Cellular immune responses in amniotic fluid of women with preterm clinical chorioamnionitis

Absolute counts of leukocyte subsets in peripheral blood in pregnancies complicated by preterm prelabour rupture of membranes

BACKGROUND

This study aimed to assess variations in the absolute counts of various leukocyte subsets in the peripheral blood of women with pregnancies affected by preterm prelabour rupture of membranes (PPROM), in relation to the presence of intra-amniotic inflammation (IAI).

METHODS

The study included fifty-two women with singleton pregnancies experiencing PPROM. Absolute counts of different leukocyte subpopulations, such as granulocytes, monocytes, lymphocytes, T cells and their subsets, B cells and their subsets, and NK cells and their subsets, were measured in maternal peripheral blood samples using multicolour flow cytometry. IAI was identified by elevated concentrations of interleukin 6 (IL-6) in the amniotic fluid, which was collected through transabdominal amniocentesis.

RESULTS

Women with IAI exhibited higher absolute counts of leukocytes (p = 0.003), granulocytes (p = 0.008), and monocytes (p = 0.009). However, the presence of IAI did not significantly affect the absolute counts of lymphocytes or their subpopulations.

CONCLUSIONS

The study found that IAI is associated with changes in the absolute counts of leukocytes from the innate immunity compartment in the peripheral blood of women with pregnancies complicated by PPROM. Conversely, it does not significantly alter the counts of cells from the adaptive immune system. The changes observed may reflect the natural, temporal, and localised characteristics of IAI.

Risk of adverse perinatal outcomes among women with clinical and subclinical histopathological chorioamnionitis

Introduction

Histologic chorioamnionitis (HCA) is a placental inflammatory condition associated with adverse perinatal outcomes (APOs). This historical cohort study explores the risk of APOs in pregnant women with HCA and compares the impact of clinical chorioamnionitis (CCA) with subclinical chorioamnionitis (SCCA).

Methodology

Placentas were evaluated by a perinatal pathologist tand all women with HCA were included. Two groups were integrated: (1) women with clinical chorioamnionitis (CCA) and (2) women with subclinical chorioamnionitis (SCCA). Additionally, we conducted a secondary analysis to compare the prevalence of APOs among stage 1, 2 and 3 of HCA and the risk of APOs between grades 1 and 2 of HCA. The APOs analyzed were preterm birth, stillbirth, neonatal weight < 1,500 g, neonatal sepsis. Relative risk with 95% confidence interval was calculated.

Results

The study included 41 cases of CCA and 270 cases of SCCA. The mean gestational age at diagnosis and birth was 30.2 ± 5.4 weeks and 32.5 ± 5.1 weeks, for group 1 and 2, respectively. The study also found that women with HCA stage 3 and grade 2 had a higher prevalence and risk of adverse perinatal outcomes.

Discussion

The findings of this study suggest the importance of placental histological study to excluded SCCA, which represents a significant risk to both maternal and neonatal health, contributing to high morbidity and mortality.

Clinical chorioamnionitis at term: definition, pathogenesis, microbiology, diagnosis, and treatment

Clinical chorioamnionitis, the most common infection-related diagnosis in labor and delivery units, is an antecedent of puerperal infection and neonatal sepsis. The condition is suspected when intrapartum fever is associated with two other maternal and fetal signs of local or systemic inflammation (eg, maternal tachycardia, uterine tenderness, maternal leukocytosis, malodorous vaginal discharge or amniotic fluid, and fetal tachycardia). Clinical chorioamnionitis is a syndrome caused by intraamniotic infection, sterile intraamniotic inflammation (inflammation without bacteria), or systemic maternal inflammation induced by epidural analgesia. In cases of uncertainty, a definitive diagnosis can be made by analyzing amniotic fluid with methods to detect bacteria (Gram stain, culture, or microbial nucleic acid) and inflammation (white blood cell count, glucose concentration, interleukin-6, interleukin-8, matrix metalloproteinase-8). The most common microorganisms are Ureaplasma species, and polymicrobial infections occur in 70% of cases. The fetal attack rate is low, and the rate of positive neonatal blood cultures ranges between 0.2% and 4%. Intrapartum antibiotic administration is the standard treatment to reduce neonatal sepsis. Treatment with ampicillin and gentamicin have been recommended by professional societies, although other antibiotic regimens, eg, cephalosporins, have been used. Given the importance of Ureaplasma species as a cause of intraamniotic infection, consideration needs to be given to the administration of antimicrobial agents effective against these microorganisms such as azithromycin or clarithromycin. We have used the combination of ceftriaxone, clarithromycin, and metronidazole, which has been shown to eradicate intraamniotic infection with microbiologic studies. Routine testing of neonates born to affected mothers for genital mycoplasmas could improve the detection of neonatal sepsis. Clinical chorioamnionitis is associated with decreased uterine activity, failure to progress in labor, and postpartum hemorrhage; however, clinical chorioamnionitis by itself is not an indication for cesarean delivery. Oxytocin is often administered for labor augmentation, and it is prudent to have uterotonic agents at hand to manage postpartum hemorrhage. Infants born to mothers with clinical chorioamnionitis near term are at risk for early-onset neonatal sepsis and for long-term disability such as cerebral palsy. A frontier is the noninvasive assessment of amniotic fluid to diagnose intraamniotic inflammation with a transcervical amniotic fluid collector and a rapid bedside test for IL-8 for patients with ruptured membranes. This approach promises to improve diagnostic accuracy and to provide a basis for antimicrobial administration.

