Switch from protective to adverse inflammation during influenza: viral determinants and hemostasis are caught as culprits

Research trends and hotspots on global influenza and inflammatory response based on bibliometrics

The influenza virus is considered as a kind of significant zoonotic infectious disease identified to date, with severe infections in humans characterized by excessive inflammation and tissue damage, usually resulting in serious complications. Although the molecular mechanisms underlying inflammation after influenza infection have been extensively studied, bibliometric analysis on the research hotspots and developing trends in this field has not been published heretofore. Articles related to influenza and inflammatory response were retrieved from the Web of Science Core Collection (WoSCC) database (1992-2024) and analyzed using various visualization tools. Finally, this study collected a total of 2,176 relevant articles, involving 13,184 researchers, 2,647 institutions, 78 countries/regions, and published in 723 journals. Most articles were published in the United States (928 articles), China (450 articles) and the United Kingdom (158 articles). Ross Vlahos was the most productive author. Furthermore, some journals, such as PLoS One and Frontiers in Immunology, made much contribution to the topic. The future research trends include airway stem cells and neuroendocrine cells as new directions for the treatment of influenza complications, as well as measures related to prevention, treatment, and research and development based on the COVID-19 pandemic. Through bibliometric analysis and summary of inflammatory response of influenza-related articles, this study ultimately summarizes new directions for preventing and treating influenza.

Regulatory role of microRNAs in virus-mediated inflammation

Viral infections in humans often cause excessive inflammation. In some viral infections, inflammation can be serious and even fatal, while in other infections it can promote viral clearance. Viruses can escape from the host immune system via regulating inflammatory pathways, thus worsening the illness. MicroRNAs (miRNAs) are tiny non-coding RNA molecules expressed within diverse tissues as well as cells and are engaged in different normal pathological and physiological pathways. Emerging proof suggests that miRNAs can impact innate and adaptive immunity, inflammatory responses, cell invasion, and the progression of viral infections. We discuss some intriguing new findings in the current work, focusing on the impacts of different miRNAs on host inflammatory responses and virus-mediated inflammation. A better understanding of dysregulated miRNAs in viral infections could improve the identification, prevention, and treatment of several serious diseases.

Effect of Haoqin Qingdan Tang on influenza A virus through the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway

OBJECTIVE

Influenza, a viral respiratory illness, leads to seasonal epidemics and occasional pandemics. Given the rising resistance and adverse reactions associated with anti-influenza drugs, Traditional Chinese Medicine (TCM) emerges as a promising approach to counteract the influenza virus. Specifically, Haoqin Qingdan Tang (HQQDT), a TCM formula, has been employed as an adjuvant treatment for influenza in China. However, the active compounds and underlying mechanisms of HQQDT remain unknown.

AIM

The aim of this study was to investigate HQQDT's antiviral and anti-inflammatory activities in both in vivo and in vitro, and further reveal its active ingredients and mechanism.

METHODS

In vivo and in vitro experiments were conducted to verify the antiviral and anti-inflammatory activities of HQQDT. Subsequently, the active ingredients and mechanism of HQQDT were explored through combining high performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (HPLC-Q-TOF-MS) analysis and network pharmacology. Finally, the examinations of cell cytokines and signaling pathways aimed to elucidate the predicted mechanisms.

RESULTS

The results indicated that HQQDT exhibited inhibitory effects on influenza viruses A/PR/8/34 (H1N1), A/HK/1/68 (H3N2), and A/California/4/2009 (H1N1) in vitro. Furthermore, HQQDT enhanced the survival rate of influenza-infected mice, reduced the lung index and lung virus titer, and mitigated lung tissue damage in vivo. The proinflammatory cytokine expression levels upon influenza virus infection in PR8-induced A549 cells or mice were suppressed by HQQDT, including IL-6, IL-1β, CCL2, CCL4, IP-10, interferon β1 (IFN-β1), the interferon regulatory factor 3 (IRF3), and hemagglutinin (HA). Twenty-two active components of HQQDT against influenza were identified using HPLC-Q-TOF-MS analysis. Based on network pharmacological predictions, the JAK/STAT signaling pathway is considered the most relevant for HQQDT's action against influenza. Finally, western blot assays revealed that HQQDT regulated the protein level of the JAK/STAT signaling pathway in PR8-infected A549 cells and lung tissue.

CONCLUSION

These findings verified the antiviral and anti-inflammatory effects of HQQDT through JAK-STAT signaling pathway in influenza infections, laying the foundation for its further development.

[Factors of the hemostasis system as biomarkers of severe course of acute viral infections]

The authors give literature review of hemostasis and immune system factors intraction as main biomarkers of a severe cause of viral infectious diseases. Pro-inflamatory cytokines as the main markers of inflammation, can serve both as biomarkers of the clinical severity of the infectious process and reflect the state of the hemostatic and fibrinolytic systems, since components of these systems are present in various structures of the central nervous system and affect the development of neurons and synaptic plasticity. An inverse correlation has been proven between the concentration of D-dimer and the oxygenation index, and the development of DIC is not associated with the presence of respiratory failure in patients with influenza type A, while the ferritin concentration directly reflects the severity of the disease. One of the markers of endothelial damage may be soluble thrombomodulin, which, however, is rarely used in routine clinical practice. Cytoflavin is a highly effective pathogenetic drug that affects various parts of the hemostasis system, has anti-ischemic, antioxidant, antihypoxic, immunocorrective effect, which is indicated for any generalized infectious disease since its debut.

