An in vitro transepithelial migration assay to evaluate the role of neutrophils in Respiratory Syncytial Virus (RSV) induced epithelial damage

A one-step method for generating antimicrobial nanofibre meshes via coaxial electrospinning

Respiratory diseases, including influenza, infectious pneumonia, and severe acute respiratory syndrome (SARS), are a leading cause of morbidity and mortality worldwide. The recent COVID-19 pandemic claimed over 6.9 million lives globally. With the possibility of future pandemics, the creation of affordable antimicrobial meshes for protective gear, such as facemasks, is essential. Electrospinning has been a focus for much of this research, but most approaches are complex and expensive, often wasting raw materials by distributing antiviral agents throughout the mesh despite the fact they can only be active if at the fibre surface. Here, we report a low cost and efficient one-step method to produce nanofibre meshes with antimicrobial activity, including against SARS-CoV-2. Cetrimonium bromide (CTAB) was deposited directly onto the surface of polycaprolactone (PCL) fibres by coaxial electrospinning. The CTAB-coated samples have denser meshes with finer nanofibres than non-coated PCL fibres (mean diameter: ∼300 nm versus ∼900 nm, with mean pore size: ∼300 nm versus > 600 nm). The formulations have > 90% coating efficiency and exhibit a burst release of CTAB upon coming into contact with aqueous media. The CTAB-coated materials have strong antibacterial activity against Staphylococcus aureus (ca. 100%) and Pseudomonas aeruginosa (96.5 ± 4.1%) bacteria, as well as potent antiviral activity with over 99.9% efficacy against both respiratory syncytial virus and SARS-CoV-2. The CTAB-coated nanofibre mesh thus has great potential to form a mask material for preventing both bacterial and viral respiratory infections.

Neutrophil responses to RSV infection show differences between infant and adult neutrophils

INTRODUCTION

Respiratory syncytial virus (RSV) causes a severe respiratory condition, bronchiolitis, in infants but not in adults. Bronchiolitis is characterised by neutrophilic infiltration in the airways, but whether neutrophils enhance recovery from infection or contribute to its pathology remains unknown.

METHODS

We used a novel in-vitro model to compare term umbilical cord blood (infant) (n=17 donors) and adult neutrophils (n=15 donors) during migration across RSV-infected differentiated human nasal airway epithelial cells (AECs) in a basolateral to apical direction.

RESULTS

Greater numbers of infant neutrophils (mean (95% CI)) (336 684 (242 352 to 431 015)) migrated across RSV-infected AECs to the apical compartment (equivalent to the airway lumen) compared with adult neutrophils (56 586 (24 954 to 88 218)) (p<0.0001). Having reached the apical compartment of infected AECs, much greater numbers of infant neutrophils (140 787 (103 117 to 178 456)) became apoptotic compared with adult (5853 (444 to 11 261)) (p=0.002). Infant neutrophils displayed much greater expression of CD11b, CD64, neutrophil elastase (NE) and myeloperoxidase (MPO) than adult neutrophils at baseline and at all points of migration. However, as adult neutrophils migrated, expression of CD11b, CD64, NE and MPO became greater than at baseline.

DISCUSSION

The high proportion of infant neutrophils migrating across RSV-infected AECs correlates with the neutrophilic infiltrate seen in infants with severe RSV bronchiolitis, with large numbers undergoing apoptosis, which may represent a protective mechanism during infection. Compared with adult neutrophils, infant neutrophils already have high expression of surface markers before contact with AECs or migration, with less capacity to increase further in response to RSV infection or migration.

Lung viral infection modelling in a bioengineered whole-organ

Lung infections are one of the leading causes of death worldwide, and this situation has been exacerbated by the emergence of COVID-19. Pre-clinical modelling of viral infections has relied on cell cultures that lack 3D structure and the context of lung extracellular matrices. Here, we propose a bioreactor-based, whole-organ lung model of viral infection. The bioreactor takes advantage of an automated system to achieve efficient decellularization of a whole rat lung, and recellularization of the scaffold using primary human bronchial cells. Automatization allowed for the dynamic culture of airway epithelial cells in a breathing-mimicking setup that led to an even distribution of lung epithelial cells throughout the distal regions. In the sealed bioreactor system, we demonstrate proof-of-concept for viral infection within the epithelialized lung by infecting primary human airway epithelial cells and subsequently injecting neutrophils. Moreover, to assess the possibility of drug screening in this model, we demonstrate the efficacy of the broad-spectrum antiviral remdesivir. This whole-organ scale lung infection model represents a step towards modelling viral infection of human cells in a 3D context, providing a powerful tool to investigate the mechanisms of the early stages of pathogenic infections and the development of effective treatment strategies for respiratory diseases.

Host Responses to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) infections are a constant public health problem, especially in infants and older adults. Virtually all children will have been infected with RSV by the age of two, and reinfections are common throughout life. Since antigenic variation, which is frequently observed among other respiratory viruses such as SARS-CoV-2 or influenza viruses, can only be observed for RSV to a limited extent, reinfections may result from short-term or incomplete immunity. After decades of research, two RSV vaccines were approved to prevent lower respiratory tract infections in older adults. Recently, the FDA approved a vaccine for active vaccination of pregnant women to prevent severe RSV disease in infants during their first RSV season. This review focuses on the host response to RSV infections mediated by epithelial cells as the first physical barrier, followed by responses of the innate and adaptive immune systems. We address possible RSV-mediated immunomodulatory and pathogenic mechanisms during infections and discuss the current vaccine candidates and alternative treatment options.

Effects of pH alteration on respiratory syncytial virus in human airway epithelial cells

Background

Respiratory syncytial virus (RSV) is a leading cause of respiratory distress and hospitalisation in the paediatric population. Low airway surface pH impairs antimicrobial host defence and worsens airway inflammation. Inhaled Optate safely raises airway surface pH in humans and raises intracellular pH in primary human airway epithelial cells (HAECs) in vitro. We aimed to determine whether raising intracellular pH with Optate would decrease infection and replication of RSV in primary HAECs.

Methods

We cultured HAECs from healthy subjects in both air-liquid interface and submerged conditions. We infected HAECs with green fluorescent protein-labelled RSV (GFP-RSV; multiplicity of infection=1) and treated them with Optate or PBS control. We collected supernatant after a 4-h incubation and then every 24 h. We used fluorescence intensity, fluorescent particle counts, plaque assays, Western blots and ELISA to quantitate infection.

