Potential role of macrophages as immunoregulators of pregnancy

Protective role of macrophages from maternal-fetal interface in unvaccinated coronavirus disease 2019 pregnant women

Pregnant women represent a high-risk population for Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection. The presence of SARS-CoV-2 has been reported in placenta from infected pregnant women, but whether the virus influences placenta immune response remains unclear. We investigated the properties of maternal-fetal interface macrophages (MFMs) in a cohort of unvaccinated women who contracted coronavirus disease 2019 (COVID-19) during their pregnancy. We reported an infiltration of CD163+ macrophages in placenta from COVID-19 women 19 whereas lymphoid compartment was not affected. Isolated MFMs exhibited nonpolarized activated signature (NOS2, IDO1, IFNG, TNF, TGFB) mainly in women infected during the second trimester of pregnancy. COVID-19 during pregnancy primed MFM to produce type I and III interferon response to SARS-CoV-2 (Wuhan and δ strains), that were unable to elicit this in MFMs from healthy pregnant women. COVID-19 also primed SARS-CoV-2 internalization by MFM in an angiotensin-converting enzyme 2-dependent manner. Activation and recall responses of MFMs were influenced by fetal sex. Collectively, these findings support a role for MFMs in the local immune response to SARS-CoV-2 infection, provide a basis for protective placental immunity in COVID-19, and highlight the interest of vaccination in pregnant women.

Hofbauer cells and fetal brain microglia share transcriptional profiles and responses to maternal diet-induced obesity

Maternal immune activation is associated with adverse offspring neurodevelopmental outcomes, many mediated by in utero microglial programming. As microglia remain inaccessible throughout development, identification of noninvasive biomarkers reflecting fetal brain microglial programming could permit screening and intervention. We used lineage tracing to demonstrate the shared ontogeny between fetal brain macrophages (microglia) and fetal placental macrophages (Hofbauer cells) in a mouse model of maternal diet-induced obesity, and single-cell RNA-seq to demonstrate shared transcriptional programs. Comparison with human datasets demonstrated conservation of placental resident macrophage signatures between mice and humans. Single-cell RNA-seq identified common alterations in fetal microglial and Hofbauer cell gene expression induced by maternal obesity, as well as sex differences in these alterations. We propose that Hofbauer cells, which are easily accessible at birth, provide insights into fetal brain microglial programs and may facilitate the early identification of offspring vulnerable to neurodevelopmental disorders.

Human anti-PSCA CAR macrophages possess potent antitumor activity against pancreatic cancer

Due to the limitations of autologous chimeric antigen receptor (CAR)-T cells, alternative sources of cellular immunotherapy, including CAR macrophages, are emerging for solid tumors. Human induced pluripotent stem cells (iPSCs) offer an unlimited source for immune cell generation. Here, we develop human iPSC-derived CAR macrophages targeting prostate stem cell antigen (PSCA) (CAR-iMacs), which express membrane-bound interleukin (IL)-15 and truncated epidermal growth factor receptor (EGFR) for immune cell activation and a suicide switch, respectively. These allogeneic CAR-iMacs exhibit strong antitumor activity against human pancreatic solid tumors in vitro and in vivo, leading to reduced tumor burden and improved survival in a pancreatic cancer mouse model. CAR-iMacs appear safe and do not exhibit signs of cytokine release syndrome or other in vivo toxicities. We optimized the cryopreservation of CAR-iMac progenitors that remain functional upon thawing, providing an off-the-shelf, allogeneic cell product that can be developed into CAR-iMacs. Overall, our preclinical data strongly support the potential clinical translation of this human iPSC-derived platform for solid tumors, including pancreatic cancer.

Blastocyst-Derived Lactic Acid May Regulate S100A6 Expression and Function in Mouse Decidualization via Stimulation of Uterine Epithelial Arachidonic Acid Secretion

(1) Background: Inflammatory responses are implicated in embryo implantation, decidualization, pregnancy maintenance and labor. Both embryo implantation and decidualization are essential to successful pregnancy in rodents and primates. S100A6 is involved in inflammation, tumor development, apoptosis and calcium homeostasis. S100A6 is strongly expressed in mouse decidua, but the underlying mechanisms of how S100A6 regulates implantation and decidualization are poorly defined. (2) Methods: Mouse endometrial stromal and epithelial cells are isolated from day 4 pseudopregnant mouse uteri. Both immunofluorescence and Western blotting are used to analyze the expression and localization of proteins. The molecular mechanism is verified in vitro by Western blotting and the quantitative polymerase chain reaction. (3) Results: From days 4 to 8 of pregnancy, S100A6 is specifically expressed in mouse subluminal stromal cells. Blastocyst-derived lactic acid induces AA secretion by activating the luminal epithelial p-cPLA2. The epithelial AA induces stromal S100A6 expression through the COX2/PGI2/PPAR δ pathway. Progesterone regulates S100A6 expression through the progesterone receptor (PR). S100A6/RAGE signaling can regulate decidualization via EGFR/ERK1/2 in vitro. (4) Conclusions: S100A6, as an inflammatory mediator, is important for mouse implantation and decidualization.

Hofbauer cells and fetal brain microglia share transcriptional profiles and responses to maternal diet-induced obesity

Maternal immune activation is associated with adverse offspring neurodevelopmental outcomes, many mediated by in utero microglial programming. As microglia remain inaccessible throughout development, identification of noninvasive biomarkers reflecting fetal brain microglial programming could permit screening and intervention. We used lineage tracing to demonstrate the shared ontogeny between fetal brain macrophages (microglia) and fetal placental macrophages (Hofbauer cells) in a mouse model of maternal diet-induced obesity, and single-cell RNA-seq to demonstrate shared transcriptional programs. Comparison with human datasets demonstrated conservation of placental resident macrophage signatures between mice and humans. Single-cell RNA-seq identified common alterations in fetal microglial and Hofbauer cell gene expression induced by maternal obesity, as well as sex differences in these alterations. We propose that Hofbauer cells, which are easily accessible at birth, provide novel insights into fetal brain microglial programs, and may facilitate the early identification of offspring vulnerable to neurodevelopmental disorders in the setting of maternal exposures.

Single-cell RNA sequencing-guided fate-mapping toolkit delineates the contribution of yolk sac erythro-myeloid progenitors

Erythro-myeloid progenitors of the yolk sac that originates during early embryo development has been suggested to generate tissue-resident macrophage, mast cell, and even endothelial cell populations from fetal to adult stages. However, the heterogeneity of erythro-myeloid progenitors (EMPs) is not well characterized. Here, we adapt single-cell RNA sequencing to dissect the heterogeneity of EMPs and establish several fate-mapping tools for each EMP subset to trace the contributions of different EMP subsets. We identify two primitive and one definitive EMP subsets from the yolk sac. In addition, we find that primitive EMPs are decoupled from definitive EMPs. Furthermore, we confirm that primitive and definitive EMPs give rise to microglia and other tissue-resident macrophages, respectively. In contrast, only Kit+ Csf1r- primitive EMPs generate endothelial cells transiently during early embryo development. Overall, our results delineate the contribution of yolk sac EMPs more clearly based on the single-cell RNA sequencing (scRNA-seq)-guided fate-mapping toolkit.

