Macrophages at the fetal-maternal interface express markers of alternative activation and are induced by M-CSF and IL-10

ZBED1 Regulates Genes Important for Multiple Biological Processes of the Placenta

The transcription factor ZBED1 is highly expressed in trophoblast cells, but its functions in the processes of trophoblast and placental biology remain elusive. Here, we characterized the role of ZBED1 in trophoblast cell differentiation using an in vitro BeWo cell model. We demonstrate that ZBED1 is enhanced in its expression early after forskolin-induced differentiation of BeWo cells and regulates many of the genes that are differentially expressed as an effect of forskolin treatment. Specifically, genes encoding markers for the differentiation of cytotrophoblast into syncytiotrophoblast and factors essential for trophoblast cell fusion and invasion were negatively regulated by ZBED1, indicating that ZBED1 might be important for maintaining a steady pool of cytotrophoblast cells. In addition, ZBED1 affected genes involved in the regulation of trophoblast cell survival and apoptosis, in agreement with the observed increase in apoptosis upon knockdown of ZBED1 in forskolin-treated BeWo cells. In addition, genes implicated in the differentiation, recruitment, and function of innate immune cells by the placenta were affected by ZBED1, further suggesting a role for this protein in the regulation of maternal immune tolerance. In conclusion, our study implicates ZBED1 in major biological processes of placental biology.

Downregulation of EZH2 in Trophoblasts Induces Decidual M1 Macrophage Polarization: a Potential Cause of Recurrent Spontaneous Abortion

Macrophages are known to be pivotal for ensuring the establishment of the immune tolerance microenvironment at the maternal–fetal interface. In particular, trophoblasts stay in close contact with decidual macrophages (DMs), which have been reported to play an active role in the modulation of the polarization of DMs. Thus, any dysfunction of trophoblasts might be associated with certain pregnancy‐related complications, such as recurrent spontaneous abortion (RSA). Enhancer of zeste homolog 2 (EZH2) is an important epigenetic regulatory gene that has been previously shown to be related to immune regulation. The present study assessed the expression of EZH2 in villi tissue obtained from healthy controls and RSA patients. Trophoblasts conditioned medium was collected to incubate macrophages differentiated from the THP‐1 cell line. The expression and function of EZH2 in trophoblasts were knocked down either by the use of siRNA or GSK126 as an inhibitor. Our results show a significant decrease in the expression of EZH2 in villi tissue from RSA patients as compared to healthy controls. Further, the inhibition of expression or function of EZH2 in trophoblasts promoted M1 macrophage polarization, which might be involved in the pathogenesis of RSA. Moreover, the suppression of EZH2 was found to affect the secretion of immune and inflammatory cytokines in trophoblasts. Altogether, these results indicated the importance of EZH2 in the regulation of immune functions of trophoblasts and thus highlighted its potential to be explored as a therapeutic target to prevent and treat pregnancy loss.

Possible impact of neutrophils on immune responses during early pregnancy in ruminants

The interaction between early embryo and maternal immune system for the establishment of pregnancy is the focus of several studies; however, it remains unclear. The maternal immune response needs to keep a balance between avoiding any damage to the conceptus and maintaining its function in combating microbes as well. When conceptus-maternal crosstalk cannot achieve this balance, pregnancy losses might occur. Intercommunication between mother and conceptus is fundamental during early pregnancy to dictate the outcome of pregnancy. In ruminants, the embryo reacts with the maternal system mainly via interferon tau (IFNT) release. IFNT can act locally on the embryo and endometrial cells and systemically in several tissues and cells to regulate their response via the expression of interferon-stimulated genes (ISGs). Also, IFNT can induce the expression of inflammatory-related genes in immune cells. Day 7 embryo induces a shift in the maternal immune response towards anti-inflammatory (Th2) immune responses. During maternal recognition of pregnancy, peripheral mononuclear cells (PBMCs) and polymorphonuclear cells (PMNs) express markers that configure an anti-inflammatory response. However, PMNs response is more sensitive to the effects of IFNT. PMNs are more likely to express interferon-stimulated genes (ISGs), transforming growth factor-beta (TGFB), interleukin 10 (IL10), and arginase-1 (ARG1), configuring one of the most rapid immune responses to early pregnancy. This review focus on the local and peripheral immune responses during early pregnancy in ruminants, mainly the PMNs function in the immune system.

Crosstalk Between Trophoblast and Macrophage at the Maternal-Fetal Interface: Current Status and Future Perspectives

The immune tolerance microenvironment is crucial for the establishment and maintenance of pregnancy at the maternal-fetal interface. The maternal-fetal interface is a complex system containing various cells, including lymphocytes, decidual stromal cells, and trophoblasts. Macrophages are the second-largest leukocytes at the maternal-fetal interface, which has been demonstrated to play essential roles in remodeling spiral arteries, maintaining maternal-fetal immune tolerance, and regulating trophoblast's biological behaviors. Many researchers, including us, have conducted a series of studies on the crosstalk between macrophages and trophoblasts at the maternal-fetal interface: on the one hand, macrophages can affect the invasion and migration of trophoblasts; on the other hand, trophoblasts can regulate macrophage polarization and influence the state of the maternal-fetal immune microenvironment. In this review, we systemically introduce the functions of macrophages and trophoblasts and the cell-cell interaction between them for the establishment and maintenance of pregnancy. Advances in this area will further accelerate the basic research and clinical translation of reproductive medicine.

Cytochrome P450 26A1 Modulates the Polarization of Uterine Macrophages During the Peri-Implantation Period

Uterine M1/M2 macrophages activation states undergo dynamic changes throughout pregnancy, and inappropriate macrophages polarization can cause adverse pregnancy outcomes, especially during the peri-implantation period. Our previous studies have confirmed that Cytochrome P450 26A1 (CYP26A1) can affect embryo implantation by regulating uterine NK cells and DCs. The aim of this study was to investigate whether CYP26A1 regulates the polarization of uterine macrophages in early pregnancy. Here, we observed that Cyp26a1 was significantly upregulated in M1 as compared with M2 of uterine macrophages, Raw264.7 and iBMDM. Knockdown of CYP26A1 in mice uterine significantly decreased the number of embryo implantation sites and the proportion of CD45⁺F4/80⁺CD206⁻ M1-like uterine macrophages. Primary uterine macrophages treated with anti-CYP26A1 antibody expressed significantly lower levels of M1 markers Nos2, Il1b, Il6 and Tnf-a. In CYP26A1 knockout Raw264.7 cells, the protein levels of M1 markers TNF-α, IL-6 and CD86 were significantly decreased as compared with the wild type cells. Moreover, CYP26A1 deficiency decreased the ability to produce nitric oxide and increased the phagocytosis capacity of Raw264.7 cells under M1 stimulation state. The re-introduction of CYP26A1 partially reversed the polarization levels of M1 in CYP26A1 knockout Raw264.7 cells. CYP26A1 may regulate the polarization of uterine macrophages to M1 through Stap1 and Slc7a2. In summary, these results indicate that CYP26A1 plays a significant role in macrophage polarization, and knockdown of CYP26A1 can cause insufficient M1 polarization during the peri-implantation period, which has adverse effects on blastocyst implantation.

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.

