Influenza A virus causes maternal and fetal pathology via innate and adaptive vascular inflammation in mice

Maternal Immune Activation: Implications for Congenital Heart Defects

Congenital heart defects (CHD) are the most common major birth defects and one of the leading causes of death from congenital defects after birth. CHD can arise in pregnancy from the combination of genetic and non-genetic factors. The maternal immune activation (MIA) hypothesis is widely implicated in embryonic neurodevelopmental abnormalities. MIA has been found to be associated with the development of asthma, diabetes mellitus, and other diseases in the offspring. Given the important role of cardiac immune cells and cytokines in embryonic heart development, it is hypothesized that MIA may play a significant role in embryonic heart development. This review aims to stimulate further investigation into the relationship between MIA and CHD and to highlight the gaps in the knowledge. It evaluates the impact of MIA on CHD in the context of pregnancy complications, immune-related diseases, infections, and environmental and lifestyle factors. The review outlines the mechanisms by which immune cells and their secretome indirectly regulate the immuno-microenvironment of the embryonic heart by influencing placental development. Furthermore, the inflammatory cytokines cross the placenta to induce related reactions including oxidative stress in the embryonic heart directly. This review delineates the role of MIA in CHD and underscores the impact of maternal factors, especially immune factors, as well as the embryonic cardiac immuno-microenvironment, on embryonic heart development. This review extends our understanding of the importance of MIA in the pathogenesis of CHD and provides important insights into prenatal prevention and treatment strategies for this congenital condition.

Maternal immune activation elicits rapid and sex-dependent changes in gene expression and vascular dysfunction in the rat placenta

INTRODUCTION

Maternal immune activation (MIA), characterized by increased circulating inflammatory mediators during pregnancy, is associated with adverse pregnancy outcomes and neurodevelopmental deficits in offspring. These health outcomes often manifest differently depending on fetal-placental sex. A well-established model of MIA involves administration of a viral mimetic, polyinosinic:polycytidilic acid (PolyI:C), to pregnant rodents. Placental responses to PolyI:C contribute to the detrimental effects of MIA on offspring, but these responses have not yet been well characterized. In the present study, we profiled acute gene expression changes in male and female placentas following PolyI:C administration to pregnant rats during late gestation.

METHODS

Pregnant rats received 4 mg/kg PolyI:C or saline intravenously on gestational day 18.5, and tissues were harvested 4-5 h later. Gene expression profiling on placental tissue was performed. Enzyme immunoassays and immunohistochemistry were conducted to determine levels of select proteins in maternal blood and placental tissue, respectively.

RESULTS

Maternal PolyI:C exposure caused a robust increase in levels of inflammatory mediators in maternal blood and placental tissue. There were more genes differentially expressed in female placentas after PolyI:C exposure (765) than male placentas (221), including reduced expression of genes associated with maternal-fetal communication. Placentas also had increased expression of genes linked with vascular dysfunction after PolyI:C-induced MIA.

DISCUSSION

PolyI:C elicited a powerful inflammatory response in the placenta along with vascular dysfunction, likely contributing to the adverse pregnancy outcomes triggered by MIA. Female placentas responded to PolyI:C more vigorously than male placentas, which could underlie the differential outcomes of MIA depending on sex.

Hippocampal reelin and GAD67 gene expression and methylation in the GFAP.HMOX1 mouse model of schizophrenia

Schizophrenia is a complex neuropsychiatric disorder featuring enhanced brain oxidative stress and deficient reelin protein. GFAP.HMOX10-12m mice that overexpress heme oxygenase-1 (HO-1) in astrocytes manifest a schizophrenia-like neurochemical, neuropathological and behavioral phenotype including brain oxidative stress and reelin downregulation. We used RT-PCR, targeted bisulfite next-generation sequencing, immunohistochemistry and in situ hybridization on hippocampal tissue of GFAP.HMOX10-12m mice to delineate a possible molecular mechanism for the downregulation of reelin and to identify the neuronal and non-neuronal (glial) cell types expressing reelin in our model. We found reduced reelin and increased DNMT1 and TET1 mRNA expression in the hippocampus of male GFAP.HMOX10-12m mice and reduced GAD67 mRNA expression in females. These mRNA changes were accompanied by sexually dimorphic alterations in DNA methylation levels of Reln and Gad1 genes. Reelin protein was expressed by oligodendrocytes and GABAergic interneurons, but not by astrocytes or microglia in GFAP.HMOX10-12m and wild-type brains of both sexes. Reelin mRNA was also observed in oligodendrocytes. Moreover, a significant downregulation of reelin-expressing oligodendrocytes was detected in the hippocampal dentate gyrus of male GFAP.HMOX10-12m mice. These results suggest a novel mechanism for brain reelin depletion in schizophrenia. Containment of the astrocytic HO-1 cascade by pharmacological or other means may protect against stress-induced brain reelin depletion in schizophrenia and other neurodevelopmental disorders.

Influenza A virus during pregnancy disrupts maternal intestinal immunity and fetal cortical development in a dose- and time-dependent manner

Epidemiological studies link exposure to viral infection during pregnancy, including influenza A virus (IAV) infection, with increased incidence of neurodevelopmental disorders (NDDs) in offspring. Models of maternal immune activation (MIA) using viral mimetics demonstrate that activation of maternal intestinal T helper 17 (TH17) cells, which produce effector cytokine interleukin (IL)-17, leads to aberrant fetal brain development, such as neocortical malformations. Fetal microglia and border-associated macrophages (BAMs) also serve as potential cellular mediators of MIA-induced cortical abnormalities. However, neither the inflammation-induced TH17 cell pathway nor fetal brain-resident macrophages have been thoroughly examined in models of live viral infection during pregnancy. Here, we inoculated pregnant mice with two infectious doses of IAV and evaluated peak innate and adaptive immune responses in the dam and fetus. While respiratory IAV infection led to dose-dependent maternal colonic shortening and microbial dysregulation, there was no elevation in intestinal TH17 cells nor IL-17. Systemically, IAV resulted in consistent dose- and time-dependent increases in IL-6 and IFN-γ. Fetal cortical abnormalities and global changes in fetal brain transcripts were observable in the high-but not the moderate-dose IAV group. Profiling of fetal microglia and BAMs revealed dose- and time-dependent differences in the numbers of meningeal but not choroid plexus BAMs, while microglial numbers and proliferative capacity of Iba1+ cells remained constant. Fetal brain-resident macrophages increased phagocytic CD68 expression, also in a dose- and time-dependent fashion. Taken together, our findings indicate that certain features of MIA are conserved between mimetic and live virus models, while others are not. Overall, we provide consistent evidence of an infection severity threshold for downstream maternal inflammation and fetal cortical abnormalities, which recapitulates a key feature of the epidemiological data and further underscores the importance of using live pathogens in NDD modeling to better evaluate the complete immune response and to improve translation to the clinic.

TLR7 Promotes Acute Inflammatory-Driven Lung Dysfunction in Influenza-Infected Mice but Prevents Late Airway Hyperresponsiveness

Severe lower respiratory tract disease following influenza A virus (IAV) infection is characterized by excessive inflammation and lung tissue damage, and this can impair lung function. The effect of toll-like receptor 7 (TLR7), which detects viral RNA to initiate antiviral and proinflammatory responses to IAV, on lung function during peak infection and in the resolution phase is not fully understood. Using wild-type (WT) C57BL/6 and TLR7 knockout (TLR7 KO) mice, we found that IAV infection induced airway dysfunction in both genotypes, although in TLR7 KO mice, this dysfunction manifested later, did not affect lung tissue elastance and damping, and was associated with a different immune phenotype. A positive correlation was found between lung dysfunction and the infiltration of neutrophils and Ly6Clo patrolling monocytes at day 7 post-infection. Conversely, in TLR7 KO mice, eosinophil and CD8+ cytotoxic T cells were associated with airway hyperactivity at day 14. IL-5 expression was higher in the airways of IAV-infected TLR7 KO mice, suggesting an enhanced Th2 response due to TLR7 deficiency. This study highlights an underappreciated duality of TLR7 in IAV disease: promoting inflammation-driven lung dysfunction during the acute infection but suppressing eosinophilic and CD8+ T cell-dependent hyperresponsiveness during disease resolution.

