The Interaction between Respiratory Pathogens and Mucus

Aerosol emission and exposure in non-invasive ventilation

From the beginning of the COVID-19 pandemic, there has been concern among clinicians whether the use of high-flow nasal cannula (HFNC) and continuous positive airway pressure (CPAP) contributes to aerosol generation and consequently spreading of pathogens. Most guidelines still classify these treatments as high-risk aerosol-generating procedures. The aim of this study was to evaluate differences in aerosol emissions and exposure with CPAP and HFNC compared to no breathing aid (NBA). Aerosol emissions of 16 healthy volunteers using CPAP, HFNC and NBA were measured with a portable aerosol spectrometer. During each measurement, the volunteers were instructed consecutively to breathe normally, breathe deeply, cough and read aloud a predefined text. The Wilcoxon signed-rank test was used in statistical analysis. Non-invasive ventilation (CPAP, HFNC) does not produce significantly more aerosol than the same respiratory activities without a breathing aid (median CPAP-NBA - 4.54 1/L, p = 0.816, and HFNC-NBA 2.27 1/L, p = 0.244), deep breathing (median CPAP-NBA - 2.27 1/L, p = 0.378 and HFNC-NBA 4.55 1/L, p = 0.623), speaking (median CPAP-NBA 0 1/L, p = 0.0523 and HFNC-NBA 9.09 1/L, p = 0.0140), or coughing (median CPAP-NBA - 17.31 1/L, p = 0.587 and HFNC-NBA 1.92 1/L, p = 0.365). The results indicate that both CPAP and HFNC have no clinically meaningful impact on aerosol emission. Therefore, the use of CPAP or HFNC does not expose healthcare personnel to greater concentrations of aerosols when compared to normal breathing in healthy participants.

Mucus Physically Restricts Influenza A Viral Particle Access to the Epithelium

Prior work suggests influenza A virus (IAV) crosses the airway mucus barrier in a sialic acid-dependent manner through the actions of the viral envelope proteins, hemagglutinin, and neuraminidase. However, host and viral factors that influence how efficiently mucus traps IAV remain poorly defined. In this work, how the physicochemical properties of mucus influence its ability to effectively capture IAV is assessed using fluorescence video microscopy and multiple particle tracking. Our studies suggest an airway mucus gel layer must be produced with virus-sized pores to physically constrain IAV. While sialic acid binding by IAV may improve mucus trapping efficiency, sialic acid binding preference is found to have little impact on IAV mobility and the fraction of viral particles expected to penetrate the mucus barrier. Further, synthetic polymeric hydrogels engineered with mucus-like architecture are similarly protective against IAV infection despite their lack of sialic acid decoy receptors. Together, this work provides new insights on mucus barrier function toward IAV with important implications on innate host defense and transmission of respiratory viruses.

Exploring Ribosomal Genes as Potential Biomarkers of the Immune Microenvironment in Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is the most common pathogen causing acute lower respiratory tract infection in infants and children. Due to limited knowledge of the pathological and molecular mechanisms of immunodeficiency underlying RSV disease, there is currently a lack of an approved and effective RSV vaccine to combat RSV infections. This study aimed to identify genes associated with immune dysfunction using bioinformatics methods to gain insights into the role of dysregulated immune genes in RSV disease progression, and to predict potential therapeutic drugs by targeting dysregulated immune-related genes. 423 immune-related differential genes (DEIRGs) were filtered from the blood samples of 87 healthy individuals and 170 RSV patients. According to CIBERSORT analysis, the blood of RSV patients showed increased infiltration of various immune cells. Subsequently, ten immune-related hub genes were screened via Protein-Protein Interaction Networks. Six signature immune-related genes (RPS2, RPS5, RPS13, RPS14, RPS18, and RPS4X) as candidate characteristic genes for the diagnostic model were identified by Lasso regression. The AUC value of the ROC curve of the six signature genes was 0.884. This result, intriguingly, suggested that all six immune-related genes with a good internal validation effect were ribosome family genes. Finally, through molecular docking analyses targeting these differential immune genes, ADO and fluperlapine were found to have high stable binding to major proteins of important immune-related genes in nine drug-protein interactions. Overall, the present study screened immune-related genes that are dysregulated in the development of RSV disease to investigate the pathogenesis of RSV infection from the standpoint of immune disorders. Unexpectedly, bioinformatics analysis revealed that ribosome family genes may be involved in the immune dysregulation of RSV disease, and these genes as targets formed the basis for potential drug modification candidates in RSV disease.

Assessment of In Vitro Models of the Human Buccal Mucosa for Vaccine and Adjuvant Development

To understand requirements for immunization via the oral mucosa, an in vitro model that recapitulates the physical barrier of the mouth, allows for quantification of antigen uptake and permeability and mounts an inflammatory response to antigen and adjuvant is needed. The physical structure of 4 models of the human oral mucosa was determined by histochemical staining and transepithelial electrical resistance (TEER) measurements. A TR146 based air-liquid interface (ALI) model most closely mimicked in vivo conditions. This was confirmed by validation studies using dextran and caffeine as diffusant molecules. Apparent permeability coefficients (Papp) of adenovirus (Ad) and adeno-associated virus (AAV) in this model were 4.3 × 10-13 and 2.2 × 10-10 respectively, while 100% of the total dose of H1N1 influenza remained in the epithelial layer. Sodium glycocholate and a hyperosmotic formulation improved the amount of Ad (p = 0.02) and AAV (p = 0.003) that entered the epithelium, respectively. Significant amounts of IL-6 (45.1 pg/mL), GM-CSF (94.7 pg/mL) and IFN-γ (4.3 pg/mL) were produced in response to influenza infection. Treatment with an AS03-like adjuvant induced production of IL-6 (34.9 pg/mL), TNF-∝ (43 pg/mL), GM-CSF (121.2 pg/mL) and IFN-γ (14.1 pg/mL). This highlights the contribution of differentiated epithelial cells to the immune response to vaccines and adjuvants.

Inhibitory Activity of Hydroxypropyl Methylcellulose on Rhinovirus and Influenza A Virus Infection of Human Nasal Epithelial Cells

The nasal epithelium is the primary site for entry of respiratory viruses. In comparison to oral administration, nasal drug applications directed locally to the site of infection can serve as early interventional barriers against respiratory virus pathogenesis by limiting viral spread in the upper airway. Experiments on the diffusion of methylene blue and nanoparticles in both water and low pH conditions revealed that hydroxypropyl methylcellulose (HPMC) can act as an effective physical barrier. This study also evaluated the activity of HPMC as a barrier against common respiratory viruses, i.e., rhinovirus (RV) and influenza A virus (IAV) using the in vitro human nasal epithelial cell (hNEC) model. Utilizing the hNEC infection model, we assessed the protective effects of HPMC in pH 3.5 and pH 7 buffers against RV and IAV. Acidic and pH-neutral buffers and HPMC dissolved in acidic and pH-neutral buffers were administered for 4 h prior to virus infection and at 4 h post-infection (hpi). The apical supernatant was harvested at 24 hpi to determine the viral loads of RV and IAV (H1N1 and H3N2). HPMC was demonstrated to exert protective effects in the infected hNECs independent of acidic pH. Pre-treatment with HPMC in acidic buffer significantly diminished viral loads for both RV and IAV infections of hNECs. Similarly, direct treatment of HPMC in acidic buffer after infection (4 hpi) also effectively decreased viral loads of both RV and IAV. Moreover, treatment using HPMC in acidic buffer before or after infection did not affect the epithelial integrity and ciliary function of hNECs. This study demonstrates the protective effects of HPMC in acidic buffer against RV and IAV infections of the human nasal epithelium.

