Inflammatory gene regulatory networks in amnion cells following cytokine stimulation: translational systems approach to modeling human parturition

Maternal plasma cytokines and the subsequent risk of uterine atony and postpartum hemorrhage

OBJECTIVES

To determine whether the maternal plasma concentrations of cytokines are higher in pregnant women with postpartum hemorrhage (PPH) compared to pregnant women without PPH.

METHODS

A retrospective case-control study included 36 women with PPH and 72 matched controls. Cases and controls were matched for gestational age at delivery, labor status, delivery route, parity, and year of sample collection. Maternal plasma samples were collected up to 3 days prior to delivery. Comparison of the plasma concentrations of 29 cytokines was performed by using linear mixed-effects models and included adjustment for covariates and multiple testing. A false discovery rate adjusted p-value <0.1 was used to infer significance. Random forest models with evaluation by leave-one-out and 9-fold cross-validation were used to assess the combined value of the proteins in predicting PPH.

RESULTS

Concentrations of interleukin (IL)-16, IL-6, IL-12/IL-23p40, monocyte chemotactic protein 1 (MCP-1), and IL-1β were significantly higher in PPH than in the control group. This difference remained significant after adjustment for maternal age, clinical chorioamnionitis, and preeclampsia. Multi-protein random forest proteomics models had moderate cross-validated accuracy for prediction of PPH [area under the ROC curve, 0.69 (0.58-0.81) by leave-one-out cross validation and 0.73 (0.65-0.81) by 9-fold cross-validation], and the inclusion of clinical and demographic information did not increase the prediction performance.

CONCLUSIONS

Pregnant women with severe PPH had higher median maternal plasma concentrations of IL-16, IL-6, IL-12/IL-23p40, MCP-1, and IL-1β than patients without PPH. These cytokines could serve as biomarkers or their pathways may be therapeutic targets.

Leveraging bioengineering to assess cellular functions and communication within human fetal membranes

The fetal membranes enclose the growing fetus and amniotic fluid. Preterm prelabor rupture of fetal membranes is a leading cause of preterm birth. Fetal membranes are composed of many different cell types, both structural and immune. These cells must coordinate functions for tensile strength and membrane integrity to contain the growing fetus and amniotic fluid. They must also balance immune responses to pathogens with maintaining maternal-fetal tolerance. Perturbation of this equilibrium can lead to preterm premature rupture of membranes without labor. In this review, we describe the formation of the fetal membranes to orient the reader, discuss some of the common forms of communication between the cell types of the fetal membranes, and delve into the methods used to tease apart this paracrine signaling within the membranes, including emerging technologies such as organ-on-chip models of membrane immunobiology.

Physiological TLR4 regulation in human fetal membranes as an explicative mechanism of a pathological preterm case

The integrity of human fetal membranes is crucial for harmonious fetal development throughout pregnancy. Their premature rupture is often the consequence of a physiological phenomenon that has been exacerbated. Beyond all the implied biological processes, inflammation is of primary importance and is qualified as ‘sterile’ at the end of pregnancy. In this study, complementary methylomic and transcriptomic strategies on amnion and choriodecidua explants obtained from the altered (cervix zone) and intact fetal membranes at term and before labour were used. By cross-analysing genome-wide studies strengthened by in vitro experiments, we deciphered how the expression of toll-like receptor 4 (TLR4), an actor in pathological fetal membrane rupture, is controlled. Indeed, it is differentially regulated in the altered zone and between both layers by a dual mechanism: (1) the methylation of TLR4 and miRNA promoters and (2) targeting by miRNA (let-7a-2 and miR-125b-1) acting on the 3’-UTR of TLR4. Consequently, this study demonstrates that fine regulation of TLR4 is required for sterile inflammation establishment at the end of pregnancy and that it may be dysregulated in the pathological premature rupture of membranes.

Progesterone Receptor Signaling Selectively Modulates Cytokine-Induced Global Gene Expression in Human Cervical Stromal Cells

