Functions of macrophages in human decidual tissue in early pregnancy

The Ferritin, Hepcidin and Cytokines Link in the Diagnoses of Iron Deficiency Anaemia during Pregnancy: A Review

Following a diagnosis of iron deficiency anaemia in pregnancy, iron supplements are prescribed using UK guidelines; however, despite this, the condition remains highly prevalent, affecting up to 30% of pregnant women in the UK. According to the World Health Organisation, it globally accounts for 45% in the most vulnerable groups of pregnant women and infants (<5 years old). Recently, the efficacy of iron replacement therapy and the effectiveness of current standard testing of iron parameters have been reviewed in order to evaluate whether a more accurate diagnosis can be made using alternative and/or supplementary markers. Furthermore, many questions remain about the mechanisms involved in iron metabolism during pregnancy. The most recent studies have shed more light on serum hepcidin and raised questions on the significance of pregnancy related inflammatory markers including cytokines in iron deficiency anaemia. However, research into this is still scarce, and this review aims to contribute to further understanding and elucidating these areas.

Setting a stage: Inflammation during preeclampsia and postpartum

Preeclampsia (PE) is a leading cause of maternal and fetal mortality worldwide. The immune system plays a critical role in normal pregnancy progression; however, inappropriate inflammatory responses have been consistently linked with PE pathophysiology. This inflammatory phenotype consists of activation of the innate immune system, adaptive immune system, and increased inflammatory mediators in circulation. Moreover, recent studies have shown that the inflammatory profile seen in PE persists into the postpartum period. This manuscript aims to highlight recent advances in research relating to inflammation in PE as well as the inflammation that persists postpartum in women after a PE pregnancy. With the advent of the COVID-19 pandemic, there has been an increase in obstetric disorders associated with COVID-19 infection during pregnancy. This manuscript also aims to shed light on the relationship between COVID-19 infection during pregnancy and the increased incidence of PE in these women.

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.

DC-SIGN expression in Hofbauer cells may play an important role in immune tolerance in fetal chorionic villi during the development of preeclampsia

Immune tolerance at feto-maternal interfaces is a complex phenomenon. Although maternal decidual macrophages are well-known immune cells, little is known about fetal-derived macrophages (Hofbauer cells) within chorionic villi. Preeclampsia (PE) is a major cause of maternal mortality in the field of obstetrics, and the innate immunological role of maternal decidual macrophages is well known. In this study, we assessed the differential phenotypes and marker expression in fetal macrophages, known as dendritic cell-specific ICAM-grabbing non-integrin (DC-SIGN)-positive Hofbauer cells. We compared Hofbauer cell properties between normal and PE placenta chorionic villi and performed sequential staining of DC-SIGN, CD14, and CD68 to evaluate the existence of Hofbauer cells. Furthermore, to evaluate the immunological function of these cells, we stained the cells for CD163, a marker of immunoregulatory type 2 (M2) macrophages. Additionally, we examined the expression of the immunosuppressive cytokine interleukin (IL)-10, which is known to be produced by M2 macrophages. DC-SIGN+/CD14+, DC-SIGN+/CD68+, and CD163+/DC-SIGN+ cells were quantified based on photomicrographs. The results showed that CD14, CD163, DC-SIGN, and IL-10 levels were significantly downregulated in PE compared with normal. Additionally, CD163+/DC-SIGN+ Hofbauer cells were significantly less frequent in PE than in normal. DC-SIGN Hofbauer cells produced IL-10 at lower levels in the PE than in the normal. Thus, we speculate that fetal-derived Hofbauer cells may play an important role in normal pregnancy with immunosuppressive effects based on their M2 macrophage characteristics to maintain immune tolerance during pregnancy. Additionally, in PE, these functions were defective, supporting the roles of these macrophages in PE development.

Effect of Cytokines on the Formation Tube-Like Structures by Endothelial Cells in the Presence of Trophoblast Cells

Despite ample data on cytokine secretion in the uteroplacental interface, the influence of microenvironment cells, in particular, trophoblast cells on angiogenesis and the role of cytokines in this process remain poorly studied. We studied the influence of cytokines on the formation of tube-like structures by endothelial cells in the presence of trophoblast cells and showed that trophoblast cells suppressed the angiogenic potential of endothelial cells. Antiangiogenic cytokines IFN-γ, IL-10, TNF-α, and TGFβ via modulation of trophoblast cells stimulated the formation of tube-like structures by endothelial cells. In the co-culture of endothelial and trophoblast cells, the effects of cytokines changed and they gained additional regulatory functions.

The decidua-the maternal bed embracing the embryo-maintains the pregnancy

The decidua has been known as maternal uterine tissue, which plays essential roles in protecting the embryo from being attacked by maternal immune cells and provides nutritional support for the developing embryo prior to placenta formation. However, there are questions that still remain to be answered: (1) How does the decidua supply nutrition and provide a physical scaffold for the growing embryo, before placental vascular connection is established? (2) How is the balance between preventing an anti-embryo immune response and protecting both embryo and mother from infections established? To understand basic personas in decidual tissues, we review the structure of the decidua composed of terminally differentiated uterine stromal cells, blood vessels, and a number of repertoire of uterine local immune cells, including the well-known uterine natural killer (uNK) cells and recently discovered innate lymphoid cells (ILCs). Decidual macrophages and uterine dendritic cells (DCs) are supposed to modulate adaptive immunity via balancing cytokines and promoting generation of regulatory T (Treg) cells. During decidualization, vascular and tissue remodeling in the uterus provide nutritional and physical support for the developing embryo. Secretion of various cytokines and chemokines from both the embryo and the decidual cells activates multiple signaling network between the mother and the embryo upon implantation. Defects in the decidual development during early pregnancy result in loss of pregnancy or complications in later gestational stage.

