The role of infection in preterm labour and birth

Understanding the Immune System in Fetal Protection and Maternal Infections during Pregnancy

The fetal-maternal immune system determines the fate of pregnancy. The trophoblast cells not only give an active response against external stimuli but are also involved in secreting most of the cytokines. These cells have an essential function in fetal acceptance or fetal rejection. Other immune cells also play a pivotal role in carrying out a successful pregnancy. The disruption in this mechanism may lead to harmful effects on pregnancy. The placenta serves as an immune barrier in fetus protection against invading pathogens. Once the infections prevail, they may localize in placental and fetal tissues, and the presence of inflammation due to cytokines may have detrimental effects on pregnancy. Moreover, some pathogens are responsible for congenital fetal anomalies and affect almost all organs of the developing fetus. This review article is designed to address the bacterial and viral infections that threaten pregnancy and their possible outcomes. Moreover, training of the fetal immune system against the exposure of infections and the role of CD49a + NK cells in embryonic development will also be highlighted.

Chromosomally normal miscarriage is associated with vaginal dysbiosis and local inflammation

BACKGROUND

Emerging evidence supports an association between vaginal microbiota composition and risk of miscarriage; however, the underlying mechanisms are poorly understood. We aim to investigate the vaginal microbial composition and the local immune response in chromosomally normal and abnormal miscarriages and compare this to uncomplicated pregnancies delivering at term.

METHODS

We used 16S rRNA gene based metataxonomics to interrogate the vaginal microbiota in a cohort of 167 women, 93 miscarriages (54 euploid and 39 aneuploid using molecular cytogenetics) and 74 women who delivered at term and correlate this with the aneuploidy status of the miscarriages. We also measured the concentrations of IL-2, IL-4, IL-6, IL-8, TNF-α, IFN-γ, IL-1β, IL-18 and IL-10 in cervical vaginal fluid.

RESULTS

We show that euploid miscarriage is associated with a significantly higher prevalence of Lactobacillus spp. deplete vaginal microbial communities compared to aneuploid miscarriage (P = 0.01). Integration of matched cervicovaginal fluid immune-profiles showed that Lactobacillus spp. depleted vaginal microbiota associated with pro-inflammatory cytokine levels most strongly in euploid miscarriage compared to viable term pregnancy (IL-1β; P < 0.001, IL-8; P = 0.01, IL-6; P < 0.001).

CONCLUSIONS

Our data suggest the vaginal microbiota plays an important aetiological role in euploid miscarriage and may represent a target to modify risk of pregnancy loss.

Antiphospholipid antibody-induced trophoblast responses are differentially modulated by viral dsRNA and viral ssRNA

PROBLEM

Women with antiphospholipid antibodies (aPL) are at increased risk for pregnancy loss and preeclampsia. aPL target the trophoblast and induce a pro-inflammatory, anti-angiogenic and anti-migratory profile. Since infection during pregnancy can increase the risk for preeclampsia, a viral infection could further increase this in women with aPL. The goal of this study was to characterize the effect of viral components on trophoblast responses to aPL.

METHOD OF STUDY

A human first trimester trophoblast cell line was treated with or without aPL or control IgG in the presence of media, viral dsRNA or viral ssRNA. Supernatants were measured for inflammatory IL-1β and IL-8; inflammasome-associated uric acid and caspase-1 activity; and anti-angiogenic sFlt-1. Trophoblast migration was measured using a two-chamber assay.

RESULTS

Viral dsRNA augmented aPL-induced trophoblast caspase-1 activity, and IL-1β and IL-8 secretion in an additive manner. Viral ssRNA inhibited aPL-induced uric acid, IL-1β and sFlt-1 secretion, and further exacerbated aPL-inhibition of trophoblast migration.

CONCLUSION

While viral ssRNA may have some protective effects on aPL-induced inflammation and anti-angiogenic responses, viral dsRNA exacerbated aPL-mediated inflammation and viral ssRNA further limited cell migration, which could prove detrimental to placentation. Thus, viral infections may contribute to adverse pregnancy outcomes in women with aPL.

