Cytokine microenvironments in human first trimester decidua are dependent on trophoblast cells

Innate immune signaling in trophoblast and decidua organoids defines differential antiviral defenses at the maternal-fetal interface

Infections at the maternal-fetal interface can directly harm the fetus and induce complications that adversely impact pregnancy outcomes. Innate immune signaling by both fetal-derived placental trophoblasts and the maternal decidua must provide antimicrobial defenses at this critical interface without compromising its integrity. Here, we developed matched trophoblast (TO) and decidua organoids (DO) from human placentas to define the relative contributions of these cells to antiviral defenses at the maternal-fetal interface. We demonstrate that TO and DO basally secrete distinct immunomodulatory factors, including the constitutive release of the antiviral type III interferon IFN-λ2 from TOs, and differentially respond to viral infections through the induction of organoid-specific factors. Finally, we define the differential susceptibility and innate immune signaling of TO and DO to human cytomegalovirus (HCMV) and develop a co-culture model of TO and DO which showed that trophoblast-derived factors protect decidual cells from HCMV infection. Our findings establish matched TO and DO as ex vivo models to study vertically transmitted infections and highlight differences in innate immune signaling by fetal-derived trophoblasts and the maternal decidua.

miR-146a-5p improves the decidual cytokine microenvironment by regulating the toll-like receptor signaling pathway in unexplained spontaneous abortion

Spontaneous abortion (SA) is a common pregnancy failure, but the cause of numerous cases remains unexplained. Decidual immune cells (DICs)-mediated cytokine microenvironment is involved in pregnancy and regulated by many microRNAs, but whether microRNA-146a-5p (miR-146a) regulate the decidual cytokine microenvironment and the potential mechanisms in unexplained SA pathogenesis have rarely been reported. In this study, the levels of cytokines and miR-146a in healthy and unexplained SA deciduae were first investigated, and the correlation between them was analyzed. Then, the effect of miR-146a inhibitor on cytokines was assessed in healthy deciduae-derived DICs. Third, the downstream targets and related molecular mechanisms of miR-146a were analyzed by bioinformatics, and the levels of the predicted targets in deciduae were assessed, followed by the correlation analysis between the levels of miR-146a and the targets. Finally, the effect of miR-146a on the predicted targets and inflammatory cytokines was validated in unexplained SA deciduae-derived DICs. As a result, decreased miR-146a correlated with the cytokine disorder in unexplained SA deciduae, and inhibition of miR-146a promoted pro-inflammatory response in healthy deciduae-derived DICs. One hundred four target genes and related molecular mechanisms of miR-146a were predicted, among which the toll-like receptor (TLR) pathway might be associated with the decidual cytokine regulation. Upregulation of miR-146a inhibited the expression of the predicted molecules enriched in the TLR pathway and improved the cytokine disorder in unexplained SA deciduae-derived DICs. Collectively, miR-146a improves the decidual cytokine microenvironment by regulating the TLR pathway in unexplained SA, providing novel potential targets for further therapeutic research.

Extracellular vesicles in host-pathogen interactions and immune regulation - exosomes as emerging actors in the immunological theater of pregnancy

This review correlates and summarizes the role of the maternal-fetal interface in the immune tolerance of the fetus and the processes that lead to infection avoidance, emphasizing the participation of exosomes and other extracellular vesicles in both situations. Exosomes are released into the extracellular medium by several cell types and are excellent carriers of biomolecules. Host-derived exosomes and the transport of pathogen-derived molecules by exosomes impact infections in different ways. The interactions of exosomes with the maternal immune system are pivotal to a favorable gestational outcome. In this review, we highlight the potential role of exosomes in the establishment of an adequate milieu that enables embryo implantation and discuss the participation of exosomes released at the maternal-fetal interface during the establishment of an immune-privileged compartment for fetal development. The placenta is a component where important strategies are used to minimize the risk of infection. To present a contrast, we also discuss possible mechanisms used by pathogens to cross the maternal-fetal interface. We review the processes, mechanisms, and potential consequences of dysregulation in all of the abovementioned phenomena. Basic information about exosomes and their roles in viral immune evasion is also presented. The interactions between extracellular vesicles and bacteria, fungi, parasites and proteinaceous infectious agents are addressed. The discovery of the placental microbiota and the implications of this new microbiota are also discussed, and current proposals that explain fetal/placental colonization by both pathogenic and commensal microbes are addressed. The comprehension of such interactions will help us to understand the immune dynamics of human pregnancy and the mechanisms of immune evasion used by different pathogens.

