Pathogenesis of influenza virus-induced pneumonia: involvement of both nitric oxide and oxygen radicals

Phosphatidyl Inositol 3 Kinase-Gamma Balances Antiviral and Inflammatory Responses During Influenza A H1N1 Infection: From Murine Model to Genetic Association in Patients

Influenza A virus (IAV) infection causes severe pulmonary disease characterized by intense leukocyte infiltration. Phosphoinositide-3 kinases (PI3Ks) are central signaling enzymes, involved in cell growth, survival, and migration. Class IB PI3K or phosphatidyl inositol 3 kinase-gamma (PI3Kγ), mainly expressed by leukocytes, is involved in cell migration during inflammation. Here, we investigated the contribution of PI3Kγ for the inflammatory and antiviral responses to IAV. PI3Kγ knockout (KO) mice were highly susceptible to lethality following infection with influenza A/WSN/33 H1N1. In the early time points of infection, infiltration of neutrophils was higher than WT mice whereas type-I and type-III IFN expression and p38 activation were reduced in PI3Kγ KO mice resulting in higher viral loads when compared with WT mice. Blockade of p38 in WT macrophages infected with IAV reduced levels of interferon-stimulated gene 15 protein to those induced in PI3Kγ KO macrophages, suggesting that p38 is downstream of antiviral responses mediated by PI3Kγ. PI3Kγ KO-derived fibroblasts or macrophages showed reduced type-I IFN transcription and altered pro-inflammatory cytokines suggesting a cell autonomous imbalance between inflammatory and antiviral responses. Seven days after IAV infection, there were reduced infiltration of natural killer cells and CD8⁺ T lymphocytes, increased concentration of inflammatory cytokines in bronchoalveolar fluid, reduced numbers of resolving macrophages, and IL-10 levels in PI3Kγ KO. This imbalanced environment in PI3Kγ KO-infected mice culminated in enhanced lung neutrophil infiltration, reactive oxygen species release, and lung damage that together with the increased viral loads, contributed to higher mortality in PI3Kγ KO mice compared with WT mice. In humans, we tested the genetic association of disease severity in influenza A/H1N1pdm09-infected patients with three potentially functional PIK3CG single-nucleotide polymorphisms (SNPs), rs1129293, rs17847825, and rs2230460. We observed that SNPs rs17847825 and rs2230460 (A and T alleles, respectively) were significantly associated with protection from severe disease using the recessive model in patients infected with influenza A(H1N1)pdm09. Altogether, our results suggest that PI3Kγ is crucial in balancing antiviral and inflammatory responses to IAV infection.

Vitamin E Supplementation Ameliorates Newcastle Disease Virus-Induced Oxidative Stress and Alleviates Tissue Damage in the Brains of Chickens

Newcastle disease (ND), characterized by visceral, respiratory, and neurological pathologies, causes heavy economic loss in the poultry industry around the globe. While significant advances have been made in effective diagnosis and vaccine development, molecular mechanisms of ND virus (NDV)-induced neuropathologies remain elusive. In this study, we report the magnitude of oxidative stress and histopathological changes induced by the virulent NDV (ZJ1 strain) and assess the impact of vitamin E in alleviating these pathologies. Comparative profiling of plasma and brains from mock and NDV-infected chicken demonstrated alterations in several oxidative stress makers such as nitric oxide, glutathione, malondialdehyde, total antioxidant capacity, glutathione S-transferase, superoxide dismutase, and catalases. While decreased levels of glutathione and total antioxidant capacity and increased concentrations of malondialdehyde and nitric oxide were observed in NDV-challenged birds at all time points, these alterations were eminent at latter time points (5 days post infection). Additionally, significant decreases in the activities of glutathione S-transferase, superoxide dismutase, and catalase were observed in the plasma and brains collected from NDV-infected chickens. Intriguingly, we observed that supplementation of vitamin E can significantly reduce the alteration of oxidative stress parameters. Under NDV infection, extensive histopathological alterations were observed in chicken brain including neural inflammation, capillary hyperemia, necrosis, and loss of prominent axons, which were reduced with the treatment of vitamin E. Taken together, our findings highlight that neurotropic NDV induces extensive tissue damage in the brain and alters plasma oxidative stress profiles. These findings also demonstrate that supplementing vitamin E ameliorates these pathologies in chickens and proposes its supplementation for NDV-induced stresses.

Analyses of repeated failures in cancer therapy for solid tumors: poor tumor-selective drug delivery, low therapeutic efficacy and unsustainable costs

For over six decades reductionist approaches to cancer chemotherapies including recent immunotherapy for solid tumors produced outcome failure-rates of 90% (±5) according to governmental agencies and industry. Despite tremendous public and private funding and initial enthusiasm about missile-therapy for site-specific cancers, molecular targeting drugs for specific enzymes such as kinases or inhibitors of growth factor receptors, the outcomes are very bleak and disappointing. Major scientific reasons for repeated failures of such therapeutic approaches are attributed to reductionist approaches to research and infinite numbers of genetic mutations in chaotic molecular environment of solid tumors that are bases of drug development. Safety and efficacy of candidate drugs tested in test tubes or experimental tumor models of rats or mice are usually evaluated and approved by FDA. Cost-benefit ratios of such ‘targeted’ therapies are also far from ideal as compared with antibiotics half a century ago. Such alarming records of failure of clinical outcomes, the increased publicity for specific vaccines (e.g., HPV or flu) targeting young and old populations, along with increasing rise of cancer incidence and death created huge and unsustainable cost to the public around the globe. This article discusses a closer scientific assessment of current cancer therapeutics and vaccines. We also present future logical approaches to cancer research and therapy and vaccines.

The Inflammasome: Regulation of Nitric Oxide and Antimicrobial Host Defence

Nitric oxide (NO) is a gaseous signalling molecule that plays diverse physiological functions including antimicrobial host defence. During microbial infection, NO is synthesized by inducible NO synthase (iNOS), which is expressed by host immune cells through the recognition of microbial pattern molecules. Therefore, sensing pathogens or their pattern molecules by pattern recognition receptors (PRRs), which are located at the cell surface, endosomal and phagosomal compartment, or in the cytosol, is key in inducing iNOS and eliciting antimicrobial host defence. A group of cytosolic PRRs is involved in inducing NO and other antimicrobial molecules by forming a molecular complex called the inflammasome. Assembled inflammasomes activate inflammatory caspases, such as caspase-1 and caspase-11, which in turn process proinflammatory cytokines IL-1β and IL-18 into their mature forms and induce pyroptotic cell death. IL-1β and IL-18 play a central role in immunity against microbial infection through activation and recruitment of immune cells, induction of inflammatory molecules, and regulation of antimicrobial mediators including NO. Interestingly, NO can also regulate inflammasome activity in an autocrine and paracrine manner. Here, we discuss molecular mechanisms of inflammasome formation and the inflammasome-mediated regulation of host defence responses during microbial infections.

Oxidant/Antioxidant Status, PON1 and ARES Activities, Trace Element Levels, and Histological Alterations in Sheep with Cystic Echinococcosis

BACKGROUND

Total antioxidant status (TAS), total oxidant status (TOS) and oxidative stress index (OSI), nitric oxide (NO), zinc (Zn), copper (Cu) levels, paraoxonase (PON1), arylesterase (ARES) activities, and biochemical changes were studied on sheep with cystic echinococcosis.