Role of Maternal Immune Factors in Neuroimmunology of Brain Development

Inflammation during pregnancy may occur due to various factors. This condition, in which maternal immune system activation occurs, can affect fetal brain development and be related to neurodevelopmental diseases. MIA interacts with the fetus's brain development through maternal antibodies, cytokines, chemokines, and microglial cells. Antibodies are associated with the development of the nervous system by two mechanisms: direct binding to brain inflammatory factors and binding to brain antigens. Cytokines and chemokines have an active presence in inflammatory processes. Additionally, glial cells, defenders of the nervous system, play an essential role in synaptic modulation and neurogenesis. Maternal infections during pregnancy are the most critical factors related to MIA; however, several studies show the relation between these infections and neurodevelopmental diseases. Infection with specific viruses, such as Zika, cytomegalovirus, influenza A, and SARS-CoV-2, has revealed effects on neurodevelopment and the onset of diseases such as schizophrenia and autism. We review the relationship between maternal infections during pregnancy and their impact on neurodevelopmental processes.

Craniofacial anomalies in schizophrenia-relevant GFAP.HMOX10-12m mice

Subtle craniofacial dysmorphology has been reported in schizophrenia patients. This dysmorphology includes midline facial elongation, frontonasal anomalies and a sexually dimorphic deviation from normal directional asymmetry of the face, with male patients showing reduced and female patients showing enhanced facial asymmetry relative to healthy control subjects. GFAP.HMOX10-12m transgenic mice (Mus musculus) that overexpress heme oxygenase-1 in astrocytes recapitulate many schizophrenia-relevant neurochemical, neuropathological and behavioral features. As morphogenesis of the brain, skull and face are highly interrelated, we hypothesized that GFAP.HMOX10-12m mice may exhibit craniofacial anomalies similar to those reported in persons with schizophrenia. We examined craniofacial anatomy in male GFAP.HMOX10-12m mice and wild-type control mice at the early adulthood age of 6-8 months. We used computer vision techniques for the extraction and analysis of mouse head shape parameters from systematically acquired 2D digital images, and confirmed our results with landmark-based geometric morphometrics. We performed skull bone morphometry using digital calipers to take linear distance measurements between known landmarks. Relative to controls, adult male GFAP.HMOX10-12m mice manifested craniofacial dysmorphology including elongation of the nasal bones, alteration of head shape anisotropy and reduction of directional asymmetry in facial shape features. These findings demonstrate that GFAP.HMOX10-12m mice exhibit craniofacial anomalies resembling those described in schizophrenia patients, implicating heme oxygenase-1 in their development. As a preclinical mouse model, GFAP.HMOX10-12m mice provide a novel opportunity for the study of the etiopathogenesis of craniofacial and other anomalies in schizophrenia and related disorders.

Early-Life Respiratory Syncytial Virus (RSV) Infection Triggers Immunological Changes in Gut-Associated Lymphoid Tissues in a Sex-Dependent Manner in Adulthood

Severe respiratory syncytial virus (RSV) infection during early life has been linked to gut dysbiosis, which correlates with increased disease severity and a higher risk of developing asthma later in life. However, the impact of such early-life RSV infections on intestinal immunity in adulthood remains unclear. Herein, we show that RSV infection in 3-week-old mice induced persistent differential natural killer (NK) and T cell profiles within the lungs and gastrointestinal (GI) lymphoid tissues (GALT) in adulthood. Notably, male mice exhibited more pronounced RSV-induced changes in immune cell populations in both the lungs and GALT, while female mice displayed greater resilience. Importantly, early-life RSV infection was associated with the chronic downregulation of CD69-expressing T lymphocytes, particularly T regulatory cells in Peyer's patches, which could have a significant impact on T cell functionality and immune tolerance. We propose that RSV infection in early life is a trigger for the breakdown in immune tolerance at mucosal surfaces, with potential implications for airways allergic disease, food allergies, and other GI inflammatory diseases.

Non-Viral RNA Delivery During Pregnancy: Opportunities and Challenges

During pregnancy, the risk of maternal and fetal adversities increases due to physiological changes, genetic predispositions, environmental factors, and infections. Unfortunately, treatment options are severely limited because many essential interventions are unsafe, inaccessible, or lacking in sufficient scientific data to support their use. One potential solution to this challenge may lie in emerging RNA therapeutics for gene therapy, protein replacement, maternal vaccination, fetal gene editing, and other prenatal treatment applications. In this review, the current landscape of RNA platforms and non-viral RNA delivery technologies that are under active development for administration during pregnancy is explored. Advancements of pregnancy-specific RNA drugs against SARS-CoV-2, Zika, influenza, preeclampsia, and for in-utero gene editing are discussed. Finally, this study highlights bottlenecks that are impeding translation efforts of RNA therapies, including the lack of accurate cell-based and animal models of human pregnancy and concerns related to toxicity and immunogenicity during pregnancy. Overcoming these challenges will facilitate the rapid development of this new class of pregnancy-safe drugs.

Gestational influenza A virus infection elicits nonresolving vascular dysfunction and T-cell accumulation in the aorta of mice

T-cell accumulation within the aorta promotes endothelial dysfunction and the genesis of cardiovascular disease, including hypertension and atherosclerosis. Viral infection during pregnancy is also known to mediate marked acute endothelial dysfunction, but it is not clear whether T cells are recruited to the aorta and whether the dysfunction persists postpartum. Here, we demonstrate that influenza A virus (IAV) infection during pregnancy in a murine model resulted in endothelial dysfunction of the aorta, which persisted for up to 60 days postinfection and was associated with higher levels of IFN-γ mRNA expression within the tissue. In the absence of infection, low numbers of naïve CD4+ and CD8+ T cells, central memory T cells, and effector memory T cells were observed in the aorta. However, with IAV infection, these T-cell subsets were significantly increased with a notable accumulation of IAV-specific CD8+ effector memory T cells. Critically, this increase was maintained out to at least 60 days. In contrast, IAV infection in nonpregnant female mice resulted in modest endothelial dysfunction with no accumulation of T cells within the aorta. These data, therefore, demonstrate that the aorta is a site of T-cell recruitment and retention after IAV infection during pregnancy. Although IAV-specific memory T cells could theoretically confer protection against future influenza infection, nonspecific memory T-cell activation and IFN-γ production in the aorta could also contribute to future endothelial dysfunction and cardiovascular disease.NEW & NOTEWORTHY Pregnancy is a risk factor for cardiovascular complications to influenza A virus (IAV) infection. We demonstrate that gestational IAV infection caused endothelial dysfunction of the maternal aorta, which persisted for 60 days postinfection in mice. Various T cells accumulated within the aorta at 60 days because of the infection, and this was associated with elevated levels of the proinflammatory cytokine, IFN-γ. Our study demonstrates a novel "long influenza" cardiovascular phenotype in female mice.

Prenatal environmental risk factors for autism spectrum disorder and their potential mechanisms

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that is globally increasing in prevalence. The rise of ASD can be partially attributed to diagnostic expansion and advocacy efforts; however, the interplay between genetic predisposition and modern environmental exposures is likely driving a true increase in incidence. A range of evidence indicates that prenatal exposures are critical. Infection during pregnancy, gestational diabetes, and maternal obesity are established risk factors for ASD. Emerging areas of research include the effects of maternal use of selective serotonin reuptake inhibitors, antibiotics, and exposure to toxicants during pregnancy on brain development and subsequent ASD. The underlying pathways of these risk factors remain uncertain, with varying levels of evidence implicating immune dysregulation, mitochondrial dysfunction, oxidative stress, gut microbiome alterations, and hormonal disruptions. This narrative review assesses the evidence of contributing prenatal environmental factors for ASD and associated mechanisms as potential targets for novel prevention strategies.

Influenza Infection During Pregnancy and Risk of Seizures in Offspring

Importance

Seizure is a common neurological problem among infants and children up to age 6 years. Prenatal exposure to maternal influenza infection has been reported to be associated with childhood seizures.

Objective

To evaluate the association between maternal influenza infection and risk of childhood seizures.

Designs, Setting, and Participants

This cohort study identified mother-offspring pairs from January 1, 2004, to December 31, 2013, using records in Taiwan's Maternal and Child Health Database. Mothers who had influenza infection during pregnancy and their first offspring were identified and assigned to the influenza group. Mothers in the control group were those without influenza during pregnancy and were matched 1:4 with mothers in the influenza group by maternal age, offspring sex, and date of delivery. Offspring were followed up until December 31, 2020. Data were analyzed between March 2023 and July 2024.

Exposure

Diagnosis of influenza infection during pregnancy defined using International Classification of Diseases, Ninth Revision, Clinical Modification codes 487.0, 487.1, and 487.8, or International Statistical Classification of Diseases, Tenth Revision, Clinical Modification codes J09, J10, and J11.