Molecular Changes on Maternal-Fetal Interface in Placental Abruption-A Systematic Review

Placental abruption is the separation of the placenta from the lining of the uterus before childbirth. It is an infrequent perinatal complication with serious after-effects and a marked risk of maternal and fetal mortality. Despite the fact that numerous placental abruption risk factors are known, the pathophysiology of this issue is multifactorial and not entirely clear. The aim of this review was to examine the current state of knowledge concerning the molecular changes on the maternal–fetal interface occurring in placental abruption. Only original research articles describing studies published in English until the 15 March 2021 were considered eligible. Reviews, book chapters, case studies, conference papers and opinions were excluded. The systematic literature search of PubMed/MEDLINE and Scopus databases identified 708 articles, 22 of which were analyzed. The available evidence indicates that the disruption of the immunological processes on the maternal–fetal interface plays a crucial role in the pathophysiology of placental abruption. The features of chronic non-infectious inflammation and augmented immunological cytotoxic response were found to be present in placental abruption samples in the reviewed studies. Various molecules participate in this process, with only a few being examined. More advanced research is needed to fully explain this complicated process.

Changes in physiology and immune system during pregnancy and coronavirus infection: A review

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the 3rd epidemic coronavirus after severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV). Since December 2019, the outbreak of the Coronavirus Disease 2019 (COVID-19) caused by SARS-CoV-2 has aroused great attention around the world. Pregnant women and their fetuses have been concerned as a high-risk population. We explained why pregnant women are susceptible to coronavirus in terms of their adaptive changes in physiology and immune system during pregnancy, and described the associations between maternal clinical symptoms, perinatal outcomes and coronavirus infections.

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.

Tribbles role in reproduction

Tribbles (TRIB) proteins, a family of evolutionary conserved psuedokinase proteins, modulate various signalling pathways within the cell. The regulatory roles of TRIB make them an important part of a number of biological processes ranging from cell proliferation to metabolism, immunity, inflammation and carcinogenesis. Innate immune system plays a pivotal role during the regulation of reproductive processes that allows successful creation of an offspring. Its involvement initiates from fertilization of the oocyte by spermatozoon and lasts throughout early embryonic development, pregnancy and labour. Therefore, there is a close cooperation between the reproductive system and the innate immune system. Evidence from our lab has demonstrated that improper activation of the innate immune system can reduce embryo implantation, thus leading to infertility. Therefore, control mechanisms regulating the innate immune system function can be critical for successful reproductive events.

Thrombin Augments LPS-Induced Human Endometrial Endothelial Cell Inflammation via PAR1 Activation

PROBLEM

Risk factors for preterm birth include placental abruption, giving rise to excessive decidual thrombin, and intrauterine bacterial infection. Human endometrial endothelial cells (HEECs) express Toll-like receptors (TLRs), and infection-derived agonists trigger HEECs to generate specific inflammatory responses. As thrombin, in addition to inducing coagulation, can contribute to inflammation, its effect on HEEC inflammatory responses to the TLR4 agonist, bacterial lipopolysaccharide (LPS), was investigated.

METHOD OF STUDY

HEECs were pre-treated with or without thrombin or specific protease-activated receptor (PAR) agonists, followed by treatment with or without LPS. Supernatants were measured for cytokines and chemokines by ELISA and multiplex analysis.

RESULTS

Thrombin significantly and synergistically augmented LPS-induced HEEC secretion of interleukin (IL)-6, IL-8, granulocyte colony-stimulating factor (G-CSF), and growth-regulated oncogene-alpha (GRO-α), and significantly augmented monocyte chemotactic protein (MCP)-1, tumor necrosis factor-alpha (TNF-α), and vascular endothelial growth factor (VEGF) secretion additively. Similar to thrombin, a PAR1 agonist synergistically augmented the LPS-induced HEEC secretion of inflammatory IL-6, IL-8, G-CSF, and GRO-α.

