Infection of macrophages by influenza A virus: characteristics of tumour necrosis factor-alpha (TNF alpha) gene expression

Influenza A viruses limit NLRP3-NEK7-complex formation and pyroptosis in human macrophages

Pyroptosis is a fulminant form of macrophage cell death, contributing to release of pro-inflammatory cytokines. In humans, it depends on caspase 1/4-activation of gasdermin D and is characterized by the release of cytoplasmic content. Pathogens apply strategies to avoid or antagonize this host response. We demonstrate here that a small accessory protein (PB1-F2) of contemporary H5N1 and H3N2 influenza A viruses (IAV) curtails fulminant cell death of infected human macrophages. Infection of macrophages with a PB1-F2-deficient mutant of a contemporary IAV resulted in higher levels of caspase-1 activation, cleavage of gasdermin D, and release of LDH and IL-1β. Mechanistically, PB1-F2 limits transition of NLRP3 from its auto-repressed and closed confirmation into its active state. Consequently, interaction of a recently identified licensing kinase NEK7 with NLRP3 is diminished, which is required to initiate inflammasome assembly.

The endotoxin-induced pulmonary inflammatory response is enhanced during the acute phase of influenza infection

Background

Influenza infections are often complicated by secondary infections, which are associated with high morbidity and mortality, suggesting that influenza profoundly influences the immune response towards a subsequent pathogenic challenge. However, data on the immunological interplay between influenza and secondary infections are equivocal, with some studies reporting influenza-induced augmentation of the immune response, whereas others demonstrate that influenza suppresses the immune response towards a subsequent challenge. These contrasting results may be due to the use of various types of live bacteria as secondary challenges, which impedes clear interpretation of causal relations, and to differences in timing of the secondary challenge relative to influenza infection. Herein, we investigated whether influenza infection results in an enhanced or suppressed innate immune response upon a secondary challenge with bacterial lipopolysaccharide (LPS) in either the acute or the recovery phase of infection.

Methods

Male C57BL/6J mice were intranasally inoculated with 5 × 10³ PFU influenza virus (pH1N1, strain A/Netherlands/602/2009) or mock treated. After 4 (acute phase) or 10 (recovery phase) days, 5 mg/kg LPS or saline was administered intravenously, and mice were sacrificed 90 min later. Cytokine levels in plasma and lung tissue, and lung myeloperoxidase (MPO) content were determined.

Results

LPS administration 4 days after influenza infection resulted in a synergistic increase in TNF-α, IL-1β, and IL-6 concentrations in lung tissue, but not in plasma. This effect was also observed 10 days after influenza infection, albeit to a lesser extent. LPS-induced plasma levels of the anti-inflammatory cytokine IL-10 were enhanced 4 days after influenza infection, whereas a trend towards increased pulmonary IL-10 concentrations was found. LPS-induced increases in pulmonary MPO content tended to be enhanced as well, but only at 4 days post-infection.

Conclusions

An LPS challenge in the acute phase of influenza infection results in an enhanced pulmonary pro-inflammatory innate immune response. These data increase our insight on influenza-bacterial interplay. Combing data of the present study with previous findings, it appears that this enhanced response is not beneficial in terms of protection against secondary infections, but rather damaging by increasing immunopathology.

Patterns in Bacterial- and Viral-Induced Immunosuppression and Secondary Infections in the ICU

Immunosuppression renders the host increased susceptible for secondary infections. It is becoming increasingly clear that not only bacterial sepsis, but also respiratory viruses with both severe and mild disease courses such as influenza, respiratory syncytial virus, and the human rhinovirus may induce immunosuppression. In this review, the current knowledge on (mechanisms of) bacterial- and virus-induced immunosuppression and the accompanying susceptibility toward various secondary infections is described. In addition, the frequently encountered secondary pathogens and their preferred localizations are presented. Finally, future perspectives in the context of the development of diagnostic markers and possibilities for personalized therapy to improve the diagnosis and treatment of immunocompromised patients are discussed.