METHODS

The materials were taken from 2-3 yr old sheep slaughtered in Van Province, Turkey in 2017. Before the slaughter, blood samples were collected from the healthy sheep, while various organs of animals were examined for hydatid cysts after the slaughter. Thirty sheep were protoscolex positive, hydatic group, while 30 sheep that did not have any pathological lesions in organ examinations were accepted as the control group. TOS levels, PON1 and ARES activities, and Zn levels were determined by commercial kits, while Cu levels were determined by atomic absorption spectrophotometer. The collected data were then statistically analyzed.

RESULTS

Serum TOS and OSI levels were significantly higher in sheep with cystic echinococcosis compared to the control group (P<0.001). TAS levels (P<0.01), PON1 and ARES activities, on the other hand, were significantly higher in control group compared to the cystic echinococcosis group (P<0.001). There were no significant differences in Zn, NO and Cu levels between the groups.

CONCLUSION

PON1 and ARES activities increased in sheep infected with cyst hydatid. The decline of antioxidant reserves in the metabolism results in excessive amounts of free radicals, along with alterations of the normal histological structure of the cystic organ and changes in trace element metabolism.

Soloxolone methyl inhibits influenza virus replication and reduces virus-induced lung inflammation

Highly pathogenic influenza viruses pose a serious public health threat to humans. Although vaccines are available, new antivirals are needed to efficiently control disease progression and virus transmission due to the emergence of drug-resistant viral strains. In this study, we describe the anti-viral properties of Soloxolone methyl (SM) (methyl 2-cyano-3,12-dioxo-18βH-olean-9(11),1(2)-dien-30-oate, a chemical derivative of glycyrrhetinic acid) against the flu virus. Anti-flu efficacy studies revealed that SM exhibits antiviral activity against the H1N1 influenza A virus in a dose-dependent manner causing a more than 10-fold decrease in virus titer and a reduction in the expression of NP and M2 viral proteins. In a time-of-addition study, SM was found to act at an early stage of infection to exhibit an inhibitory effect on both the attachment step and virus uptake into cells. Also, in infected cells SM downregulates the expression of the inflammatory cytokines IL-6 and TNF-α. In infected mice, SM administered intranasally prior to and after infection significantly decreases virus titers in the lung and prevents post-challenge pneumonia. Together, these results suggest that Soloxolone methyl might serve as an effective therapeutic agent to manage influenza outbreaks and virus-associated complications, and further preclinical and clinical investigation may be warranted.

A Role for Neutrophils in Viral Respiratory Disease

Neutrophils are immune cells that are well known to be present during many types of lung diseases associated with acute respiratory distress syndrome (ARDS) and may contribute to acute lung injury. Neutrophils are poorly studied with respect to viral infection, and specifically to respiratory viral disease. Influenza A virus (IAV) infection is the cause of a respiratory disease that poses a significant global public health concern. Influenza disease presents as a relatively mild and self-limiting although highly pathogenic forms exist. Neutrophils increase in the respiratory tract during infection with mild seasonal IAV, moderate and severe epidemic IAV infection, and emerging highly pathogenic avian influenza (HPAI). During severe influenza pneumonia and HPAI infection, the number of neutrophils in the lower respiratory tract is correlated with disease severity. Thus, comparative analyses of the relationship between IAV infection and neutrophils provide insights into the relative contribution of host and viral factors that contribute to disease severity. Herein, we review the contribution of neutrophils to IAV disease pathogenesis and to other respiratory virus infections.

Inflammatory Responses Regulating Alveolar Ion Transport during Pulmonary Infections

The respiratory epithelium is lined by a tightly balanced fluid layer that allows normal O₂ and CO₂ exchange and maintains surface tension and host defense. To maintain alveolar fluid homeostasis, both the integrity of the alveolar–capillary barrier and the expression of epithelial ion channels and pumps are necessary to establish a vectorial ion gradient. However, during pulmonary infection, auto- and/or paracrine-acting mediators induce pathophysiological changes of the alveolar–capillary barrier, altered expression of epithelial Na,K-ATPase and of epithelial ion channels including epithelial sodium channel and cystic fibrosis membrane conductance regulator, leading to the accumulation of edema and impaired alveolar fluid clearance. These mediators include classical pro-inflammatory cytokines such as TGF-β, TNF-α, interferons, or IL-1β that are released upon bacterial challenge with Streptococcus pneumoniae, Klebsiella pneumoniae, or Mycoplasma pneumoniae as well as in viral infection with influenza A virus, pathogenic coronaviruses, or respiratory syncytial virus. Moreover, the pro-apoptotic mediator TNF-related apoptosis-inducing ligand, extracellular nucleotides, or reactive oxygen species impair epithelial ion channel expression and function. Interestingly, during bacterial infection, alterations of ion transport function may serve as an additional feedback loop on the respiratory inflammatory profile, further aggravating disease progression. These changes lead to edema formation and impair edema clearance which results in suboptimal gas exchange causing hypoxemia and hypercapnia. Recent preclinical studies suggest that modulation of the alveolar–capillary fluid homeostasis could represent novel therapeutic approaches to improve outcomes in infection-induced lung injury.

Combinations of L-NG-monomethyl-arginine and oseltamivir against pandemic influenza A virus infections in mice

L-N^G-monomethyl-arginine (L-NMMA) is an experimental compound that suppresses nitric oxide production in animals. The compound was combined with oseltamivir to treat lethal influenza A/California/04/2009 (H1N1) pandemic virus infections in mice. Treatments were given twice a day for five days starting 4 h (oseltamivir, by oral gavage) or three days (L-NMMA, by intraperitoneal route; corresponding to the time previously reported for nitric oxide induction in the animals) after infection. Low doses of oseltamivir were used in order to demonstrate synergy or antagonism. Oseltamivir monotherapy protected 70% of mice from death at 1 mg/kg/day. L-NMMA (40 and 80 mg/kg/day) was ineffective alone in preventing mortality. Compared to oseltamivir treatment alone, L-NMMA combined with oseltamivir was synergistically effective (as evaluated by three-dimensional MacSynergy analysis), resulting in survival increases from 20 to 70% when 40 or 80 mg/kg/day of L-NMMA was combined with 0.3 mg/kg/day of oseltamivir, and from 70 to 100% survival increases when these doses were combined with 1 mg/kg/day of oseltamivir. These data demonstrate that a nitric oxide inhibitor such as L-NMMA has the potential to be beneficial when combined with oseltamivir in treating influenza virus infections.

Progress of small molecular inhibitors in the development of anti-influenza virus agents

The influenza pandemic is a major threat to human health, and highly aggressive strains such as H1N1, H5N1 and H7N9 have emphasized the need for therapeutic strategies to combat these pathogens. Influenza anti-viral agents, especially active small molecular inhibitors play important roles in controlling pandemics while vaccines are developed. Currently, only a few drugs, which function as influenza neuraminidase (NA) inhibitors and M2 ion channel protein inhibitors, are approved in clinical. However, the acquired resistance against current anti-influenza drugs and the emerging mutations of influenza virus itself remain the major challenging unmet medical needs for influenza treatment. It is highly desirable to identify novel anti-influenza agents. This paper reviews the progress of small molecular inhibitors act as antiviral agents, which include hemagglutinin (HA) inhibitors, RNA-dependent RNA polymerase (RdRp) inhibitors, NA inhibitors and M2 ion channel protein inhibitors etc. Moreover, we also summarize new, recently reported potential targets and discuss strategies for the development of new anti-influenza virus drugs.