Results

In submerged culture, fluorescence intensity decreased in Optate-treated cells (48 h p=0.0174, 72 h p≤0.001). Similarly, Optate treatment resulted in decreased fluorescent particle count (48 h p=0.0178, 72 h p=0.0019) and plaque-forming units (48 h p=0.0011, 72 h p=0.0148) from cell culture supernatant. In differentiated HAECs cultured at ALI, Optate treatment decreased fluorescence intensity (p≤0.01), GFP via Western blot and ELISA (p<0.0001), and RSV-fusion protein via ELISA (p=0.001). Additionally, RSV infection decreased as Optate concentration increased in a dose-dependent manner (p<0.001).

Conclusions

Optate inhibits RSV infection in primary HAECs in a dose-dependent manner. These findings suggest that Optate may have potential as an inhaled therapeutic for patients with RSV.

Myeloperoxidase-derived hypochlorous acid targets human airway epithelial plasmalogens liberating protein modifying electrophilic 2-chlorofatty aldehydes

Neutrophil and airway epithelial cell interactions are critical in the inflammatory response to viral infections including respiratory syncytial virus, Sendai virus, and SARS-CoV-2. Airway epithelial cell dysfunction during viral infections is likely mediated by the interaction of virus and recruited neutrophils at the airway epithelial barrier. Neutrophils are key early responders to viral infection. Neutrophil myeloperoxidase catalyzes the conversion of hydrogen peroxide to hypochlorous acid (HOCl). Previous studies have shown HOCl targets host neutrophil and endothelial cell plasmalogen lipids, resulting in the production of the chlorinated lipid, 2-chlorofatty aldehyde (2-ClFALD). We have previously shown that the oxidation product of 2-ClFALD, 2-chlorofatty acid (2-ClFA) is present in bronchoalveolar lavage fluid of Sendai virus-infected mice, which likely results from the attack of the epithelial plasmalogen by neutrophil-derived HOCl. Herein, we demonstrate small airway epithelial cells contain plasmalogens enriched with oleic acid at the sn-2 position unlike endothelial cells which contain arachidonic acid enrichment at the sn-2 position of plasmalogen. We also show neutrophil-derived HOCl targets epithelial cell plasmalogens to produce 2-ClFALD. Further, proteomics and over-representation analysis using the ω-alkyne analog of the 2-ClFALD molecular species, 2-chlorohexadecanal (2-ClHDyA) showed cell adhesion molecule binding and cell-cell junction enriched categories similar to that observed previously in endothelial cells. However, in contrast to endothelial cells, proteins in distinct metabolic pathways were enriched with 2-ClFALD modification, particularly pyruvate metabolism was enriched in epithelial cells and mitochondrial pyruvate respiration was reduced. Collectively, these studies demonstrate, for the first time, a novel plasmalogen molecular species distribution in airway epithelial cells that are targeted by myeloperoxidase-derived hypochlorous acid resulting in electrophilic 2-ClFALD, which potentially modifies epithelial physiology by modifying proteins.

The tumor stroma influences immune cell distribution and recruitment in a PDAC-on-a-chip model

The dense tumor stroma of pancreatic ductal adenocarcinoma (PDAC) and its secreted immune active molecules provide a barrier for chemotherapy treatment as well as for immune cell infiltration to the tumor core, providing a challenge for immunotherapeutic strategies. Consequently, the investigation of processes underlying the interaction between the tumor stroma, particularly activated pancreatic stellate cells (PSCs), and immune cells may offer new therapeutic approaches for PDAC treatment. In this study, we established a 3D PDAC model cultured under flow, consisting of an endothelial tube, PSCs and PDAC organoids. This was applied to study the role of the tumor microenvironment (TME) on immune cell recruitment and its effect on partly preventing their interaction with pancreatic cancer cells. We observed that stromal cells form a physical barrier, partly shielding the cancer cells from migrating immune cells, as well as a biochemical microenvironment, that seems to attract and influence immune cell distribution. In addition, stromal targeting by Halofuginone led to an increase in immune cell infiltration. We propose that the here developed model setups will support the understanding of the cellular interplay influencing the recruitment and distribution of immune cells, and contribute to the identification of key players in the PDAC immunosuppressive TME as well as support the discovery of new strategies to treat this immune unresponsive tumor.

Airway Epithelial Cell Junctions as Targets for Pathogens and Antimicrobial Therapy

Intercellular contacts between epithelial cells are established and maintained by the apical junctional complexes (AJCs). AJCs conserve cell polarity and build epithelial barriers to pathogens, inhaled allergens, and environmental particles in the respiratory tract. AJCs consist of tight junctions (TJs) and adherens junctions (AJs), which play a key role in maintaining the integrity of the airway barrier. Emerging evidence has shown that different microorganisms cause airway barrier dysfunction by targeting TJ and AJ proteins. This review discusses the pathophysiologic mechanisms by which several microorganisms (bacteria and viruses) lead to the disruption of AJCs in airway epithelial cells. We present recent progress in understanding signaling pathways involved in the formation and regulation of cell junctions. We also summarize the potential chemical inhibitors and pharmacological approaches to restore the integrity of the airway epithelial barrier. Understanding the AJCs-pathogen interactions and mechanisms by which microorganisms target the AJC and impair barrier function may further help design therapeutic innovations to treat these infections.

Chemokine/Interleukin Imbalance Aggravates the Pathology of Respiratory Syncytial Virus Infection

(1) Background: Almost 100% of children are initially infected by respiratory syncytial virus (RSV) by the age of 2 years, with 30% to 40% of children developing lower respiratory tract infections, of which 1% to 3% become severe. The severity of RSV-induced disease correlates with the influx of leukocytes, which leads to damage of the airways. We hence performed an immunological study based on the assumption that a chemokine/interleukin imbalance affects respiratory disorders caused by bronchiolitis and severe pneumonia. (2) Methods: The subjects were 19 infants without any underlying diseases, who developed respiratory symptoms owing to RSV infection. The subjects were stratified by their symptom severity, and chemokine and interleukin levels in their serum and tracheal aspirate fluid (TAF) were measured. (3) Results: The data of TAF, which were only obtained from subjects with severe symptoms, indicated that levels of inflammatory interleukins were much lower than the levels of chemokines. Three out of 6 subjects with severe symptoms showed below detectable levels of IL-6. TNF-α and IFN-γ levels were also lower than those of chemokines. The main increased CCL chemokines were CCL21 and CCL25, and the main increased CXCL chemokines were CXCL5, 8, 10, 12, and CX3CL1 in the lower respiratory region. Multiple regression analysis demonstrated that serum CX3CL1 and IL-6 levels were most strongly associated with symptom severity. This is the first report to date demonstrating that serum CX3CL1 level is associated with the severity of RSV infection. (4) Conclusions: Our results demonstrated that specific chemokines and the imbalance of cytokines are suspected to be associated with aggravated symptoms of RSV infection.