Mono-ethylhexyl phthalate stimulates prostaglandin secretion in human placental macrophages and THP-1 cells

BACKGROUND

Diethylhexyl phthalate (DEHP) is widely used as a plasticizer in polyvinyl chloride products. DEHP exposure, which is widespread in the US, increases preterm birth risk; however, the mechanisms driving this relationship are unclear. Because cyclooxygenase-2 (COX-2) dependent prostaglandin synthesis is implicated in preterm birth, we evaluated effects of mono-2-ethylhexyl phthalate (MEHP), the active metabolite of DEHP, on prostaglandin E2 (PGE2) synthesis and COX expression in human placental macrophages (PM). In addition, responses in PM were compared to those in a human macrophage-like cell line, THP-1.

METHODS

PM and THP-1 cells were treated for 2, 4, 8, or 24 h with MEHP concentrations ranging from 10 to 180 micromolar. PGE2 concentrations were assessed in culture medium using ELISA, and COX expression was determined by western blot.

RESULTS

Treatment of PM and THP-1 cells with 180 micromolar MEHP for 24 h significantly increased PGE2 release. Co-treatment of PMs or THP-1 cells with 180 micromolar MEHP and the non-selective COX inhibitor indomethacin reduced MEHP-stimulated PGE2 production. Similarly, co-treatment of PM and THP-1 cells with the COX-2 selective inhibitor NS-398 resulted in a significant decrease in PGE2, suggesting that MEHP-stimulated PGE2 is dependent specifically on increased COX-2 expression. Western blot analysis revealed a significant increase in COX-2 expression in PM and THP-1 cells treated with 180 micromolar MEHP, and no changes in COX-1 expression, supporting the role of COX-2 in MEHP-stimulated PGE2 synthesis.

CONCLUSIONS

The findings from this study are the first to demonstrate phthalate-stimulated PGE2 synthesis in PM and warrant future studies into COX-2-dependent prostaglandin synthesis as a mechanism of toxicant-associated preterm birth.

HLA Class Ib Molecules and Immune Cells in Pregnancy and Preeclampsia

Despite decades of research, the highly prevalent pregnancy complication preeclampsia, “the disease of theories,” has remained an enigma. Indeed, the etiology of preeclampsia is largely unknown. A compiling amount of studies indicates that the pathological basis involves a complex array of genetic predisposition and immunological maladaptation, and that a contribution from the mother, the father, and the fetus is likely to be important. The Human Leukocyte Antigen (HLA)-G is an increasing focus of research in relation to preeclampsia. The HLA-G molecule is primarily expressed by the extravillous trophoblast cells lining the placenta together with the two other HLA class Ib molecules, HLA-E and HLA-F. Soluble isoforms of HLA-G have been detected in the early endometrium, the matured cumulus–oocyte complex, maternal blood of pregnant women, in umbilical cord blood, and lately, in seminal plasma. HLA-G is believed to be involved in modulating immune responses in the context of vascular remodeling during pregnancy as well as in dampening potential harmful immune attacks raised against the semi-allogeneic fetus. In addition, HLA-G genetic variants are associated with both membrane-bound and soluble forms of HLA-G, and, in some studies, with preeclampsia. In this review, a genetic contribution from the mother, the father, and the fetus, together with the presence and function of various immune cells of relevance in pregnancy are reviewed in relation to HLA-G and preeclampsia.

Major histocompatibility complex I mediates immunological tolerance of the trophoblast during pregnancy and may mediate rejection during parturition

During pregnancy in larger mammals, the maternal immune system must tolerate the fetus for months while resisting external infection. This tolerance is facilitated by immunological communication between the fetus and the mother, which is mediated by Major Histocompatibility Complex I (MHC I) proteins, by leukocytes, and by the cytokines secreted by the leukocytes. Fetal-maternal immunological communication also supports pregnancy by inducing physiological changes in the mother. If the mother “misunderstands” the signal sent by the fetus during pregnancy, the fetus will be miscarried or delivered preterm. Unlike any other maternal organ, the placenta can express paternal antigens. At parturition, paternal antigens are known to be expressed in cows and may be expressed in horses, possibly so that the maternal immune system will reject the placenta and help to expel it. This review compares fetal-maternal crosstalk that is mediated by the immune system in three species with pregnancies that last for nine months or longer: humans, cattle, and horses. It raises the possibility that immunological communication early in pregnancy may prepare the mother for successful expulsion of fetal membranes at parturition.

Innate and adaptive immune interactions at the fetal-maternal interface in healthy human pregnancy and pre-eclampsia

Maternal immune tolerance of the fetus is indispensable for a healthy pregnancy outcome. Nowhere is this immune tolerance more important than at the fetal–maternal interface – the decidua, the site of implantation, and placentation. Indeed, many lines of evidence suggest an immunological origin to the common pregnancy-related disorder, pre-eclampsia. Within the innate immune system, decidual NK cells and antigen presenting cells (including dendritic cells and macrophages) make up a large proportion of the decidual leukocyte population, and are thought to modulate vascular remodeling and trophoblast invasion. On the other hand, within the adaptive immune system, Foxp3⁺ regulatory T cells are crucial for ensuring immune tolerance toward the semi-allogeneic fetus. Additionally, another population of CD4⁺HLA-G⁺ suppressor T cells has also been identified as a potential player in the maintenance of immune tolerance. More recently, studies are beginning to unravel the potential interactions between the innate and the adaptive immune system within the decidua, that are required to maintain a healthy pregnancy. In this review, we discuss the recent advances exploring the complex crosstalk between the innate and the adaptive immune system during human pregnancy.