MAIT Cells Balance the Requirements for Immune Tolerance and Anti-Microbial Defense During Pregnancy

Mucosal-associated invariant T (MAIT) cells are an innate-like T cell subset with proinflammatory and cytotoxic effector functions. During pregnancy, modulation of the maternal immune system, both at the fetal-maternal interface and systemically, is crucial for a successful outcome and manifests through controlled enhancement of innate and dampening of adaptive responses. Still, immune defenses need to efficiently protect both the mother and the fetus from infection. So far, it is unknown whether MAIT cells are subjected to immunomodulation during pregnancy, and characterization of decidual MAIT cells as well as their functional responses during pregnancy are mainly lacking. We here characterized the presence and phenotype of Vα7.2⁺CD161⁺ MAIT cells in blood and decidua (the uterine endometrium during pregnancy) from women pregnant in the 1^st trimester, i.e., the time point when local immune tolerance develops. We also assessed the phenotype and functional responses of MAIT cells in blood of women pregnant in the 3^rd trimester, i.e., when systemic immunomodulation is most pronounced. Multi-color flow cytometry panels included markers for MAIT subsets, and markers of activation (CD69, HLA-DR, Granzyme B) and immunoregulation (PD-1, CTLA-4). MAIT cells were numerically decreased at the fetal-maternal interface and showed, similar to other T cells in the decidua, increased expression of immune checkpoint markers compared with MAIT cells in blood. During the 3^rd trimester, circulating MAIT cells showed a higher expression of CD69 and CD56, and their functional responses to inflammatory (activating anti-CD3/CD28 antibodies, and IL-12 and IL-18) and microbial stimuli (Escherichia coli, group B streptococci and influenza A virus) were generally increased compared with MAIT cells from non-pregnant women, indicating enhanced antimicrobial defenses during pregnancy. Taken together, our findings indicate dual roles for MAIT cells during pregnancy, with an evidently well-adapted ability to balance the requirements of immune tolerance in parallel with maintained antimicrobial defenses. Since MAIT cells are easily activated, they need to be strictly regulated during pregnancy, and failure to do so could contribute to pregnancy complications.

Hofbauer Cells Spread Listeria monocytogenes among Placental Cells and Undergo Pro-Inflammatory Reprogramming while Retaining Production of Tolerogenic Factors

Pregnant women are highly susceptible to infection by the bacterial pathogen Listeria monocytogenes, leading to miscarriage, premature birth, and neonatal infection. L. monocytogenes is thought to breach the placental barrier by infecting trophoblasts at the maternal/fetal interface. However, the fate of L. monocytogenes within chorionic villi and how infection reaches the fetus are unsettled. Hofbauer cells (HBCs) are fetal placental macrophages and the only leukocytes residing in healthy chorionic villi, forming a last immune barrier protecting fetal blood from infection. Little is known about the HBCs’ antimicrobial responses to pathogens. Here, we studied L. monocytogenes interaction with human primary HBCs. Remarkably, despite their M2 anti-inflammatory phenotype at basal state, HBCs phagocytose and kill non-pathogenic bacteria like Listeria innocua and display low susceptibility to infection by L. monocytogenes. However, L. monocytogenes can exploit HBCs to spread to surrounding placental cells. Transcriptomic analyses by RNA sequencing revealed that HBCs undergo pro-inflammatory reprogramming upon L. monocytogenes infection, similarly to macrophages stimulated by the potent M1-polarizing agents lipopolysaccharide (LPS)/interferon gamma (IFN-γ). Infected HBCs also express pro-inflammatory chemokines known to promote placental infiltration by maternal leukocytes. However, HBCs maintain the expression of a collection of tolerogenic genes and secretion of tolerogenic cytokines, consistent with their tissue homeostatic role in prevention of fetal rejection. In conclusion, we propose a previously unrecognized model in which HBCs promote the spreading of L. monocytogenes among placental cells and transition to a pro-inflammatory state likely to favor innate immune responses, while maintaining the expression of tolerogenic factors known to prevent maternal anti-fetal adaptive immunity.

Histone deacetylase 9 deficiency exaggerates uterine M2 macrophage polarization

The maternal‐foetal interface is an immune‐privileged site where the semi‐allogeneic embryo is protected from attacks by the maternal immune system. Uterine macrophages are key players in establishing and maintaining pregnancy, and the dysregulation of the M1‐M2 subpopulation balance causes abortion. We separated two distinct mouse uterine macrophage subpopulations during early pregnancy, CD45⁺F4/80⁺CD206⁻ M1‐like (M1) and CD45⁺F4/80⁺CD206⁺ M2‐like (M2) cells. The M1 preponderance was significantly exaggerated at 6 hours after lipopolysaccharide (LPS) treatment, and adoptive transfer of M2 macrophages partially rescued LPS‐induced abortion. RNA sequencing analysis of mouse uterine M2 versus M1 revealed 1837 differentially expressed genes (DEGs), among which 629 was up‐regulated and 1208 was down‐regulated. Histone deacetylase 9 (Hdac9) was one of the DEGs and validated to be significantly up‐regulated in uterine M2 as compared with M1. Remarkably, this differential expression profile between M1 and M2 was also evident in primary splenic macrophages and in vitro polarized murine peritoneal, bone marrow–derived and RAW 264.7 macrophages. In Hdac9/HDAC9 knockout RAW 264.7 and human THP‐1–derived macrophages, the expression of M1 differentiation markers was unchanged or decreased whereas M2 markers were increased compared with the wild‐type cells, and these effects were unrelated to compromised proliferation. Furthermore, Hdac9/HDAC9 ablation significantly enhanced the phagocytosis of fluorescent microspheres in M2 Raw 264.7 cells yet decreased the capacity of THP‐1‐derived M1 macrophages. The above results demonstrate that Hdac9/HDAC9 deficiency exaggerates M2 macrophage polarization in mouse and human macrophages, which may provide clues for our understanding of the epigenetic regulation on macrophage M1/M2 polarization in maternal‐foetal tolerance.

Immune Cell Modulation of the Extracellular Matrix Contributes to the Pathogenesis of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy with a five-year survival rate of only 9%. PDAC is characterized by a dense, fibrotic stroma composed of extracellular matrix (ECM) proteins. This desmoplastic stroma is a hallmark of PDAC, representing a significant physical barrier that is immunosuppressive and obstructs penetration of cytotoxic chemotherapy agents into the tumor microenvironment (TME). Additionally, dense ECM promotes hypoxia, making tumor cells refractive to radiation therapy and alters their metabolism, thereby supporting proliferation and survival. In this review, we outline the significant contribution of fibrosis to the pathogenesis of pancreatic cancer, with a focus on the cross talk between immune cells and pancreatic stellate cells that contribute to ECM deposition. We emphasize the cellular mechanisms by which neutrophils and macrophages, specifically, modulate the ECM in favor of PDAC-progression. Furthermore, we investigate how activated stellate cells and ECM influence immune cells and promote immunosuppression in PDAC. Finally, we summarize therapeutic strategies that target the stroma and hinder immune cell promotion of fibrogenesis, which have unfortunately led to mixed results. An enhanced understanding of the complex interactions between the pancreatic tumor ECM and immune cells may uncover novel treatment strategies that are desperately needed for this devastating disease.

An in silico glioblastoma microenvironment model dissects the immunological mechanisms of resistance to PD-1 checkpoint blockade immunotherapy

The PD-1 immune checkpoint-based therapy has emerged as a promising therapy strategy for treating the malignant brain tumor glioblastoma (GBM). However, patient response varies in clinical trials due in large to the tumor heterogeneity and immunological resistance in the tumor microenvironment. To further understand how mechanistically the niche interplay and competition drive anti-PD-1 resistance, we established an in-silico model to quantitatively describe the biological rationale of critical GBM-immune interactions, such as tumor growth and apoptosis, T cell activation and cytotoxicity, and tumor-associated macrophage (TAM) mediated immunosuppression. Such an in-silico experimentation and predictive model, based on the in vitro microfluidic chip-measured end-point data and patient-specific immunological characteristics, allowed for a comprehensive and dynamic analysis of multiple TAM-associated immunosuppression mechanisms against the anti-PD-1 immunotherapy. Our computational model demonstrated that the TAM-associated immunosuppression varied in severity across different GBM subtypes, which resulted in distinct tumor responses. Our prediction results indicated that a combination therapy co-targeting of PD-1 checkpoint and TAM-associated CSF-1R signaling could enhance the immune responses of GBM patients, especially those patients with mesenchymal GBM who are irresponsive to the single anti-PD-1 therapy. The development of a patient-specific in silico-in vitro GBM model would help navigate and personalize immunotherapies for GBM patients.