CONCLUSION

Thrombin, via PAR1 activation, synergistically augments LPS-induced HEEC production of chemokines involved in immune cell recruitment and survival, suggesting a mechanism by which intrauterine abruption and bacterial infection may together be associated with an aggravated uterine inflammatory response.

Trophoblast-microbiome interaction: a new paradigm on immune regulation

The immunologic paradigm of pregnancy led to the conceptualization of pregnancy as an organ transplant that requires, for its success, suppression of the maternal immune system. Growing scientific evidence suggests that in many ways the placenta functions as a tumor rather than a transplant and the immune regulation of the maternal-fetal interface is the result of the coordinated interaction between all its cellular components, including bacteria. Examining the role of microbiota in reproduction is in its infancy, but there is growing literature that supports its relevance. We discuss a potential normal function of bacteria in the establishment of immune tolerance and compelling evidence that a viral infection might be the underlying cause of perturbation of homeostasis. There is compelling evidence that many infectious diseases of human beings are caused by >1 microorganism and are defined as polymicrobial infections. We propose that pregnancy complications, such as preterm birth, are the result of polymicrobial infections. We examine the potential cellular and molecular mechanisms by which a viral infection of the placenta might disrupt the normal interaction between the cellular component of the implantation site and bacteria. As we better understand the normal homeostasis among the maternal immune system, placenta, and commensal, we will be able to elucidate pathogenic conditions and design better approaches to treat pregnancy complications associated with infection.

Viral infections during pregnancy

Viral infections during pregnancy have long been considered benign conditions with a few notable exceptions, such as herpes virus. The recent Ebola outbreak and other viral epidemics and pandemics show how pregnant women suffer worse outcomes (such as preterm labor and adverse fetal outcomes) than the general population and non-pregnant women. New knowledge about the ways the maternal-fetal interface and placenta interact with the maternal immune system may explain these findings. Once thought to be 'immunosuppressed', the pregnant woman actually undergoes an immunological transformation, where the immune system is necessary to promote and support the pregnancy and growing fetus. When this protection is breached, as in a viral infection, this security is weakened and infection with other microorganisms can then propagate and lead to outcomes, such as preterm labor. In this manuscript, we review the major viral infections relevant to pregnancy and offer potential mechanisms for the associated adverse pregnancy outcomes.

Biological functions of thyroid hormone in placenta

The thyroid hormone, 3,3,5-triiodo-l-thyronine (T₃), modulates several physiological processes, including cellular growth, differentiation, metabolism, inflammation and proliferation, via interactions with thyroid hormone response elements (TREs) in the regulatory regions of target genes. Infection and inflammation are critical processes in placental development and pregnancy-related diseases. In particular, infection is the leading cause of neonatal mortality and morbidity worldwide. However, to date, no successful approach has been developed for the effective diagnosis of infection in preterm infants. Pre-eclampsia (PE) is a serious disorder that adversely affects ~5% of human pregnancies. Recent studies identified a multiprotein complex, the inflammasome, including the Nod-like receptor (NLR) family of cytosolic pattern recognition receptors, the adaptor protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and caspase-1, which plays a vital role in the placenta. The thyroid hormone modulates inflammation processes and is additionally implicated in placental development and disease. Therefore, elucidation of thyroid hormone receptor-regulated inflammation-related molecules, and their underlying mechanisms in placenta, should facilitate the identification of novel predictive and therapeutic targets for placental disorders. This review provides a detailed summary of current knowledge with respect to identification of useful biomarkers and their physiological significance in placenta.

Viral single stranded RNA induces a trophoblast pro-inflammatory and antiviral response in a TLR8-dependent and -independent manner

