Ikkepsilon regulates viral-induced interferon regulatory factor-3 activation via a redox-sensitive pathway

Oxidative stress and ROS-mediated cellular events in RSV infection: potential protective roles of antioxidants

Respiratory syncytial virus (RSV), a member of the Pneumoviridae family, can cause severe acute lower respiratory tract infection in infants, young children, immunocompromised individuals and elderly people. RSV is associated with an augmented innate immune response, enhanced secretion of inflammatory cytokines, and necrosis of infected cells. Oxidative stress, which is mainly characterized as an imbalance in the production of reactive oxygen species (ROS) and antioxidant responses, interacts with all the pathophysiologic processes above and is receiving increasing attention in RSV infection. A gradual accumulation of evidence indicates that ROS overproduction plays an important role in the pathogenesis of severe RSV infection and serves as a major factor in pulmonary inflammation and tissue damage. Thus, antioxidants seem to be an effective treatment for severe RSV infection. This article mainly reviews the information on oxidative stress and ROS-mediated cellular events during RSV infection for the first time.

Hepatitis C Virus Nonstructural Protein 5A Interacts with Immunomodulatory Kinase IKKε to Negatively Regulate Innate Antiviral Immunity

Hepatitis C virus (HCV) infection can lead to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. HCV employs diverse strategies to evade host antiviral innate immune responses to mediate a persistent infection. In the present study, we show that nonstructural protein 5A (NS5A) interacts with an NF-κB inhibitor immunomodulatory kinase, IKKε, and subsequently downregulats beta interferon (IFN-β) promoter activity. We further demonstrate that NS5A inhibits DDX3-mediated IKKε and interferon regulatory factor 3 (IRF3) phosphorylation. We also note that hyperphosphorylation of NS5A mediats protein interplay between NS5A and IKKε, thereby contributing to NS5A-mediated modulation of IFN-β signaling. Lastly, NS5A inhibits IKKε-dependent p65 phosphorylation and NF-κB activation. Based on these findings, we propose NS5A as a novel regulator of IFN signaling events, specifically by inhibiting IKKε downstream signaling cascades through its interaction with IKKε. Taken together, these data suggest an additional mechanistic means by which HCV modulates host antiviral innate immune responses to promote persistent viral infection.

IRF3 inhibits nuclear translocation of NF-κB to prevent viral inflammation

Interferon (IFN) regulatory factor 3 (IRF3) is a transcription factor activated by phosphorylation in the cytoplasm of a virus-infected cell; by translocating to the nucleus, it induces transcription of IFN-β and other antiviral genes. We have previously reported IRF3 can also be activated, as a proapoptotic factor, by its linear polyubiquitination mediated by the RIG-I pathway. Both transcriptional and apoptotic functions of IRF3 contribute to its antiviral effect. Here, we report a nontranscriptional function of IRF3, namely, the repression of IRF3-mediated NF-κB activity (RIKA), which attenuated viral activation of NF-κB and the resultant inflammatory gene induction. In Irf3^-/- mice, consequently, Sendai virus infection caused enhanced inflammation in the lungs. Mechanistically, RIKA was mediated by the direct binding of IRF3 to the p65 subunit of NF-κB in the cytoplasm, which prevented its nuclear import. A mutant IRF3 defective in both the transcriptional and the apoptotic activities was active in RIKA and inhibited virus replication. Our results demonstrated IRF3 deployed a three-pronged attack on virus replication and the accompanying inflammation.

Early innate immune response triggered by the human respiratory syncytial virus and its regulation by ubiquitination/deubiquitination processes

The human respiratory syncytial virus (HRSV) causes severe lower respiratory tract infections in infants and the elderly. An exuberant inadequate immune response is behind most of the pathology caused by the HRSV. The main targets of HRSV infection are the epithelial cells of the respiratory tract, where the immune response against the virus begins. This early innate immune response consists of the expression of hundreds of pro-inflammatory and anti-viral genes that stimulates subsequent innate and adaptive immunity. The early innate response in infected cells is mediated by intracellular signaling pathways composed of pattern recognition receptors (PRRs), adapters, kinases, and transcriptions factors. These pathways are tightly regulated by complex networks of post-translational modifications, including ubiquitination. Numerous ubiquitinases and deubiquitinases make these modifications reversible and highly dynamic. The intricate nature of the signaling pathways and their regulation offers the opportunity for fine-tuning the innate immune response against HRSV to control virus replication and immunopathology.

Antioxidant and antiviral activity of fullerol against Zika virus

Neglected for years, Zika virus (ZIKV) has become one of the most relevant arboviruses in current public health. The recent Zika fever epidemic in the Americas generated a worldwide alert due to the association with diseases such as Guillain-Barré syndrome and congenital syndromes. Among the pathogenesis of ZIKV, recent studies suggest that oxidative stress plays an important role during infection and that compounds capable of modulating oxidative stress are promising as therapeutics. Furthermore, so far there are no specific and efficient antiviral drug or vaccine available against ZIKV. Thus, fullerol was evaluated in the context of infection by ZIKV, since it is a carbon nanomaterial known for its potent antioxidant action. In this study, fullerol did not alter cell viability at the concentrations tested, proving to be inert, beyond to presenting high antioxidant power at low concentrations. ZIKV infection of human glioblastoma increased the production of reactive oxygen species by 60% and modulated the Nrf-2 pathway activity negatively. After treatment with fullerol, both conditions were restored to baseline levels. Additionally, fullerol was able to reduce viral production by up to 90%. Therefore, our results suggest that fullerol as a promising candidate in the control of ZIKV infections, presenting both antioxidant and antiviral action.