Distinct Responses of Cystic Fibrosis Epithelial Cells to SARS-CoV-2 and Influenza A Virus

The coronavirus disease (COVID-19) pandemic has underscored the impact of viral infections on individuals with cystic fibrosis (CF). Initial observations suggested lower COVID-19 rates among CF populations; however, subsequent clinical data have presented a more complex scenario. This study aimed to investigate how bronchial epithelial cells from individuals with and without CF, including various CFTR (CF transmembrane conductance regulator) mutations, respond to in vitro infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and SARS-CoV. Comparisons with the influenza A virus (IAV) were included based on evidence that patients with CF experience heightened morbidity from IAV infection. Our findings showed that CF epithelial cells exhibited reduced replication of SARS-CoV-2, regardless of the type of CFTR mutation or SARS-CoV-2 variant, as well as the original 2003 SARS-CoV. In contrast, these cells displayed more efficient IAV replication than non-CF cells. Interestingly, the reduced susceptibility to SARS-CoV-2 in CF was not linked to the expression of ACE2 (angiotensin-converting enzyme 2) receptor or to CFTR dysfunction, as pharmacological treatments to restore CFTR function did not normalize the viral response. Both SARS-CoV-2 infection and CFTR function influenced the concentrations of certain cytokines and chemokines, although these effects were not correlated. Overall, this study reveals a unique viral response in CF epithelial cells, characterized by reduced replication for some viruses like SARS-CoV-2, while showing increased susceptibility to others, such as IAV. This research offers a new perspective on CF and viral interactions, emphasizing the need for further investigation into the mechanisms underlying these differences.

Lignin-Based Mucus-Mimicking Antiviral Hydrogels with Enzyme Stability and Tunable Porosity

Mucus is a complex hydrogel that acts as a defensive and protective barrier in various parts of the human body. The rise in the level of viral infections has underscored the importance of advancing research into mucus-mimicking hydrogels for the efficient design of antiviral agents. Herein, we demonstrate the gram-scale synthesis of biocompatible, lignin-based virus-binding inhibitors that reduce waste and ensure long-term availability. The lignin-based inhibitors are equipped with sulfate moieties, which are known binding partners for many viruses, including SARS-CoV-2 and herpes viruses. In addition, cross-linking the synthesized inhibitors yielded hydrogels that mimicked native mucus concerning surface functionality and rheology. The degree of sulfation exhibits a very strong impact on the mesh size distribution of the hydrogels, which provides a new means to fine-tune the steric and electrostatic contributions of the virus-hydrogel interaction. This feature strongly impacts the sequestration capability of the lignin-based hydrogels, which is demonstrated by infection inhibition assays involving human herpes simplex virus 1, influenza A viruses, and the bacterium Escherichia coli (E. coli). These measurements showed a reduction in plaque-forming units (HSV-1) and colony-forming units (E. coli) by more than 4 orders of magnitude, indicating the potent inhibition by the lignin-based hydrogels.

Mucin Colocalizes with Influenza Virus and Preserves Infectivity in Deposited Model Respiratory Droplets

The stability of influenza virus in respiratory particles varies with relative humidity (RH) and protein content. This study investigated the decay, or loss of infectivity, of influenza A virus (IAV) in 1-μL respiratory droplets deposited on a surface with varying concentrations of mucin, one of the most abundant proteins in respiratory mucus, and examined the localization of virions within droplets. IAV remained stable at 0.1% and 0.5% mucin in phosphate-buffered saline (PBS) over 4 h at 20%, 50%, and 80% RH, with a maximum decay of 1.2 log10/mL. In contrast, in pure PBS droplets, the virus decayed by at least 2.6 log10/mL after 4 h at 50% and 80% RH. Mucin's protective effect was independent of its concentration, except at 80% RH after 4 h. Confocal microscopy of the particles revealed that at 20% and 50% RH, mucin led to thicker coffee rings and dendritic patterns where virions colocalized with mucin. At 80% RH, no morphological difference was observed between PBS-only and mucin-containing droplets, but virions still colocalized with mucin in the center of droplets with 0.5% mucin. Analysis by digital droplet PCR showed that mucin helped maintain virus integrity. To our knowledge, this is the first study to localize influenza virus in model respiratory droplets. The results suggest that mucin's colocalization with virions in droplets may protect the virus from environmental stressors, enhancing its stability.

Pathogenesis of influenza and SARS-CoV-2 co-infection at the extremes of age: decipher the ominous tales of immune vulnerability

The co-circulation of influenza and SARS-CoV-2 has led to co-infection events, primarily affecting children and older adults, who are at higher risk for severe disease. Although co-infection prevalence is relatively low, it is associated with worse outcomes compared to mono-infections. Previous studies have shown that the outcomes of co-infection depend on multiple factors, including viral interference, virus-host interaction and host response. Children and the elderly exhibit distinct patterns of antiviral response, which involve airway epithelium, mucociliary clearance, innate and adaptive immune cells, and inflammatory mediators. This review explores the pathogeneses of SARS-CoV-2 and influenza co-infection, focusing on the antiviral responses in children and the elderly. By comparing immature immunity in children and immune senescence in older adults, we aim to provide insights for the clinical management of severe co-infection cases.

Sulfated Cellulose Nanofiber Hydrogel with Mucus-Like Activities for Virus Inhibition

Mucus is the first defense barrier against viruses in the human immune system. Inspired by the mucus structure, we designed a highly sulfated hydrogel to bind viruses and prevent infection of the underlying cells. The hydrogel was formed by gelation of sulfated cellulose nanofiber (SCNF) with Ca2+. SCNF exhibited a mucin-like nanofiber structure with high numbers of sulfated groups. Based on the electrostatic interactions with a virus, SCNF could efficiently inhibit herpes simplex virus-1 (HSV-1) infection with a half-maximal inhibitory concentration (IC50) of 0.43 μg/mL, which is comparable to that of heparin (IC50 = 0.30 μg/mL). Benefiting from the multiporous structure and sulfate groups, the Ca2+-SCNF hydrogel could efficiently trap HSV-1 and inhibit the virus from attacking the underlying cells in a transwell model. Furthermore, SCNF also inhibited SARS-CoV-2 infection in a similar experimental setting. By integrating the advantages of high and broad-spectrum virus inhibitory activity as well as low toxicity, it is believed that the Ca2+-SCNF hydrogel can promote the development of highly biocompatible and efficient antiviral material with "binding and inhibition" capability and other diverse strategies.

Respiratory tract barrier dysfunction in viral-bacterial co-infection cases

A preceding viral infection of the respiratory tract predisposes the host to secondary bacterial pneumonia, known as a major cause of morbidity and mortality. However, the underlying mechanism of the viral-bacterial synergy that leads to disease progression has remained elusive, thus hampering the production of effective prophylactic and therapeutic intervention options. In addition to viral-induced airway epithelial damage, which allows dissemination of bacteria to the lower respiratory tract and increases their invasiveness, dysfunction of immune defense following a viral infection has been implicated as a factor for enhanced susceptibility to secondary bacterial infections. Given the proximity of the oral cavity to the respiratory tract, where viruses enter and replicate, it is also well-established that oral health status can significantly influence the initiation, progression, and pathology of respiratory viral infections. This review was conducted to focus on the dysfunction of the respiratory barrier, which plays a crucial role in providing physical and secretory barriers as well as immune defense in the context of viral-bacterial synergy. Greater understanding of barrier response to viral-bacterial co-infections, will ultimately lead to development of effective, broad-spectrum therapeutic approaches for prevention of enhanced susceptibility to these pathogens.