Immunophenotyping of Leukocytes in Amniotic Fluid

Immunophenotyping allows for the deep characterization of leukocytes present in biological samples. Here, we describe a complete procedure for the immunophenotyping of amniotic fluid, which can provide information into the immune processes taking place in the amniotic cavity. The protocol describes amniotic fluid cell count determination, processing, and the use of viability, extracellular antibody, and intracellular/intranuclear antibody staining prior to flow cytometer acquisition.

Evidence for the participation of CHCHD2/MNRR1, a mitochondrial protein, in spontaneous labor at term and in preterm labor with intra-amniotic infection

OBJECTIVE

Intra-amniotic inflammation (IAI), associated with either microbe (infection) or danger signals (sterile), plays a major role in the pathophysiology of preterm labor and delivery. Coiled-Coil-Helix-Coiled-Coil-Helix Domain Containing 2 (CHCHD2) [also known as Mitochondrial Nuclear Retrograde Regulator 1 (MNRR1)], a mitochondrial protein involved in oxidative phosphorylation and cell survival, is capable of sensing tissue hypoxia and inflammatory signaling. The ability to maintain an appropriate energy balance at the cellular level while adapting to environmental stress is essential for the survival of an organism. Mitochondrial dysfunction has been observed in acute systemic inflammatory conditions, such as sepsis, and is proposed to be involved in sepsis-induced multi-organ failure. The purpose of this study was to determine the amniotic fluid concentrations of CHCHD2/MNRR1 in pregnant women, women at term in labor, and those in preterm labor (PTL) with and without IAI.

METHODS

This cross-sectional study comprised patients allocated to the following groups: (1) mid-trimester (n = 16); (2) term in labor (n = 37); (3) term not in labor (n = 22); (4) PTL without IAI who delivered at term (n = 25); (5) PTL without IAI who delivered preterm (n = 47); and (6) PTL with IAI who delivered preterm (n = 53). Diagnosis of IAI (amniotic fluid interleukin-6 concentration ≥2.6 ng/mL) included cases associated with microbial invasion of the amniotic cavity and those of sterile nature (absence of detectable bacteria, using culture and molecular microbiology techniques). Amniotic fluid and maternal plasma CHCHD2/MNRR1 concentrations were determined with a validated and sensitive immunoassay.

RESULTS

(1) CHCHD2/MNRR1 was detectable in all amniotic fluid samples and women at term without labor had a higher amniotic fluid CHCHD2/MNRR1 concentration than those in the mid-trimester (p = 0.003); (2) the amniotic fluid concentration of CHCHD2/MNRR1 in women at term in labor was higher than that in women at term without labor (p = 0.01); (3) women with PTL and IAI had a higher amniotic fluid CHCHD2/MNRR1 concentration than those without IAI, either with preterm (p < 0.001) or term delivery (p = 0.01); (4) women with microbial-associated IAI had a higher amniotic fluid CHCHD2/MNRR1 concentration than those with sterile IAI (p < 0.001); (5) among women with PTL and IAI, the amniotic fluid concentration of CHCHD2/MNRR1 correlated with that of interleukin-6 (Spearman's Rho = 0.7; p < 0.001); and (6) no correlation was observed between amniotic fluid and maternal plasma CHCHD2/MNRR1 concentrations among women with PTL.

CONCLUSION

CHCHD2/MNRR1 is a physiological constituent of human amniotic fluid in normal pregnancy, and the amniotic concentration of this mitochondrial protein increases during pregnancy, labor at term, and preterm labor with intra-amniotic infection. Hence, CHCHD2/MNRR1 may be released into the amniotic cavity by dysfunctional mitochondria during microbial-associated IAI.

Thymic stromal lymphopoietin participates in the host response to intra-amniotic inflammation leading to preterm labor and birth

The aim of this study was to establish the role of thymic stromal lymphopoietin (TSLP) in the intra-amniotic host response of women with spontaneous preterm labor (sPTL) and birth. Amniotic fluid and chorioamniotic membranes (CAM) were collected from women with sPTL who delivered at term (n = 30) or preterm without intra-amniotic inflammation (n = 34), with sterile intra-amniotic inflammation (SIAI, n = 27), or with intra-amniotic infection (IAI, n = 17). Amnion epithelial cells (AEC), Ureaplasma parvum, and Sneathia spp. were also utilized. The expression of TSLP, TSLPR, and IL-7Rα was evaluated in amniotic fluid or CAM by RT-qPCR and/or immunoassays. AEC co-cultured with Ureaplasma parvum or Sneathia spp. were evaluated for TSLP expression by immunofluorescence and/or RT-qPCR. Our data show that TSLP was elevated in amniotic fluid of women with SIAI or IAI and expressed by the CAM. TSLPR and IL-7Rα had detectable gene and protein expression in the CAM; yet, CRLF2 was specifically elevated with IAI. While TSLP localized to all layers of the CAM and increased with SIAI or IAI, TSLPR and IL-7Rα were minimal and became most apparent with IAI. Co-culture experiments indicated that Ureaplasma parvum and Sneathia spp. differentially upregulated TSLP expression in AEC. Together, these findings indicate that TSLP is a central component of the intra-amniotic host response during sPTL.