Preterm birth (PTB) is the leading cause of morbidity and mortality in infants <1 year of age. Intrauterine inflammation is a hallmark of preterm and term parturition; however, this alone cannot fully explain the pathobiology of PTB. For example, the cervix undergoes a prolonged series of biochemical and biomechanical events, including extracellular matrix (ECM) remodeling and mechanochemical changes, culminating in ripening. Vaginal progesterone (P₄) prophylaxis demonstrates great promise in preventing PTB in women with a short cervix (<25 mm). We used a primary culture model of human cervical stromal fibroblasts to investigate gene expression signatures in cells treated with interleukin-1β (IL-1β) in the presence or absence of P₄ following 17β-estradiol (17β-E₂) priming for 7–10 days. Microarrays were used to measure global gene expression in cells treated with cytokine or P₄ alone or in combination, followed by validation of select transcripts by semiquantitative polymerase chain reactions (qRT-PCR). Primary/precursor (MIR) and mature microRNAs (miR) were quantified by microarray and NanoString^® platforms, respectively, and validated by qRT-PCR. Differential gene expression was computed after data normalization followed by pathway analysis using Kyoto Encyclopedia Genes and Genomes (KEGG), Panther, Gene Ontology (GO), and Ingenuity Pathway Analysis (IPA) upstream regulator algorithm tools. Treatment of fibroblasts with IL-1β alone resulted in the differential expression of 1432 transcripts (protein coding and non-coding), while P₄ alone led to the expression of only 43 transcripts compared to untreated controls. Cytokines, chemokines, and their cognate receptors and prostaglandin endoperoxide synthase-2 (PTGS-2) were among the most highly upregulated transcripts following either IL-1β or IL-1β + P₄. Other prominent differentially expressed transcripts were those encoding ECM proteins, ECM-degrading enzymes, and enzymes involved in glycosaminoglycan (GAG) biosynthesis. We also detected differential expression of bradykinin receptor-1 and -2 transcripts, suggesting (prominent in tissue injury/remodeling) a role for the kallikrein–kinin system in cervical responses to cytokine and/or P₄ challenge. Collectively, this global gene expression study provides a rich database to interrogate stromal fibroblasts in the setting of a proinflammatory and endocrine milieu that is relevant to cervical remodeling/ripening during preparation for parturition.

Functional Genomics of Healthy and Pathological Fetal Membranes

Premature preterm rupture of membranes (PPROM), rupture of fetal membranes before 37 weeks of gestation, is the leading identifiable cause of spontaneous preterm births. Often there is no obvious cause that is identified in a patient who presents with PPROM. Identifying the upstream molecular events that lead to fetal membrane weakening presents potentially actionable mechanisms which could lead to the identification of at-risk patients and to the development of new therapeutic interventions. Functional genomic studies have transformed understanding of the role of gene regulation in diverse cells and tissues involved health and disease. Here, we review the results of those studies in the context of fetal membranes. We will highlight relevant results from major coordinated functional genomics efforts and from targeted studies focused on individual cell or tissue models. Studies comparing gene expression and DNA methylation between healthy and pathological fetal membranes have found differential regulation between labor and quiescent tissue as well as in preterm births, preeclampsia, and recurrent pregnancy loss. Whole genome and exome sequencing studies have identified common and rare fetal variants associated with preterm births. However, few fetal membrane tissue studies have modeled the response to stimuli relevant to pregnancy. Fetal membranes are readily adaptable to cell culture and relevant cellular phenotypes are readily observable. For these reasons, this is now an unrealized opportunity for genomic studies isolating the effect of cell signaling cascades and mapping the fetal membrane responses that lead to PPROM and other pregnancy complications.

Maternal and fetal intrauterine tissue crosstalk promotes proinflammatory amplification and uterine transition†

Birth is a complex biological event requiring genetic, cellular, and physiological changes to the uterus, resulting in a uterus activated for completing the physiological processes of labor. We define the change from the state of pregnancy to the state of parturition as uterine transitioning, which requires the actions of inflammatory mediators and localized paracrine interactions between intrauterine tissues. Few studies have examined the in vitro interactions between fetal and maternal gestational tissues within this proinflammatory environment. Thus, we designed a co-culture model to address this gap, incorporating primary term human myometrium smooth muscle cells (HMSMCs) with human fetal membrane (hFM) explants to study interactions between the tissues. We hypothesized that crosstalk between tissues at term promotes proinflammatory expression and uterine transitioning for parturition. Outputs of 40 cytokines and chemokines encompassing a variety of proinflammatory roles were measured; all but one increased significantly with co-culture. Eighteen of the 39 cytokines increased to a higher abundance than the sum of the effect of each tissue cultured separately. In addition, COX2 and IL6 but not FP and OXTR mRNA abundance significantly increased in both HMSMCs and hFM in response to co-culture. These data suggest that synergistic proinflammatory upregulation within intrauterine tissues is involved with uterine transitioning.