Priming of macrophage by glycosphingolipids from extracellular vesicles facilitates immune tolerance for embryo-maternal crosstalk

Glycosphingolipids (GSLs) display diverse functions during embryonic development. Here, we examined the GSL profiles of extracellular vesicles (EVs) secreted from human embryonic stem cells (hESCs) and investigated their functions in priming macrophages to enhance immune tolerance of embryo implantation. When peripheral blood mononuclear cells were incubated with ESC-secreted EVs, globo-series GSLs (GHCer, SSEA3Cer, and SSEA4Cer) were transferred via EVs into monocytes/macrophages. Incubation of monocytes during their differentiation into macrophages with either EVs or synthetic globo-series GSLs induced macrophages to exhibit phenotypic features that imitate immune receptivity, i.e., macrophage polarization, augmented phagocytic activity, suppression of T cell proliferation, and the increased trophoblast invasion. It was also demonstrated that decidual macrophages in first-trimester tissues expressed globo-series GSLs. These findings highlight the role of globo-series GSLs via transfer from EVs in priming macrophages to display decidual macrophage phenotypes, which may facilitate healthy pregnancy.

Cuyun Recipe ameliorates pregnancy loss by regulating macrophage polarization and hypercoagulable state during the peri-implantation period in an ovarian hyperstimulation mouse model

BACKGROUND

The Chinese herbal prescription Cuyun Recipe (CYR) has been widely used to treat clinical infertility and has shown good efficacy. Animal experiments have shown that CYR can promote implantation in mice, however, the exact mechanism underlying the implantation has not been elucidated.

PURPOSE

To investigate the effect and mechanism of CYR on regulating macrophage polarization and hypercoagulability during the peri-implantation period in mice with ovarian hyperstimulation.

METHODS

An ovarian hyperstimulation mouse model was developed, followed by treatment with CYR. Mice were sacrificed on day (D)4.5, D6, or D8 of gestation. The number of implantation sites, the pathological changes of the uterus and ovaries were assessed. The polarization of monocytes/macrophages in the spleen and endometrium, the expression and localization of cytokines were further detected. Furthermore, analyses of hypercoagulable state of the blood were also performed.

RESULTS

Treatment with CYR increased the average number of implantation sites, promoted angiogenesis in endometrial, and regulated monocytes/macrophages and the cytokine levels. Moreover, CYR downregulated the overexpression of D-dimer and fgl2 after ovarian hyperstimulation.

CONCLUSION

CYR facilitates embryo implantation by alleviating ovarian hyperstimulation, promoting endometrial decidualization and angiogenesis, regulating macrophage polarization, and reversing the hypercoagulable state of the blood.

The transcriptional foundations of interferon-λ-mediated endometrial cell to uterine receptivity

PROBLEM

Interferon-λ (IFN-λ) is a novel non-redundant regulator that participates in the fetal-maternal immune interaction, including immune regulation, uterine receptivity, cell migration and adhesion, and endometrium apoptosis. However, the exact transcriptional foundation for endometrial signaling of IFN-λ is not completely understood, and studies regarding IFN-λ to implantation failure in vivo are limited.

METHOD OF STUDY

The gene expression profile of human endometrial Ishikawa cell line treated with IFN-λ or IFN-α (100 ng/mL) for 6 h was analyzed using RNA-sequencing. Real-time qPCR, western blotting, and enzyme-linked immunosorbent assay (ELISA) tests were used to validate these sequencing data. An in vivo IFN-λ knock-down mouse pregnancy model was performed, and the phenotype analysis and the intrauterine biomarkers detection were applied with the uterus samples.

RESULTS

High levels of messenger RNA (mRNA) were detected for genes previously associated with endometrial receptivity, including LIF, AXL, CRYAB, EPHB2, CCL5, and DDX58, following IFN-λ treatment. Moreover, the data indicated IFN-λ reduced pro-inflammatory gene activity compared with IFN-α, including members of the ISG, TNF, SP100 and interleukin genes. The in vivo mouse pregnancy model showed that inhibition of intrauterine IFN-λ results in aberrant epithelial phenotype and significantly decreases the embryo implantation rates and derails normal uterine receptivity.

CONCLUSIONS

These findings demonstrate the antagonistic and agonistic roles of IFNs in the endometrial cell, suggesting a selective role of IFN-λ in endometrial receptivity and immunological tolerance regulation. Moreover, the findings provide valuable insight into potential biomarkers related to endometrial receptivity and facilitate an understanding of the molecular changes observed during infertility treatment and contraception usage.

Updates of placental macrophages: Origins, molecular markers, functions, and related diseases

Placental macrophages are highly heterogeneous cells with differential phenotypes and functions defined by differential origins and modulated by the changing placental environment. During pregnancy, placental macrophages play a critical role in embryo implantation, placenta formation and homeostasis, fetal development and parturition. This review summarizes recent findings on the cellular origin of placental macrophages, and provide a comprehensive description of their phenotypes, corresponding molecular markers and functions in human placenta. Finally, alterations of placental macrophages in pregnancy-related diseases are discussed.

Immune Cell Functionality during Decidualization and Potential Clinical Application

Due to a vast influx in the secretory phase of the menstrual cycle, leukocytes represent 40-50% of the decidua at the time of implantation. Their importance for the implantation, maintenance of pregnancy, and parturition are known yet not fully understood. Thus, in idiopathic infertility, decidual immune-related factors are speculated to be the cause. In this review, the immune cell functions in the decidua were summarized, and clinical diagnostics, as well as interventions, were discussed. There is a rising number of commercially available diagnostic tools. However, the intervention options are still limited and/or poorly studied. In order for us to make big steps towards the proper use of reproductive immunology findings, we need to understand the mechanisms and especially support translational research.

The Distribution of Foxp3 and CD68 in Preeclamptic and Healthy Placentas: A Histomorphological Evaluation

Preeclampsia is a complication of pregnancy that affects 3-5% of pregnancies and is one of the major causes of maternal/neonatal mortality and morbidities worldwide. We aimed to investigate the distribution of Foxp3+ regulatory T-cells and CD68+ Hofbauer cells in the placenta of preeclamptic and healthy pregnant women with a special focus on correlating these findings with placental histology. Decidua and chorionic villi of the placenta obtained from healthy and preeclamptic pregnancies were evaluated in full-thickness sections. Sections were stained with hematoxylin and eosin and Masson's trichrome and immunostained for Foxp3 and CD68 for histological analyses. The total histomorphological score for placentas was found to be higher in preeclamptic placentas than that in the controls. The CD68 immunoreactivity was higher in the chorionic villi of preeclamptic placentas than that in the controls. The immunoreactivity of Foxp3 was found widely distributed within the decidua in both the groups and did not differ significantly. Interestingly, Foxp3 immunoreactivity in the chorionic villi was found mainly in the villous core and, to a lesser extent, in the syncytiotrophoblasts. We found no significant relation between Foxp3 expressions and morphological changes observed in preeclamptic placentas. Although extensive research is being carried out regarding the pathophysiology of preeclampsia, the findings are still controversial.

Innate and Adaptive Immune Systems in Physiological and Pathological Pregnancy

The dynamic immunological changes occurring throughout pregnancy are well-orchestrated and important for the success of the pregnancy. One of the key immune adaptations is the maternal immune tolerance towards the semi-allogeneic fetus. In this review, we provide a comprehensive overview of what is known about the innate and adaptive immunological changes in pregnancy and the role(s) of specific immune cells during physiological and pathological pregnancy. Alongside this, we provided details of remaining questions and challenges, as well as future perspectives for this growing field of research. Understanding the immunological changes that occur can inform potential strategies on treatments for the optimal health of the neonate and pregnant individual both during and after pregnancy.