Interest is growing in the role of viral infections and their association with adverse pregnancy outcomes. The trophoblast is permissive to viruses, but little is known about their impact on the placenta. We previously established that viral single stranded RNA (ssRNA), a Toll-like receptor 8 (TLR8) agonist, induces a restricted trophoblast pro-inflammatory cytokine/chemokine response by upregulating the secretion of interleukin (IL)-6 and IL-8. In parallel, the type I interferon, IFNbeta, is produced and acts back on the cell in an autocrine/paracrine manner to trigger caspase-3-dependent apoptosis. In this study, we sought to extend these findings by determining the mechanisms involved, examining whether viral ssRNA could induce a trophoblast antiviral response, and evaluating the influence of viral ssRNA on pregnancy outcome using a mouse model. Viral ssRNA induced human first-trimester trophoblast inflammation, type I interferon production, an antiviral response, and apoptosis in both a TLR8/MyD88-dependent and -independent manner. Furthermore, administration of viral ssRNA to pregnant mice induced placental caspase-3 activation, a pro-inflammatory cytokine/chemokine, type I interferon, and antiviral response as well as immune cell infiltration. Thus, ssRNA viral infections may compromise pregnancy by altering placental trophoblast survival and function through both TLR8 and non-TLR8 signaling pathways, leading to immune changes at the maternal-fetal interface.

Expression and functional characterization of NOD2 in decidual stromal cells isolated during the first trimester of pregnancy

NOD2, one of the cytosolic proteins that contain a nuclear oligomerization domain (NOD), is a pattern recognition receptor (PRR) involved in innate immune responses to intracellular pathogens. Little is known, however, about the effect of NOD2 expression on the maternal–fetal relationship. Our aim was to elucidate the functions of NOD2 in normal decidual stromal cells (DSCs) from the first trimester. Tissues and DSCs were isolated from 26 patients with normal pregnancies that required abortion. The expression of NOD2 in deciduas/decidual stromal cells (DSCs) was examined by real-time PCR, immunohistochemistry, and In-cell western. DSCs containing NOD2 were stimulated by its ligand, muramyl dipeptide (MDP). The secretion of various cytokines and chemokines were measured by ELISA and the apoptotic rate was determined by flow cytometry. Treatment with MDP significantly elevated the expression of both NOD2 mRNA and protein levels in DSCs. In addition, MDP activation of NOD2 significantly increased IL-1β and MCP-1 cytokine expression in a dose dependent manner but had no effect on IL-12 expression. IL-1β and TNF-α also significantly increased the expression of NOD2 in DSCs, suggesting a positive feedback loop mechanism. Moreover, MDP stimulation augmented DSC apoptosis. In summary, the results suggest that NOD2 expression in DSCs plays an important role in protecting the embryo and preventing infection in the maternal-fetal interface.

Single- and double-stranded viral RNA generate distinct cytokine and antiviral responses in human fetal membranes

There has been growing interest in the role of viral infections and their association with adverse pregnancy outcomes. However, little is known about the impact viral infections have on the fetal membranes (FM). Toll-like receptors (TLR) are thought to play a role in infection-associated inflammation at the maternal-fetal interface. Therefore, the objective of this study was to characterize the cytokine profile and antiviral response in human FMs exposed to viral dsRNA, which activates TLR3, and viral ssRNA, which activates TLR8; and to determine the mechanisms involved. The viral dsRNA analog, Poly(I:C), induced up-regulated secretion of MIP-1α, MIP-1β, RANTES and TNF-α, and down-regulated interleukin (IL)-2 and VEGF secretion. In contrast, viral ssRNA induced a broader panel of cytokines in the FMs by up-regulating the secretion of IL-1β, IL-2, IL-6, G-CSF, MCP-1, MIP-1α, MIP-1β, RANTES, TNF-α and GRO-α. Using inhibitory peptides against TLR adapter proteins, FM secretion of MIP-1β and RANTES in response to Poly(I:C) was MyD88 dependent; MIP-1α secretion was dependent on MyD88 and TRIF; and TNF-α production was independent of MyD88 and TRIF. Viral ssRNA-induced FM secretion of IL-1β, IL-2, IL-6, G-CSF, MIP-1α, RANTES and GRO-α was dependent on MyD88 and TRIF; MIP-1β was dependent upon TRIF, but not MyD88; and TNF-α and MCP-1 secretion was dependent on neither. Poly(I:C), but not ssRNA, induced an FM antiviral response by up-regulating the expression of IFNβ, myxovirus-resistance A, 2',5'-oligoadenylate synthetase and apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G. These findings demonstrate that human FMs respond to two viral signatures by generating distinct inflammatory cytokine/chemokine profiles and antiviral responses through different mechanisms.