Decidual cytokines and pregnancy complications: focus on spontaneous miscarriage

The establishment of pregnancy requires the co-ordinated implantation of the embryo into the receptive decidua, placentation, trophoblast invasion of the maternal decidua and myometrium in addition to remodelling of the uterine spiral arteries. Failure of any of these steps can lead to a range of pregnancy complications, including miscarriage, pre-eclampsia, fetal growth restriction, placenta accreta and pre-term birth. Cytokines are small multifunctional proteins often derived from leucocytes and have primarily been described through their immunomodulatory actions. The maternal-fetal interface is considered to be immunosuppressed to allow development of the semi-allogeneic placental fetal unit. However, cytokine profiles of the decidua and different decidual cell types suggest that the in vivo situation might be more complex. Data suggest that decidual-derived cytokines not only play roles in immunosuppression, but also in other aspects of the establishment of pregnancy, including the regulation of trophoblast invasion and spiral artery remodelling. This review focuses on the potential role of decidua-derived cytokines in the aetiology of unexplained spontaneous miscarriage.

Trophoblast-derived exosomes mediate monocyte recruitment and differentiation

INTRODUCTION

trophoblast cells have been demonstrated to regulate monocyte migration and differentiation, leading to pro-inflammatory profiles. Because trophoblast cells release exosomes with immunoregulatory properties, trophoblast-derived exosomes are proposed to 'educate' monocytes, creating a pro-inflammatory environment.

METHOD OF STUDY

exosomes were isolated from conditioned media of Swan71 cells by ultrafiltration and ultracentrifugation. Exosome-induced migration was assessed using a two-chamber system. Cytokine profiles were defined using cytokine arrays, and mRNA levels of affected cytokines were examined by qRT-PCR and ELISA.

RESULTS

within 20 min, 8-10% of monocytes took up labeled exosomes isolated from Swan71 cells. Trophoblast-derived exosomes increased monocyte migration in a dose-dependent manner and produced significant increases in production of interleukin (IL)-1β, IL-6, Serpin-E1, granulocyte colony-stimulating factor, granulocyte/monocyte colony-stimulating factor, and tumor necrosis factor-α.

CONCLUSION

this study presents the initial demonstration that trophoblast-derived exosomes are capable of recruiting and 'educating' monocytes to produce pro-inflammatory cytokine/chemokine profiles in a cell-contact-independent manner.

A genomic and proteomic investigation of the impact of preimplantation factor on human decidual cells

OBJECTIVE

Preimplantation factor (PIF) is a novel, 15 amino acid peptide, secreted by viable embryos. This study aims to elucidate PIF's effects in human endometrial stromal cells (HESC) decidualized by estrogen and progestin, which mimics the preimplantation milieu, and in first-trimester decidua cultures (FTDC).

STUDY DESIGN

HESC or FTDC were incubated with 100 nmol/L synthetic PIF or vehicle control. Global gene expression was analyzed using microarray and pathway analysis. Proteins were analyzed using quantitative mass spectrometry, and PIF binding by protein array.

RESULTS

Gene and proteomic analysis demonstrate that PIF affects immune, adhesion, and apoptotic pathways. Significant up-regulation in HESC (fold change) include: nuclear factor-k-beta activation via interleukin-1 receptor-associated kinase binding protein 1 (53); Toll-like receptor 5 (9); FK506 binding protein 15, 133kDa protein (2.3); and Down syndrome cell adhesion molecule like 1 (16). B-cell lymphoma protein 2 was down-regulated in HESC (21.1) and FTDC (27.1). Protein array demonstrates PIF interaction with intracellular targets insulin-degrading enzyme and beta-K+ channels.

CONCLUSION

PIF displays essential multitargeted effects, of regulating immunity, promoting embryo-decidual adhesion, and regulating adaptive apoptotic processes.