The role of neutrophils in chorioamnionitis

Chorioamnionitis, commonly referred to as intrauterine infection or inflammation, is pathologically defined by neutrophil infiltration and inflammation at the maternal-fetal interface. Chorioamnionitis is the common complication during late pregnancy, which lead to a series of serious consequences, such as preterm labor, preterm premature rupture of the fetal membranes, and fetal inflammatory response syndrome. During infection, a large number of neutrophils migrate to the chorio-decidua in response to chemokines. Although neutrophils, a crucial part of innate immune cells, have strong anti-inflammatory properties, over-activating them can harm the body while also eliminating pathogens. This review concentrated on the latest studies on chorioamnionitis-related consequences as well as the function and malfunction of neutrophils. The release of neutrophil extracellular traps, production of reactive oxygen species, and degranulation from neutrophils during intrauterine infection, as well as their pathological roles in complications related to chorioamnionitis, were discussed in detail, offering fresh perspectives on the treatment of chorioamnionitis.

A single-cell atlas of murine reproductive tissues during preterm labor

Preterm birth, the leading cause of perinatal morbidity and mortality worldwide, frequently results from the syndrome of preterm labor. The best-established causal link to preterm labor is intra-amniotic infection, which involves premature activation of the parturition cascade in the reproductive tissues. Herein, we utilize single-cell RNA sequencing (scRNA-seq) to generate a single-cell atlas of the murine uterus, decidua, and cervix in a model of infection-induced preterm labor. We show that preterm labor affects the transcriptomic profiles of specific immune and non-immune cell subsets. Shared and tissue-specific gene expression signatures are identified among affected cells. Determination of intercellular communications implicates specific cell types in preterm labor-associated signaling pathways across tissues. In silico comparison of murine and human uterine cell-cell interactions reveals conserved signaling pathways implicated in labor. Thus, our scRNA-seq data provide insights into the preterm labor-driven cellular landscape and communications in reproductive tissues.

Preterm labor with intact membranes: a simple noninvasive method to identify patients at risk for intra-amniotic infection and/or inflammation

OBJECTIVE

To develop a noninvasive scoring system to identify patients at high risk for intra-amniotic infection and/or inflammation, which would reduce the need for amniocentesis.

METHODS

This prospective cohort study comprised patients admitted with preterm labor and intact membranes (20-34 weeks of gestation) who underwent a transabdominal amniocentesis and for whom concentrations of quantitative cervical fetal fibronectin and of maternal serum C-reactive protein (CRP) were determined. Intra-amniotic infection was defined as a positive amniotic fluid culture for microorganisms. Intra-amniotic inflammation was defined as an amniotic fluid matrix metalloproteinase-8 concentration >23 ng/mL. Multivariate logistic regression analysis was performed to identify intra-amniotic infection/inflammtion with noninvasive parameters that had a significant relationship with univariate analysis. With four parameters identified by multivariate analysis, we generated a noninvasive risk scoring system.

RESULTS

Of the study population consisting of 138 singleton pregnant women, (1) the overall rate of intra-amniotic infection/inflammation was 28.3% (39/138); (2) four parameters were used to develop a noninvasive risk scoring system [i.e. cervical fetal fibronectin concentration (score 0-2), maternal serum CRP concentration (score 0-2), cervical dilatation (score 0-2), and gestational age at presentation (score 0-1)]; the total score ranges from 0 to 7; 3) the area under the curve of the risk score was 0.96 (95% confidence interval (CI), 0.92-0.99), significantly higher than that of each predictor in the identification of intra-amniotic infection/inflammation (p < .001, for all); 4) the risk score with a cutoff of 4 had a sensitivity of 94.9% (37/39), a specificity of 90.9% (90/99), a positive predictive value of 80.4% (37/46), a negative predictive value of 97.8% (90/92), a positive likelihood ratio of 10.4 (95% CI, 5.6-19.5), and a negative likelihood ratio of 0.06 (95% CI, 0.15-0.22) in the identification of intra-amniotic infection/inflammation.

CONCLUSIONS

(1) The combination of four parameters (concentrations of cervical fetal fibronectin and maternal serum CRP, cervical dilatation, and gestational age) was independently associated with intra-amniotic infection and/or inflammation; and (2) the risk scoring system comprised of the combination of 4 noninvasive parameters was sensitive and specific to identify the patients at risk for intra-amniotic infection and/or inflammation.

The Role of Neutrophils in Pregnancy, Term and Preterm Labour

Neutrophils are surveillance cells, and the first to react and migrate to sites of inflammation and infection following a chemotactic gradient. Neutrophils play a key role in both sterile inflammation and infection, performing a wide variety of effector functions such as degranulation, phagocytosis, ROS production and release of neutrophil extracellular traps (NETs). Healthy term labour requires a sterile pro-inflammatory process, whereas one of the most common causes of spontaneous preterm birth is microbial driven. Peripheral neutrophilia has long been described during pregnancy, and evidence exists demonstrating neutrophils infiltrating the cervix, uterus and foetal membranes during both term and preterm deliveries. Their presence supports a role in tissue remodelling via their effector functions. In this review, we describe the effector functions of neutrophils. We summarise the evidence to support their role in healthy pregnancy and labour and describe their potential contribution to microbial driven preterm birth.

