Effect Of Influenza Virus Infection Research Articles

Defining the kinetic effects of infection with influenza virus A/PR8/34 (H1N1) on sphingosine-1-phosphate signaling in mice by targeted LC/MS

Influenza remains a world-wide health concern, causing 290,000–600,000 deaths and up to 5 million cases of severe illnesses annually. Noticing the host factors that control biological responses, such as inflammatory cytokine secretion, to influenza virus infection is important for the development of novel drugs. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite and has essential biological functions in inflammation. However, the kinetic effects of influenza virus infection on physiological S1P levels and their signaling in multiple tissues remain unknown. In this study, we utilized a mouse model intranasally infected with 50 or 500 plaque forming units (PFU) of A/Puerto Rico/8/34 (H1N1; PR8) virus to investigate how S1P levels and expression of its regulating factors are affected by influenza virus infection by the liquid-chromatography/mass spectrometry and real-time PCR, respectively. The S1P level was significantly high in the plasma of mice infected with 500 PFU of the virus than that in control mice at 6 day-post-infection (dpi). Elevated gene expression of sphingosine kinase-1 (Sphk1), an S1P synthase, was observed in the liver, lung, white adipose tissue, heart, and aorta of infected mice. This could be responsible for the increased plasma S1P levels as well as the decrease in the hepatic S1P lyase (Sgpl1) gene in the infected mice. These results indicate modulation of S1P-signaling by influenza virus infection. Since S1P regulates inflammation and leukocyte migration, it must be worth trying to target this signaling to control influenza-associated symptoms.

Immune Mechanisms in Cardiovascular Diseases Associated With Viral Infection.

Influenza virus infection causes 3–5 million cases of severe illness and 250,000–500,000 deaths worldwide annually. Although pneumonia is the most common complication associated with influenza, there are several reports demonstrating increased risk for cardiovascular diseases. Several clinical case reports, as well as both prospective and retrospective studies, have shown that influenza can trigger cardiovascular events including myocardial infarction (MI), myocarditis, ventricular arrhythmia, and heart failure. A recent study has demonstrated that influenza-infected patients are at highest risk of having MI during the first seven days of diagnosis. Influenza virus infection induces a variety of pro-inflammatory cytokines and chemokines and recruitment of immune cells as part of the host immune response. Understanding the cellular and molecular mechanisms involved in influenza-associated cardiovascular diseases will help to improve treatment plans. This review discusses the direct and indirect effects of influenza virus infection on triggering cardiovascular events. Further, we discussed the similarities and differences in epidemiological and pathogenic mechanisms involved in cardiovascular events associated with coronavirus disease 2019 (COVID-19) compared to influenza infection.

Influenza virus infection affects insulin signaling, fatty acid-metabolizing enzyme expressions, and the tricarboxylic acid cycle in mice

Although the severity of influenza virus infections has been associated with host energy metabolism, the related mechanisms have not yet been clarified. Here we examined the effects of influenza virus infection on host energy metabolism in mice. After infecting mice with intranasal applications of 500 plaque-forming units of A/Puerto Rico/8/34 (H1N1; PR8) virus, the serum levels of most intermediates in the tricarboxylic acid (TCA) cycle and related metabolic pathways were significantly reduced. These data suggest that substrate supply to the TCA cycle is reduced under these conditions, rather than specific metabolic reactions being inhibited. Then, we focused on glucose and fatty acid metabolism that supply substrates to the TCA cycle. Akt phosphorylation following insulin injections was attenuated in the livers of PR8 virus-infected mice. Furthermore, glucose tolerance tests revealed that the PR8 virus-infected mice showed higher blood glucose levels than the vehicle-inoculated control mice. These results suggest that influenza virus infection impairs insulin signaling, which regulates glucose uptake. However, increases in the hepatic expressions of fatty acid-metabolizing enzymes suggest that fatty acids accumulate in liver cells of infected mice. Collectively, our data indicate that influenza virus infection dysregulates host energy metabolism. This line of investigation provides novel insights into the pathogenesis of influenza.