3D Lung Tissue Models for Studies on SARS-CoV-2 Pathophysiology and Therapeutics

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing the coronavirus disease 2019 (COVID-19), has provoked more than six million deaths worldwide and continues to pose a major threat to global health. Enormous efforts have been made by researchers around the world to elucidate COVID-19 pathophysiology, design efficacious therapy and develop new vaccines to control the pandemic. To this end, experimental models are essential. While animal models and conventional cell cultures have been widely utilized during these research endeavors, they often do not adequately reflect the human responses to SARS-CoV-2 infection. Therefore, models that emulate with high fidelity the SARS-CoV-2 infection in human organs are needed for discovering new antiviral drugs and vaccines against COVID-19. Three-dimensional (3D) cell cultures, such as lung organoids and bioengineered organs-on-chips, are emerging as crucial tools for research on respiratory diseases. The lung airway, small airway and alveolus organ chips have been successfully used for studies on lung response to infection by various pathogens, including corona and influenza A viruses. In this review, we provide an overview of these new tools and their use in studies on COVID-19 pathogenesis and drug testing. We also discuss the limitations of the existing models and indicate some improvements for their use in research against COVID-19 as well as future emerging epidemics.

Serpine1 Regulates Peripheral Neutrophil Recruitment and Acts as Potential Target in Ischemic Stroke

Introduction

Peripheral neutrophil infiltration can exacerbate ischemia–reperfusion injury. We focused on the relationship between various peripheral immune cells and cerebral ischemia–reperfusion (I/R) injury.

Methods

In this study, we investigated the effects of dauricine on neuronal injury induced by ischemia–reperfusion and peripheral immune cells after ischemic stroke in mouse model, and we explored the undefined mechanisms of regulating peripheral immune cells through RNA sequencing and various biochemical verification in vitro and in vivo.

Results

We found that dauricine improved the neurological deficits of I/R injury, reduced the infarct volume, and improved the neurological scores. Furthermore, dauricine reduced the infiltration of neutrophils into the brain after MCAO-R and increased peripheral neutrophils but unchanged the permeability of the endotheliocyte Transwell system in an in vitro blood-brain barrier (BBB) model. RNA sequencing showed that chemotaxis factors, such as CXCL3, CXCL11, CCL20, CCL22, IL12a, IL23a, and serpine1, might play a crucial role. Overexpression of serpine1 reversed LPS-induced migration of neutrophils. Dauricine can directly bind with serpine1 in ligand–receptor docking performed with the Autodock and analyzed with PyMOL.

Conclusion

We identified chemotaxis factor serpine1 played a crucial role in peripheral neutrophil infiltration, which may contribute to reduce the neuronal injury induced by ischemia–reperfusion. These findings reveal that serpine1 may act as a potential treatment target in the acute stage of ischemic stroke.

Neutrophil Extracellular Traps Do Not Induce Injury and Inflammation in Well-Differentiated RSV-Infected Airway Epithelium

Respiratory syncytial virus (RSV) lower respiratory tract infection (LRTI) causes a major burden of disease. The host response in RSV-LRTI is characterized by airway epithelial injury, inflammation and neutrophil influx, with the formation of neutrophil extracellular traps (NETs). However, the precise role of NETs in the pathophysiology of RSV-LRTI remains to be elucidated. Here, we used well-differentiated human airway epithelial cultures (HAE) of a pediatric and adult donor to study whether NETs cause airway epithelial injury and inflammation in the setting of RSV infection. The exposure of uninfected and RSV-infected HAE cultures to NETs, as produced by stimulation of neutrophils by a low dose of phorbol 12-myristate 13-acetate (PMA), did not induce or aggravate cell injury or inflammation. RSV infection of HAE cultures caused release of pro-inflammatory cytokines such as IL-6 and RANTES in both adult and pediatric cultures, but the differential gene expression for regulated cell death differed between culture donors. In this in vitro airway epithelial model, NETs in the setting of RSV infection did not cause or aggravate epithelial injury or inflammation.

Immune Response to Viruses

Viruses are essentially, obligate intracellular parasites. They require a host to replicate their genetic material, spread to other cells, and eventually to other hosts. For humans, most viral infections are not considered lethal, regardless if at the cellular level, the virus can obliterate individual cells. Constant genomic mutations, (which can alter the antigenic content of viruses such as influenza or coronaviruses), zoonosis or immunosuppression/immunocompromisation, is when viruses achieve higher host mortality. Frequent examples of the severe consequenses of viral infection can be seen in children and the elderly. In most instances, the immune system will take a multifaceted approach in defending the host against viruses. Depending on the virus, the individual, and the point of entry, the immune system will initiate a robust response which involves multiple components. In this chapter, we expand on the total immune system, breaking it down to the two principal types: Innate and Adaptive Immunity, their different roles in viral recognition and clearance. Finally, how different viruses activate and evade different arms of the immune system.

Chromatin Remodeling of Colorectal Cancer Liver Metastasis is Mediated by an HGF-PU.1-DPP4 Axis

Colorectal cancer (CRC) metastasizes mainly to the liver, which accounts for the majority of CRC-related deaths. Here it is shown that metastatic cells undergo specific chromatin remodeling in the liver. Hepatic growth factor (HGF) induces phosphorylation of PU.1, a pioneer factor, which in turn binds and opens chromatin regions of downstream effector genes. PU.1 increases histone acetylation at the DPP4 locus. Precise epigenetic silencing by CRISPR/dCas9KRAB or CRISPR/dCas9HDAC revealed that individual PU.1-remodeled regulatory elements collectively modulate DPP4 expression and liver metastasis growth. Genetic silencing or pharmacological inhibition of each factor along this chromatin remodeling axis strongly suppressed liver metastasis. Therefore, microenvironment-induced epimutation is an important mechanism for metastatic tumor cells to grow in their new niche. This study presents a potential strategy to target chromatin remodeling in metastatic cancer and the promise of repurposing drugs to treat metastasis.

Human models for COVID-19 research

Currently, therapeutics for COVID-19 are limited. To overcome this, it is important that we use physiologically relevant models to reproduce the pathology of infection and evaluate the efficacy of antiviral drugs. Models of airway infection, including the use of a human infection challenge model or well-defined, disease relevant in vitro systems can help determine the key components that perpetuate the severity of the disease. Here, we briefly review the human models that are currently being used in COVID-19 research and drug development.