Mechanistic perspective of the oxido-immunopathologic resolution property of kolaviron in mice influenza pneumonitis

Implicated in influenza-associated pathology are innate defence overzealousness and unabated secretion of oxidative tissue-sensitive antimicrobial agents. At different time points, mice were pre-treated with kolaviron (400 mg/kg), a natural antioxidant and anti-inflammatory agent, and subsequently challenged with 2 LD₅₀ influenza A/H3N2/Perth/16/09 virus. After euthanasia at day 6, blood, lungs, liver and spleen were collected and processed for biochemical, immunohistochemical and flow cytometric assessment of redo-inflammatory imbalance, cytokine storm indices and T helper 1 host response. Previously kolaviron was reported to delay mortality onset, improve morbidity and attenuate myeloperoxidase activity and nitric oxide production with minimal impact on viral clearance. This study additionally confirmed nitric oxide, but not hydrogen peroxide, as the major culprit implicated in influenza virus-induced oxido-pathology. Systemic effect of the sustained inflammation and nitrosative stress was more prominent in the spleen and lung than in the liver of mice infected with A/H3N2/Perth/16/09. Influential to immunopathology was heightened pulmonary expression of IL-1β, RANTES, IL-10, MCP-1, NF-κB, iNOS and COX-2. However, kolaviron combated the influenza-established nitrative stress, reversed the elicited cytokine storm and restored the oxidized environment to a reductive milieu. Our data also suggest that kolaviron administration early in infection may foster CD4⁺ response. These data indicate that kolaviron may confer disease-dwindling properties during acute influenza infection via a system-wide protective approach involving multiple targets especially at the early stage of the infection.

Implications of oxidative stress on viral pathogenesis

Reactive species are frequently formed after viral infections. Antioxidant defences, including enzymatic and non-enzymatic components, protect against reactive species, but sometimes these defences are not completely adequate. An imbalance in the production of reactive species and the body's inability to detoxify these reactive species is referred to as oxidative stress. The aim of this review is to analyse the role of oxidative stress in the pathogenesis of viral infections and highlight some major therapeutic approaches that have gained importance, with regards to controlling virus-induced oxidative injury. Attention will be focused on DNA viruses (papillomaviruses, hepadnaviruses), RNA viruses (flaviviruses, orthomyxoviruses, paramyxoviruses, togaviruses) and retroviruses (human immunodeficiency virus). In general, viruses cause an imbalance in the cellular redox environment, which depending on the virus and the cell can result in different responses, e.g. cell signaling, antioxidant defences, reactive species, and other processes. Therefore, the modulation of reactive species production and oxidative stress potentially represents a novel pharmacological approach for reducing the consequences of viral pathogenesis.

Avian metapneumovirus infection of chicken and turkey tracheal organ cultures: comparison of virus-host interactions

Avian metapneumovirus (aMPV) is a pathogen with worldwide distribution, which can cause high economic losses in infected poultry. aMPV mainly causes infection of the upper respiratory tract in both chickens and turkeys, although turkeys seem to be more susceptible. Little is known about virus-host interactions at epithelial surfaces after aMPV infection. Tracheal organ cultures (TOC) are a suitable model to investigate virus-host interaction in the respiratory epithelium. Therefore, we investigated virus replication rates and lesion development in chicken and turkey TOC after infection with a virulent aMPV subtype A strain. Aspects of the innate immune response, such as interferon-α and inducible nitric oxide synthase mRNA expression, as well as virus-induced apoptosis were determined. The aMPV-replication rate was higher in turkey (TTOC) compared to chicken TOC (CTOC) (P < 0.05), providing circumstantial evidence that indeed turkeys may be more susceptible. The interferon-α response was down-regulated from 2 to 144 hours post infection in both species compared to virus-free controls (P < 0.05); this was more significant for CTOC than TTOC. Inducible nitric oxide synthase expression was significantly up-regulated in aMPV-A-infected TTOC and CTOC compared to virus-free controls (P < 0.05). However, the results suggest that NO may play a different role in aMPV pathogenesis between turkeys and chickens as indicated by differences in apoptosis rate and lesion development between species. Overall, our study reveals differences in innate immune response regulation and therefore may explain differences in aMPV - A replication rates between infected TTOC and CTOC, which subsequently lead to more severe clinical signs and a higher rate of secondary infections in turkeys.

The NS1 protein of avian influenza virus H9N2 induces oxidative-stress-mediated chicken oviduct epithelial cells apoptosis

The pathogenesis of H9N2 subtype avian influenza virus infection (AIV) in hens is often related to oviduct tissue damage. The viral non-structural NS1 protein is thought to play a key role in regulating the pathogenicity of AIV, but its exact function in this process remains elusive. In this study, the pro-apoptosis effect of H9N2 NS1 protein was examined on chicken oviduct epithelial cells (COECs) and our data indicated that NS1-induced oxidative stress was a contributing factor in apoptosis. Our data indicate that NS1 protein level was correlated with reactive oxygen species (ROS) in COECs transfected with NS1 expression plasmids. Interestingly, decreased activities of antioxidant enzymes, superoxide dismutase and catalase, were observed in NS1-transfected COECs. Treatment of COECs with antioxidants, such as pyrrolidine dithiocarbamate (PDTC) or N-acetylcysteine (NAC), significantly inhibited NS1-induced apoptosis. Moreover, although antioxidant treatment has little effect on the activation of caspase-8 in NS1-transfected cells, the activation of caspase-3/9 and Bax/Bcl-2 were significantly downregulated. Taken together, the results of our study demonstrated that expression of H9N2 NS1 alone is sufficient to trigger oxidative stress in COECs. Additionally, NS1 protein can induce cellular apoptosis via activating ROS accumulation and mitochondria-mediated apoptotic signalling in COECs.

[Host defense and oxidative stress signaling in bacterial infection ]

Nitric oxide (NO) and reactive oxygen species (ROS) produced during infection are involved critically in host defense mechanisms. It is quite important to physiologically regulate ROS, such as superoxide, and NO. These reactive species produced in excess may cause oxidative damage of biological molecules. An important cytoprotective and antimicrobial function of NO and ROS is mediated by induction of heme oxygenase (HO)-1. The signaling mechanism of this HO-1 induction has remained unclear, however. We discovered in 2007 a unique second messenger, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), that mediates electrophilic signal transduction during oxidative stress and other cellular redox signaling in general. 8-Nitro-cGMP is formed via guanine nitration with NO and ROS, and in fact, NO-dependent 8-nitro-cGMP formation and HO-1 induction were identified in Salmonella-infected mice. HO-1 induction was regulated solely by 8-nitro-cGMP formed in cells, and more important, its potent anti-apoptotic function was evident in such a Salmonella infection. 8-Nitro-cGMP has a potent cytoprotective function, of which signaling appears to be mediated via protein sulfhydryls to generate a post-translational modification called protein S-guanylation. 8-Nitro-cGMP specifically S-guanylates Keap1, a negative regulator of transcription factor Nrf2, which in turn up-regulates transcription of HO-1. Our recent study revealed that the autophagy might be involved in the 8-nitro-cGMP-dependent antimicrobial effect. The 8-nitro-cGMP signaling was also found to be regulated by reactive sulfur species that have superior antioxidant activity and unique signaling function. This review will discuss a new paradigm of the host defense that operates via formation of a unique cell signaling molecule, 8-nitro-cGMP, during microbial infections.