PD-1 IC Inhibition Synergistically Improves Influenza A Virus-Mediated Oncolysis of Metastatic Pulmonary Melanoma

Recently, we showed that infection of primary lung tumor-bearing mice with oncolytic influenza A viruses (IAVs) led to strong virus-induced tumor cell lysis but also to restoration of immune competence of innate immune cells. Murine B16-F10 melanoma cells are known for their high lung tropism and progressive growth. As these cells are also highly permissive for IAVs, we analyzed their oncolytic and immunomodulatory efficiency against pulmonary B16-F10 lung metastases in vivo. IAV infection abrogated the melanoma-mediated immune suppression in the lung and induced a more than 50% cancer cell lysis. The oncolytic effect reached maximal efficacy 3 days post-infection, but it was not sustained over time. In order to maintain the virus-induced anti-tumor effect, mice with melanoma-derived lung cancers were treated in addition to influenza virus infection with an immune checkpoint inhibitor against programmed death-1 receptor (PD-1). The combined IAV and immune checkpoint inhibition (ICI) therapy resulted in a sustained anti-tumor efficacy, keeping the lung melanoma mass at day 12 of IAV infection still reduced by 50% over the control mice. In conclusion, ICI treatment strongly enhanced the oncolytic effect of influenza virus infection, suggesting that combined treatment is a promising approach against metastatic pulmonary melanoma.

The respiratory microbiome and susceptibility to influenza virus infection.

Influenza is a major cause of morbidity and mortality worldwide. However, vaccine effectiveness has been low to moderate in recent years and vaccine coverage remains low, especially in low- and middle-income countries. Supplementary methods of prevention should be explored to reduce the high burden of influenza. A potential target is the respiratory tract microbiome, complex microbial communities which envelop the respiratory epithelium and play an important role in shaping host immunity. Using a household transmission study, we examined whether the nose/throat microbiota was associated with influenza susceptibility among participants exposed to influenza virus in the household. Further, we characterized changes in the nose/throat microbiota to explore whether community stability was influenced by influenza virus infection. Using a generalized linear mixed effects model, we found a nasal/oropharyngeal community state type (CST) associated with decreased susceptibility to influenza. The CST was rare and transitory among young children but a prevalent and stable CST among adults. Using boosting and linear mixed effects models, we found associations between the nose/throat microbiota and influenza also existed at the taxa level, specifically with the relative abundance of Alloprevotella, Prevotella, and Bacteroides oligotypes. We found high rates of change between bacterial community states among both secondary cases and household contacts who were not infected during follow up. Further work is needed to separate the effect of influenza virus infection from the considerable short-term changes that occur even in the absence of virus. Lastly, age was strongly associated with susceptibility to influenza and the nose/throat bacterial community structure. Although additional studies are needed to determine causality, our results suggest the nose/throat microbiome may be a potential target for reducing the burden of influenza.

Heatr9 is upregulated during influenza virus infection in lung alveolar epithelial cells

Abstract Influenza virus infection poses a serious threat to public health. Influenza virus infects lung alveolar epithelial cells in the respiratory tract and utilizes them to produce more virus, spreading the infection. Understanding genes that are dynamically regulated during influenza virus infection may help elucidate essential genes and pathways that affect influenza virus infection. We examined by RNAseq the in vivo gene expression profiles of alveolar epithelial cells sorted from A/Puerto Rico/8/1934-GFP (PR8-GFP) expressing influenza virus infected mice. We identified a novel influenza virus-induced gene, Heatr9 (also known as Gm11435), that was upregulated by >200-fold in vivo in mouse alveolar epithelial cells. The upregulation of Heatr9 by influenza virus was further confirmed in vitro in PR8-GFP influenza virus infected human lung A549 cells. In vivo Heatr9 upregulation was found to be an indirect effect of influenza virus infection as bystander alveolar epithelial cells in lungs exhibited similar levels of Heatr9 induction as directly infected cells. Furthermore, supernatants of influenza virus infected A549 cells were capable of potently inducing Heatr9 mRNA even in the absence of infection. To identify factors that upregulate Heatr9 we examined the effect of cytokines on Heatr9 expression in vitro. Heatr9 expression was not induced by type I IFN, TNFα, and IL-1β alone in A549 cell, however when used in combination IFNβ and TNFα or IFNβ and IL-1β potently induced Heatr9 mRNA. Currently, we are generating Heatr9 deficient cell lines to examine the function of this gene in infection. In summary, we have identified Heatr9 as a cytokine-induced gene during influenza virus infection, the function of which has a yet to be determined.