Microglial lnc-U90926 facilitates neutrophil infiltration in ischemic stroke via MDH2/CXCL2 axis

Dysregulated long non-coding RNAs (lncRNAs) have been shown to contribute to the pathogenesis of ischemic stroke. However, the potential role of lncRNAs in post-stroke microglial activation remains largely unknown. Here, we uncovered that lncRNA-U90926 was significantly increased in microglia exposed to ischemia/reperfusion both in vivo and in vitro. In addition, adenovirus-associated virus (AAV)-mediated microglial U90926 silencing alleviated neurological deficits and reduced infarct volume in experimental stroke mice. Microglial U90926 knockdown could reduce the infiltration of neutrophils into ischemic lesion site, which might be attributed to the downregulation of C-X-C motif ligand 2 (CXCL2). Mechanistically, U90926 directly bound to malate dehydrogenase 2 (MDH2) and competitively inhibited the binding of MDH2 to the CXCL2 3' untranslated region (UTR), thus protecting against MDH2-mediated decay of CXCL2 mRNA. Taken together, our study demonstrated that microglial U90926 aggravated ischemic brain injury via facilitating neutrophil infiltration, suggesting that U90926 might be a potential biomarker and therapeutic target for ischemic stroke.

A Microfluidic 3D Endothelium-on-a-Chip Model to Study Transendothelial Migration of T Cells in Health and Disease

The recruitment of T cells is a crucial component in the inflammatory cascade of the body. The process involves the transport of T cells through the vascular system and their stable arrest to vessel walls at the site of inflammation, followed by extravasation and subsequent infiltration into tissue. Here, we describe an assay to study 3D T cell dynamics under flow in real time using a high-throughput, artificial membrane-free microfluidic platform that allows unimpeded extravasation of T cells. We show that primary human T cells adhere to endothelial vessel walls upon perfusion of microvessels and can be stimulated to undergo transendothelial migration (TEM) by TNFα-mediated vascular inflammation and the presence of CXCL12 gradients or ECM-embedded melanoma cells. Notably, migratory behavior was found to differ depending on T cell activation states. The assay is unique in its comprehensiveness for modelling T cell trafficking, arrest, extravasation and migration, all in one system, combined with its throughput, quality of imaging and ease of use. We envision routine use of this assay to study immunological processes and expect it to spur research in the fields of immunological disorders, immuno-oncology and the development of novel immunotherapeutics.

Airway Gene Expression Correlates of Respiratory Syncytial Virus Disease Severity and Microbiome Composition in Infants

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory disease in infants. The causes and correlates of severe illness in the majority of infants are poorly defined.

METHODS

We recruited a cohort of RSV-infected infants and simultaneously assayed the molecular status of their airways and the presence of airway microbiota. We used rigorous statistical approaches to identify gene expression patterns associated with disease severity and microbiota composition, separately and in combination.

RESULTS

We measured comprehensive airway gene expression patterns in 106 infants with primary RSV infection. We identified an airway gene expression signature of severe illness dominated by excessive chemokine expression. We also found an association between Haemophilus influenzae, disease severity, and airway lymphocyte accumulation. Exploring the time of onset of clinical symptoms revealed acute activation of interferon signaling following RSV infection in infants with mild or moderate illness, which was absent in subjects with severe illness.

CONCLUSIONS

Our data reveal that airway gene expression patterns distinguish mild/moderate from severe illness. Furthermore, our data identify biomarkers that may be therapeutic targets or useful for measuring efficacy of intervention responses.

Reconstruction of Ultra-thin Alveolar-capillary Basement Membrane Mimics

Alveolar-capillary basement membrane (BM) is ultra-thin (<2 µm) extracellular matrix that maintains integral epithelial-endothelial cell layers. In vitro reconstructions of alveolar-capillary barrier supported on synthetic scaffolds closely resembling the fibrous and ultra-thin natural BM are essential in mimicking the lung pathophysiology. Although BM topology and dimensions are well known to significantly influence cellular behavior, conventionally used BM mimics fail to recreate this natural niche. To overcome this, electrospun ultra-thin 2 µm poly(caprolactone) (PCL) nanofibrous mesh is used to establish an alveolar-capillary barrier model of lung endothelial/epithelial cells. Transepithelial electrical resistance (TEER) and permeability studies reveal integral tight junctions and improved mass transport through the highly porous PCL meshes compared to conventional dense membranes with etched pores. The chemotaxis of neutrophils is shown across the barrier in presence of inflammatory response that is naturally impeded in confined regions. Conventional requirement of 3 µm or larger pore size can lead to barrier disruption due to epithelial/endothelial cell invasion. Despite high porosity, the interconnected BM mimic prevents barrier disruption and allows neutrophil transmigration, thereby demonstrating the physiological relevance of the thin nanofibrous meshes. It is envisioned that these bipolar cultured barriers would contribute to an organ-level in vitro model for pathological disease, environmental pollutants, and nanotoxicology.

Microphysiological Systems for Studying Cellular Crosstalk During the Neutrophil Response to Infection

Neutrophils are the primary responders to infection, rapidly migrating to sites of inflammation and clearing pathogens through a variety of antimicrobial functions. This response is controlled by a complex network of signals produced by vascular cells, tissue resident cells, other immune cells, and the pathogen itself. Despite significant efforts to understand how these signals are integrated into the neutrophil response, we still do not have a complete picture of the mechanisms regulating this process. This is in part due to the inherent disadvantages of the most-used experimental systems: in vitro systems lack the complexity of the tissue microenvironment and animal models do not accurately capture the human immune response. Advanced microfluidic devices incorporating relevant tissue architectures, cell-cell interactions, and live pathogen sources have been developed to overcome these challenges. In this review, we will discuss the in vitro models currently being used to study the neutrophil response to infection, specifically in the context of cell-cell interactions, and provide an overview of their findings. We will also provide recommendations for the future direction of the field and what important aspects of the infectious microenvironment are missing from the current models.

A 3D In Vitro Model of the Human Airway Epithelium Exposed to Tritiated Water: Dosimetric Estimate and Cytotoxic Effects

Tritium has been receiving worldwide attention, particularly because of its production and use in existing fission reactors and future nuclear fusion technologies, leading to an increased risk of release in the environment. Linking human health effects to low-dose tritium exposures presents a challenge for many reasons. Among these: biological effects strongly depend on the speciation of tritiated products and exposure pathway; large dosimetric uncertainties may exist; measurements using in vitro cell cultures generally lack a description of effects at the tissue level, while large-scale animal studies might be ethically questionable and too highly demanding in terms of resources. In this context, three-dimensional models of the human airway epithelium are a powerful tool to investigate potential toxicity induced upon inhalation of radioactive products in controlled physiological conditions. In this study we exposed such a model to tritiated water (HTO) for 24 h, with a range of activity levels (up to ∼33 kBq µl-1 cm-2). After the exposures, we measured cell viability, integrity of epithelial layer and pro-inflammatory response at different post-exposure time-points. We also quantified tritium absorption and performed dosimetric estimates considering HTO passage through the epithelial layer, leading to reconstructed upper limits for the dose to the tissue of less than 50 cGy cumulative dose for the highest activity. Upon exposure to the highest activity, cell viability was not decreased; however, we observed a small effect on epithelial integrity and an inflammatory response persisting after seven days. These results represent a reference condition and will guide future experiments using human airway epithelium to investigate the effects of other peculiar tritiated products.