Nox2-derived oxidative stress results in inefficacy of antibiotics against post-influenza S. aureus pneumonia

Phagocyte oxidative burst is the primary source of lethal lung injury during influenza and MRSA coinfection.

Clinical post-influenza Staphylococcus aureus pneumonia is characterized by extensive lung inflammation associated with severe morbidity and mortality even after appropriate antibiotic treatment. In this study, we show that antibiotics rescue nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (Nox2)–deficient mice but fail to fully protect WT animals from influenza and S. aureus coinfection. Further experiments indicate that the inefficacy of antibiotics against coinfection is attributable to oxidative stress–associated inflammatory lung injury. However, Nox2-induced lung damage during coinfection was not associated with aggravated inflammatory cytokine response or cell infiltration but rather caused by reduced survival of myeloid cells. Specifically, oxidative stress increased necrotic death of inflammatory cells, thereby resulting in lethal damage to surrounding tissue. Collectively, our results demonstrate that influenza infection disrupts the delicate balance between Nox2-dependent antibacterial immunity and inflammation. This disruption leads to not only increased susceptibility to S. aureus infection, but also extensive lung damage. Importantly, we show that combination treatment of antibiotic and NADPH oxidase inhibitor significantly improved animal survival from coinfection. These findings suggest that treatment strategies that target both bacteria and oxidative stress will significantly benefit patients with influenza-complicated S. aureus pneumonia.

PA-X-associated early alleviation of the acute lung injury contributes to the attenuation of a highly pathogenic H5N1 avian influenza virus in mice

PA-X is a novel discovered accessory protein encoded by the PA mRNA. Our previous study demonstrated that PA-X decreases the virulence of a highly pathogenic H5N1 strain A/Chicken/Jiangsu/k0402/2010 in mice. However, the underlying mechanism of virulence attenuation associated with PA-X is still unknown. In this study, we compared two PA-X-deficient mutant viruses and the parental virus in terms of induction of pathology and manipulation of host response in the mouse lung, stimulation of cell death and PA nuclear accumulation. We first found that down-regulated PA-X expression markedly aggravated the acute lung injury of the infected mice early on day 1 post-infection (p.i.). We then determined that loss of PA-X expression induced higher levels of cytokines, chemokines and complement-derived peptides (C3a and C5a) in the lung, especially at early time point’s p.i. In addition, in vitro assays showed that the PA-X-deficient viruses enhanced cell death and increased expression of reactive oxygen species (ROS) in mammalian cells. Moreover, we also found that PA nuclear accumulation of the PA-X-null viruses accelerated in MDCK cells. These results demonstrate that PA-X decreases the level of complement components, ROS, cell death and inflammatory response, which may together contribute to the alleviated lung injury and the attenuation of the virulence of H5N1 virus in mice.

Activation of toll-like receptor signaling pathways leading to nitric oxide-mediated antiviral responses

Toll-like receptors (TLRs), well-characterized pattern-recognizing receptors of the innate arm of the immune system, are vital in detecting pathogen-associated molecular patterns (PAMPs). The TLR-PAMP interaction initiates an intracellular signaling cascade, predominantly culminating in upregulation of antiviral components, including inducible nitric oxide synthase (iNOS). After activation, various TLR pathways can promote iNOS production via the myeloid differentiation primary response-88 (MyD-88) adapter protein. Subsequently, iNOS facilitates production of nitric oxide (NO), a highly reactive and potent antiviral molecule that can inhibit replication of RNA and DNA viruses. Furthermore, NO can diffuse freely across cell membranes and elicit antiviral mechanisms in various ways, including direct and indirect damage to viral genomes. This review emphasizes current knowledge of NO-mediated antiviral responses elicited after activation of TLR signaling pathways.

Dengue Virus Immunopathogenesis: Lessons Applicable to the Emergence of Zika Virus

Dengue is the leading mosquito-transmitted viral infection in the world. There are more than 390 million new infections annually; while the majority of infected individuals are asymptomatic or develop a self-limited dengue fever, up to 1 million clinical cases develop severe manifestations, including dengue hemorrhagic fever and shock syndrome, resulting in ~25,000 deaths annually, mainly in children. Gaps in our understanding of the mechanisms that contribute to dengue infection and immunopathogenesis have hampered the development of vaccines and antiviral agents. Some of these limitations are highlighted by the explosive re-emergence of another arthropod-borne flavivirus-Zika virus-spread by the same vector, the Aedes aegypti mosquito, that also carries dengue, yellow fever and chikungunya viruses. This review will discuss the early virus-host interactions in dengue infection, with emphasis on the interrelationship between oxidative stress and innate immune pathways, and will provide insight as to how lessons learned from dengue research may expedite therapeutic strategies for Zika virus.

NADPH Oxidase 1 Is Associated with Altered Host Survival and T Cell Phenotypes after Influenza A Virus Infection in Mice

The role of the reactive oxygen species-producing NADPH oxidase family of enzymes in the pathology of influenza A virus infection remains enigmatic. Previous reports implicated NADPH oxidase 2 in influenza A virus-induced inflammation. In contrast, NADPH oxidase 1 (Nox1) was reported to decrease inflammation in mice within 7 days post-influenza A virus infection. However, the effect of NADPH oxidase 1 on lethality and adaptive immunity after influenza A virus challenge has not been explored. Here we report improved survival and decreased morbidity in mice with catalytically inactive NADPH oxidase 1 (Nox1*/Y) compared with controls after challenge with A/PR/8/34 influenza A virus. While changes in lung inflammation were not obvious between Nox1*/Y and control mice, we observed alterations in the T cell response to influenza A virus by day 15 post-infection, including increased interleukin-7 receptor-expressing virus-specific CD8+ T cells in lungs and draining lymph nodes of Nox1*/Y, and increased cytokine-producing T cells in lungs and spleen. Furthermore, a greater percentage of conventional and interstitial dendritic cells from Nox1*/Y draining lymph nodes expressed the co-stimulatory ligand CD40 within 6 days post-infection. Results indicate that NADPH oxidase 1 modulates the innate and adaptive cellular immune response to influenza virus infection, while also playing a role in host survival. Results suggest that NADPH oxidase 1 inhibitors may be beneficial as adjunct therapeutics during acute influenza infection.

The Influenza Virus H5N1 Infection Can Induce ROS Production for Viral Replication and Host Cell Death in A549 Cells Modulated by Human Cu/Zn Superoxide Dismutase (SOD1) Overexpression

Highly pathogenic H5N1 infections are often accompanied by excessive pro-inflammatory response, high viral titer, and apoptosis; as such, the efficient control of these infections poses a great challenge. The pathogenesis of influenza virus infection is also related to oxidative stress. However, the role of endogenic genes with antioxidant effect in the control of influenza viruses, especially H5N1 viruses, should be further investigated. In this study, the H5N1 infection in lung epithelial cells decreased Cu/Zn superoxide dismutase (SOD1) expression at mRNA and protein levels. Forced SOD1 expression significantly inhibited the H5N1-induced increase in reactive oxygen species, decreased pro-inflammatory response, prevented p65 and p38 phosphorylation, and impeded viral ribonucleoprotein nuclear export and viral replication. The SOD1 overexpression also rescued H5N1-induced cellular apoptosis and alleviated H5N1-caused mitochondrial dysfunction. Therefore, this study described the role of SOD1 in the replication of H5N1 influenza virus and emphasized the relevance of this enzyme in the control of H5N1 replication in epithelial cells. Pharmacological modulation or targeting SOD1 may open a new way to fight H5N1 influenza virus.