The amniotic fluid proteome predicts imminent preterm delivery in asymptomatic women with a short cervix

Preterm birth, the leading cause of perinatal morbidity and mortality, is associated with increased risk of short- and long-term adverse outcomes. For women identified as at risk for preterm birth attributable to a sonographic short cervix, the determination of imminent delivery is crucial for patient management. The current study aimed to identify amniotic fluid (AF) proteins that could predict imminent delivery in asymptomatic patients with a short cervix. This retrospective cohort study included women enrolled between May 2002 and September 2015 who were diagnosed with a sonographic short cervix (< 25 mm) at 16-32 weeks of gestation. Amniocenteses were performed to exclude intra-amniotic infection; none of the women included had clinical signs of infection or labor at the time of amniocentesis. An aptamer-based multiplex platform was used to profile 1310 AF proteins, and the differential protein abundance between women who delivered within two weeks from amniocentesis, and those who did not, was determined. The analysis included adjustment for quantitative cervical length and control of the false-positive rate at 10%. The area under the receiver operating characteristic curve was calculated to determine whether protein abundance in combination with cervical length improved the prediction of imminent preterm delivery as compared to cervical length alone. Of the 1,310 proteins profiled in AF, 17 were differentially abundant in women destined to deliver within two weeks of amniocentesis independently of the cervical length (adjusted p-value < 0.10). The decreased abundance of SNAP25 and the increased abundance of GPI, PTPN11, OLR1, ENO1, GAPDH, CHI3L1, RETN, CSF3, LCN2, CXCL1, CXCL8, PGLYRP1, LDHB, IL6, MMP8, and PRTN3 were associated with an increased risk of imminent delivery (odds ratio > 1.5 for each). The sensitivity at a 10% false-positive rate for the prediction of imminent delivery by a quantitative cervical length alone was 38%, yet it increased to 79% when combined with the abundance of four AF proteins (CXCL8, SNAP25, PTPN11, and MMP8). Neutrophil-mediated immunity, neutrophil activation, granulocyte activation, myeloid leukocyte activation, and myeloid leukocyte-mediated immunity were biological processes impacted by protein dysregulation in women destined to deliver within two weeks of diagnosis. The combination of AF protein abundance and quantitative cervical length improves prediction of the timing of delivery compared to cervical length alone, among women with a sonographic short cervix.

The immunobiology of preterm labor and birth: intra-amniotic inflammation or breakdown of maternal-fetal homeostasis

In brief

The syndrome of preterm labor comprises multiple established and novel etiologies. This review summarizes the distinct immune mechanisms implicated in preterm labor and birth and highlights potential strategies for its prevention.

Abstract

Preterm birth, the leading cause of neonatal morbidity and mortality worldwide, results from preterm labor, a syndrome that includes multiple etiologies. In this review, we have summarized the immune mechanisms implicated in intra-amniotic inflammation, the best-characterized cause of preterm labor and birth, as well as novel etiologies non-associated with intra-amniotic inflammation (i.e. formally known as idiopathic). While the intra-amniotic inflammatory responses driven by microbes (infection) or alarmins (sterile) have some overlap in the participating cellular and molecular processes, the distinct natures of these two conditions necessitate the implementation of specific approaches to prevent adverse pregnancy and neonatal outcomes. Intra-amniotic infection can be treated with the correct antibiotics, whereas sterile intra-amniotic inflammation could potentially be treated by administering a combination of anti-inflammatory drugs (e.g. betamethasone, inflammasome inhibitors, etc.). Recent evidence also supports the role of fetal T-cell activation as a newly described trigger for preterm labor and birth in a subset of cases diagnosed as idiopathic. Moreover, herein we also provide evidence of two maternally-driven immune mechanisms responsible for preterm births formerly considered to be idiopathic. First, the impairment of maternal Tregs can lead to preterm birth, likely due to the loss of immunosuppressive activity resulting in unleashed effector T-cell responses. Secondly, homeostatic macrophages were shown to be essential for maintaining pregnancy and promoting fetal development, and the adoptive transfer of homeostatic M2-polarized macrophages shows great promise for preventing inflammation-induced preterm birth. Collectively, in this review, we discuss the established and novel immune mechanisms responsible for preterm birth and highlight the potential targets for novel strategies aimed at preventing the multi-etiological syndrome of preterm labor leading to preterm birth.

Calprotectin levels in amniotic fluid in relation to intra-amniotic inflammation and infection in women with preterm labor with intact membranes: A retrospective cohort study

OBJECTIVE

To evaluate the concentrations of calprotectin in amniotic fluid with respect to intra-amniotic inflammation and infection and to assess the presence or absence of bacteria in the amnio-chorionic niche with respect to presence or absence of intra-amniotic inflammation.

STUDY DESIGN

Seventy-nine women with singleton pregnancies and preterm labor with intact membranes (PTL) were included in the study. Amniotic fluid was collected at the time of admission by amniocentesis and calprotectin levels were analyzed from frozen/thawed samples using ELISA. Interleukin (IL)-6 concentration was measured by point-of-care test. Samples from amniotic fluid and the amnio-chorionic niche (space between amniotic and chorionic membranes) were microbiologically analyzed. Microbial invasion of the amniotic cavity (MIAC) was diagnosed based on a positive PCR result for Ureaplasma species, Mycoplasma hominis, 16S rRNA or positive culture. Intra-amniotic inflammation (IAI) was defined as amniotic fluid point-of-care IL-6 concentration ≥ 745 pg/mL. The cohort of included women was divided into 4 subgroups based on the presence or absence of IAI/MIAC; i) intra-amniotic infection, ii) sterile IAI, iii) intra-amniotic colonization and iv) neither MIAC nor IAI.

RESULTS

Women with intra-amniotic infection had a significantly higher intra-amniotic calprotectin concentration (median; 101.6 µg/mL) compared with women with sterile IAI (median; 9.2 µg/mL), women with intra-amniotic colonization (median; 2.6 µg/mL) and women with neither MIAC nor IAI (median 4.6 µg/mL) (p = 0.001). Moreover, significantly higher amniotic fluid calprotectin concentration was seen in women who delivered within 7 days (p = 0.003). A significant negative correlation was found between amniotic fluid calprotectin and gestational age at delivery (rho = 0.32, p = 0.003). Relatively more bacteria in the amnio-chorionic niche were found in the sterile IAI group compared with the other groups.