Role of cathepsin E in decidual macrophage of patients with recurrent miscarriage

In a previous study, we reported that the cathepsin-cystatin system caused endometrial dysfunction in early pregnancy. Here, we investigated the existence and contribution of cathepsin E in early pregnancy in patients with recurrent miscarriage (RM). The effect of cathepsin deficiency on fertility and female reproductive organs were also analyzed in CatE(-/-) mice. Human studies were conducted in a hospital setting, with informed consent. Cervical mucus was collected from RM patients in early pregnancy (4-6 gestational weeks, n = 21), and the pregnancy outcome was compared prospectively. The cathepsin E expression in decidua of RM patients (n = 49) and normal pregnant women undergoing elective surgical abortion (n = 24) was measured using SDS-PAGE, and western blot analysis. Decidual macrophages were isolated from RM patients (n = 6) and stimulated by lipopolysaccharide (LPS) and interferon gamma (IFN-γ). Results from the mouse model showed that CatE(-/-) mice were fertile, but the litter number was significantly smaller. The uterus of CatE(-/-) mice showed granulation tissue. In human samples, protease activity of cathepsin E measured with Fluorescence-Quenching Substrate (KYS-1) in cervical mucus of patients who developed miscarriage was markedly decreased compared with patients without RM. The expression of cathepsin E in decidua, semi-quantified by SDS-PAGE, western blot analysis was significantly lower in RM patients compared with patients without RM. By double staining immunofluorescence, the staining of cathepsin E was observed in CD14 or CD68 positive cells in all deciduas. Upon stimulation with LPS and IFN-γ, the expression of cathepsin E in cell lysate of decidual macrophages was markedly reduced in RM patients compared with controls. The results suggested that decreased activity of cathepsin E produced by decidual macrophages might be responsible for the induction of miscarriages in some RM patients.

The Placenta in Toxicology. Part II

During pregnancy, the maternal immune system is challenged by the semiallogeneic fetus, which must be tolerated without compromising fetal or maternal health. This review updates the systemic and local immune changes taking place during human pregnancy, including some examples in rodents. Systemic changes are induced by contact of maternal blood with placental factors and include enhanced innate immunity with increased activation of granulocytes and nonclassical monocytes. Although a bias toward T helper (Th2) and regulatory T cell (Treg) immunity has been associated with healthy pregnancy, the relationship between different circulating Th cell subsets is not straightforward. Instead, these adaptations appear most evidently at the fetal–maternal interface, where for instance Tregs are enriched and promote fetal tolerance. Also innate immune cells, that is, natural killer cells and macrophages, are enriched, constituting the majority of decidual leukocytes. These cells not only contribute to immune regulation but also aid in establishing the placenta by promoting trophoblast recruitment and angiogenesis. Thus, proper interaction between leukocytes and placental trophoblasts is necessary for normal placentation and immune adaptation. Consequently, spontaneous maladaptation or interference of the immune system with toxic substances may be important contributing factors for the development of pregnancy complications such as preeclampsia, preterm labor, and recurrent miscarriages.

Placental Hofbauer cells limit HIV-1 replication and potentially offset mother to child transmission (MTCT) by induction of immunoregulatory cytokines

Background

Despite readily detectable levels of the HIV-1 (co)-receptors CD4, CCR5 and DC-SIGN on placental macrophages (Hofbauer Cells [HCs]), the rate of HIV-1 infection in utero in the absence of interventions is only 7% of exposed infants. Here, we examine the replication kinetics of human HCs to the primary isolate HIV-1_BaL. We also determined the infectivity of HIV-1-exposed HCs by co-culturing with isolated cord and peripheral blood mononuclear cells [CBMCs, PBMCs]. To understand the limiting nature of HCs to HIV-1 replication, we examined the effect of endogenously secreted cytokines on replication kinetics.

Results

HCs have reduced ability to replicate HIV-1 in vitro (p < 0.01) and to transmit virus to CBMCs and PBMCs (p < 0.001 for both) compared to standard infections of MDMs. HCs were shown to release HIV-1 particles at levels comparable to MDMs, however exhibit significant decreases in viral transcription (gag and env), which may account for lower levels of HIV-1 replication. Un-stimulated HCs constitutively express significantly higher levels of regulatory cytokines, IL-10 and TGF-β, compared to MDMs (p < 0.01), which may contribute to immunoregulatory predominance at the placenta and possibly account for down-regulation of HIV-1 replication and infectivity by HCs. We further demonstrate that these regulatory cytokines inhibit HIV-1 replication within HCs in vitro.

Conclusion

HCs have reduced ability to replicate and disseminate R5-tropic HIV-1_BaLin vitro and potentially offset mother to child transmission (MTCT) of HIV-1 by the induction of immunoregulatory cytokines. Despite the potential for migration and infectivity, HCs are not present in the neighboring fetal circulation. These results implicate HCs as important mediators of protection at the feto-maternal interface during ongoing HIV-1 exposure.

Decidual macrophages are significantly increased in spontaneous miscarriages and over-express FasL: a potential role for macrophages in trophoblast apoptosis

Decidual macrophages (DM) are the second most abundant population in the fetal-maternal interface. Their role has been so far identified as being local immuno-modulators favoring the maternal tolerance to the fetus. Herein we investigated tissue samples from 11 cases of spontaneous miscarriages and from 9 cases of elective terminations of pregnancy. Using immunohistochemistry and dual immunofluorescence we have demonstrated that in spontaneous miscarriages the DM are significantly increased. Additionally, we noted a significant up-regulation of macrophage FasL expression. Our results further support a dual role for DM during pregnancy and miscarriages. We hypothesize that the baseline DM population in normal pregnancy is in line with an M2 phenotype supporting the ongoing gestation. In contrast, during spontaneous miscarriages, the increased FasL-expressing population could be a part of an M1 phenotype participating in Fas/FasL-related apoptosis. Our results highlight a new aspect of macrophage biology in pregnancy physiology and pathophysiology. Further studies with larger samples are needed to verify the current results and evaluate their clinical impact.