Functional Interplay between Type I and II Interferons Is Essential to Limit Influenza A Virus-Induced Tissue Inflammation

Host control of influenza A virus (IAV) is associated with exuberant pulmonary inflammation characterized by the influx of myeloid cells and production of proinflammatory cytokines including interferons (IFNs). It is unclear, however, how the immune system clears the virus without causing lethal immunopathology. Here, we demonstrate that in addition to its known anti-viral activity, STAT1 signaling coordinates host inflammation during IAV infection in mice. This regulatory mechanism is dependent on both type I IFN and IFN-γ receptor signaling and, importantly, requires the functional interplay between the two pathways. The protective function of type I IFNs is associated with not only the recruitment of classical inflammatory Ly6C^hi monocytes into IAV-infected lungs, but also the prevention of excessive monocyte activation by IFN-γ. Unexpectedly, type I IFNs preferentially regulate IFN-γ signaling in Ly6C^lo rather than inflammatory Ly6C^hi mononuclear cell populations. In the absence of type I IFN signaling, Ly6C^lo monocytes/macrophages, become phenotypically and functionally more proinflammatory than Ly6C^hi cells, revealing an unanticipated function of the Ly6C^lo mononuclear cell subset in tissue inflammation. In addition, we show that type I IFNs employ distinct mechanisms to regulate monocyte and neutrophil trafficking. Type I IFN signaling is necessary, but not sufficient, for preventing neutrophil recruitment into the lungs of IAV-infected mice. Instead, the cooperation of type I IFNs and lymphocyte-produced IFN-γ is required to regulate the tissue neutrophilic response to IAV. Our study demonstrates that IFN interplay links innate and adaptive anti-viral immunity to orchestrate tissue inflammation and reveals an additional level of complexity for IFN-dependent regulatory mechanisms that function to prevent excessive immunopathology while preserving anti-microbial functions.

Influenza A virus (IAV) is a leading cause of respiratory infection and induces a strong acute inflammation manifested by the recruitment of monocytes and neutrophils as well as the production of proinflammatory cytokines in infected lungs. The interferons (IFNs) are strongly induced by IAV and are known to mediate host resistance to the infection. However, in contrast to their well-studied inhibitory effect on viral replication, the effects of IFNs on host inflammatory responses are less well understood. In this manuscript, we demonstrate that anti-viral IFN signaling is also required for the orchestration of a tissue response associated with the protection against IAV infection in mice. Importantly, we identify that type I IFNs cross-regulate and cooperate with IFN-γ to inhibit monocyte activation and neutrophil infiltration, respectively. This study also demonstrates that Ly6C^lo monocytes/macrophages can potentially mediate influenza virus-induced inflammation, suggesting that IFNs dictate the homeostasis versus inflammatory function of mononuclear phagocytes in viral infection. Our study reveals a novel IFN-dependent regulatory mechanism designed to prevent the excessive immunopathology while preserving its anti-microbial functions. Moreover, these observations have particular relevance for understanding the mechanisms underlying the strong inflammatory response associated with lethal IAV strains and have implications for the development of new immunotherapies to treat influenza.

CD11b(+)Ly6C(++)Ly6G(-) Cells with Suppressive Activity Towards T Cells Accumulate in Lungs of Influenza a Virus-Infected Mice

Influenza A virus (IAV) infection causes an acute respiratory disease characterized by a strong inflammatory immune response and severe immunopathology. Proinflammatory mechanisms are well described in the murine IAV infection model, but less is known about the mechanisms leading to the resolution of inflammation. Here, we analyzed the contribution of CD11b⁺Ly6C⁺⁺Ly6G^– cells to this process. An accumulation of CD11b⁺Ly6C⁺⁺Ly6G^– cells within the lungs was observed during the course of IAV infection. Phenotypic characterization of these CD11b⁺Ly6C⁺⁺Ly6G^– cells by flow cytometry and RNA-Seq revealed an activated phenotype showing both pro- and anti-inflammatory features, including the expression of inducible nitric oxide synthase (iNOS) by a fraction of cells in an IFN-γ-dependent manner. Moreover, CD11b⁺Ly6C⁺⁺Ly6G^– cells isolated from lungs of IAV-infected animals displayed suppressive activity when tested in vitro, and iNOS inhibitors could abrogate this suppressive activity. Collectively, our data suggest that during IAV infection, CD11b⁺Ly6C⁺⁺Ly6G^– cells acquire immunoregulatory function, which might contribute to the prevention of pathology during this life-threatening disease.

Respiratory syncytial virus infection down-regulates antioxidant enzyme expression by triggering deacetylation-proteasomal degradation of Nrf2

Respiratory syncytial virus (RSV) is the most important cause of viral acute respiratory tract infections and hospitalizations in children, for which no vaccine or treatment is available. RSV infection in cells, mice, and children leads to rapid generation of reactive oxygen species, which are associated with oxidative stress and lung damage, due to a significant decrease in the expression of airway antioxidant enzymes (AOEs). Oxidative stress plays an important role in the pathogenesis of RSV-induced lung disease, as antioxidants ameliorate clinical disease and inflammation in vivo. The aim of this study is to investigate the unknown mechanism(s) of virus-induced inhibition of AOE expression. RSV infection is shown to induce a progressive reduction in nuclear and total cellular levels of the transcription factor NF-E2-related factor 2 (Nrf2), resulting in decreased binding to endogenous AOE gene promoters and decreased AOE expression. RSV induces Nrf2 deacetylation and degradation via the proteasome pathway in vitro and in vivo. Histone deacetylase and proteasome inhibitors block Nrf2 degradation and increase Nrf2 binding to AOE endogenous promoters, resulting in increased AOE expression. Known inducers of Nrf2 are able to increase Nrf2 activation and subsequent AOE expression during RSV infection in vitro and in vivo, with significant amelioration of oxidative stress. This is the first study to investigate the mechanism(s) of virus-induced inhibition of AOE expression. RSV-induced inhibition of Nrf2 activation, due to deacetylation and proteasomal degradation, could be targeted for therapeutic intervention aimed to increase airway antioxidant capacity during infection.

Intracellular redox state as target for anti-influenza therapy: are antioxidants always effective?

Influenza virus infections represent a big issue for public health since effective treatments are still lacking. In particular, the emergence of strains resistant to drugs limits the effectiveness of anti-influenza agents. For this reason, many efforts have been dedicated to the identification of new therapeutic strategies aimed at targeting the virus-host cell interactions. Oxidative stress is a characteristic of some viral infections including influenza. Because antioxidants defend cells from damage caused by reactive oxygen species induced by different stimuli including pathogens, they represent interesting molecules to fight infectious diseases. However, most of the available studies have found that these would-be panaceas could actually exacerbate the diseases they claim to prevent, and have thus revealed "the dark side" of these molecules. This review article discusses the latest opportunities and drawbacks of the antioxidants used in anti-influenza therapy and new perspectives.