Main Outcomes and Measures

The primary outcome was the association between maternal influenza infection during pregnancy and risk of any type of seizures during childhood, including both epilepsy and febrile seizures. Adjusted hazard ratios (AHRs) and 95% CIs were estimated using Cox proportional hazards regression models. Pregnancy-related complications were collected as covariates.

Results

A total of 1 316 107 mother-offspring pairs were enrolled, of whom 75 835 mothers (predominant maternal age, 25-29 years; 39 324 male offspring [51.9%]) were assigned to the influenza group and 1 240 272 were matched and assigned to the control group (n = 303 340; predominant maternal age, 30-34 years; 157 296 male offspring [51.9%]). In the influenza group, there was a slightly higher prevalence of placenta previa or abruption compared with the control group (1.6% [1241] vs 1.4% [4350]; P < .001). The cumulative risk of seizures was higher among offspring whose mothers had influenza infection. After controlling for potential confounders, the AHRs were 1.09 (95% CI, 1.05-1.14) for seizures, 1.11 (95% CI, 1.06-1.17) for febrile convulsions, and 1.04 (95% CI, 0.97-1.13) for epilepsy. In the subgroup analysis, no statistically significant differences were observed between the trimesters regarding the timing of influenza infection.

Conclusions and Relevance

Results of this cohort study suggest that maternal influenza infection during pregnancy was associated with an increased risk of childhood seizures, especially febrile seizures, but not epilepsy. Further studies are needed to elucidate the mechanisms underlying childhood neurological development.

Single-cell RNA sequencing reveals placental response under environmental stress

The placenta is crucial for fetal development, yet the impact of environmental stressors such as arsenic exposure remains poorly understood. We apply single-cell RNA sequencing to analyze the response of the mouse placenta to arsenic, revealing cell-type-specific gene expression, function, and pathological changes. Notably, the Prap1 gene, which encodes proline-rich acidic protein 1 (PRAP1), is significantly upregulated in 26 placental cell types including various trophoblast cells. Our study shows a female-biased increase in PRAP1 in response to arsenic and localizes it in the placenta. In vitro and ex vivo experiments confirm PRAP1 upregulation following arsenic treatment and demonstrate that recombinant PRAP1 protein reduces arsenic-induced cytotoxicity and downregulates cell cycle pathways in human trophoblast cells. Moreover, PRAP1 knockdown differentially affects cell cycle processes, proliferation, and cell death depending on the presence of arsenic. Our findings provide insights into the placental response to environmental stress, offering potential preventative and therapeutic approaches for environment-related adverse outcomes in mothers and children.

Brain region-specific alterations in gene expression trajectories in the offspring born from influenza A virus infected mice

Influenza A virus (IAV) infection during pregnancy can increase the risk for neurodevelopmental disorders in the offspring, however, the underlying neurobiological mechanisms are largely unknown. To recapitulate viral infection, preclinical studies have traditionally focused on using synthetic viral mimetics, rather than live IAV, to examine consequences of maternal immune activation (MIA)-dependent processes on offspring. In contrast, few studies have used live IAV to assess effects on global gene expression, and none to date have addressed whether moderate IAV, mimicking seasonal influenza disease, alters normal gene expression trajectories in different brain regions across different stages of development. Herein, we show that moderate IAV infection during pregnancy, which causes mild maternal disease and no overt foetal complications in utero, induces lasting effects on the offspring into adulthood. We observed behavioural changes in adult offspring, including disrupted prepulse inhibition, dopaminergic hyper-responsiveness, and spatial recognition memory deficits. Gene profiling in the offspring brain from neonate to adolescence revealed persistent alterations to normal gene expression trajectories in the prefronal cortex, hippocampus, hypothalamus and cerebellum. Alterations were found in genes involved in inflammation and neurogenesis, which were predominately dysregulated in neonatal and early adolescent offspring. Notably, late adolescent offspring born from IAV infected mice displayed altered microglial morphology in the hippocampus. In conclusion, we show that moderate IAV during pregnancy perturbs neurodevelopmental trajectories in the offspring, including alterations in the neuroinflammatory gene expression profile and microglial number and morphology in the hippocampus, resulting in behavioural changes in adult offspring. Such early perturbations may underlie the vulnerability in human offspring for the later development of neurodevelopmental disorders, including schizophrenia. Our work highlights the importance of using live IAV in developing novel preclinical models that better recapitulate the real-world impact of inflammatory insults during pregnancy on offspring neurodevelopmental trajectories and disease susceptibility later in life.

Safety and Efficacy of Antiviral Drugs and Vaccines in Pregnant Women: Insights from Physiologically Based Pharmacokinetic Modeling and Integration of Viral Infection Dynamics

Addressing the complexities of managing viral infections during pregnancy is essential for informed medical decision-making. This comprehensive review delves into the management of key viral infections impacting pregnant women, namely Human Immunodeficiency Virus (HIV), Hepatitis B Virus/Hepatitis C Virus (HBV/HCV), Influenza, Cytomegalovirus (CMV), and SARS-CoV-2 (COVID-19). We evaluate the safety and efficacy profiles of antiviral treatments for each infection, while also exploring innovative avenues such as gene vaccines and their potential in mitigating viral threats during pregnancy. Additionally, the review examines strategies to overcome challenges, encompassing prophylactic and therapeutic vaccine research, regulatory considerations, and safety protocols. Utilizing advanced methodologies, including PBPK modeling, machine learning, artificial intelligence, and causal inference, we can amplify our comprehension and decision-making capabilities in this intricate domain. This narrative review aims to shed light on diverse approaches and ongoing advancements, this review aims to foster progress in antiviral therapy for pregnant women, improving maternal and fetal health outcomes.

Fetal cord plasma herpesviruses and preeclampsia: an observational cohort study

A previous study suggested that fetal inheritance of chromosomally integrated human herpesvirus 6 (ici-HHV6) is associated with the hypertensive pregnancy disorder preeclampsia (PE). We aimed to study this question utilizing cord plasma samples (n = 1276) of the Finnish Genetics of Preeclampsia Consortium (FINNPEC) cohort: 539 from a pregnancy with PE and 737 without. We studied these samples and 30 placentas from PE pregnancies by a multiplex qPCR for the DNAs of all nine human herpesviruses. To assess the population prevalence of iciHHV-6, we studied whole-genome sequencing data from blood-derived DNA of 3421 biobank subjects. Any herpes viral DNA was detected in only two (0.37%) PE and one (0.14%) control sample (OR 2.74, 95% CI 0.25-30.4). One PE sample contained iciHHV-6B and another HHV-7 DNA. The control's DNA was of iciHHV-6B; the fetus having growth restriction and preterm birth without PE diagnosis. Placentas showed no herpesviruses. In the biobank data, 3 of 3421 subjects (0.08%) had low level HHV-6B but no iciHHV-6. While iciHHV-6 proved extremely rare, both fetuses with iciHHV-6B were growth-restricted, preterm, and from a pregnancy with maternal hypertension. Our findings suggest that human herpesviruses are not a significant cause of PE, whereas iciHHV-6 may pose some fetal risk.

Impact of SARS-CoV-2 infection during pregnancy on the placenta and fetus

Pregnant people and their fetuses are vulnerable to adverse health outcomes from coronavirus 2019 disease (COVID-19) due to infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 has been associated with higher rates of maternal mortality, preterm birth, and stillbirth. While SARS-CoV-2 infection of the placenta and vertical transmission is rare, this may be due to the typically longer time interval between maternal infection and testing of the placenta and neonate. Placental injury is evident in cases of SARS-CoV-2-associated stillbirth with massive perivillous fibrin deposition, chronic histiocytic intervillositis, and trophoblast necrosis. Maternal COVID-19 can also polarize fetal immunity, which may have long-term effects on neurodevelopment. Although the COVID-19 pandemic continues to evolve, the impact of emerging SARS-CoV-2 variants on placental and perinatal injury/mortality remains concerning for maternal and perinatal health. Here, we highlight the impact of COVID-19 on the placenta and fetus and remaining knowledge gaps.