Selective inhibition and augmentation of alternative macrophage activation by progesterone

Progesterone is the female sex hormone necessary for the maintenance of pregnancy, and is known to modulate macrophage activation. However, studies have concentrated exclusively on the ability of progesterone to negatively regulate the innate and classical pathways of activation, associated with nitric oxide (NO) and interleukin (IL)-12 production. Our aim was to examine the ability of progesterone to modulate alternative macrophage activation. Bone marrow cells were isolated and differentiated from male BALB/c mice, exposed to varying concentrations of progesterone and stimulated with lipopolysaccharide (LPS) (innate activation), IL-4 (alternative activation) or LPS in combination with IL-4. Our present study demonstrates that progesterone not only down-regulates inducible nitric oxide synthase 2 (iNOS) activity in macrophages but also arginase activity, in a dose-dependent manner, independent of the stimuli, whether it is induced by LPS (innate activation), IL-4 (alternative activation) or LPS in combination with IL-4. The ability of progesterone to down-modulate IL-4-induced cell surface expression of the mannose receptor further suggested a negative regulation of alternative macrophage activation by this hormone. Analysis of mRNA expression, by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), of genes associated with innate and alternative macrophage activation revealed that progesterone down-regulated LPS-induced macrophage nos2, argI and p40 (IL-12/IL-23) expression and IL-4-induced argI, mrc-1 and fizz1 expression. However, progesterone up-regulated IL-4-induced macrophage expression of ym1, while dectin-1 expression remained unaltered. Following treatment of macrophages with LPS and IL-4 in combination a similar pattern was observed, with the exception that progesterone up-regulated macrophage expression of fizz1 as well as ym1 and did not modify mrc-1 expression. Our data demonstrate for the first time that a hormone has the ability to regulate selectively the expression of different genes associated with alternative macrophage activation.

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

During pregnancy, the maternal immune system is challenged by the presence of the fetus, which must be tolerated despite being semiallogeneic. Uterine mucosal (or decidual) macrophages (M), one of the major leukocyte populations at the fetal-maternal interface, have been implicated in fetal tolerance, but information regarding their regulation is scarce. In this study, we investigated the role of several factors potentially involved in the differentiation and polarization of decidual M with an in vitro M differentiation model. By using flow cytometry, we showed that M-CSF and IL-10 were potent inducers of M2 (immunoregulatory) M markers expressed on human decidual M (CD14, CD163, CD206, CD209). In contrast, proinflammatory stimuli, and unexpectedly also the Th2-associated IL-4 and IL-13, induced different patterns of expression, indicating that a Th2-dominated environment is not required for decidual M polarization. M-CSF/IL-10-stimulated and decidual M also showed similar cytokine secretion patterns, with production of IL-10 as well as IL-6, TNF, and CCL4. Conversely, the proinflammatory, LPS/IFN-γ-stimulated M produced significantly higher levels of TNF and no IL-10. We also used a gene array with 420 M-related genes, of which 100 were previously reported to be regulated in a global gene expression profiling of decidual M, confirming that M-CSF/IL-10-induced M are closely related to decidual M. Taken together, our results consistently point to a central role for M-CSF and in particular IL-10 in the shaping of decidual M with regulatory properties. These cytokines may therefore play an important role in supporting the homeostatic and tolerant immune milieu required for a successful pregnancy.

Differential distribution and phenotype of decidual macrophages in preeclamptic versus control pregnancies

Maternal immune tolerance of the semiallogeneic fetus is a complex phenomenon. Macrophages are an abundant cell population in the human decidua, and changes in distribution or phenotype may be involved in the development of preeclampsia. The aim of this study was to assess the distribution and phenotype of macrophages in preterm preeclamptic, preterm control, and term control placentas. Placentas of preterm preeclamptic (n = 6), preterm control (n = 5), and term control pregnancies (n = 6) were sequentially immunohistochemically stained for CD14, CD163, DC SIGN, and IL-10. The distributions of CD14(+), CD163(+), DC SIGN(+), IL-10(+), CD163(+)/CD14(+), DC SIGN(+)/CD14(+), and Flt-1/CD14(+) cells were determined by double staining and by digital image analysis of sequential photomicrographs. CD14 and CD163 expression increased significantly in preterm preeclamptic decidua basalis compared with preterm control pregnancies (P = 0.0006 and P = 0.034, respectively). IL-10 expression was significantly lower in the decidua parietalis of preterm preeclamptic pregnancies compared with preterm control pregnancies (P = 0.03). The CD163/CD14 ratio was significantly lower in the decidua basalis (P = 0.0293) and the DC SIGN/CD14 ratio was significantly higher in the decidua basalis (P < 0.0001) and parietalis (P < 0.0001) of preterm preeclamptic pregnancies compared with preterm control pregnancies. CD14(+) macrophages did express Flt-1. Alterations in distribution and phenotype of macrophages in the decidua of preterm preeclamptic pregnancies compared with control pregnancies may contribute to the pathogenesis of preeclampsia.