Cohort profile: China respiratory illness surveillance among pregnant women (CRISP), 2015–2018

PurposeWe established the China Respiratory Illness Surveillance among Pregnant women (CRISP) to conduct active surveillance for influenza-associated respiratory illness during pregnancy in China from 2015 to 2018. Among annual cohorts...

Metabolic pathways of lung inflammation revealed by high-resolution metabolomics (HRM) of H1N1 influenza virus infection in mice.

Influenza is a significant health concern worldwide. Viral infection induces local and systemic activation of the immune system causing attendant changes in metabolism. High-resolution metabolomics (HRM) uses advanced mass spectrometry and computational methods to measure thousands of metabolites inclusive of most metabolic pathways. We used HRM to identify metabolic pathways and clusters of association related to inflammatory cytokines in lungs of mice with H1N1 influenza virus infection. Infected mice showed progressive weight loss, decreased lung function, and severe lung inflammation with elevated cytokines [interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ] and increased oxidative stress via cysteine oxidation. HRM showed prominent effects of influenza virus infection on tryptophan and other amino acids, and widespread effects on pathways including purines, pyrimidines, fatty acids, and glycerophospholipids. A metabolome-wide association study (MWAS) of the aforementioned inflammatory cytokines was used to determine the relationship of metabolic responses to inflammation during infection. This cytokine-MWAS (cMWAS) showed that metabolic associations consisted of distinct and shared clusters of 396 metabolites highly correlated with inflammatory cytokines. Strong negative associations of selected glycosphingolipid, linoleate, and tryptophan metabolites with IFN-γ contrasted strong positive associations of glycosphingolipid and bile acid metabolites with IL-1β, TNF-α, and IL-10. Anti-inflammatory cytokine IL-10 had strong positive associations with vitamin D, purine, and vitamin E metabolism. The detailed metabolic interactions with cytokines indicate that targeted metabolic interventions may be useful during life-threatening crises related to severe acute infection and inflammation.

Regulation of Matrix Metalloproteinases-2 and -9 Gene Expression in Cultured Human Fetal Membrane Cells by Influenza Virus Infection.

In order to understand a possible etiology of adverse pregnancy outcomes associated with intrauterine influenza virus infection, we examined the effect of influenza virus infection on gene expression of matrix metalloproteinases (MMPs) in cultured amnion epithelial, amnion mesenchymal and chorion trophoblast cells prepared from human fetal membrane tissues by gelatin zymography, Western blotting and reverse transcriptase-PCR. The cells were infected with influenza A (H1N1) virus. The levels of pro-MMP-9 activity in culture supernatants of three types of cells were increased during the period of 24-48 h after the virus infection as compared to those of mock infection. Chorion trophoblast cells spontaneously released a much greater level of pro-MMP-2 activity than amnion epithelial and amnion mesenchymal cells. The cleavage of pro-MMP-2 into an active intermediate form was enhanced in chorion trophoblast cells by the virus infection. The activity levels of MMP-2 and MMP-9 in culture supernatants were consistent with their protein levels. The virus infection induced the mRNA expression of MMP-9, but not MMP-2, in three types of cells. These results suggest that influenza virus infection induces the gene expression of MMP-9 and the cleavage of pro-MMP-2 into an active intermediate form in human fetal membrane cells, resulting in weakening of the membranes through extracellular matrix degradation. Therefore, it is possible that the regulation of MMPs gene expression in fetal membrane cells by influenza virus infection is implicated in a part of the etiology of adverse pregnancy outcomes associated with intrauterine infection with the virus.