HIF-1α Regulation of Cytokine Production following TLR3 Engagement in Murine Bone Marrow-Derived Macrophages Is Dependent on Viral Nucleic Acid Length and Glucose Availability

Hypoxia-inducible factor-1α (HIF-1α) is an important regulator of glucose metabolism and inflammatory cytokine production in innate immune responses. Viruses modulate HIF-1α to support viral replication and the survival of infected cells, but it is unclear if this transcription factor also plays an important role in regulating antiviral immune responses. In this study, we found that short and long dsRNA differentially engage TLR3, inducing distinct levels of proinflammatory cytokine production (TNF-α and IL-6) in bone marrow-derived macrophages from C57BL/6 mice. These responses are associated with differential accumulation of HIF-1α, which augments NF-κB activation. Unlike TLR4 responses, increased HIF-1α following TLR3 engagement is not associated with significant alterations in glycolytic activity and was more pronounced in low glucose conditions. We also show that the mechanisms supporting HIF-1α stabilization may differ following stimulation with short versus long dsRNA and that pyruvate kinase M2 and mitochondrial reactive oxygen species play a central role in these processes. Collectively, this work suggests that HIF-1α may fine-tune proinflammatory cytokine production during early antiviral immune responses, particularly when there is limited glucose availability or under other conditions of stress. Our findings also suggest we may be able to regulate the magnitude of proinflammatory cytokine production during antiviral responses by targeting proteins or molecules that contribute to HIF-1α stabilization.

Regulation of the Dimerization and Activity of SARS-CoV-2 Main Protease through Reversible Glutathionylation of Cysteine 300

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for coronavirus disease 2019 (COVID-19), encodes two proteases required for replication. The main protease (M^pro), encoded as part of two polyproteins, pp1a and pp1ab, is responsible for 11 different cleavages of these viral polyproteins to produce mature proteins required for viral replication. M^pro is therefore an attractive target for therapeutic interventions. Certain proteins in cells under oxidative stress undergo modification of reactive cysteines. We show M^pro is susceptible to glutathionylation, leading to inhibition of dimerization and activity. Activity of glutathionylated M^pro could be restored with reducing agents or glutaredoxin. Analytical studies demonstrated that glutathionylated M^pro primarily exists as a monomer and that modification of a single cysteine with glutathione is sufficient to block dimerization and inhibit its activity. Gel filtration studies as well as analytical ultracentrifugation confirmed that glutathionylated M^pro exists as a monomer. Tryptic and chymotryptic digestions of M^pro as well as experiments using a C300S M^pro mutant revealed that Cys300, which is located at the dimer interface, is a primary target of glutathionylation. Moreover, Cys300 is required for inhibition of activity upon M^pro glutathionylation. These findings indicate that M^pro dimerization and activity can be regulated through reversible glutathionylation of a non-active site cysteine, Cys300, which itself is not required for M^pro activity, and provides a novel target for the development of agents to block M^pro dimerization and activity. This feature of M^pro may have relevance to the pathophysiology of SARS-CoV-2 and related bat coronaviruses.

ER stress protein PERK promotes inappropriate innate immune responses and pathogenesis during RSV infection

The activation of dendritic cells (DC) during respiratory viral infections is central to directing the immune response and the pathologic outcome. In these studies, the effect of RSV infection on development of ER stress responses and the impact on innate immunity was examined. The upregulation of ER stress was closely associated with the PERK pathway through the upregulation of CHOP in RSV infected DC. The inhibition of PERK corresponded with decreased EIF2a phosphorylation but had no significant effect on Nrf2 in DC, two primary pathways regulated by PERK. Subsequent studies identified that by blocking PERK activity in infected DC an altered ER stress response and innate cytokine profile was observed with the upregulation of IFNβ and IL-12, coincident to the down regulation of IL-1β. When mitochondria respiration was assessed in PERK deficient DC there were increased dysfunctional mitochondria after RSV infection that resulted in reduced oxygen consumption rates (OCR) and ATP production indicating altered cellular metabolism. Use of a CD11c targeted genetic deleted murine model, RSV infection was characterized by reduced inflammation and diminished mucus staining as well as reduced mucus-associated gene gob5 expression. The assessment of the cytokine responses showed decreased IL-13 and IL-17 along with diminished IL-1β in the lungs of PERK deficient infected mice. When PERK-deficient animals were assessed in parallel for lung leukocyte numbers, animals displayed significantly reduced myeloid and activated CD4 and CD8 T cell numbers. Thus, the PERK activation pathway may provide a rational target for altering the severe outcome of an RSV infection through modifying immune responses.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

Selection of an Optimal Combination Panel to Better Triage COVID-19 Hospitalized Patients

PURPOSE

It is difficult to predict the prognosis of COVID-19 patients at the disease onset. This study was designed to add new biomarkers into conventional inflammatory panels to build an optimal combination panel, to better triage patients and predict their outcomes.

PATIENTS AND METHODS

Biochemical parameters representing multi-organ functions, cytokines, acute-phase proteins, and other inflammatory markers were measured in COVID-19 patients on hospital admission. Receiver operating characteristic (ROC) curves, logistic regression, event-free survival (EFS), and Cox analyses were performed to screen and compare the predictive capabilities of the new panel in patients with different illness severity and outcome.

RESULTS

This study included 120 patients with COVID-19, consisting of 32 critical, 28 severe, and 60 mild/moderate patients. Initial levels of the selected biomarkers showed a significant difference in the three groups, all of which influenced patient outcome and EFS to varying degrees. Cox proportional hazard model revealed that procalcitonin (PCT) and interleukin 10 (IL-10) were independent risk factors, while superoxide dismutase (SOD) was an independent protective factor influencing EFS. In discriminating the critical and mild patients, a panel combining PCT, IL-6, and neutrophil (NEUT) yielded the best diagnostic performance with an AUC of 0.99, the sensitivity of 90.60% and specificity of 100%. In distinguishing between severe and mild patients, SOD's AUC of 0.89 was higher than any other single biomarker. In differentiating the critical and severe patients, the combination of white blood cell count (WBC), PCT, IL-6, IL-10, and SOD achieved the highest AUC of 0.95 with a sensitivity of 75.00% and specificity of 100%.

CONCLUSION

The optimal combination panel has a substantial potential to better triage COVID-19 patients on admission. Better triage of patients will benefit the rational use of medical resources.