Antibiotic administration can eradicate intra-amniotic infection or intra-amniotic inflammation in a subset of patients with preterm labor and intact membranes

BACKGROUND

Intra-amniotic infection is present in 10% of patients with an episode of preterm labor, and is a risk factor for impending preterm delivery and neonatal morbidity/mortality. Intra-amniotic inflammation is often associated with intra-amniotic infection, but is sometimes present in the absence of detectable microorganisms. Antibiotic treatment of intra-amniotic infection has traditionally been considered to be ineffective. Intra-amniotic inflammation without microorganisms has a prognosis similar to that of intra-amniotic infection.

OBJECTIVE

To determine whether antibiotics can eradicate intra-amniotic infection or intra-amniotic inflammation in a subset of patients with preterm labor and intact membranes.

MATERIALS AND METHODS

The study population consisted of women who met the following criteria: 1) singleton gestation between 20 and 34 weeks; 2) preterm labor and intact membranes; 3) transabdominal amniocentesis performed for the evaluation of the microbiologic/inflammatory status of the amniotic cavity; 4) intra-amniotic infection and/or intra-amniotic inflammation; and 5) received antibiotic treatment that consisted of ceftriaxone, clarithromycin, and metronidazole. Follow-up amniocentesis was performed in a subset of patients. Amniotic fluid was cultured for aerobic and anaerobic bacteria and genital mycoplasmas, and polymerase chain reaction was performed for Ureaplasma spp. Intra-amniotic infection was defined as a positive amniotic fluid culture or positive polymerase chain reaction, and intra-amniotic inflammation was suspected when there was an elevated amniotic fluid white blood cell count or a positive result of a rapid test for matrix metalloproteinase-8. For this study, the final diagnosis of intra-amniotic inflammation was made by measuring the interleukin-6 concentration in stored amniotic fluid (>2.6 ng/mL). These results were not available to managing clinicians. Treatment success was defined as eradication of intra-amniotic infection and/or intra-amniotic inflammation or delivery ≥37 weeks.

RESULTS

Of 62 patients with intra-amniotic infection and/or intra-amniotic inflammation, 50 received the antibiotic regimen. Of those patients, 29 were undelivered for ≥7 days and 19 underwent a follow-up amniocentesis. Microorganisms were identified by culture or polymerase chain reaction of amniotic fluid obtained at admission in 21% of patients (4/19) who had a follow-up amniocentesis, and were eradicated in 3 of the 4 patients. Resolution of intra-amniotic infection/inflammation was confirmed in 79% of patients (15/19), and 1 other patient delivered at term, although resolution of intra-amniotic inflammation could not be confirmed after a follow-up amniocentesis. Thus, resolution of intra-amniotic inflammation/infection or term delivery (treatment success) occurred in 84% of patients (16/19) who had a follow-up amniocentesis. Treatment success occurred in 32% of patients (16/50) with intra-amniotic infection/inflammation who received antibiotics. The median amniocentesis-to-delivery interval was significantly longer among women who received the combination of antibiotics than among those who did not (11.4 days vs 3.1 days: P = .04).

CONCLUSION

Eradication of intra-amniotic infection/inflammation after treatment with antibiotics was confirmed in 79% of patients with preterm labor, intact membranes, and intra-amniotic infection/inflammation who had a follow-up amniocentesis. Treatment success occurred in 84% of patients who underwent a follow-up amniocentesis and in 32% of women who received the antibiotic regimen.

Characteristic Changes in Decidual Gene Expression Signature in Spontaneous Term Parturition

Background

The decidua has been implicated in the “terminal pathway” of human term parturition, which is characterized by the activation of pro-inflammatory pathways in gestational tissues. However, the transcriptomic changes in the decidua leading to terminal pathway activation have not been systematically explored. This study aimed to compare the decidual expression of developmental signaling and inflammation-related genes before and after spontaneous term labor in order to reveal their involvement in this process.

Methods

Chorioamniotic membranes were obtained from normal pregnant women who delivered at term with spontaneous labor (TIL, n = 14) or without labor (TNL, n = 15). Decidual cells were isolated from snap-frozen chorioamniotic membranes with laser microdissection. The expression of 46 genes involved in decidual development, sex steroid and prostaglandin signaling, as well as pro- and anti-inflammatory pathways, was analyzed using high-throughput quantitative real-time polymerase chain reaction (qRT-PCR). Chorioamniotic membrane sections were immunostained and then semi-quantified for five proteins, and immunoassays for three chemokines were performed on maternal plasma samples.