Influenza virus infection in pregnancy: a review.

Influenza virus infection is very common and a significant cause of morbidity and mortality in specific populations like pregnant women. Following the 2009 pandemic, several reports on the effects of influenza virus infection on maternal health and pregnancy outcome have been published. Also the safety and efficacy of antiviral treatment and vaccination of pregnant women have been studied. In this review, we have analyzed and summarized these data. To provide information on the influence of influenza virus infection during pregnancy on maternal health and pregnancy outcome and on the effect of treatment and vaccination. We have searched Medline, Embase and the Cochrane Library. We used influenza, influenz*, pregnancy and pregnan* as search terms. In total, 294 reports were reviewed and judged according to the STROBE guidelines or CONSORT statement. In all, 100 studies, published between 1961 and 2015, were included. Compared to the general population, pregnant women are more often hospitalized and admitted to an intensive care unit due to influenza virus infection. For hospitalized patients, increased rates of preterm birth and fetal/neonatal death are reported. Early treatment with oseltamivir is associated with a reduced risk of severe disease. Vaccination of pregnant women is safe and reduces maternal and neonatal morbidity. There is level 2b evidence that maternal health and pregnancy outcome can be severely affected by influenza virus infection. Antiviral treatment may diminish these effects and vaccination protects pregnant women and neonates from infection (level of evidence 2b and 1b, respectively).

Effect of influenza virus infection on key metabolic enzyme activities in MDCK cells

BackgroundInfluenza, or “flu”, is an upper respiratory tract infectioncaused by a virus belonging to the family ofOrthomyxo-viridae. Influenza can pose a serious risk to the health ofmainly the elderly, the very young, and to people suffer-ing from medical conditions (e.g. weak immune system).For example, seasonal influenza strains are fatal to morethan 50,000 people annually in the United States alone[1]. The most effective measure for preventing influenza-related morbidity and mortality is annual vaccination.Seasonal influenza vaccines are almost exclusively pro-duced using the traditional egg-based manufacturing pro-cess. However, the main limitation of egg-basedtechnology (especially in the case of a pandemic) is thetime-consuming production process (~6 months).Furthermore, people with serious egg allergy cannot bevaccinated when trace amounts of egg protein remain inthe final formulation. Therefore, new production pro-cesses using continuous cell lines for influenza vaccinemanufacturing are currently being established [2].Influenza viruses take advantage of the host cell meta-bolism to replicate their genetic material and to synthe-size viral proteins. The influenza virus particle consistsof three major parts: the ribonucleocapsid, the matrixprotein M1, and the envelope, which is derived from theplasma membrane of the host cell. The lipid bilayer con-tains the ion channel protein M2 and the immunogenicglycoproteins hemagglutinin and neuraminidase [3]. Thereplication cycle of influenza viruses including entry,uncoating, genome transcription and replication, assem-bly and release has been studied extensively with type Astrains [4]. So far, only few studies have characterizedthe influence of influenza infection on the centralcarbon metabolism of host cells [5]. Madin-Darbycanine kidney (MDCK) cells are considered a suitablesubstrate for cell culture-based influenza vaccine manu-facturing [2,6]. In this study, key metabolic enzymeactivities were analyzed in MDCK cells infected with aninfluenza A virus strain to improve our understandingof virus-host cell interaction and cell response.Materials and methodsAll chemicals and enzymes were purchased from Sigma(Taufkirchen, Germany) or Roche (Mannheim, Ger-many). Adherent MDCK cells obtained from theECACC (No. 84121903) were routinely cultured in 6-well plates containing 4 mL of GMEM-based medium(2 mM glutamine, 30 mM glucose, 10 % (v/v) fetal calfserum, 2 g/L peptone, 48 mM NaHCO