Influenza A virus infection disrupts the function of syncytiotrophoblast cells and contributes to adverse pregnancy outcomes

Pregnancy heightens susceptibility to influenza A virus (IAV) infection, thereby increasing the risk of severe pneumonia and maternal mortality. It also raises the chances of adverse outcomes in offspring, such as fetal growth restriction, preterm birth, miscarriage, and stillbirth in offsprings. However, the underlying mechanisms behind these effects remain largely unknown. Syncytiotrophoblast cells, crucial in forming the placental barrier, nutrient exchange and hormone secretion, have not been extensively studied for their responses to IAV. In our experiment, we used Forskolin-treated BeWo cells to mimic syncytiotrophoblast cells in vitro, and infected them with H1N1, H5N1 and H7N9 virus stains. Our results showed that syncytiotrophoblast cells, with their higher intensity of sialic acid receptors, strongly support IAV infection and replication. Notably, high-dose viral infection and prolonged exposure resulted in a significant decrease in fusion index, as well as gene and protein expression levels associated with trophoblast differentiation, β-human chorionic gonadotropin secretion, estrogen and progesterone biosynthesis, and nutrient transport. In pregnant BALB/c mice infected with the H1N1 virus, we observed significant decreases in trophoblast differentiation and hormone secretion gene expression levels. IAV infection also resulted in preterm labor, fetal growth restriction, and increased maternal and fetal morbidity and mortality. Our findings indicate that IAV infection in syncytiotrophoblastic cells can result in adverse pregnancy outcomes by altering trophoblast differentiation, suppressing of β-hCG secretion, and disrupting placental barrier function.

Genital Dysbiosis and Different Systemic Immune Responses Based on the Trimester of Pregnancy in SARS-CoV-2 Infection

Respiratory infections are common in pregnancy with conflicting evidence supporting their association with neonatal congenital anomalies, especially during the first trimester. We profiled cytokine and chemokine systemic responses in 242 pregnant women and their newborns after SARS-CoV-2 infection, acquired in different trimesters. Also, we tested transplacental IgG passage and maternal vaginal-rectal microbiomes. IgG transplacental passage was evident, especially with infection acquired in the first trimester. G-CSF concentration-involved in immune cell recruitment-decreased in infected women compared to uninfected ones: a beneficial event for the reduction of inflammation but detrimental to ability to fight infections at birth. The later the infection was acquired, the higher the systemic concentration of IL-8, IP-10, and MCP-1, associated with COVID-19 disease severity. All infected women showed dysbiosis of vaginal and rectal microbiomes, compared to uninfected ones. Two newborns tested positive for SARS-CoV-2 within the first 48 h of life. Notably, their mothers had acute infection at delivery. Although respiratory infections in pregnancy are reported to affect babies' health, with SARS-CoV-2 acquired early during gestation this risk seems low because of the maternal immune response. The observed vaginal and rectal dysbiosis could be relevant for neonatal microbiome establishment, although in our series immediate neonatal outcomes were reassuring.

Low dose aspirin prevents endothelial dysfunction in the aorta and foetal loss in pregnant mice infected with influenza A virus

Influenza A virus (IAV) infection in pregnancy resembles a preeclamptic phenotype characterised by vascular dysfunction and foetal growth retardation. Given that low dose aspirin (ASA) is safe in pregnancy and is used to prevent preeclampsia, we investigated whether ASA or NO-conjugated aspirin, NCX4016, resolve vascular inflammation and function to improve offspring outcomes following IAV infection in pregnant mice. Pregnant mice were intranasally infected with a mouse adapted IAV strain (Hkx31; 104 plaque forming units) and received daily treatments with either 200µg/kg ASA or NCX4016 via oral gavage. Mice were then culled and the maternal lungs and aortas collected for qPCR analysis, and wire myography was performed on aortic rings to assess endothelial and vascular smooth muscle functionality. Pup and placentas were weighed and pup growth rates and survival assessed. IAV infected mice had an impaired endothelial dependent relaxation response to ACh in the aorta, which was prevented by ASA and NCX4016 treatment. ASA and NCX4016 treatment prevented IAV dissemination and inflammation of the aorta as well as improving the pup placental ratios in utero, survival and growth rates at post-natal day 5. Low dose ASA is safe to use during pregnancy for preeclampsia and this study demonstrates that ASA may prove a promising treatment for averting the significant vascular complications associated with influenza infection during pregnancy.

Implication of viruses in the etiology of preeclampsia

Preeclampsia is one of the most common disorders that poses threat to both mothers and neonates and a major contributor to perinatal morbidity and mortality worldwide. Viral infection during pregnancy is not typically considered to cause preeclampsia; however, syndromic nature of preeclampsia etiology and the immunomodulatory effects of viral infections suggest that microbes could trigger a subset of preeclampsia. Notably, SARS-CoV-2 infection is associated with an increased risk of preeclampsia. Herein, we review the potential role of viral infections in this great obstetrical syndrome. According to in vitro and in vivo experimental studies, viral infections can cause preeclampsia by introducing poor placentation, syncytiotrophoblast stress, and/or maternal systemic inflammation, which are all known to play a critical role in the development of preeclampsia. Moreover, clinical and experimental investigations have suggested a link between several viruses and the onset of preeclampsia via multiple pathways. However, the results of experimental and clinical research are not always consistent. Therefore, future studies should investigate the causal link between viral infections and preeclampsia to elucidate the mechanism behind this relationship and the etiology of preeclampsia itself.

Influenza A virus infection during pregnancy causes immunological changes in gut-associated lymphoid tissues of offspring mice

Maternal influenza A virus (IAV) infection during pregnancy can affect offspring immune programming and development. Offspring born from influenza-infected mothers are at increased risk of neurodevelopmental disorders and have impaired respiratory mucosal immunity against pathogens. The gut-associated lymphoid tissue (GALT) represents a large proportion of the immune system in the body and plays an important role in gastrointestinal (GI) homeostasis. This includes immune modulation to antigens derived from food or microbes, gut microbiota composition, and gut-brain axis signaling. Therefore, in this study, we investigated the effect of maternal IAV infection on mucosal immunity of the GI tract in the offspring. There were no major anatomical changes to the gastrointestinal tract of offspring born to influenza-infected dams. In contrast, maternal IAV did affect the mucosal immunity of offspring, showing regional differences in immune cell profiles within distinct GALT. Neutrophils, monocytes/macrophages, CD4+ and CD8+ T cells infiltration was increased in the cecal patch offspring from IAV-infected dams. In the Peyer's patches, only activated CD4+ T cells were increased in IAV offspring. IL-6 gene expression was also elevated in the cecal patch but not in the Peyer's patches of IAV offspring. These findings suggest that maternal IAV infection perturbs homeostatic mucosal immunity in the offspring gastrointestinal tract. This could have profound ramifications on the gut-brain axis and mucosal immunity in the lungs leading to increased susceptibility to respiratory infections and neurological disorders in the offspring later in life.NEW & NOTEWORTHY Influenza A virus (IAV) infection during pregnancy is associated with changes in gut-associated lymphoid tissue (GALT) in the offspring in a region-dependent manner. Neutrophils and monocytes/macrophages were elevated in the cecal patch of offspring from infected dams. This increase in innate immune cell infiltration was not observed in the Peyer's patches. T cells were also elevated in the cecal patch but not in the Peyer's patches.

Pregnancy-induced differential expression of SARS-CoV-2 and influenza a viral entry factors in the lower respiratory tract

Despite differences in the clinical presentation of coronavirus disease-19 and pandemic influenza in pregnancy, fundamental mechanistic insights are currently lacking because of the difficulty in recruiting critically ill pregnant subjects for research studies. Therefore, to better understand host-pathogen interaction during pregnancy, we performed a series of foundational experiments in pregnant rats at term gestation to assess the expression of host entry factors for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus (IAV) and genes associated with innate immune response in the lower respiratory tract. We report that pregnancy is characterized by a decrease in host factors mediating SARS-CoV-2 entry and an increase in host factors mediating IAV entry. Furthermore, using flow cytometric assessment of immune cell populations and immune provocation studies, we show an increased prevalence of plasmacytoid dendritic cells and a Type I interferon-biased environment in the lower respiratory tract of pregnancy, contrary to the expected immunological indolence. Our findings, therefore, suggest that the dissimilar clinical presentation of COVID-19 and pandemic influenza A in pregnancy could partly be due to differences in the extent of innate immune activation from altered viral tropism and indicate the need for comparative mechanistic investigations with live virus studies.

Maternal Vaccination to Prevent Adverse Pregnancy Outcomes: An Underutilized Molecular Immunological Intervention?

Adverse pregnancy outcomes including maternal mortality, stillbirth, preterm birth, intrauterine growth restriction cause millions of deaths each year. More effective interventions are urgently needed. Maternal immunization could be one such intervention protecting the mother and newborn from infection through its pathogen-specific effects. However, many adverse pregnancy outcomes are not directly linked to the infectious pathogens targeted by existing maternal vaccines but rather are linked to pathological inflammation unfolding during pregnancy. The underlying pathogenesis driving such unfavourable outcomes have only partially been elucidated but appear to relate to altered immune regulation by innate as well as adaptive immune responses, ultimately leading to aberrant maternal immune activation. Maternal immunization, like all immunization, impacts the immune system beyond pathogen-specific immunity. This raises the possibility that maternal vaccination could potentially be utilised as a pathogen-agnostic immune modulatory intervention to redirect abnormal immune trajectories towards a more favourable phenotype providing pregnancy protection. In this review we describe the epidemiological evidence surrounding this hypothesis, along with the mechanistic plausibility and present a possible path forward to accelerate addressing the urgent need of adverse pregnancy outcomes.