Differential remodeling of the electron transport chain is required to support TLR3 and TLR4 signaling and cytokine production in macrophages

Increasing evidence suggests that mitochondria play a critical role in driving innate immune responses against bacteria and viruses. However, it is unclear if differential reprogramming of mitochondrial function contributes to the fine tuning of pathogen specific immune responses. Here, we found that TLR3 and TLR4 engagement on murine bone marrow derived macrophages was associated with differential remodeling of electron transport chain complex expression. This remodeling was associated with differential accumulation of mitochondrial and cytosolic ROS, which were required to support ligand specific inflammatory and antiviral cytokine production. We also found that the magnitude of TLR3, but not TLR4, responses were modulated by glucose availability. Under conditions of low glucose, TLR3 engagement was associated with increased ETC complex III expression, increased mitochondrial and cytosolic ROS and increased inflammatory and antiviral cytokine production. This amplification was selectively reversed by targeting superoxide production from the outer Q-binding site of the ETC complex III. These results suggest that ligand specific modulation of the ETC may act as a rheostat that fine tunes innate immune responses via mitochondrial ROS production. Modulation of these processes may represent a novel mechanism to modulate the nature as well as the magnitude of antiviral vs. inflammatory immune responses.

Flaviviridae Viruses and Oxidative Stress: Implications for Viral Pathogenesis

Oxidative stress is induced once the balance of generation and neutralization of reactive oxygen species (ROS) is broken in the cell, and it plays crucial roles in a variety of natural and diseased processes. Infections of Flaviviridae viruses trigger oxidative stress, which affects both the cellular metabolism and the life cycle of the viruses. Oxidative stress associated with specific viral proteins, experimental culture systems, and patient infections, as well as its correlations with the viral pathogenesis attracts much research attention. In this review, we primarily focus on hepatitis C virus (HCV), dengue virus (DENV), Zika virus (ZIKV), Japanese encephalitis virus (JEV), West Nile virus (WNV), and tick-borne encephalitis virus (TBEV) as representatives of Flaviviridae viruses and we summarize the mechanisms involved in the relevance of oxidative stress for virus-associated pathogenesis. We discuss the current understanding of the pathogenic mechanisms of oxidative stress induced by Flaviviridae viruses and highlight the relevance of autophagy and DNA damage in the life cycle of viruses. Understanding the crosstalk between viral infection and oxidative stress-induced molecular events may offer new avenues for antiviral therapeutics.

Redox Biology of Respiratory Viral Infections

Respiratory viruses cause infections of the upper or lower respiratory tract and they are responsible for the common cold—the most prevalent disease in the world. In many cases the common cold results in severe illness due to complications, such as fever or pneumonia. Children, old people, and immunosuppressed patients are at the highest risk and require fast diagnosis and therapeutic intervention. However, the availability and efficiencies of existing therapeutic approaches vary depending on the virus. Investigation of the pathologies that are associated with infection by respiratory viruses will be paramount for diagnosis, treatment modalities, and the development of new therapies. Changes in redox homeostasis in infected cells are one of the key events that is linked to infection with respiratory viruses and linked to inflammation and subsequent tissue damage. Our review summarizes current knowledge on changes to redox homeostasis, as induced by the different respiratory viruses.

Protective Role of Nuclear Factor Erythroid 2-Related Factor 2 Against Respiratory Syncytial Virus and Human Metapneumovirus Infections

The pathogenesis of respiratory syncytial virus (RSV) infections is characterized by lower airway obstruction driven at great extent by the exuberant production of inflammatory cytokines. We have previously shown that RSV infection in vitro and in vivo results in production of reactive oxygen species along with reduction in the expression of antioxidant enzymes (AOEs), which are involved in maintaining the cellular oxidant-antioxidant balance. These events were associated with the concomitant reduction in nuclear factor erythroid 2-related factor 2 (Nrf2), a key transcription factor that controls AOE expression. The objective of the current study was to establish the role of Nrf2 in shaping innate immune responses, clinical disease, airway inflammation, and viral replication in established experimental models of intranasal RSV and human metapneumovirus (hMPV) infections, by employing mice genetically deficient for the Nrf2 gene. Compared to control wild type (WT), mice genetically deficient in Nrf2 (Nrf2 KO) developed enhanced clinical disease, airway inflammation and pathology, and significantly greater lung viral titers following experimental infection with either RSV or hMPV. In particular, compared to control mice, RSV-infected Nrf2 KO mice lost more body weight and had increased airway obstruction at time points characterized by a remarkable increase in inflammatory cytokines and airway neutrophilia. Airway levels of AOEs and enzymes that regulate synthesis of the endogenous hydrogen sulfide (H2S) pathway, which we showed to play an important antiviral function, were also decreased in RSV-infected Nrf2 KO compared to WT. In conclusion, these results suggest that Nrf2 is a critical regulator of innate, inflammatory, and disease-associated responses in the airways of mice infected with viruses that are members of the Pneumoviridae family. Importantly, the results of this study suggest that Nrf2-dependent genes, including those controlling the cellular antioxidant and H2S-generating enzymes and cytokines can affect several aspects of the antiviral response, such as airway neutrophilia, clinical disease, airway obstruction, and viral replication.

Sphingosine 1-Phosphate Lyase Enhances the Activation of IKKε To Promote Type I IFN-Mediated Innate Immune Responses to Influenza A Virus Infection

Sphingosine 1-phosphate (S1P) lyase (SPL) is an intracellular enzyme that mediates the irreversible degradation of the bioactive lipid S1P. We have previously reported that overexpressed SPL displays anti-influenza viral activity; however, the underlying mechanism is incompletely understood. In this study, we demonstrate that SPL functions as a positive regulator of IKKε to propel type I IFN-mediated innate immune responses against viral infection. Exogenous SPL expression inhibited influenza A virus replication, which correlated with an increase in type I IFN production and IFN-stimulated gene accumulation upon infection. In contrast, the lack of SPL expression led to an elevated cellular susceptibility to influenza A virus infection. In support of this, SPL-deficient cells were defective in mounting an effective IFN response when stimulated by influenza viral RNAs. SPL augmented the activation status of IKKε and enhanced the kinase-induced phosphorylation of IRF3 and the synthesis of type I IFNs. However, the S1P degradation-incompetent form of SPL also enhanced IFN responses, suggesting that SPL's pro-IFN function is independent of S1P. Biochemical analyses revealed that SPL, as well as the mutant form of SPL, interacts with IKKε. Importantly, when endogenous IKKε was downregulated using a small interfering RNA approach, SPL's anti-influenza viral activity was markedly suppressed. This indicates that IKKε is crucial for SPL-mediated inhibition of influenza virus replication. Thus, the results illustrate the functional significance of the SPL-IKKε-IFN axis during host innate immunity against viral infection.