Macrophages Derived From Human Induced Pluripotent Stem Cells: The Diversity of Protocols, Future Prospects, and Outstanding Questions

Macrophages (Mφ) derived from induced pluripotent stem cells (iMphs) represent a novel and promising model for studying human Mφ function and differentiation and developing new therapeutic strategies based on or oriented at Mφs. iMphs have several advantages over the traditionally used human Mφ models, such as immortalized cell lines and monocyte-derived Mφs. The advantages include the possibility of obtaining genetically identical and editable cells in a potentially scalable way. Various applications of iMphs are being developed, and their number is rapidly growing. However, the protocols of iMph differentiation that are currently used vary substantially, which may lead to differences in iMph differentiation trajectories and properties. Standardization of the protocols and identification of minimum required conditions that would allow obtaining iMphs in a large-scale, inexpensive, and clinically suitable mode are needed for future iMph applications. As a first step in this direction, the current review discusses the fundamental basis for the generation of human iMphs, performs a detailed analysis of the generalities and the differences between iMph differentiation protocols currently employed, and discusses the prospects of iMph applications.

Circadian rhythm-associated Rev-erbα modulates polarization of decidual macrophage via the PI3K/Akt signaling pathway

PROBLEM

Circadian rhythms are involved not only in the repair and regeneration of the immune system, but may also be associated with regulation of inflammation and immune responses. Rev-erbα could constitute a link between immunity and circadian rhythms since it is a transcription factor that regulates circadian rhythms and has functions in multiple physiological and pathological processes. Decidual macrophages (dMφs) play crucial roles in immune balance at the maternal-fetal interface, and abnormal macrophage polarization is related to adverse pregnancy outcomes, such as infertility, recurrent spontaneous abortion, and preterm labor. However, whether Rev-erbα could modulate the polarization of macrophages is unknown.

METHODS OF STUDY

In this study, we analyzed the phenotype of dMφs and the expression of Rev-erbα in dMφs from normal pregnancies and miscarriages. The effect of Rev-erbα on macrophage polarization was evaluated by its knockdown or pharmacological activation. The mechanism by which the Rev-erbα agonist SR9009 regulates macrophage polarization was also estimated.

RESULTS

A type-1 macrophage (M1)-like dominance was observed in dMφs from human miscarriages, with a decreased expression of Rev-erbα compared to that from normal pregnancies. Rev-erbα knockdown promoted M1 polarization in macrophages differentiated from the THP1 cell line, whereas pharmacological activation of Rev-erbα by SR9009 induced type-2 macrophage (M2)-like polarization in dMφs. Furthermore, we found that SR9009 induced M2 polarization in macrophages differentiated from the U937 cell line via the PI3K/Akt signaling pathway.

CONCLUSION

Rev-erbα may play an essential role in macrophage polarization. These findings might help elucidate the role of Rev-erbα in regulating the differentiation and functions of macrophages and suggest a therapeutic target for pregnancy loss and pregnancy complications.

Decidual stromal cells support tolerance at the human foetal-maternal interface by inducing regulatory M2 macrophages and regulatory T-cells

During pregnancy, the semi-allogeneic nature of the foetus requires maternal immune adaption and acquisition of tolerance at the foetal-maternal interface. Macrophages with regulatory properties and regulatory T (Treg) cells are central in promoting foetal tolerance and are enriched in the decidua (the uterine endometrium during pregnancy). Although tissue-resident decidual stromal cells (DSC) have been implicated in regulatory functions, it is not known if they are able to induce the regulatory phenotype of macrophages and T-cells. In this study we report that maternally derived DSC are able to induce homeostatic M2 macrophages and Treg cells. CD14⁺ monocytes and CD4⁺ T-cells from healthy non-pregnant women were cultured in the presence or absence of conditioned medium (CM) from DSC isolated from 1^st trimester and term placentas. DSC-CM alone was able to promote the survival of macrophages and to induce a regulatory CD14^brightCD163⁺CD209⁺CD86^dim phenotype, typical for decidual macrophages and similar to that induced by M-CSF. Interestingly, DSC-CM was also able to overrule the pro-inflammatory effects of GM-CSF by upregulating CD14, CD163 and CD209. Protein-profiling showed that M-CSF was secreted by DSC, and blocking of M-CSF partially reversed the M2 phenotype and reduced viability. DSC-CM also expanded CD25^brightFoxp3⁺ Treg cells, an expansion that was abolished by a SMAD3-inhibitor, indicating the contribution of TGF-β signaling. In conclusion, our findings collectively emphasize the role of tissue-resident stromal cells in shaping the tolerogenic environment at the foetal-maternal interface.

Placenta-Derived Exosomes as a Modulator in Maternal Immune Tolerance During Pregnancy

Exosomes are a subset of extracellular vesicles with an average diameter of ~100nm. Exosomes are released by all cells through an endosome-dependent pathway and carry nucleic acids, proteins, lipids, cytokines and metabolites, mirroring the state of the originating cells. The function of exosomes has been implicated in various reproduction processes, such as embryo development, implantation, decidualization and placentation. Placenta-derived exosomes (pEXO) can be detected in the maternal blood as early as 6 weeks after conception and their levels increase with gestational age. Importantly, alternations in the molecular signatures of pEXO are observed in pregnancy-related complications. Thus, these differentially expressed molecules could be the potential biomarkers for diagnosis of the pregnancy-associated diseases. Recent studies have demonstrated that pEXO play a key role in the establishment of maternal immune tolerance, which is critical for a successful pregnancy. To gain a better understanding of the underlying mechanism, we highlighted the advanced studies of pEXO on immune cells in pregnancy.

The anti-inflammatory role of placental Hofbauer cells is altered in patients with chorioamnionitis: Are CYP2C8 and soluble epoxide hydrolase involved in immunomodulation?

AIMS

Hofbauer cells (HBCs) are placental macrophages playing various roles during normal and complicated pregnancies, and of the latter, chorioamnionitis is the most frequent.

METHODS

In placenta with chorioamnionitis, we examined immunohistochemical expression profiles of IL-1β, IL-10, and their potential regulators, CYP2C8 and soluble epoxide hydrolase (sEH), in Hofbauer cells and compared the results with our previously published data for normal placenta.

RESULTS

We found that the expression profiles of the studied proteins in Hofbauer cells in chorioamnionitis differs from normal placenta. In chorioamnionitis, HBCs showed a moderate expression of IL-1β together with a weak expression of IL-10 and CYP2C8. Contrary to normal placenta, HBCs in chorioamnionitis express sEH. We demonstrated a moderate positive correlation between the expression of CYP2C8 and sEH in chorioamnionitis (Spearman r = 0.5654), suggesting enhanced degradation of anti-inflammatory epoxyeicosatrienoic acids. Moreover, the relations of IL-1β and IL-10 to CYP2C8, previously described in normal placenta, disappeared. Furthermore, a weak expression of anti-inflammatory IL-10 in chorioamnionitis was accompanied by change in circularity of HBCs (Spearman r = 0.8193).

CONCLUSION

Taken together, these findings suggest a possible alteration of the anti-inflammatory role of HBCs and its regulation in chorioamnionitis.

Gestational Diabetes Mellitus and Maternal Immune Dysregulation: What We Know So Far

Gestational diabetes mellitus (GDM) is an obstetric complication that affects approximately 5-10% of all pregnancies worldwide. GDM is defined as any degree of glucose intolerance with onset or first recognition during pregnancy, and is characterized by exaggerated insulin resistance, a condition which is already pronounced in healthy pregnancies. Maternal hyperglycaemia ensues, instigating a 'glucose stress' response and concurrent systemic inflammation. Previous findings have proposed that both placental and visceral adipose tissue play a part in instigating and mediating this low-grade inflammatory response which involves altered infiltration, differentiation and activation of maternal innate and adaptive immune cells. The resulting maternal immune dysregulation is responsible for exacerbation of the condition and a further reduction in maternal insulin sensitivity. GDM pathology results in maternal and foetal adverse outcomes such as increased susceptibility to diabetes mellitus development and foetal neurological conditions. A clearer understanding of how these pathways originate and evolve will improve therapeutic targeting. In this review, we will explore the existing findings describing maternal immunological adaption in GDM in an attempt to highlight our current understanding of GDM-mediated immune dysregulation and identify areas where further research is required.

