Placenta-derived interferon-stimulated gene 20 controls ZIKA virus infection

Zika virus is a positive-sense single-stranded RNA virus, which can be transmitted across the placenta and has adverse effects on fetal development during pregnancy. The severity of these complications highlights the importance of prevention and treatment. However, no vaccines or drugs are currently available. In this study, we characterize the IFNβ-mediated anti-viral response in trophoblast cells in order to identify critical components that are necessary for the successful control of viral replication and determine whether components of the IFN-induced response can be used as a replacement therapy for ZIKA virus infection during pregnancy. We identify and characterize interferon-stimulated gene 20 (ISG20) as playing a central role in controlling Zika virus infection in trophoblast cells and successfully establish a recombinant ISG20-Fc protein that effectively decreases viral titers in vitro and in vivo by maintaining its exonuclease activity and displaying potential immune modulatory functions. Recombinant ISG20-Fc has thus the potential to be further developed as an anti-viral treatment against ZIKA viral infection in high-risk populations, particularly in pregnant women.

Peri-implantation cytokine profile differs between singleton and twin IVF pregnancies

PROBLEM

It is unknown whether maternal cytokine production differs between twin and singleton gestations in the implantation phase. A difference in maternal serum cytokine concentrations in twins would imply a dose-response to the invading embryos, as opposed to a general immune reaction.

METHOD OF STUDY

A prospective longitudinal cohort of women aged 18-45 at an academic fertility center undergoing in vitro fertilization and embryo transfer (IVF-ET) underwent routine collection of serial serum samples starting 9 days after ET and then approximately every 48 hours thereafter. Cryopreserved aliquots of these samples were assayed for interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-α), and C-X-C motif chemokine ligand 10 (CXCL10) using the SimplePlex immunoassay platform. Pregnancies were followed until delivery. Serial measures of serum concentrations of IL-10, CXCL10, and TNF-α in singleton or di-di twin pregnancies from 9 to 15 days after IVF-ET were compared.

RESULTS

Maternal serum levels of CXCL10 are significantly lower in women with di-di twin pregnancies in early implantation compared to those with singleton gestation (day 9-11, P = .02). Serum levels of TNF-α and IL-10 were comparable at all studied time points (P > .05).

CONCLUSION

Maternal serum levels of CXCL10 are significantly lower in the earliest implantation phase in di-di twins compared to singleton conceptions. Given the known anti-angiogenic role of CXCL10, we hypothesize that lower CXCL10 levels in twin implantations allow an environment that is conducive for the greater vascularization required for the establishment of dual placentation in di-di twins.

Establishment and characterization of a new human first trimester Trophoblast cell line, AL07

INTRODUCTION

The limited cell number of primary trophoblasts and contamination of trophoblast cell lines promote us to develop a novel stable trophoblast cell line.

METHOD OF STUDY

Primary trophoblast cells were isolated from first-trimester placenta and telomerase-induced immortalization was used to immortalize these cells. Subsets of cells were then evaluated by flow cytometry using CK7, HLA-G, CD45 and CD14, specific markers for trophoblast cells, extra-villous trophoblast, pan leucocyte and monocyte/macrophage, respectively. Immunofluorescence staining and immunocytochemistry were used to detect CK7 expression in trophoblast cells. The level of secreted human Chorionic Gonadotropin (hCG) was measured by electrochemiluminescence (ECL). The Bio-Plex MAGPIX System was used to analyze the cytokines and chemokines produced by AL07 cell line.

RESULTS

We were able to isolate primary trophoblast cells from several first-trimester placentas. One clone, AL07 trophoblast cells, isolated from a week 7 placenta, was morphologically stable and positive for the expression of CK7 by immunofluorescence and immunocytochemistry staining. Characterization of AL07 cells reveled that they are CD45 or CD14 negative and had constitutive secretion of hCG and low HLA-G expression. Furthermore, clone AL07 secret high levels of several cytokines and chemokines, including IL-6, IL-8 and VEGF, and moderately secreted MCP-1 IP-10 and RANTES.