The innate immune response to RSV: Advances in our understanding of critical viral and host factors

Respiratory syncytial virus (RSV) causes mild to severe respiratory illness in humans and is a major cause of hospitalizations of infants and the elderly. Both the innate and the adaptive immune responses contribute to the control of RSV infection, but despite successful viral clearance, protective immunity against RSV re-infection is usually suboptimal and infections recur. Poor understanding of the mechanisms limiting the induction of long-lasting immunity has delayed the development of an effective vaccine. The innate immune response plays a critical role in driving the development of adaptive immunity and is thus a crucial determinant of the infection outcome. Advances in recent years have improved our understanding of cellular and viral factors that influence the onset and quality of the innate immune response to RSV. These advances include the identification of a complex system of cellular sensors that mediate RSV detection and stimulate transcriptome changes that lead to virus control and the discovery that cell stress and apoptosis participate in the control of RSV infection. In addition, it was recently demonstrated that defective viral genomes (DVGs) generated during RSV replication are the primary inducers of the innate immune response. Newly discovered host pathways involved in the innate response to RSV, together with the potential generation of DVG-derived oligonucleotides, present various novel opportunities for the design of vaccine adjuvants able to induce a protective response against RSV and similar viruses.

Respiratory Syncytial Virus and Cellular Stress Responses: Impact on Replication and Physiopathology

Human respiratory syncytial virus (RSV), a member of the Paramyxoviridae family, is a major cause of severe acute lower respiratory tract infection in infants, elderly and immunocompromised adults. Despite decades of research, a complete integrated picture of RSV-host interaction is still missing. Several cellular responses to stress are involved in the host-response to many virus infections. The endoplasmic reticulum stress induced by altered endoplasmic reticulum (ER) function leads to activation of the unfolded-protein response (UPR) to restore homeostasis. Formation of cytoplasmic stress granules containing translationally stalled mRNAs is a means to control protein translation. Production of reactive oxygen species is balanced by an antioxidant response to prevent oxidative stress and the resulting damages. In recent years, ongoing research has started to unveil specific regulatory interactions of RSV with these host cellular stress responses. Here, we discuss the latest findings regarding the mechanisms evolved by RSV to induce, subvert or manipulate the ER stress, the stress granule and oxidative stress responses. We summarize the evidence linking these stress responses with the regulation of RSV replication and the associated pathogenesis.

Cellular oxidative stress response controls the antiviral and apoptotic programs in dengue virus-infected dendritic cells

Dengue virus (DENV) is a re-emerging arthropod borne flavivirus that infects more than 300 million people worldwide, leading to 50,000 deaths annually. Because dendritic cells (DC) in the skin and blood are the first target cells for DENV, we sought to investigate the early molecular events involved in the host response to the virus in primary human monocyte-derived dendritic cells (Mo-DC). Using a genome-wide transcriptome analysis of DENV2-infected human Mo-DC, three major responses were identified within hours of infection - the activation of IRF3/7/STAT1 and NF-κB-driven antiviral and inflammatory networks, as well as the stimulation of an oxidative stress response that included the stimulation of an Nrf2-dependent antioxidant gene transcriptional program. DENV2 infection resulted in the intracellular accumulation of reactive oxygen species (ROS) that was dependent on NADPH-oxidase (NOX). A decrease in ROS levels through chemical or genetic inhibition of the NOX-complex dampened the innate immune responses to DENV infection and facilitated DENV replication; ROS were also essential in driving mitochondrial apoptosis in infected Mo-DC. In addition to stimulating innate immune responses to DENV, increased ROS led to the activation of bystander Mo-DC which up-regulated maturation/activation markers and were less susceptible to viral replication. We have identified a critical role for the transcription factor Nrf2 in limiting both antiviral and cell death responses to the virus by feedback modulation of oxidative stress. Silencing of Nrf2 by RNA interference increased DENV-associated immune and apoptotic responses. Taken together, these data demonstrate that the level of oxidative stress is critical to the control of both antiviral and apoptotic programs in DENV-infected human Mo-DC and highlight the importance of redox homeostasis in the outcome of DENV infection.

Dengue virus (DENV), the leading arthropod-borne viral infection in the world, represents a major human health concern with a global at risk population of over 3 billion people. Currently, there are no antivirals or vaccines available to treat patients with dengue fever, nor is it possible to predict which patients will progress to life-threatening severe dengue fever. Markers associated with oxidative stress responses have been reported in patients with severe DENV infection, suggesting a relationship between oxidative stress and viral pathogenesis. In order to uncover biological processes that determine the outcome of disease in patients, we utilized human dendritic cells, the primary target of DENV infection, in an in vitro model. Transcriptional analysis of pathways activated upon de novo DENV infection revealed a major role for cellular oxidative stress in the induction of antiviral, inflammatory, and cell death responses. We also demonstrated that antioxidant mechanisms play a critical role in controlling antiviral and cell death responses to the virus, acting as feedback regulators of the oxidative stress response. This report highlights the importance of oxidative stress responses in the outcome of DENV infection, and identifies this pathway as a potential new entry-point for treating dengue-associated diseases.

Respiratory Viral Infections and Subversion of Cellular Antioxidant Defenses

Reactive oxygen species (ROS) formation is part of normal cellular aerobic metabolism, due to respiration and oxidation of nutrients in order to generate energy. Low levels of ROS are involved in cellular signaling and are well controlled by the cellular antioxidant defense system. Elevated levels of ROS generation due to pollutants, toxins and radiation exposure, as well as infections, are associated with oxidative stress causing cellular damage. Several respiratory viruses, including respiratory syncytial virus (RSV), human metapneumovirus (hMPV) and influenza, induce increased ROS formation, both intracellularly and as a result of increased inflammatory cell recruitment at the site of infection. They also reduce antioxidant enzyme (AOE) levels and/or activity, leading to unbalanced oxidative-antioxidant status and subsequent oxidative cell damage. Expression of several AOE is controlled by the activation of the nuclear transcription factor NF-E2-related factor 2 (Nrf2), through binding to the antioxidant responsive element (ARE) present in the AOE gene promoters. While exposure to several pro-oxidant stimuli usually leads to Nrf2 activation and upregulation of AOE expression, respiratory viral infections are associated with inhibition of AOE expression/activity, which in the case of RSV and hMPV is associated with reduced Nrf2 nuclear localization, decreased cellular levels and reduced ARE-dependent gene transcription. Therefore, administration of antioxidant mimetics or Nrf2 inducers represents potential viable therapeutic approaches to viral-induced diseases, such as respiratory infections and other infections associated with decreased cellular antioxidant capacity.