Interferon gamma modulation of disease manifestation and the local antibody response to alphavirus encephalomyelitis

Infection of mice with Sindbis virus (SINV) produces encephalomyelitis and provides a model for examination of the central nervous system (CNS) immune response to alphavirus infection. Clearance of infectious virus is accomplished through a cooperative effort between SINV-specific antibody and IFN-γ, but the regulatory interactions are poorly understood. To determine the effects of IFN-γ on clinical disease and the antiviral immune response, C57BL/6 mice lacking IFN-γ (Ifng-/-) or IFN-γ receptor (Ifngr1-/-) were studied in comparison to WT mice. Maximum production of Ifng mRNA and IFN-γ protein in the CNS of WT and Ifngr1-/- mice occurred 5-7 days after infection, with higher levels of IFN-γ in Ifngr1-/- mice. Onset of clinical disease was earlier in mice with impaired IFN-γ signalling, although Ifngr1-/- mice recovered more rapidly. Ifng-/- and Ifngr1-/- mice maintained body weight better than WT mice, associated with better food intake and lower brain levels of inflammatory cytokines. Clearance of infectious virus from the spinal cords was slower, and CNS, but not serum, levels of SINV-specific IgM, IgG2a and IgG2b were lower in Ifngr1-/- and Ifng-/- mice compared to WT mice. Decreased CNS antiviral antibody was associated with lower expression of mRNAs for B-cell attracting chemokines CXCL9, CXCL10 and CXCL13 and fewer B cells in the CNS. Therefore, IFN-γ signalling increases levels of CNS pro-inflammatory cytokines, leading to clinical disease, but synergistically clears virus with SINV-specific antibody at least in part by increasing chemokine production important for infiltration of antibody-secreting B cells into the CNS.

Cytokine and chemokine mRNA expression profiles in BALF cells isolated from pigs single infected or co-infected with swine influenza virus and Bordetella bronchiseptica

Pigs serve as a valuable animal experimental model for several respiratory pathogens, including Swine Influenza Virus (SIV) and Bordetella bronchiseptica (Bbr). To investigate the effect of SIV and Bbr coinfection on cytokine and viral RNA expression, we performed a study in which pigs were inoculated with SIV, Bbr or both pathogens (SIV/Bbr). Our results indicate that Bbr infection alters SIV clearance. Pulmonary lesions in the SIV/Bbr group were more severe when compared to SIV or Bbr groups and Bbr did not cause significant lesions. Broncho-alveolar lavage fluid (BALF) was examined for inflammatory mediators by qPCR. Interferon (IFN)-α, interleukin IL-8, IL-1 peaked in BALF at 2 DPI, while the virus titres and severity of clinical signs were maximal at the same time. Despite its increased expression in co-infected pigs, interferon-α did not enhance SIV clearance, since the viral replication was detected at the same day as the highest IFN levels. The mRNA levels for IFN-α, IL-1β and IL-8 were significantly higher in BALF of co-infected pigs and correlated with enhanced viral RNA titers in lungs, trachea and nasal swabs. Transcription of mRNA for IL-1β was stable in SIV and SIV/Bbr groups throughout all the study. In Bbr group, the levels of mRNAs for IL-1β were significantly higher at 2, 4 and 9 DPI. The mean levels of mRNAs for TNF-α were lower than the levels of other chemokines and cytokines in all infected groups. Transcript levels of IL-10 and IL-4 did not increase at each time points. Overall, SIV replication was increased by Bbr presence and the enhanced production of pro-inflammatory mediators could contribute to the exacerbated pulmonary lesions.