Using Bioluminescent Imaging to Investigate Synergism Between <em>Streptococcus pneumoniae</em> and Influenza A Virus in Infant Mice

During the 1918 influenza virus pandemic, which killed approximately 50 million people worldwide, the majority of fatalities were not the result of infection with influenza virus alone. Instead, most individuals are thought to have succumbed to a secondary bacterial infection, predominately caused by the bacterium Streptococcus pneumoniae (the pneumococcus). The synergistic relationship between infections caused by influenza virus and the pneumococcus has subsequently been observed during the 1957 Asian influenza virus pandemic, as well as during seasonal outbreaks of the virus (reviewed in (1, 2)). Here, we describe a protocol used to investigate the mechanism(s) that may be involved in increased morbidity as a result of concurrent influenza A virus and S. pneumoniae infection. We have developed an infant murine model to reliably and reproducibly demonstrate the effects of influenza virus infection of mice colonised with S. pneumoniae. Using this protocol, we have provided the first insight into the kinetics of pneumococcal transmission between co-housed, neonatal mice using in vivo imaging.

Using Bioluminescent Imaging to Investigate Synergism Between <em>Streptococcus pneumoniae</em> and Influenza A Virus in Infant Mice

During the 1918 influenza virus pandemic, which killed approximately 50 million people worldwide, the majority of fatalities were not the result of infection with influenza virus alone. Instead, most individuals are thought to have succumbed to a secondary bacterial infection, predominately caused by the bacterium Streptococcus pneumoniae (the pneumococcus). The synergistic relationship between infections caused by influenza virus and the pneumococcus has subsequently been observed during the 1957 Asian influenza virus pandemic, as well as during seasonal outbreaks of the virus (reviewed in 1, 2). Here, we describe a protocol used to investigate the mechanism(s) that may be involved in increased morbidity as a result of concurrent influenza A virus and S. pneumoniae infection. We have developed an infant murine model to reliably and reproducibly demonstrate the effects of influenza virus infection of mice colonised with S. pneumoniae. Using this protocol, we have provided the first insight into the kinetics of pneumococcal transmission between co-housed, neonatal mice using in vivo imaging 3.

Metabolic effects of influenza virus infection in cultured animal cells: Intra- and extracellular metabolite profiling

BackgroundMany details in cell culture-derived influenza vaccine production are still poorly understood and approaches for process optimization mainly remain empirical. More insights on mammalian cell metabolism after a viral infection could give hints on limitations and cell-specific virus production capacities. A detailed metabolic characterization of an influenza infected adherent cell line (MDCK) was carried out based on extracellular and intracellular measurements of metabolite concentrations.ResultsFor most metabolites the comparison of infected (human influenza A/PR/8/34) and mock-infected cells showed a very similar behavior during the first 10-12 h post infection (pi). Significant changes were observed after about 12 h pi: (1) uptake of extracellular glucose and lactate release into the cell culture supernatant were clearly increased in infected cells compared to mock-infected cells. At the same time (12 h pi) intracellular metabolite concentrations of the upper part of glycolysis were significantly increased. On the contrary, nucleoside triphosphate concentrations of infected cells dropped clearly after 12 h pi. This behaviour was observed for two different human influenza A/PR/8/34 strains at slightly different time points.ConclusionsComparing these results with literature values for the time course of infection with same influenza strains, underline the hypothesis that influenza infection only represents a minor additional burden for host cell metabolism. The metabolic changes observed after12 h pi are most probably caused by the onset of apoptosis in infected cells. The comparison of experimental data from two variants of the A/PR/8/34 virus strain (RKI versus NIBSC) with different productivities and infection dynamics showed comparable metabolic patterns but a clearly different timely behavior. Thus, infection dynamics are obviously reflected in host cell metabolism.