Results

The genes with the highest expression in the decidua at term gestation included insulin-like growth factor-binding protein 1 (IGFBP1), galectin-1 (LGALS1), and progestogen-associated endometrial protein (PAEP); the expression of estrogen receptor 1 (ESR1), homeobox A11 (HOXA11), interleukin 1β (IL1B), IL8, progesterone receptor membrane component 2 (PGRMC2), and prostaglandin E synthase (PTGES) was higher in TIL than in TNL cases; the expression of chemokine C-C motif ligand 2 (CCL2), CCL5, LGALS1, LGALS3, and PAEP was lower in TIL than in TNL cases; immunostaining confirmed qRT-PCR data for IL-8, CCL2, galectin-1, galectin-3, and PAEP; and no correlations between the decidual gene expression and the maternal plasma protein concentrations of CCL2, CCL5, and IL-8 were found.

Conclusions

Our data suggests that with the initiation of parturition, the decidual expression of anti-inflammatory mediators decreases, while the expression of pro-inflammatory mediators and steroid receptors increases. This shift may affect downstream signaling pathways that can lead to parturition.

IL-1-induced Bhlhe40 identifies pathogenic T helper cells in a model of autoimmune neuroinflammation

Lin et al. show that Bhlhe40 expression identifies encephalitogenic CD4⁺ T helper cells and define a pertussis toxin–IL-1–Bhlhe40 pathway active in experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis.

The features that define autoreactive T helper (Th) cell pathogenicity remain obscure. We have previously shown that Th cells require the transcription factor Bhlhe40 to mediate experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Here, using Bhlhe40 reporter mice and analyzing both polyclonal and TCR transgenic Th cells, we found that Bhlhe40 expression was heterogeneous after EAE induction, with Bhlhe40-expressing cells displaying marked production of IFN-γ, IL-17A, and granulocyte-macrophage colony-stimulating factor. In adoptive transfer EAE models, Bhlhe40-deficient Th1 and Th17 cells were both nonencephalitogenic. Pertussis toxin (PTX), a classical co-adjuvant for actively induced EAE, promoted IL-1β production by myeloid cells in the draining lymph node and served as a strong stimulus for Bhlhe40 expression in Th cells. Furthermore, PTX co-adjuvanticity was Bhlhe40 dependent. IL-1β induced Bhlhe40 expression in polarized Th17 cells, and Bhlhe40-expressing cells exhibited an encephalitogenic transcriptional signature. In vivo, IL-1R signaling was required for full Bhlhe40 expression by Th cells after immunization. Overall, we demonstrate that Bhlhe40 expression identifies encephalitogenic Th cells and defines a PTX–IL-1–Bhlhe40 pathway active in EAE.

Inflammatory gene networks in term human decidual cells define a potential signature for cytokine-mediated parturition

BACKGROUND

Inflammation is a proximate mediator of preterm birth and fetal injury. During inflammation several microRNAs (22 nucleotide noncoding ribonucleic acid (RNA) molecules) are up-regulated in response to cytokines such as interleukin-1β. MicroRNAs, in most cases, fine-tune gene expression, including both up-regulation and down-regulation of their target genes. However, the role of pro- and antiinflammatory microRNAs in this process is poorly understood.

OBJECTIVE

The principal goal of the work was to examine the inflammatory genomic profile of human decidual cells challenged with a proinflammatory cytokine known to be present in the setting of preterm parturition. We determined the coding (messenger RNA) and noncoding (microRNA) sequences to construct a network of interacting genes during inflammation using an in vitro model of decidual stromal cells.

STUDY DESIGN

The effects of interleukin-1β exposure on mature microRNA expression were tested in human decidual cell cultures using the multiplexed NanoString platform, whereas the global inflammatory transcriptional response was measured using oligonucleotide microarrays. Differential expression of select transcripts was confirmed by quantitative real time-polymerase chain reaction. Bioinformatics tools were used to infer transcription factor activation and regulatory interactions.

RESULTS

Interleukin-1β elicited up- and down-regulation of 350 and 78 nonredundant transcripts (false discovery rate < 0.1), respectively, including induction of numerous cytokines, chemokines, and other inflammatory mediators. Whereas this transcriptional response included marked changes in several microRNA gene loci, the pool of fully processed, mature microRNA was comparatively stable following a cytokine challenge. Of a total of 6 mature microRNAs identified as being differentially expressed by NanoString profiling, 2 (miR-146a and miR-155) were validated by quantitative real time-polymerase chain reaction. Using complementary bioinformatics approaches, activation of several inflammatory transcription factors could be inferred downstream of interleukin-1β based on the overall transcriptional response. Further analysis revealed that miR-146a and miR-155 both target genes involved in inflammatory signaling, including Toll-like receptor and mitogen-activated protein kinase pathways.