DISCUSSION

We report the successful isolation, immortalization and characterization of AL07 cells, a novel cell clone isolated from first trimester human placenta. The clone is free of contamination of immune cells, and exhibits similar cytokine profile as other trophoblast cell lines. This new cytotrophoblast-like AL07 cell, can be a valuable tool for in-vitro trophoblast studies in the future.

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

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

Viral infection dampens human fetal membrane type I interferon responses triggered by bacterial LPS

The maternal-fetal interface possesses innate immune strategies to protect against infections. We previously reported that prior viral infection of human fetal membranes (FMs) in vitro and mouse FMs in vivo sensitized the tissue to low dose bacterial LPS leading to augmented inflammation. The objective of this study was to examine FM production of type I interferons (IFNs) and IFN-stimulated genes (ISGs) in the context of this polymicrobial model. Human FM explants and pregnant C57BL/6 mice were treated with or without low dose LPS following exposure to media or the γ-herpes virus, MHV-68. FM RNA was analyzed by qRT-PCR for type I IFNs, ISGs, upstream signaling, and MHV-68 open reading frames (ORFs). Pre-exposure to MHV-68 followed by LPS treatment inhibited the ability of LPS to induce human FM type I IFNs (IFNA, IFNB); ISGs (OAS, MxA, APOBEC3G) and upstream signaling mediators (RIG-I, TBK-1). Signaling mediators IRF-3 and IRF-7 were also reduced. In mouse FMs, pre-exposure to MHV-68 followed by LPS treatment reduced the ability of LPS to upregulate Ifna, Ifnb, Mxa, Irf7, and also reduced Irf3. MHV-68 infection of FMs induced ORF45 which targets IRF-7, and this was further augmented in response to a combination of MHV-68 and LPS. Together, these findings indicate that a viral infection blunts FM type I IFN production and signaling in response to LPS leading to a suppressed ISG response. Our studies suggest that a viral infection inhibits this protective FM response by negatively regulating IRF-7 through ORF45, leaving the maternal-fetal interface vulnerable to further viral attack.

Human Chorionic Gonadotropin modulates CXCL10 Expression through Histone Methylation in human decidua

The process of implantation, trophoblast invasion and placentation demand continuous adaptation and modifications between the trophoblast (embryonic) and the decidua (maternal). Within the decidua, the maternal immune system undergoes continued changes, as the pregnancy progress, in terms of the cell population, phenotype and production of immune factors, cytokines and chemokines. Human chorionic gonadotropin (hCG) is one of the earliest hormones produced by the blastocyst and has potent immune modulatory effects, especially in relation to T cells. We hypothesized that trophoblast-derived hCG modulates the immune population present at the maternal fetal interface by modifying the cytokine profile produced by the stromal/decidual cells. Using in vitro models from decidual samples we demonstrate that hCG inhibits CXCL10 expression by inducing H3K27me3 histone methylation, which binds to Region 4 of the CXCL10 promoter, thereby suppressing its expression. hCG-induced histone methylation is mediated through EZH2, a functional member of the PRC2 complex. Regulation of CXCL10 expression has a major impact on the capacity of endometrial stromal cells to recruit CD8 cells. We demonstrate the existence of a cross talk between the placenta (hCG) and the decidua (CXCL10) in the control of immune cell recruitment. Alterations in this immune regulatory function, such as during infection, will have detrimental effects on the success of the pregnancy.

IL-10 to TNFα ratios throughout early first trimester can discriminate healthy pregnancies from pregnancy losses

PROBLEM

Embryo implantation and placentation require a careful immunological balance. Cytokines such as IL-10 and TNFα have been implicated as markers of dysregulation, but have only been studied at a single time point or after a pregnancy loss. Our objective was to determine normative patterns of serum levels of IL-10 and TNFα and their ratio throughout the first trimester in healthy pregnancies and to determine if this pattern differs from pregnancy loss.

METHOD OF STUDY

Two prospective longitudinal cohorts of gravidae including in vitro fertilization (IVF) and naturally conceived pregnancies with serial blood draws. Cytokines were assayed using Simple Plex. In the IVF cohort, we monitored from the implantation day up to 6 weeks of gestation; whereas in the naturally conceived cohort, sample collection began at 4 weeks and throughout the whole first trimester.