Therapeutic Strategy for the Prevention of Pseudorabies Virus Infection in C57BL/6 Mice by 3D8 scFv with Intrinsic Nuclease Activity

3D8 single chain variable fragment (scFv) is a recombinant monoclonal antibody with nuclease activity that was originally isolated from autoimmune-prone MRL mice. In a previous study, we analyzed the nuclease activity of 3D8 scFv and determined that a HeLa cell line expressing 3D8 scFv conferred resistance to herpes simplex virus type 1 (HSV-1) and pseudorabies virus (PRV). In this study, we demonstrate that 3D8 scFv could be delivered to target tissues and cells where it exerted a therapeutic effect against PRV. PRV was inoculated via intramuscular injection, and 3D8 scFv was injected intraperitoneally. The observed therapeutic effect of 3D8 scFv against PRV was also supported by results from quantitative reverse transcription polymerase chain reaction, southern hybridization, and immunohistochemical assays. Intraperitoneal injection of 5 and 10 μg 3D8 scFv resulted in no detectable toxicity. The survival rate in C57BL/6 mice was 9% after intramuscular injection of 10 LD50 PRV. In contrast, the 3D8 scFv-injected C57BL/6 mice showed survival rates of 57% (5 μg) and 47% (10 μg). The results indicate that 3D8 scFv could be utilized as an effective antiviral agent in several animal models.

Carnosine markedly ameliorates H9N2 swine influenza virus-induced acute lung injury

Oxidative stress injury is an important pathogenesis of influenza virus in critically ill patients. The present study investigated the efficacy of carnosine, an antioxidant and free radical scavenger, on a model of acute lung injury (ALI) induced by H9N2 swine influenza virus. Female specific-pathogen-free BALB/c mice were randomized into four groups and treated as follows: (1) H9N2 group, (2) mock control group, (3) H9N2+carnosine group and (4) carnosine control group. The H9N2 group mice were inoculated intranasally with A/Swine/Hebei/012/2008/ (H9N2) virus (100 μl) in allantoic fluid (AF), whilst mock-infected animals were intranasally inoculated with non-infectious AF. Carnosine [10 mg (kg body mass)- 1] was administered orally (100 μl) for 7 days consecutively. The survival rate, lung water content, TNF-α and IL-1β levels, lung histopathology, myeloperoxidase (MPO) activity, and Toll-like receptor (TLR)-4 levels were determined at 2, 4, 6, 8 and 14 days after inoculation. Carnosine treatment effectively decreased the mortality (43 versus 75 %, P < 0.05), significantly ameliorated pathological lesions in lungs and decreased the lung wet/dry mass ratio (P < 0.05). It also inhibited MPO activity, suppressed TNF-α and IL-1β release, decreased the H9N2 viral titre, and markedly inhibited levels of TLR-4 mRNA and protein in the lungs of infected mice (P < 0.05), which supported the use of carnosine for managing severe influenza cases.

Oxidative stress in Nipah virus-infected human small airway epithelial cells

Nipah virus (NiV) is a zoonotic emerging pathogen that can cause severe and often fatal respiratory disease in humans. The pathogenesis of NiV infection of the human respiratory tract remains unknown. Reactive oxygen species (ROS) produced by airway epithelial cells in response to viral infections contribute to lung injury by inducing inflammation and oxidative stress; however, the role of ROS in NiV-induced respiratory disease is unknown. To investigate whether NiV induces oxidative stress in human respiratory epithelial cells, we used oxidative stress markers and monitored antioxidant gene expression. We also used ROS scavengers to assess their role in immune response modulation. Oxidative stress was confirmed in infected cells and correlated with the reduction in antioxidant enzyme gene expression. Infected cells treated by ROS scavengers resulted in a significant decrease of the (F2)-8-isoprostane marker, inflammatory responses and virus replication. In conclusion, ROS are induced during NiV infection in human respiratory epithelium and contribute to the inflammatory response. Understanding how oxidative stress contributes to NiV pathogenesis is crucial for therapeutic development.

Pleiotropic Effects of Levofloxacin, Fluoroquinolone Antibiotics, against Influenza Virus-Induced Lung Injury

Reactive oxygen species (ROS) and nitric oxide (NO) are major pathogenic molecules produced during viral lung infections, including influenza. While fluoroquinolones are widely used as antimicrobial agents for treating a variety of bacterial infections, including secondary infections associated with the influenza virus, it has been reported that they also function as anti-oxidants against ROS and as a NO regulator. Therefore, we hypothesized that levofloxacin (LVFX), one of the most frequently used fluoroquinolone derivatives, may attenuate pulmonary injuries associated with influenza virus infections by inhibiting the production of ROS species such as hydroxyl radicals and neutrophil-derived NO that is produced during an influenza viral infection. The therapeutic impact of LVFX was examined in a PR8 (H1N1) influenza virus-induced lung injury mouse model. ESR spin-trapping experiments indicated that LVFX showed scavenging activity against neutrophil-derived hydroxyl radicals. LVFX markedly improved the survival rate of mice that were infected with the influenza virus in a dose-dependent manner. In addition, the LVFX treatment resulted in a dose-dependent decrease in the level of 8-hydroxy-2'-deoxyguanosine (a marker of oxidative stress) and nitrotyrosine (a nitrative marker) in the lungs of virus-infected mice, and the nitrite/nitrate ratio (NO metabolites) and IFN-γ in BALF. These results indicate that LVFX may be of substantial benefit in the treatment of various acute inflammatory disorders such as influenza virus-induced pneumonia, by inhibiting inflammatory cell responses and suppressing the overproduction of NO in the lungs.

A Newly Emerged Swine-Origin Influenza A(H3N2) Variant Dampens Host Antiviral Immunity but Induces Potent Inflammasome Activation

We compared the innate immune response to a newly emerged swine-origin influenza A(H3N2) variant containing the M gene from 2009 pandemic influenza A(H1N1), termed "A(H3N2)vpM," to the immune responses to the 2010 swine-origin influenza A(H3N2) variant and seasonal influenza A(H3N2). Our results demonstrated that A(H3N2)vpM-induced myeloid dendritic cells secreted significantly lower levels of type I interferon (IFN) but produced significantly higher levels of proinflammatory cytokines and induced potent inflammasome activation. The reduction in antiviral immunity with increased inflammatory responses upon A(H3N2)vpM infection suggest that these viruses have the potential for increased disease severity in susceptible hosts.

Anti-high mobility group box-1 monoclonal antibody treatment provides protection against influenza A virus (H1N1)-induced pneumonia in mice

INTRODUCTION

Provision for the emergence of an influenza pandemic is an urgent issue. The discovery of a novel anti-influenza therapeutic approach would increase the effectiveness of traditional virus-based strategies. This study was undertaken to evaluate the therapeutic effects of anti-high mobility group box-1 (HMGB1) monoclonal antibody (mAb) treatment on influenza A virus (H1N1)-induced pneumonia in mice.

METHODS

Nine-week-old male C57BL/6 mice were inoculated with H1N1, then anti-HMGB1 mAb or control mAb were administered intravenously at 1, 24 and 48 hours after H1N1 inoculation and the survival rate was analyzed. Lung lavage and histopathological analysis were performed on days 3, 5, 7 and 10 after inoculation.