Human fetal membranes generate distinct cytokine profiles in response to bacterial Toll-like receptor and nod-like receptor agonists

Bacterial infection-associated inflammation is thought to be a major cause of preterm premature rupture of membranes. Proinflammatory cytokines, such as interleukin 1B (IL1B), can weaken fetal membranes (FM) by upregulating matrix metalloproteinases and inducing apoptosis. The mechanism by which infection leads to inflammation at the maternal-fetal interface and subsequent preterm birth is thought to involve innate immune pattern recognition receptors (PRR), such as the Toll-like receptors (TLR) and Nod-like receptors (NLR), which recognize pathogen-associated molecular patterns (PAMPs). The objective of this study was to determine the cytokine profile generated by FMs in response to the bacterial TLR and NLR agonists peptidoglycan (PDG; TLR2), lipopolysaccharide (LPS; TLR4), flagellin (TLR5), CpG ODN (TLR9), iE-DAP (Nod1), and MDP (Nod2). PDG, LPS, flagellin, iE-DAP, and MDP triggered FMs to generate an inflammatory response, but the cytokine profiles were distinct for each TLR and NLR agonist, and only IL1B and RANTES were commonly upregulated in response to all five PAMPs. CpG ODN, in contrast, had a mild stimulatory effect only on MCP-1 and primarily downregulated basal FM cytokine production. IL1B secretion induced by PDG, LPS, flagellin, iE-DAP, and MDP was associated with its processing. Furthermore, FM IL1B secretion in response to TLR2, TLR4, and TLR5 activation was caspase 1-dependent, whereas Nod1 and Nod2 induced IL1B secretion independent of caspase 1. These findings demonstrate that FMs respond to different bacterial TLR and NLR PAMPs by generating distinct inflammatory cytokine profiles through distinct mechanisms that are specific to the innate immune PRR activated.

Nod1, but not the ASC inflammasome, contributes to induction of IL-1β secretion in human trophoblasts after sensing of Chlamydia trachomatis

Chlamydia trachomatis (Ct) is an obligate intracellular bacterial pathogen. Previously, we showed that infection of human trophoblast cells by Ct triggers the secretion of the pro-inflammatory cytokine, interleukin (IL)-1β. The aim of this study was to understand the innate immune pathways involved in trophoblast production of IL-1β after Ct infection. The approach we took was to inhibit the expression or function of the key Toll-like receptors (TLRs), Nod-like receptors, and inflammasome components that have been associated with chlamydia infection. In this study, we report that Ct-induced trophoblast IL-1β secretion is associated with the transcription of IL-1β mRNA, the translation and processing of pro-IL-1β, and the activation of caspase-1. In addition, we demonstrate that Ct-induced IL-1β production and secretion by the trophoblast is independent of TLR2, TLR4, MyD88, and the Nalp3/ASC inflammasome. Instead we report, for the first time, the importance of Nod1 for mediating trophoblast IL-1β secretion in response to a Ct infection.

Trophoblast cells are able to regulate monocyte activity to control Toxoplasma gondii infection

INTRODUCTION

Toxoplasma gondii is an intracellular parasite that causes severe disease when the infection occurs during pregnancy. Trophoblast cells constitute an important maternal-fetal barrier, with monocytes concentrating around them. Thus, interactions between trophoblasts and monocytes are important for maintaining a successful pregnancy, especially in cases of infection. This study aimed to evaluate the role of trophoblast cells (BeWo line) on monocyte (THP-1 line) activity in the presence or absence of T. gondii infection.

METHODS

THP-1 cells were stimulated with supernatants of BeWo cells, previously infected or not with T. gondii, and then infected with parasites. The supernatant of both cells were collected and analyzed for cytokine production and T. gondii proliferation in THP-1 cells was determined.