Decidual macrophages in recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is defined as two or more pregnancy loss, affecting the happiness index of fertility couples. The mechanisms involved in the occurrence of RSA are not clear to date. The primary problem for the maternal immune system is how to establish and maintain the immune tolerance to the semi-allogeneic fetuses. During the pregnancy, decidual macrophages mainly play an important role in the immunologic dialogue. The purpose of this study is to explore decidual macrophages, and to understand whether there is a connection between these cells and RSA by analyzing their phenotypes and functions. Pubmed, Web of Science and Embase were searched. The eligibility criterion for this review was evaluating the literature about the pregnancy and macrophages. Any disagreement between the authors was resolved upon discussion and if required by the judgment of the corresponding author. We summarized the latest views on the phenotype, function and dysfunction of decidual macrophages to illuminate its relationship with RSA.

Identification and validation of a signature based on macrophage cell marker genes to predict recurrent miscarriage by integrated analysis of single-cell and bulk RNA-sequencing

Recurrent miscarriage (RM) is a chronic, heterogeneous autoimmune disease that has serious social and personal consequences. No valid and reliable diagnostic markers or therapeutic targets for RM have been identified. Macrophages impact the innate immune system and can be used as diagnostic and prognostic markers for many diseases. We first collected 16 decidua and villi tissue samples from 5 normal patients and 3 RM patients for single-cell RNA sequencing data analysis and identified 1293 macrophage marker genes. We then screened a recurrent miscarriage cohort (GSE165004) for 186 macrophage-associated marker genes that were significantly differentially expressed between RM patients and the normal pregnancy endometrial tissues, and performed a functional enrichment analysis of differentially expressed genes. We then identified seven core genes (ACTR2, CD2AP, MBNL2, NCSTN, PUM1, RPN2, and TBC1D12) from the above differentially expressed gene group that are closely related to RM using the LASSO, Random Forest and SVM-RFE algorithms. We also used GSE26787 and our own collection of clinical specimens to further evaluate the diagnostic value of the target genes. A nomogram was constructed of the expression levels of these seven target genes to predict RM, and the ROC and calibration curves showed that our nomogram had a high diagnostic value for RM. These results suggest that ACTR2 and NCSTN may be potential targets for preventative RM treatments.

Placental Therapeutic Targets and Nanodelivery Systems

Pregnancy complications affect millions of women each year. Some of these diseases have high morbidity and mortality such as preeclampsia. At present, there is no safe and effective treatment for pregnancy complications, so it is still a difficult clinical problem. As many pregnancy complications are closely related to placental dysplasia, placenta-specific therapy, as an important method, is expected to be a safe, effective, and specific therapeutic strategy. This review explains in detail the placenta physiological structure, characteristics, and action mechanism of some biomolecules and signaling pathways that play roles in normal development and disorders of the development of the placenta, and how to use these biomolecules as therapeutic targets when the placenta disorder causes disease, combining the latest progress in the field of nanodelivery systems, so as to lay a foundation for the development of placenta-specific therapy of pregnancy complications.

Oxygen regulates ILC3 antigen presentation potential and pregnancy-related hormone actions

Early pregnancy is marked by placentation and embryogenesis, which take place under physiological low oxygen concentrations. This oxygen condition is crucial for many aspects of placentation, trophoblast function, vascularization and immune function. Recently, a new family of innate lymphoid cells has been found to be expressed at the fetomaternal interface. Among these, type 3 innate lymphoid cells (ILC3) are important antigen presenting cells in the context of MHC-II. The expression of MHC-II on ILC3s during pregnancy is reduced. We tested the hypothesis that low oxygen concentrations reduce the potential of ILC3s to present antigens promoting fetal tolerance.Using an in vitro approach, NCR⁺ ILC3s generated from cord blood stem cell precursors were incubated under different O₂ concentrations in the presence or absence of the pregnancy-related hormones hCG and TGF-β1. The expression of MHC-II, accessory molecules and an activation marker were assessed by flow cytometry. We observed that 1% O₂ reduced the expression of the MHC-II molecule HLA-DR as compared to 21% O₂ and modulated the relative effects of hCG and TGF-β1.Our data indicate that low oxygen concentrations reduce the antigen presentation potential of NCR⁺ ILC3s and suggest that it may promote fetal tolerance during the first trimester of pregnancy.

Deletion of ACLY Disrupts Histone Acetylation and IL-10 Secretion in Trophoblasts, Which Inhibits M2 Polarization of Macrophages: A Possible Role in Recurrent Spontaneous Abortion

Changes to macrophage polarization affect the local microenvironment of the placenta, resulting in pathological pregnancy diseases such as recurrent spontaneous abortion (RSA). Macrophages are in close contact with trophoblasts during placental development, and trophoblast-derived cytokines are important regulators of macrophage polarization and function. Histone acetylation can affect the expression and secretion of cytokines, and ATP citrate lyase (ACLY) is an important factor that regulates histone acetylation. The aim of this study was to investigate the effect of ACLY expression differences in trophoblast on macrophage polarization and its mechanism. Our data demonstrate that ACLY level in placental villi of patients with RSA is decreased, which may lead to the inhibition of histone acetylation in trophoblasts, thereby reducing the secretion of IL-10. Reduced IL-10 secretion activates endoplasmic reticulum stress in macrophages, thus inhibiting their M2 polarization.

Differential effects of early or late exposure to prenatal maternal immune activation on mouse embryonic neurodevelopment

Prenatal exposure to maternal infection increases the risk of developing mental health disorders, such as schizophrenia and autism spectrum disorder. Exposure to maternal immune activation has been associated with a number of neuroanatomical deficits in adolescent and adult offspring, with differing effects based on the gestational timing of infection. However, little is known about how the embryo brain is affected. We show, using whole-brain MRI, that maternal immune activation significantly affects brain anatomy. When the exposure occurs early in pregnancy, volume reductions are mainly observed, while the opposite is true for exposure later in pregnancy. Furthermore, we identify alterations to the density of certain classes of neurons and glia, which have been associated with stress and inflammation in the brain.

Exposure to maternal immune activation (MIA) in utero is a risk factor for neurodevelopmental and psychiatric disorders. MIA-induced deficits in adolescent and adult offspring have been well characterized; however, less is known about the effects of MIA exposure on embryo development. To address this gap, we performed high-resolution ex vivo MRI to investigate the effects of early (gestational day [GD]9) and late (GD17) MIA exposure on embryo (GD18) brain structure. We identify striking neuroanatomical changes in the embryo brain, particularly in the late-exposed offspring. We further examined the putative neuroanatomical underpinnings of MIA timing in the hippocampus using electron microscopy and identified differential effects due to MIA timing. An increase in apoptotic cell density was observed in the GD9-exposed offspring, while an increase in the density of neurons and glia with ultrastructural features reflective of increased neuroinflammation and oxidative stress was observed in GD17-exposed offspring, particularly in females. Overall, our findings integrate imaging techniques across different scales to identify differential impact of MIA timing on the earliest stages of neurodevelopment.

Modeling Trophoblast Cell-Guided Uterine Spiral Artery Transformation in the Rat

The rat possesses hemochorial placentation with deep intrauterine trophoblast cell invasion and trophoblast-guided uterine spiral artery remodeling, which resembles human placentation. Uterine spiral arteries are extensively remodeled to deliver sufficient supply of maternal blood and nutrients to the developing fetus. Inadequacies in these key processes negatively impact fetal growth and development. Recent innovations in genome editing combined with effective phenotyping strategies have provided new insights into placental development. Application of these research approaches has highlighted both conserved and species-specific features of hemochorial placentation. The review provides foundational information on rat hemochorial placental development and function during physiological and pathological states, especially as related to the invasive trophoblast cell-guided transformation of uterine spiral arteries. Our goal is to showcase the utility of the rat as a model for in vivo mechanistic investigations targeting regulatory events within the uterine-placental interface.