Severe respiratory syncytial virus disease in preterm infants: a case of innate immaturity

Respiratory syncytial virus (RSV) is the most common viral pathogen associated with acute lower respiratory tract infection (LRTI) in children under 5 years of age. Severe RSV disease is associated with the development of chronic respiratory complications such as recurrent wheezing and asthma. A common risk factor for developing severe RSV disease is premature gestation and this is largely due to an immature innate immune system. This increases susceptibility to RSV since the innate immune system is less able to protect against pathogens at a time when adaptive immunity has not fully developed. This review focuses on comparing different aspects of innate immunity between preterm and term infants to better understand why preterm infants are more susceptible to severe RSV disease. Identifying early life innate immune biomarkers associated with the development of severe RSV disease, and understanding how these compare between preterm and term infants, remains a critically important question that would aid the development of interventions to reduce the burden of disease in this vulnerable population.

Getting Your Neutrophil: Neutrophil Transepithelial Migration in the Lung

Neutrophil transepithelial migration is a fundamental process that facilitates the rapid trafficking of neutrophils to inflammatory foci and occurs across a diverse range of tissues. For decades there has been widespread interest in understanding the mechanisms that drive this migratory process in response to different pathogens and organ systems. This has led to the successful integration of key findings on neutrophil transepithelial migration from the intestines, lungs, liver, genitourinary tract, and other tissues into a single, cohesive model. However, recent studies have identified organ specific differences in neutrophil transepithelial migration. These findings support a model where the tissue in concert with the pro-inflammatory stimuli dictate a unique collection of signals that drive neutrophil trafficking. This review focuses on the mechanisms that drive neutrophil transepithelial migration in response to microbial infection of a single organ, the lung. Herein we provide a detailed analysis of the adhesion molecules and chemoattractants that contribute to the recruitment of neutrophil into the airways. We also highlight important advances in experimental models for studying neutrophil transepithelial migration in the lung over the last decade.

Triple co-culture and perfusion bioreactor for studying the interaction between Neisseria gonorrhoeae and neutrophils: A novel 3D tissue model for bacterial infection and immunity

Gonorrhea, a sexually transmitted disease caused by the bacteria Neisseria gonorrhoeae, is characterized by a large number of neutrophils recruited to the site of infection. Therefore, proper modeling of the N. gonorrhoeae interaction with neutrophils is very important for investigating and understanding the mechanisms that gonococci use to evade the immune response. We have used a combination of a unique human 3D tissue model together with a dynamic culture system to study neutrophil transmigration to the site of N. gonorrhoeae infection. The triple co-culture model consisted of epithelial cells (T84 human colorectal carcinoma cells), human primary dermal fibroblasts, and human umbilical vein endothelial cells on a biological scaffold (SIS). After the infection of the tissue model with N. gonorrhoeae, we introduced primary human neutrophils to the endothelial side of the model using a perfusion-based bioreactor system. By this approach, we were able to demonstrate the activation and transmigration of neutrophils across the 3D tissue model and their recruitment to the site of infection. In summary, the triple co-culture model supplemented by neutrophils represents a promising tool for investigating N. gonorrhoeae and other bacterial infections and interactions with the innate immunity cells under conditions closely resembling the native tissue environment.

STAT1 participates in the induction of substance P expression in airway epithelial cells by respiratory syncytial virus

PURPOSE

The regulation effect and mechanism of respiratory syncytial virus (RSV) infection on the expression of tachykinin substance P (SP) in airway epithelial cells was investigated.

METHODS

The regulation of SP expression by RSV was investigated in the BEAS-2B airway epithelial cell line. RT-qPCR, immunofluorescence, and ELISA assay were used to examine the expression of the SP encoding gene TAC1, the intracellular SP protein expression, and the extracellular SP secretion.

RESULTS

The mRNA expression of TAC1 and the intracellular SP protein level in BEAS-2B cells were significantly enhanced by RSV infection with multiplicity of infection (MOI) values of both 1 and 0.1 at 48 hours post infection. Heat-inactivated and UV-inactivated RSV, but not live RSV, significantly induced SP secretion in both control BEAS-2B cells and CX3CR1 receptor knockout cells without affecting the TAC1 gene expression or cell viability. RSV G protein (2-10 μg/ml) and fractalkine (10-50 ng/ml), both CX3CR1 receptor ligands, did not affect SP secretion in BEAS-2B cells. Inhibition of STAT1 phosphorylation by fludarabine (1 μM) markedly reduced the RSV-induced TAC1 gene expression and antagonized the inhibition of RSV replication by interferon-α in BEAS-2B cells.

CONCLUSIONS

STAT1 participates in RSV infection-induced SP expression in airway epithelial cells.

Characterization of the Impact of Oncolytic Vesicular Stomatitis Virus on the Trafficking, Phenotype, and Antigen Presentation Potential of Neutrophils and Their Ability to Acquire a Non-Structural Viral Protein

Neutrophils are innate leukocytes that mount a rapid response to invading pathogens and sites of inflammation. Although neutrophils were traditionally considered responders to bacterial infections, recent advances have demonstrated that they are interconnected with both viral infections and cancers. One promising treatment strategy for cancers is to administer an oncolytic virus to activate the immune system and directly lyse cancerous cells. A detailed characterization of how the innate immune system responds to a viral-based therapy is paramount in identifying its systemic effects. This study analyzed how administering the rhabdovirus vesicular stomatitis virus (VSV) intravenously at 1 × 10⁹ PFU acutely influenced neutrophil populations. Bone marrow, blood, lungs, and spleen were acquired three- and 24-h after administration of VSV for analysis of neutrophils by flow cytometry. Infection with VSV caused neutrophils to rapidly egress from the bone marrow and accumulate in the lungs. A dramatic increase in immature neutrophils was observed in the lungs, as was an increase in the antigen presentation potential of these cells within the spleen. Furthermore, the potential for neutrophils to acquire viral transgene-encoded proteins was monitored using a variant of VSV that expressed enhanced green fluorescent protein (GFP). If an in vitro population of splenocytes were exposed to αCD3 and αCD28, a substantial proportion of the neutrophils would become GFP-positive. This suggested that the neutrophils could either acquire more virus-encoded antigens from infected splenocytes or were being directly infected. Five different dosing regimens were tested in mice, and it was determined that a single dose of VSV or two doses of VSV administered at a 24-h interval, resulted in a substantial proportion of neutrophils in the bone marrow becoming GFP-positive. This correlated with a decrease in the number of splenic neutrophils. Two doses administered at intervals longer than 24-h did not have these effects, suggesting that neutrophils became resistant to antigen uptake or direct infection with VSV beyond 24-h of activation. These findings implicated neutrophils as major contributors to oncolytic rhabdoviral therapies. They also provide several clear future directions for research and suggest that neutrophils should be carefully monitored during the development of all oncolytic virus-based treatment regimens.