Decidual leucocyte populations in early to late gestation normal human pregnancy

Most research on human decidual leucocytes to date has focused on the predominant CD56+ uterine natural killer (uNK) cell population in early pregnancy. Few reports have documented decidual leucocyte populations after 13 weeks gestation and in late pregnancy. Placental bed (decidua basalis) and non-placental bed (decidua parietalis) biopsies from normal pregnancies were taken from women undergoing termination of pregnancy in the 1st and 2nd trimesters and following Caesarean section in the 3rd trimester. Immunohistochemistry was used to quantify the numbers of decidual cells expressing CD56, CD3, CD8, CD94, NKG2A and CD14 and double labelled CD161+CD3+ NKT-like cells. Although a significant reduction in CD56+ uNK cells was found in 3rd trimester samples compared with 1st and 2nd trimester decidua, a substantial residual CD56+ leucocyte population was identified in 3rd trimester decidua. Expression of the KIR CD94/NKG2A mirrored that of CD56 at all gestational ages, providing an explanation for the absence of cytotoxic responses at the fetal-maternal interface. There was no difference in leucocyte populations between decidua basalis and decidua parietalis. Double immunohistochemical labelling revealed small numbers of decidual CD3+CD56+ and CD8+CD56+ cells, which decreased in number at term, and CD161+CD3+ cells, which increased in number at term. No differences in leucocyte populations were detected between decidua parietalis and decidua basalis. In contrast to previous reports, a substantial residual CD56+ cell population was demonstrated in 3rd trimester decidua. Decidual cytotoxic T-lymphocytes did not alter in number during gestation, while in contrast CD14+ macrophages decreased at term, representing the smallest decidual population assessed.

Priming of peripheral monocytes with prolactin (PRL) sensitizes IFN-gamma-mediated indoleamine 2,3-dioxygenase (IDO) expression without affecting IFN-gamma signaling

Prolactin (PRL) was originally identified by its ability to stimulate mammary development and lactation, and its essential roles other than lactation have recently been implicated in female reproduction. However, little is known about PRL-mediated events in pregnancy. The tryptophan catabolism enzyme indoleamine 2,3-dioxygenase (IDO) is interferon-gamma (IFN-gamma)-inducible and has recently become a focus for maternal-fetal tolerance for successful pregnancy. Based on recognition that PRL is one of the up-regulated hormones in pregnancy, in a previous study we have shown that PRL induces IDO expression in monocytes in cooperation with a suboptimal concentration of IFN-gamma. Here, we demonstrate that PRL sensitizes monocytes to induce IDO expression in response to low doses of IFN-gamma without affecting the typical IFN-gamma signaling events, such as STAT1 phosphorylation and IRF-1 induction. In addition, IDO induction in these cell cultures was observed only after 24 h pre-exposure to PRL. These results indicate a priming effect of PRL on monocytes that occurs before IFN-gamma signaling and increases their sensitivity to IFN-gamma for IDO induction, rather than a synergistic effect of PRL and IFN-gamma on IDO induction. These results offer new insights into the roles of PRL in female reproduction, as well as provide a better understanding as to how IDO expression is regulated and achieved in pregnancy.

Analysis of metallothionein, RCAS1 immunoreactivity regarding immune cell concentration in the endometrium and tubal mucosa in ectopic pregnancy during the course of tubal rupture

INTRODUCTION

Tubal rupture seems to be linked to a disturbance in maternal immune response and trophoblast cell invasion. The immunomodulating activity of endometrial cells is necessary for the coexistence of activated immune cells and endometrial cells. RCAS1 and metallothionein (MT) participate in this process.

MATERIAL AND METHODS

Tissue samples derived from fallopian tubes and endometrium were collected during one surgical procedure and divided into three groups: unruptured ectopic pregnancy (EP) without bleeding, unruptured EP with hemorrhage into the peritoneal cavity, and ruptured tubal pregnancy. Immunoreactivity of MT, RCAS1, CD56, CD3, CD69 and CD25 were assessed by immunohistochemical methods.

RESULTS

The number of CD3+ and CD56+ cells as well as CD69 antigen immunoreactivity in ruptured tubal mucosa of EP were statistically significantly higher than those measured for unruptured EP without bleeding, while at the same time the number of CD56+ cells in endometrium was statistically significantly lower. The growth of immune cell numbers in tubal mucosa during tubal rupture was not associated with an adequate MT and RCAS1 level.