Associations between severe and notifiable respiratory infections during the first trimester of pregnancy and congenital anomalies at birth: a register-based cohort study

BACKGROUND

Evidence regarding the association between acute respiratory infections during pregnancy and congenital anomalies in babies, is limited and conflicting. The aim of this study was to examine the association between acute respiratory infections during the first trimester of pregnancy and congenital anomalies in babies using record linkage.

METHODS

We linked a perinatal register to hospitalisation and disease notifications in the Australian state of New South Wales (NSW) between 2001 to 2016. We quantified the risk of congenital anomalies, identified from the babies' linked hospital record in relation to notifiable respiratory and other infections during pregnancy using generalized Estimating Equations (GEE) adjusted for maternal sociodemographic and other characteristics.

RESULTS

Of 1,453,037 birth records identified from the perinatal register between 2001 and 2016, 11,710 (0.81%) mothers were hospitalised for acute respiratory infection, 2850 (0.20%) had influenza and 1011 (0.07%) had high risk infections (a record of cytomegalovirus, rubella, herpes simplex, herpes zoster, toxoplasmosis, syphilis, chickenpox (varicella) and zika) during the pregnancy. During the first trimester, acute respiratory infection, influenza and high-risk infections were reported by 1547 (0.11%), 399 (0.03%) and 129 (0.01%) mothers. There were 15,644 (1.08%) babies reported with major congenital anomalies, 2242 (0.15%) with cleft lip/ plate, 7770 (0.53%) with all major cardiovascular anomalies and 1746 (0.12%) with selected major cardiovascular anomalies. The rate of selected major cardiovascular anomalies was significantly higher if the mother had an acute respiratory infection during the first trimester of pregnancy (AOR 3.64, 95% CI 1.73 to 7.66). The rates of all major congenital anomalies and all major cardiovascular anomalies were also higher if the mother had an acute respiratory infection during the first trimester of pregnancy, however the difference was no statistically significant. Influenza during the first trimester was not associated with major congenital anomalies, selected major cardiovascular anomalies or all major cardiovascular anomalies in this study.

CONCLUSION

This large population-based study found severe acute respiratory infection in first trimester of pregnancy was associated with a higher risk of selected major cardiovascular anomalies in babies. These findings support measures to prevent acute respiratory infections in pregnant women including through vaccination.

Establish a Pregnant Sow–Neonate Model to Assess Maternal Immunity of a Candidate Influenza Vaccine

While it is well appreciated that maternal immunity can provide neonatal protection, the contribution of maternal vaccination toward generating such immunity is not well characterized. In our previous work, we created a candidate influenza vaccine using our chimeric hemagglutinin (HA) construct, HA-129. The HA-129 was expressed as part of a whole-virus vaccine that was built on the A/swine/Texas/4199-2/98-H3N2 backbone to generate the recombinant virus TX98-129. The TX98-129 candidate vaccine has the ability to induce broadly protective immune responses against genetically diversified influenza viruses in both mice and nursery pigs. In the current study, we established a pregnant sow–neonate model to evaluate the maternal immunity induced by this candidate vaccine to protect pregnant sows and their neonatal piglets against influenza virus infection. In pregnant sows, the results consistently show that TX98-129 induced a robust immune response against the TX98-129 virus and the parental viruses that were used to construct HA-129. After challenge with a field strain of influenza A virus, a significant increase in antibody titers was observed in vaccinated sows at both 5 and 22 days post challenge (dpc). The challenge virus was detected at a low level in the nasal swab of only one vaccinated sow at 5 dpc. Evaluation of cytokine responses in blood and lung tissue showed that levels of IFN-α and IL-1β were increased in the lung of vaccinated sows at 5 dpc, when compared to unvaccinated pigs. Further analysis of the T-cell subpopulation in PBMCs showed a higher ratio of IFN-γ-secreting CD4+CD8+ and CD8+ cytotoxic T cells in vaccinated sows at 22 dpc after stimulation with either challenge virus or vaccine virus. Finally, we used a neonatal challenge model to demonstrate that vaccine-induced maternal immunity can be passively transferred to newborn piglets. This was observed in the form of both increased antibody titers and deceased viral loads in neonates born from immunized sows. In summary, this study provides a swine model system to evaluate the impact of vaccination on maternal immunity and fetal/neonatal development.

The differential expression of toll like receptors and RIG-1 in the placenta of neonates with in utero infections

Novel biomarkers of in utero infections are needed to help guide early therapy. The toll like receptors (TLRs) and retinoic acid-inducible gene 1 (RIG-1) are proteins involved in the initial reaction of the innate immune system to infectious diseases. This study tested the hypothesis that a panel of TLRs and RIG-1 in the placenta could serve as an early biomarker of in utero infections. The TLRs and RIG-1 expression as determined by immunohistochemistry was scored in 10 control placentas (normal delivery or neonatal damage from known non-infectious cause), 8 placentas from documented in utero bacterial infection, and 7 placentas from documented in utero viral infections blinded to the clinical information. The non-infected placentas showed the following profile: no expression (TLR1, TLR3, TLR4, TLR7, TLR8), moderate expression (TLR2), and strong expression (RIG-1). The bacterial and viral infection cases shared the following profile: no to mild expression (TLR 2, TLR7, and RIG1), moderate expression (TLR4), and strong expression (TLR1, TLR3, and TLR8). The histologic findings in the chorionic villi were equivalent in the infected cases and controls, underscoring the need for molecular testing by the surgical pathologist when in utero infection is suspected. The results suggest that a panel of TLRs/RIG-1 analyses can allow the pathologist and/or clinician to diagnose in utero infections soon after birth. Also, treatments to antagonize the effects of TLR1, 3, and 8 may help abrogate in utero neonatal damage.

Biological Sex and Pregnancy Affect Influenza Pathogenesis and Vaccination

Males and females differ in the outcome of influenza A virus (IAV) infections, which depends significantly on age. During seasonal influenza epidemics, young children (< 5 years of age) and aged adults (65+ years of age) are at greatest risk for severe disease, and among these age groups, males tend to suffer a worse outcome from IAV infection than females. Following infection with pandemic strains of IAVs, females of reproductive ages (i.e., 15-49 years of age) experience a worse outcome than their male counterparts. Although females of reproductive ages experience worse outcomes from IAV infection, females typically have greater immune responses to influenza vaccination as compared with males. Among females of reproductive ages, pregnancy is one factor linked to an increased risk of severe outcome of influenza. Small animal models of influenza virus infection and vaccination illustrate that immune responses and repair of damaged tissue following IAV infection also differ between the sexes and impact the outcome of infection. There is growing evidence that sex steroid hormones, including estrogens, progesterone, and testosterone, directly impact immune responses during IAV infection and vaccination. Greater consideration of the combined effects of sex and age as biological variables in epidemiological, clinical, and animal studies of influenza pathogenesis is needed.

Topography of respiratory tract and gut microbiota in mice with influenza A virus infection

Introduction

Influenza A virus (IAV)-induced dysbiosis may predispose to severe bacterial superinfections. Most studies have focused on the microbiota of single mucosal surfaces; consequently, the relationships between microbiota at different anatomic sites in IAV-infected mice have not been fully studied.

Methods

We characterized respiratory and gut microbiota using full-length 16S rRNA gene sequencing by Nanopore sequencers and compared the nasopharyngeal, oropharyngeal, lung and gut microbiomes in healthy and IAV-infected mice.

Results

The oropharyngeal, lung and gut microbiota of healthy mice were dominated by Lactobacillus spp., while nasopharyngeal microbiota were comprised primarily of Streptococcus spp. However, the oropharyngeal, nasopharyngeal, lung, and gut microbiota of IAV-infected mice were dominated by Pseudomonas, Escherichia, Streptococcus, and Muribaculum spp., respectively. Lactobacillus murinus was identified as a biomarker and was reduced at all sites in IAV-infected mice. The microbiota composition of lung was more similar to that of the nasopharynx than the oropharynx in healthy mice.