CONCLUSIONS

Calprotectin concentrations in amniotic fluid were significantly higher in the intra-amniotic infection group compared with the other groups. Moreover, the bacterial presence in the amnio-chorionic niche was higher in IAI group.

Pregnancy tailors endotoxin-induced monocyte and neutrophil responses in the maternal circulation

Objective

To comprehensively characterize monocyte and neutrophil responses to E. coli and its product [lipopolysaccharide (LPS) or endotoxin] in vitro during pregnancy.

Material or subjects

Peripheral blood was collected from pregnant women during the third trimester (n = 20) and from non-pregnant women (n = 20).

Methods

The number, phagocytic activity, and reactive oxygen species (ROS) production of peripheral monocytes and neutrophils were investigated using flow cytometry. The phenotypes of peripheral monocytes and neutrophils after acute or chronic LPS stimulation were also determined using flow cytometry. Cytokine profiles were quantified for LPS-stimulated peripheral blood mononuclear cells (PBMCs) and a whole blood TruCulture^® system using a multiplex immunoassay.

Results

Increased number, phagocytic activity, and ROS production capacity of monocytes and neutrophils were found in pregnant compared to non-pregnant women. Additionally, specific subsets of pro-inflammatory monocytes (IL-6⁺CD14⁺ or MIP-1α⁺CD14⁺ cells) and neutrophils (IL-1β⁺CD15⁺ or MIP-1β⁺CD15⁺ cells) were increased in pregnant women in response to acute LPS stimulation. Moreover, distinct subsets of intermediate-activated monocytes expressing CD142, IL-6, and IL-1RA were increased in pregnant women upon chronic LPS stimulation. Last, pregnant women displayed a different cytokine profile than non-pregnant women in LPS-stimulated PBMCs and in whole blood.

Conclusions

Pregnancy tailors the immune responses of circulating monocytes and neutrophils to endotoxin, a Gram-negative bacterial product.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00011-022-01569-z.

IL-22 Plays a Dual Role in the Amniotic Cavity: Tissue Injury and Host Defense against Microbes in Preterm Labor

IL-22 is a multifaceted cytokine with both pro- and anti-inflammatory functions that is implicated in multiple pathologies. However, the role of IL-22 in maternal-fetal immunity in late gestation is poorly understood. In this study, we first showed that IL-22+ T cells coexpressing retinoic acid-related orphan receptor γt (ROR-γt) are enriched at the human maternal-fetal interface of women with preterm labor and birth, which was confirmed by in silico analysis of single-cell RNA sequencing data. T cell activation leading to preterm birth in mice was preceded by a surge in IL-22 in the maternal circulation and amniotic cavity; however, systemic administration of IL-22 in mice did not induce adverse perinatal outcomes. Next, using an ex vivo human system, we showed that IL-22 can cross from the choriodecidua to the intra-amniotic space, where its receptors (Il22ra1, Il10rb, and Il22ra2) are highly expressed by murine gestational and fetal tissues in late pregnancy. Importantly, amniotic fluid concentrations of IL-22 were elevated in women with sterile or microbial intra-amniotic inflammation, suggesting a dual role for this cytokine. The intra-amniotic administration of IL-22 alone shortened gestation and caused neonatal death in mice, with the latter outcome involving lung maturation and inflammation. IL-22 plays a role in host response by participating in the intra-amniotic inflammatory milieu preceding Ureaplasma parvum-induced preterm birth in mice, which was rescued by the deficiency of IL-22. Collectively, these data show that IL-22 alone is capable of causing fetal injury leading to neonatal death and can participate in host defense against microbial invasion of the amniotic cavity leading to preterm labor and birth.

Does the Amniotic Fluid of Mice Contain a Viable Microbiota?

The existence of an amniotic fluid microbiota (i.e., a viable microbial community) in mammals is controversial. Its existence would require a fundamental reconsideration of fetal in utero exposure to and colonization by microorganisms and the role of intra-amniotic microorganisms in fetal immune development as well as in pregnancy outcomes. In this study, we determined whether the amniotic fluid of mice harbors a microbiota in late gestation. The profiles of the amniotic fluids of pups located proximally or distally to the cervix were characterized through quantitative real-time PCR, 16S rRNA gene sequencing, and culture (N = 21 dams). These profiles were compared to those of technical controls for bacterial and DNA contamination. The load of 16S rRNA genes in the amniotic fluid exceeded that in controls. Additionally, the 16S rRNA gene profiles of the amniotic fluid differed from those of controls, with Corynebacterium tuberculostearicum being differentially more abundant in amniotic fluid profiles; however, this bacterium was not cultured from amniotic fluid. Of the 42 attempted bacterial cultures of amniotic fluids, only one yielded bacterial growth – Lactobacillus murinus. The 16S rRNA gene of this common murine-associated bacterium was not detected in any amniotic fluid sample, suggesting it did not originate from the amniotic fluid. No differences in the 16S rRNA gene load, 16S rRNA gene profile, or bacterial culture were observed between the amniotic fluids located Proximally and distally to the cervix. Collectively, these data indicate that, although there is a modest DNA signal of bacteria in murine amniotic fluid, there is no evidence that this signal represents a viable microbiota. While this means that amniotic fluid is not a source of microorganisms for in utero colonization in mice, it may nevertheless contribute to fetal exposure to microbial components. The developmental consequences of this observation warrant further investigation.