RESULTS

The results showed that after infection, the pattern of cytokines secreted by THP-1 and BeWo cells was characterized as a pro-inflammatory profile. Furthermore, supernatant of BeWo cells infected or not, was able to change the cytokine profile secreted by infected THP-1 cells, and this supernatant became THP-1 cells more able to control T. gondii proliferation than those that had not been stimulated.

DISCUSSION

This effect was associated with secretion of interleukin (IL)-6 by the THP-1 cells and soluble factors secreted by BeWo cells, such as IL-6 and MIF.

CONCLUSION

Together, these results suggest that trophoblast cells are able to modulate monocyte activity, resulting in the control of T. gondii infection and subsequent maintenance of pregnancy.

Bacterial modulation of human fetal membrane Toll-like receptor expression

PROBLEM

Preterm premature rupture of fetal membranes (pPROM) occurs in 30-40% of spontaneous preterm births (PTB) and is associated with intra-amniotic infection and inflammation. The membranes may sense and respond to microbes via Toll-like receptors (TLRs); however, little is known about their expression and regulation in this tissue. The objective of this study was to evaluate the expression of TLRs 1-10 in fetal membranes after exposure to pathogens associated with intra-amniotic infection and PTB.

METHOD OF STUDY

Normal human term fetal membrane explants were exposed to various bacteria. After 24 hrs, RNA was extracted and quantitative RT-PCR performed for TLRs1-10.

RESULTS

Treatment of fetal membranes with Mycoplasma hominis increased expression of TLR4, TLR6, and TLR8 mRNA. Ureaplasma parvum upregulated TLR8 mRNA, and Porphyromonas gingivalis significantly increased fetal membrane TLR7 expression. In contrast, treatment with Gram-negative Escherichia coli (and its cell wall component lipopolysaccharide) downregulated TLR10 mRNA. No effect was detected for Ureaplasma urealyticum, Gardnerella vaginalis, or Group B Streptococcus.

CONCLUSION

These findings demonstrate that different types of bacteria have distinct effects on fetal membrane TLR expression patterns. Moreover, these findings highlight the disparity of fetal membrane responses to infection and thus suggest heterogeneity in the mechanisms by which infection-associated pregnancy complications, such as pPROM and PTB, arise.

Nod1 activation by bacterial iE-DAP induces maternal-fetal inflammation and preterm labor

There is a strong association between infection and prematurity; however, the underlying mechanisms remain largely unknown. Nod1 and Nod2 are intracellular pattern recognition receptors that are activated by bacterial peptides and mediate innate immunity. We previously demonstrated that human first-trimester trophoblasts express Nod1 and Nod2, which trigger inflammation upon stimulation. This study sought to determine the expression and function of Nod1 and Nod2 in third-trimester trophoblasts, and to characterize the in vivo effects of Nod1 activation on pregnancy outcome. Human term placental tissues and isolated term trophoblast expressed Nod1, but not Nod2. Activation of Nod1 by its agonist, bacterial γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP), in term trophoblast cultures induced a proinflammatory cytokine profile, characterized by elevated levels of secreted IL-6, GRO-α, and MCP-1, when compared with the control. However, these cytokines were not upregulated in response to Nod2 stimulation with bacterial MDP. Administration of high-dose bacterial iE-DAP to pregnant C57BL/6J mice on embryonic day 14.5 triggered preterm delivery within 24 h. iE-DAP at a lower dose that did not induce prematurity, reduced fetal weight, altered the cytokine profile at the maternal-fetal interface, and induced fetal inflammation. Thus, functional Nod1 is expressed by trophoblast cells across gestation and may have a role in mediating infection-associated inflammation and prematurity. This study demonstrates that pattern recognition receptors, other than the TLRs, may be implicated or involved in infection-associated preterm labor.