The Association between Influenza Vaccine and Risk of Chronic Kidney Disease/Dialysis in Patients with Hypertension

BACKGROUNDS

Influenza vaccination could decrease the risk of major cardiac events in patients with hypertension. However, the vaccine's effects on decreasing the risk of chronic kidney disease (CKD) development in such patients remain unclear.

METHODS

We retrospectively analysed the data of 37,117 patients with hypertension (≥55 years old) from the National Health Insurance Research Database during 1 January 2001 to 31 December 2012. After a 1:1 propensity score matching by the year of diagnosis, we divided the patients into vaccinated (n = 15,961) and unvaccinated groups (n = 21,156).

RESULTS

In vaccinated group, significantly higher prevalence of comorbidities such as diabetes, cerebrovascular disease, dyslipidemia, heart and liver disease were observed compared with unvaccinated group. After adjusting age, sex, comorbidities, medications (anti-hypertensive agents, metformin, aspirin and statin), level of urbanization and monthly incomes, significantly lower risk of CKD occurrence was observed among vaccinated patients in influenza season, non-influenza season and all season (Adjusted hazard ratio [aHR]: 0.39, 95% confidence level [C.I.]: 0.33-0.46; 0.38, 95% C.I.: 0.31-0.45; 0.38, 95% C.I.: 0.34-0.44, respectively). The risk of hemodialysis significantly decreased after vaccination (aHR: 0.40, 95% C.I.: 0.30-0.53; 0.42, 95% C.I.: 0.31-0.57; 0.41, 95% C.I.: 0.33-0.51, during influenza season, non-influenza season and all season). In sensitivity analysis, patients with different sex, elder and non-elder age, with or without comorbidities and with or without medications had significant decreased risk of CKD occurrence and underwent hemodialysis after vaccination. Moreover, the potential protective effect appeared to be dose-dependent.

CONCLUSIONS

Influenza vaccination decreases the risk of CKD among patients with hypertension and also decrease the risk of receiving renal replacement therapy. Its potential protective effects are dose-dependent and persist during both influenza and noninfluenza seasons.

Development of a live biotherapeutic throat spray with lactobacilli targeting respiratory viral infections

Respiratory viruses such as influenza viruses, respiratory syncytial virus (RSV), and coronaviruses initiate infection at the mucosal surfaces of the upper respiratory tract (URT), where the resident respiratory microbiome has an important gatekeeper function. In contrast to gut-targeting administration of beneficial bacteria against respiratory viral disease, topical URT administration of probiotics is currently underexplored, especially for the prevention and/or treatment of viral infections. Here, we report the formulation of a throat spray with live lactobacilli exhibiting several in vitro mechanisms of action against respiratory viral infections, including induction of interferon regulatory pathways and direct inhibition of respiratory viruses. Rational selection of Lactobacillaceae strains was based on previously documented beneficial properties, up-scaling and industrial production characteristics, clinical safety parameters, and potential antiviral and immunostimulatory efficacy in the URT demonstrated in this study. Using a three-step selection strategy, three strains were selected and further tested in vitro antiviral assays and in formulations: Lacticaseibacillus casei AMBR2 as a promising endogenous candidate URT probiotic with previously reported barrier-enhancing and anti-pathogenic properties and the two well-studied model strains Lacticaseibacillus rhamnosus GG and Lactiplantibacillus plantarum WCFS1 that display immunomodulatory capacities. The three strains and their combination significantly reduced the cytopathogenic effects of RSV, influenza A/H1N1 and B viruses, and HCoV-229E coronavirus in co-culture models with bacteria, virus, and host cells. Subsequently, these strains were formulated in a throat spray and human monocytes were employed to confirm the formulation process did not reduce the interferon regulatory pathway-inducing capacity. Administration of the throat spray in healthy volunteers revealed that the lactobacilli were capable of temporary colonization of the throat in a metabolically active form. Thus, the developed spray with live lactobacilli will be further explored in the clinic as a potential broad-acting live biotherapeutic strategy against respiratory viral diseases.

IL-23 production in human macrophages is regulated negatively by tumor necrosis factor α-induced protein 3 and positively by specificity protein 1 after stimulation of the toll-like receptor 7/8 signaling pathway

The IL-23/IL-17 axis plays an important role in the development of autoimmune diseases, but the mechanism regulating IL-23 production is mainly unknown. We investigated how TNFAIP3 and Sp1 affect IL-23 production by human macrophages after exposure to resiquimod, a TLR7/8 agonist.