RESULTS

Anti-HMGB1 mAb significantly improved the survival rate of H1N1-inoculated mice (1 out of 15 versus 8 out of 15 deaths in the anti-HMGB1 mAb-treated group versus the control mAb-treated group, p < 0.01), although the treatment did not affect virus propagation in the lungs. The treatment also significantly attenuated histological changes and neutrophil infiltration in the lungs of H1N1-inoculated mice. This was associated with inhibition of HMGB1 and suppression of inflammatory cytokine/chemokine expression and oxidative stress enhancement, which were observed in H1N1-inoculated mice. The expression of receptor for advanced glycation end products and nuclear factor κB was attenuated by the treatment.

CONCLUSIONS

Anti-HMGB1 mAb may provide a novel and effective pharmacological strategy for severe influenza virus infection in humans by reducing the inflammatory responses induced by HMGB1.

Influenza A virus PB1-F2 is involved in regulation of cellular redox state in alveolar epithelial cells

Occurrence of oxidative stress is common in influenza, and renders the host more susceptible to pathogenic effects including cell death. We previously reported that down-regulation of superoxide anion dismutase 1 (SOD1) by influenza A virus (IAV) resulted in a significant increase in the levels of reactive oxygen species (ROS) and viral PB1 polymerase gene product in the early stage of infection. However, the precise molecular mechanism of IAV-mediated ROS generation is not yet fully understood. In this study, we investigated the possible involvement of the key virulence factor PB1-F2 in ROS generation and its contribution to the viral propagation and cell death. The key virulence factor PB1-F2 was found to be responsible, at least in part, for the ROS generation through lowering the SOD1 level in alveolar epithelial A549 cells. PB1-F2 overexpression resulted in SOD1 diminishment and ROS enhancement, while another virulent factor, NS1, did not show significant changes. Inversely, we examined the effects of the absence of PB1-F2 using mutant IAV lacking PB1-F2 expression (mutantΔF2). Infection with mutantΔF2 virus did not significantly lower the SOD1 level, and thus generated moderately low levels of ROS. In addition, the oxidative activity of PB1-F2 was directly reflected by cell viability and death. Infection with the mutant virus reduced the percentage of apoptotic cells more than two-fold compared to the wild-type IAV in A549 cells. Furthermore, expression of exogenous SOD1 gene abrogated a large portion of the PB1-F2-induced apoptosis of cells infected with wild-type IAV, but affected much less of the mutantΔF2 virus-infected cells. These results suggest that the PB1-F2 is directly implicated in virus-induced oxidative stress, thereby contributing to the early stages of IAV replication cycle and ultimately to disease severity.

Angiopoietin-like 4 Increases Pulmonary Tissue Leakiness and Damage during Influenza Pneumonia

Excessive host inflammatory responses negatively impact disease outcomes in respiratory infection. Host-pathogen interactions during the infective phase of influenza are well studied, but little is known about the host's response during the repair stage. Here, we show that influenza infection stimulated the expression of angiopoietin-like 4 (ANGPTL4) via a direct IL6-STAT3-mediated mechanism. ANGPTL4 enhanced pulmonary tissue leakiness and exacerbated inflammation-induced lung damage. Treatment of infected mice with neutralizing anti-ANGPTL4 antibodies significantly accelerated lung recovery and improved lung tissue integrity. ANGPTL4-deficient mice also showed reduced lung damage and recovered faster from influenza infection when compared to their wild-type counterparts. Retrospective examination of human lung biopsy specimens from infection-induced pneumonia with tissue damage showed elevated expression of ANGPTL4 when compared to normal lung samples. These observations underscore the important role that ANGPTL4 plays in lung infection and damage and may facilitate future therapeutic strategies for the treatment of influenza pneumonia.

Thiol-based redox proteomics in cancer research

Cancer cells maintain their intracellular ROS concentrations at required levels for their survival. Changes in ROS concentrations can regulate biochemical signaling mechanisms that control cell function. It has been demonstrated that ROS regulate the cellular events through redox regulation of redox-sensitive proteins (redox sensors). Upon oxidative stress, redox sensors undergo redox modifications that cause the allosteric changes of these proteins and endow them with different functions. Understanding the altered functions of redox sensors and the underlying mechanisms is critical for the development of novel cancer therapeutics. Recently, a series of high-throughput proteomics approaches have been developed for screening redox processes. In this manuscript, we review these methodologies and discuss the important redox sensors recently identified that are related to cancer.

Therapeutic impact of human serum albumin-thioredoxin fusion protein on influenza virus-induced lung injury mice

Reactive oxygen species (ROS) are the primary pathogenic molecules produced in viral lung infections. We previously reported on the use of a recombinant human serum albumin (HSA)–thioredoxin 1 (Trx) fusion protein (HSA–Trx) for extending the half-life Trx, an endogenous protein with anti-oxidant properties. As a result, it was possible to overcome the unfavorable pharmacokinetic and short pharmacological properties of Trx. We hypothesized that HSA–Trx would attenuate the enhanced ROS production of species such as hydroxyl radicals by neutrophils during an influenza viral infection. The levels of 8-hydroxy-2′-deoxyguanosine and 3-nitrotyrosine were used as indices of the anti-oxidant activity of HSA–Trx. In addition, the cytoprotective effects of HSA–Trx were examined in PR8 (H1N1) influenza virus-induced lung injured mice. The findings show that HSA–Trx reduced the number of total cells, neutrophils, and total protein in BALF of influenza virus-induced lung injured mice. The HSA–Trx treatment significantly decreased the level of 8-hydroxy-2′-deoxyguanosine and 3-nitrotyrosine, but failed to inhibit inducible nitric oxide synthase expression, in the lungs of the virus-infected mice. On the other hand, Tamiflu^® treatment also significantly suppressed the production of inflammatory cells and neutrophil infiltration, as well as the protein level in BALF and lung histopathological alterations caused by the influenza virus. The suppressive effect of Tamiflu^® was slightly stronger than that of HSA–Trx. Interestingly, Tamiflu^® significantly decreased virus proliferation, while HSA–Trx had no effect. These results indicate that HSA–Trx may be of therapeutic value for the treatment of various acute inflammatory disorders such as influenza-virus-induced pneumonia, by inhibiting inflammatory-cell responses and suppressing the overproduction of NO in the lung.

NADPH oxidases: an overview from structure to innate immunity-associated pathologies

Oxygen-derived free radicals, collectively termed reactive oxygen species (ROS), play important roles in immunity, cell growth, and cell signaling. In excess, however, ROS are lethal to cells, and the overproduction of these molecules leads to a myriad of devastating diseases. The key producers of ROS in many cells are the NOX family of NADPH oxidases, of which there are seven members, with various tissue distributions and activation mechanisms. NADPH oxidase is a multisubunit enzyme comprising membrane and cytosolic components, which actively communicate during the host responses to a wide variety of stimuli, including viral and bacterial infections. This enzymatic complex has been implicated in many functions ranging from host defense to cellular signaling and the regulation of gene expression. NOX deficiency might lead to immunosuppression, while the intracellular accumulation of ROS results in the inhibition of viral propagation and apoptosis. However, excess ROS production causes cellular stress, leading to various lethal diseases, including autoimmune diseases and cancer. During the later stages of injury, NOX promotes tissue repair through the induction of angiogenesis and cell proliferation. Therefore, a complete understanding of the function of NOX is important to direct the role of this enzyme towards host defense and tissue repair or increase resistance to stress in a timely and disease-specific manner.