Discussion

These findings suggest that the main source of lung microbiota in mice differs from that of adults. Moreover, the similarity between the nasopharyngeal and lung microbiota was increased in IAV-infected mice. We found that IAV infection reduced the similarity between the gut and oropharyngeal microbiota. L. murinus was identified as a biomarker of IAV infection and may be an important target for intervention in post-influenza bacterial superinfections.

Tropism and Infectivity of Pandemic Influenza A H1N1/09 Virus in the Human Placenta

Influenza virus infection in pregnant women may put the fetus at higher risk; however, to date, there has been no detailed research about the expression of influenza virus receptors in the human placenta. We employed the lectin staining technique, which is a classic influenza virus receptor research method for studying the distribution of viral receptors in the human placenta. In addition, we examined the susceptibility of the human placenta to H1N1/09, by detecting viral proteins and RNA at different time points post-infection. We found that the human placenta expressed both avian and human influenza A virus receptors (α-2, 3-linked sialic acid and α-2, 6-linked sialic acid). In addition, H1N1/09 did not only infect the human placenta, but also replicated and was released into the culture media. We concluded that the human placenta is susceptible to the 2009 influenza A virus (H1N1/09) infection, and that particular attention should be paid to shielding pregnant women from infection during influenza season.

Influenza Virus Infection during Pregnancy as a Trigger of Acute and Chronic Complications

Influenza A virus (IAV) infection during pregnancy disrupts maternal and fetal health through biological mechanisms, which are to date poorly characterised. During pregnancy, the viral clearance mechanisms from the lung are sub-optimal and involve hyperactive innate and adaptive immune responses that generate wide-spread inflammation. Pregnancy-related adaptations of the immune and the cardiovascular systems appear to result in delayed recovery post-viral infection, which in turn promotes a prolonged inflammatory phenotype, increasing disease severity, and causing maternal and fetal health problems. This has immediate and long-term consequences for the mother and fetus, with complications including acute cardiopulmonary distress syndrome in the mother that lead to perinatal complications such as intrauterine growth restriction (IUGR), and birth defects; cleft lip, cleft palate, neural tube defects and congenital heart defects. In addition, an increased risk of long-term neurological disorders including schizophrenia in the offspring is reported. In this review we discuss the pathophysiology of IAV infection during pregnancy and its striking similarity to other well-established complications of pregnancy such as preeclampsia. We discuss general features of vascular disease with a focus on vascular inflammation and define the "Vascular Storm" that is triggered by influenza infection during pregnancy, as a pivotal disease mechanism for short and long term cardiovascular complications.

At the crux of maternal immune activation: Viruses, microglia, microbes, and IL-17A

Inflammation during prenatal development can be detrimental to neurodevelopmental processes, increasing the risk of neuropsychiatric disorders. Prenatal exposure to maternal viral infection during pregnancy is a leading environmental risk factor for manifestation of these disorders. Preclinical animal models of maternal immune activation (MIA), established to investigate this link, have revealed common immune and microbial signaling pathways that link mother and fetus and set the tone for prenatal neurodevelopment. In particular, maternal intestinal T helper 17 cells, educated by endogenous microbes, appear to be key drivers of effector IL-17A signals capable of reaching the fetal brain and causing neuropathologies. Fetal microglial cells are particularly sensitive to maternally derived inflammatory and microbial signals, and they shift their functional phenotype in response to MIA. Resulting cortical malformations and miswired interneuron circuits cause aberrant offspring behaviors that recapitulate core symptoms of human neurodevelopmental disorders. Still, the popular use of "sterile" immunostimulants to initiate MIA has limited translation to the clinic, as these stimulants fail to capture biologically relevant innate and adaptive inflammatory sequelae induced by live pathogen infection. Thus, there is a need for more translatable MIA models, with a focus on relevant pathogens like seasonal influenza viruses.

FDA-Approved Inhibitors of RTK/Raf Signaling Potently Impair Multiple Steps of In Vitro and Ex Vivo Influenza A Virus Infections

Influenza virus (IV) infections pose a burden on global public health with significant morbidity and mortality. The limited range of currently licensed IV antiviral drugs is susceptible to the rapid rise of resistant viruses. In contrast, FDA-approved kinase inhibitors can be repurposed as fast-tracked host-targeted antivirals with a higher barrier of resistance. Extending our recent studies, we screened 21 FDA-approved small-molecule kinase inhibitors (SMKIs) and identified seven candidates as potent inhibitors of pandemic and seasonal IV infections. These SMKIs were further validated in a biologically and clinically relevant ex vivo model of human precision-cut lung slices. We identified steps of the virus infection cycle affected by these inhibitors (entry, replication, egress) and found that most SMKIs affected both entry and egress. Based on defined and overlapping targets of these inhibitors, the candidate SMKIs target receptor tyrosine kinase (RTK)-mediated activation of Raf/MEK/ERK pathways to limit influenza A virus infection. Our data and the established safety profiles of these SMKIs support further clinical investigations and repurposing of these SMKIs as host-targeted influenza therapeutics.

Influenza A virus elicits peri-vascular adipose tissue inflammation and vascular dysfunction of the aorta in pregnant mice

Influenza A virus (IAV) infection during pregnancy initiates significant aortic endothelial and vascular smooth muscle dysfunction, with inflammation and T cell activation, but the details of the mechanism are yet to be clearly defined. Here we demonstrate that IAV disseminates preferentially into the perivascular adipose tissue (PVAT) of the aorta in mice. IAV mRNA levels in the PVAT increased at 1–3 days post infection (d.p.i) with the levels being ~4–8 fold higher compared with the vessel wall. IAV infection also increased Ly6C^low patrolling monocytes and Ly6C^high pro-inflammatory monocytes in the vessel wall at 3 d.p.i., which was then followed by a greater homing of these monocytes into the PVAT at 6 d.p.i. The vascular immune phenotype was characteristic of a “vascular storm”- like response, with increases in neutrophils, pro-inflammatory cytokines and oxidative stress markers in the PVAT and arterial wall, which was associated with an impairment in endothelium-dependent relaxation to acetylcholine. IAV also triggered a PVAT compartmentalised elevation in CD4⁺ and CD8⁺ activated T cells. In conclusion, the PVAT of the aorta is a niche that supports IAV dissemination and a site for perpetuating a profound innate inflammatory and adaptive T cell response. The manifestation of this inflammatory response in the PVAT following IAV infection may be central to the genesis of cardiovascular complications arising during pregnancy.

Influenza A virus (IAV) infection remains a major cause of significant disease during pregnancy. IAV infection in pregnancy results in virus dissemination from the lung to the systemic vasculature, thereby initiating profound vascular inflammation and T cell activation that leads to vascular damage. Currently, the details of the mechanism that facilitates this vascular pathology and the influence of IAV dissemination to the vasculature on the perivascular adipose tissue (PVAT) is not clearly defined. Here, we show that IAV disseminates to the PVAT compartment of the vessel at a much larger rate than the vessel wall. We found that IAV infection increased PVAT inflammation characterised by immune cell infiltration, oxidative stress and pro-inflammatory cytokines. This was accompanied by a preferential immune T cell activation in the PVAT. We also found that this vascular inflammatory burden results in vascular endothelial dysfunction that is characterised by an impairment in endothelium dependent relaxation. Our study provides new insights into how IAV utilises the PVAT to promote the vascular inflammatory pathology that disrupts the vasculature in pregnancy and lead to pregnancy complications.

Nonrespiratory sites of influenza-associated disease: mechanisms and experimental systems for continued study

The productive replication of human influenza viruses is almost exclusively restricted to cells in the respiratory tract. However, a key aspect of the host response to viral infection is the production of inflammatory cytokines and chemokines that are not similarly tissue restricted. As such, circulating inflammatory mediators, as well as the resulting activated immune cells, can induce damage throughout the body, particularly in individuals with underlying conditions. As a result, more holistic experimental approaches are required to fully understand the pathogenesis and scope of influenza virus-induced disease. This review summarizes what is known about some of the most well-appreciated nonrespiratory tract sites of influenza virus-induced disease, including neurological, cardiovascular, gastrointestinal, muscular and fetal developmental phenotypes. In the context of this discussion, we describe the in vivo experimental systems currently being used to study nonrespiratory symptoms. Finally, we highlight important future questions and potential models that can be used for a more complete understanding of influenza virus-induced disease.