The role of innate immunity in conditioning mosquito susceptibility to West Nile virus

Arthropod-borne viruses (arboviruses) represent an emerging threat to human and livestock health globally. In particular, those transmitted by mosquitoes present the greatest challenges to disease control efforts. An understanding of the molecular basis for mosquito innate immunity to arbovirus infection is therefore critical to investigations regarding arbovirus evolution, virus-vector ecology, and mosquito vector competence. In this review, we discuss the current state of understanding regarding mosquito innate immunity to West Nile virus. We draw from the literature with respect to other virus-vector pairings to attempt to draw inferences to gaps in our knowledge about West Nile virus and relevant vectors.

Nuclear factor κB2 p52 protein has a role in antiviral immunity through IκB kinase epsilon-dependent induction of Sp1 protein and interleukin 15

In this study we describe a previously unreported function for NFκB2, an NFκB family transcription factor, in antiviral immunity. NFκB2 is induced in response to poly(I:C), a mimic of viral dsRNA. Poly(I:C), acting via TLR3, induces p52-dependent transactivation of a reporter gene in a manner that requires the kinase activity of IκB kinase ε (IKKε) and the transactivating potential of RelA/p65. We identify a novel NFκB2 binding site in the promoter of the transcription factor Sp1 that is required for Sp1 gene transcription activated by poly(I:C). We show that Sp1 is required for IL-15 induction by both poly(I:C) and respiratory syncytial virus, a response that also requires NFκB2 and IKKε. Our study identifies NFκB2 as a target for IKKε in antiviral immunity and describes, for the first time, a role for NFκB2 in the regulation of gene expression in response to viral infection.

Respiratory syncytial virus infection: mechanisms of redox control and novel therapeutic opportunities

Respiratory syncytial virus (RSV) is one of the most important causes of upper and lower respiratory tract infections in infants and young children, for which no effective treatment is currently available. Although the mechanisms of RSV-induced airway disease remain incompletely defined, the lung inflammatory response is thought to play a central pathogenetic role. In the past few years, we and others have provided increasing evidence of a role of reactive oxygen species (ROS) as important regulators of RSV-induced cellular signaling leading to the expression of key proinflammatory mediators, such as cytokines and chemokines. In addition, RSV-induced oxidative stress, which results from an imbalance between ROS production and airway antioxidant defenses, due to a widespread inhibition of antioxidant enzyme expression, is likely to play a fundamental role in the pathogenesis of RSV-associated lung inflammatory disease, as demonstrated by a significant increase in markers of oxidative injury, which correlate with the severity of clinical illness, in children with RSV infection. Modulation of ROS production and oxidative stress therefore represents a potential novel pharmacological approach to ameliorate RSV-induced lung inflammation and its long-term consequences.

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) activates stimulator of interferon gene (STING)-dependent innate immune pathways and is regulated by mitochondrial membrane potential

The chemotherapeutic agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is a potent inducer of type I IFNs and other cytokines. This ability is essential for its chemotherapeutic benefit in a mouse cancer model and suggests that it might also be useful as an antiviral agent. However, the mechanism underlying DMXAA-induced type I IFNs, including the host proteins involved, remains unclear. Recently, it was reported that the antioxidant N-acetylcysteine (NAC) decreased DMXAA-induced TNF-α and IL-6, suggesting that oxidative stress may play a role. The goal of this study was to identify host proteins involved in DMXAA-dependent signaling and determine how antioxidants modulate this response. We found that expression of IFN-β in response to DMXAA in mouse macrophages requires the mitochondrial and endoplasmic reticulum resident protein STING. Addition of the antioxidant diphenylene iodonium (DPI) diminished DMXAA-induced IFN-β, but this decrease was independent of both the NADPH oxidase, Nox2, and de novo generation of reactive oxygen species. Additionally, IFN-β up-regulation by DMXAA was inhibited by agents that target the mitochondrial electron transport chain and, conversely, loss of mitochondrial membrane potential correlated with diminished innate immune signaling in response to DMXAA. Up-regulation of Ifnb1 gene expression mediated by cyclic dinucleotides was also impaired by DPI, whereas up-regulation of Ifnb1 mRNA due to cytosolic double-stranded DNA was not. Although both stimuli signal through STING, cyclic dinucleotides interact directly with STING, suggesting that recognition of DMXAA by STING may also be mediated by direct interaction.

Antioxidant mimetics modulate oxidative stress and cellular signaling in airway epithelial cells infected with respiratory syncytial virus

Respiratory syncytial virus (RSV) is one of the most common causes of bronchiolitis and pneumonia among infants and young children worldwide. In previous investigations, we have shown that RSV infection induces rapid generation of reactive oxygen species (ROS), which modulate viral-induced cellular signaling, and downregulation of antioxidant enzyme (AOE) expression, resulting in oxidative stress in vitro and in vivo, which plays a pathogenetic role in RSV-induced lung disease. In this study, we determined whether pharmacological intervention with synthetic catalytic scavengers could reduce RSV-induced proinflammatory gene expression and oxidative cell damage in an in vitro model of infection. Treatment of airway epithelial cells (AECs) with the salen-manganese complexes EUK-8 or EUK-189, which possess superoxide dismutase, catalase, and glutathione peroxidase activity, strongly reduced RSV-induced ROS formation by increasing cellular AOE enzymatic activity and levels of the lipid peroxidation products F(2)-8-isoprostane and malondialdehyde, which are markers of oxidative stress. Treatment of AECs with AOE mimetics also significantly inhibited RSV-induced cytokine and chemokine secretion and activation of the transcription factors nuclear factor-κB and interferon regulatory factor-3, which orchestrate proinflammatory gene expression. Both EUKs were able to reduce viral replication, when used at high doses. These results suggest that increasing antioxidant cellular capacities can significantly impact RSV-associated oxidative cell damage and cellular signaling and could represent a novel therapeutic approach in modulating virus-induced lung disease.