Current and Future Anti-Influenza Virus Drugs

In 2009, we have been experiencing a new pandemic of novel influenza virus type A (H1N1) infection. The human beings still face the threat of highly pathogenic avian influenza A (H5N1) virus. Many patients with influenza virus infection have died due to severe complications even though receiving intensive care. This suggests the need for new treatment strategies of severe influenza-associated complications. In cases of severe influenza-associated complications, pathological manifestations are as a result of complex biological consequences, such as apoptosis induction, macrophage activation, oxidative damage and increased production of pro-inflammatory cytokines. Recent studies have revealed that the pathogenesis of severe influenza-associated complications involves not only the virus replication-mediated apoptotic cell death in the infected cells but also non-infected cell injury by toxicity of reactive oxygen species derived from macro- phages phagocytosing apoptotic cells, and that pro-inflammatory cytokines produced by the virus-infected host cells play a critical role in the activation of macrophages. These findings provide a possibility that an agent with antiviral and antioxidant activities can be a drug of choice for the treatment of patients with severe influenza-associated complications. Selected antioxidants, such as pyrrolidine dithiocarbamate, N-acetyl-L-cysteine, glutathione, nordihydroguaiaretic acid, thujaplicin and certain types of flavonoids, possess both activities. The combination of antioxidants, such as superoxide dismutase and N-acetyl-L-cysteine, with antiviral drug ribavirin synergistically reduced the lethal effect of influenza virus infection. Accumulating a number of evidence highlights a potential of selected antioxidants for treatment of severe influenza-associated complications and a possibility that combination of antioxidants with current anti-influenza drugs can improve conventional influenza chemotherapy.

Interaction of Respiratory Dendritic cells with Influenza Virus Infection in vitro (43.44)

Abstract Influenza A virus is a major cause of infection of the respiratory tract worldwide. Approximately 10–20% of U.S. population is estimated to be infected by this virus each year. Respiratory tract dendritic cells (RDC) are believed to play a major role as antigen presenting cells in initiating adaptive immune response to influenza virus infection. We have examined the effect of influenza virus infection of purified RDC in vitro at different MOI (Multiplicity of Infection) on virus protein expression, co-stimulatory molecules expression, and cytokines production. We found that there is not only an MOI dependent increase in the percentage of infected RDC, but also the infection of RDC at high MOI results in higher level and accelerated viral protein synthesis at early time post infection. Production of tested cytokines and chemokines by RDC increases with increasing of MOI except for IL-12 p40. Furthermore, we found that at high MOI total RDCs can be divided to several populations based on CD40 and influenza nucleoprotein (NP) expression: CD40high NPlow, CD40low NPhigh, and CD40negNPnegDCs. In conclusion, our results suggest that there is a diverse response of RDC to influenza virus at different MOI as reflected by their susceptibility to infection and cytokine production. These results may provide insight into how RDC modulate host response in the lung to influenza virus infection. (Support: USPHS grant, NIH AI-15608, HL-33391,HL-71875)

The many faces of the hygiene hypothesis

About 15 years have gone by since Strachan first proposed the idea that infections and unhygienic contact might confer protection against the development of allergic illnesses. The so-called hygiene hypothesis has ever since undergone numerous more or less subtle modifications by various researchers in the fields of epidemiology, clinical science, and immunology. Three major tracts have developed exploring the role of overt viral and bacterial infections, the significance of environmental exposure to microbial compounds, and the effect of both on underlying responses of the innate and adaptive immunity. To date, a truly unifying concept has not yet emerged, but various pieces of a complex interplay between immune responses of the host, characteristics of the invading microorganism, the level and variety of the environmental exposure, and the interactions between a genetic background and a range of exposures becomes apparent. These influences are discussed as determinants for a number of complex allergic illnesses in this review, while we attempt to pay attention to the importance of different phenotypes, namely of the asthma syndrome. Even if today practical implications cannot directly be deduced from these findings, there is great potential for the development of novel preventive and therapeutic strategies in the future.