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.

The amniotic fluid proteome changes with gestational age in normal pregnancy: a cross-sectional study

The cell-free transcriptome in amniotic fluid (AF) has been shown to be informative of physiologic and pathologic processes in pregnancy; however, the change in AF proteome with gestational age has mostly been studied by targeted approaches. The objective of this study was to describe the gestational age-dependent changes in the AF proteome during normal pregnancy by using an omics platform. The abundance of 1310 proteins was measured on a high-throughput aptamer-based proteomics platform in AF samples collected from women during midtrimester (16-24 weeks of gestation, n = 15) and at term without labor (37-42 weeks of gestation, n = 13). Only pregnancies without obstetrical complications were included in the study. Almost 25% (320) of AF proteins significantly changed in abundance between the midtrimester and term gestation. Of these, 154 (48.1%) proteins increased, and 166 (51.9%) decreased in abundance at term compared to midtrimester. Tissue-specific signatures of the trachea, salivary glands, brain regions, and immune system were increased while those of the gestational tissues (uterus, placenta, and ovary), cardiac myocytes, and fetal liver were decreased at term compared to midtrimester. The changes in AF protein abundance were correlated with those previously reported in the cell-free AF transcriptome. Intersecting gestational age-modulated AF proteins and their corresponding mRNAs previously reported in the maternal blood identified neutrophil-related protein/mRNA pairs that were modulated in the same direction. The first study to utilize an aptamer-based assay to profile the AF proteome modulation with gestational age, it reveals that almost one-quarter of the proteins are modulated as gestation advances, which is more than twice the fraction of altered plasma proteins (~ 10%). The results reported herein have implications for future studies focused on discovering biomarkers to predict, monitor, and diagnose obstetrical diseases.

The Role of Innate Immune System in the Human Amniotic Membrane and Human Amniotic Fluid in Protection Against Intra-Amniotic Infections and Inflammation

Intra-amniotic infection and inflammation (IAI) affect fetal development and are highly associated with preterm labor and premature rupture of membranes, which often lead to adverse neonatal outcomes. Human amniotic membrane (hAM), the inner part of the amnio-chorionic membrane, protects the embryo/fetus from environmental dangers, including microbial infection. However, weakened amnio-chorionic membrane may be breached or pathogens may enter through a different route, leading to IAI. The hAM and human amniotic fluid (hAF) respond by activation of all components of the innate immune system. This includes changes in 1) hAM structure, 2) presence of immune cells, 3) pattern recognition receptors, 4) cytokines, 5) antimicrobial peptides, 6) lipid derivatives, and 7) complement system. Herein we provide a comprehensive and integrative review of the current understanding of the innate immune response in the hAM and hAF, which will aid in design of novel studies that may lead to breakthroughs in how we perceive the IAI.

The Distinct Immune Nature of the Fetal Inflammatory Response Syndrome Type I and Type II

Fetal inflammatory response syndrome (FIRS) is strongly associated with neonatal morbidity and mortality and can be classified as type I or type II. Clinically, FIRS type I and type II are considered as distinct syndromes, yet the molecular underpinnings of these fetal inflammatory responses are not well understood because of their low prevalence and the difficulty of postdelivery diagnosis. In this study, we performed RNA sequencing of human cord blood samples from preterm neonates diagnosed with FIRS type I or FIRS type II. We found that FIRS type I was characterized by an upregulation of host immune responses, including neutrophil and monocyte functions, together with a proinflammatory cytokine storm and a downregulation of T cell processes. In contrast, FIRS type II comprised a mild chronic inflammatory response involving perturbation of HLA transcripts, suggestive of fetal semiallograft rejection. Integrating single-cell RNA sequencing-derived signatures with bulk transcriptomic data confirmed that FIRS type I immune responses were mainly driven by monocytes, macrophages, and neutrophils. Last, tissue- and cell-specific signatures derived from the BioGPS Gene Atlas further corroborated the role of myeloid cells originating from the bone marrow in FIRS type I. Collectively, these data provide evidence that FIRS type I and FIRS type II are driven by distinct immune mechanisms; whereas the former involves the innate limb of immunity consistent with host defense, the latter resembles a process of semiallograft rejection. These findings shed light on the fetal immune responses caused by infection or alloreactivity that can lead to deleterious consequences in neonatal life.

RNA Sequencing Reveals Distinct Immune Responses in the Chorioamniotic Membranes of Women with Preterm Labor and Microbial or Sterile Intra-amniotic Inflammation

Preterm labor precedes premature birth, the leading cause of neonatal morbidity and mortality worldwide. Preterm labor can occur in the context of either microbe-associated intra-amniotic inflammation (i.e., intra-amniotic infection) or intra-amniotic inflammation in the absence of detectable microorganisms (i.e., sterile intra-amniotic inflammation). Both intra-amniotic infection and sterile intra-amniotic inflammation trigger local immune responses that have deleterious effects on fetal life. Yet, the extent of such immune responses in the fetal tissues surrounding the amniotic cavity (i.e., the chorioamniotic membranes) is poorly understood. By using RNA sequencing (RNA seq) as a discovery approach, we found that there were significant transcriptomic differences involving host response to pathogens in the chorioamniotic membranes of women with intra-amniotic infection compared to those from women without inflammation. In addition, the sterile or microbial nature of intra-amniotic inflammation was associated with distinct transcriptomic profiles in the chorioamniotic membranes. Moreover, the immune response in the chorioamniotic membranes of women with sterile intra-amniotic inflammation was milder in nature than that induced by microbes and involved the upregulation of alarmins and inflammasome-related molecules. Lastly, the presence of maternal and fetal inflammatory responses in the placenta was associated with the upregulation of immune processes in the chorioamniotic membranes. Collectively, these findings provide insight into the immune responses against microbes or alarmins that take place in the fetal tissues surrounding the amniotic cavity, shedding light on the immunobiology of preterm labor and birth.