β2-integrin LFA1 mediates airway damage following neutrophil transepithelial migration during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) bronchiolitis is the most common cause of infant hospital admissions, but there is limited understanding of the mechanisms of disease, and no specific antiviral treatment. Using a novel in vitro primary transepithelial neutrophil migration model and innovative imaging methods, we show that RSV infection of nasal airway epithelium increased neutrophil transepithelial migration and adhesion to infected epithelial cells, which is associated with epithelial cell damage and reduced ciliary beat frequency, but also with a reduction in infectious viral load.Following migration, RSV infection results in greater neutrophil activation, degranulation and release of neutrophil elastase into the airway surface media compared to neutrophils that migrated across mock-infected nasal epithelial cells. Blocking of the interaction between the ligand on neutrophils (the β₂-integrin LFA-1) for intracellular adhesion molecule (ICAM)-1 on epithelial cells reduced neutrophil adherence to RSV-infected cells and epithelial cell damage to pre-infection levels, but did not reduce the numbers of neutrophils that migrated or prevent the reduction in infectious viral load.These findings have provided important insights into the contribution of neutrophils to airway damage and viral clearance, which are relevant to the pathophysiology of RSV bronchiolitis. This model is a convenient, quantitative preclinical model that will further elucidate mechanisms that drive disease severity and has utility in antiviral drug discovery.

The Contribution of Neutrophils to the Pathogenesis of RSV Bronchiolitis

Acute viral bronchiolitis causes significant mortality in the developing world, is the number one cause of infant hospitalisation in the developed world, and is associated with the later development of chronic lung diseases such as asthma. A vaccine against respiratory syncytial virus (RSV), the leading cause of viral bronchiolitis in infancy, remains elusive, and hence new therapeutic modalities are needed to limit disease severity. However, much remains unknown about the underlying pathogenic mechanisms. Neutrophilic inflammation is the predominant phenotype observed in infants with both mild and severe disease, however, a clear understanding of the beneficial and deleterious effects of neutrophils is lacking. In this review, we describe the multifaceted roles of neutrophils in host defence and antiviral immunity, consider their contribution to bronchiolitis pathogenesis, and discuss whether new approaches that target neutrophil effector functions will be suitable for treating severe RSV bronchiolitis.

Innate Immune Components that Regulate the Pathogenesis and Resolution of hRSV and hMPV Infections

The human respiratory syncytial virus (hRSV) and human Metapneumovirus (hMPV) are two of the leading etiological agents of acute lower respiratory tract infections, which constitute the main cause of mortality in infants. However, there are currently approved vaccines for neither hRSV nor hMPV. Moreover, despite the similarity between the pathology caused by both viruses, the immune response elicited by the host is different in each case. In this review, we discuss how dendritic cells, alveolar macrophages, neutrophils, eosinophils, natural killer cells, innate lymphoid cells, and the complement system regulate both pathogenesis and the resolution of hRSV and hMPV infections. The roles that these cells play during infections by either of these viruses will help us to better understand the illnesses they cause. We also discuss several controversial findings, relative to some of these innate immune components. To better understand the inflammation in the lungs, the role of the respiratory epithelium in the recruitment of innate immune cells is briefly discussed. Finally, we review the main prophylactic strategies and current vaccine candidates against both hRSV and hMPV.

Control of neutrophil influx during peritonitis by transcriptional cross-regulation of chemokine CXCL1 by IL-17 and IFN-γ

Neutrophil infiltration is a hallmark of peritoneal inflammation, but mechanisms regulating neutrophil recruitment in patients with peritoneal dialysis (PD)-related peritonitis are not fully defined. We examined 104 samples of PD effluent collected during acute peritonitis for correspondence between a broad range of soluble parameters and neutrophil counts. We observed an association between peritoneal IL-17 and neutrophil levels. This relationship was evident in effluent samples with low but not high IFN-γ levels, suggesting a differential effect of IFN-γ concentration on neutrophil infiltration. Surprisingly, there was no association of neutrophil numbers with the level of CXCL1, a key IL-17-induced neutrophil chemoattractant. We investigated therefore the production of CXCL1 by human peritoneal mesothelial cells (HPMCs) under in vitro conditions mimicking clinical peritonitis. Stimulation of HPMCs with IL-17 increased CXCL1 production through induction of transcription factor SP1 and activation of the SP1-binding region of the CXCL1 promoter. These effects were amplified by TNFα. In contrast, IFN-γ dose-dependently suppressed IL-17-induced SP1 activation and CXCL1 production through a transcriptional mechanism involving STAT1. The SP1-mediated induction of CXCL1 was also observed in HPMCs exposed to PD effluent collected during peritonitis and containing IL-17 and TNFα, but not IFN-γ. Supplementation of the effluent with IFN-γ led to a dose-dependent activation of STAT1 and a resultant inhibition of SP1-induced CXCL1 expression. Transmesothelial migration of neutrophils in vitro increased upon stimulation of HPMCs with IL-17 and was reduced by IFN-γ. In addition, HPMCs were capable of binding CXCL1 at their apical cell surface. These observations indicate that changes in relative peritoneal concentrations of IL-17 and IFN-γ can differently engage SP1-STAT1, impacting on mesothelial cell transcription of CXCL1, whose release and binding to HPMC surface may determine optimal neutrophil recruitment and retention during peritonitis. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Nontypeable Haemophilus influenzae Responds to Virus-Infected Cells with a Significant Increase in Type IV Pilus Expression

Nontypeable Haemophilus influenzae (NTHI) is the predominant bacterial causative agent of many chronic and recurrent diseases of the upper and lower respiratory tracts. NTHI-induced chronic rhinosinusitis, otitis media, and exacerbations of cystic fibrosis and chronic obstructive pulmonary disease often develop during or just after an upper respiratory tract viral infection. We have developed a vaccine candidate immunogen for NTHI-induced diseases that targets the majority subunit (PilA) of the type IV twitching pilus (T4P), which NTHI uses to adhere to respiratory tract epithelial cells and that also plays a role in disease. Here, we showed that NTHI cocultured with virus-infected respiratory tract epithelial cells express significantly more of the vaccine-targeted T4P than NTHI that encounters mock-infected (healthy) cells. These results strongly suggest that a vaccine strategy that targets the NTHI T4P will be effective under the most common predisposing condition: when the human host has a respiratory tract virus infection.