Mitochondria-derived reactive oxygen species negatively regulates immune innate signaling pathways triggered by a DNA virus, but not by an RNA virus

Reactive oxygen species (ROS) are crucial secondary messengers of signaling pathways. Redox-dependent signaling events have been previously described in the innate immune response. However, the mechanism by which ROS modulates anti-viral innate immune signaling is not fully clarified. Here, we report that mitochondria-derived ROS differentially regulate the innate response to DNA and RNA viruses (herpes simplex virus (HSV) and Sendai virus (SeV), respectively), with the cytokine response to HSV being negatively regulated by mitochondrial ROS. Importantly, specific activation of Toll-like receptors (TLRs) and DNA receptors (DNARs) but not retinoic acid inducible gene I (RIG-I)-like receptors (RLRs), led to signaling cascades that were inhibited by mitochondrial ROS production. Thus, localized mitochondrial ROS exerts negative modulation of innate immune responses to the DNA virus HSV-2 but not the RNA virus SeV.

HSV infection induces production of ROS, which potentiate signaling from pattern recognition receptors: role for S-glutathionylation of TRAF3 and 6

The innate immune response constitutes the first line of defense against infections. Pattern recognition receptors recognize pathogen structures and trigger intracellular signaling pathways leading to cytokine and chemokine expression. Reactive oxygen species (ROS) are emerging as an important regulator of some of these pathways. ROS directly interact with signaling components or induce other post-translational modifications such as S-glutathionylation, thereby altering target function. Applying live microscopy, we have demonstrated that herpes simplex virus (HSV) infection induces early production of ROS that are required for the activation of NF-κB and IRF-3 pathways and the production of type I IFNs and ISGs. All the known receptors involved in the recognition of HSV were shown to be dependent on the cellular redox levels for successful signaling. In addition, we provide biochemical evidence suggesting S-glutathionylation of TRAF family proteins to be important. In particular, by performing mutational studies we show that S-glutathionylation of a conserved cysteine residue of TRAF3 and TRAF6 is important for ROS-dependent activation of innate immune pathways. In conclusion, these findings demonstrate that ROS are essential for effective activation of signaling pathways leading to a successful innate immune response against HSV infection.

Herpes simplex virus (HSV) type 1 and 2 are important human pathogens, which can give rise to severe diseases during both primary and recurrent infections. In addition to activating “classical” innate and adaptive immune responses, many infections stimulate other cellular activities such as and production of reactive oxygen species (ROS). However, there is little knowledge on the cross-talk between ROS and the innate antiviral response. In this article we show that HSV infection leads to production of ROS, and that ROS play a critical role in activation of innate immune responses to these viruses. At the mechanistic level, we show that ROS stimulate glutathionylation (a protein modification) of the signaling molecules TRAF3 and 6, which promotes redox-sensitive signaling. Our data support the idea that the innate immune system not only detects specific HSV molecules but also senses the cellular oxidative stress level, and integrates this into the innate immune response to infections.

Autophagy-mediated dendritic cell activation is essential for innate cytokine production and APC function with respiratory syncytial virus responses

The regulation of innate immune responses during viral infection is a crucial step to promote antiviral reactions. Recent studies have drawn attention to a strong relationship of pathogen-associated molecular pattern recognition with autophagy for activation of APC function. Our initial observations indicated that autophagosomes formed in response to respiratory syncytial virus (RSV) infection of dendritic cells (DC). To further investigate whether RSV-induced DC activation and innate cytokine production were associated with autophagy, we used several methods to block autophagosome formation. Using 3-MA, small interfering RNA inhibition of LC3, or Beclin(+/-) mouse-derived DC, studies established a relationship between RSV-induced autophagy and enhanced type I IFN, TNF, IL-6, and IL-12p40 expression. Moreover, autophagosome formation induced by starvation also promoted innate cytokine expression in DC. The induction of starvation-induced autophagy in combination with RSV infection synergistically enhanced DC cytokine expression that was blocked by an autophagy inhibitor. The latter synergistic responses were differentially altered in DC from MyD88(-/-) and TRIF(-/-) mice, supporting the concept of autophagy-mediated TLR signaling. In addition, blockade of autophagy in RSV-infected DC inhibited the maturation of DC as assessed by MHC class II and costimulatory molecule expression. Subsequently, we demonstrated that inhibition of autophagy in DC used to stimulate primary OVA-induced and secondary RSV-infected responses significantly attenuated cytokine production by CD4(+) T cells. Thus, these studies have outlined that autophagy in DC after RSV infection is a crucial mechanism for driving innate cytokine production, leading to altered acquired immune responses.

Viral-mediated inhibition of antioxidant enzymes contributes to the pathogenesis of severe respiratory syncytial virus bronchiolitis

RATIONALE

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in children, for which no specific treatment or vaccine is currently available. We have previously shown that RSV induces reactive oxygen species in cultured cells and oxidative injury in the lungs of experimentally infected mice. The mechanism(s) of RSV-induced oxidative stress in vivo is not known.

OBJECTIVES

To measure changes of lung antioxidant enzymes expression/activity and activation of NF-E2-related factor 2 (Nrf2), a transcription factor that regulates detoxifying and antioxidant enzyme gene expression, in mice and in infants with naturally acquired RSV infection.

METHODS

Superoxide dismutase 1 (SOD 1), SOD 2, SOD 3, catalase, glutathione peroxidase, and glutathione S-transferase, as well as Nrf2 expression, were measured in murine bronchoalveolar lavage, cell extracts of conductive airways, and/or in human nasopharyngeal secretions by Western blot and two-dimensional gel electrophoresis. Antioxidant enzyme activity and markers of oxidative cell injury were measured in either murine bronchoalveolar lavage or nasopharyngeal secretions by colorimetric/immunoassays.

MEASUREMENTS AND MAIN RESULTS

RSV infection induced a significant decrease in the expression and/or activity of SOD, catalase, glutathione S-transferase, and glutathione peroxidase in murine lungs and in the airways of children with severe bronchiolitis. Markers of oxidative damage correlated with severity of clinical illness in RSV-infected infants. Nrf2 expression was also significantly reduced in the lungs of viral-infected mice.

CONCLUSIONS

RSV infection induces significant down-regulation of the airway antioxidant system in vivo, likely resulting in lung oxidative damage. Modulation of oxidative stress may pave the way toward important advances in the therapeutic approach of RSV-induced acute lung disease.