CONCLUSION

Tubal perforation seems to be linked to a concentration of immune cells and a growth of their activity without an adequate increase of the level of proteins compensating for immune cell response.

Indoleamine-dioxygenase is expressed in human decidua at the time maternal tolerance is established

The semi-allogeneic fetus has to be tolerated by the maternal immune system. In mice, it has been shown that inhibiting indoleamine-dioxygenase (IDO) leads to fetal rejection, suggesting a central significance for IDO in establishing maternal tolerance. Consequently, we have analyzed IDO expression in human endometrium and decidua to determine whether it may be of significance in human reproduction. Endometrial (n=60) and decidual (n=68; first and second trimester) tissue samples and isolated cells were analyzed for IDO mRNA and protein expression by real-time PCR, Western blot and immunohistochemistry. IDO expression in the decidua of proven fertile women (n=34) was compared to women presenting with their first pregnancy (n=22) and women with a history of miscarriages (n=12). Expression of IDO was localized in glandular epithelial cells and scattered stromal leukocytes. Expression started at the mid-luteal phase in the menstrual cycle and was high until the second trimester of pregnancy. However, glandular expression of IDO decreased during the second trimester, whereas expression in villous trophoblast started at this time. There were no significant differences in decidual IDO expression between proven fertile women and women presenting with their first pregnancy or women with a history of miscarriages. From the expression pattern we conclude that IDO may play a central role in human pregnancies for the establishment of maternal tolerance of fetal antigens. Thereby, IDO expression may be needed in each pregnancy independently from prior pregnancies, and a history of miscarriage may not reflect a general deficiency in IDO expression.

Tubal abortions but not viable tubal pregnancies are characterized by an increased number of CD8 + T cells

OBJECTIVE

To examine immune cell phenotypes in viable tubal pregnancies (VTP) and in tubal abortions (TA).

METHODS

Paraffin-embedded specimens of VTP (n=7) and ongoing TA (n=6) were double-stained for cytokeratin for trophoblast as well as for CD45, CD3, CD8, CD68 and CD20 for immune cell phenotypes. In all cases, the amniotic sac was detected by ultrasound. Histological examination showed no evidence of necrosis within the tissues included in this study. Quantification of the subpopulations was performed in each slide by two independent examiners in five areas (0.085 mm2 each) of the invasion zone as marked by cytokeratin-positive stromal extravillous trophoblast (EVT) cells. For statistical analysis, the non-parametric two-tailed t-test was used (p<0.05).

RESULTS

The differences in the number of CD45(+), CD68(+) and CD20(+) cells was significant (p=0.0423, p=0.0469 and p=0.0494, respectively); however, the number of CD3(+), and among those the number of CD8(+) cells, was approximately eight-fold higher in TA than in VTP (p<0.0001 and p=0.0012, respectively).

CONCLUSION

The unequal distribution of CD8(+) cells in VTP and TA suggests a significant role of this immune cell phenotype in the further outcome of a tubal pregnancy either to an abortive or a viable, potentially life-threatening, entity.

Interferon-gamma inhibits extravillous trophoblast cell invasion by a mechanism that involves both changes in apoptosis and protease levels

BACKGROUND

Extravillous trophoblast cell (EVT) invasion of decidua and inner third of the myometrium is critical for a successful pregnancy. Many decidual factors are likely to play a role in regulating this process, including uterine natural killer (uNK) cell-derived cytokines.

HYPOTHESES

1) uNK cells are a major source of IFN gamma (IFN-gamma) and 2) IFN-gamma inhibits EVT invasion via an increase in EVT apoptosis and/or a decrease in active protease levels.

METHODS

Total decidual and uNK cells from 8-10 wk and 12-14 wk gestational age were cultured. IFN-gamma mRNA (real-time RT-polymerase chain reaction) and protein levels (FastQuant multicytokine analysis) were determined. EVT invasion in the presence of IFN-gamma or anti-IFN-gamma-neutralizing antibodies was assessed. Trophoblast apoptosis and proliferation was assessed in explants by immunohistochemistry for M30 and Ki67. Substrate zymography was performed to determine levels of secreted MMP2, MMP9, and uPA.