IL-23 production was significantly upregulated by resiquimod but only slightly by LPS (a TLR4 agonist). Interestingly, IL-23 levels were significantly attenuated after sequential stimulation with LPS and resiquimod, but IL-12p40 and IL-18 levels were not. TLR4-related factors induced by LPS may regulate IL-23 expression via TLR7/8 signaling. LPS significantly enhanced TNFAIP3 and IRAK-M levels but reduced Sp1 levels. After exposure to resiquimod, RNA interference of TNFAIP3 upregulated IL-23 significantly more than siRNA transfection of IRAK-M did. In contrast, knockdown of Sp1 by RNA interference significantly attenuated IL-23 production. Transfection with siRNA for TNFAIP3 enhanced IL-23 expression significantly. After stimulation with resiquimod, GW7647—an agonist for PPARα (an inducer of NADHP oxidase)—and siRNA for UCP2 (a negative regulator of mitochondrial ROS generation) enhanced TNFAIP3 and reduced IL-23. siRNA for p22phox and gp91phox slightly increased Sp1 levels. However, after exposure to resiquimod siRNA-mediated knockout of DUOX1/2 significantly enhanced Sp1 and IL-23 levels, and decreased TNFα-dependent COX-2 expression. Concomitantly, TNFAIP3 levels was attenuated by DUOX1/2 siRNA. TNFAIP3 and Sp1 levels are reciprocally regulated through ROS generation.

In conclusion, after stimulation of the TLR7/8 signaling pathway IL-23 production in human macrophages is regulated negatively by TNFAIP3.

The Roles of Neutrophils in Cytokine Storms

A cytokine storm is an abnormal discharge of soluble mediators following an inappropriate inflammatory response that leads to immunopathological events. Cytokine storms can occur after severe infections as well as in non-infectious situations where inflammatory cytokine responses are initiated, then exaggerated, but fail to return to homeostasis. Neutrophils, macrophages, mast cells, and natural killer cells are among the innate leukocytes that contribute to the pathogenesis of cytokine storms. Neutrophils participate as mediators of inflammation and have roles in promoting homeostatic conditions following pathological inflammation. This review highlights the advances in understanding the mechanisms governing neutrophilic inflammation against viral and bacterial pathogens, in cancers, and in autoimmune diseases, and how neutrophils could influence the development of cytokine storm syndromes. Evidence for the destructive potential of neutrophils in their capacity to contribute to the onset of cytokine storm syndromes is presented across a multitude of clinical scenarios. Further, a variety of potential therapeutic strategies that target neutrophils are discussed in the context of suppressing multiple inflammatory conditions.

Platelet-Mediated NET Release Amplifies Coagulopathy and Drives Lung Pathology During Severe Influenza Infection

The influenza A virus (IAV) causes a respiratory tract infection with approximately 10% of the population infected by the virus each year. Severe IAV infection is characterized by excessive inflammation and tissue pathology in the lungs. Platelet and neutrophil recruitment to the lung are involved in the pathogenesis of IAV, but the specific mechanisms involved have not been clarified. Using confocal intravital microscopy in a mouse model of IAV infection, we observed profound neutrophil recruitment, platelet aggregation, neutrophil extracellular trap (NET) production and thrombin activation within the lung microvasculature in vivo. Importantly, deficiency or antagonism of the protease-activated receptor 4 (PAR4) reduced platelet aggregation, NET production, and neutrophil recruitment. Critically, inhibition of thrombin or PAR4 protected mice from virus-induced lung tissue damage and edema. Together, these data imply thrombin-stimulated platelets play a critical role in the activation/recruitment of neutrophils, NET release and directly contribute to IAV pathogenesis in the lung.

Antiinflammatory phytochemicals against virus-induced hyperinflammatory responses: Scope, rationale, application, and limitations

Uncontrolled inflammatory responses or cytokine storm associated with viral infections results in deleterious consequences such as vascular leakage, severe hemorrhage, shock, immune paralysis, multi-organ failure, and even death. With the emerging new viral infections and lack of effective prophylactic vaccines, evidence-based complementary strategies that limit viral infection-mediated hyperinflammatory responses could be a promising approach to limit host tissue injury. The present review emphasizes the potentials of antiinflammatory phytochemicals in limiting hyperinflammatory injury caused by viral infections. The predominant phytochemicals along with their mechanism in limiting hyperimmune and pro-inflammatory responses under viral infection have been reviewed comprehensively. How certain phytochemicals can be effective in limiting hyper-inflammatory response indirectly by favorably modulating gut microbiota and maintaining a functional intestinal barrier has also been presented. Finally, we have discussed improved systemic bioavailability of phytochemicals, efficient delivery strategies, and safety measures for effective antiinflammatory phytotherapies, in addition to emphasizing the requirement of tightly controlled clinical studies to establish the antiinflammatory efficacy of the phytochemicals. Collectively, the review provides a scooping overview on the potentials of bioactive phytochemicals to mitigate pro-inflammatory injury associated with viral infections.

The Anti-Viral and Anti-Inflammatory Properties of Edible Bird's Nest in Influenza and Coronavirus Infections: From Pre-Clinical to Potential Clinical Application