IKKε modulates RSV-induced NF-κB-dependent gene transcription

Respiratory syncytial virus (RSV), a negative-strand RNA virus, is the most common cause of epidemic respiratory disease in infants and young children. RSV infection of airway epithelial cells induces the expression of immune/inflammatory genes through the activation of a subset of transcription factors, including Nuclear Factor-κB (NF-κB). In this study we have investigated the role of the non canonical IκB kinase (IKK)ε in modulating RSV-induced NF-κB activation. Our results show that inhibition of IKKε activation results in significant impairment of viral-induced NF-κB-dependent gene expression, through a reduction in NF-κB transcriptional activity, without changes in nuclear translocation or DNA-binding activity. Absence of IKKε results in a significant decrease of RSV-induced NF-κB phosphorylation on serine 536, a post-translational modification important for RSV-induced NF-κB-dependent gene expression, known to regulate NF-κB transcriptional activity without affecting nuclear translocation. This study identifies a novel mechanism by which IKKε regulates viral-induced cellular signaling.

Requirement of NOX2 and reactive oxygen species for efficient RIG-I-mediated antiviral response through regulation of MAVS expression

The innate immune response is essential to the host defense against viruses, through restriction of virus replication and coordination of the adaptive immune response. Induction of antiviral genes is a tightly regulated process initiated mainly through sensing of invading virus nucleic acids in the cytoplasm by RIG-I like helicases, RIG-I or Mda5, which transmit the signal through a common mitochondria-associated adaptor, MAVS. Although major breakthroughs have recently been made, much remains unknown about the mechanisms that translate virus recognition into antiviral genes expression. Beside the reputed detrimental role, reactive oxygen species (ROS) act as modulators of cellular signaling and gene regulation. NADPH oxidase (NOX) enzymes are a main source of deliberate cellular ROS production. Here, we found that NOX2 and ROS are required for the host cell to trigger an efficient RIG-I-mediated IRF-3 activation and downstream antiviral IFNbeta and IFIT1 gene expression. Additionally, we provide evidence that NOX2 is critical for the expression of the central mitochondria-associated adaptor MAVS. Taken together these data reveal a new facet to the regulation of the innate host defense against viruses through the identification of an unrecognized role of NOX2 and ROS.

Respiratory syncytial virus nonstructural proteins decrease levels of multiple members of the cellular interferon pathways

Viruses of the Paramyxoviridae family, such as the respiratory syncytial virus (RSV), suppress cellular innate immunity represented by type I interferon (IFN) for optimal growth in their hosts. The two unique nonstructural (NS) proteins, NS1 and NS2, of RSV suppress IFN synthesis, as well as IFN function, but their exact targets are still uncharacterized. Here, we investigate if either or both of the NS proteins affect the steady-state levels of key members of the IFN pathway. We found that both NS1 and NS2 decreased the levels of TRAF3, a strategic integrator of multiple IFN-inducing signals, although NS1 was more efficient. Only NS1 reduced IKKepsilon, a key protein kinase that specifically phosphorylates and activates IFN regulatory factor 3. Loss of the TRAF3 and IKKepsilon proteins appeared to involve a nonproteasomal mechanism. Interestingly, NS2 modestly increased IKKepsilon levels. In the IFN response pathway, NS2 decreased the levels of STAT2, the essential transcription factor for IFN-inducible antiviral genes. Preliminary mapping revealed that the C-terminal 10 residues of NS1 were essential for reducing IKKepsilon levels and the C-terminal 10 residues of NS2 were essential for increasing and reducing IKKepsilon and STAT2, respectively. In contrast, deletion of up to 20 residues of the C termini of NS1 and NS2 did not diminish their TRAF3-reducing activity. Coimmunoprecipitation studies revealed that NS1 and NS2 form a heterodimer. Clearly, the NS proteins of RSV, working individually and together, regulate key signaling molecules of both the IFN activation and response pathways.

Respiratory syncytial virus induces oxidative stress by modulating antioxidant enzymes

Oxidative stress plays an important role in the pathogenesis of lung inflammation. Respiratory syncytial virus (RSV) infection induces reactive oxygen species (ROS) production in vitro and oxidative injury in lungs in vivo; however, the mechanism of RSV-induced cellular oxidative stress has not been investigated. Therefore, we determined whether RSV infection of airway epithelial cells modified the expression and/or activities of antioxidant enzymes (AOE). A549 cells, a human alveolar type II-like epithelial cell line, and small airway epithelial (SAE) cells, normal human cells derived from terminal bronchioli, were infected with RSV and harvested at various time points to measure F(2)-8 isoprostanes by enzyme-linked immunosorbent assay and total and reduced glutathione (GSH and GSSG) by colorimetric assay. Superoxide dismutase (SOD) 1, 2, and 3, catalase, glutathione peroxidase (GPx), and glutathione S-transferase (GST) expression was determined by quantitative real-time PCR and Western blot, and their activity was measured by colorimetric assays. RSV infection induced a significant increase of lipid peroxidation products as well as a significant decrease in the GSH/GSSG ratio. There was a significant decrease in SOD 1, SOD 3, catalase, and GST expression with a concomitant increase of SOD 2 in RSV-infected cells, compared with uninfected cells. Total SOD activity was increased, but catalase, GPx, and GST activities were decreased, after RSV infection. Our findings suggest that RSV-induced cellular oxidative damage is the result of an imbalance between ROS production and antioxidant cellular defenses. Modulation of oxidative stress represents a potential novel pharmacologic approach to ameliorate RSV-induced acute lung inflammation.