RESULTS

mRNA and protein for IFN-gamma was detected in both total decidual and uNK cell fractions. Trophoblast invasion was inhibited by IFN-gamma. The level of M30-positive EVT was increased in the presence of IFN-gamma whereas levels of secreted MMP2 were decreased.

CONCLUSIONS

uNK cells are a source of IFN-gamma within early human pregnancy decidua. Mechanisms of IFN-gamma inhibition of EVT invasion include both increased EVT apoptosis and reduced levels of active proteases.

Immunobiology of gestational trophoblastic diseases

Gestational trophoblastic diseases (GTDs) comprise a group of interrelated diseases characterized by development after gestation, widespread metastases, and high curability with chemotherapy. The good prognosis of GTDs is considered partly a result of the host immune response to paternal antigens expressed on trophoblastic cells. In this study, we review current understanding of the immunobiology of GTDs. First of all, we describe the microenvironment between trophoblastic cells and subpopulation of immune cells. Second, immunogenetics, immune microenvironment around abnormal trophoblast, and mechanism of GTDs escaping from maternal immune system surveillance were also discussed. Third, we propose the possible immunotherapy for persistent GTDs, particularly the vaccine designed on human chorionic gonadotrophin, which is generally accepted as a tumor marker for GTDs diagnosis. Due to the low incidence of GTDs and high response to chemotherapy, there have been few literatures about immunobiologic characteristics of GTDs compared with the other gynecologic malignancies, such as ovarian cancer, but the immunologic behavior of GTDs should be explored for further understanding of the etiology of these diseases and to help designing immunotherapeutic strategies for persistent GTDs.

Lack of site-specific production of decidual alpha-2 macroglobulin in human pregnancy

BACKGROUND

Alpha-2 Macroglobulin (A2M) is a protease inhibitor that is present in both human and rat decidual tissue. In mice, decidual A2M prevents excessive trophoblastic invasion; however, its role in human decidual tissue is unknown. It is possible that A2M may also influence trophoblast invasion in human pregnancy, which would be reflected in increased A2M production in decidua basalis. The aim of the current study was to determine and compare A2M production from first trimester human decidua basalis and decidua parietalis.

METHODS

Human decidual tissues were obtained from patients undergoing surgical termination at 9 to 12 gestational weeks. Strips of decidua basalis and decidua parietalis were obtained by uterine curettage under real-time ultrasound guidance. Tissue samples were fixed in 10% formalin or snap-frozen for immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, respectively. Protein and mRNA production between the two sites were compared using the Mann-Whitney U test.

RESULTS

Paired basal and parietal decidua were analyzed by immunohistochemistry (n = 9) and by RT-PCR (n = 10). There was no significant difference in A2M mRNA expression between decidua basalis and decidua parietalis (P = .5). Immunohistochemical staining intensity for A2M protein was significantly higher in basalis than in parietalis (P = .004), but the extent of positively stained cells were not significantly different (P = .051). Strong A2M staining in decidua basalis was mainly localized in the intracellular storage vesicles, which may suggest a role of A2M in this site.

CONCLUSIONS

We conclude that the expression pattern of A2M in human decidua basalis and decidua parietalis is not consistent with an important role of this gene during the observed gestational period. Contrary to its role in rodent implantation, A2M is probably not involved in regulating human implantation and trophoblastic invasion during this gestational window frame.

Th1/Th2 cytokines balance--yin and yang of reproductive immunology

For years conception of Th2 overbalance during pregnancy has been a paradigm for immunology of reproduction, while Th1 activity has been presented as unwanted component. Studies concerning Th1/Th2 balance in physiological and complicated pregnancy have been reviewed. Th1 activity during early peri-implantation period, premature and term labour not only accompanies but even predominates over Th2 activity. Th1 activity plays important role in promotion of Th2 response, regulation of placentation process, defense against infections and initiation of delivery. Together with Th2 activity it is necessary component of immunological reactions during pregnancy, both activities being inseparable like yin and yang. So paradigm of "Th1-Th2 cooperation" is much closer to reality than "Th2 phenomenon".