Contribution of macrophages to fetomaternal immunological tolerance

The semi-allogeneic fetus develops in a uniquely immune tolerant environment within the uterus. For successful pregnancy, both the innate and adaptive immune systems must favor acceptance of the fetal allograft. Macrophages are the second most abundant immune cells after natural killer (NK) cells in the decidua. In coordination with decidual NK cells and dendritic cells, macrophages aid in implantation, vascular remodeling, placental development, immune tolerance to placental cells, and maintenance of tissue homeostasis at the maternal-fetal interface. Decidual macrophages show the classical activated (M1) and alternatively activated (M2) phenotypes under the influence of the local milieu of growth factors and cytokines, and appropriate temporal regulation of the M1/M2 switch is vital for successful pregnancy. Disturbances in the mechanisms that control the M1/M2 balance and associated functions during pregnancy can trigger a spectrum of pregnancy complications ranging from preeclampsia and fetal growth restriction to preterm delivery. This review addresses various mechanisms of tolerance, focusing on the basic biology of macrophages, their plasticity and polarization, and their protective roles at the immune-privileged maternal-fetal interface, including direct and indirect roles in promoting fetomaternal immune tolerance.

Expression of Estrogen Receptor α by Decidual Macrophages in Preeclampsia

Preeclampsia is a gestation-associated hypertensive syndrome that threatens the life and health of the mother and the child. The condition is presumably caused by systemic failure with a strong involvement of innate immunity. In particular, it has been associated with flexible phenotypes of macrophages, which depend on the molecules circulating in the blood and tissue fluid, such as cytokines and hormones. This study aimed at a comparative evaluation of pro-inflammatory (TNFα) and anti-inflammatory (CD206, MMP9, HGF) markers, as well as the levels of estrogen receptor α, expressed by decidual macrophages in normal pregnancy and in patients with early- and late-onset preeclampsia. The tissue samples of decidua basalis were examined by immunohistochemistry and Western blotting. Isolation of decidual macrophages and their characterization were performed using cultural methods, flow cytometry and real-time PCR. Over 50% of the isolated decidual macrophages were positive for the pan-macrophage marker CD68. In the early-onset preeclampsia group, the levels of estrogen receptor α in decidua were significantly decreased. Furthermore, significantly decreased levels of HGF and CD206 were observed in both preeclampsia groups compared with the control group. The observed downregulation of estrogen receptor α, HGF and CD206 may contribute to the balance of pro- and anti-inflammatory macrophages and thereby to pathogenesis of preeclampsia.

VAR2CSA-Mediated Host Defense Evasion of Plasmodium falciparum Infected Erythrocytes in Placental Malaria

Over 30 million women living in P. falciparum endemic areas are at risk of developing malaria during pregnancy every year. Placental malaria is characterized by massive accumulation of infected erythrocytes in the intervillous space of the placenta, accompanied by infiltration of immune cells, particularly monocytes. The consequent local inflammation and the obstruction of the maternofetal exchanges can lead to severe clinical outcomes for both mother and child. Even if protection against the disease can gradually be acquired following successive pregnancies, the malaria parasite has developed a large panel of evasion mechanisms to escape from host defense mechanisms and manipulate the immune system to its advantage. Infected erythrocytes isolated from placentas of women suffering from placental malaria present a unique phenotype and express the pregnancy-specific variant VAR2CSA of the Plasmodium falciparum Erythrocyte Membrane Protein (PfEMP1) family at their surface. The polymorphic VAR2CSA protein is able to mediate the interaction of infected erythrocytes with a variety of host cells including placental syncytiotrophoblasts and leukocytes but also with components of the immune system such as non-specific IgM. This review summarizes the described VAR2CSA-mediated host defense evasion mechanisms employed by the parasite during placental malaria to ensure its survival and persistence.

Macrophage Plasticity in Reproduction and Environmental Influences on Their Function

Macrophages are key components of the innate immune system and exhibit extensive plasticity and heterogeneity. They play a significant role in the non-pregnant cycling uterus and throughout gestation they contribute to various processes underpinning reproductive success including implantation, placentation and parturition. Macrophages are also present in breast milk and impart immunomodulatory benefits to the infant. For a healthy pregnancy, the maternal immune system must adapt to prevent fetal rejection and support development of the semi-allogenic fetus without compromising host defense. These functions are dependent on macrophage polarization which is governed by the local tissue microenvironmental milieu. Disruption of this microenvironment, possibly by environmental factors of infectious and non-infectious origin, can affect macrophage phenotype and function and is linked to adverse obstetric outcomes, e.g. spontaneous miscarriage and preterm birth. Determining environmental influences on cellular and molecular mechanisms that control macrophage polarization at the maternal-fetal interface and the role of this in pregnancy complications could support approaches to alleviating adverse pregnancy outcomes.

Single-cell profiling of the human decidual immune microenvironment in patients with recurrent pregnancy loss

Maintaining homeostasis of the decidual immune microenvironment at the maternal–fetal interface is essential for placentation and reproductive success. Although distinct decidual immune cell subpopulations have been identified under normal conditions, systematic understanding of the spectrum and heterogeneity of leukocytes under recurrent miscarriage in human deciduas remains unclear. To address this, we profiled the respective transcriptomes of 18,646 primary human decidual immune cells isolated from patients with recurrent pregnancy loss (RPL) and healthy controls at single-cell resolution. We discovered dramatic differential distributions of immune cell subsets in RPL patients compared with the normal decidual immune microenvironment. Furthermore, we found a subset of decidual natural killer (NK) cells that support embryo growth were diminished in proportion due to abnormal NK cell development in RPL patients. We also elucidated the altered cellular interactions between the decidual immune cell subsets in the microenvironment and those of the immune cells with stromal cells and extravillous trophoblast under disease state. These results provided deeper insights into the RPL decidual immune microenvironment disorder that are potentially applicable to improve the diagnosis and therapeutics of this disease.

Morphometric analysis of Hofbauer cells in normal placenta and chorioamnionitis in humans

Hofbauer cells are macrophages residing in the stroma of placental villi and play a number of roles during normal pregnancy, as well as pathological conditions. A morphometric analysis of Hofbauer cells, in particular to investigate the number of cells, their size and shape in samples of normal human placenta from 1st trimester, term and with chorioamnionitis was performed. Tissue samples were immunostained for CD206 antigen and evaluated using ImageJ software. We detected significant changes in number and morphology of HBCs between normal placenta and placenta with chorioamnionitis samples. In chorioamnionitis, the cells were unevenly distributed within the villi, generally present in higher numbers, larger and more elongated than those in normal 1st trimester and term placenta.

Functional regulation of decidual macrophages during pregnancy

A successful pregnancy requires that the maternal immune system recognizes and tolerates the semi-allogeneic fetus without compromising the capability of protecting both mother and fetus from various pathogens. Decidual macrophages present unique phenotypes to play a key role in the establishment of the immunological aspects of maternal-fetal interaction. Dysfunction of decidual macrophages gives rise to pregnancy complications such as preeclampsia, recurrent spontaneous miscarriage, preterm labor and fetal growth restriction. Here, we reviewed the latest knowledge on the origin, differentiation, unique phenotype and function of macrophages in normal pregnancy and in pregnancy complications. We mainly focused on the significant roles of decidual macrophages in the process of extravillous trophoblast invasion, spiral arterial remodeling, decidual stromal cells cultivation and immune tolerance maintenance in normal pregnancy, and their pathological roles in pregnancy-related complications, offering more integrated information in maternal-fetal immunity.