Edible bird's nest (BN) is a Chinese traditional medicine with innumerable health benefits, including anti-viral, anti-inflammatory, neuroprotective, and immunomodulatory effects. A small number of studies have reported the anti-viral effects of EBN against influenza infections using in vitro and in vivo models, highlighting the importance of sialic acid and thymol derivatives in their therapeutic effects. At present, studies have reported that EBN suppresses the replicated virus from exiting the host cells, reduces the viral replication, endosomal trafficking of the virus, intracellular viral autophagy process, secretion of pro-inflammatory cytokines, reorient the actin cytoskeleton of the infected cells, and increase the lysosomal degradation of viral materials. In other models of disease, EBN attenuates oxidative stress-induced cellular apoptosis, enhances proliferation and activation of B-cells and their antibody secretion. Given the sum of its therapeutic actions, EBN appears to be a candidate that is worth further exploring for its protective effects against diseases transmitted through air droplets. At present, anti-viral drugs are employed as the first-line defense against respiratory viral infections, unless vaccines are available for the specific pathogens. In patients with severe symptoms due to exacerbated cytokine secretion, anti-inflammatory agents are applied. Treatment efficacy varies across the patients, and in times of a pandemic like COVID-19, many of the drugs are still at the experimental stage. In this review, we present a comprehensive overview of anti-viral and anti-inflammatory effects of EBN, chemical constituents from various EBN preparation techniques, and drugs currently used to treat influenza and novel coronavirus infections. We also aim to review the pathogenesis of influenza A and coronavirus, and the potential of EBN in their clinical application. We also describe the current literature in human consumption of EBN, known allergenic or contaminant presence, and the focus of future direction on how these can be addressed to further improve EBN for potential clinical application.

Viral-Host Interactome Analysis Reveals Chicken STAU2 Interacts With Non-structural Protein 1 and Promotes the Replication of H5N1 Avian Influenza Virus

As a highly pathogenic influenza virus, H5N1 avian influenza virus (AIV) poses a great threat to poultry production and public health. H5N1 AIV has a small genome and, therefore, relies heavily on its host cellular machinery to replicate. To develop a comprehensive understanding of how H5N1 AIV rewires host cellular machinery during the course of infection, it is crucial to identify which host proteins and complexes come into physical contact with the viral proteins. Here, we utilized affinity purification mass spectrometry (AP-MS) to systematically determine the physical interactions of 11 H5N1 AIV proteins with host proteins in chicken DF1 cells. We identified with high confidence 1,043 H5N1 AIV–chicken interactions involving 621 individual chicken proteins and uncovered a number of host proteins and complexes that were targeted by the viral proteins. Specifically, we revealed that chicken Staufen double-stranded RNA-binding protein 2 interacts with AIV non-structural protein 1 (NS1) and promotes the replication of the virus by enhancing the nuclear export of NS1 mRNA. This dataset facilitates a more comprehensive and detailed understanding of how the host machinery is manipulated during the course of H5N1 AIV infection.

Topical Microbial Therapeutics against Respiratory Viral Infections

Emerging evidence suggests that microbial therapeutics can prevent and treat respiratory viral diseases, especially when applied directly to the airways. This review presents established beneficial effects of locally administered microbial therapeutics against respiratory viral diseases and the inferred related molecular mechanisms. Several mechanisms established in the intestinal probiotics field as well as novel, niche-specific insights are relevant in the airways. Studies at cellular and organism levels highlight biologically plausible but strain-specific and host and virus context-dependent mechanisms, underlying the potential of beneficial bacteria. Large-scale clinical studies can now be rationally designed to provide a bench-to-bedside translation of the multifactorial bacterial mechanisms within the host respiratory tract, to diminish the incidence and severity of viral infections and the concomitant complications.

The influenza virus RNA polymerase as an innate immune agonist and antagonist

Influenza A viruses cause a mild-to-severe respiratory disease that affects millions of people each year. One of the many determinants of disease outcome is the innate immune response to the viral infection. While antiviral responses are essential for viral clearance, excessive innate immune activation promotes lung damage and disease. The influenza A virus RNA polymerase is one of viral proteins that affect innate immune activation during infection, but the mechanisms behind this activity are not well understood. In this review, we discuss how the viral RNA polymerase can both activate and suppress innate immune responses by either producing immunostimulatory RNA species or directly targeting the components of the innate immune signalling pathway, respectively. Furthermore, we provide a comprehensive overview of the polymerase residues, and their mutations, associated with changes in innate immune activation, and discuss their putative effects on polymerase function based on recent advances in our understanding of the influenza A virus RNA polymerase structure.

Role of the Innate Cytokine Storm Induced by the Influenza A Virus

Influenza A viruses (IAVs) can be classified into dozens of subtypes based on their hemagglutinin (HA) and neuraminidase (NA) proteins. To date, 18 HA subtypes and 11 NA subtypes of IAVs that spread in animals and humans have been found. Following infection, the IAV first induces the innate immune system, which can rapidly recruit innate immune cells and cytokines to the site of infection. Influenza-induced cytokine storms have been associated with uncontrolled proinflammatory responses, which may lead to significant immunopathy and severe disease. Cytokine storms are complicated by several types of cytokines and chemokines that have various activities. In addition to their direct effects, their crossregulation causes cytokine networks to form; these networks determine the outcome of viral infections. In this review, we focus on cytokine storms and their signaling pathways that are triggered by the different subtypes of IAV.

The PA-interacting host protein nucleolin acts as an antiviral factor during highly pathogenic H5N1 avian influenza virus infection

Polymerase acidic (PA) protein is a multifunctional regulator of influenza A virus (IAV) replication and pathogenesis. In a previous study, we reported that nucleolin (NCL) is a novel PA-interacting host protein. In this study, we further explored the role of NCL during highly pathogenic H5N1 avian influenza virus infection. We found that depletion of endogenous NCL in mammalian cells by siRNA targeting during H5N1 infection resulted in significantly increased viral polymerase activity, elevated viral mRNA, cRNA and vRNA synthesis, accelerated viral replication, and enhanced apoptosis and necrosis. Moreover, siRNA silencing of NCL significantly exacerbated the inflammatory response, resulting in increased secretion of IL-6, TNF-α, TNF-β, CCL-4, CCL-8, IFN-α, IFN-β and IFN-γ. Conversely, overexpression of NCL significantly decreased IAV replication. Collectively, these data show that NCL acts as a novel potential antiviral factor during H5N1 infection. Further studies exploring the antiviral mechanisms of NCL may accelerate the development of new anti-influenza drugs.