Metallothionein expression and infiltration of cytotoxic lymphocytes in uterine and tubal implantation sites

INTRODUCTION

In spite of increasing number of immune cells in the endometrium during the decidualization, the integrity of endometrial tissue in each menstrual cycle is maintained by adaptive changes in expression of several factors that regulate activity of immune cells and concomitant hormonal alterations during the menstrual cycle. This regulatory function of endometrium is also related to resistance to apoptosis, in which metallothionein (MT) may play a role.

MATERIALS AND METHODS

Study group included 26 women with spontaneous abortion and 18 patients with tubal ectopic pregnancy. Control group included 17 women whose endometrial tissue samples were taken during the normal secretory cycle phase. Expression of metallothionein (MT), CD56 and CD69 were assessed in tissue samples by immunohistochemistry.

RESULTS

The number of CD56-positive cells was significantly higher in women with ruptured than unruptured ectopics. MT expression was higher in tubal mucosa distant from the implantation site in ruptured compared to unruptured ectopics. It was found also to be significantly lower than in decidua taken from women with spontaneous abortion. CD69 expression was similar in women with spontaneous abortion as well as patients with ruptured ectopics compared to the control group. On the other hand, CD69 expression in unruptured ectopics was significantly lower than in women with spontaneous abortion and the control group.

CONCLUSION

The concentration of immune cells and increase of their activity in tubal mucosa, with insufficient protection against immune-mediated apoptosis assessed by MT expression, might result in tubal rupture during ectopic pregnancy.

Perforin and Fas/FasL Cytolytic Pathways at the Maternal-Fetal Interface

The immunogenetic enigma of maternal acceptance of the fetal semiallograft has been termed an immunological paradox. The first trimester decidua is heavily infiltrated with CD56(bright) CD16- uterine natural killer (uNK) cells which must be prepared to respond to potential pathogen challenges and still be able to control immune responses that allow the development of the fetus. The significant presence of cytolytic mediators, perforin and Fas/Fas ligand (FasL), at the maternal-fetal interface raises a question of their role(s) in the immunological interrelations between maternal tissues and trophoblast cells. As uNK cells in vitro lyse target cell lines (K562, P815 and P815Fas) using these effector molecules, it seems that, although immunocompetent, their cytotoxicity is not directed against trophoblast during normal pregnancy. Therefore, it is generally believed that the hormonal and Th1/Th2 cytokine balance plays an important role in the tolerance and maintenance of pregnancy. This paper gives an overview of the recent findings on the complex immunological events that occur at the maternal-fetal interface.

Human uterine natural killer cells: a reappraisal

The presence of granulated cells within the uterus of many species has been recognised for many years but only recently have these been recognised to be a type of NK cell. Various terms have been applied to the cells, including endometrial granulocyte, K cell and, in mouse and rat, granulated metrial gland cell. Although early studies are often based on histology and electron microscopy, these often include important information for current studies. In vitro studies of purified cells have focused particularly on cytotoxicity and cytokine production and roles in the control of trophoblast invasion and spiral artery remodelling in human pregnancy have been proposed. Evidence in mouse has implicated uNK cell production of IFN-gamma in vascular remodelling but evidence for such a role for human uNK cells remains to be established. Investigation of uNK cells in human pregnancy is hampered by the lack of availability of tissues from the first half of the second trimester of pregnancy when vascular remodelling occurs and also by possible differences between cells from different regions of decidua. The presence of similar cells in species with no trophoblast invasion into the uterus and epitheliochorial placentation raises the question of whether control of trophoblast invasion by human uNK cells is important in vivo and raises the possibility of another function which is conserved between species.

Inhibition of Cytotrophoblastic (JEG-3) Cell Invasion by Interleukin 12 Involves an Interferon γ-mediated Pathway