Cigarette smoke condensate enhances respiratory syncytial virus-induced chemokine release by modulating NF-kappa B and interferon regulatory factor activation

Exposure to cigarette smoke is a risk factor contributing to the severity of respiratory tract infections associated with respiratory syncytial virus (RSV). Stimulation of airway epithelial cells by either RSV or cigarette smoke condensate (CSC) has been shown to induce secretion of the proinflammatory chemokines. However, the effect of coexposure of airway epithelial cells to CSC and RSV on inducible chemokine production has not been previously investigated. The results of this study indicate that CSC costimulation significantly increased RSV-induced interleukin-8 (IL-8) and monocyte chemoattactant protein-1 gene and protein expression when compared with each stimulus alone. Promoter deletion studies identified the interferon stimulatory response element (ISRE) of the IL-8 promoter as a critical region responsible for the synergistic increase of IL-8 gene transcription during mixed exposure. CSC costimulation enhanced RSV-induced activation of interferon regulatory factor (IRF)-1 and IRF-7, which bind to the ISRE site. CSC also furthered RSV-induced activation of the transcription factor nuclear factor kappa B (NF-kappaB), as shown by increased NF-kappaB DNA binding to its specific site of the IL-8 promoter and increased NF-kappaB-driven gene transcription. Therefore, our data demonstrate that a combined exposure to CSC and RSV synergistically increases chemokine expression in airway epithelial cells, suggesting that CSC contributes to an exuberant immune response to RSV by stimulating overlapping signal transduction pathways.

Respiratory syncytial virus (RSV) attachment and nonstructural proteins modify the type I interferon response associated with suppressor of cytokine signaling (SOCS) proteins and IFN-stimulated gene-15 (ISG15)

Respiratory syncytial virus (RSV) is a major cause of severe lower airway disease in infants and young children, but no safe and effective RSV vaccine is yet available. Factors attributing to this problem are associated with an incomplete understanding of the mechanisms by which RSV modulates the host cell response to infection. In the present study, we investigate suppressor of cytokine signaling (SOCS)-1 and SOCS3 expression associated with the type I IFN and IFN-stimulated gene (ISG)-15 response following infection of mouse lung epithelial (MLE-15) cells with RSV or RSV mutant viruses lacking the G gene, or NS1 and NS2 gene deletions. Studies in MLE-15 cells are important as this cell line represents the distal bronchiolar and alveolar epithelium of mice, the most common animal model used to evaluate the host cell response to RSV infection, and exhibit morphologic characteristics of alveolar type II cells, a primary cell type targeted during RSV infection. These results show an important role for SOCS1 regulation of the antiviral host response to RSV infection, and demonstrate a novel role for RSV G protein manipulation of SOCS3 and modulation of ISG15 and IFNβ mRNA expression.

The requirement of reactive oxygen intermediates for lymphocytic choriomeningitis virus binding and growth

Multiple viruses induce reactive oxygen intermediate (ROI) generation during infection that plays an important role in growth. We have examined the importance of ROI during lymphocytic choriomeningitis virus (LCMV) infection of immortalized BHK-21 cells and murine peritoneal macrophages. Within 15 min of virus addition, intracellular ROI levels increased. To examine the contribution of ROI to LCMV infection, cells were pretreated with antioxidant prior to virus addition. Antioxidant treatment inhibited low and high MOI growth of virus. The requirement for ROI was greatest during the initial phase of infection, as antioxidant treatment after 6 h post infection had a weaker inhibitory effect. Furthermore, antioxidant treatment of cells inhibited virus binding, while treatment of virus stocks with N-ethyl malemide, which blocks free thiols, eliminated infectious virus. This illustrates that ROI are critical to the regulation of virus binding and growth and has important implications for understanding the infectivity of related viruses.

Dual role of NOX2 in respiratory syncytial virus- and sendai virus-induced activation of NF-kappaB in airway epithelial cells

Human respiratory syncytial virus (RSV), a member of the Paramyxoviridae family, is the most important viral agent of pediatric respiratory tract disease worldwide. Human airway epithelial cells (AEC) are the primary targets of RSV. AEC are responsible for the secretion of a wide spectrum of cytokines and chemokines that are important mediators of the exacerbated airway inflammation triggered by the host in response to RSV infection. NF-kappaB is a key transcription factor responsible for the regulation of cytokine and chemokine gene expression and thus represents a potential therapeutic target. In the present study, we sought to delineate the role of RSV-induced reactive oxygen species in the regulation of the signaling pathways leading to NF-kappaB activation. First, we demonstrate that besides the well-characterized IkappaBalpha-dependent pathway, phosphorylation of p65 at Ser(536) is an essential event regulating NF-kappaB activation in response to RSV in A549. Using antioxidant and RNA-interference strategies, we show that a NADPH oxidase 2 (NOX2)-containing NADPH oxidase is an essential regulator of RSV-induced NF-kappaB activation. Molecular analyses revealed that NOX2 acts upstream of both the phosphorylation of IkappaBalpha at Ser(32) and of p65 at Ser(536) in A549 and normal human bronchial epithelial cells. Similar results were obtained in the context of infection by Sendai virus, thus demonstrating that the newly identified NOX2-dependent NF-kappaB activation pathway is not restricted to RSV among the Paramyxoviridae. These results illustrate a previously unrecognized dual role of NOX2 in the regulation of NF-kappaB in response to RSV and Sendai virus in human AEC.

Identification of human metapneumovirus-induced gene networks in airway epithelial cells by microarray analysis

Human metapneumovirus (hMPV) is a major cause of lower respiratory tract infections in infants, elderly and immunocompromised patients. Little is known about the response to hMPV infection of airway epithelial cells, which play a pivotal role in initiating and shaping innate and adaptive immune responses. In this study, we analyzed the transcriptional profiles of airway epithelial cells infected with hMPV using high-density oligonucleotide microarrays. Of the 47,400 transcripts and variants represented on the Affimetrix GeneChip Human Genome HG-U133 plus 2 array, 1601 genes were significantly altered following hMPV infection. Altered genes were then assigned to functional categories and mapped to signaling pathways. Many up-regulated genes are involved in the initiation of pro-inflammatory and antiviral immune responses, including chemokines, cytokines, type I interferon and interferon-inducible proteins. Other important functional classes up-regulated by hMPV infection include cellular signaling, gene transcription and apoptosis. Notably, genes associated with antioxidant and membrane transport activity, several metabolic pathways and cell proliferation were down-regulated in response to hMPV infection. Real-time PCR and Western blot assays were used to confirm the expression of genes related to several of these functional groups. The overall result of this study provides novel information on host gene expression upon infection with hMPV and also serves as a foundation for future investigations of genes and pathways involved in the pathogenesis of this important viral infection. Furthermore, it can facilitate a comparative analysis of other paramyxoviral infections to determine the transcriptional changes that are conserved versus the one that are specific to individual pathogens.