The Annexin A1 Receptor FPR2 Regulates the Endosomal Export of Influenza Virus

The Formyl Peptide Receptor 2 (FPR2) is a novel promising target for the treatment of influenza. During viral infection, FPR2 is activated by annexinA1, which is present in the envelope of influenza viruses; this activation promotes virus replication. Here, we investigated whether blockage of FPR2 would affect the genome trafficking of influenza virus. We found that, upon infection and cell treatment with the specific FPR2 antagonist WRW4 or the anti-FPR2 monoclonal antibody, FN-1D6-AI, influenza viruses were blocked into endosomes. This effect was independent on the strain and was observed for H1N1 and H3N2 viruses. In addition, blocking FPR2signaling in alveolar lung A549 epithelial cells with the monoclonal anti-FPR2 antibody significantly inhibited virus replication. Altogether, these results show that FPR2signaling interferes with the endosomal trafficking of influenza viruses and provides, for the first time, the proof of concept that monoclonal antibodies directed against FPR2 inhibit virus replication. Antibodies-based therapeutics have emerged as attractive reagents in infectious diseases. Thus, this study suggests that the use of anti-FPR2 antibodies against influenza hold great promise for the future.

Immune responses in influenza A virus and human coronavirus infections: an ongoing battle between the virus and host

Respiratory viruses, especially influenza A viruses and coronaviruses such as MERS-CoV, represent continuing global threats to human health. Despite significant advances, much needs to be learned. Recent studies in virology and immunology have improved our understanding of the role of the immune system in protection and in the pathogenesis of these infections and of co-evolution of viruses and their hosts. These findings, together with sophisticated molecular structure analyses, omics tools and computer-based models, have helped delineate the interaction between respiratory viruses and the host immune system, which will facilitate the development of novel treatment strategies and vaccines with enhanced efficacy.

Altered virulence of Highly Pathogenic Avian Influenza (HPAI) H5N8 reassortant viruses in mammalian models

Recently identified highly pathogenic avian influenza (HPAI) H5N8 viruses (clade 2.3.4.4) are relatively low to moderately pathogenic in mammalian hosts compared with HPAI H5N1 viruses. In this study, we generated reassortant viruses comprised of A/MD/Korea/W452/2014(H5N8) with substitution of individual genes from A/EM/Korea/W149/2006(H5N1) to understand the contribution of each viral gene to virulence in mammals. Substituting the PB2 gene segment or the NA gene segment of the H5N8 virus by that from the H5N1 virus resulted in significantly enhanced pathogenicity compared with the parental H5N8 virus in mice. Of note, substitution of the PB2 gene segment of the H5N8 virus by that from the H5N1 virus resulted in a 1000-fold increase in virulence for mice compared with the parental virus (MLD50 decreased from 105.8 to 102.5 EID50). Further, the W452W149PB2 virus also induced the highest virus titers in lungs at all time points and the highest levels of inflammatory cytokine responses among all viruses tested. This high virulence phenotype was also confirmed by high viral titers in the respiratory tracts of infected ferrets. Further, a mini-genome assay revealed that W452W149PB2 has significantly increased polymerase activity (p < 0.001). Taken together, our study demonstrates that a single gene substitution from other avian influenza viruses can alter the pathogenicity of recent H5N8 viruses, and therefore emphasizes the need for intensive monitoring of reassortment events among co-circulating avian and mammalian viruses.

Protease-activated receptor 1 inhibition protects mice against thrombin-dependent respiratory syncytial virus and human metapneumovirus infections

BACKGROUND AND PURPOSE

Protease-activated receptor 1 (PAR1) has been demonstrated to be involved in the pathogenesis of viral diseases. However, its role remains controversial. The goal of our study was to investigate the contribution of PAR1 to respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) infections.

EXPERIMENTAL APPROACH

Pharmacological approaches were used to investigate the role of PAR1 during RSV and hMPV infection, in vitro using epithelial A549 cells and in vivo using a mouse model of virus infection.

KEY RESULTS

In vitro, the PAR1 antagonist RWJ-56110 reduced the replication of RSV and hMPV in A549 cells. In agreement with these results, RWJ-56110-treated mice were protected against RSV and hMPV infections, as indicated by less weight loss and mortality. This protective effect in mice correlated with decreased lung viral replication and inflammation. In contrast, hMPV-infected mice treated with the PAR1 agonist TFLLR-NH₂ showed increased mortality, as compared to infected mice, which were left untreated. Thrombin generation was shown to occur downstream of PAR1 activation in infected mice via tissue factor exposure as part of the inflammatory response, and thrombin inhibition by argatroban reduced the pathogenicity of the infection with no additive effect to that induced by PAR1 inhibition.