Trophoblast invasion, like tumor invasion, shares common biochemical mechanisms. However, in contrast to tumor invasion of a host tissue, trophoblastic invasion during implantation is strictly regulated, temporospatially. Factors responsible for these important regulatory processes are presently unknown; however, studies indicate that cytokines and growth factors represent in the peri-implantation uterine milieu as the possible candidates. In this study we investigated the role of interleukin (IL) 12 in regulating trophoblast invasion and the expression of trophoblast proteases (matrix metalloprotease (MMP)-2, MMP-9, and urokinase-type plasminogen activators) and their inhibitors (tissue inhibitors of metalloprotease (TIMP) 1, TIMP-2, and plasminogen activator inhibitor (PAI)-1) using an in vitro tissue culture system of human choriocarcinoma cell line JEG-3. Our major findings show an anti-invasive role of IL-12, associated with an inhibitory effect on the proteases but with an opposite up-regulating influence on the protease inhibitor, TIMP-1, whereas TIMP-2 and plasminogen activator inhibitor 1 remained unaltered. Stimulation of JEG-3 cells with IL-12 also induced interferon (IFN)-gamma production, which when neutralized using a monoclonal anti-IFN-gamma antibody, F12, abrogates its ability to down-regulate the MMPs. IL-12 also mediates an IFN-gamma-dependent up-regulation of E-cadherin, thereby implying that alteration in cell-cell adhesion besides regulating the proteases and the inhibitors possibly contributes to the observed anti-invasive role of this cytokine. TIMP-1, although stimulated by IL-12, was found to be unaltered by antibody F12, thereby implying a possibility of an IL-12-dependent-IFN-gamma independent regulation. These findings thereby suggest an important role of IL-12 in modulation of trophoblast proteases and their inhibitors besides regulating cell-cell interactions and invasion during implantation, with far reaching possibilities for understanding the mechanism(s) and regulations of invasion and metastasis.

Interleukin-11 expression: its significance in eutopic and ectopic human implantation

Embryo implantation and subsequent decidualization, trophoblast invasion and formation of a functional placenta are crucial for establishment and maintenance of pregnancy. Interleukin-11 signalling has been shown to be obligatory for adequate decidualization and trophoblast invasion in mice. Defects in IL-11 signalling in mice result in trophoblast over-invasion and fetal loss. The pathological situation of human tubal pregnancy resembles that of IL-11Ralpha(-/-) mice concerning these symptoms. As our interest is focused on the human early pregnancy, we compared IL-11 expression at the implantation site of ectopic tubal pregnancy (EP) to 1st and 2nd trimester of normal intrauterine pregnancies (IP), and to the normal cycling endometrium. The mRNA expression of IL-11 and IL-11Ralpha was analysed by semiquantitative RT-PCR. Protein expression was detected by western blotting and immunohistochemistry. IL-11Ralpha is expressed constitutively in all tissue specimens analysed. IL-11 is expressed predominantly during follicular and early luteal phase of the menstrual cycle. In IP, IL-11 expression peaks during the 1st trimester and declines from the beginning of the 2nd trimester onwards. In tubal abortions, IL-11 expression is reduced in comparison to vital EP and IP. Cultured primary endometrial and decidual epithelial cells were analysed for hormonal regulation of IL-11 by enzyme-linked immunosorbent assay and RT-PCR. IL-11 is up-regulated by estrogen and down-regulated by progesterone. Overall, our results indicate that in humans, IL-11 signalling is significantly involved in regulation of trophoblast invasion. In the case of tubal abortion, inadequate IL-11 signalling may therefore result in dysregulation of trophoblast invasion.

Macrophages and apoptotic cell clearance during pregnancy

BACKGROUND

During implantation, apoptosis is critical for the appropriate tissue remodeling of the maternal decidua and invasion of the developing embryo, yet the regulation of apoptosis is also imperative for a successful pregnancy. The quick and effective removal of apoptotic cells by tissue macrophages represents an essential process, which prevents the release of self-antigens, and in the case of pregnancy, paternal alloantigens.

METHODS OF STUDY

Recent studies have shown that the process of apoptotic cell clearance is not a neutral event, but rather an active one that induces macrophage production of anti-inflammatory cytokines and survival factors. Apoptotic cell clearance is, therefore, necessary for the resolution of inflammatory conditions, which during pregnancy could have lethal consequences.

CONCLUSIONS

The function of the maternal immune system during implantation and throughout pregnancy is, therefore, an important area of investigation. This review will discuss the role of decidual macrophages in apoptotic cell clearance during pregnancy.