TLRs, macrophages, and NK cells: our understandings of their functions in uterus and ovary

Inflammation involves multiple changes in many aspects of immune system. Interactions between immune system and female reproductive system strongly impact fertility and reproductive health in general. Many normal events of female reproduction system including ovulation, menstruation, implantation and labor onset are considered as inflammatory process. Emerging evidence reveals that three components of immune system that are critical to initiate and resolve inflammation, Toll-like receptors (TLRs), macrophages, and natural killer (NK) cells, play important roles not only to provide protection against infections by exogenous pathogens but also to regulate essential functions of uterus and ovary. This review will briefly summarize our understanding of the functions of TLRs, macrophages and NK cells in uterus and ovary.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes apoptosis during its replication in fetal implantation sites

Reproductive failure due to porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by late-term abortions, early farrowing and an increase of dead and mummified fetuses and weak-born piglets. The mechanism of PRRSV-induced reproductive failure is poorly understood. Human pregnancies, complicated by some pathogens leading to reproductive disorders exhibit increased apoptosis in the fetal membranes. Because PRRSV-target cells are present in endometrium/fetal placentas from healthy sows and PRRSV-infected macrophages in other organs die by apoptosis, we hypothesized that PRRSV can replicate and induce apoptosis in the fetal implantation sites at the last stage of gestation. In the present study, identification, localization and quantification of the PRRSV-positive and apoptotic cells were performed in the fetal implantation sites. Three dams were inoculated intranasally with 10(5) TCID(50) PRRSV 07V063 at 90 days of gestation and sampled at 10 days post-inoculation. Two non-inoculated dams that were euthanized at 100 days of gestation served as control animals. Inoculation of the dams resulted in a viremia that lasted until the end of the study. Transplacental PRRSV spread was detected in all inoculated dams. Using immunofluorescence staining, single PRRSV-positive cells were found in the endometrial connective tissues adjacent to both PRRSV-positive and PRRSV-negative fetuses. In the fetal placental mesenchyme of the PRRSV-positive fetuses, infected cells were more abundant and spread focally. Double staining showed that all PRRSV-positive cells in the fetal implantation sites were positive for sialoadhesin and CD163. Apoptotic cells (TUNEL+) were detected in endometrium and fetal placentas of both non- and PRRSV-inoculated dams. The number of apoptotic cells was significantly higher in PRRSV-positive endometrium/fetal placentas. PRRSV caused apoptosis in infected cells since 20-61% of PRRSV-positive cells were apoptotic and in surrounding cells since 43-91% of the apoptotic cells were virus-negative. The main conclusion obtained from the present study is that PRRSV replicates in the fetal implantation sites and causes apoptosis in infected macrophages and surrounding cells at the last stage of gestation. The possible mode of PRRSV replication in the fetal implantation sites and the events that might contribute to the reproductive disorders are discussed.

Human trophoblast-derived exosomal fibronectin induces pro-inflammatory IL-1β production by macrophages

PROBLEM  Our previous studies demonstrated that trophoblast-derived exosomes induced synthesis and release of pro-inflammatory cytokines, including interleukin-1β (IL-1β) by macrophages. The objective of this study was to characterize the mechanism and receptors associated with this induction. METHOD OF STUDY  Exosomes were isolated from Sw71 trophoblast-conditioned media by ultrafiltration and ultracentrifugation. Using macrophages isolated from normal donors, cytochalasin D was used to block exosome uptake. Induction of IL-1β mRNA was investigated by qRT-PCR, pro-IL-1β protein by western immunoblotting, and mature IL-1β release by ELISA. RGD peptides were used to block fibronectin binding by macrophage α5β1 integrin. RESULTS  Uptake of exosomes by macrophages was completely blocked by pre-treatment with cytochalasin D. Although induction of some cytokines (such as C4A and CCL11) requires uptake, induction of IL-1β occurred without exosome internalization. Cytochalasin D treatment did not inhibit exosome-mediated induction of IL-1β mRNA, production of the pro-protein, or release of mature IL-1β. Blocking of fibronectin binding using RGD peptides demonstrated the abrogation of exosome-mediated IL-1β production. CONCLUSION  Although trophoblast-derived exosomes have been demonstrated to induce IL-1β, this is the first demonstration of IL-1β induction by exosome-associated fibronectin. Based on this pro-inflammatory role of exosome-associated fibronectin, it may represent an important general immunoregulatory mechanism.

The immunomodulatory roles of macrophages at the maternal-fetal interface

Macrophages are versatile cells that play a central role in innate and adaptive immunity and participate in a wide variety of biological processes. In the uterine decidua, macrophages represent a major leukocyte subset throughout pregnancy. Here, decidual macrophages exert an immunosuppressive phenotype characterized by abundant production of interleukin (IL)-10 and indoleamine 2,3-dioxygenase activity. Their polarized cytokine secretion pattern has recently been classified as an M2 phenotype. These features of decidual macrophages favor maternal immune tolerance to semiallogenic fetus. In addition, macrophages cooperate with trophoblast cells during the early stages of human pregnancy to support uterine vasculature remodeling by removing apoptotic cells and through the production of proteases that degrade the extracellular matrix. In the peripartum period, macrophages also participate in the regulation of cervical ripening and the initiation of parturition through the production of proinflammatory cytokines and prostaglandin E(2) (PGE(2)). Aberrant activity of uterine macrophages is linked to the pathogenesis of preeclampsia and preterm delivery. Here, we review the immunomodulatory roles of decidual macrophages during pregnancy.

Programming of human monocytes by the uteroplacental environment

During human pregnancy, monocytes recruited to the uterus (decidua) are modified to promote immune defense and semiallogeneic pregnancy. The purpose of this study was to identify decidual factors involved in programming of monocytes into decidual macrophages by comparing the surface and secretory phenotypes of resting and interferon- gamma (IFN-gamma)-activated monocytes, unfractionated decidual cells, purified term decidual macrophages, and monocyte-derived macrophages. Surface markers for antigen presentation (HLA-DR, CD86), a membrane-bound cytokine interleukin (IL)-15, leukocyte immunoglobulin-like receptors (LILRB1, LILRB2), and secreted anti-inflammatory cytokines (transforming growth factor [TGF]-beta1 and IL-10) were assessed. The results demonstrate that differentiated, activated monocytes closely resemble but are not identical to decidual macrophages. In addition to differential IFN-gamma responsiveness, decidual macrophages were smaller than monocyte-derived macrophages and produced IL-10, which monocyte-derived macrophages did not. Only the unfractionated decidual cells secreted TGF-beta1. These results suggest that activation, differentiation, and decidual signals cooperate to program monocytes into the decidual macrophage phenotype.