Nontypeable Haemophilus influenzae (NTHI) colonizes the human nasopharynx, but when the host immune response is dysregulated by upper respiratory tract (URT) virus infection, NTHI can gain access to more distal airway sites and cause disease. The NTHI type IV pilus (T4P) facilitates adherence, benign colonization, and infection, and its majority subunit PilA is in clinical trials as a vaccinogen. To further validate the strategy of immunization with PilA against multiple NTHI-induced diseases, it is important to demonstrate T4P expression under microenvironmental conditions that predispose to NTHI infection of the airway. Because URT infection commonly facilitates NTHI-induced diseases, we examined the influence of ongoing virus infection of respiratory tract epithelial cells on NTHI T4P expression in vitro. Polarized primary human airway epithelial cells (HAEs) were sequentially inoculated with one of three common URT viruses, followed by NTHI. Use of a reporter construct revealed that NTHI upregulated pilA promoter activity when cultured with HAEs infected with adenovirus (AV), respiratory syncytial virus (RSV), or rhinovirus (RV) versus that in mock-infected HAEs. Consistent with these results, pilA expression and relative PilA/pilin abundance, as assessed by quantitative reverse transcription-PCR (qRT-PCR) and immunoblot, respectively, were also significantly increased when NTHI was cultured with virus-infected HAEs. Collectively, our data strongly suggest that under conditions of URT virus infection, PilA vaccinogen induction of T4P-directed antibodies is likely to be highly effective against multiple NTHI-induced diseases by interfering with T4P-mediated adherence. We hypothesize that this outcome could thereby limit or prevent the increased load of NTHI in the nasopharynx that characteristically precedes these coinfections.

IMPORTANCE Nontypeable Haemophilus influenzae (NTHI) is the predominant bacterial causative agent of many chronic and recurrent diseases of the upper and lower respiratory tracts. NTHI-induced chronic rhinosinusitis, otitis media, and exacerbations of cystic fibrosis and chronic obstructive pulmonary disease often develop during or just after an upper respiratory tract viral infection. We have developed a vaccine candidate immunogen for NTHI-induced diseases that targets the majority subunit (PilA) of the type IV twitching pilus (T4P), which NTHI uses to adhere to respiratory tract epithelial cells and that also plays a role in disease. Here, we showed that NTHI cocultured with virus-infected respiratory tract epithelial cells express significantly more of the vaccine-targeted T4P than NTHI that encounters mock-infected (healthy) cells. These results strongly suggest that a vaccine strategy that targets the NTHI T4P will be effective under the most common predisposing condition: when the human host has a respiratory tract virus infection.

Progress in Model Systems of Cystic Fibrosis Mucosal Inflammation to Understand Aberrant Neutrophil Activity

In response to recurrent infection in cystic fibrosis (CF), powerful innate immune signals trigger polymorphonuclear neutrophil recruitment into the airway lumen. Exaggerated neutrophil proteolytic activity results in sustained inflammation and scarring of the airways. Consequently, neutrophils and their secretions are reliable clinical biomarkers of lung disease progression. As neutrophils are required to clear infection and yet a direct cause of airway damage, modulating adverse neutrophil activity while preserving their pathogen fighting function remains a key area of CF research. The factors that drive their pathological behavior are still under investigation, especially in early disease when aberrant neutrophil behavior first becomes evident. Here we examine the latest findings of neutrophils in pediatric CF lung disease and proposed mechanisms of their pathogenicity. Highlighted in this review are current and emerging experimental methods for assessing CF mucosal immunity and human neutrophil function in the laboratory.

Chemokine regulation of inflammation during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) can cause severe lower respiratory tract infections especially in infants, immunocompromised individuals and the elderly and is the most common cause of infant hospitalisation in the developed world. The immune responses against RSV are crucial for viral control and clearance but, if dysregulated, can also result in immunopathology and impaired gas exchange. Lung immunity to RSV and other respiratory viruses begins with the recruitment of immune cells from the bloodstream into the lungs. This inflammatory process is controlled largely by chemokines, which are small proteins that are produced in response to innate immune detection of the virus or the infection process. These chemokines serve as chemoattractants for granulocytes, monocytes, lymphocytes and other leukocytes. In this review, we highlight recent advances in the field of RSV infection and disease, focusing on how chemokines regulate virus-induced inflammation.

Identifying novel biomarkers of the pediatric influenza infection by weighted co-expression network analysis

Background

Despite the high yearly prevalence of Influenza, the pathogenesis mechanism and involved genes have not been fully known. Finding the patterns and mapping the complex interactions between different genes help us to find the possible biomarkers and treatment targets.

Methods

Herein, weighted gene co-expression network analysis (WGCNA) was employed to construct a co-expression network among genes identified by microarray analysis of the pediatric influenza-infected samples.

Results

Three of the 38 modules were found as the most related modules to influenza infection. At a functional level, we found that the genes in these modules regulate the immune responses, protein targeting, and defense to virus. Moreover, the analysis of differentially expressed genes disclosed 719 DEGs between the normal and infected subjects. The comprehensive investigation of genes in the module involved in immune system and viral defense (yellow module) revealed that SP110, HERC5, SAMD9L, RTP4, C19orf66, HELZ2, EPSTI1, and PHF11 which were also identified as DEGs (except C19orf66) have the potential to be as the biomarkers and also drug targeting for the treatment of pediatric influenza.

Conclusions

The WGCN analysis revealed co-expressed genes which were involved in the innate immune system and defense to virus. The differentially expressed genes in the identified modules can be considered for designing drug targets. Moreover, modules can help to find pathogenesis routes in the future.