Mucosal immune responses to infection and vaccination in the respiratory tract

The lungs are constantly exposed to inhaled debris, allergens, pollutants, commensal or pathogenic microorganisms, and respiratory viruses. As a result, innate and adaptive immune responses in the respiratory tract are tightly regulated and are in continual flux between states of enhanced pathogen clearance, immune-modulation, and tissue repair. New single-cell-sequencing techniques are expanding our knowledge of airway cellular complexity and the nuanced connections between structural and immune cell compartments. Understanding these varied interactions is critical in treatment of human pulmonary disease and infections and in next-generation vaccine design. Here, we review the innate and adaptive immune responses in the lung and airways following infection and vaccination, with particular focus on influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The ongoing SARS-CoV-2 pandemic has put pulmonary research firmly into the global spotlight, challenging previously held notions of respiratory immunity and helping identify new populations at high risk for respiratory distress.

Upregulated influenza A viral entry factors and enhanced interferon-alpha response in the nasal epithelium of pregnant rats

Despite the increased severity of influenza A infection in pregnancy, knowledge about the expression of cell entry factors for influenza A virus (IAV) and the innate immune response in the nasal epithelium, the primary portal of viral entry, is limited. Here, we compared the expression of IAV cell entry factors and the status of the innate immune response in the nasal epithelium of pregnant vs. non-pregnant female rats. IAV cell entry factors — sialic acid [SA] α-2,3- and α-2,6-linked glycans for avian and human IAV, respectively — were detected and quantified with lectin-based immunoblotting and flow cytometry. Baseline frequencies of innate immune cell phenotypes in single cell suspensions of the nasal epithelium were studied with flow cytometry. Subsequently, the magnitude of interferon and cytokine responses was studied with ELISA and cytokine arrays after intranasal resiquimod, a Toll-like receptor 7/8 agonist that mimics IAV infection. We noted substantially increased expression of cell entry factors for both avian and human IAV in the nasal epithelium during pregnancy. Assessment of the innate immune state of the nasal epithelium during pregnancy revealed two previously unreported features: (i) increased presence of tissue-resident plasmacytoid dendritic cells, and (ii) markedly enhanced release of interferon-α but not of the other interferons or cytokines 2 h after intranasal resiquimod. Collectively, our findings challenge the conventional notion of pregnancy-induced immunosuppression as a cause for severe influenza A disease and suggest the need for focused studies on viral tropism during pregnancy to better understand the proximate cause for the observed immunopathology.

Ebselen abolishes vascular dysfunction in influenza A virus-induced exacerbations of cigarette smoke-induced lung inflammation in mice

People with chronic obstructive pulmonary disease (COPD) are susceptible to respiratory infections which exacerbate pulmonary and/or cardiovascular complications, increasing their likelihood of death. The mechanisms driving these complications remain unknown but increased oxidative stress has been implicated. Here we investigated whether influenza A virus (IAV) infection, following chronic cigarette smoke (CS) exposure, worsens vascular function and if so, whether the antioxidant ebselen alleviates this vascular dysfunction. Male BALB/c mice were exposed to either room air or CS for 8 weeks followed by inoculation with IAV (Mem71, 1 × 104.5 pfu). Mice were treated with ebselen (10 mg/kg) or vehicle (5% w/v CM-cellulose in water) daily. Mice were culled 3- and 10-days post-infection, and their lungs lavaged to assess inflammation. The thoracic aorta was excised to investigate endothelial and smooth muscle dilator responses, expression of key vasodilatory and oxidative stress modulators, infiltrating immune cells and vascular remodelling. CS increased lung inflammation and caused significant vascular endothelial dysfunction, which was worsened by IAV infection. CS-driven increases in vascular oxidative stress, aortic wall remodelling and suppression of endothelial nitric oxide synthase (eNOS) were not affected by IAV infection. CS and IAV infection significantly enhanced T cell recruitment into the aortic wall. Ebselen abolished the exaggerated lung inflammation, vascular dysfunction and increased T cell infiltration in CS and IAV-infected mice. Our findings showed that ebselen treatment abolished vascular dysfunction in IAV-induced exacerbations of CS-induced lung inflammation indicating it may have potential for the treatment of cardiovascular comorbidities seen in acute exacerbations of COPD (AECOPD).

Consequences of Viral Infection and Cytokine Production During Pregnancy on Brain Development in Offspring

Infections during pregnancy can seriously damage fetal neurodevelopment by aberrantly activating the maternal immune system, directly impacting fetal neural cells. Increasing evidence suggests that these adverse impacts involve alterations in neural stem cell biology with long-term consequences for offspring, including neurodevelopmental disorders such as autism spectrum disorder, schizophrenia, and cognitive impairment. Here we review how maternal infection with viruses such as Influenza A, Cytomegalovirus, and Zika during pregnancy can affect the brain development of offspring by promoting the release of maternal pro-inflammatory cytokines, triggering neuroinflammation of the fetal brain, and/or directly infecting fetal neural cells. In addition, we review insights into how these infections impact human brain development from studies with animal models and brain organoids. Finally, we discuss how maternal infection with SARS-CoV-2 may have consequences for neurodevelopment of the offspring.

Proteome Profiling of Serum Exosomes from Newborns Delivered by Mothers with Preeclampsia

Background:

Preeclampsia (PE) is a common pregnancy-specific disease with potential adverse maternal and neonatal outcomes.

Objective:

We aimed to estimate proteomic profiles of serum-derived exosomes obtained from PE offspring with bioinformatics methods.

Method:

Serum samples were collected from 12 h, 24 h, and 72 h newborns delivered by preeclamptic and normal pregnant women. Exosomes were extracted, and the concentration and size distribution were determined. The exosome surface markers CD9, CD63, CD81, and TSG101, were assayed by Western blot. The exosome proteins were screened by quantitative proteomics with tandem mass tag (TMT). All the identified proteins were subjected to the Weighted Gene Co-Expression Network Analysis (WGCNA), GO function, and KEGG pathway analysis. A protein-protein interaction network (PPI) was used to extract hub proteins through the Cytohubba plugin of Cytoscape

Results:

The extracted exosomes were round or oval vesicular structures at a 100-200 nm concentration, and the size distribution was standard and uniform. Exosome surface markers CD9, CD63, and CD81 were detected, and TSG101 was not detected. A total of 450 expressed proteins were selected, and 444 proteins were mapped with gene names. A blue module with 66 proteins highly correlated with phenotype at 12 h. Functional analyses revealed that module proteins were mainly enriched in extracellular matrix. The top 10 selected hub proteins were identified as hub proteins, including COL6A2, HSPG2, COL4A1, COL3A1, etc.

Conclusion:

Our study provides important information for exploring molecular mechanisms of preeclampsia and potential biomarkers for future diagnosis and treatment in the clinic.

Effects of Vertical Transmission of Respiratory Viruses to the Offspring

Overt and subclinical maternal infections in pregnancy can have multiple and significant pathological consequences for the developing fetus, leading to acute perinatal complications and/or chronic disease throughout postnatal life. In this context, the current concept of pregnancy as a state of systemic immunosuppression seems oversimplified and outdated. Undoubtedly, in pregnancy the maternal immune system undergoes complex changes to establish and maintain tolerance to the fetus while still protecting from pathogens. In addition to downregulated maternal immunity, hormonal changes, and mechanical adaptation (e.g., restricted lung expansion) make the pregnant woman more susceptible to respiratory pathogens, such as influenza virus, respiratory syncytial virus (RSV), and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Depending on the infectious agent and timing of the infection during gestation, fetal pathology can range from mild to severe, and even fatal. Influenza is associated with a higher risk of morbidity and mortality in pregnant women than in the general population, and, especially during the third trimester of pregnancy, mothers are at increased risk of hospitalization for acute cardiopulmonary illness, while their babies show higher risk of complications such as prematurity, respiratory and neurological illness, congenital anomalies, and admission to neonatal intensive care. RSV exposure in utero is associated with selective immune deficit, remodeling of cholinergic innervation in the developing respiratory tract, and abnormal airway smooth muscle contractility, which may predispose to postnatal airway inflammation and hyperreactivity, as well as development of chronic airway dysfunction in childhood. Although there is still limited evidence supporting the occurrence of vertical transmission of SARS-CoV-2, the high prevalence of prematurity among pregnant women infected by SARS-CoV-2 suggests this virus may alter immune responses at the maternal-fetal interface, affecting both the mother and her fetus. This review aims at summarizing the current evidence about the short- and long-term consequences of intrauterine exposure to influenza, RSV, and SARS-CoV-2 in terms of neonatal and pediatric outcomes.