CONCLUSION

Stimulation of decidual cells with interleukin-1β alters the expression of microRNAs that function to temper proinflammatory signaling. In this setting, some microRNAs may be involved in tissue-level inflammation during the bulk of gestation and assist in pregnancy maintenance.

Gestational tissue transcriptomics in term and preterm human pregnancies: a systematic review and meta-analysis

BACKGROUND

Preterm birth (PTB), or birth before 37 weeks of gestation, is the leading cause of newborn death worldwide. PTB is a critical area of scientific study not only due to its worldwide toll on human lives and economies, but also due to our limited understanding of its pathogenesis and, therefore, its prevention. This systematic review and meta-analysis synthesizes the landscape of PTB transcriptomics research to further our understanding of the genes and pathways involved in PTB subtypes.

METHODS

We evaluated published genome-wide pregnancy studies across gestational tissues and pathologies, including those that focus on PTB, by performing a targeted PubMed MeSH search and systematically reviewing all relevant studies.

RESULTS

Our search yielded 2,361 studies on gestational tissues including placenta, decidua, myometrium, maternal blood, cervix, fetal membranes (chorion and amnion), umbilical cord, fetal blood, and basal plate. Selecting only those original research studies that measured transcription on a genome-wide scale and reported lists of expressed genetic elements identified 93 gene expression, 21 microRNA, and 20 methylation studies. Although 30 % of all PTB cases are due to medical indications, 76 % of the preterm studies focused on them. In contrast, only 18 % of the preterm studies focused on spontaneous onset of labor, which is responsible for 45 % of all PTB cases. Furthermore, only 23 of the 10,993 unique genetic elements reported to be transcriptionally active were recovered 10 or more times in these 134 studies. Meta-analysis of the 93 gene expression studies across 9 distinct gestational tissues and 29 clinical phenotypes showed limited overlap of genes identified as differentially expressed across studies.

CONCLUSIONS

Overall, profiles of differentially expressed genes were highly heterogeneous both between as well as within clinical subtypes and tissues as well as between studies of the same clinical subtype and tissue. These results suggest that large gaps still exist in the transcriptomic study of specific clinical subtypes as well in the generation of the transcriptional profile of well-studied clinical subtypes; understanding the complex landscape of prematurity will require large-scale, systematic genome-wide analyses of human gestational tissues on both understudied and well-studied subtypes alike.

Transcriptomic profiling of human choriodecidua during term labor: inflammation as a key driver of labor

PROBLEM

Inflammation is a driver of labor in myometrium and cervix; however, the involvement of decidua is poorly defined. We have reported decidual leukocyte infiltration prior to and during labor; the regulators of these inflammatory processes are unknown.

METHOD OF STUDY

Choriodecidua RNA obtained after term labor or elective cesarean delivery was applied to Affymetrix GeneChips. Pathway analysis and gene validation were performed.

RESULTS

Extensive inflammatory activation was identified in choriodecidua following labor, predominantly upregulation of genes regulating leukocyte trafficking and cytokine signalling. Genes governing cell fate, tissue remodelling, and translation were also altered. Upregulation of candidate genes (ICAM1, CXCR4, CD44, TLR4, SOCS3, BCL2A, and IDO) was confirmed. NFκB, STAT1&3, HMGB1, and miRNA-21, miRNA-46, miRNA-141, and miRNA-200 were predicted upstream regulators.

CONCLUSION

This study confirms inflammatory processes are major players in labor events in choriodecidua, as in other gestational tissues. Suppressing uterine inflammation is likely to be critical for arresting premature labor.

A computational model of lipopolysaccharide-induced nuclear factor kappa B activation: a key signalling pathway in infection-induced preterm labour