Nrf2 downregulates zymosan-induced neutrophil activation and modulates migration

Polymorphonuclear neutrophils (PMNs) are the first line of defense against pathogens and their activation needs to be tightly regulated in order to limit deleterious effects. Nrf2 (Nuclear factor (erythroïd-derived 2)-like 2) transcription factor regulates oxidative stress and/or represses inflammation in various cells such as dendritic cells or macrophages. However, its involvement in PMN biology is still unclear. Using Nrf2 KO mice, we thus aimed to investigate the protective role of Nrf2 in various PMN functions such as oxidative burst, netosis, migration, cytokine production and phagocytosis, mainly in response to zymosan. We found that zymosan induced Nrf2 accumulation in PMNs leading to the upregulation of some target genes including Hmox-1, Nqo1 and Cat. Nrf2 was able to decrease zymosan-induced PMN oxidative burst; sulforaphane-induced Nrf2 hyperexpression confirmed its implication. Tnfα, Ccl3 and Cxcl2 gene transcription was decreased in zymosan-stimulated Nrf2 KO PMNs, suggesting a role for Nrf2 in the regulation of proinflammatory cytokine production. However, Nrf2 was not involved in phagocytosis. Finally, spontaneous migration of Nrf2 KO PMNs was lower than that of WT PMNs. Moreover, in response to low concentrations of CXCL2 or CXCL12, Nrf2 KO PMN migration was decreased despite similar CXCR2 and CXCR4 expression and ATP levels in PMNs from both genotypes. Nrf2 thus seems to be required for an optimal migration. Altogether these results suggest that Nrf2 has a protective role in several PMN functions. In particular, it downregulates their activation in response to zymosan and is required for an adequate migration.

PD-1 of Sigmodon hispidus: Gene identification, characterization and preliminary evaluation of expression in inactivated RSV vaccine-induced enhanced respiratory disease

Sigmodon hispidus or cotton rat is an excellent animal model for studying human infections of respiratory viruses including respiratory syncytial virus (RSV), which is the leading cause of hospitalization in infants and causes high rates of infection in the elderly and immunocompromised patient populations. Despite several decades of research, no vaccine has been licensed whereas inactivated vaccines have been shown to induce severe adverse reaction in a clinical trial, with other forms of RSV vaccine also found to induce enhanced disease in preclinical animal studies. While arguably the cotton rat is the best small animal model for evaluation of RSV vaccines and antivirals, many important genes of the immune system remain to be isolated. Programmed cell death-1 (PD-1) plays an integral role in regulating many aspects of immunity by inducing suppressive signals. In this study, we report the isolation of mRNA encoding the cotton rat PD-1 (crPD-1) and characterization of the PD-1 protein. crPD-1 bound to its cognate ligand on dendritic cells and effectively suppressed cytokine secretion. Moreover, using the newly acquired gene sequence, we observed a decreased level of crPD-1 levels in cotton rats with enhanced respiratory disease induced by inactivated RSV vaccine, unraveling a new facet of vaccine-induced disease.

Airway Epithelial Derived Cytokines and Chemokines and Their Role in the Immune Response to Respiratory Syncytial Virus Infection

The airway epithelium is the primary target of respiratory syncytial virus infection. It is an important component of the antiviral immune response. It contributes to the recruitment and activation of innate immune cells from the periphery through the secretion of cytokines and chemokines. This paper provides a broad review of the cytokines and chemokines secreted from human airway epithelial cell models during respiratory syncytial virus (RSV) infection based on a comprehensive literature review. Epithelium-derived chemokines constitute most inflammatory mediators secreted from the epithelium during RSV infection. This suggests chemo-attraction of peripheral immune cells, such as monocytes, neutrophils, eosinophils, and natural killer cells as a key function of the epithelium. The reports of epithelium-derived cytokines are limited. Recent research has started to identify novel cytokines, the functions of which remain largely unknown in the wider context of the RSV immune response. It is argued that the correct choice of in vitro models used for investigations of epithelial immune functions during RSV infection could facilitate greater progress in this field.

Respiratory epithelial cells as master communicators during viral infections

PURPOSE OF REVIEW

Communication by epithelial cells during respiratory viral infections is critical in orchestrating effective anti-viral responses but also can lead to excessive inflammation. This review will evaluate studies that investigate how respiratory epithelial cells influence the behavior of immune cells and how epithelial cell/immune cell interactions contribute to antiviral responses and immunopathology outcomes.

RECENT FINDINGS

Previous studies have characterized cytokine responses of virus-infected epithelial cells. More recent studies have carefully demonstrated the effects of these cytokines on cellular behaviors within the infected lung. Infected epithelial cells release exosomes that specifically regulate responses of monocytes and neighboring epithelial cells without promoting spread of virus. In contrast, rhinovirus-infected cells induce monocytes to upregulate expression of the viral receptor, promoting spread of the virus to alternate cell types. The precise alteration of PDL expression on infected epithelial cells has been shown to switch between inhibition and activation of antiviral responses.

SUMMARY

These studies have more precisely defined the interactions between epithelial and immune cells during viral infections. This level of understanding is critical for the development of novel therapeutic strategies that promote effective antiviral responses or epithelial repair, or inhibit damaging inflammatory responses during severe respiratory viral infections.

Myeloid Cells during Viral Infections and Inflammation

Myeloid cells represent a diverse range of innate leukocytes that are crucial for mounting successful immune responses against viruses. These cells are responsible for detecting pathogen-associated molecular patterns, thereby initiating a signaling cascade that results in the production of cytokines such as interferons to mitigate infections. The aim of this review is to outline recent advances in our knowledge of the roles that neutrophils and inflammatory monocytes play in initiating and coordinating host responses against viral infections. A focus is placed on myeloid cell development, trafficking and antiviral mechanisms. Although known for promoting inflammation, there is a growing body of literature which demonstrates that myeloid cells can also play critical regulatory or immunosuppressive roles, especially following the elimination of viruses. Additionally, the ability of myeloid cells to control other innate and adaptive leukocytes during viral infections situates these cells as key, yet under-appreciated mediators of pathogenic inflammation that can sometimes trigger cytokine storms. The information presented here should assist researchers in integrating myeloid cell biology into the design of novel and more effective virus-targeted therapies.

Targeting CD40 enhances antibody- and CD8-mediated protection against respiratory syncytial virus infection

Respiratory Syncytial Virus (RSV) infects almost all children under the age of one and is the leading cause of hospitalization among infants. Despite several decades of research with dozens of candidate vaccines being vigorously evaluated in pre-clinical and clinical studies, there is no licensed vaccine available to date. Here, the RSV fusion protein (F) was fused with CD40 ligand and delivered by an adenoviral vector into BALB/c mice where the CD40 ligand serves two vital functions as a molecular adjuvant and an antigen-targeting molecule. In contrast to a formaldehyde-inactivated vaccine, the vectored vaccine effectively protected animals against RSV without inducing enhanced respiratory disease. This protection involved a robust induction of neutralizing antibodies and memory CD8 T cells, which were not observed in the inactivated vaccine group. Finally, the vectored vaccine was able to elicit long-lasting protection against RSV, one of the most challenging issues in RSV vaccine development. Further studies indicate that the long lasting protection elicited by the CD40 ligand targeted vaccine was mediated by increased levels of effector memory CD8 T cell 3 months post-vaccination.