RESULTS

IL-10 concentrations in normal pregnancies were significantly higher than in pregnancies ending in a loss starting at 6-8 weeks of gestation, while TNFα concentrations were significantly lower in normal than in pregnancies ending in a loss starting at 3-5 of gestation weeks. The IL-10 to TNFα ratio in normal pregnancies was significantly higher from 4 to 9 weeks compared to pregnancies that were lost (t test, P < .05). Changes were observed before any symptoms of miscarriage were present.

CONCLUSION

We provide evidences of differences in early immunomodulation in healthy pregnancies vs those destined to end in first-trimester loss. The ratio of IL-10 to TNFα rises significantly higher in viable pregnancies as early as 4.5 weeks compared to pregnancies loss.

Trophoblasts promote induction of a regulatory phenotype in B cells that can protect against detrimental T cell-mediated inflammation

PROBLEM

A successful outcome to pregnancy is critically dependent on the initiation of maternal immune tolerance before embryo implantation. Cells of embryonic origin that come in contact with the uterine microenvironment can exert influence over the phenotype and function of immune cells to facilitate robust implantation; however, what influence they may have on B cells remains unknown. In this study, we investigate the effect of human trophoblast cells on B-cell phenotype and the subsequent effect on peri-implantation events.

METHOD OF STUDY

We cultured purified human B cells with the first-trimester human trophoblast cell line Swan 71 to investigate trophoblast-B-cell interactions and utilized trophoblast spheroids in an in vitro implantation model of migration and invasion.

RESULTS

Trophoblast-educated B cells or TE-B cells were found to consist of B cells in committed lineages such as plasmablasts and memory B cells, as well as increased proportions in subsets of CD24^hi CD27⁺ regulatory B cells and CD19⁺ IL-10⁺ B cells. Conditioned media from the TE-B cells showed reduced production of pro-inflammatory cytokines that influenced the T-cell proliferation and cytokine production. Using trophoblast spheroids, we assessed the role of TE-B cells in trophoblast invasion and migration. Our results demonstrate a protective effect of TE-B-conditioned media against deleterious inflammation as evidenced by survival of the trophoblast spheroid in the presence of an immune assault and promotion of a migratory phenotype.

CONCLUSION

We posit that trophoblast-mediated education of B cells leads to their acquisition of properties capable of modulating inflammation in the uterine environment during the peri-implantation period.

Viral Infection Sensitizes Human Fetal Membranes to Bacterial Lipopolysaccharide by MERTK Inhibition and Inflammasome Activation

Chorioamnionitis, premature rupture of fetal membranes (FMs), and subsequent preterm birth are associated with local infection and inflammation, particularly IL-1β production. Although bacterial infections are commonly identified, other microorganisms may play a role in the pathogenesis. Because viral pandemics, such as influenza, Ebola, and Zika, are becoming more common, and pregnant women are at increased risk for associated complications, this study evaluated the impact that viral infection had on human FM innate immune responses. This study shows that a herpes viral infection of FMs sensitizes the tissue to low levels of bacterial LPS, giving rise to an exaggerated IL-1β response. Using an ex vivo human FM explant system and an in vivo mouse model of pregnancy, we report that the mechanism by which this aggravated inflammation arises is through the inhibition of the TAM receptor, MERTK, and activation of the inflammasome. The TAM receptor ligand, growth arrest specific 6, re-establishes the normal FM response to LPS by restoring and augmenting TAM receptor and ligand expression, as well as by preventing the exacerbated IL-1β processing and secretion. These findings indicate a novel mechanism by which viruses alter normal FM immune responses to bacteria, potentially giving rise to adverse pregnancy outcomes.

The unique immunological and microbial aspects of pregnancy

The comparison of the immunological state of pregnancy to an immunosuppressed host-graft model continues to lead research and clinical practice to ill-defined approaches. This Review discusses recent evidence that supports the idea that immunological responses at the receptive maternal-fetal interface are not simply suppressed but are instead highly dynamic. We discuss the crucial role of trophoblast cells in shaping not only the way in which immune cells respond to the invading blastocyst but also how they collectively react to external stimuli. We also discuss the role of the microbiota in promoting a tolerogenic maternal immune system and highlight how subclinical viral infections can disrupt this status quo, leading to pregnancy complications.