The role of the Nod-like receptor family in trophoblast innate immune responses

There is a strong clinical association between intrauterine infections and pregnancy complications, such as preterm labor. The placenta functions as an active barrier whereby the trophoblast recognizes microbes through pattern recognition receptors, such as the well characterized Toll-like receptors, in order to respond to pathogens at the maternal-fetal interface. Consequently, either an inefficient or overactive placental response to an infectious trigger, may have a significant impact on pregnancy outcome. Recently the placenta has been shown to express a newly identified family of pattern recognition receptors, the cytoplasmic-based Nod-like receptors (NLRs). As a result of their restricted localization, NLRs function as intracellular receptors that respond to infectious components, which have gained access to the cytoplasmic compartment. Thus, NLRs may provide the trophoblast with a recognition system that may be critical in placental responses to microorganisms or their cell wall components that have gained access to the cell's intracellular space, or that have evaded recognition by the TLRs. This review will discuss what is currently known about the role of NOD proteins, NALP proteins, and the inflammasome at the maternal-fetal interface, and their potential role in infection-associated pregnancy complications, like preterm labor. As we learn more about their function at the maternal-fetal interface, we will have a better understanding of their function in normal pregnancy and their potential to contribute to the pathogenesis of infection- and inflammation-associated pregnancy complications.

Viral ssRNA induces first trimester trophoblast apoptosis through an inflammatory mechanism

PROBLEM

Infection during pregnancy represents a significant cause of mobility and mortality. While viruses pose a major threat, little is known about their effect on early pregnancy, or the mechanisms involved. The objective of this study was to characterize the trophoblast response following exposure to viral ssRNA.

METHOD OF STUDY

First trimester trophoblast cells were treated with or without viral ssRNA. Cytokine production was measured using multiplex analysis and ELISA. Apoptosis was determined using Hoechst staining, cell viability, and caspase activity assays.

RESULTS

Treatment of trophoblasts with viral ssRNA increased their secretion of IL-8, IL-6, and IFNbeta. However, the ssRNA also induced trophoblast apoptosis. To test whether the viral ssRNA-induced inflammatory response was responsible for this induction of apoptosis, conditioned media (CM) from trophoblasts were added to a fresh culture of cells. The CM from viral ssRNA-treated induced higher levels of trophoblast apoptosis than the control CM. Moreover, recombinant IFNbeta induced trophoblast apoptosis.

CONCLUSION

We demonstrate that viral ssRNA induces a pro-inflammatory and type I interferon response in the trophoblast and this inflammatory process may indirectly induce trophoblast apoptosis. These results provide a novel mechanism by which certain viral infections might compromise placental integrity and function, and therefore, pregnancy outcome.

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.

Pattern recognition at the maternal-fetal interface

Intrauterine infections represent a significant threat to fetal well-being and pregnancy outcome. Recent studies suggest that non-immune cells of the maternal-fetal interface can actively recognize and respond to microbes through pattern recognition receptors, in order to control pathogens that may compromise the pregnancy. However, these same innate immune responses may inadvertently lead to excessive inflammation or apoptosis at the maternal-fetal interface. Thus, pattern recognition receptors may play a key role in infection-related pregnancy complications. This review discusses what is currently known about the role of Toll-like receptors and NOD-like receptors in controlling infections at the maternal-fetal interface, and what impact their function may have on pregnancy.

Inflammation and pregnancy: the role of toll-like receptors in trophoblast-immune interaction

During normal pregnancy, the decidua is populated by a variety of leucocytes; however, cells of the innate immune system seem to dominate this tissue. Their presence suggests that the innate immune system is not indifferent to the fetus and has been associated with a response of the maternal immune system to the "semi-allograft fetus." New evidences, however, indicates that these immune cells are critical for decidual and trophoblast development, rather than induction of tolerance. We hypothesized that, during implantation, an inflammatory environment is necessary for the attachment and invasion of the blastocyst. Therefore, we propose the existence of an "inflammatory-mediated embryo implantation" condition that is dependent on the proper "education" of the innate immune system by the trophoblast. Here we postulate that trophoblast cells successfully orchestrate their inflammatory environment and regulate immune cell differentiation and activation.

Detection of bacteria in placental tissues obtained from extremely low gestational age neonates

OBJECTIVE

The objective of the study was to quantify and identify aerobic and anaerobic bacteria as well as Mycoplasma and Ureaplasma in the chorionic parenchyma.