Gene expression profiling of human decidual macrophages: evidence for immunosuppressive phenotype

Background

Although uterine macrophages are thought to play an important regulatory role at the maternal-fetal interface, their global gene expression profile is not known.

Methodology/Principal Findings

Using micro-array comprising approximately 14,000 genes, the gene expression pattern of human first trimester decidual CD14+ monocytes/macrophages was characterized and compared with the expression profile of the corresponding cells in blood. Some of the key findings were confirmed by real time PCR or by secreted protein. A unique gene expression pattern intrinsic of first trimester decidual CD14+ cells was demonstrated. A large number of regulated genes were functionally related to immunomodulation and tissue remodelling, corroborating polarization patterns of differentiated macrophages mainly of the alternatively activated M2 phenotype. These include known M2 markers such as CCL-18, CD209, insulin-like growth factor (IGF)-1, mannose receptor c type (MRC)-1 and fibronectin-1. Further, the selective up-regulation of triggering receptor expressed on myeloid cells (TREM)-2, alpha-2-macroglobulin (A2M) and prostaglandin D2 synthase (PGDS) provides new insights into the regulatory function of decidual macrophages in pregnancy that may have implications in pregnancy complications.

Conclusions/Significance

The molecular characterization of decidual macrophages presents a unique transcriptional profile replete with important components for fetal immunoprotection and provides several clues for further studies of these cells.

Antenatal risk factors, cytokines and the development of atopic disease in early childhood

Atopic diseases are complex entities influenced by an array of risk factors, including genetic predisposition, environmental allergens, antenatal exposures, infections and psychosocial factors. One proposed mechanism by which these risk factors contribute to the development of atopic disease is through changes in the production of T helper cell type 1 (Th1) and T helper cell type 2 (Th2) cytokines. The objectives of this review are to discuss antenatal exposures that are associated with paediatric atopic diseases, to discuss the influence of the intrauterine environment on neonatal immune responses, to provide an overview of the Th1 and Th2 pathways and how they relate to atopic disease, and to summarise our current understanding of the association between cytokine responses in cord blood and the development of atopic disease in early childhood.

Natural Killer Cells and Dendritic Cells at the Human Feto-maternal Interface: an Effective Cooperation?

Human endometrium and in particular decidua, harbours a considerable population of immunocompetent cells. The most prominent of these are uterine natural killer (uNK) cells, which differ considerably from their peripheral blood counterparts in terms of both gene expression and function. Recently, the existence of DC-SIGN positive immature dendritic cells (DCs) in human decidua has been demonstrated. Evidence exists that immature DCs are required for the initiation and maintenance of peripheral tolerance, whereas mature DCs, which are only found in minimal amounts in human decidua, are associated with a Th1 polarization of T cells. Although the study of uNK-DC cross-talk is only beginning, it may in the future provide important insights into how acceptance of the fetus by the maternal immune system is mediated.

Stress and substance P but not the substance P-metabolite SP5-11 trigger murine abortion by augmenting TNF-alpha levels at the feto-maternal interface

In a well-established murine abortion model, stress is thought to trigger fetal rejection by inducing a proinflammatory immune response via substance P (SP), being tumour necrosis factor (TNF)-alpha-producing CD8+ T cells involved. Interestingly, the SP metabolite SP5-11 also binds to SP receptors and mediates SP-like effects on immune cells at sites of inflammation. No data were available regarding the effects of SP5-11 on pregnancy outcome in the CBA/J x DBA/2J abortion-prone combination. We investigated the influence of SP5-11 in contrast to stress or SP on the abortion rate and the cytokine production by lymphocytes as well as on the levels of CD8+ T cells. Stress and SP boosted the abortion rate and increased the percentage of type 1 [TNF-alpha, interferon-gamma, interleukin (IL)-12] and type 2 (IL-4 and IL-10) cytokine-producing lymphocytes in blood and decidua, predominantly CD8+ T cells. Interestingly, SP5-11 did not significantly affect the abortion rate or cytokine production in the decidua, while increasing the Th1 and Th2 cytokine production systemically. Our data suggest that stress and SP induce abortion by augmenting the local levels of TNF-alpha, which seems therefore to be a potent trigger of miscarriage. On the contrary, the SP metabolite SP5-11 only affects the systemic cytokine production without boosting the abortion rate in this experimental model.

HLA-G and immune tolerance in pregnancy

Multiple mechanisms underlie the surprising willingness of mothers to tolerate genetically different fetal tissues during pregnancy. Chief among these is the choice of HLA-G, a gene with few alleles, rather than the highly polymorphic HLA-A and -B genes, for expression by the placental cells that interface directly with maternal blood and tissues. Novel aspects of this major histocompatibility complex class Ib gene include alternative splicing to permit production of membrane and soluble isoforms, deletions that dampen responses to interferons, and a shortened cytoplasmic tail that affects expression at the cell surface. Placental cells migrating into the maternal uterus synthesize both membrane and soluble isoforms, which interact with inhibitory receptors on leukocytes such as ILT2 and ILT4. Cytotoxic T lymphocytes either die or reduce production of one of their major coreceptor/activator cell surface molecules, CD8; natural killer cells are immobilized and mononuclear phagocytes are programmed into suppressive modes characterized by high production of anti-inflammatory cytokines. The idea that placental HLA-G proteins facilitate semiallogeneic pregnancy by inhibiting maternal immune responses to foreign (paternal) antigens via these actions on immune cells is now well established, and the postulate that the recombinant counterparts of these proteins may be used as powerful tools for preventing immune rejection of transplanted organs is gaining in popularity.