Cutting Edge: Fetal/Placental Type I IFN Can Affect Maternal Survival and Fetal Viral Load during Viral Infection

Pregnant women have greater mortality and complications associated with viral infections compared with the general population, but the reason for the increased susceptibility is not well defined. Placenta type I IFN is an important immune modulator and protects the pregnancy. We hypothesized that loss of placental IFN affects the regulation of the maternal immune system, resulting in the differential response to infections observed in pregnancy. Pregnant mice lacking the IFN-α/β receptor (IFNAR) became viremic and had higher mortality compared with nonpregnant animals. Notably, an embryo with functional IFN signaling alone was sufficient to rescue the pregnant IFNAR^-/- dam from virus-associated demise. Placental IFN was also an important regulator of viral replication in placental tissue and significantly affected viral transmission to the fetus. These findings highlight the role of fetal/placental IFN in the modulation of viral infection in the mother and fetus.

HSV-2 enhances ZIKV infection of the placenta and induces apoptosis in first-trimester trophoblast cells

PROBLEM

Zika virus (ZIKV) has gained public concern for its association with microcephaly in infants born to ZIKV-infected mothers. To reach the fetus the virus must overcome the defense mechanisms provided by trophoblast cells. Additionally, in the first trimester, the integrity of the placenta is critical for fetal protection as damage to differentiating trophoblast can affect placental formation and function. We sought to investigate the effect of ZIKV infection on trophoblast cells and the factors that might increase the risk for ZIKV infection during pregnancy.

METHODS

First-trimester human trophoblast cells, Swan 7.1, were infected with ZIKV, herpes simplex virus-2 (HSV-2), and yellow fiver (YFV). C57BL/6 pregnant mice were infected with HSV-2, ZIKV, or coinfection. Placental viral titers were determined by RT-PCR.

RESULTS

ZIKV infection induces apoptosis in first-trimester trophoblasts and prevents differentiation of these cells. Furthermore, HSV-2 infection enhances placental sensitivity to ZIKV by enhancing the expression of TAM receptors, which facilitate ZIKV cell entry.

CONCLUSION

These findings may explain the mechanism by which ZIKV breaches the placental barrier to access the fetus. Furthermore, our results suggest that patients with HSV-2 infection are at a higher risk for the teratogenic effects induced by ZIKV.

Simple Plex(™) : A Novel Multi-Analyte, Automated Microfluidic Immunoassay Platform for the Detection of Human and Mouse Cytokines and Chemokines

Problem

Quantitative measurement of proteins in bodily fluids or cellular preparations is critical for the evaluation of biomarkers or the study of complex cellular processes. While immunoassays are the most common quantitative approach used so far, they are not practical for the evaluation of multiple proteins. Microfluidic technology allows a fine spatial control in immobilizing proteins and biomolecules inside microchannels, eliminating cross‐reactivity between competing analytes, and allowing rapid and sensitive detection of targeted antigens for multiple applications. We report the characterization and validation of the Simple Plex^™ platform for the detection and quantification of cytokines and chemokines from human and mouse samples.

Method

Cytokine and chemokine expression levels were determined using Simple Plex cartridges from ProteinSimple. Serum samples were obtained from the Yale Biorepository.

Results

Our data demonstrate an excellent correlation between the results obtained with Simple Plex and conventional immunoassays such as ELISA and Luminex.

Conclusion

We describe the characterization and validation of Simple Plex, a novel multi‐analyte, automated microfluidic platform that allows the evaluation of cytokines and chemokines from human and mice biological samples. Simple Plex showed significant advantages over traditional approaches in terms of low sample volume requirements, sensitivity and dynamic range, coefficient of variation, and reproducibility.

Type I Interferon Regulates the Placental Inflammatory Response to Bacteria and is Targeted by Virus: Mechanism of Polymicrobial Infection-Induced Preterm Birth

PROBLEM

Preterm birth (PTB) affects approximately 12% of pregnancies and at least 50% of cases have no known risk factors. We hypothesize that subclinical viral infections of the placenta are a factor sensitizing women to intrauterine bacterial infection. Specifically, we propose that viral-induced placental IFN-β inhibition results in a robust inflammatory response to low concentrations of bacteria.