Grim-19 deficiency promotes decidual macrophage autophagy in recurrent spontaneous abortion

Dysregulation of decidual macrophages leads to the occurrence of recurrent spontaneous abortion (RSA). However, the role of macrophages in RSA occurrence remains unclear. In this study, we found that the expression of Grim-19 was decreased, and the expression of autophagy related proteins Beclin1, LC3B II/I and BNIP3 was markedly upregulated in decidual macrophages of RSA patients compared with the normal pregnancy group. Furthermore, we demonstrated that downregulation of GRIM-19 increased the expression of autophagy related proteins Beclin1, LC3B II/I, BNIP3 and the proinflammatory cytokines IL1B, IL6 and TNFa in uterine mononuclear cells of GRIM-19^+/- mice. The proportion of CD45+CD11b+F4/80+LC3B+ cells in GRIM-19^+/- mouse uteri was significantly higher than that in WT mouse uteri. In addition, we confirmed that inhibition of Grim-19 by siRNA enhanced the expression of autophagy related proteins in RAW264.7 cells and THP-1 cells. More importantly, downregulation of Grim-19 in RAW264.7 cells promoted the release of proinflammatory cytokines and promoted phagocytic activity, which could be reversed by autophagy blockade. For THP-1-derived macrophages, the results of RNA-seq suggested that Grim-19 mainly modulates immune and inflammatory-related pathways, leading to cytokine production, and thus contributing to inflammation. Therefore, our data reveal that Grim-19 deficiency influences macrophage function, characterized by enhanced proinflammatory cytokines and phagocytic activity, and this might be regulated by autophagy. This may represent a novel mechanism for the occurrence of RSA.

The role of IP-10 and its receptor CXCR3 in early pregnancy

The local immune microenvironment of the uterus plays an important role in a successful pregnancy. IP-10 (CXCL10) has been extensively studied in many immune-related diseases. However, the immune role of IP-10 in early pregnancy has not been fully recognized. This study mainly investigated the role of pro-inflammatory chemokine IP-10 in pregnancy. The levels of IP-10 and its receptor chemokine receptor 3 (CXCR3) were lower in the decidual tissues of an abortion-prone mice than in normal pregnant mice. Meantime, the expression of IP-10 and CXCR3 was higher in the decidual tissues of early pregnant women than in the endometrial tissues of non-pregnant women. IP-10 promoted the production of interleukin 17 (IL-17) and interferon gamma (IFN-γ), and also promoted the migration and differentiation of uterine decidual T cells to type 1 T helper (Th1) cells and Th17 cells. The abortion rate of early pregnant mice increased but the number of CD49b+, CD11b+, and CD3ε+ cells in the decidual tissues decreased upon treatment with anti-IP-10 antibody. Moreover, anti IP-10 antibody decreased the expression of RANTES but increased the expression of anti-inflammatory cytokines IL-6 and IL-10. A successful pregnancy requires the participation of IP-10. IP-10 participates in formation of the pro-inflammatory immune microenvironment during early pregnancy by regulating the distribution of immune cells and promoting the production of pro-inflammatory cytokines.

Decreased nitric oxide content mediated by asymmetrical dimethylarginine and protein l-arginine methyltransferase 3 in macrophages induces trophoblast apoptosis: a potential cause of recurrent miscarriage

STUDY QUESTION

Is the protein l-arginine methyltransferase 3 (PRMT3)/asymmetrical dimethylarginine (ADMA)/nitric oxide (NO) pathway involved in the development of recurrent miscarriage (RM), and what is the potential mechanism?

SUMMARY ANSWER

Elevated levels of PRMT3 and ADMA inhibit NO formation in the decidua, thereby impairing the functions of trophoblast cells at the maternal-foetal interface.

WHAT IS KNOWN ALREADY

Decreased NO bioavailability is associated with RM. ADMA, an endogenous inhibitor of nitric oxide synthase (NOS), is derived from the methylation of protein arginine residues by PRMTs and serves as a predictor of mortality in critical illness.

STUDY DESIGN, SIZE, DURATION

A total of 145 women with RM and 149 healthy women undergoing elective termination of an early normal pregnancy were enrolled. Ninety-six female CBA/J, 24 male DBA/2 and 24 male BALB/c mice were included. CBA/J × DBA/2 matings represent the abortion group, while CBA/J × BALB/c matings represent the normal control group. The CBA/J pregnant mice were then categorised into four groups: (i) normal + vehicle group (n = 28), (ii) abortion + vehicle group (n = 28), (iii) normal + SGC707 (a PRMT3 inhibitor) group (n = 20) and (iv) abortion + SGC707 group (n = 20). All injections were made intraperitoneally on Days 0.5, 3.5 and 6.5 of pregnancy. Decidual tissues were collected on Days 8.5, 9.5 and 10.5 of gestation. The embryo resorption rates were calculated on Day 9.5 and Day 10.5 of gestation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

NO concentration, ADMA content, NOS activity, expression levels of NOS and PRMTs in decidual tissues were determined using conventional assay kits or western blotting. PRMT3 expression was further analysed in decidual stromal cells, macrophages and natural killer cells. A co-culture system between decidual macrophages (DMs) and HTR-8/SVneo trophoblasts was constructed to study the roles of the PRMT3/ADMA/NO signalling pathway. Trophoblast apoptosis was analysed via Annexin V-fluorescein isothiocyanate/propidium iodide staining. CBA/J × DBA/2 mouse models were used to investigate the effects of SGC707 on embryo resorption rates.

MAIN RESULTS AND THE ROLE OF CHANCE

Our results show that NO concentration and NOS activity were decreased, but ADMA content and PRMT3 expression were increased in the decidua of RM patients. Moreover, compared with the normal control subjects, PRMT3 expression was significantly up-regulated in the macrophages but not in the natural killer cells or stromal cells of the decidua from RM patients. The inhibition of PRMT3 results in a significant decrease in ADMA accumulation and an increase in NO concentration in macrophages. When co-cultured with DMs, which were treated with SGC707 and ADMA, trophoblast apoptosis was suppressed and induced, respectively. In vivo experiments revealed that the administration of SGC707 reduced the embryo resorption rate of CBA/J × DBA/2 mice.

LIMITATIONS, REASONS FOR CAUTION

All sets of experiments were not performed with the same samples. The main reason is that each tissue needs to be reserved for clinical diagnosis and only a small piece of each tissue can be cut and collected for this study.