Pregnancy Alters Innate and Adaptive Immune Responses to Zika Virus Infection in the Reproductive Tract

Recent outbreaks of Zika virus (ZIKV) have been associated with birth defects, including microcephaly and neurologic impairment. However, the mechanisms that confer potential susceptibility to ZIKV during pregnancy remain unclear. We hypothesized that poor outcomes from ZIKV infection during pregnancy are due in part to pregnancy-induced alteration of innate immune cell frequencies and cytokine expression. To examine the impact of pregnancy on innate immune responses, we inoculated immunocompetent pregnant and nonpregnant female C57BL/6 mice with 5 × 105 focus-forming units of ZIKV intravaginally. Innate immune cell frequencies and cytokine expression were measured by flow cytometry at day 3 postinfection. Compared with nonpregnant mice, pregnant mice exhibited higher frequencies of uterine macrophages (CD68+) and CD11c+ CD103+ and CD11c+ CD11b+ dendritic cells. Additionally, ZIKV-infected pregnant mice had lower frequencies of CD45+ IL-12+ and CD11b+ IL-12+ cells in the uterus and spleen. Next, we measured the frequencies of Ag-experienced CD4 (CD4+ CD11a+ CD49d+) and CD8 (CD8lo CD11ahi) T cells at day 10 postinfection to determine the impact of pregnancy-associated changes in innate cellular IL-12 responses on the adaptive immune response. We found that pregnant mice had lower frequencies of uterine Ag-experienced CD4 T cells and ZIKV-infected pregnant mice had lower frequencies of uterine Ag-experienced CD8 T cells compared with ZIKV-infected nonpregnant mice. These data show that pregnancy results in altered innate and adaptive immune responses to ZIKV infection in the reproductive tract of mice and that pregnancy-associated immune modulation may play an important role in the severity of acute ZIKV infection.

Molecules and Prostaglandins Related to Embryo Tolerance

It is generally understood that the entry of semen into the female reproductive tract provokes molecular and cellular changes facilitating conception and pregnancy. We show a broader picture of the participation of prostaglandins in the fertilization, implantation and maintenance of the embryo. A large number of cells and molecules are related to signaling networks, which regulate tolerance to implantation and maintenance of the embryo and fetus. In this work, many of those cells and molecules are analyzed. We focus on platelets, polymorphonuclear leukocytes, and group 2 innate lymphoid cells involved in embryo tolerance in order to have a wider view of how prostaglandins participate. The combination of platelets and neutrophil extracellular traps (Nets), uterine innate lymphoid cells (uILC), Treg cells, NK cells, and sex hormones have an important function in immunological tolerance. In both animals and humans, the functions of these cells can be regulated by prostaglandins and soluble factors in seminal plasma to achieve an immunological balance, which maintains fetal-maternal tolerance. Prostaglandins, such as PGI2 and PGE2, play an important role in the suppression of the previously mentioned cells. PGI2 inhibits platelet aggregation, in addition to IL-5 and IL-13 expression in ILC2, and PGE2 inhibits some neutrophil functions, such as chemotaxis and migration processes, leukotriene B4 (LTB4) biosynthesis, ROS production, and the formation of extracellular traps, which could help prevent trophoblast injury and fetal loss. The implications are related to fertility in female when seminal fluid is deposited in the vagina or uterus.

PlGF Immunological Impact during Pregnancy

During pregnancy, the mother’s immune system has to tolerate the persistence of paternal alloantigens without affecting the anti-infectious immune response. Consequently, several mechanisms aimed at preventing allograft rejection, occur during a pregnancy. In fact, the early stages of pregnancy are characterized by the correct balance between inflammation and immune tolerance, in which proinflammatory cytokines contribute to both the remodeling of tissues and to neo-angiogenesis, thus, favoring the correct embryo implantation. In addition to the creation of a microenvironment able to support both immunological privilege and angiogenesis, the trophoblast invades normal tissues by sharing the same behavior of invasive tumors. Next, the activation of an immunosuppressive phase, characterized by an increase in the number of regulatory T (Treg) cells prevents excessive inflammation and avoids fetal immuno-mediated rejection. When these changes do not occur or occur incompletely, early pregnancy failure follows. All these events are characterized by an increase in different growth factors and cytokines, among which one of the most important is the angiogenic growth factor, namely placental growth factor (PlGF). PlGF is initially isolated from the human placenta. It is upregulated during both pregnancy and inflammation. In this review, we summarize current knowledge on the immunomodulatory effects of PlGF during pregnancy, warranting that both innate and adaptive immune cells properly support the early events of implantation and placental development. Furthermore, we highlight how an alteration of the immune response, associated with PlGF imbalance, can induce a hypertensive state and lead to the pre-eclampsia (PE).

Polysaccharides Derived from Saposhnikovia divaricata May Suppress Breast Cancer Through Activating Macrophages

Background

Saposhnikovia divaricata (SD) has been used in traditional Chinese medicine to treat pain, inflammation, and arthritis. Recently, it has been reported that SD extract may inhibit tumor growth, but the mechanism involved is elusive. The aim of this study was to investigate the anti-tumor activity of polysaccharides derived from SD in breast cancer and the underlying mechanisms.

Materials and Methods

Polysaccharides isolated from SD were analyzed using Fourier transform infrared (FT-IR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS). Their effects on cell growth of U937, MCF-7, and MDA-MB-231, and tumor growth in a mouse MDA-MB 231 xenograft model were examined. Their role in U937 activation, MCF-7, and MDA-MB 231 cytokine release profiles were also tested.

Results

In vitro studies showed that SD polysaccharides (SDPs) promoted U937 cell growth dose-dependently, with no obvious effect on growth of breast cancer cell lines MCF-7 and MDA-MB-231. SDP also showed an antagonistic effect against the growth inhibition of U937 by the culture supernatants of MCF-7 and MDA-MB-231, and reversed the polarization status of U937. Treatment of SCID mice bearing MDA-MB-231-derived xenograft tumors with SDP significantly reduced tumor growth. At all tested concentrations, no obvious toxic side-effects were recorded.

Discussion

We tentatively concluded that SDPs potently promote the growth of U937 and activate it to inhibit the tumor growth of SCID mice bearing MDA-MB-231-derived xenograft tumors indirectly, with no obvious growth inhibition effects on MCF-7 and MDA-MB-231 in vitro. Our finding indicated that SDP could be a potential anticancer agent for breast cancer.

Changes in peripheral immune populations during pregnancy and modulation by probiotics and ω-3 fatty acids

Allergic diseases have become a major health problem, partly due to reduced microbial stimulation and a decreased dietary ω-3/ω-6 long-chain polyunsaturated fatty acid ratio. Prenatal exposures have been reported to influence allergy development, possibly induced via changes in maternal immune regulation. In a randomized double-blind placebo-controlled multicenter allergy prevention trial (PROOM-3), pregnant women were recruited at gestational week 20, and randomized to four study groups, one receiving both L. reuteri oil drops and ω-3 PUFA capsules (n = 22), the second receiving ω-3 PUFA supplementation and placebo regarding L. reuteri (n = 21), the third receiving L. reuteri and placebo regarding ω-3 PUFA (n = 22) and the fourth group receiving placebo capsules and placebo oil drops (n = 23). In this substudy, supplemental and pregnancy-related effects on maternal peripheral immune cell populations during pregnancy were assessed by flow cytometry immune phenotyping at gestational week 20, 32 and 4 days after delivery. The numbers of activated and regulatory T (Treg) cells (CD45RA⁻ Foxp3⁺⁺/CD45RA⁺Foxp3⁺) were reduced after delivery, with the lowest count in the L. reuteri supplemented group compared with the placebo group 4 days after delivery, while the ω-3 PUFA group did not differ from the placebo group. Several treatment-independent changes were observed during and after pregnancy in lymphocytes (CD4⁺/8⁺/19⁺/56⁺/45RA^+/−), CD14⁺16^+/− monocytes, and in subpopulations of T helper cells (Th) CD4⁺CD45RA⁻Tbet⁺ (Th1) and CD4⁺CD45RA⁻RORC⁺ (Th17) cells. In conclusion, probiotic supplementation to the mother during the second half of pregnancy resulted in immunomodulatory effects among activated and resting Treg cells. Furthermore, several systemic immune modifying effects of pregnancy were observed.