Sneathia: an emerging pathogen in female reproductive disease and adverse perinatal outcomes

Sneathia is an emerging pathogen implicated in adverse reproductive and perinatal outcomes. Although scarce, recent data suggest that vaginally residing Sneathia becomes pathogenic following its ascension into the upper urogenital tract, amniotic fluid, placenta, and foetal membranes. The role of Sneathia in women's health and disease is generally underappreciated because the cultivation of these bacteria is limited by their complex nutritional requirements, slow growth patterns, and anaerobic nature. For this reason, molecular methods are typically required for the detection and differential diagnosis of Sneathia infections. Here, we review the laboratory methods used for the diagnosis of Sneathia infections, the molecular mechanisms underlying its virulence, and its sensitivity to antibiotics. We further review the evidence of Sneathia's contributions to the pathogenesis of bacterial vaginosis, chorioamnionitis, preterm prelabour rupture of membranes, spontaneous preterm labour, stillbirth, maternal and neonatal sepsis, HIV infection, and cervical cancer. Collectively, growing evidence indicates that Sneathia represents an important yet underappreciated pathogen affecting the development and progression of several adverse clinical conditions diagnosed in pregnant women and their neonates, as well as in non-pregnant women.

Immune Regulation, Maternal Infection, Vaccination, and Pregnancy Outcome

About 12.5% of all maternal deaths in the United States are due to infectious causes. This proportion, although stable during the past three decades, represents an increase in infectious causes of mortality, as the overall mortality rate in U.S. pregnant women had increased steadily during that same period. During healthy pregnancies, a delicate immunological balance-in which a mother's immune system tolerates the semi-allogeneic fetus yet maintains immune competency against infectious agents-is achieved and maintained. This immunological paradigm, however, results in increased susceptibility to infectious diseases during pregnancy, particularly in later stages and during the early postpartum period. The inflammatory process induced by these infectious insults, as well as some noninfectious insults, occurring during pregnancy can disrupt this carefully achieved balance and, in turn, lead to a state of rampant inflammation, immune activation, and dysregulation with deleterious health outcomes for the mother and fetus. Elucidating mechanisms contributing to the disruption of this immunologic homeostasis, and its disruption by infectious pathogens, might offer opportunities for interventions to reduce maternal and fetal morbidity and mortality.

Management of clinical chorioamnionitis: an evidence-based approach

This review aimed to examine the existing evidence about interventions proposed for the treatment of clinical chorioamnionitis, with the goal of developing an evidence-based contemporary approach for the management of this condition. Most trials that assessed the use of antibiotics in clinical chorioamnionitis included patients with a gestational age of ≥34 weeks and in labor. The first-line antimicrobial regimen for the treatment of clinical chorioamnionitis is ampicillin combined with gentamicin, which should be initiated during the intrapartum period. In the event of a cesarean delivery, patients should receive clindamycin at the time of umbilical cord clamping. The administration of additional antibiotic therapy does not appear to be necessary after vaginal or cesarean delivery. However, if postdelivery antibiotics are prescribed, there is support for the administration of an additional dose. Patients can receive antipyretic agents, mainly acetaminophen, even though there is no clear evidence of their benefits. Current evidence suggests that the administration of antenatal corticosteroids for fetal lung maturation and of magnesium sulfate for fetal neuroprotection to patients with clinical chorioamnionitis between 24 0/7 and 33 6/7 weeks of gestation, and possibly between 23 0/7 and 23 6/7 weeks of gestation, has an overall beneficial effect on the infant. However, delivery should not be delayed to complete the full course of corticosteroids and magnesium sulfate. Once the diagnosis of clinical chorioamnionitis has been established, delivery should be considered, regardless of the gestational age. Vaginal delivery is the safer option and cesarean delivery should be reserved for standard obstetrical indications. The time interval between the diagnosis of clinical chorioamnionitis and delivery is not related to most adverse maternal and neonatal outcomes. Patients may require a higher dose of oxytocin to achieve adequate uterine activity or greater uterine activity to effect a given change in cervical dilation. The benefit of using continuous electronic fetal heart rate monitoring in these patients is unclear. We identified the following promising interventions for the management of clinical chorioamnionitis: (1) an antibiotic regimen including ceftriaxone, clarithromycin, and metronidazole that provides coverage against the most commonly identified microorganisms in patients with clinical chorioamnionitis; (2) vaginal cleansing with antiseptic solutions before cesarean delivery with the aim of decreasing the risk of endometritis and, possibly, postoperative wound infection; and (3) antenatal administration of N-acetylcysteine, an antioxidant and antiinflammatory agent, to reduce neonatal morbidity and mortality. Well-powered randomized controlled trials are needed to assess these interventions in patients with clinical chorioamnionitis.