Pathogenesis of influenza-induced acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a fatal complication of influenza infection. In this Review we provide an integrated model for its pathogenesis. ARDS involves damage to the epithelial-endothelial barrier, fluid leakage into the alveolar lumen, and respiratory insufficiency. The most important part of the epithelial-endothelial barrier is the alveolar epithelium, strengthened by tight junctions. Influenza virus targets these epithelial cells, reducing sodium pump activity, damaging tight junctions, and killing infected cells. Infected epithelial cells produce cytokines that attract leucocytes--neutrophils and macrophages--and activate adjacent endothelial cells. Activated endothelial cells and infiltrated leucocytes stimulate further infiltration, and leucocytes induce production of reactive oxygen species and nitric oxide that damage the barrier. Activated macrophages also cause direct apoptosis of epithelial cells. This model for influenza-induced ARDS differs from the classic model, which is centred on endothelial damage, and provides a rationale for therapeutic intervention to moderate host response in influenza-induced ARDS.

Genetic characterization of H1N2 swine influenza virus isolated in China and its pathogenesis and inflammatory responses in mice

In 2009, two H1N2 influenza viruses were isolated from trachea swabs of pigs in Hubei in China. We compared these sequences with the other 18 complete genome sequences of swine H1N2 isolates from China during 2004 to 2010 and undertook extensive analysis of their evolutionary patterns. Six different genotypes - two reassortants between triple reassortant (TR) H3N2 and classical swine (CS) H1N1 virus, three reassortants between TR H1N2, Eurasian avian-like H1N1 swine virus and H9N2 swine virus, and one reassortant between H1N1, H3N2 human virus and CS H1N1 virus - were observed in these 20 swine H1N2 isolates. The TR H1N2 swine virus is the predominant genotype, and the two Hubei H1N2 isolates were located in this cluster. We also used a mouse model to examine the pathogenesis and inflammatory responses of the two isolates. The isolates replicated efficiently in the lung, and exhibited a strong inflammatory response, serious pathological changes and mortality in infected mice. Given the role that swine can play as putative "genetic mixing vessels" and the observed transmission of TR H1N2 in ferrets, H1N2 influenza surveillance in pigs should be increased to minimize the potential threat to public health.

Innate immunity to H5N1 influenza viruses in humans

Avian influenza virus infections in the human population are rare due to their inefficient direct human-to-human transmission. However, when humans are infected, a strong inflammatory response is usually induced, characterized by elevated levels of cytokines and chemokines in serum, believed to be important in the severe pathogenesis that develops in a high proportion of these patients. Extensive research has been performed to understand the molecular viral mechanisms involved in the H5N1 pathogenesis in humans, providing interesting insights about the virus-host interaction and the regulation of the innate immune response by these highly pathogenic viruses. In this review we summarize and discuss the most important findings in this field, focusing mainly on H5N1 virulence factors and their impact on the modulation of the innate immunity in humans.

Inhibitory Effect of TNF-α Produced by Macrophages Stimulated withGrifola frondosaExtract (ME) on the Growth of Influenza A/Aichi/2/68 Virus in MDCK Cells

We investigated the inhibitory effect of the conditioned medium (CM) from P338D1 (D1) cells, a murine macrophage cell line, stimulated for 10 hours with a fixed dose (100 μg/ml) of the extracts from the fruit bodies of Grifola frondosa (ME) or its ultra filtration-based fractions (MFs), on the growth of influenza A/Aichi/2/68 virus in Madin-Darby canine kidney cells. Direct addition of ME and 3 kinds of MFs (MF1, MF2 and MF3) to the infected cells had no obvious inhibitory effect. However, virus yields were reduced in the presence of CMs. Notably, the inhibitory effect of the CM prepared by using MF2 (molecular weight of 30 Kd to 100 Kd) was the strongest (28% reduction compared to the control). RT-PCR and ELISA assays showed that the CMs could induce the expression of TNF-α mRNA in D1 cells leading to production of TNF-α, known as an antiviral cytokine. These findings suggest that ME and MFs (especially MF-2) might induce the production of certain factors, including TNF-α, which are responsible for the inhibition of viral growth in vitro.