CONCLUSION AND IMPLICATIONS

These data show that PAR1 plays a detrimental role during RSV and hMPV infections in mice via, at least, a thrombin-dependent mechanism. Thus, the use of PAR1 antagonists and thrombin inhibitors may have potential as a novel approach for the treatment of RSV and hMPV infections.

FPR2: A Novel Promising Target for the Treatment of Influenza

The Formyl-peptide receptor-2 (FPR2) is a seven transmembrane G protein-coupled receptor, which plays an important role in sensing of bacteria and modulation of immune responses. FPR2 is also used by viruses for their own profit. Annexin A1, one of the multiple ligands of FPR2, is incorporated in the budding virus membrane of influenza A viruses (IAV). Thereby, once IAV infect a host cell, FPR2 is activated. FPR2-signaling leads to an increase in viral replication, a dysregulation of the host immune response and a severe disease. Conversely, experiments using FPR2 antagonists in a preclinical model of IAV infections in mice showed that blocking FPR2 protects animals from lethal infections. Thus, FPR2 represents a very attractive host target against influenza. In this review we will give an overview on the pathogenesis of influenza with a focus on the role of FPR2 and we will discuss the advantages of using FPR2 antagonists to treat the flu.

Generation and Comprehensive Analysis of Host Cell Interactome of the PA Protein of the Highly Pathogenic H5N1 Avian Influenza Virus in Mammalian Cells

Accumulating data have identified the important roles of PA protein in replication and pathogenicity of influenza A virus (IAV). Identification of host factors that interact with the PA protein may accelerate our understanding of IAV pathogenesis. In this study, using immunoprecipitation assay combined with liquid chromatography-tandem mass spectrometry, we identified 278 human cellular proteins that might interact with PA of H5N1 IAV. Gene Ontology annotation revealed that the identified proteins are highly associated with viral translation and replication. Further KEGG pathway analysis of the interactome profile highlighted cellular pathways associated with translation, infectious disease, and signal transduction. In addition, Diseases and Functions analysis suggested that these cellular proteins are highly related with Organismal Injury and Abnormalities and Cell Death and Survival. Moreover, two cellular proteins (nucleolin and eukaryotic translation elongation factor 1-alpha 1) identified both in this study and others were further validated to interact with PA using co-immunoprecipitation and co-localization assays. Therefore, this study presented the interactome data of H5N1 IAV PA protein in human cells which may provide novel cellular target proteins for elucidating the potential molecular functions of PA in regulating the lifecycle of IAV in human cells.

The inflammatory response triggered by Influenza virus: a two edged sword

Influenza A virus (IAV) is a relevant respiratory tract pathogen leading to a great number of deaths and hospitalizations worldwide. Secondary bacterial infections are a very common cause of IAV associated morbidity and mortality. The robust inflammatory response that follows infection is important for the control of virus proliferation but is also associated with lung damage, morbidity and death. The role of the different components of immune response underlying protection or disease during IAV infection is not completely elucidated. Overall, in the context of IAV infection, inflammation is a 'double edge sword' necessary to control infection but causing disease. Therefore, a growing number of studies suggest that immunomodulatory strategies may improve disease outcome without affecting the ability of the host to deal with infection. This review summarizes recent aspects of the inflammatory responses triggered by IAV that are preferentially involved in causing severe pulmonary disease and the anti-inflammatory strategies that have been suggested to treat influenza induced immunopathology.

Involvement of the different lung compartments in the pathogenesis of pH1N1 influenza virus infection in ferrets

Severe cases after pH1N1 infection are consequence of interstitial pneumonia triggered by alveolar viral replication and an exacerbated host immune response, characterized by the up-regulation of pro-inflammatory cytokines and the influx of inflammatory leukocytes to the lungs. Different lung cell populations have been suggested as culprits in the unregulated innate immune responses observed in these cases. This study aims to clarify this question by studying the different induction of innate immune molecules by the distinct lung anatomic compartments (vascular, alveolar and bronchiolar) of ferrets intratracheally infected with a human pH1N1 viral isolate, by means of laser microdissection techniques. The obtained results were then analysed in relation to viral quantification in the different anatomic areas and the histopathological lesions observed. More severe lung lesions were observed at 24 h post infection (hpi) correlating with viral antigen detection in bronchiolar and alveolar epithelial cells. However, high levels of viral RNA were detected in all anatomic compartments throughout infection. Bronchiolar areas were the first source of IFN-α and most pro-inflammatory cytokines, through the activation of RIG-I. In contrast, vascular areas contributed with the highest induction of CCL2 and other pro-inflammatory cytokines, through the activation of TLR3.

Combination activity of neuraminidase inhibitor oseltamivir and α-tocopherol in influenza virus A (H3N2) infection in mice

BACKGROUND

Influenza is a highly contagious viral infection of the respiratory system. To attack two processes involved in flu pathogenesis-viral replication in the infected body and oxidative damages, we studied the combination effect of neuraminidase inhibitor oseltamivir and antioxidant α-tocopherol in experimental model of influenza.

METHODS

After inoculation of albino mice with 10 MLD50 (50% mouse lethal dose) of influenza virus A/Aichi/2/68 (H3N2), oseltamivir was applied orally at three doses, 2.5 mg/kg, 1.25 mg/kg, and 0.625 mg/kg, for five days post infection. α-Tocopherol (120 mg/kg, in sunflower oil) was administered intraperitoneally. Three schemes of α-tocopherol five-day course were tested: onset five or two days before infection, or on the virus inoculation day.