Immunological properties of human decidual macrophages--a possible role in intrauterine immunity

Our aim was to investigate the contribution of decidual macrophages, which constitute an important immune component of the decidua in late gestation, to intrauterine defence mechanisms. Using flow cytometry we examined the ability of decidual macrophages, isolated from term decidua, to bind and phagocytose fluorescence-labelled bacterial and yeast bioparticles. We also assessed their ability to generate superoxide radicals and tumour necrosis factor-alpha following lipopolysaccharide challenge. Decidual macrophages bound bacterial and yeast particles in a dose-dependent manner, which subsequently led to phagocytosis. These macrophages also produced superoxide radicals and the pro-inflammatory cytokine TNF-alpha when challenged with bacterial lipopolysaccharides. These results suggest a role for decidual macrophages in pathogen recognition and clearance during pregnancy, and, therefore, they are likely to protect the fetus against intrauterine infections which might otherwise lead to preterm labour.

Antigen presenting cells and HLA-G – a review

Maternal antigen presenting cells, which are macrophages and dendritic cells, are scattered throughout human decidualized endometrium during all stages of pregnancy. These powerful, multi-functional leukocytes reside in close proximity to uterine glandular epithelium, uterine blood vessels, and HLA-G-producing invasive cytotrophoblast cells. Macrophages and dendritic cells, which express the HLA-G receptors, ILT2 and ILT4, play major roles in driving innate and adaptive immune responses, altering the behavior of local stromal cells, shaping the cytokine microenvironment, and protecting the tissue from infection. Therefore, encounters between decidual antigen presenting cells and HLA-G molecules are likely to influence uterine and placental homeostasis as well as local maternal immune responses to the fetus during pregnancy.

Phenotypic characterization of human decidual macrophages

Pregnancy is a challenge to the immune system, which not only has to protect the mother and the fetus from invading pathogens but to also maintain immunological tolerance against the fetus. However, the mechanisms inhibiting local immune responses in the maternal decidual tissue are poorly understood. We have studied decidual CD14+ macrophages, which may be important in the maintenance of a tolerance against the developing fetus. Decidual macrophages expressed HLA-DR, but lower levels of costimulatory molecule CD86 than peripheral blood CD14+ monocytes from pregnant and non-pregnant women. Decidual macrophages produced spontaneously high levels of interleukin-10. Our findings suggest that decidual macrophages could represent an inhibitory type of APCs. Supporting this conclusion indoleamine 2,3-dioxygenase (IDO), suggested to have an immunosuppressive role in pregnancy, was expressed in decidual macrophages. Furthermore, decidual macrophages were not able to differentiate into dendritic cells under the influence of IL-4 + GM-CSF. These results suggest an immunoinhibitory function of decidual macrophages at the maternal-fetal interface.

Decidual macrophages are potentially susceptible to inhibition by class Ia and class Ib HLA molecules

Several members of the immunoglobulin-like transcript (ILT), also called leukocyte immunoglobulin-like receptor (LIR), family of transmembrane proteins have been identified as receptors for class I HLA molecules and transduce inhibitory signals to leukocytes upon binding of these ligands. The ligands for ILT2 (LIR1/CD85j) and ILT4 (LIR2/CD85d) include HLA-A, -B, and -G, the last of which is highly expressed in fetal trophoblast cells in both membrane-bound and soluble isoforms. To investigate the potential of fetally-derived HLA class I molecules to interact with maternal macrophages through these receptors, we examined the expression patterns of ILT2 and ILT4 in decidual macrophages. Highly purified populations of decidual macrophages were obtained by fluorescence activated cell sorting and were examined by RT-PCR for these messages. Analysis of mRNA from first trimester and term macrophages, as well as the monocyte cell line U937, resulted in amplicons of similar size to those expected for ILT2 and ILT4. Sequence analysis of the amplicons revealed that the messages from decidual macrophages corresponded to ILT2 and ILT4 messages. The message amplified from the U937 cells using the ILT2 primers was also found to be identical to ILT2; however, sequence analysis revealed that the ILT4 message amplified from these cells is a truncated form of the message. Dual label flow cytometry confirmed the expression of ILT2 and ILT4 on CD14-positive first trimester decidual macrophages and U937 cells. These results reveal that inhibitory HLA receptors are expressed in decidual macrophages and suggest that HLA-G may deliver negative signals to maternal decidual macrophages through interaction with these receptors.

Prenatal exposure, maternal sensitization, and sensitization in utero to indoor allergens in an inner-city cohort

Primary sensitization to antigens may occur prenatally. We hypothesized that high prenatal exposure to indoor antigens increases the risk for sensitization in newborns in New York City populations with increased risk for asthma. We also investigated whether maternal sensitization is required for in utero sensitization to occur. One hundred sixty-seven pregnant African American or Dominican women residing in northern Manhattan were recruited and antigen was measured from home dust. After delivery, newborn cord and maternal blood were assayed for IgE and mononuclear cell proliferation and cytokine production in response to antigen. Cockroach, mouse, but not dust mite antigens, were commonly elevated in the kitchens and pregnant mothers' beds. Increased mononuclear cell proliferation occurred in 54% of newborns in response to cockroach, 25% in response to dust mite Dermatophagoides pteronyssinus, 40% in response to dust mite D. farinae, and 34% in response to mouse protein extracts. Antigen-induced mononuclear cell proliferation occurred in cord blood even in the absence of antigen-induced mononuclear cell proliferation in the mother. Proliferation in response to antigens did not correlate with IgE levels, but proliferation in response to dust mite extracts correlated with interluekin-5 (IL-5) production in cord blood. These results suggest that (1) high prenatal exposures to cockroach and mouse antigens are prevalent; (2) in utero sensitization to multiple indoor antigens is common, occurs to a different degree than maternal sensitization, and may involve IL-5 upregulation.