METHODS

Human trophoblast SW.71, C57BL/6, and interferon (IFN) receptor knockout animals were used to determine IFN function. Illumina and Bio-Rad microarrays identified pathways.

RESULTS

Inhibiting the IFN-β pathway resulted in a significant increase in inflammatory cytokines such as IL-1B in response to LPS. Twist was positively correlated with IFN-β expression and STAT3 phosphorylation and overexpressing Twist reduced IL-1B. Treating IFNAR-/- mice with low-dose LPS at E15.5 caused preterm birth.

CONCLUSION

IFN-β was identified as a key modulator of placental inflammation and, importantly, is commonly affected by viruses. We propose dysregulation of IFN-β is a major determinant for preterm birth associated with polymicrobial infection.

Biopsy-induced inflammatory conditions improve endometrial receptivity: the mechanism of action

A decade ago, we first reported that endometrial biopsy significantly improves the success of pregnancy in IVF patients with recurrent implantation failure, an observation that was later confirmed by others. Recently, we have demonstrated that this treatment elevated the levels of endometrial pro-inflammatory cytokines and increased the abundance of macrophages (Mac) and dendritic cells (DCs). We therefore hypothesised that the biopsy-related successful pregnancy is secondary to an inflammatory response, and aimed at deciphering its mechanism of action. Supporting our hypothesis, we found that the pro-inflammatory TNFα stimulated primary endometrial stromal cells to express cytokines that attracted monocytes and induced their differentiation into DCs. These monocyte-derived DCs stimulated endometrial epithelial cells to express the adhesive molecule SPP1 (osteopontin (OPN)) and its receptors ITGB3 and CD44, whereas MUC16, which interferes with adhesion, was downregulated. Other implantation-associated genes, such as CHST2, CCL4 (MIP1B) and GROA, were upregulated by monocyte-derived Mac. These findings suggest that uterine receptivity is mediated by the expression of molecules associated with inflammation. Such an inflammatory milieu is not generated in some IVF patients with recurrent implantation failure in the absence of local injury provoked by the biopsy treatment.

Understanding the complexity of the immune system during pregnancy

Progress in our understanding of the role of the maternal immune system during healthy pregnancy will help us better understand the role of the immune system in adverse pregnancy outcomes. In this review, we discuss our present understanding of the 'immunity of pregnancy' in the context of the response to cervical and placental infections and how these responses affect both the mother and the fetus. We discuss novel and challenging concepts that help explain the immunological aspects of pregnancy and how the mother and fetus respond to infection.

Human chorionic gonadotropin enhances trophoblast-epithelial interaction in an in vitro model of human implantation

Embryo implantation, which is an absolute requirement for reproduction, starts with blastocyst apposition to the uterine endometrium, followed by attachment to the endometrial surface epithelium. Recent clinical studies reported an increase in implantation and pregnancy rates among women receiving intrauterine human chorionic gonadotropin (hCG) prior to embryo transfer suggesting that, at least in some cases, female infertility is a result of inadequate secretion of hCG. In this study, we characterized the effect of hCG on trophoblast-epithelial interaction by further developing our recently described in vitro model of implantation. Here, we confirmed hCG increased attachment of trophoblast to epithelial cells, using a single-cell trophoblast-epithelial coculture system in addition to a blastocyst-like spheroid-epithelial coculture system. Furthermore, we discovered that the source and concentration was pivotal; the first preparation of hCG affected 2 molecules related to implantation, MUC16 and osteopontin, while the second preparation required additional cytokines to mimic the effects. Using this system, we can develop a comprehensive knowledge of the cellular and gene targets of hCG and other factors involved in embryo apposition and implantation and potentially increase the number of therapeutic targets for subfertile patients.

Viral infection of the pregnant cervix predisposes to ascending bacterial infection

Preterm birth is the major cause of neonatal mortality and morbidity, and bacterial infections that ascend from the lower female reproductive tract are the most common route of uterine infection leading to preterm birth. The uterus and growing fetus are protected from ascending infection by the cervix, which controls and limits microbial access by the production of mucus, cytokines, and antimicrobial peptides. If this barrier is compromised, bacteria may enter the uterine cavity, leading to preterm birth. Using a mouse model, we demonstrate, to our knowledge for the first time, that viral infection of the cervix during pregnancy reduces the capacity of the female reproductive tract to prevent bacterial infection of the uterus. This is due to differences in susceptibility of the cervix to infection by virus during pregnancy and the associated changes in TLR and antimicrobial peptide expression and function. We suggest that preterm labor is a polymicrobial disease, which requires a multifactorial approach for its prevention and treatment.