The role of myeloid cell activation and arginine metabolism in the pathogenesis of virus-induced diseases

When an antiviral immune response is generated, a balance must be reached between two opposing pathways: the production of proinflammatory and cytotoxic effectors that drive a robust antiviral immune response to control the infection and regulators that function to limit or blunt an excessive immune response to minimize immune-mediated pathology and repair tissue damage. Myeloid cells, including monocytes and macrophages, play an important role in this balance, particularly through the activities of the arginine-hydrolyzing enzymes nitric oxide synthase 2 (Nos2; iNOS) and arginase 1 (Arg1). Nitric oxide (NO) production by iNOS is an important proinflammatory mediator, whereas Arg1-expressing macrophages contribute to the resolution of inflammation and wound repair. In the context of viral infections, expression of these enzymes can result in a variety of outcomes for the host. NO has direct antiviral properties against some viruses, whereas during other virus infections NO can mediate immunopathology and/or inhibit the antiviral immune response to promote chronic infection. Arg1 activity not only has important wound healing functions but can also inhibit the antiviral immune response during some viral infections. Thus, depending on the specific virus and the tissue(s) involved, the activity of both of these arginine-hydrolyzing enzymes can either exacerbate or limit the severity of virus-induced disease. In this review, we will discuss a variety of viral infections, including HIV, SARS-CoV, LCMV, HCV, RSV, and others, where myeloid cells influence the control and clearance of the virus from the host, as well as the severity and resolution of tissue damage, via the activities of iNOS and/or Arg1. Clearly, monocyte/macrophage activation and arginine metabolism will continue to be important areas of investigation in the context of viral infections.

Alteration of copper-zinc superoxide dismutase 1 expression by influenza A virus is correlated with virus replication

Viruses have evolved mechanisms designated to potentiate virus replication by modulating the physiological condition of host cells. The generation of reactive oxygen species (ROS) during infection with influenza virus A (IAV) is a well-established mechanism in animals, but little is known about the generation of ROS in in vitro cell culture models and about its role in virus replication. We show here that IAV H1N1 infected human alveolar cells increased superoxide anion level mainly by suppressing the copper-zinc superoxide dismutase 1 (SOD1) gene, and that the SOD1-controlled generation of ROS was tightly correlated with virus replication. The transcription factor Sp1, which is a major element of the proximal region of the sod1 promoter, was slightly downregulated at the transcriptional level during IAV infection, and subsequently modulated by post-translational control. A gradual reduction of whole Sp1 was largely responsible for the repression of sod1 transcription with increasing time post-infection, and their rescue by the proteasome inhibitor, MG132, proved the involvement of proteasomal degradation in Sp1 regulation during IAV infection. Furthermore, we observed that expression of viral polymerase PB1 was inversely proportional to SOD1 level. The antioxidant N-acetyl-cysteine (NAC) neutralized IAV-mediated oxidative stress, and either NAC treatment or sod1 transfection considerably diminished viral polymerase activity. These data indicate that IAV-induced SOD1 repression, which may cause impaired redox balance in host cells, can be attributed, at least in part, to enhance viral replication.

Protective immunity and safety of a genetically modified influenza virus vaccine

Recombinant influenza viruses are promising viral platforms to be used as antigen delivery vectors. To this aim, one of the most promising approaches consists of generating recombinant viruses harboring partially truncated neuraminidase (NA) segments. To date, all studies have pointed to safety and usefulness of this viral platform. However, some aspects of the inflammatory and immune responses triggered by those recombinant viruses and their safety to immunocompromised hosts remained to be elucidated. In the present study, we generated a recombinant influenza virus harboring a truncated NA segment (vNA-Δ) and evaluated the innate and inflammatory responses and the safety of this recombinant virus in wild type or knock-out (KO) mice with impaired innate (Myd88 -/-) or acquired (RAG -/-) immune responses. Infection using truncated neuraminidase influenza virus was harmless regarding lung and systemic inflammatory response in wild type mice and was highly attenuated in KO mice. We also demonstrated that vNA-Δ infection does not induce unbalanced cytokine production that strongly contributes to lung damage in infected mice. In addition, the recombinant influenza virus was able to trigger both local and systemic virus-specific humoral and CD8+ T cellular immune responses which protected immunized mice against the challenge with a lethal dose of homologous A/PR8/34 influenza virus. Taken together, our findings suggest and reinforce the safety of using NA deleted influenza viruses as antigen delivery vectors against human or veterinary pathogens.

Influenza infection suppresses NADPH oxidase-dependent phagocytic bacterial clearance and enhances susceptibility to secondary methicillin-resistant Staphylococcus aureus infection

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a leading contributor to mortality during recent influenza pandemics. The mechanism for this influenza-induced susceptibility to secondary S. aureus infection is poorly understood. In this study, we show that innate antibacterial immunity was significantly suppressed during the recovery stage of influenza infection, even though MRSA superinfection had no significant effect on viral burdens. Compared with mice infected with bacteria alone, postinfluenza MRSA-infected mice exhibited impaired bacterial clearance, which was not due to defective phagocyte recruitment, but rather coincided with reduced intracellular reactive oxygen species levels in alveolar macrophages and neutrophils. NADPH oxidase is responsible for reactive oxygen species production during phagocytic bacterial killing, a process also known as oxidative burst. We found that gp91(phox)-containing NADPH oxidase activity in macrophages and neutrophils was essential for optimal bacterial clearance during respiratory MRSA infections. In contrast to wild-type animals, gp91(phox-/-) mice exhibited similar defects in MRSA clearance before and after influenza infection. Using gp91(phox+/-) mosaic mice, we further demonstrate that influenza infection inhibits a cell-intrinsic contribution of NADPH oxidase to phagocyte bactericidal activity. Taken together, our results establish that influenza infection suppresses NADPH oxidase-dependent bacterial clearance and leads to susceptibility to secondary MRSA infection.

Treatment with the reactive oxygen species scavenger EUK-207 reduces lung damage and increases survival during 1918 influenza virus infection in mice

The 1918 influenza pandemic caused over 40 million deaths worldwide, with 675,000 deaths in the United States alone. Studies in several experimental animal models showed that 1918 influenza virus infection resulted in severe lung pathology associated with dysregulated immune and cell death responses. To determine if reactive oxygen species produced by host inflammatory responses play a central role in promoting severity of lung pathology, we treated 1918 influenza virus-infected mice with the catalytic catalase/superoxide dismutase mimetic, salen-manganese complex EUK-207 beginning 3 days postinfection. Postexposure treatment of mice infected with a lethal dose of the 1918 influenza virus with EUK-207 resulted in significantly increased survival and reduced lung pathology without a reduction in viral titers. In vitro studies also showed that EUK-207 treatment did not affect 1918 influenza viral replication. Immunohistochemical analysis showed a reduction in the detection of the apoptosis marker cleaved caspase-3 and the oxidative stress marker 8-oxo-2'-deoxyguanosine in lungs of EUK-207-treated animals compared to vehicle controls. High-throughput sequencing and RNA expression microarray analysis revealed that treatment resulted in decreased expression of inflammatory response genes and increased lung metabolic and repair responses. These results directly demonstrate that 1918 influenza virus infection leads to an immunopathogenic immune response with excessive inflammatory and cell death responses that can be limited by treatment with the catalytic antioxidant EUK-207.