Euphorbium compositum SN improves the innate defenses of the airway mucosal barrier network during rhinovirus infection

BACKGROUND

Rhinoviruses (RV) are the major cause of common colds in healthy individuals and are associated with acute exacerbations in patients with chronic lung diseases. Yet, no vaccines or effective treatment against RV are available. This study investigated the effect of Euphorbium compositum SN (ECSN6), a multicomponent, multitarget medication made from natural ingredients, on the mucosal barrier network during RV infection.

METHODS

Mucociliary-differentiated airway epithelial cell cultures were infected with RV or sham, and treated with 20% ECSN6 or placebo twice daily. Barrier integrity was assessed by measuring transepithelial resistance (TER), permeability to inulin, and expression and localization of intercellular junctions proteins (IJ). Ciliary beat frequency (CBF), expression of pro-inflammatory cytokines, antiviral interferons and mucins, and viral load were also measured. C57BL/6 mice were infected intranasally with RV or sham and treated with 40% ECSN6 or placebo twice daily. Inflammation of sinunasal mucosa, localization of E-cadherin, viral load and mucin gene expression were determined.

RESULTS

ECSN6-treated, uninfected cell cultures showed small, but significant increase in TER over placebo, which was associated with enhanced localization of E-cadherin and ZO-1 to IJ. In RV-infected cultures, treatment with ECSN6, but not placebo prevented RV-induced (1) reduction in TER, (2) dissociation of E-cadherin and ZO-1 from the IJ, (3) mucin expression, and (4) CBF attenuation. ECSN6 also decreased RV-stimulated expression of pro-inflammatory cytokines and permeability to inulin. Although ECSN6 significantly increased the expression of some antiviral type I and type III interferons, it did not alter viral load. In vivo, ECSN6 reduced RV-A1-induced moderate inflammation of nasal mucosa, beneficially affected RV-A1-induced cytokine responses and Muc5ac mRNA expression and prevented RV-caused dissociation of E-cadherin from the IJ of nasal mucosa without an effect on viral clearance.

CONCLUSIONS

ECSN6 prevents RV-induced airway mucosal barrier dysfunction and improves the immunological and mucociliary barrier function. ECSN6 may maintain integrity of barrier function by promoting localization of tight and adherence junction proteins to the IJ. This in turn may lead to the observed decrease in RV-induced pro-inflammatory responses in vitro. By improving the innate defenses of the airway mucosal barrier network, ECSN6 may alleviate respiratory symptoms caused by RV infections.

In Vitro Culture of Human Norovirus in the Last 20 Years

Human noroviruses (HuNoVs) are the main pathogens that cause acute gastroenteritis and lead to huge economic losses annually. Due to the lack of suitable culture systems, the pathogenesis of HuNoVs and the development of vaccines and drugs have progressed slowly. Although researchers have employed various methods to culture HuNoVs in vitro in the last century, problems relating to the irreducibility, low viral titer, and non-infectiousness of the progeny virus should not be ignored. In 2016, researchers achieved the cultivation and successive passaging of some HuNoV genotypes using human intestinal enteroids, initially demonstrating the potential use of organoids in overcoming this challenge. This paper reviews the efforts made in the last 20 years to culture HuNoVs in vitro and discusses the superiority and limitations of employing human intestinal enteroids/organoids as an in vitro culture model for HuNoVs.

Chemoenzymatic synthesis of sialyl-α2,3-lactoside-functionalized BSA conjugate inhibits influenza infection

Influenza remains a global public health threat, and the development of new antivirals is crucial to combat emerging drug-resistant influenza strains. In this study, we report the synthesis and evaluation of a sialyl lactosyl (TS)-bovine serum albumin (BSA) conjugate as a potential multivalent inhibitor of the influenza virus. The key trisaccharide component, TS, was efficiently prepared via a chemoenzymatic approach, followed by conjugation to dibenzocyclooctyne-modified BSA via a strain-promoted azide-alkyne cycloaddition reaction. Biophysical and biochemical assays, including surface plasmon resonance, isothermal titration calorimetry, hemagglutination inhibition, and neuraminidase inhibition, demonstrated the strong binding affinity of TS-BSA to the hemagglutinin (HA) and neuraminidase (NA) proteins of the influenza virus as well as intact virion particles. Notably, TS-BSA exhibited potent inhibitory activity against viral entry and release, preventing cytopathic effects in cell culture. This multivalent presentation strategy highlights the potential of glycocluster-based antivirals for combating influenza and other drug-resistant viral strains.

Mucin-Inspired Polymeric Fibers for Herpes Simplex Virus Type 1 Inhibition

Mucus lines the epithelial cells at the biological interface and is the first line of defense against multiple viral infections. Mucins, the gel-forming components of mucus, are high molecular weight glycoproteins and crucial for preventing infections by binding pathogens. Consequently, mimicking mucins is a promising strategy for new synthetic virus inhibitors. In this work, synthetic mucin-inspired polymers (MIPs) as potential inhibitors of herpes simplex virus 1 (HSV-1) are investigated. By using a telechelic reversible addition-fragmentation chain-transfer (RAFT) polymerization technique, a new dendronized polysulfate p(G1AAm-OSO3)PDS with an amide-backbone similar to the native mucin glycoproteins is synthesized. p(G1AAm-OSO3)PDS shows mucin-like elongated fiber structure, as revealed in cryo-electron microscopy (cryo-EM) imaging, and its HSV-1 inhibition activity together with its previously reported methacrylate analogue p(G1MA-OSO3)PDS is tested. Both of the sulfated MIPs show strong HSV-1 inhibition in plaque reduction assays with IC50 values in lower nanomolar range (<3 × 10-9 m) and demonstrate a high cell compatibility (CC50 > 1.0 mg mL-1) with lower anticoagulant activity than heparin. In addition, the prophylactic and therapeutic activity of both MIPs is assessed in pre- and post-infection inhibition assays and clearly visualize their high potential for application using fluorescent microscopy imaging of infected cells.

Mucus-Inspired Self-Healing Hydrogels: A Protective Barrier for Cells against Viral Infection

Mucus is a dynamic biological hydrogel, composed primarily of the glycoprotein mucin, exhibits unique biophysical properties and forms a barrier protecting cells against a broad-spectrum of viruses. Here, this work develops a polyglycerol sulfate-based dendronized mucin-inspired copolymer (MICP-1) with ≈10% repeating units of activated disulfide as cross-linking sites. Cryo-electron microscopy (Cryo-EM) analysis of MICP-1 reveals an elongated single-chain fiber morphology. MICP-1 shows potential inhibitory activity against many viruses such as herpes simplex virus 1 (HSV-1) and SARS-CoV-2 (including variants such as Delta and Omicron). MICP-1 produces hydrogels with viscoelastic properties similar to healthy human sputum and with tuneable microstructures using linear and branched polyethylene glycol-thiol (PEG-thiol) as cross-linkers. Single particle tracking microrheology, electron paramagnetic resonance (EPR) and cryo-scanning electron microscopy (Cryo-SEM) are used to characterize the network structures. The synthesized hydrogels exhibit self-healing properties, along with viscoelastic properties that are tuneable through reduction. A transwell assay is used to investigate the hydrogel's protective properties against viral infection against HSV-1. Live-cell microscopy confirms that these hydrogels can protect underlying cells from infection by trapping the virus, due to both network morphology and anionic multivalent effects. Overall, this novel mucin-inspired copolymer generates mucus-mimetic hydrogels on a multi-gram scale. These hydrogels can be used as models for disulfide-rich airway mucus research, and as biomaterials.