ウイルスとインターフェロン ４．インフルエンザウイルス感染細胞における宿主遺伝子の発現

The NS1 protein of influenza virus shuts off host gene expression by inhibiting the polyadenylation-site cleavage of host pre-mRNAs, resulting in a general decline in cellular protein synthesis. On the other hand, an activation of several host genes related to host antiviral defense such as interferon- alpha/beta, MxA, 2',5'-oligoadenylate synthetase, and Fas occures upon infection. Therefore, balance of the shut-off and the activation of cellular genes during virus growth may be crucial in determining the outcome of infection. To obtain a comprehensive view of the global effects of influenza virus infection on human respiratory epithelial cells at the cytoplasmic mRNA level, we performed oligo DNA microarray analysis using GeneChip arrays (Affymetrix). In NCl-H292 cells infected with A/Udorn/72 virus, more than 4-fold increase of expression level was observed for 164 genes at 12 h pi. Approximately 60% of the virus-stimulated genes (VSGs) were also stimulated with interferon-beta treatment and contained the genes known to possess antiviral activity. Interestingly, majority of the VSGs were stimulated before induction of interferons, suggesting that the stimulation of the VSGs during early phase of infection is not mediated by interferons, but it is triggered from within by the virus infection.

Enhanced resistancy of thioredoxin-transgenic mice against influenza virus-induced pneumonia

Thioredoxin (TRX) is a small redox-active protein with anti-oxidant effect and redox-regulating functions. Using TRX transgenic (Tg) mice in which human TRX is overexpressed systemically under the control of β-actin promoter, the effects of influenza virus infection were examined in TRX Tg mice and wild type C57BL/6 mice. (1) Median lethal dose (LD 50) against influenza virus infection in wild-type C57BL/6 mice was 10 −5.3 dilution, while that of TRX Tg mice was 10 −4.2 dilution. Thus, TRX Tg mice were more resistant against the virus infection than wild-type mice. (2) The body weights of wild-type mice 7 days after infection with a sublethal dose of the virus (10 −6 dilution) decreased significantly, whereas those of TRX Tg mice increased slightly. (3) Histopathology of the lung at 3 weeks after sublethal infection of influenza virus showed that severe alveolar or bronchiolar destruction was observed in wild-type mice, while mild viral pneumonia was seen in the TRX Tg mice. (4) Local (IgA) and systemic (IgG) antibody productions against influenza virus hemagglutinin in mice surviving 3 weeks after infection were similar between wild-type and TRX Tg mice. These results indicate that overexpression of TRX in Tg mice suppresses the inflammatory overshoot of viral pneumonia caused by influenza virus infection, resulting in the reduction of mortality without affecting the host's systemic immune responses to the infection. TRX may play some important roles in regulating the inflammatory process in the primary host defense against infection.

Dose-dependent changes in influenza virus-infected dendritic cells result in increased allogeneic T-cell proliferation at low, but not high, doses of virus.

During the acute phase of infection with influenza A virus, the degree of lymphopenia correlates with severity of disease. Factors that contribute to T-cell activation during influenza virus infection may contribute to this observation. Since the immune response is initiated when dendritic cells (DC) interact with T cells, we have established an in vitro system to examine the effects of influenza virus infection on DC function. Our results show that allogeneic T-cell proliferation was dependent on the dose of A/PR/8/34 used to infect DC, with enhanced responses at low, but not high, multiplicities of infection. The lack of enhancement at high virus doses was not primarily due to the increased rate of DC apoptosis, but required viral replication and neuraminidase (NA) activity. Clusters that formed between DC or between DC and T cells were also dependent on the viral dose. This change in cellular interaction may oppose T-cell proliferation in response to DC infected with high doses of PR8, since the increased contact between DC resulted in the exclusion of T cells. The enhanced alloreactive T-cell response was restored by neutralization of transforming growth factor beta1 (TGF-beta1). It is likely that NA present on viral particles released from DC infected with high doses of PR8 activates TGF-beta1. Future studies will determine the mechanism by which TGF-beta1 modifies the in vitro T-cell response and address the contribution of this cytokine to the lymphopenia observed in severe disease.