STUDY DESIGN

A sample of the chorionic parenchyma from neonates delivered between 23-27 completed weeks was cultured and tested by polymerase chain reaction (PCR) methods using universal bacterial primers for the presence of bacteria and mycoplasmas.

RESULTS

The culture positive rate was higher for vaginal deliveries (333/489; 68%) than for cesarean sections (363/876; 41%). Thirty percent of all culture-positive samples had only aerobic bacteria, 21% of the samples had only anaerobic bacteria, and 9% of the samples had only Mycoplasma/Ureaplasma. The mean concentration of Mycoplasma/Ureaplasma (4.00 +/- 1.11 log10 CFU/g) was significantly higher (P < .001) than the total count of either aerobes (3.24 +/- 1.12 log10 CFU/g) or anaerobes (2.89 +/- 0.99 log10 CFU/g). Staphylococcus sp. and Corynebacterium sp. as well as organisms associated with bacterial vaginosis were the most frequently recovered. A PCR product was not detected from either randomly selected or known culture-positive samples.

CONCLUSION

Approximately half of second-trimester placentas harbor organisms within the chorionic plate. The chorion parenchyma appears to harbor constituents that prevent the identification of bacterial deoxyribonucleic acid by PCR methods.

NOD protein expression and function in first trimester trophoblast cells

PROBLEM

Through the expression of pattern recognition receptors, the trophoblast can recognize and respond to infectious microorganisms and, therefore, participate in the control of pathogens that may compromise fetal well-being. We hypothesize that the trophoblast has the ability to sense invasive intracellular bacteria through the cytoplasmic-based nucleotide-binding oligomerization domain (NOD) proteins. The aim of this study was to characterize the expression and function of NOD proteins in first trimester trophoblast cells.

METHOD OF STUDY

NOD1 and NOD2 expressions by first trimester trophoblast cells were evaluated by immunohistochemistry, Western blot analysis and reverse transcription-polymerase chain reaction. The effect of NOD2 activation on trophoblast cells was determined by analyzing the cytokine response following treatment with muramyl dipeptide (MDP).

RESULTS

Both NOD1 and NOD2 were expressed by first trimester placental villi and localized to trophoblast cells. Moreover, NOD1, NOD2 and the signaling effector protein, RIP-like interacting CLARP kinase (RICK), were all expressed by isolated trophoblast cells. Following exposure to the NOD2 ligand, MDP, trophoblast cells generated a pro-inflammatory cytokine response. This response was confirmed to be specific, as an NOD2-deficient trophoblast cell line failed to respond to MDP unless transfected with NOD2.

CONCLUSION

These findings suggest that, through the expression and function of NOD proteins, first trimester trophoblast cells are able to recognize and respond to invasive intracellular pathogens that may have evaded other forms of pattern recognition.

Exposure to ambient air pollution and prenatal and early childhood health effects

Over the last years, concern for the possible influence of exposure to air pollutants in children during gestation or the first years of life has grown; exposure levels which may be reached nowadays in our dwellings and in our streets. In the present study evidence over the possible impact of ambient air pollution on the foetus and the infants (i.e.: less than 1 year) published during the last decade, 1994--2003, are revised. Studies on infant mortality and exposure to particles show an outstanding consistence in the magnitude of the effects, despite the different designs used. As a whole, data show that an increase in 10 microg/m3 of particle concentration (measured as PM10) is associated with to about 5% increase in post-neonatal mortality for all causes and around 22% for post-neonatal mortality for respiratory diseases. Regarding damage in foetal health, although results are not always consistent, most studies show associations with exposure to air pollution during pregnancy. However, the precise mechanisms of action of air pollutants on adverse reproductive results are still unknown, so is the period of exposure most relevant during pregnancy and the specific pollutant which may represent a higher risk. Follow-up studies evaluating personal exposure to different air pollutants are required, allowing for the adequate evaluation of the impact of each pollutant in different periods of pregnancy, as well as providing hypotheses on their possible mechanisms of action.