A Zanamivir-protein conjugate mimicking mucin for trapping influenza virion particles and inhibiting neuraminidase activity

Influenza viruses contribute significantly to the global health burden, necessitating the development of strategies against transmission as well as effective antiviral treatments. The present study reports a biomimetic strategy inspired by the natural antiviral properties of mucins. A bovine serum albumin (BSA) conjugate decorated with the multivalent neuraminidase inhibitor Zanamivir (ZA-BSA) was synthesized using copper-free click chemistry. This synthetic pseudo-mucin exhibited potent neuraminidase inhibitory activity against several influenza strains. Virus capture and growth inhibition assays demonstrated its effective absorption of virion particles and ability to prevent viral infection in nanomolar concentrations. Investigation of the underlying antiviral mechanism of ZA-BSA revealed a dual mode of action, involving disruption of the initial stages of host-cell binding and fusion by inducing viral aggregation, followed by blocking the release of newly assembled virions by targeting neuraminidase activity. Notably, the conjugate also exhibited potent inhibitory activity against Oseltamivir-resistant neuraminidase variant comparable to the monomeric Zanamivir. These findings highlight the application of multivalent drug presentation on protein scaffold to mimic mucin adsorption of viruses, together with counteracting drug resistance. This innovative approach has potential for the creation of antiviral agents against influenza and other viral infections.

MUC5AC: A potential biomarker of severity in pediatric patients infected with influenza

Numerous factors can increase the risk of severe influenza; however, a majority of severe cases occur in previously healthy children. Identification of high-risk children is important for targeted preventive interventions and prompt treatment. The aim of this study was to evaluate MUC5AC as a biomarker for influenza disease severity in children. For this, a prospective cohort study was conducted in 2019. Children hospitalized with acute respiratory infection (ARI) with confirmed positive influenza infection were enrolled. Influenza cases were identified by reverse transcriptase-polymerase chain reaction. Life-threatening disease (LTD) was defined by the need for intensive care and ventilatory support. MUC5AC, epidemiologic, and clinical risk factors were assessed. Three hundred and forty-two patients were hospitalized with ARI, of which 49 (14%) had confirmed influenza infection and 6 (12%) of them developed LTD. MUC5AC levels were higher in those patients with mild disease compared to cases with poorer outcomes. Our results show that the severity of influenza infection in children is significantly associated with low levels of MUC5AC. These findings suggest its potential as a suitable biomarker for predicting disease severity.

Mucus physically restricts influenza A viral particle access to the epithelium

Prior work suggests influenza A virus (IAV) crosses the airway mucus barrier in a sialic acid-dependent manner through the actions of the viral envelope proteins, hemagglutinin and neuraminidase. However, host and viral factors that influence how efficiently mucus traps IAV remain poorly defined. In this work, we assessed how the physicochemical properties of mucus influence its ability to effectively capture IAV with altered sialic acid preference using fluorescence video microscopy and multiple particle tracking. We found an airway mucus gel layer must be produced with pores on the order of size of the virus to physically constrain IAV. Sialic acid binding by IAV also improves mucus trapping efficiency, but interestingly, sialic acid preferences had little impact on the fraction of IAV particles expected to penetrate the mucus barrier. Together, this work provides new insights on mucus barrier function toward IAV with important implications on innate host defense and interspecies transmission.

Spontaneous oscillation of an active filament under viscosity gradients

We investigate the effects of uniform viscosity gradients on the spontaneous oscillations of an elastic, active filament in viscous fluids. Combining numerical simulations and linear stability analysis, we demonstrate that a viscosity gradient increasing from the filament's base to tip destabilises the system, facilitating its self-oscillation. This effect is elucidated through a reduced-order model, highlighting the delicate balance between destabilising active forces and stabilising viscous forces. Additionally, we reveal that while a perpendicular viscosity gradient to the filament's orientation minimally affects instability, it induces asymmetric ciliary beating, thus generating a net flow along the gradient. Our findings offer new insights into the complex behaviours of biological and artificial filaments in complex fluid environments, contributing to the broader understanding of filament dynamics in heterogeneous viscous media.

Interaction of Neisseria meningitidis carrier and disease isolates of MenB cc32 and MenW cc22 with epithelial cells of the nasopharyngeal barrier

Neisseria meningitidis (Nm, the meningococcus) is considered an asymptomatic colonizer of the upper respiratory tract and a transient member of its microbiome. It is assumed that the spread of N. meningitidis into the bloodstream occurs via transcytosis of the nasopharyngeal epithelial barrier without destroying the barrier layer. Here, we used Calu-3 respiratory epithelial cells that were grown under air-liquid-interface conditions to induce formation of pseudostratified layers and mucus production. The number of bacterial localizations in the outer mucus, as well as cellular adhesion, invasion and transmigration of different carrier and disease N. meningitidis isolates belonging to MenB:cc32 and MenW:cc22 lineages was assessed. In addition, the effect on barrier integrity and cytokine release was determined. Our findings showed that all strains tested resided primarily in the outer mucus layer after 24 h of infection (>80%). Nonetheless, both MenB:cc32 and MenW:cc22 carrier and disease isolates reached the surface of the epithelial cells and overcame the barrier. Interestingly, we observed a significant difference in the number of bacteria transmigrating the epithelial cell barrier, with the representative disease isolates being more efficient to transmigrate compared to carrier isolates. This could be attributed to the capacity of the disease isolates to invade, however could not be assigned to expression of the outer membrane protein Opc. Moreover, we found that the representative meningococcal isolates tested in this study did not damage the epithelial barrier, as shown by TEER measurement, FITC-dextran permeability assays, and expression of cell-junction components.

Insights on Pseudomonas aeruginosa Carbohydrate Binding from Profiles of Cystic Fibrosis Isolates Using Multivalent Fluorescent Glycopolymers Bearing Pendant Monosaccharides

Pseudomonas aeruginosa contributes to frequent, persistent, and, often, polymicrobial respiratory tract infections for individuals with cystic fibrosis (CF). Chronic CF infections lead to bronchiectasis and a shortened lifespan. P. aeruginosa expresses numerous adhesins, including lectins known to bind the epithelial cell and mucin glycoconjugates. Blocking carbohydrate-mediated host-pathogen and intra-biofilm interactions critical to the initiation and perpetuation of colonization offer promise as anti-infective treatment strategies. To inform anti-adhesion therapies, we profiled the monosaccharide binding of P. aeruginosa from CF and non-CF sources, and assessed whether specific bacterial phenotypic characteristics affected carbohydrate-binding patterns. Focusing at the cellular level, microscopic and spectrofluorometric tools permitted the solution-phase analysis of P. aeruginosa binding to a panel of fluorescent glycopolymers possessing distinct pendant monosaccharides. All P. aeruginosa demonstrated significant binding to glycopolymers specific for α-D-galactose, β-D-N-acetylgalactosamine, and β-D-galactose-3-sulfate. In each culture, a small subpopulation accounted for the binding. The carbohydrate anomeric configuration and sulfate ester presence markedly influenced binding. While this opportunistic pathogen from CF hosts presented with various colony morphologies and physiological activities, no phenotypic, physiological, or structural feature predicted enhanced or diminished monosaccharide binding. Important to anti-adhesive therapeutic strategies, these findings suggest that, regardless of phenotype or clinical source, P. aeruginosa maintain a small subpopulation that may readily associate with specific configurations of specific monosaccharides. This report provides insights into whole-cell P. aeruginosa carbohydrate-binding profiles and into the context within which successful anti-adhesive and/or anti-virulence anti-infective agents for CF must contend.