Highly pathogenic avian influenza viruses inhibit effective immune responses of human blood-derived macrophages

Systemic infections with HPAIVs, such as H5N1, are characterized by cytokine burst and sepsis. We investigated the role of human monocyte-derived macrophages in these events after infection with different influenza virus strains. Macrophages were infected with low pathogenic H1N1 (PR8) or high pathogenic H7N7 (FPV) and H5N1 (KAN-1) subtypes. Macrophages were found to be nonpermissive for influenza virus propagation. Surprisingly, transcriptome analysis revealed an insufficient innate immune response of macrophages only to HPAIV infections. Induction of inflammatory cytokines, as well as type I IFNs, was significantly attenuated in H5N1- and H7N7-infected cells, contradicting a primary role of macrophages for the cytokine burst. Furthermore, inflammasome activation was impaired significantly in HPAIV-infected macrophages. Interestingly, this finding correlated with a complete suppression of viral protein M2 expression after HPAIV infection, which is known to be involved in influenza viral inflammasome activation. In summary, our data provide first evidences for a strategy of how HPAIVs avoid initial inflammatory responses of macrophages facilitating virus spreading and progression to the systemic stage of disease.

Inhibition of H1N1 influenza A virus growth and induction of inflammatory mediators by the isoquinoline alkaloid berberine and extracts of goldenseal (Hydrastis canadensis)

In this study we tested whether the isoquinoline alkaloid berberine can inhibit the growth of influenza A. Our experiments showed strong inhibition of the growth of H1N1 influenza A strains PR/8/34 or WS/33 in RAW 264.7 macrophage-like cells, A549 human lung epithelial-derived cells and murine bone marrow derived macrophages, but not MDCK canine kidney cells. Studies of the mechanism underlying this effect suggest that berberine acts post-translationally to inhibit virus protein trafficking/maturation which in turn inhibits virus growth. Berberine was also evaluated for its ability to inhibit production of TNF-α and PGE(2) from A/PR/8/34 infected-RAW 264.7 cells. Our studies revealed strong inhibition of production of both mediators and suggest that this effect is distinct from the anti-viral effect. Finally, we asked whether berberine-containing ethanol extracts of goldenseal also inhibit the growth of influenza A and production of inflammatory mediators. We found strong effectiveness at high concentrations, although upon dilution extracts were somewhat less effective than purified berberine. Taken together, our results suggest that berberine may indeed be useful for the treatment of infections with influenza A.

Interleukin-6⁻¹⁷⁴ and tumor necrosis factor α⁻³⁰⁸ polymorphisms enhance cytokine production by human macrophages exposed to respiratory viruses

Interleukin-6⁻¹⁷⁴ (IL-6⁻¹⁷⁴) and tumor necrosis factor α⁻³⁰⁸ (TNFα⁻³⁰⁸) are high-cytokine-producing genotypes that are known to increase the susceptibility to infectious diseases, but their influence on cytokine production induced by respiratory viruses is unknown. We exposed human monocyte-derived macrophages from IL-6⁻¹⁷⁴, TNFα⁻³⁰⁸, and normal genotype donors to different respiratory viruses. Respiratory syncytial virus (RSV) stimulation was associated with higher IL-6 concentrations in IL-6⁻¹⁷⁴ donors than in normal donors (P = 0.015); 2 of 7 (29%) polymorphic donors were poor responders compared with 6 of 7 (86%) normal donors (P = 0.002). Adenovirus, influenza virus, and RSV stimulations were associated with higher TNFα concentrations in TNFα⁻³⁰⁸ donors than in normal donors (P = 0.03, <0.01, <0.01). A similar trend was seen with rhinovirus stimulation, but this was not significant. These results show that IL-6⁻¹⁷⁴ and TNFα⁻³⁰⁸ gene polymorphisms lead to enhanced production of the respective cytokines when exposed to specific respiratory viruses. This, in turn, may influence the susceptibility to, severity of, and recovery from respiratory virus infections, or influence the immune response to and reactogenicity of viral vaccines.