CD206+ M2-Like Macrophages Are Essential for Successful Implantation

Macrophages (MΦs) play important roles in implantation. Depletion of CD11b+ pan-MΦs in CD11b-diphtheria-toxin-receptor (DTR) mice is reported to cause implantation failure due to decreased progesterone production in the corpus luteum. However, of the M1 and M2, the type of MΦs that is important for implantation is unknown. In this study, we investigated the role of M2 MΦ in implantation using CD206-DTR mice. To deplete M2-MΦ, female CD206-DTR C57/BL6 mice were injected with DT before implantation. These M2-MΦ depleted mice (M2(-)) were naturally mated with Balb/C mice. As the control group, female C57/BL6 wild type (WT) mice injected with DT were mated with male Balb/C mice. The number of implantation sites and plasma progesterone levels at implantation were examined. Implantation-related molecule expression was determined using quantitative-PCR and immunohistochemistry of uterine tissues. The mRNA expression in the endometrial tissues of 38 patients with implantation failure was examined during the implantation window. In WT mice, CD206+M2-like MΦs accumulated in the endometrium at the implantation period, on embryonic (E) 4.5. In M2(-), the implantation number was significantly lower than that in control (p < 0.001, 7.8 ± 0.8 vs. 0.2 ± 0.4), although the plasma progesterone levels were not changed. Leukemia inhibitory factor (LIF) and CD206 mRNA expression was significantly reduced (p < 0.01), whereas the levels of TNFα were increased on E4.5 (p < 0.05). In M2(-), the number of Ki-67+ epithelial cells was higher than that in control at the pre-implantation period. Accelerated epithelial cell proliferation was confirmed by significantly upregulated uterine fibroblast growth factor (FGF)18 mRNA (P < 0.05), and strong FGF18 protein expression in M2(-) endometrial epithelial cells. Further, M2(-) showed upregulated uterine Wnt/β-catenin signals at the mRNA and protein levels. In the non-pregnant group, the proportion of M2-like MΦ to pan MΦ, CD206/CD68, was significantly reduced (p < 0.05) and the TNFα mRNA expression was significantly increased (p < 0.05) in the endometrial tissues compared to those in the pregnant group. CD206+ M2-like MΦs may be essential for embryo implantation through the regulation of endometrial proliferation via Wnt/β-catenin signaling.

Viral-Immune Cell Interactions at the Maternal-Fetal Interface in Human Pregnancy

The human decidua and placenta form a distinct environment distinguished for its promotion of immunotolerance to infiltrating semiallogeneic trophoblast cells to enable successful pregnancy. The maternal-fetal interface also successfully precludes transmission of most pathogens. This barrier function occurs in conjunction with a diverse influx of decidual immune cells including natural killer cells, macrophages and T cells. However, several viruses, among other microorganisms, manage to escape destruction by the host adaptive and innate immune system, leading to congenital infection and adverse pregnancy outcomes. In this review, we describe mechanisms of pathogenicity of two such viral pathogens, Human cytomegalovirus (HCMV) and Zika virus (ZIKV) at the maternal-fetal interface. Host decidual immune cell responses to these specific pathogens will be considered, along with their interactions with other cell types and the ways in which these immune cells may both facilitate and limit infection at different stages of pregnancy. Neither HCMV nor ZIKV naturally infect commonly used animal models [e.g., mice] which makes it challenging to understand disease pathogenesis. Here, we will highlight new approaches using placenta-on-a-chip and organoids models that are providing functional and physiologically relevant ways to study viral-host interaction at the maternal-fetal interface.

Immunogenicity and Toxicity of Different Adjuvants Can Be Characterized by Profiling Lung Biomarker Genes After Nasal Immunization

The efficacy of vaccine adjuvants depends on their ability to appropriately enhance the immunogenicity of vaccine antigens, which is often insufficient in non-adjuvanted vaccines. Genomic analyses of immune responses elicited by vaccine adjuvants provide information that is critical for the rational design of adjuvant vaccination strategies. In this study, biomarker genes from the genomic analyses of lungs after priming were used to predict the efficacy and toxicity of vaccine adjuvants. Based on the results, it was verified whether the efficacy and toxicity of the tested adjuvants could be predicted based on the biomarker gene profiles after priming. Various commercially available adjuvants were assessed by combining them with the split influenza vaccine and were subsequently administered in mice through nasal inoculation. The expression levels of lung biomarker genes within 24 h after priming were analyzed. Furthermore, we analyzed the antibody titer, cytotoxic T lymphocyte (CTL) induction, IgG1/IgG2a ratio, leukopenic toxicity, and cytotoxicity in mice vaccinated at similar doses. The association between the phenotypes and the changes in the expression levels of biomarker genes were analyzed. The ability of the adjuvants to induce the production of antigen-specific IgA could be assessed based on the levels of Timp1 expression. Furthermore, the expression of this gene partially correlated with the levels of other damage-associated molecular patterns in bronchoalveolar lavage fluid. Additionally, the changes in the expression of proteasome- and transporter-related genes involved in major histocompatibility complex class 1 antigen presentation could be monitored to effectively assess the expansion of CTL by adjuvants. The monitoring of certain genes is necessary for the assessment of leukopenic toxicity and cytotoxicity of the tested adjuvant. These results indicate that the efficacy and toxicity of various adjuvants can be characterized by profiling lung biomarker genes after the first instance of immunization. This approach could make a significant contribution to the development of optimal selection and exploratory screening strategies for novel adjuvants.

First-trimester trophoblasts obtained by chorionic villus sampling maintain tolerogenic and proteomic features in successful pregnancies despite a history of unexplained recurrent pregnancy loss

PROBLEM

While there are several known causes for recurrent pregnancy loss (RPL), about 50% are unexplained (uRPL), and in these cases, an aberrant immune regulation seems to be involved. Although fetally derived trophoblast cells have a key role in immune regulation, it is difficult to study their immune function during pregnancy, and it is not known whether trophoblast function may be an inherent aberration in uRPL or whether it is associated with the outcome of the current pregnancy.

METHOD OF STUDY

Chorionic villus sampling (CVS) was performed for clinical indications at 12 weeks of gestation. Superfluous materials, divided in small explants, were cultured for 20-24 hours, and supernatants (conditioned medium) were collected from 36 women with singleton normal pregnancies, of whom 9 women had a history of RPL. The secreted immune protein profile was measured by proximity extension assay, and the conditioned medium was further used in functional ex vivo models to assess ability to polarize blood monocytes and CD4⁺ T cells into immune regulatory phenotypes, as detected by flow cytometry.

RESULTS

Conditioned medium from chorionic villi, human fetally derived placental tissue, was able to induce a decidual-type of M2-like macrophages, as well as an expansion of Treg cells ex vivo, both in women with uRPL and in control women. The preserved immunological properties were confirmed by a maintained immune protein profile in RPL compared with controls.

CONCLUSION

Trophoblasts in an ex vivo model maintain tolerogenic and proteomic profile features in successful pregnancies, despite a previous history of RPL.