How Does Airway Surface Liquid Composition Vary in Different Pulmonary Diseases, and How Can We Use This Knowledge to Model Microbial Infections?

Growth environment greatly alters many facets of pathogen physiology, including pathogenesis and antimicrobial tolerance. The importance of host-mimicking environments for attaining an accurate picture of pathogen behaviour is widely recognised. Whilst this recognition has translated into the extensive development of artificial cystic fibrosis (CF) sputum medium, attempts to mimic the growth environment in other respiratory disease states have been completely neglected. The composition of the airway surface liquid (ASL) in different pulmonary diseases is far less well characterised than CF sputum, making it very difficult for researchers to model these infection environments. In this review, we discuss the components of human ASL, how different lung pathologies affect ASL composition, and how different pathogens interact with these components. This will provide researchers interested in mimicking different respiratory environments with the information necessary to design a host-mimicking medium, allowing for better understanding of how to treat pathogens causing infection in these environments.

Mucus Structure, Viscoelastic Properties, and Composition in Chronic Respiratory Diseases

The respiratory mucus, a viscoelastic gel, effectuates a primary line of the airway defense when operated by the mucociliary clearance. In chronic respiratory diseases (CRDs), such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), the mucus is overproduced and its solid content augments, changing its structure and viscoelastic properties and determining a derangement of essential defense mechanisms against opportunistic microbial (virus and bacteria) pathogens. This ensues in damaging of the airways, leading to a vicious cycle of obstruction and infection responsible for the harsh clinical evolution of these CRDs. Here, we review the essential features of normal and pathological mucus (i.e., sputum in CF, COPD, and asthma), i.e., mucin content, structure (mesh size), micro/macro-rheology, pH, and osmotic pressure, ending with the awareness that sputum biomarkers (mucins, inflammatory proteins and peptides, and metabolites) might serve to indicate acute exacerbation and response to therapies. There are some indications that old and novel treatments may change the structure, viscoelastic properties, and biomarker content of sputum; however, a wealth of work is still needed to embrace these measures as correlates of disease severity in association with (or even as substitutes of) pulmonary functional tests.

CALB1: Anovel antiviral factor in chicken ileal mucus

Intestinal mucus is the first line of defense against pathogens and has several active components. Poultry have a short intestine, the mucus of which may contain antiviral components. We hence investigated the antiviral components of mucus and explored their mechanisms of action. Initially, we isolated chicken intestinal mucus proteins that significantly inhibited the replication of avian viruses. The ileum 10-30 kDa protein fraction showed the greatest inhibition of viral replication. Moreover, liquid chromatography-mass spectrometry revealed 12 high-abundance proteins in the ileum 10-30 kDa protein fraction. Among them, we investigated the antiviral activity of calcium binding protein 1 (CALB1). Furthermore, eukaryotically and prokaryotically expressed CALB1 significantly suppressed the replication of avian viruses, possibly by binding calcium ions and/or inducing autophagy. In conclusion, we isolated and identified CALB1 from chicken intestinal mucus, which suppressed replication of avian viruses by regulating cellular calcium-ion homeostasis and autophagy.

Nose-to-Brain (N2B) Delivery: An Alternative Route for the Delivery of Biologics in the Management and Treatment of Central Nervous System Disorders

In recent years, there have been a growing number of small and large molecules that could be used to treat diseases of the central nervous system (CNS). Nose-to-brain delivery can be a potential option for the direct transport of molecules from the nasal cavity to different brain areas. This review aims to provide a compilation of current approaches regarding drug delivery to the CNS via the nose, with a focus on biologics. The review also includes a discussion on the key benefits of nasal delivery as a promising alternative route for drug administration and the involved pathways or mechanisms. This article reviews how the application of various auxiliary agents, such as permeation enhancers, mucolytics, in situ gelling/mucoadhesive agents, enzyme inhibitors, and polymeric and lipid-based systems, can promote the delivery of large molecules in the CNS. The article also includes a discussion on the current state of intranasal formulation development and summarizes the biologics currently in clinical trials. It was noted that significant progress has been made in this field, and these are currently being applied to successfully transport large molecules to the CNS via the nose. However, a deep mechanistic understanding of this route, along with the intimate knowledge of various excipients and their interactions with the drug and nasal physiology, is still necessary to bring us one step closer to developing effective formulations for nasal-brain drug delivery.

Viral expansion after transfer is a primary driver of influenza A virus transmission bottlenecks

For many viruses, narrow bottlenecks acting during transmission sharply reduce genetic diversity in a recipient host relative to the donor. Since genetic diversity represents adaptive potential, such losses of diversity are though to limit the opportunity for viral populations to undergo antigenic change and other adaptive processes. Thus, a detailed picture of evolutionary dynamics during transmission is critical to understanding the forces driving viral evolution at an epidemiologic scale. To advance this understanding, we used a novel barcoded virus library and a guinea pig model of transmission to decipher where in the transmission process diversity is lost for influenza A viruses. In inoculated guinea pigs, we show that a high level of viral genetic diversity is maintained across time. Continuity in the barcodes detected furthermore indicates that stochastic effects are not pronounced within inoculated hosts. Importantly, in both aerosol-exposed and direct contact-exposed animals, we observed many barcodes at the earliest time point(s) positive for infectious virus, indicating robust transfer of diversity through the environment. This high viral diversity is short-lived, however, with a sharp decline seen 1-2 days after initiation of infection. Although major losses of diversity at transmission are well described for influenza A virus, our data indicate that events that occur following viral transfer and during the earliest stages of natural infection have a predominant role in this process. This finding suggests that immune selection may have greater opportunity to operate during influenza A transmission than previously recognized.

Evaporation of Concentrated Polymer Solutions Is Insensitive to Relative Humidity

A recent theory suggests that the evaporation kinetics of macromolecular solutions is insensitive to the ambient relative humidity (RH) due to the formation of a "polarization layer" of solutes at the air-solution interface. We confirm this insensitivity up to RH≈80% in the evaporation of polyvinyl alcohol solutions from open-ended capillaries. To explain the observed drop in evaporation rate at higher RH, we need to invoke compressive stresses due to interfacial polymer gelation. Moreover, RH-insensitive evaporation sets in earlier than theory predicts, suggesting a further role for a gelled "skin." We discuss the relevance of these observations for respiratory virus transmission via aerosols.

Host-microbe interactions in chronic rhinosinusitis biofilms and models for investigation

Chronic rhinosinusitis (CRS) is a debilitating condition characterized by long-lasting inflammation of the paranasal sinuses. It affects a significant portion of the population, causing a considerable burden on individuals and healthcare systems. The pathogenesis of CRS is multifactorial, with bacterial infections playing a crucial role in CRS development and persistence. In recent years, the presence of biofilms has emerged as a key contributor to the chronicity of sinusitis, further complicating treatment and exacerbating symptoms. This review aims to explore the role of biofilms in CRS, focusing on the involvement of the bacterial species Staphylococcus aureus and Pseudomonas aeruginosa, their interactions in chronic infections, and model systems for studying biofilms in CRS. These species serve as an example of how microbial interplay can influence disease progression and exemplify the need for continued investigation and innovation in CRS research.