WIDER IMPLICATIONS OF THE FINDINGS

Our results indicate that the PRMT3/ADMA/NO pathway is a potential marker and target for the clinical diagnosis and therapy of RM.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Key Research and Development Program of China (2017YFC1001401), National Natural Science Foundation of China (81730039, 82071653, 81671460, 81971384 and 82171657) and Shanghai Municipal Medical and Health Discipline Construction Projects (2017ZZ02015). The authors have declared no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Low Abundance Fusobacterium Nucleatum Supports Early Pregnancy Development - An In Vitro Study

Pregnancy success depends greatly on a balanced immune homeostasis. The detection of bacterial components in the upper reproductive tract in non-pregnant and pregnant women raised questions on its possible beneficial role in reproductive health. The local conditions that allow the presence of bacteria to harmonize with the establishment of pregnancy are still unknown. Among the described bacterial species in endometrial and placental samples, Fusobacterium nucleatum was found. It has been observed that F. nucleatum can induce tumorigenesis in colon carcinoma, a process that shares several features with embryo implantation. We propose that low concentrations of F. nucleatum may improve trophoblast function without exerting destructive responses. Inactivated F. nucleatum and E. coli were incubated with the trophoblastic cell lines HTR8/SVneo, BeWo, and JEG-3. Viability, proliferation, migratory capacity, invasiveness and the secretion of chemokines, other cytokines and matrix metalloproteinases were assessed. The presence of F. nucleatum significantly induced HTR8/SVneo invasion, accompanied by the secretion of soluble mediators (CXCL1, IL-6 and IL-8) and metalloproteinases (MMP-2 and MMP-9). However, as concentrations of F. nucleatum increased, these did not improve invasiveness, hindered migration, reduced cell viability and induced alterations in the cell cycle. Part of the F. nucleatum effects on cytokine release were reverted with the addition of a TLR4 blocking antibody. Other effects correlated with the level of expression of E-cadherin on the different cell lines tested. Low amounts of F. nucleatum promote invasion of HTR8/SVneo cells and induce the secretion of important mediators for pregnancy establishment. Some effects were independent of LPS and correlated with the expression of E-cadherin on trophoblasts.

Human Chorionic Gonadotropin and Related Peptides: Candidate Anti-Inflammatory Therapy in Early Stages of Sepsis

Sepsis continues to be a major cause of morbidity, mortality, and post-recovery disability in patients with a wide range of non-infectious and infectious inflammatory disorders, including COVID-19. The clinical onset of sepsis is often marked by the explosive release into the extracellular fluids of a multiplicity of host-derived cytokines and other pro-inflammatory hormone-like messengers from endogenous sources ("cytokine storm"). In patients with sepsis, therapies to counter the pro-inflammatory torrent, even when administered early, typically fall short. The major focus of our proposed essay is to promote pre-clinical studies with hCG (human chorionic gonadotropin) as a potential anti-inflammatory therapy for sepsis.

Functional and genomic adaptations of blood monocytes to pregravid obesity during pregnancy

Pregravid obesity is associated with several adverse maternal health outcomes, such as increased risk of infection, suggesting an altered immunological state. However, the mechanisms by which obesity disrupts the pregnancy “immune clock” are still unknown. Here, we profiled circulating immune mediators, immune cell subset frequencies, and peripheral immune responses during the first and third trimesters of pregnancy in lean and obese mothers. While both Th1 and Th2 cytokines were elevated with pregnancy regardless of BMI, obese subjects had dysregulated myeloid factors in circulation at term. Pregnancy in lean subjects was associated with enhanced monocyte activation, augmented chromatin accessibility at inflammatory loci, and heightened responses to LPS. Pregravid obesity disrupted this trajectory, resulting in a lack of transcriptional, epigenetic, and metabolic changes strongly suggesting a skewing toward innate immune tolerance. These findings provide novel insight into the increased susceptibility to infections in women with obesity during pregnancy and following cesarean delivery.

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Pregnancy is associated with activation and enhanced responses of monocytes

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Heightened monocyte response is associated with epigenetic adaptions

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Pregravid obesity leads to a state akin to LPS tolerance in monocytes

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Pregravid obesity is associated with a lack of epigenetic and metabolic plasticity

Decidual factors and vasoactive intestinal peptide guide monocytes to higher migration, efferocytosis and wound healing in term human pregnancy

AIM

To explore the functional profile of circulating monocytes and decidual macrophages at term human pregnancy and their contribution to tissue repair upon stimulation ex vivo with decidual factors and the vasoactive intestinal peptide (VIP).

METHODS

Peripheral blood monocytes were isolated from pregnant and non-pregnant volunteers and tested in vitro with decidual explants from term placenta and VIP. The effect of VIP on decidual explants and the effect of its conditioned media on monocytes or decidual macrophages isolated by magnetic beads was carried out by RT-qPCR and ELISA for cytokines expression and release. Migration assays were performed in transwell systems. Efferocytosis was assessed in monocytes or decidual macrophages with CFSE-labelled autologous apoptotic neutrophils and quantified by flow cytometry. Monocyte and decidual macrophages wound healing capacity was evaluated using human endometrial stromal cell monolayers. Immunohistochemistry was performed in serial tissue sections of different placentas.

RESULTS

VIP is expressed in the villi as well as in trophoblast giant cells distributed within the decidua of term placenta. VIP induced the expression of antiinflmammatory markers and monocyte chemoattractant CCL2 and CCL3 in decidual tissues. Monocytes presented higher migration towards decidual explants than CD4 and CD8 cells. VIP-conditioned monocytes displayed an enhanced efferocytosis and wound healing capacity comparable to that of decidual macrophages. Moreover limited efferocytosis of pregnant women monocytes was restored by VIP-induced decidual factors.

CONCLUSION

Results show the conditioning of monocytes by decidual factors and VIP to sustain processes required for tissue repair and homeostasis maintenance in term placenta.

SARS-CoV-2 Infection in Pregnant Women: Neuroimmune-Endocrine Changes at the Maternal-Fetal Interface

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has devastating effects on the population worldwide. Given this scenario, the extent of the impact of the disease on more vulnerable individuals, such as pregnant women, is of great concern. Although pregnancy may be a risk factor in respiratory virus infections, there are no considerable differences regarding COVID-19 severity observed between pregnant and nonpregnant women. In these circumstances, an emergent concern is the possibility of neurodevelopmental and neuropsychiatric harm for the offspring of infected mothers. Currently, there is no stronger evidence indicating vertical transmission of SARS-CoV-2; however, the exacerbated inflammatory response observed in the disease could lead to several impairments in the offspring's brain. Furthermore, in the face of historical knowledge on possible long-term consequences for the progeny's brain after infection by viruses, we must consider that this might be another deleterious facet of COVID-19. In light of neuroimmune interactions at the maternal-fetal interface, we review here the possible harmful outcomes to the offspring brains of mothers infected by SARS-CoV-2.

Placental macrophages: Origin, heterogeneity, function and role in pregnancy-associated infections

Placental macrophages are a heterogenous population of immune cells present throughout pregnancy. They are essential for maintenance of the homeostatic placenta environment and host defense against infections. The characterization of placental macrophages as well as their activation have been limited for a long time by the lack of convenient tools. The emergence of unbiased methods makes it possible to reappraise the study of placental macrophages. In this review, we discuss the diversity and the functions of placental macrophages to better understand their dysfunctions during placental infections.

Decidual glycodelin-A polarizes human monocytes into a decidual macrophage-like phenotype through Siglec-7

Decidual macrophages constitute 20-30% of the total leukocytes in the uterus of pregnant women, regulating the maternal immune tolerance and placenta development. Abnormal number or activities of decidual macrophages (dMs) are associated with fetal loss and pregnancy complications, such as preeclampsia. Monocytes differentiate into dMs in a decidua-specific microenvironment. Despite their important roles in pregnancy, the exact factors that regulate the differentiation into dMs remain unclear. Glycodelin-A (PAEP, hereafter referred to as GdA) is a glycoprotein that is abundantly present in the decidua, and plays an important role in fetomaternal defense and placental development. It modulates the differentiation and activity of several immune cell types residing in the decidua. In this study, we demonstrated that GdA induces the differentiation of human monocytes into dM-like phenotypes in terms of transcriptome, cell surface marker expression, secretome, and regulation of trophoblast and endothelial cell functions. We found that Sialic acid-binding Ig-like lectin 7 (Siglec-7) mediates the binding and biological actions of GdA in a sialic acid-dependent manner. We, therefore, suggest that GdA, induces the polarization of monocytes into dMs to regulate fetomaternal tolerance and placental development.