RESULTS

Strongly dose-dependent augmented antiviral effect of the combination α-tocopherol and 0.625 mg/kg oseltamivir was demonstrated when α-tocopherol was administered simultaneously with oseltamivir: a pronounced decrease in mortality rate (a 78% protection), and a lengthening of mean survival time by 3.2-4 days. Lung parameters showed a substantial decrease in infectious virus content (Δ logs = 3.8/4.1) and a marked diminishment of lung index and pathology. Combination α-tocopherol with 1.25 mg/kg oseltamivir manifested a marked protective effect, but the effect on lung parameters was less. The combination effect of α-tocopherol with 2.5 mg/kg oseltamivir did not surpass the monotherapeutic effect of oseltamivir. When α-tocopherol was applied in courses starting five or two days before infection, its combination with oseltamivir was ineffective.

CONCLUSIONS

Evidently, α-tocopherol could be considered as prospective component of influenza therapy in combination with oseltamivir.

Host Immunological Factors Enhancing Mortality of Young Adults during the 1918 Influenza Pandemic

During the 1918 influenza pandemic, healthy young adults unusually succumbed to infection and were considered more vulnerable than young children and the elderly. The pathogenesis of this pandemic in the young adult population remains poorly understood. As this population is normally the least likely to die during seasonal influenza outbreaks, thought to be due to their appropriate pre-existing and robust immune responses protecting them from infection, we sought to review existing literature for immunological reasons for excessive mortality during the 1918 pandemic. We propose the novelty of the H1N1 pandemic virus to an H1N1 naïve immune system, the virulence of this virus, and dysfunctional host inflammatory and immunological responses, shaped by past influenza infections could have each contributed to their overall susceptibility. Additionally, in the young adult population, pre-exposure to past influenza infection of different subtypes, such as a H3N8 virus, during their infancy in 1889-1892, may have shaped immunological responses and enhanced vulnerability via humoral immunity effects with cross-reactive or non-neutralizing antibodies; excessive and/or ineffective cellular immunity from memory T lymphocytes; and innate dysfunctional inflammation. Multiple mechanisms likely contributed to the increased young adult mortality in 1918 and are the focus of this review.

Platelet activation and aggregation promote lung inflammation and influenza virus pathogenesis

RATIONALE

The hallmark of severe influenza virus infection is excessive inflammation of the lungs. Platelets are activated during influenza, but their role in influenza virus pathogenesis and inflammatory responses is unknown.

OBJECTIVES

To determine the role of platelets during influenza A virus infections and propose new therapeutics against influenza.

METHODS

We used targeted gene deletion approaches and pharmacologic interventions to investigate the role of platelets during influenza virus infection in mice.

MEASUREMENTS AND MAIN RESULTS

Lungs of infected mice were massively infiltrated by aggregates of activated platelets. Platelet activation promoted influenza A virus pathogenesis. Activating protease-activated receptor 4, a platelet receptor for thrombin that is crucial for platelet activation, exacerbated influenza-induced acute lung injury and death. In contrast, deficiency in the major platelet receptor glycoprotein IIIa protected mice from death caused by influenza viruses, and treating the mice with a specific glycoprotein IIb/IIIa antagonist, eptifibatide, had the same effect. Interestingly, mice treated with other antiplatelet compounds (antagonists of protease-activated receptor 4, MRS 2179, and clopidogrel) were also protected from severe lung injury and lethal infections induced by several influenza strains.

CONCLUSIONS

The intricate relationship between hemostasis and inflammation has major consequences in influenza virus pathogenesis, and antiplatelet drugs might be explored to develop new antiinflammatory treatment against influenza virus infections.

Dietary selenium in adjuvant therapy of viral and bacterial infections

Viral and bacterial infections are often associated with deficiencies in macronutrients and micronutrients, including the essential trace element selenium. In selenium deficiency, benign strains of Coxsackie and influenza viruses can mutate to highly pathogenic strains. Dietary supplementation to provide adequate or supranutritional selenium supply has been proposed to confer health benefits for patients suffering from some viral diseases, most notably with respect to HIV and influenza A virus (IAV) infections. In addition, selenium-containing multimicronutrient supplements improved several clinical and lifestyle variables in patients coinfected with HIV and Mycobacterium tuberculosis. Selenium status may affect the function of cells of both adaptive and innate immunity. Supranutritional selenium promotes proliferation and favors differentiation of naive CD4-positive T lymphocytes toward T helper 1 cells, thus supporting the acute cellular immune response, whereas excessive activation of the immune system and ensuing host tissue damage are counteracted through directing macrophages toward the M2 phenotype. This review provides an up-to-date overview on selenium in infectious diseases caused by viruses (e.g., HIV, IAV, hepatitis C virus, poliovirus, West Nile virus) and bacteria (e.g., M. tuberculosis, Helicobacter pylori). Data from epidemiologic studies and intervention trials, with selenium alone or in combination with other micronutrients, and animal experiments are discussed against the background of dietary selenium requirements to alter immune functions.