Advances in the Evaluation of Gastrointestinal Absorption Considering the Mucus Layer

Because of the increasing sophistication of formulation technology and the increasing polymerization of compounds directed toward undruggable drug targets, the influence of the mucus layer on gastrointestinal drug absorption has received renewed attention. Therefore, understanding the complex structure of the mucus layer containing highly glycosylated glycoprotein mucins, lipids bound to the mucins, and water held by glycans interacting with each other is critical. Recent advances in cell culture and engineering techniques have led to the development of evaluation systems that closely mimic the ecological environment and have been applied to the evaluation of gastrointestinal drug absorption while considering the mucus layer. This review provides a better understanding of the mucus layer components and the gastrointestinal tract's biological defense barrier, selects an assessment system for drug absorption in the mucus layer based on evaluation objectives, and discusses the overview and features of each assessment system.

The neuraminidase activity of influenza A virus determines the strain-specific sensitivity to neutralization by respiratory mucus

IMPORTANCE

The respiratory tract of humans is constantly exposed to potentially harmful agents, such as small particles or pathogens, and thus requires protective measures. Respiratory mucus that lines the airway epithelia plays a major role in the prevention of viral infections by limiting the mobility of viruses, allowing subsequent mucociliary clearance. Understanding the interplay between respiratory mucus and viruses can help elucidate host and virus characteristics that enable the initiation of infection. Here, we tested a panel of primary influenza A viruses of avian or human origin for their sensitivity to mucus derived from primary human airway cultures and found that differences between virus strains can be mapped to viral neuraminidase activity. We also show that binding of influenza A viruses to decoy receptors on highly glycosylated mucus components constitutes the major inhibitory function of mucus against influenza A viruses.

Nanoparticle-Mediated Strategies for Enhanced Drug Penetration and Retention in the Airway Mucosa

Airway mucus is a complex viscoelastic gel composed mainly of water, glycoproteins, lipids, enzymes, minerals, etc. Among them, glycoproteins are the main factors determining mucus's gel-like rheology. Airway mucus forms a protective barrier by secreting mucin, which represents a barrier for absorption, especially for more lipophilic drugs. It rapidly removes drugs from the airway through the physiological mucus clearance mechanism so drugs cannot remain in the lungs or reach the airway epithelial tissue for a long time. Significant progress has been made in enhancing drug lung deposition recently, but strategies are still needed to help drugs break through the lung mucosal barrier. Based on the physiopathological mechanisms of airway mucus, this paper reviews and summarizes strategies to enhance drug penetration and retention in the airway mucosa mediated by nano-delivery systems, including mucosal permeation systems, mucosal adhesion systems, and enzyme-modified delivery systems. On this basis, the potential and challenges of nano-delivery systems for improving airway mucus clearance are revealed. New ideas and approaches are provided for designing novel nano-delivery systems that effectively improve drug retention and penetration in the airway mucus layer.

Using model systems to unravel host-Pseudomonas aeruginosa interactions

Using model systems in infection biology has led to the discoveries of many pathogen-encoded virulence factors and critical host immune factors to fight pathogenic infections. Studies of the remarkable Pseudomonas aeruginosa bacterium that infects and causes disease in hosts as divergent as humans and plants afford unique opportunities to shed new light on virulence strategies and host defence mechanisms. One of the rationales for using model systems as a discovery tool to characterise bacterial factors driving human infection outcomes is that many P. aeruginosa virulence factors are required for pathogenesis in diverse different hosts. On the other side, many host signalling components, such as the evolutionarily conserved mitogen-activated protein kinases, are involved in immune signalling in a diverse range of hosts. Some model organisms that have less complex immune systems also allow dissection of the direct impacts of innate immunity on host defence without the interference of adaptive immunity. In this review, we start with discussing the occurrence of P. aeruginosa in the environment and the ability of this bacterium to cause disease in various hosts as a natural opportunistic pathogen. We then summarise the use of some model systems to study host defence and P. aeruginosa virulence.

Block the Spread: Barriers to Transmission of Influenza Viruses

Respiratory viruses, such as influenza viruses, cause significant morbidity and mortality worldwide through seasonal epidemics and sporadic pandemics. Influenza viruses transmit through multiple modes including contact (either direct or through a contaminated surface) and inhalation of expelled aerosols. Successful human to human transmission requires an infected donor who expels virus into the environment, a susceptible recipient, and persistence of the expelled virus within the environment. The relative efficiency of each mode can be altered by viral features, environmental parameters, donor and recipient host characteristics, and viral persistence. Interventions to mitigate transmission of influenza viruses can target any of these factors. In this review, we discuss many aspects of influenza virus transmission, including the systems to study it, as well as the impact of natural barriers and various nonpharmaceutical and pharmaceutical interventions.

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.

The role of mucosal barriers in disease progression and transmission

Mucus is a biological hydrogel that coats and protects all non-keratinized wet epithelial surfaces. Mucins, the primary structural components of mucus, are critical components of the gel layer that protect against invading pathogens. For communicable diseases, pathogen-mucin interactions contribute to the pathogen's fate and the potential for disease progression in-host, as well as the potential for onward transmission. We begin by reviewing in-host mucus filtering mechanisms, including size filtering and interaction filtering, which regulate the permeability of mucus barriers to all molecules including pathogens. Next, we discuss the role of mucins in communicable diseases at the point of transmission (i.e. how the encapsulation of pathogens in emitted mucosal droplets externally to hosts may modulate pathogen infectivity and viability). Overall, mucosal barriers modulate both host susceptibility as well as the dynamics of population-level disease transmission. The study of mucins and their use in models and experimental systems are therefore crucial for understanding the mechanistic biophysical principles underlying disease transmission and the early stages of host infection.

Mucin 4 is a cellular biomarker of necrotizing bronchiolitis in influenza A virus infection

Influenza A virus (IAV) in the human and swine host infects epithelial cells lining the respiratory tract causing a necrotizing bronchitis and bronchiolitis. These epithelial surfaces are protected by large glycoproteins called mucins. Mucin 4 (MUC4) is a transmembrane mucin that consists of an alpha subunit responsible for surface protection and intracellular beta subunit involved in signal transduction which repress apoptosis and stimulate epithelial proliferation. This study was designed to determine the expression and potential role of MUC4 during IAV infection. We used immunohistochemistry in combination with machine learning image analysis to quantify differential protein expression of MUC4 subunits in IAV-infected and uninfected lung in a porcine model. MUC4 protein basal expression in control animals varied significantly by litter. MUC4 protein expression was significantly increased in bronchioles with necrotizing bronchiolitis compared to histologically normal bronchioles, likely representing a regenerative response to restore mucosal integrity of conducting airways. Understanding the impact of differential MUC4 expression among healthy individuals and during IAV infection will facilitate control strategies by elucidating mechanisms associated with susceptibility to IAV that can be therapeutically or genetically regulated and may be extended to other respiratory diseases.