TLR2 enhances ovarian cancer stem cell self-renewal and promotes tumor repair and recurrence

Primary ovarian cancer is responsive to treatment, but chemoresistant recurrent disease ensues in majority of patients. Recent compelling evidence demonstrates that a specific population of cancer cells, the cancer stem cells, initiates and sustains tumors. It is therefore possible that this cell population is also responsible for recurrence. We have shown previously that CD44+/MyD88+ epithelial ovarian cancer stem cells (CD44+/MyD88+ EOC stem cells) are responsible for tumor initiation. In this study, we demonstrate that this population drives tumor repair following surgery- and chemotherapy-induced tumor injury. Using in vivo and in vitro models, we also demonstrate that during the process of tumor repair, CD44+/MyD88+ EOC stem cells undergo self-renewal as evidenced by upregulation of stemness-associated genes. More importantly, we show that a pro-inflammatory microenvironment created by the TLR2-MyD88-NFκB pathway supports EOC stem cell-driven repair and self-renewal. Overall, our findings point to a specific cancer cell population, the CD44+/MyD88+ EOC stem cells and a specific pro-inflammatory pathway, the TLR2-MyD88-NFκB pathway, as two of the required players promoting tumor repair, which is associated with enhanced cancer stem cell load. Identification of these key players is the first step in elucidating the steps necessary to prevent recurrence in EOC patients.

Modulation and recruitment of inducible regulatory T cells by first trimester trophoblast cells

PROBLEM  The specialized regulatory T-cells (Treg) population, essential for maternal tolerance of the fetus, performs its suppressive actions in the critical peri-implantation phase of pregnancy. In the present work, we investigated whether trophoblast cells are able to induce Treg recruitment, differentiation, and whether these mechanisms are modified by a bacterial or viral infection. METHOD OF STUDY  Human T-regulatory cells were differentiated from naïve CD45RA(+) CCR7(+) cells obtained from peripheral blood mononuclear cells cultured with IL-2 and TGFβ over 5 days. Induction of iTregs (CD4(+)  Foxp3(+) cells) was evaluated using low serum conditioned media (LSCM), obtained from two first trimester trophoblast cell lines, Swan-71 and HTR8. Coculture experiments were carried out using transwell assays where trophoblast cells were in the absence or presence of PGN, LPS, or Poly [I:C]. Cytokine production was measured by multiplex analysis. RESULTS  Trophoblast cells constitutively secrete high levels of TGFβ and induced a significant increase of Foxp3 expression accompanied by a specific T-reg cytokine profile. Moreover, trophoblast cells were able to recruit iTregs in a specific manner. CONCLUSION  We demonstrate that trophoblast cells have an active role on the recruitment and differentiation of iTregs, therefore, contributing to the process of immune regulation at the placental-maternal interface.

Placental viral infection sensitizes to endotoxin-induced pre-term labor: a double hit hypothesis

PROBLEM

Among pregnant women, acquired viral infections with a concurrent bacterial infection is a detrimental factor associated to poor prognosis. We evaluate the effect of a viral infection that does not lead to pre-term labor on the response to low doses of lipopolysaccharide (LPS). Our objectives were (i) to characterize the effect of a viral infection concurrent with exposure to microbial products on pregnancy outcome and (ii) to characterize the placental and fetal immune responses to the viral sensitization to LPS.

METHOD

C57B/6 wild-type mice were injected with murine gammaherpesvirus 68 (MHV68) at E8.5. Either PBS or LPS was injected i.p. at E15.5. Pregnancy outcome and cytokine/chemokine profile from implantation sites were analyzed by multiplex.

RESULTS

LPS treatment of MHV-68-infected animals induced pre-term delivery and fetal death in 100% of the mice. Pre-term labor was characterized by a upregulation of pro-inflammatory cytokines and chemokines in both placenta and decidua. Similar profiles were observed from MHV-68-infected human primary trophoblast and trophoblast cell lines in response to LPS.