Annexin V incorporated into influenza virus particles inhibits gamma interferon signaling and promotes viral replication

During the budding process, influenza A viruses (IAVs) incorporate multiple host cell membrane proteins. However, for most of them, their significance in viral morphogenesis and infectivity remains unknown. We demonstrate here that the expression of annexin V (A5) is upregulated at the cell surface upon IAV infection and that a substantial proportion of the protein is present in lipid rafts, the site of virus budding. Western blotting and immunogold analysis of highly purified IAV particles showed the presence of A5 in the virion. Significantly, gamma interferon (IFN-γ)-induced Stat phosphorylation and IFN-γ-induced 10-kDa protein (IP-10) production in macrophage-derived THP-1 cells was inhibited by purified IAV particles. Disruption of the IFN-γ signaling pathway was A5 dependent since downregulation of its expression or its blockage reversed the inhibition and resulted in decreased viral replication in vitro. The functional significance of these results was also observed in vivo. Thus, IAVs can subvert the IFN-γ antiviral immune response by incorporating A5 into their envelope during the budding process.

IMPORTANCE

Many enveloped viruses, including influenza A viruses, bud from the plasma membrane of their host cells and incorporate cellular surface proteins into viral particles. However, for the vast majority of these proteins, only the observation of their incorporation has been reported. We demonstrate here that the host protein annexin V is specifically incorporated into influenza virus particles during the budding process. Importantly, we showed that packaged annexin V counteracted the antiviral activity of gamma interferon in vitro and in vivo. Thus, these results showed that annexin V incorporated in the viral envelope of influenza viruses allow viral escape from immune surveillance. Understanding the role of host incorporated protein into virions may reveal how enveloped RNA viruses hijack the host cell machinery for their own purposes.

Activation of coagulation and tissue fibrin deposition in experimental influenza in ferrets

Background

Epidemiological studies relate influenza infection with vascular diseases like myocardial infarction. The hypothesis that influenza infection has procoagulant effects on humans has been investigated by experimental animal models. However, these studies often made use of animal models only susceptible to adapted influenza viruses (mouse adapted influenza strains) or remained inconclusive. Therefore, we decided to study the influence of infection with human influenza virus isolates on coagulation in the well-established ferret influenza model.

Results

After infection with either a seasonal-, pandemic- or highly pathogenic avian influenza (HPAI-H5N1) virus strain infected animals showed alterations in hemostasis compared to the control animals. Specifically on day 4 post infection, a four second rise in both PT and aPTT was observed. D-dimer concentrations increased in all 3 influenza groups with the highest concentrations in the pandemic influenza group. Von Willebrand factor activity levels increased early in infection suggesting endothelial cell activation. Mean thrombin-antithrombin complex levels increased in both pandemic and HPAI-H5N1 virus infected ferrets. At tissue level, fibrin staining showed intracapillary fibrin deposition especially in HPAI-H5N1 virus infected ferrets.

Conclusion

This study showed hemostatic alterations both at the circulatory and at the tissue level upon infection with different influenza viruses in an animal model closely mimicking human influenza virus infection. Alterations largely correlated with the severity of the respective influenza virus infections.

The zoonotic potential of avian influenza viruses isolated from wild waterfowl in Zambia

Whilst remarkable progress in elucidating the mechanisms governing interspecies transmission and pathogenicity of highly pathogenic avian influenza viruses (AIVs) has been made, similar studies focusing on low-pathogenic AIVs isolated from the wild waterfowl reservoir are limited. We previously reported that two AIV strains (subtypes H6N2 and H3N8) isolated from wild waterfowl in Zambia harbored some amino acid residues preferentially associated with human influenza virus proteins (so-called human signatures) and replicated better in the lungs of infected mice and caused more morbidity than a strain lacking such residues. To further substantiate these observations, we infected chickens and mice intranasally with AIV strains of various subtypes (H3N6, H3N8, H4N6, H6N2, H9N1 and H11N9) isolated from wild waterfowl in Zambia. Although some strains induced seroconversion, all of the tested strains replicated poorly and were nonpathogenic for chickens. In contrast, most of the strains having human signatures replicated well in the lungs of mice, and one of these strains caused severe illness in mice and induced lung injury that was characterized by a severe accumulation of polymorphonuclear leukocytes. These results suggest that some strains tested in this study may have the potential to infect mammalian hosts directly without adaptation, which might possibly be associated with the possession of human signature residues. Close monitoring and evaluation of host-associated signatures may help to elucidate the prevalence and emergence of AIVs with potential for causing zoonotic infections.

Multiple roles of the coagulation protease cascade during virus infection

The coagulation cascade is activated during viral infections. This response may be part of the host defense system to limit spread of the pathogen. However, excessive activation of the coagulation cascade can be deleterious. In fact, inhibition of the tissue factor/factor VIIa complex reduced mortality in a monkey model of Ebola hemorrhagic fever. Other studies showed that incorporation of tissue factor into the envelope of herpes simplex virus increases infection of endothelial cells and mice. Furthermore, binding of factor X to adenovirus serotype 5 enhances infection of hepatocytes but also increases the activation of the innate immune response to the virus. Coagulation proteases activate protease-activated receptors (PARs). Interestingly, we and others found that PAR1 and PAR2 modulate the immune response to viral infection. For instance, PAR1 positively regulates TLR3-dependent expression of the antiviral protein interferon β, whereas PAR2 negatively regulates expression during coxsackievirus group B infection. These studies indicate that the coagulation cascade plays multiple roles during viral infections.