Altered Levels of Decidual Immune Cell Subsets in Fetal Growth Restriction, Stillbirth, and Placental Pathology

Immune cells are critically involved in placental development and functioning, and inadequate regulation of the maternal immune system is associated with placental pathology and pregnancy complications. This study aimed to explore numbers of decidual immune cells in pregnancies complicated with fetal growth restriction (FGR) and stillbirth (SB), and in placentas with histopathological lesions: maternal vascular malperfusion (MVM), fetal vascular malperfusion (FVM), delayed villous maturation (DVM), chorioamnionitis (CA), and villitis of unknown etiology (VUE). Placental tissue from FGR (n = 250), SB (n = 64), and healthy pregnancies (n = 42) was included. Histopathological lesions were classified according to criteria developed by the Amsterdam Placental Workshop Group. Tissue slides were stained for CD68 (macrophages), CD206 (M2-like macrophages), CD3 (T cells), FOXP3 [regulatory T (Treg) cells], and CD56 [natural killer (NK) cells]. Cell numbers were analyzed in the decidua basalis using computerized morphometry. The Mann-Whitney U-test and Kruskal Wallis test with the Dunn's as post-hoc test were used for statistical analysis. Numbers of CD68⁺ macrophages were higher in FGR compared to healthy pregnancies (p < 0.001), accompanied by lower CD206⁺/CD68⁺ ratios (p < 0.01). In addition, in FGR higher numbers of FOXP3⁺ Treg cells were seen (p < 0.01) with elevated FOXP3⁺/CD3⁺ ratios (p < 0.01). Similarly, in SB elevated FOXP3⁺ Treg cells were found (p < 0.05) with a higher FOXP3+/CD3+ ratio (p < 0.01). Furthermore, a trend toward higher numbers of CD68⁺ macrophages was found (p < 0.1) in SB. Numbers of CD3⁺ and FOXP3⁺ cells were higher in placentas with VUE compared to placentas without lesions (p < 0.01 and p < 0.001), accompanied by higher FOXP3⁺/CD3⁺ ratios (p < 0.01). Elevated numbers of macrophages with a lower M2/total macrophage ratio in FGR suggest a role for a macrophage surplus in its pathogenesis and could specifically indicate involvement of inflammatory macrophages. Higher numbers of FOXP3⁺ Treg cells with higher Treg/total T cell ratios in VUE may be associated with impaired maternal-fetal tolerance and a compensatory response of Treg cells. The abundant presence of placental lesions in the FGR and SB cohorts might explain the increase of Treg/total T cell ratios in these groups. More functionality studies of the observed altered immune cell subsets are needed.

Trophoblast-derived IL-6 serves as an important factor for normal pregnancy by activating Stat3-mediated M2 macrophages polarization

Macrophages are major components of decidual microenvironment that play an important role in human implantation and placentation. Trophoblasts which migrate into the endometrium and interplay with decidual cells, have been reported to participate in the polarization of macrophages. However, the potential mechanisms of trophoblasts modulating M2 macrophages polarization still need further exploration. Herein, we used the co-cultured model to investigate the interaction between macrophages and trophoblasts. Our results illustrated that when co-cultured with trophoblasts, macrophages tended to polarize to M2-subtype, accompanied by increased expression of multiple M2 markers including CD206 and CCL18 mRNA expression and IL-10 and TGF-β protein level. Further experiments identified that trophoblast-derived IL-6, as the major contributor, promoted M2 macrophages polarization by activating Stat3 pathway. Moreover, activated M2 macrophages exerted a promoting role in the invasion and migration of trophoblasts in a feedback manner. Clinically, results from histology demonstrated that IL-6 expression in placental villous tissues was positive correlated with CD206-positive macrophage infiltration in decidua in normal pregnancy patients. Altogether, our findings indicate that trophoblasts induce M2 macrophages polarization via IL-6/Stat3 signal pathway, which in turn promote the invasion and migration of trophoblasts. These results provide insights into the crosstalk between macrophages and trophoblasts at maternal-fetal microenvironment in normal pregnancy.

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.

Does the human placenta express the canonical cell entry mediators for SARS-CoV-2?

The pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected more than 10 million people, including pregnant women. To date, no consistent evidence for the vertical transmission of SARS-CoV-2 exists. The novel coronavirus canonically utilizes the angiotensin-converting enzyme 2 (ACE2) receptor and the serine protease TMPRSS2 for cell entry. Herein, building upon our previous single-cell study (Pique-Regi et al., 2019), another study, and new single-cell/nuclei RNA-sequencing data, we investigated the expression of ACE2 and TMPRSS2 throughout pregnancy in the placenta as well as in third-trimester chorioamniotic membranes. We report that co-transcription of ACE2 and TMPRSS2 is negligible in the placenta, thus not a likely path of vertical transmission for SARS-CoV-2. By contrast, receptors for Zika virus and cytomegalovirus, which cause congenital infections, are highly expressed by placental cell types. These data show that the placenta minimally expresses the canonical cell-entry mediators for SARS-CoV-2.

Regulatory T Cells Play a Role in a Subset of Idiopathic Preterm Labor/Birth and Adverse Neonatal Outcomes

Regulatory T cells (Tregs) have been exhaustively investigated during early pregnancy; however, their role later in gestation is poorly understood. Herein, we report that functional Tregs are reduced at the maternal-fetal interface in a subset of women with idiopathic preterm labor/birth, which is accompanied by a concomitant increase in Tc17 cells. In mice, depletion of functional Tregs during late gestation induces preterm birth and adverse neonatal outcomes, which are rescued by the adoptive transfer of such cells. Treg depletion does not alter obstetrical parameters in the mother, yet it increases susceptibility to endotoxin-induced preterm birth. The mechanisms whereby depletion of Tregs induces adverse perinatal outcomes involve tissue-specific immune responses and mild systemic maternal inflammation, together with dysregulation of developmental and cellular processes in the placenta, in the absence of intra-amniotic inflammation. These findings provide mechanistic evidence supporting a role for Tregs in the pathophysiology of idiopathic preterm labor/birth and adverse neonatal outcomes.

Decidual stromal cells maintain decidual macrophage homeostasis by secreting IL-24 in early pregnancy

PROBLEM

The state of self-renewal and self-maintain of decidual macrophages would be important for immune homeostasis at the maternal-fetal interface. The roles of interleukin (IL)-24 derived from decidual stromal cells (DSCs) on decidual macrophages have not been explored.

METHOD OF STUDY

IL-24 expression in DSCs was interfered by lentivirus, and the transcription levels of IL-24 in DSCs were verified by real time (RT)-PCR. The levels of IL-24 receptors were determined by flow cytometry assays. The effect of recombination human IL-24 (rhIL-24) on the differentiation and apoptosis of macrophages was analyzed by flow cytometry in vitro. The viability of macrophages was detected by Cell Counting Kit-8 assays.

RESULTS

The growth of DSCs was not affected obviously only by IL-24 knockdown while the growth of knockdown DSCs was inhibited significantly after co-cultured with decidual macrophages. The levels of IL-24 receptors (IL-20R1 and IL-22R1) were moderately to highly expressed on decidual macrophages and human macrophage cell line U937. The differentiation of decidual macrophages treated by rhIL-24 or co-cultured with IL-24 knockdown DSCs was not affected. Both apoptosis and viability of U937 cells were promoted by rhIL-24. The ratio of Bcl-2/Bax was down-regulated and Ki-67 was up-regulated by IL-24 treatment. The expression of Bcl-2/Bax was up-regulated while Ki-67 was down-regulated in U937 cells after co-cultured by IL-24 knockdown DSCs.

CONCLUSION

IL-24 secreted by DSCs promotes the renewal and homeostasis of decidual macrophages possibly via down-regulating the ratio of Bcl-2/Bax and up-regulating of the expression of Ki-67 in early pregnancy.

Maternal and fetal T cells in term pregnancy and preterm labor

Pregnancy is a state of immunological balance during which the mother and the developing fetus must tolerate each other while maintaining sufficient immunocompetence to ward off potential threats. The site of closest contact between the mother and fetus is the decidua, which represents the maternal-fetal interface. Many of the immune cell subsets present at the maternal-fetal interface have been well described; however, the importance of the maternal T cells in this compartment during late gestation and its complications, such as preterm labor and birth, has only recently been established. Moreover, pioneer and recent studies have indicated that fetal T cells are activated in different subsets of preterm labor and may elicit distinct inflammatory responses in the amniotic cavity, leading to preterm birth. In this review, we describe the established and proposed roles for maternal T cells at the maternal-fetal interface in normal term parturition, as well as the demonstrated contributions of such cells to the pathological process of preterm labor and birth. We also summarize the current knowledge of and proposed roles for fetal T cells in the pathophysiology of the preterm labor syndrome. It is our hope that this review provides a solid conceptual framework highlighting the importance of maternal and fetal T cells in late gestation and catalyzes new research questions that can further scientific understanding of these cells and their role in preterm labor and birth, the leading cause of neonatal mortality and morbidity worldwide.