Phylogenetic analysis and docking study of neuraminidase gene of influenza A/H1N1 viruses circulating in Iran from 2010 to 2019

Influenza A viruses (H1N1) have been consistently one of the most evolving viruses that escape from vaccine-induced immunity. Although there has been a rapid rise in human influenza virus knowledge since the 2009 pandemic, the molecular information about Iranian strains is still inadequate. The aim of this study was to analyze the neuraminidase (NA) segment of the Iranian isolates in terms of phylogenetic, antiviral resistance, and vaccine efficiency. Ninety-three NA sequences collected among 1758 nasopharyngeal swab samples during the 2015-2016 influenza season were sequenced and submitted to NCBI. Moreover, all the submitted Iranian influenza H1N1 NA sequences since 2010 till 2019 were included in the study. Software including MEGA-X, MODELLER, UCSF ChimeraX, Auto-Dock 4.2, and other online tools were used to analyze the phylogenetic relationship, vaccine efficiency, and binding affinity to sialic acid of the selected NA proteins. Moreover, the information about antiviral drug resistance mutations of NA were gathered and compared to the Iranian NA segments to check the presence of antiviral drug-resistant strains. The phylogenetic study showed that most Iranian NA sequences (between 2015 and 2016) were located in a single clade and following years were located in its subclade by 3 major mutations (G77R/K, V81A, and J188T). Resistant mutations in drug targets of NA including I117M, D151E, I223V, and S247N were ascertained in 10 isolates during the 2015-2016 flu seasons. Investigation of vaccination effect revealed that Iranian isolates in 2017 and 2018 were best matched to A/Brisbane/02/2018 (H1N1), and in 2019 to A/Guangdong-Maonan/SWL1536/2019 (H1N1). Furthermore, we performed an in-silico analysis of NA enzymatic activity of all Iranian sequences by assessment of enzyme stability, ligand affinity, and active site availability. Overall, the enzyme activity of four Iranian strains (AUG84119, AUG84157, AUG84095, and AUG84100) was assumed as the maximum enzyme activity. This study highlighted the evolutionary trend of influenza A virus/H1N1 circulating in Iran, which provides a preliminary viewpoint for a better comprehension of new emerging strains' virulence and thus, more appropriate monitoring of influenza virus A/H1N1 during each outbreak season.

A Moonlighting Protein Secreted by a Nasal Microbiome Fortifies the Innate Host Defense Against Bacterial and Viral Infections

Evidence suggests that the human respiratory tract, as with the gastrointestinal tract, has evolved to its current state in association with commensal microbes. However, little is known about how the airway microbiome affects the development of airway immune system. Here, we uncover a previously unidentified mode of interaction between host airway immunity and a unique strain (AIT01) of Staphylococcus epidermidis, a predominant species of the nasal microbiome. Intranasal administration of AIT01 increased the population of neutrophils and monocytes in mouse lungs. The recruitment of these immune cells resulted in the protection of the murine host against infection by Pseudomonas aeruginosa, a pathogenic bacterium. Interestingly, an AIT01-secreted protein identified as GAPDH, a well-known bacterial moonlighting protein, mediated this protective effect. Intranasal delivery of the purified GAPDH conferred significant resistance against other Gram-negative pathogens (Klebsiella pneumoniae and Acinetobacter baumannii) and influenza A virus. Our findings demonstrate the potential of a native nasal microbe and its secretory protein to enhance innate immune defense against airway infections. These results offer a promising preventive measure, particularly relevant in the context of global pandemics.

Size-Dependent Diffusion and Dispersion of Particles in Mucin

Mucus, composed significantly of glycosylated mucins, is a soft and rheologically complex material that lines respiratory, reproductive, and gastrointestinal tracts in mammals. Mucus may present as a gel, as a highly viscous fluid, or as a viscoelastic fluid. Mucus acts as a barrier to the transport of harmful microbes and inhaled atmospheric pollutants to underlying cellular tissue. Studies on mucin gels have provided critical insights into the chemistry of the gels, their swelling kinetics, and the diffusion and permeability of molecular constituents such as water. The transport and dispersion of micron and sub-micron particles in mucin gels and solutions, however, differs from the motion of small molecules since the much larger tracers may interact with microstructure of the mucin network. Here, using brightfield and fluorescence microscopy, high-speed particle tracking, and passive microrheology, we study the thermally driven stochastic movement of 0.5-5.0 μm tracer particles in 10% mucin solutions at neutral pH, and in 10% mucin mixed with industrially relevant dust; specifically, unmodified limestone rock dust, modified limestone, and crystalline silica. Particle trajectories are used to calculate mean square displacements and the displacement probability distributions; these are then used to assess tracer diffusion and transport. Complex moduli are concomitantly extracted using established microrheology techniques. We find that under the conditions analyzed, the reconstituted mucin behaves as a weak viscoelastic fluid rather than as a viscoelastic gel. For small- to moderately sized tracers with a diameter of lessthan 2 μm, we find that effective diffusion coefficients follow the classical Stokes-Einstein relationship. Tracer diffusivity in dust-laden mucin is surprisingly larger than in bare mucin. Probability distributions of mean squared displacements suggest that heterogeneity, transient trapping, and electrostatic interactions impact dispersion and overall transport, especially for larger tracers. Our results motivate further exploration of physiochemical and rheological mechanisms mediating particle transport in mucin solutions and gels.

Advanced fluorescence microscopy in respiratory virus cell biology

Respiratory viruses are a major public health burden across all age groups around the globe, and are associated with high morbidity and mortality rates. They can be transmitted by multiple routes, including physical contact or droplets and aerosols, resulting in efficient spreading within the human population. Investigations of the cell biology of virus replication are thus of utmost importance to gain a better understanding of virus-induced pathogenicity and the development of antiviral countermeasures. Light and fluorescence microscopy techniques have revolutionized investigations of the cell biology of virus infection by allowing the study of the localization and dynamics of viral or cellular components directly in infected cells. Advanced microscopy including high- and super-resolution microscopy techniques available today can visualize biological processes at the single-virus and even single-molecule level, thus opening a unique view on virus infection. We will highlight how fluorescence microscopy has supported investigations on virus cell biology by focusing on three major respiratory viruses: respiratory syncytial virus (RSV), Influenza A virus (IAV) and SARS-CoV-2. We will review our current knowledge of virus replication and highlight how fluorescence microscopy has helped to improve our state of understanding. We will start by introducing major imaging and labeling modalities and conclude the chapter with a perspective discussion on remaining challenges and potential opportunities.

Toxicity assessment of lead, nickel and cadmium on zebra fish augmented with Bacillus xiamenensis VITMSJ3: An insight on the defense mechanism against oxidative stress due to heavy metals

Increase urbanization in recent years has let to discharge of heavy metals into the environment which has caused severe impacts on soil as well as water. Therefore the current study was aimed to assess the toxicity of lead (Pb), nickel (Ni), and cadmium (Cd) from the contaminated water using zebra fish Danio rerio and detoxification of metals upon augmentation with Bacillus xiamenensis. Exposure doses till 150 mg L^-1 of Pb, Ni and Cd in water showed lethal effects on fish. Similarly the histopathological analysis showed severe tissue disruption in the gills and liver which were less upon supplementation with bacterial strain VITMSJ3. On the 20th day, the uptake concentration of Pb, Ni and Cd in zebra fish was found to be 87 mg L^-1, 89 mg L^-1 and 91 mg L^-1 respectively with VITMSJ3, from the water. Antioxidant enzymatic activities showed an increase upon bacterial supplementation, which reduced the oxidative stress. Further SEM-EDAX analysis confirmed the presence of Pb, Ni and Cd ions adsorbed on the gills. The results clearly showed less oxidative damages in fish with increased head and reduced tail %. Overall, the results showed a significant difference (p < 0.05) among the treatments compared with the control.

Crosslink between SARS-CoV-2 replication and cystic fibrosis hallmarks

SARS-CoV-2, the etiological cause of the COVID-19 pandemic, can cause severe illness in certain at-risk populations, including people with cystic fibrosis (pwCF). Nevertheless, several studies indicated that pwCF do not have higher risks of SARS-CoV-2 infection nor do they demonstrate worse clinical outcomes than those of the general population. Recent in vitro studies indicate cellular and molecular processes to be significant drivers in pwCF lower infection rates and milder symptoms than expected in cases of SARS-CoV-2 infection. These range from cytokine releases to biochemical alterations leading to morphological rearrangements inside the cells associated with CFTR impairment. Based on available data, the reported low incidence of SARS-CoV-2 infection among pwCF is likely a result of several variables linked to CFTR dysfunction, such as thick mucus, IL-6 reduction, altered ACE2 and TMPRSS2 processing and/or functioning, defective anions exchange, and autophagosome formation. An extensive analysis of the relation between SARS-CoV-2 infection and pwCF is essential to elucidate the mechanisms involved in this lower-than-expected infection impact and to possibly suggest potential new antiviral strategies.