Systems Pharmacology-Based Research on the Mechanism of Tusizi-Sangjisheng Herb Pair in the Treatment of Threatened Abortion

Threatened abortion (TA) is a common complication with high incidence in the first trimester of pregnancy, which will end in miscarriage if not treated properly. The Chinese herbs Cuscutae Semen (Tusizi in Chinese) and Herba Taxilli (Sangjisheng in Chinese) first recorded in the ancient classic medical book Shennong Bencao Jing are effective and widely used as an herb pair for the treatment of TA, while the active ingredients and the functional mechanism of Tusizi-Sangjisheng herb pair treating TA are still unknown. In order to exploit the relationship between those two herbs and TA, systems pharmacology analysis was carried out in this study. A total of 75 ingredients of Tusizi-Sangjisheng were collected from Traditional Chinese Medicine System Pharmacology Database and Analysis Platform (TCMSP). 12 bioactive compounds were screened, and 153 directly related targets were predicted by systematic models. Besides, Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were used to systematically explore the potential mechanisms of Tusizi-Sangjisheng treating TA. Meanwhile, Compound-Target (C-T), Target-Disease (T-D), and Target-Pathway (T-P) networks were constructed to further quest the underlying functional mechanisms of Tusizi-Sangjisheng. As a result, 31 targets and 3 key pathways were found to be directly related to TA that includes mitogen-activated protein kinases (MAPKs), phosphatidylinositol-3-kinase/protein kinase B (PI3K-Akt), and transforming growth factor-β (TGF-β) signaling pathways. The results in this study may provide some valuable clues about the molecular mechanisms of the efficient Chinese herb pair Tusizi-Sangjisheng in the treatment of TA.

Changing the paradigm of IFN-γ at the interface between innate and adaptive immunity: Macrophage-derived IFN-γ

IFN-γ plays a critical role in the immune response to bacterial infections. It is established that IFN-γ is mainly produced by NK/ILC1 cells and T cells, and most of papers have rejected the biologic reality of alternative sources for more than 20 years. Here, we are proposing to revisit this dogma and discuss the role of macrophage-derived IFN-γ in bacterial infections. Our hypothesis is based on a panel of publications and is recently revived by our results on placenta, a chimeric organ in which the immune response is tailored to protect the fetus from mother's immune response. The culture of purified placental macrophages is associated with a production of IFN-γ that may contribute to fetal protection from bacterial infections before eliciting a Th1-like immune response potentially pathogenic for pregnancy. Hence, macrophage IFN-γ may be a novel actor of early crosstalk between innate and adaptive immunity in the context of host defense against bacterial infections.

MiR-103 protects from recurrent spontaneous abortion via inhibiting STAT1 mediated M1 macrophage polarization

Recurrent spontaneous abortion (RSA) is a common complication of early pregnancy. Excessive M1 macrophage was found to be involved in RSA, but the underlying mechanisms remains unclear. MicroRNAs play critical roles in RSA as well as the polarization of macrophages; however, the regulatory effect of miRNAs on M1 differentiation in RSA has not been fully investigated. In this study, miRNA microarray assay revealed that miR-103 was significantly decreased in RAW264.7-derived M1 macrophages upon IFNγ and LPS stimulation. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that in RSA patients, miR-103 expression was decreased substantially, and negatively correlated with that of STAT1. Moreover, down-regulation of miR-103 could sensitively discriminate RSA patients from normal pregnancies (NP) subjects. Experiments in vitro showed that overexpression of miR-103 suppressed M1 polarization by inhibiting STAT1/IRF1 signaling pathway and vice versa. miR-103 regulated STAT1 expression by direct binding to its 3'-UTR. Moreover, our in vivo study demonstrated that overexpressed miR-103 could reduce mice embryo resorption and M1 polarization effectively. Overall, the results suggested that decreased miR-103 was involved in RSA by increasing M1 macrophage polarization via promoting STAT1/IRF1 signaling pathway. miR-103 may be explored as a promising diagnostic marker and therapeutic target for RSA.

Trophoblast-secreted soluble-PD-L1 modulates macrophage polarization and function

Decidual macrophages are in close contact with trophoblast cells during placenta development, and an appropriate crosstalk between these cellular compartments is crucial for the establishment and maintenance of a healthy pregnancy. During different phases of gestation, macrophages undergo dynamic changes to adjust to the different stages of fetal development. Trophoblast-secreted factors are considered the main modulators responsible for macrophage differentiation and function. However, the phenotype of these macrophages induced by trophoblast-secreted factors and the factors responsible for their polarization has not been elucidated. In this study, we characterized the phenotype and function of human trophoblast-induced macrophages. Using in vitro models, we found that human trophoblast-educated macrophages were CD14⁺ CD206⁺ CD86^- and presented an unusual transcriptional profile in response to TLR4/LPS activation characterized by the expression of type I IFN-β expression. IFN-β further enhances the constitutive production of soluble programmed cell death ligand 1 (PD-L1) from trophoblast cells. PD-1 blockage inhibited trophoblast-induced macrophage differentiation. Soluble PD-L1 (sPD-L1) was detected in the blood of pregnant women and increased throughout the gestation. Collectively, our data suggest the existence of a regulatory circuit at the maternal fetal interface wherein IFN-β promotes sPD-L1 expression/secretion by trophoblast cells, which can then initiate a PD-L1/PD-1-mediated macrophage polarization toward an M2 phenotype, consequently decreasing inflammation. Macrophages then maintain the expression of sPD-L1 by the trophoblasts through IFN-β production induced through TLR4 ligation.

The Interplay Between Reproductive Tract Microbiota and Immunological System in Human Reproduction

In the last decade, the microbiota, i.e., combined populations of microorganisms living inside and on the surface of the human body, has increasingly attracted attention of researchers in the medical field. Indeed, since the completion of the Human Microbiome Project, insight and interest in the role of microbiota in health and disease, also through study of its combined genomes, the microbiome, has been steadily expanding. One less explored field of microbiome research has been the female reproductive tract. Research mainly from the past decade suggests that microbial communities residing in the reproductive tract represent a large proportion of the female microbial network and appear to be involved in reproductive failure and pregnancy complications. Microbiome research is facing technological and methodological challenges, as detection techniques and analysis methods are far from being standardized. A further hurdle is understanding the complex host-microbiota interaction and the confounding effect of a multitude of constitutional and environmental factors. A key regulator of this interaction is the maternal immune system that, during the peri-conceptional stage and even more so during pregnancy, undergoes considerable modulation. This review aims to summarize the current literature on reproductive tract microbiota describing the composition of microbiota in different anatomical locations (vagina, cervix, endometrium, and placenta). We also discuss putative mechanisms of interaction between such microbial communities and various aspects of the immune system, with a focus on the characteristic immunological changes during normal pregnancy. Furthermore, we discuss how abnormal microbiota composition, “dysbiosis,” is linked to a spectrum of clinical disorders related to the female reproductive system and how the maternal immune system is involved. Finally, based on the data presented in this review, the future perspectives in diagnostic approaches, research directions and therapeutic opportunities are explored.