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.

Baby's First Macrophage: Temporal Regulation of Hofbauer Cell Phenotype Influences Ligand-Mediated Innate Immune Responses across Gestation

The importance of fetal placental macrophages (Hofbauer cell [HCs]) is underscored by their appearance 18 d postconception and maintenance through term; however, how human HCs evolve during healthy pregnancy and how microenvironment and ontogeny impact phenotype and function remain unknown. In this study, we comprehensively classify human HCs ex vivo, interrogate phenotypic plasticity, and characterize antiviral immune responses through gestation. Activated HCs were abundant in early pregnancy and decreased by term; molecular signatures emphasize inflammatory phenotypes early in gestation. Frequency of HCs with regulatory phenotypes remained high through term. Furthermore, term HCs exhibited blunted responses to stimulation, indicating reduced plasticity. IFN-λ1 is a key placental IFN that appeared less protective than IFN-α, suggesting a potential weakness in antiviral immunity. Ligand-specific responses were temporally regulated: we noted an absence of inflammatory mediators and reduced antiviral gene transcription following RIG-I activation at term despite all HCs producing inflammatory mediators following IFN-γ plus LPS stimulation. Collectively, we demonstrate sequential, evolving immunity as part of the natural history of HCs through gestation.

Endometrial Cancer Immune Escape Mechanisms: Let Us Learn From the Fetal-Maternal Interface

The immune escape mechanisms at the base of tumor progression in endometrial cancer mimic immune tolerance mechanisms occurring at the maternal-fetal interface. The biological and immunological processes behind the maternal-fetal interface are finely tuned in time and space during embryo implantation and subsequent pregnancy stages; conversely, those behind cancer progression are often aberrant. The environment composition at the maternal-fetal interface parallels the pro-tumor microenvironment identified in many cancers, pointing to the possibility for the use of the maternal-fetal interface as a model to depict immune therapeutic targets in cancer. The framework of cancer environment signatures involved in immune adaptations, precisely timed in cancer progression, could reveal a specific "immune clock" in endometrial cancer, which might guide clinicians in patient risk class assessment, diagnostic workup, management, surgical and therapeutic approach, and surveillance strategies. Here, we review studies approaching this hypothesis, focusing on what is known so far about oncofetal similarities in immunity with the idea to individualize personalized immunotherapy targets, through the downregulation of the immune escape stage or the reactivation of the pro-inflammatory processes suppressed by the tumor.

Tumor-Cell-Macrophage Fusion Cells as Liquid Biomarkers and Tumor Enhancers in Cancer

Although molecular mechanisms driving tumor progression have been extensively studied, the biological nature of the various populations of circulating tumor cells (CTCs) within the blood is still not well understood. Tumor cell fusion with immune cells is a longstanding hypothesis that has caught more attention in recent times. Specifically, fusion of tumor cells with macrophages might lead to the development of metastasis by acquiring features such as genetic and epigenetic heterogeneity, chemotherapeutic resistance, and immune tolerance. In addition to the traditional FDA-approved definition of a CTC (CD45-, EpCAM+, cytokeratins 8+, 18+ or 19+, with a DAPI+ nucleus), an additional circulating cell population has been identified as being potential fusions cells, characterized by distinct, large, polymorphonuclear cancer-associated cells with a dual epithelial and macrophage/myeloid phenotype. Artificial fusion of tumor cells with macrophages leads to migratory, invasive, and metastatic phenotypes. Further studies might investigate whether these have a potential impact on the immune response towards the cancer. In this review, the background, evidence, and potential relevance of tumor cell fusions with macrophages is discussed, along with the potential role of intercellular connections in their formation. Such fusion cells could be a key component in cancer metastasis, and therefore, evolve as a diagnostic and therapeutic target in cancer precision medicine.

Immune Cells in the Uterine Remodeling: Are They the Target of Endocrine Disrupting Chemicals?

Sufficient uterine remodeling is essential for fetal survival and development. Pathologies related to poor remodeling have a negative impact on maternal and fetal health even years after birth. Research of the last decades yielded excellent studies demonstrating the key role of immune cells in the remodeling processes. This review summarizes the current knowledge about the relevance of immune cells for uterine remodeling during pregnancy and further discusses immunomodulatory effects of man-made endocrine disrupting chemicals on immune cells.

Placental Hofbauer Cell Polarization Resists Inflammatory Cues In Vitro

Feto-placental Hofbauer cells (HBCs) are macrophages residing in placental stroma. They are generally described as anti-inflammatory M2 polarized cells, promoting tolerance and tissue remodeling. In certain pathologies, however, a possible phenotypical switch towards pro-inflammatory M1 macrophages has been proposed. The study aimed to determine if HBCs can acquire an M1 phenotype under pro-inflammatory conditions in vitro. HBCs were isolated from healthy human term placentas. Cells were cultivated upon addition of LPS and INF-γ or IL-4 and IL-13 to induce the M1 and M2 phenotype, respectively. Specific cell polarization markers and cytokines, associated with respective phenotypes, were investigated by flow cytometry and ELISA. THP-1 macrophages served as positive control. Pro-inflammatory stimuli reduced M2 markers CD163 and DC-SIGN, but did not induce M1 markers. TNF-α release was increased, but at the same time TGF-β and IL-10 release was upregulated, resembling in part the M2b sub-phenotype. Anti-inflammatory stimuli had no effect on HBC polarization. HBCs maintain their M2 phenotype in vitro despite inflammatory stimuli, which might represent a state of adaption and tolerance to avoid rejection of the semiallogeneic feto-placental unit.

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

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

Neutrophils, monocytes and other immune components in the equine endometrium: Friends or foes?

The innate and adaptive immune mechanisms are key components of regulation of reproductive physiological function and uterine disorders in equine uterus. The predominant immunological response in equine endometrium, characterized by an innate immune response, occurs under estrogens influence, in the follicular phase. Although, the increase in immune-related genes in equine endometrium during estrus has been suggested to play a role in uterine clearance after mating, immune cells and their product, i.e. cytokines play also mandatory role in the luteal development and maintenance, regression of equine corpus luteum, as well as in early pregnancy. Innate immune response is nonspecific and acts as the first line of defense against pathogens, foreign stimuli that include constituents of seminal fluid and local infections (endometritis). It has been recently established that a phagocytosis-independent mechanism to restrain bacteria, by means of neutrophil extracellular traps (NETs) formation, is involved in pathogenesis of in mare endometrial fibrosis (endometrosis). Moreover, persistent macrophages and mast cell activation could also have pro-fibrotic roles by secreting great amounts of pro-fibrotic factors and lead to fibrosis. This review will highlight the involvement of immune key components of the innate and adaptive immune system and their products in equine uterus and their contribution to reproductive physiological function and uterine disorders.

NLRP7 Is Involved in the Differentiation of the Decidual Macrophages

Macrophage polarization, regulated appropriately, may play important roles in successful pregnancy. In the face of the vital roles of decidua macrophages in pregnancy, it is insufficient to recognize the trigger of macrophage differentiation and polarization. We aimed to explore the link between the NLRP7 gene and macrophage polarization in human deciduas. Here, we enrolled the endometrial tissues from eight pregnant women in the first trimester. We found that NLRP7 was abundant in endometrial tissues and that NLRP7 was expressed in decidual macrophages of the first-trimester pregnancy. NLRP7 was predominately expressed in the decidual M2 macrophages, as compared with the M1 macrophages. Furthermore, our results suggest that NLRP7 is associated with decidual macrophage differentiation. NLRP7 over-expression suppresses the expression of M1 markers and enhances the expression of the M2 markers. Considering that NLRP7 relates to decidualization and macrophage differentiation, we propose that NLRP7 is a primate-specific multitasking gene to maintain endometrial hemostasis and reproductive success. This finding may pave the way for therapies of pathological pregnancies.