CONCLUSION

We describe for the first time that a sub-clinical viral infection in pregnant mice might sensitize to a bacterial infection leading to pre-term delivery. We propose the 'Double Hit Hypothesis' where the presence of a viral infection enhances the effect of bacterial products during pregnancy leading not only to pre-term labor but likely larger adverse outcomes.

Viral infection of the placenta leads to fetal inflammation and sensitization to bacterial products predisposing to preterm labor

Pandemics pose a more significant threat to pregnant women than to the nonpregnant population and may have a detrimental effect on the well being of the fetus. We have developed an animal model to evaluate the consequences of a viral infection characterized by lack of fetal transmission. The experiments described in this work show that viral infection of the placenta can elicit a fetal inflammatory response that, in turn, can cause organ damage and potentially downstream developmental deficiencies. Furthermore, we demonstrate that viral infection of the placenta may sensitize the pregnant mother to bacterial products and promote preterm labor. It is critical to take into consideration the fact that during pregnancy it is not only the maternal immune system responding, but also the fetal/placental unit. Our results further support the immunological role of the placenta and the fetus affecting the global response of the mother to microbial infections. This is relevant for making decisions associated with treatment and prevention during pandemics.

Phagocytosis of apoptotic trophoblast cells by human endometrial endothelial cells induces proinflammatory cytokine production

PROBLEM

Apoptosis is a normal constituent of trophoblast turnover in the placenta; however in some cases, this process is related to pregnancy complications such as preeclampsia. Recognition and engulfment of these apoptotic trophoblast cells is important for clearance of dying cells. The aim of this study was to show the cross talk between human endometrial endothelial cells (HEECs) and apoptotic trophoblast cells in an in vitro coculture model and its effect on cytokine production by HEECs.

METHOD OF STUDY

Fluorescent-labeled HEECs were cocultured with fluorescent-labeled apoptotic human trophoblast cells. Confocal microscopy and flow cytometry were used to show the interaction between these two types of cells. Cytokine profiles were determined using multiplex analysis.

RESULTS

HEECs are capable to phagocytose apoptotic trophoblasts. This activity is inhibited by the phagocytosis inhibitor cytochalasin B. Phagocytosis of apoptotic trophoblast cells induced the secretion of the proinflammatory cytokines interleukin-6 and monocyte chemoattractant protein-1 by HEECs.

CONCLUSION

This study provides the first evidence that HEECs have an ability to phagocytose apoptotic trophoblasts. Furthermore, we demonstrated an inflammatory response of HEECs after phagocytosing the apoptotic trophoblast cells. This event may contribute to the inflammatory response in both normal pregnancy and pathologic pregnancy such as preeclampsia.

Activation of TLR3 in the trophoblast is associated with preterm delivery

PROBLEM

Toll-like receptors (TLRs) recognize conserved sequences on the surface of pathogens and trigger effector cell functions. Previously, we described the expression of TLR3 by human trophoblast and their ability to respond to (Poly[I:C]). Here we evaluate the effect of Poly[I:C] on mouse pregnancy and characterize the local and systemic response.

METHOD OF STUDY

C57B/6 wild type (wt) and TLR3 knockout (TLR3KO) mice were treated with Poly[I:C] at 16.5 dpc and pregnancy outcome recorded. Morphologic changes, cytokines and chemokines levels in blood and utero-placental tissue were determined. NF-kappaB pathway was evaluated in vivo and in vitro.

RESULTS

Poly[I:C] in C57B/6 wt mice caused preterm delivery within 24 hr (4.5 mg/kg). No effect was observed in TLR3KO mice. In addition, we observed local (placenta) and systemic (serum) response characterized by increased production of proinflammatory cytokines and chemokines. The NF-kappaB pathway was activated by Poly[I:C] in human and mice trophoblast cells.

CONCLUSION

We report that Poly[I:C] induces preterm delivery via TLR3-dependent manner. Furthermore, we demonstrate that the trophoblast is able to recognize Poly[I:C] through TLR3 and respond to viral infection, modulating the immune system at the feto-maternal interface.