Toxoplasma gondii ROP16I Deletion: The Exacerbated Impact on Adverse Pregnant Outcomes in Mice

Imbalance of Th1 and Th2 response at the maternal-fetal interface is considered as a radical event in the pathogenesis of immunity-related pregnant diseases. It has been demonstrated that the ROP16_I, a rhoptry protein of Toxoplasma gondii, and the viable parasite with ROP16_I may induce M2 macrophage polarization in host innate immunity and may be involved in the adverse pregnant outcomes. However, the mechanisms by which T. gondii-derived effectors subvert the immune tolerance in the pathology of pregnancy remain unclear. Here, we constructed the RH strain with ROP16_I deletion (RHΔrop16) to explore the pathogenesis of abnormal pregnancy. We found that C57BL/6 mice infected with RHΔrop16 exhibited the increased resorption of fetuses and more severe adverse pathology of placentae at the early phase of gestation, as compared to the mice infected with RH wild type (RH WT) parasite. Additionally, RHΔrop16 strain infection significantly promoted M1 macrophage phenotypes of CD80 and CD86, and decreased CD206 expression of M2 macrophages, with upregulation of the iNOS and downregulation of the Arg-1 expression in placental homogenates. Simultaneously, the pro-inflammatory cytokines of IL-12 and TNF-α were elevated whereas the anti-inflammatory cytokine of TGF-β1 was dampened. Moreover, the p38α mitogen-activated protein kinase (p38α MAPK) was notably phosphorylated in placental macrophages infected with both RHΔrop16 and RH WT strains compared with the control. Taken together, our findings indicated that ROP16_I deletion of type I RH strain may cause exacerbated adverse pregnant outcomes, which is attributable to subversion of the maternal immune tolerance due to the increased pro-inflammatory cytokines in the pregnant animals. The results also suggest that ROP16_I might be a protective factor and other T. gondii-derived molecules might be involved in the M1-Th1 biased pathological process in aberrant pregnancy at the early phase of gestation.

Role of Macrophages in Pregnancy and Related Complications

Macrophages (MФs) are the leukocytes produced from differentiation of monocytes and are located in almost all tissues of human body. They are involved in various processes, such as phagocytosis, innate and adaptive immunity, proinflammatory (M1) and anti-inflammatory (M2) activity, depending on the tissue microenvironment. They play a crucial role in pregnancy, and their dysfunction or alteration of polarity is involved in pregnancy disorders, like preeclampsia, recurrent spontaneous abortion, infertility, intrauterine growth restriction, and preterm labor. About 50-60% of decidual leukocytes are natural killer (NK) cells followed by MФs (the second largest population). MФs are actively involved in trophoblast invasion, tissue and vascular remodeling during early pregnancy, besides their role as major antigen-presenting cells in the decidua. These cells have different phenotypes and polarities in different stages of pregnancy. They have also been observed to enhance tumor growth by their anti-inflammatory activity (M2 type) and prevent immunogenic rejection. Targeted alteration of polarity (M1-M2 or vice versa) could be a major focus in the future treatment of pregnancy complications. This review is focused on the role of MФs in pregnancy, their involvement in pregnancy disorders, and decidual MФs as possible therapeutic targets for the treatment of pregnancy complications.

The role of the PD-1/PD-L1 axis in macrophage differentiation and function during pregnancy

STUDY QUESTION

What is the role of the programmed cell death-1 (PD-1)/PD-1 ligand-1 (PD-L1) axis in macrophage polarization during early pregnancy?

SUMMARY ANSWER

PD-1 signaling is a major regulator of macrophage differentiation and function, and it is critical for the success of a pregnancy.

WHAT IS KNOWN ALREADY

The predominance of decidual macrophages (DMs) with an M2 phenotype is an important contributor to maternal-fetal tolerance during early pregnancy.

STUDY DESIGN, SIZE, DURATION

Twenty-four women with recurrent miscarriage (RM) and 70 women undergoing elective termination of an early normal pregnancy (NP) were included. Twelve female CBA/J, four male DBA/2, and four male BALB/c mice were included and mating carried out. The 12 CBA/J pregnant mice were then categorized into three groups of four mice: healthy control group CBA/J×BALB/c, abortion-prone pregnant group CBA/J×DBA/2 and normal pregnancies CBA/J×BALB/c treated with anti-PD-1 monoclonal antibodies.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The profile of DMs, and the expression of PD-1 and PD-L1 in DMs from women with NP and RM were measured by flow cytometry. PD-L1 expression in human villi was determined by quantitative RT-PCR (qRT-PCR) and western blot. An in vitro model consisting of peripheral CD14+ monocytes isolated from women with NP was used. The profile of differentiated macrophages and their phagocytotic activity were then measured by flow cytometry. The mRNA levels of genes potentially underlying macrophage polarization modulated by PD-1 signaling were determined by qRT-PCR. Twelve pregnant mice were included in our in vivo model and underwent different treatment. The embryo resorption rate, and macrophage profile as well as PD-1 expression in murine spleens and uterus were analyzed by flow cytometry.

MAIN RESULTS AND THE ROLE OF CHANCE

Compared with NP, women with RM had elevated percentages of M1 DMs (P < 0.01), and reduced frequencies of M2 DMs (P < 0.05), as well as decreased PD-1 protein expression (P < 0.05) in the DMs. In addition, decreased mRNA and protein levels of PD-L1 expression in placental villi were observed in women with RM (P < 0.001). Using in vitro experiments, compared to the control group, we found that PD-1 activation by recombinant human (rh) PD-L1 Fc (human PD-L1 fused to the Fc region of human IgG1) drove the differentiation of macrophages with immuno-modulatory characteristics (P < 0.01). However, PD-1 blockade promoted dominance of the M1 phenotype (P < 0.01). PD-1 polarized macrophages showed enhanced phagocytic activity (P < 0.01), which was decreased with PD-1 blockade (P < 0.001). Furthermore, PD-1 blockade promoted the expression of pro-inflammatory cytokines and interferon regulatory factor (IRF) 5 (P < 0.05), while IRF4 expression was inhibited (P < 0.05). In addition, PD-1 blockade promoted macrophage glycolysis (P < 0.01) and inhibited fatty acid oxidation (P < 0.05). The mRNA expression levels of both phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin and mitogen-activated protein kinase/extracellular signal-regulated kinase/extracellular signal-regulated kinase were upregulated (P < 0.05) with PD-1 blockade during DM metabolic reprogramming. Moreover, in vivo mice data showed that PD-1 blockade or deficiency was associated with decreased M2 percentages at the maternal-fetal interface (P < 0.05) and embryo loss (P < 0.05).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Whether the changes in DM polarization seen in miscarriage tissues are a cause or consequence of the demise of the pregnancy still requires further investigation. In addition, conducting metabolite analysis is required to further measure bioenergetic profiles.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study on the role of the PD-1/PD-L1 axis in macrophage polarization during early pregnancy; such exploration enhances our understanding of the physiology of early pregnancy. Our study also indicates that targeting the PD-1 pathway may represent a novel therapeutic strategy to prevent pregnancy loss.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Nature Science Foundation of China (No. 81671490) and Integrated Innovative Team for Major Human Diseases Program of Tongji Medical College, HUST (No. 5001519002). None of the authors has any conflict of interest to declare.

