meaningfully alter the expression of inflammatory markers in the mouse model. Preterm birth and inflammation in this model are not likely to depend on neutrophil function.

Trophoblast-microbiome interaction: a new paradigm on immune regulation

The immunologic paradigm of pregnancy led to the conceptualization of pregnancy as an organ transplant that requires, for its success, suppression of the maternal immune system. Growing scientific evidence suggests that in many ways the placenta functions as a tumor rather than a transplant and the immune regulation of the maternal-fetal interface is the result of the coordinated interaction between all its cellular components, including bacteria. Examining the role of microbiota in reproduction is in its infancy, but there is growing literature that supports its relevance. We discuss a potential normal function of bacteria in the establishment of immune tolerance and compelling evidence that a viral infection might be the underlying cause of perturbation of homeostasis. There is compelling evidence that many infectious diseases of human beings are caused by >1 microorganism and are defined as polymicrobial infections. We propose that pregnancy complications, such as preterm birth, are the result of polymicrobial infections. We examine the potential cellular and molecular mechanisms by which a viral infection of the placenta might disrupt the normal interaction between the cellular component of the implantation site and bacteria. As we better understand the normal homeostasis among the maternal immune system, placenta, and commensal, we will be able to elucidate pathogenic conditions and design better approaches to treat pregnancy complications associated with infection.

Cell-Free Fetal DNA, Telomeres, and the Spontaneous Onset of Parturition

Multiple previous reports have provided compelling support for the premise that spontaneous parturition is mediated by activation of inflammation-related signaling pathways leading to increased secretion of cytokines and chemokines, the influx of neutrophils and macrophages into the pregnant uterus, increased production of uterine activation proteins (eg, connexin-43, cyclo-oxygenase-2, oxytocin receptors, etc), activation of matrix metalloproteinases, and the release of uterotonins leading to cervical ripening, membrane rupture, and myometrial contractions. The missing link has been the fetal/placental signal that triggers these proinflammatory events in the absence of microbial invasion and intrauterine infection. This article reviews the biomedical literature regarding the increase in cell-free fetal DNA (cffDNA), which is released during apoptosis in the placenta and fetal membranes at term, the ability of apoptosis modified vertebrate DNA to stimulate toll-like receptor-9 (TLR9) leading to increased release of cytokines and chemokines, and the potential "fail-safe" role for the anti-inflammatory cytokine IL-10. This article also reviews the literature supporting the key role that telomere loss plays in regard to increasing the ability of vertebrate (including placental) DNA to stimulate TLR9, and in regard to signaling the onset of apoptosis in the placenta and fetal membranes, thereby providing a biologic clock that determines the length of gestation and the timing for the onset of parturition. In summary, this literature review provides a strong rationale for future research to test the hypothesis that telomere loss and increased cffDNA levels trigger the proinflammatory events leading to the spontaneous onset of parturition in mammals: the "cffDNA/telomere hypothesis."

Prevention of Defective Placentation and Pregnancy Loss by Blocking Innate Immune Pathways in a Syngeneic Model of Placental Insufficiency

Defective placentation and subsequent placental insufficiency lead to maternal and fetal adverse pregnancy outcome, but their pathologic mechanisms are unclear, and treatment remains elusive. The mildly hypertensive BPH/5 mouse recapitulates many features of human adverse pregnancy outcome, with pregnancies characterized by fetal loss, growth restriction, abnormal placental development, and defects in maternal decidual arteries. Using this model, we show that recruitment of neutrophils triggered by complement activation at the maternal/fetal interface leads to elevation in local TNF-α levels, reduction of the essential angiogenic factor vascular endothelial growth factor, and, ultimately, abnormal placentation and fetal death. Blockade of complement with inhibitors specifically targeted to sites of complement activation, depletion of neutrophils, or blockade of TNF-α improves spiral artery remodeling and rescues pregnancies. These data underscore the importance of innate immune system activation in the pathogenesis of placental insufficiency and identify novel methods for treatment of pregnancy loss mediated by abnormal placentation.

Effect of TIM-3 Blockade on the Immunophenotype and Cytokine Profile of Murine Uterine NK Cells

NK cells are the most abundant lymphocyte population in the feto-maternal interface during gestation. The uterine NK cells (uNK) are transient, have a unique immunophenotype and produce a number of cytokines. These cytokines play an important role in establishment and maintenance of vascular remodeling and tolerance associated with successful pregnancy. The uNK cells also express TIM-3 during gestation and blockade of TIM-3 expression results in fetal loss in mice. In this study we determined the effect of TIM-3 blockade on uNK cells. Specifically we observed surface receptor phenotype and cytokine production by uNK cells following TIM-3 blockade. Our results show that TIM-3 plays a role in regulating the uNK cells and contributes to the maintenance of tolerance at the feto-maternal interface.

15-epi-lipoxin A4 reduces the mortality of prematurely born pups in a mouse model of infection-induced preterm birth

Preterm birth remains the leading cause of neonatal mortality and morbidity worldwide. There are currently few effective therapies and therefore an urgent need for novel treatments. Although there is much focus on trying to alter gestation of delivery, the primary aim of preterm birth prevention therapies should be to reduce prematurity related mortality and morbidity. Given the link between intrauterine infection and inflammation and preterm labour (PTL), we hypothesized that administration of lipoxins, key anti-inflammatory and pro-resolution mediators, could be a useful novel treatment for PTL. Using a mouse model of infection-induced PTL, we investigated whether 15-epi-lipoxin A₄ could delay lipopolysaccharide (LPS)-induced PTL and reduce pup mortality. On D17 of gestation mice (n = 9–12) were pretreated with vehicle or 15-epi-lipoxin A₄ prior to intrauterine administration of LPS or PBS. Although pretreatment with 15-epi-lipoxin A₄ did not delay LPS-induced PTL, there was a significant reduction in the mortality amongst prematurely delivered pups (defined as delivery within 36 h of surgery) in mice treated with 15-epi-lipoxin A₄ prior to LPS treatment, compared with those receiving LPS alone (P < 0.05). Quantitative real-time (QRT)-PCR analysis of utero-placental tissues harvested 6 h post-treatment demonstrated that 15-epi-lipoxin A₄ treatment increased Ptgs2 expression in the uterus, placenta and fetal membranes (P < 0.05) and decreased 15-Hpgd expression (P < 0.05) in the placenta and uterus, suggesting that 15-epi-lipoxin A₄ may regulate the local production and activity of prostaglandins. These data suggest that augmenting lipoxin levels could be a useful novel therapeutic option in the treatment of PTL, protecting the fetus from the adverse effects of infection-induced preterm birth.