Apoptosis of extravillous trophoblast cells limits the trophoblast invasion in uterine but not in tubal pregnancy during first trimester

During the first trimester of pregnancy extravillous trophoblast cells (EVT) invade the maternal decidua. Invasion normally is reduced from the second trimester onwards and stops in the inner third of the myometrium. By contrast, in extrauterine tubal pregnancy, trophoblast invasion may even penetrate the tubal wall, which ultimately leads to the rupture of the fallopian tube. Induction of apoptosis of EVT cells, by maternal immune competent cells, may be an important mechanism to limit EVT invasion in uterine pregnancy. Tissue specimens from first and second trimester uterine pregnancy and first trimester tubal pregnancy were analyzed for apoptosis by TUNEL- and M30-staining. By immunohistochemical double labelling, maternal leukocyte subtypes were co-localized to apoptotic cells and in this context, the number of CD56(+)NK cells was analyzed. Our data show that apoptosis is confined to the decidua basalis. Most apoptotic cells are single cytokeratin-positive epithelial cells residing in the stromal compartment. Consequently these cells can only be EVT cells. Maternal leukocytes are not apoptotic. They are located in close contact to apoptotic cells. The number of apoptotic cells in the second trimester (1.8+/-0.7 per cent) is reduced compared to first trimester (5.6+/-0.7 per cent) of uterine pregnancy. In parallel, the number of NK cells declines from first (24.4+/-2.9) to second (12.4+/-1.8) trimester. Furthermore, apoptosis is significantly reduced in ectopic (0.9+/-0.3 per cent) compared to eutopic first trimester pregnancies. Consequently, we suggest that in first trimester uterine pregnancy, induction of EVT cell apoptosis by the maternal immune system is one mechanism to limit EVT invasion. During the second trimester, in parallel to declining numbers of NK cells, the mechanism changes. However, in tubal pregnancy due to differing immunological microenvironments at the ectopic implantation site, apoptosis induction fails, which deleteriously may result in uncontrolled invasion and penetration of the tubal wall.

Potential role of macrophages as immunoregulators of pregnancy

The role of the maternal immune system during pregnancy has focused mainly on the aspect of immune tolerance to the invading trophoblast and, therefore, fetus. While this is a critical aspect of reproductive immunology, it is also important to consider the function of the maternal immune system in the promotion of implantation and maintenance of pregnancy. Apoptosis or cell death is not the final stage in tissue development. The quick and effective removal of apoptotic cells by tissue macrophages represents a vital process preventing "leak" of self-antigens and promoting the production of proliferative/survival factors. One of the key requirements of apoptotic cell clearance is the resolution of inflammatory conditions, which, as in the case of pregnancy, may have lethal consequences. This review will focus on decidual macrophages and their role on apoptosis and cell clearance during pregnancy.

Embryo-maternal signalling: how the embryo starts talking to its mother to accomplish implantation

The process of implantation and trophoblast invasion is currently considered as the most limiting factor for the establishment of pregnancy. Molecular interactions at the embryo-maternal interface during the time of adhesion and subsequent invasion are crucial to the process of embryonic implantation. Both partners, the mother as well as the embryo, play equal roles in the embryo-maternal dialogue, the embryonic part being the main topic in this study. Investigations of the proteins in the extra-embryonic matrices (i.e. zona pellucida) indicate that the embryo participates intensively in this early embryo-maternal signalling. One unique feature during implantation process of primate embryos is the release of chorionic gonadotrophin, which seems to influence endometrial activity by two different mechanisms: (i) luteotrophic activity with increasing progesterone release and (ii) a direct action on the endometrium. Furthermore, embryonic interleukin-1beta may be involved in embryo-maternal signalling. Other significant signals in this interaction are most likely leukaemia inhibitory factor (LIF) and colony-stimulating factor (CSF), which stimulate matrix metalloproteinase (MMP)/insulin-like growth factor binding protein-1 (IGFBP-1) activity and the insulin-like growth factor (IGF) system, which is modulated by embryonic IGFBP-3. Similar significances are discussed for uteroglobin and haptoglobin. Finally, the phenomenon of maternal immunological tolerance, triggered by the presence of the early embryo, is fundamental to the understanding of implantation and trophoblast invasion. A tightly regulated balance between activated and inactivated T cells at the implantation site may control the beginning of adequate trophoblast invasion and also limit this invasion to a tolerable extent for the maternal system, consequently ensuring a biologically healthy haemo-chorial placenta.