The Elusive Role of Placental Macrophages: The Hofbauer Cell

In this review, we discuss the often overlooked tissue-resident fetal macrophages, Hofbauer cells, which are found within the chorionic villi of the human placenta. Hofbauer cells have been shown to have a phenotype associated with regulatory and anti-inflammatory functions. They are thought to play a crucial role in the regulation of pregnancy and in the maintenance of a homeostatic environment that is crucial for fetal development. Even though the numbers of these macrophages are some of the most abundant immune cells in the human placenta, which are sustained throughout pregnancy, there are very few studies that have identified their origin, their phenotype, and functions and why they are maintained throughout gestation. It is not yet understood how Hofbauer cells may change in function throughout normal pregnancy, and especially in those complicated by maternal gestational diabetes, preeclampsia, and viral infections, such as Zika, cytomegalovirus, and human immunodeficiency virus. We review what is known about the origin of these macrophages and explore how common complications of pregnancy dysregulate these cells leading to adverse birth outcomes in humans. Our synthesis sheds light on areas for human studies that can further define these innate regulatory cells.

FasL on decidual macrophages mediates trophoblast apoptosis: A potential cause of recurrent miscarriage

Macrophages can induce Fas ligand (FasL)-mediated apoptosis, and the deregulation of apoptosis is known to be associated with recurrent miscarriage (RM). The aim of the present study was to investigate the possible involvement of FasL in macrophage-mediated trophoblast apoptosis and its potential role in RM. Human decidual and placental villous tissues were collected from 81 women (21 for the RM group, 26 for the spontaneous abortion group and 34 for the control group) at 7-9 weeks of gestation. The distribution changes of macrophages and the expression of FasL on macrophages were evaluated by immunohistochemical, immunofluorescence and western blot analyses. A macrophage and trophoblast co-culture model was used to determine the effects of FasL on the apoptosis of trophoblasts. The results indicated that CD86⁺ macrophage populations in decidual tissues were significantly increased, accompanied by reduced CD163⁺ macrophages in the abortion and RM groups. Furthermore, the distribution of CD68⁺ macrophages was also significantly altered in specimens from the abortion and RM groups, and they were observed to have infiltrated into the trophoblast cells. In addition, elevated expression of FasL on CD68⁺ and CD86⁺ macrophages in the decidua was observed in the spontaneous abortion and RM groups of patients, and FasL was demonstrated to mediate the induction of trophoblast apoptosis by macrophages in co-culture. These results indicate that the aberration of macrophage-induced FasL-mediated apoptosis may represent one of the causes of RM.

Silencing of Annexin A1 suppressed the apoptosis and inflammatory response of preeclampsia rat trophoblasts

Preeclampsia (PE) is a disorder that is characterized by pregnancy-induced hypertension. It has been reported that Annexin A1 (ANXA1) is highly expressed in the plasma of women diagnosed with PE. Therefore, the present study aimed to examine the effect of ANXA1 on PE rats. The PE animal model was constructed in rats using Nω-nitro-L-arginine methyl ester (L-NAME), and the blood pressure and urine protein levels of rats were detected. The pathological features of placental tissue, and the levels of inflammatory factors and ANXA1 were respectively measured by hematoxylin-eosin staining, enzyme-linked immunosorbent assay and immunohistochemical assay. The activity of trophoblasts obtained from PE placental tissue was measured using immunofluorescence staining, while cell apoptosis was assessed using flow cytometry. The levels of associated factors were determined by reverse transcription-quantitative polymerase chain reaction and western blot analysis. The results identified that systolic blood pressure, diastolic blood pressure, mean arterial pressure and urine protein levels were enhanced, and that the contents of ANXA1, tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, IL-6 and IL-8 were increased in the L-NAME group. Transfection with small interfering RNA (siRNA)-ANXA1 markedly decreased the apoptosis and inflammatory response of trophoblasts. In addition, siRNA-ANXA1 upregulated the levels of B-cell lymphoma-2 (Bcl-2) and pro-caspase-3, and downregulated the levels of Bcl-2-associated X protein, cleaved-caspase-3, TNF-α, IL-1β, IL-6 and IL-8. Furthermore, siRNA-ANXA1 repressed the phosphorylation of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3); however, siRNA-ANXA1 did not alter the levels of JAK2 and STAT3. Therefore, silencing of ANXA1 suppressed the apoptosis and inflammatory response of PE rat trophoblasts, and downregulated JAK2/STAK3 pathway.

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.

Placental protein 13: An important biological protein in preeclampsia

Placental protein 13 (PP13), a glycan binding protein predominantly expressed in syncytiotrophoblast, dimeric in nature, lacks N-terminal signal peptide, bypasses the endoplasmic reticulum, and secretes into maternal circulation as exosomes or microvesicles. PP13 has jelly roll fold conformation with conserved carbohydrate recognition domain which specifically binds to β-galactosides of the glycan receptors during placentation. PP13 binds to glycosylated receptors on human erythrocytes and brings about hemagglutination by the property of lectin activity; other functions are immunoregulation and vasodilation during placentation and vascularization. The gene LGALS13 located on 19q13.2 comprising four exons expresses a 32-kDa protein with 139 amino acid residues, PP13. Impaired expression due to mutation in the gene leads to a nonfunctional truncated PP13. The low serum levels predict high risk for the onset of preeclampsia or obstetric complications. Hence, PP13 turned to be an early marker for risk assessment of preeclampsia. The recombinant PP13 and monoclonal antibodies availability help for replenishing PP13 in conditions with low serum levels and for detection and prevention of preeclampsia, respectively.

The treatment with selenium increases placental parasitismin pregnant Wistar rats infected with the Y strain of Trypanosoma cruzi

Selenium (Se) is an essential micronutrient in the diet of mammals and has an important role in the immune function. Selenium is a key element in selenoproteins involved in the in the maintenance of the antioxidant defense. Diet with selenium is beneficial for the treatment of diseases correlated with high levels of oxidative stress, also observed in the Chagas disease. Chagas disease is a neglected disease caused by the protozoan Trypanosoma cruzi and several research groups are focused on the illness treatment. Immunomodulation of the infection using microelements is an important tool to avoid deleterious effects of the Chagas disease. Therefore, our objective was to evaluate the effects of selenium supplementation on pregnant Wistar rats infected with T. cruzi. Selenium treatment stimulated the weight and length of fetuses and placentas allied to the decrease of blood parasitemia. However, selenium demonstrated a low influence on T cells, diminishing the B cell population (CD45RA⁺). Moreover, the production of pro-inflammatory cytokines was downregulated under selenium administration. Low pro-inflammatory cytokines levels probably are related to the increase in the number of amastigote nests in infected and treated animals. Thus, selenium supplementation during pregnancy could impair the local placental immune response. Further studies are necessary to assess the interaction between selenium and the acute Chagas' disease during pregnancy, which will base future supplementation strategies.

Death begets a new beginning

Cell death is a perpetual feature of tissue microenvironments; each day under homeostatic conditions, billions of cells die and must be swiftly cleared by phagocytes. However, cell death is not limited to this natural turnover-apoptotic cell death can be induced by infection, inflammation, or severe tissue injury. Phagocytosis of apoptotic cells is thus coupled to specific functions, from the induction of growth factors that can stimulate the replacement of dead cells to the promotion of tissue repair or tissue remodeling in the affected site. In this review, we outline the mechanisms by which phagocytes sense apoptotic cell death and discuss how phagocytosis is integrated with environmental cues to drive appropriate responses.