Preterm birth is the single biggest cause of significant neonatal morbidity and mortality, and the incidence is rising. Development of new therapies to treat and prevent preterm labour is seriously hampered by incomplete understanding of the molecular mechanisms that initiate labour at term and preterm. Computational modelling provides a new opportunity to improve this understanding. It is a useful tool in (i) identifying gaps in knowledge and informing future research, and (ii) providing the basis for an in silico model of parturition in which novel drugs to prevent or treat preterm labour can be "tested". Despite their merits, computational models are rarely used to study the molecular events initiating labour. Here, we present the first attempt to generate a dynamic kinetic model that has relevance to the molecular mechanisms of preterm labour. Using published data, we model an important candidate signalling pathway in infection-induced preterm labour: that of lipopolysaccharide (LPS) -induced activation of Nuclear Factor kappa B. This is the first model of this pathway to explicitly include molecular interactions upstream of Nuclear Factor kappa B activation. We produced a formalised graphical depiction of the pathway and built a kinetic model based on ordinary differential equations. The kinetic model accurately reproduced published in vitro time course plots of Lipopolysaccharide-induced Nuclear Factor kappa B activation in mouse embryo fibroblasts. In this preliminary work we have provided proof of concept that it is possible to build computational models of signalling pathways that are relevant to the regulation of labour, and suggest that models that are validated with wet-lab experiments have the potential to greatly benefit the field.

Inflammatory and steroid receptor gene methylation in the human amnion and decidua

Correct timing of parturition requires inflammatory gene activation in the gestational tissues at term and repression during pregnancy. Promoter methylation at CpG dinucleotides represses gene activity; therefore, we examined the possibility that DNA methylation is involved in the regulation of labour-associated genes in human pregnancy. Amnion and decidua were collected at 11-17 weeks of gestation and at term following elective Caesarean delivery or spontaneous labour. Methylation of the inflammatory genes PTGS2, BMP2, NAMPT and CXCL2 was analysed using the Methyl-Profiler PCR System and bisulphite sequencing. Methylation of the glucocorticoid, progesterone and oestrogen receptor genes, involved in the hormonal regulation of gestational tissue function, and the expression of the DNA methyltransferases DNMT1, -3A and -3B were also determined. Variable proportions of inflammatory and steroid receptor gene copies, to a maximum of 50.9%, were densely methylated in both tissues consistent with repression. Densely methylated copy proportions were significantly different between genes showing no relationship with varying expression during pregnancy, between tissues and in individuals. Methylated copy proportions of all genes in amnion and most genes in decidua were highly correlated in individuals. DNMT1 and -3A were expressed in both tissues with significantly higher levels in the amnion at 11-17 weeks than at term. We conclude that the unmethylated portion of gene copies is responsible for the full range of regulated expression in the amnion and decidua during normal pregnancy. Dense methylation of individually variable gene copy proportions happens in the first trimester amnion influenced by sequence context and affected strongly by individual circumstances.

The entry of fetal and amniotic fluid components into the uterine vessel circulation leads to sterile inflammatory processes during parturition

Pro-inflammatory cytokines play an important role during the process of human parturition. The focus of this review was to explore the contribution of biological, biochemical, and genetic changes in the onset of term labor. This article reviews the English-language literature on inflammatory, hormonal, and immunological factors in an effort to identify the molecular basis of human parturition. The majority of the genes and proteins up-regulated in parturition at term are related to four functional categories, mechanical stretch-mediated damage-associated molecular patterns (DAMPs) activation, response to immunity, induction of inflammatory signaling, and progressive uterine myometrial contractility and resultant term birth. Mechanical stretch could promote the entry of amniotic fluid components into the uterine vessel circulation that is the common physiologic mechanism at term prior to labor. The fetal or amniotic fluid-derived DAMPs could activate the immune system. The inflammatory mediators are produced by infiltrating activated leukocytes and by the reproductive tissues themselves such as myometrium, and subsequently lead to uterine contractions. This review supports the sterile inflammation hypothesis that there are at least two phases of human parturition: the initial wave of the entry of amniotic fluid components into uterine vasculatures would be followed by the second big wave of subsequent myometrial contraction.

Current concepts of immunology and diagnosis in amniotic fluid embolism

Amniotic fluid embolism (AFE) is one of the leading causes of maternal mortality and morbidity in developed countries. Current thinking about pathophysiology has shifted away from embolism toward a maternal immune response to the fetus. Two immunologic mechanisms have been studied to date. Anaphylaxis appears to be doubtful while the available evidence supports a role for complement activation. With the mechanism remaining to be elucidated, AFE remains a clinical diagnosis. It is diagnosed based on one or more of four key signs/symptoms: cardiovascular collapse, respiratory distress, coagulopathy, and/or coma/seizures. The only laboratory test that reliably supports the diagnosis is the finding of fetal material in the maternal pulmonary circulation at autopsy. Perhaps the most compelling mystery surrounding AFE is not why one in 20,000 parturients are afflicted, but rather how the vast majority of women can tolerate the foreign antigenic presence of their fetus both within their uterus and circulation?