Maternal inflammation and its ramifications on fetal neurodevelopment

Exposure to heightened inflammation in pregnancy caused by infections or other inflammatory insults has been associated with the onset of neurodevelopmental and psychiatric disorders in children. Rodent models have provided unique insights into how this maternal immune activation (MIA) disrupts brain development. Here, we discuss the key immune factors involved, highlight recent advances in determining the molecular and cellular pathways of MIA, and review how the maternal immune system affects fetal development. We also examine the roles of microbiomes in shaping maternal immune function and the development of autism-like phenotypes. A comprehensive understanding of the gut bacteria-immune-neuro interaction in MIA is essential for developing diagnostic and therapeutic measures for high-risk pregnant women and identifying targets for treating inflammation-induced neurodevelopmental disorders.

Viral Infections During Pregnancy: The Big Challenge Threatening Maternal and Fetal Health

Viral infections during pregnancy are associated with adverse pregnancy outcomes, including maternal and fetal mortality, pregnancy loss, premature labor, and congenital anomalies. Mammalian gestation encounters an immunological paradox wherein the placenta balances the tolerance of an allogeneic fetus with protection against pathogens. Viruses cannot easily transmit from mother to fetus due to physical and immunological barriers at the maternal-fetal interface posing a restricted threat to the fetus and newborns. Despite this, the unknown strategies utilized by certain viruses could weaken the placental barrier to trigger severe maternal and fetal health issues especially through vertical transmission, which was not fully understood until now. In this review, we summarize diverse aspects of the major viral infections relevant to pregnancy, including the characteristics of pathogenesis, related maternal-fetal complications, and the underlying molecular and cellular mechanisms of vertical transmission. We highlight the fundamental signatures of complex placental defense mechanisms, which will prepare us to fight the next emerging and re-emerging infectious disease in the pregnancy population.

From maternal breath to infant's cells: Impact of maternal respiratory infections on infants 'immune responses

In utero exposure to maternally-derived antigens following chronic infection is associated with modulation of infants 'immune response, differential susceptibility to post-natal infections and immune response toward vaccines. The maternal environment, both internal (microbiota) and external (exposure to environmental microbes) also modulates infant's immune response but also the clinical phenotype after birth. Vertical transmission of ubiquitous respiratory pathogens such as influenza and COVID-19 is uncommon. Evidence suggest that in utero exposure to maternal influenza and SARS-CoV-2 infections may have a significant impact on the developing immune system with activation of both innate and adaptive responses, possibly related to placental inflammation. Here in, we review how maternal respiratory infections, associated with airway, systemic and placental inflammation but also changes in maternal microbiota might impact infant's immune responses after birth. The clinical impact of immune modifications observed following maternal respiratory infections remains unexplored. Given the high frequencies of respiratory infections during pregnancy (COVID-19, influenza but also RSV and HMPV), the impact on global child health could be important.

Potential Neurocognitive Symptoms Due to Respiratory Syncytial Virus Infection

Respiratory infections are among the major public health burdens, especially during winter. Along these lines, the human respiratory syncytial virus (hRSV) is the principal viral agent causing acute lower respiratory tract infections leading to hospitalization. The pulmonary manifestations due to hRSV infection are bronchiolitis and pneumonia, where the population most affected are infants and the elderly. However, recent evidence suggests that hRSV infection can impact the mother and fetus during pregnancy. Studies have indicated that hRSV can infect different cell types from the placenta and even cross the placenta barrier and infect the fetus. In addition, it is known that infections during the gestational period can lead to severe consequences for the development of the fetus due not only to a direct viral infection but also because of maternal immune activation (MIA). Furthermore, it has been described that the development of the central nervous system (CNS) of the fetus can be affected by the inflammatory environment of the uterus caused by viral infections. Increasing evidence supports the notion that hRSV could invade the CNS and infect nervous cells, such as microglia, neurons, and astrocytes, promoting neuroinflammation. Moreover, it has been described that the hRSV infection can provoke neurological manifestations, including cognitive impairment and behavioral alterations. Here, we will review the potential effect of hRSV in brain development and the potential long-term neurological sequelae.

Increased cell-free fetal DNA release after apoptosis and sterile inflammation in human trophoblast cells

PROBLEM

Cell-free fetal DNA (cffDNA) shed from the placenta can be detected in maternal blood and increases incrementally during gestation. Concentrations are further elevated with pregnancy complications. Specific activators of cffDNA release in such complications have not been identified. Here, we use trophoblast cells from early and term placenta to examine cffDNA release following apoptosis, infection, and sterile inflammatory stress.

METHOD OF STUDY

HTR8/SVneo cells were used to model first-trimester trophoblasts, and term cytotrophoblasts (CTBs) were isolated from placentae collected after uncomplicated deliveries. Trophoblasts were treated with varying concentrations of doxorubicin (DOX), lipopolysaccharide (LPS), or high-mobility group box protein 1 (HMGB1) for 18 h. Cells or supernatants were quantified for caspase-3/7 cleavage, pro-inflammatory cytokine secretion, and cffDNA release.

RESULTS

Both HTR8/SVneo and CTBs underwent caspase-3/7 cleavage following DOX treatment, with HTR8/SVneo cells more sensitive to apoptosis than term CTBs. Apoptotic cells released more cffDNA in a dose-dependent manner. Treatment with LPS resulted in an increase in pro-inflammatory IL-6 release, particularly in term CTBs compared to early trophoblasts; however, LPS did not affect cffDNA release. Lastly, while neither cell released more TNF-α following stimulation with HMGB1, both HTR8/SVneo and CTBs released significantly more cffDNA in the presence of HMGB1.

CONCLUSIONS

These data show that apoptosis and sterile inflammation induced by DOX and HMGB1, respectively, cause an increase in cffDNA concentrations in both first-trimester and term trophoblasts. Understanding physiologic release of cffDNA during healthy and complicated pregnancy can identify new targets for the diagnosis and treatment of gestational complications.

Pregnancy and pandemics: Interaction of viral surface proteins and placenta cells

Throughout history, pandemics of infectious diseases caused by emerging viruses have spread worldwide. Evidence from previous outbreaks demonstrated that pregnant women are at high risk of contracting the diseases and suffering from adverse outcomes. However, while some viruses can cause major health complications for the mother and her fetus, others do not appear to affect pregnancy. Viral surface proteins bind to specific receptors on the cellular membrane of host cells and begin therewith the infection process. During pregnancy, the molecular features of these proteins may determine specific target cells in the placenta, which may explain the different outcomes. In this review, we display information on Variola, Influenza, Zika and Corona viruses focused on their surface proteins, effects on pregnancy, and possible target placental cells. This will contribute to understanding viral entry during pregnancy, as well as to develop strategies to decrease the incidence of obstetrical problems in current and future infections.

Moderately pathogenic maternal influenza A virus infection disrupts placental integrity but spares the fetal brain

Maternal infection during pregnancy is a known risk factor for offspring mental health disorders. Animal models of maternal immune activation (MIA) have implicated specific cellular and molecular etiologies of psychiatric illness, but most rely on pathogen mimetics. Here, we developed a mouse model of live H3N2 influenza A virus (IAV) infection during pregnancy that induces a robust inflammatory response but is sublethal to both dams and offspring. We observed classic indicators of lung inflammation and severely diminished weight gain in IAV-infected dams. This was accompanied by immune cell infiltration in the placenta and partial breakdown of placental integrity. However, indications of fetal neuroinflammation were absent. Further hallmarks of mimetic-induced MIA, including enhanced circulating maternal IL-17A, were also absent. Respiratory IAV infection did result in an upregulation in intestinal expression of transcription factor RORγt, master regulator of a subset of T lymphocytes, TH17 cells, which are heavily implicated in MIA-induced etiologies. Nonetheless, subsequent augmentation in IL-17A production and concomitant overt intestinal injury was not evident. Our results suggest that mild or moderately pathogenic IAV infection during pregnancy does not inflame the developing fetal brain, and highlight the importance of live pathogen infection models for the study of MIA.

Clinical Effectiveness and Safety of Antivirals for Influenza in Pregnancy

Seasonal influenza epidemics result in substantial health care burden annually. Early initiation of antiviral treatment of influenza has been shown to reduce the risk of complications and duration of illness. Pregnant and postpartum women may be at increased risk for influenza-associated complications; however, pregnant women have been generally excluded from clinical trials of antiviral treatment of influenza. In this review, we summarize the available evidence on the clinical effectiveness and safety of antiviral treatment of pregnant women with influenza. Observational data show a reduction of severe outcomes when pregnant and postpartum women are treated with oseltamivir and other neuraminidase inhibitors without increased risk of adverse maternal, fetal, or neonatal outcomes. Due to lack of safety and efficacy data for baloxavir treatment of pregnant and postpartum women, baloxavir is currently not recommended for use in these populations.