Human decidua contains potent immunostimulatory CD83(+) dendritic cells

Dendritic cells (DCs) are sentinel cells of the immune system important in initiating antigen-specific T-cell responses to microbial and transplantation antigens. DCs are particularly found in surface tissues such as skin and mucosa, where the organism is threatened by infectious agents. The human decidua, despite its proposed immunosuppressive function, hosts a variety of immunocompetent CD45 cells such as natural killer cells, macrophages, and T cells. Here we describe the detection, isolation, and characterization of CD45(+), CD40(+), HLA-DR(++), and CD83(+) cells from human early pregnancy decidua with typical DC morphology. CD83(+) as well as CD1a(+) cells were found in close vicinity to endometrial glands, with preference to the basal layer of the decidua. In vitro, decidual CD83(+) cells could be enriched to approximately 30%, with the remainder of cells encompassing DC-bound CD3(+) T cells. Stimulation of allogeneic T cells in a mixed leukocyte reaction by the decidual cell fraction enriched for CD83(+) cells, was similar to that obtained with blood monocyte-derived DCs, demonstrating the potent immunostimulatory capacity of these cells. Decidual DCs with morphological, phenotypic, and functional characteristics of immunostimulatory DCs might be important mediators in the regulation of immunological balance between maternal and fetal tissue, leading to successful pregnancy.

Interleukin-1 beta levels in human embryo culture supernatants and their predictive value for pregnancy

Interleukin 1 (IL-1) is possibly one factor produced by the embryo that might have a role in the maternal immunological recognition of pregnancy. The purpose of this study was to identify an embryo-related factor suitable for prediction of pregnancy during IVF procedures. For this purpose, IL-1 beta levels were measured in 21 samples of human embryo culture-conditioned media. The average number of embryos per sample was 5 +/- 1. Simultaneously, 16 cell culture media containing 10% autologous serum but no embryos were tested as controls. IL-1 beta levels were measured using the ELISA technique, and the biological activity of IL-1 was measured by means of a C3H/HeJ mice thymocyte proliferation assay. The average IL-1 beta level +/- S.E.M. was 49 +/- 7 pg/ml in embryo culture-conditioned media and 12 +/- 2 pg/ml in controls (P < 0.001). The average IL-1 beta level in embryo culture-conditioned media from viable pregnancy cycles was 82 +/- 6 pg/ml (n = 8), while in those cases that did not result in viable pregnancies the IL-1 beta level was significantly lower (28 +/- 4 pg/ml, n = 13, P < 0.001). The IL-1 activity of embryo culture-conditioned media, measured by [3H]thymidine incorporation in thymocytes was increased, compared with control media (442 +/- 51 counts/min vs. 337 +/- 13 counts/min, P < 0.05), and the highest values corresponded to media containing those embryos that resulted in pregnancies (589 +/- 41 counts/min, P < 0.01 vs. controls). We conclude that the determination of the levels of this cytokine in embryo culture-conditioned media might be a predictive parameter for pregnancies in patients undergoing IVF-ET.

Human decidual leukocytes do not proliferate in response to either extravillous trophoblast or allogeneic peripheral blood lymphocytes

The maternal leukocytes present in human decidua during the early weeks of pregnancy are composed of CD56+ NK cells (approximately 80%), CD3+ T cells (approximately 10%), and CD14+ macrophages (approximately 10%). These leukocytes are present in large numbers at the implantation site where trophoblast invades. The migrating extravillous trophoblast (EVT) cells express HLA class I antigens HLA-G and HLA-C. To examine whether EVT or other allogeneic cells are capable of inducing a local proliferative response in maternal decidual leukocytes, we have assayed [3H]thymidine incorporation by decidual leukocytes co-cultured with irradiated trophoblast or peripheral blood lymphocytes (PBL). No proliferative response was seen in decidual leukocytes either to trophoblast or to PBL as stimulators. In addition trophoblast did not stimulate a proliferative response in PBL. These findings indicate that extravillous trophoblast is not capable of initiating a classical immune response at the implantation site.

Lymphocyte subsets and mitogen stimulation of blood lymphocytes in normal pregnancy

PROBLEM

In normal pregnancy the maternal immune system should be directed towards tolerance or suppression in order not to reject the partly foreign feto-placental unit. The aim of this investigation was to find hallmarks of systemic immunosuppression during normal pregnancy.

METHODS

Five healthy primigravidae were examined during pregnancy and postpartum with flow cytometric analysis to define T and B lymphocyte subsets in peripheral blood. In addition, we studied the proliferative response of lymphocytes to mitogens or interleukin-2 (IL-2) alone or in combination with immunomodulating drugs or interleukin-4 (IL-4). The results were compared to healthy, non-pregnant women.

RESULTS

During pregnancy and early puerperium we noted an immune balance in favour of suppression, as measured by increased numbers of T "helper/suppressor" (CD4+CD45RA+) and "suppressor"/effector T cells (CD8+S6F1-), and decreased numbers of T "helper/inducer" (CD4+CD29+), T "helper/memory" (CD4+CD45RO+), killer/effector T cells (CD8+S6F1+), and Natural Killer cells (CD56+), as well as decreased numbers of activated lymphocytes expressing IL-2 receptor (CD25+) and T cells expressing HLA-DR (HLA-DR+CD3+). During pregnancy, lymphocyte proliferation was impaired in autologous serum with concanavalin A (ConA), phytohemagglutinin (PHA), or IL-2. A difference in proliferative response to PHA or IL-2 between cultures with AB serum and autologous serum is suggestive of an immunosuppressor factor in serum during pregnancy. Indomethacin significantly increased lymphocyte proliferation in autologous serum with ConA, indicating PGE2 mediated suppressor activity during pregnancy. Chlorambucil and cimetidine modulated the proliferative response to ConA, indicating an alkylating agent sensitive and a histamine dependent suppressor activity during pregnancy.

CONCLUSIONS

During normal pregnancy, a state of systemic suppression of the maternal immune system seems to be present.