RNA Sequencing Reveals Diverse Functions of Amniotic Fluid Neutrophils and Monocytes/Macrophages in Intra-Amniotic Infection

Intra-amniotic infection, the invasion of microbes into the amniotic cavity resulting in inflammation, is a clinical condition that can lead to adverse pregnancy outcomes for the mother and fetus as well as severe long-term neonatal morbidities. Despite much research focused on the consequences of intra-amniotic infection, there remains little knowledge about the innate immune cells that respond to invading microbes. We performed RNA-seq of sorted amniotic fluid neutrophils and monocytes/macrophages from women with intra-amniotic infection to determine the transcriptomic differences between these innate immune cells. Further, we sought to identify specific transcriptomic pathways that were significantly altered by the maternal or fetal origin of amniotic fluid neutrophils and monocytes/macrophages, the presence of a severe fetal inflammatory response, and pregnancy outcome (i.e., preterm or term delivery). We show that significant transcriptomic differences exist between amniotic fluid neutrophils and monocytes/macrophages from women with intra-amniotic infection, indicating the distinct roles these cells play. The transcriptome of amniotic fluid immune cells varies based on their maternal or fetal origin, and the significant transcriptomic differences between fetal and maternal monocytes/macrophages imply that those of fetal origin exhibit impaired functions. Notably, transcriptomic changes in amniotic fluid monocytes/macrophages suggest that these immune cells collaborate with neutrophils in the trafficking of fetal leukocytes throughout the umbilical cord (i.e., funisitis). Finally, amniotic fluid neutrophils and monocytes/macrophages from preterm deliveries display enhanced transcriptional activity compared to those from term deliveries, highlighting the protective role of these cells during this vulnerable period. Collectively, these findings demonstrate the underlying complexity of local innate immune responses in women with intra-amniotic infection and provide new insights into the functions of neutrophils and monocytes/macrophages in the amniotic cavity.

Cellular immune responses in amniotic fluid of women with a sonographic short cervix

Objectives A sonographic short cervix is one of the strongest predictors of preterm delivery. However, the cellular immune composition of amniotic fluid in women with a short cervix has not yet been described. Herein, we determined cellular and soluble immune responses in amniotic fluid from pregnant women with a mid-trimester asymptomatic short cervix. Methods Amniotic fluid samples (n=77) were collected from asymptomatic women with a cervical length between 15 and 25 mm (n=36, short cervix) or ≤15 mm (n=41, severely short cervix) diagnosed by ultrasound. Flow cytometry and multiplex measurement of cytokines/chemokines were performed. Results (1) The cellular immune composition of amniotic fluid did not differ between women with a severely short cervix (≤15 mm) and those with a short cervix 15-25 mm; (2) amniotic fluid concentrations of multiple cytokines/chemokines were higher in women with a severely short cervix (≤15 mm) than in those with a short cervix 15-25 mm; (3) the cellular immune composition of amniotic fluid did not differ between women with a severely short cervix (≤15 mm) who ultimately underwent preterm delivery and those who delivered at term; and (4) amniotic fluid concentrations of IL-2, but not other immune mediators, were increased in women with a severely short cervix (≤15 mm) who ultimately delivered preterm compared to those who delivered at term. Conclusions Women with a severely short cervix (≤15 mm) have increased concentrations of pro-inflammatory mediators in the amniotic cavity; yet, these do not translate to changes in the cellular immune response.

Maternal and fetal T cells in term pregnancy and preterm labor

Pregnancy is a state of immunological balance during which the mother and the developing fetus must tolerate each other while maintaining sufficient immunocompetence to ward off potential threats. The site of closest contact between the mother and fetus is the decidua, which represents the maternal-fetal interface. Many of the immune cell subsets present at the maternal-fetal interface have been well described; however, the importance of the maternal T cells in this compartment during late gestation and its complications, such as preterm labor and birth, has only recently been established. Moreover, pioneer and recent studies have indicated that fetal T cells are activated in different subsets of preterm labor and may elicit distinct inflammatory responses in the amniotic cavity, leading to preterm birth. In this review, we describe the established and proposed roles for maternal T cells at the maternal-fetal interface in normal term parturition, as well as the demonstrated contributions of such cells to the pathological process of preterm labor and birth. We also summarize the current knowledge of and proposed roles for fetal T cells in the pathophysiology of the preterm labor syndrome. It is our hope that this review provides a solid conceptual framework highlighting the importance of maternal and fetal T cells in late gestation and catalyzes new research questions that can further scientific understanding of these cells and their role in preterm labor and birth, the leading cause of neonatal mortality and morbidity worldwide.

Cellular immune responses in amniotic fluid of women with preterm prelabor rupture of membranes

Background Preterm birth is the leading cause of perinatal morbidity and mortality. Preterm prelabor rupture of membranes (pPROM) occurs in 30% of preterm births; thus, this complication is a major contributor to maternal and neonatal morbidity. However, the cellular immune responses in amniotic fluid of women with pPROM have not been investigated. Methods Amniotic fluid samples were obtained from women with pPROM and a positive (n = 7) or negative (n = 10) microbiological culture. Flow cytometry was performed to evaluate the phenotype and number of amniotic fluid leukocytes. The correlation between amniotic fluid immune cells and an interleukin-6 (IL-6) concentration or a white blood cell (WBC) count in amniotic fluid was calculated. Results Women with pPROM and a positive amniotic fluid culture had (1) a greater number of total leukocytes in amniotic fluid, including neutrophils and monocytes/macrophages and (2) an increased number of total T cells in amniotic fluid, namely CD4+ T cells and CD8+ T cells, but not B cells. The numbers of neutrophils and monocytes/macrophages were positively correlated with IL-6 concentrations and WBC counts in amniotic fluid of women with pPROM. Conclusion Women with pPROM and a positive amniotic fluid culture exhibit a more severe cellular immune response than those with a negative culture, which is associated with well-known markers of intra-amniotic inflammation.