Adenoid hypertrophy in children: a narrative review of pathogenesis and clinical relevance

Adenoids (nasopharyngeal tonsils), being part of Waldeyer's ring, are masses of lymphoid tissues located at the junction of the roof and the posterior wall of the nasopharynx. Adenoids play an important role in the development of the immune system and serve as a defence against infections, being the first organs that come into contact with respiratory and digestive antigens. The causes of adenoid hypertrophy are not fully known. They are most likely associated with aberrant immune reactions, infections, environmental exposures and hormonal or genetic factors. The aim of this review is to summarise the current knowledge of adenoid hypertrophy in children and associated diseases. Adenoid hypertrophy has many clinical manifestations that are frequent in the paediatric population and is accompanied by various comorbidities.

Mucociliary clearance affected by mucus-periciliary interface stimulations using analytical solution during cough and sneeze

Assessment of mucus velocity variations under different conditions including viscosity variation and boundary conditions is useful to develop mucosal-based medical treatments. This paper deals with the analytical investigation of mucus-periciliary velocities under mucus-periciliary interface movements and mucus viscosity variations. The results for mucus velocity show that there is no difference between the two cases under the free-slip condition. Therefore, power-law mucus can be substituted with a high viscosity Newtonian fluid since the upper boundary of the mucus layer is exposed to the free-slip condition. However, when the upper boundary of the mucus layer is under nonzero shear stress levels, including cough or sneeze, the assumption of a high viscosity Newtonian mucus layer is invalid. Moreover, mucus viscosity variations are investigated for both Newtonian and power-law mucus layers under sneeze and cough to propose a mucosal-based medical treatment. The results indicate by varying mucus viscosity up to a critical value, the direction of mucus movement changes. The critical values of viscosity in sneezing and coughing for Newtonian and power-law mucus layers are 10-4 and 5 × 10-5 and 0.0263 and 006.024 m2 s-1, respectively. Therefore, the pathogen entry into the respiratory system can be prevented by varying mucus viscosity during sneeze and cough.

The respiratory syncytial virus SH protein is incorporated into infectious virus particles that form on virus-infected cells

The association of the SH protein with respiratory syncytial virus (RSV) particles was examined in HEp2 cells and human ciliated nasal epithelial cells. Imaging of infected cells demonstrated the presence of the SH protein in virus filaments, and analysis of purified RSV particles revealed a SH protein species whose size was consistent with the glycosylated SH protein. Although the SH protein was detected in virus filaments it was not required for virus filament formation. Analysis of RSV-infected ciliated cells also revealed that the SH protein was trafficked into the cilia, and this correlated with reduced cilia density on these cells. Reduced cilia loss was not observed on ciliated cells infected with a RSV isolate that failed to express the SH protein. These data provide direct evidence that the SH protein is trafficked into virus particles, and suggests that the SH protein may also promote cilia dysfunction on nasal epithelial cells.

Virus-like Particle Vaccine Expressing the Respiratory Syncytial Virus Pre-Fusion and G Proteins Confers Protection against RSV Challenge Infection

Respiratory syncytial virus (RSV) causes severe lower respiratory tract disease in children and the elderly. However, there are no effective antiviral drugs or licensed vaccines available for RSV infection. Here, RSV virus-like particle (VLP) vaccines expressing Pre-F, G, or Pre-F and G proteins on the surface of influenza virus matrix protein 1 (M1) were produced using the baculovirus expression system, and their protective efficacy was evaluated in mice. The morphology and successful assembly of VLPs were confirmed by transmission electron microscope (TEM) and Western blot. High levels of serum IgG antibody response were detected in VLP-immunized mice, and significantly higher levels of IgG2a and IgG2b were found in the Pre-F+G VLP immunization group compared to the unimmunized control. Serum-neutralizing activity was higher in the VLP immunization groups compared to the naïve group, with Pre-F+G VLPs demonstrating superior neutralizing activity to the single antigen-expressing VLP groups. Pulmonary IgA and IgG responses were generally comparable across the immunization groups, with VLPs expressing the Pre-F antigen eliciting higher IFN-γ in spleens. The frequencies of eosinophils and IL-4-producing CD4+ T cell populations were substantially lower in the lungs of VLP-immunized mice, with the PreF+G vaccine inducing a significant increase in CD4+ and CD8+ T cells. VLP immunization significantly decreased the viral titer and inflammation in the lungs of mice, with Pre-F+G VLPs conferring the best protection. In conclusion, our present study suggests that the Pre-F+G VLPs could be a potential vaccine candidate against RSV infection.

Mucus Penetration of Surface-Engineered Nanoparticles in Various pH Microenvironments

The penetration behavior of nanoparticles in mucous depends on physicochemical properties of the nanoparticles and the mucus microenvironment, due to particle-mucin interactions and the presence of the mucin mesh space filtration effect. To date, it is still unclear how the surface properties of nanoparticles influence their mucus penetration behaviors in various physiological and pathophysiological conditions. In this study, we have prepared a comprehensive library of amine-, carboxyl-, and PEG-modified silica nanoparticles (SNPs) with controlled surface ligand densities. Using multiple particle tracking, we have studied the mechanism responsible for the mucus penetration behaviors of these SNPs. It was found that PEG- and amine-modified SNPs exhibited pH-independent immobilization under iso-density conditions, while carboxyl-modified SNPs exhibited enhanced movement only in weakly alkaline mucus. Biophysical characterizations demonstrated that amine- and carboxyl-modified SNPs were trapped in mucus due to electrostatic interactions and hydrogen bonding with mucin. In contrast, high-density PEGylated surface formed a brush conformation that shields particle-mucin interactions. We have further investigated the surface property-dependent mucus penetration behavior using a murine airway distribution model. This study provides insights for designing efficient transmucosal nanocarriers for prevention and treatment of pulmonary diseases.

Numerical investigation of mucociliary clearance using power law and thixotropic mucus layers under discrete and continuous cilia motion

Mucus layer movement inside the airway system is an important phenomenon as the first defensive mechanism against pathogens. This research deals with the mucus velocity variations inside the nasal cavity using two different power law and thixotropic mucus layers. The cilia movement is replaced with four cyclic velocity profiles at the lower boundary of the mucus layer, while the upper boundary is exposed to the free-slip condition. The effects of boundary conditions and different fluid parameters are evaluated on the mucus flow. Furthermore, the replacement of power law and thixotropic mucus layers with a high viscous Newtonian mucus is examined under the free-slip condition at the mucus upper boundary. The adaptation rate is used as the criteria for replacing fluids instead of each other. The results show the mucus flow has enough time to adjust the changes from the lower boundary and the recovery stroke does not affect the mucus velocity in the effective stroke. Moreover, it is observed that the mucus flow variations are the same under the influence of recovery, breakdown, and breakdown exponent parameters. However, the effects of the exponent parameter on the mucus flow are more than the other two parameters in the recovery stroke. It is concluded that the assumption for replacing the power law mucus with a high viscous Newtonian one is acceptable. However, this assumption leads to the maximum error of 98.5% for thixotropic mucus in the recovery stroke.