P58(IPK): a novel "CIHD" member of the host innate defense response against pathogenic virus infection

To support their replication, viruses take advantage of numerous cellular factors and processes. Recent large-scale screens have identified hundreds of such factors, yet little is known about how viruses exploit any of these. Influenza virus infection post-translationally activates P58(IPK), a cellular inhibitor of the interferon-induced, dsRNA-activated eIF2alpha kinase, PKR. Here, we report that infection of P58(IPK) knockout mice with influenza virus resulted in increased lung pathology, immune cell apoptosis, PKR activation, and mortality. Analysis of lung transcriptional profiles, including those induced by the reconstructed 1918 pandemic virus, revealed increased expression of genes associated with the cell death, immune, and inflammatory responses. These experiments represent the first use of a mammalian infection model to demonstrate the role of P58(IPK) in the antiviral response. Our results suggest that P58(IPK) represents a new class of molecule, a cellular inhibitor of the host defense (CIHD), as P58(IPK) is activated during virus infection to inhibit virus-induced apoptosis and inflammation to prolong host survival, even while prolonging viral replication.

Avian influenza virus A/HK/483/97(H5N1) NS1 protein induces apoptosis in human airway epithelial cells

Avian H5N1 influenza virus causes a remarkably severe disease in humans, with an overall case fatality rate of greater than 50%. Human influenza A viruses induce apoptosis in infected cells, which can lead to organ dysfunction. To verify the role of H5N1-encoded NS1 in inducing apoptosis, the NS1 gene was cloned and expressed in human airway epithelial cells (NCI-H292 cells). The apoptotic events posttransfection were examined by a terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end-labeling assay, flow cytometric measurement of propidium iodide, annexin V staining, and Western blot analyses with antibodies specific for proapoptotic and antiapoptotic proteins. We demonstrated that the expression of H5N1 NS1 protein in NCI-H292 cells was sufficient to induce apoptotic cell death. Western blot analyses also showed that there was prominent cleavage of poly(ADP-ribose) polymerase and activation of caspase-3, caspase-7, and caspase-8 during the NS1-induced apoptosis. The results of caspase inhibitor assays further confirmed the involvement of caspase-dependent pathways in the NS1-induced apoptosis. Interestingly, the ability of H5N1 NS1 protein to induce apoptosis was much enhanced in cells pretreated with Fas ligand (the time posttransfection required to reach >30% apoptosis was reduced from 24 to 6 h). Furthermore, 24 h posttransfection, an increase in Fas ligand mRNA expression of about 5.6-fold was detected in cells transfected with H5N1 NS1. In conclusion, we demonstrated that the NS1 protein encoded by avian influenza A virus H5N1 induced apoptosis in human lung epithelial cells, mainly via the caspase-dependent pathway, which encourages further investigation into the potential for the NS1 protein to be a novel therapeutic target.

Alveolar Epithelial Cells Direct Monocyte Transepithelial Migration upon Influenza Virus Infection: Impact of Chemokines and Adhesion Molecules

Influenza A virus pneumonia is characterized by severe lung injury and high mortality. Early infection elicits a strong recruitment of monocytes from the peripheral blood across the endo-/epithelial barrier into the alveolar air space. However, it is currently unclear which of the infected resident lung cell populations, alveolar epithelial cells or alveolar macrophages, elicit monocyte recruitment during influenza A virus infection. In the current study, we investigated whether influenza A virus infection of primary alveolar epithelial cells and resident alveolar macrophages would elicit a basal-to-apical monocyte transepithelial migration in vitro. We found that infection of alveolar epithelial cells with the mouse-adapted influenza A virus strain PR/8 strongly induced the release of monocyte chemoattractants CCL2 and CCL5 followed by a strong monocyte transepithelial migration, and this monocytic response was strictly dependent on monocyte CCR2 but not CCR5 chemokine receptor expression. Analysis of the adhesion molecule pathways demonstrated a role of ICAM-1, VCAM-1, integrin-associated protein (CD47), and junctional adhesion molecule-c on the epithelial cell surface interacting with monocyte beta(1) and beta(2) integrins and integrin-associated protein in the monocyte transmigration process. Importantly, addition of influenza A virus-infected alveolar macrophages further enhanced monocyte transmigration across virus-infected epithelium in a TNF-alpha-dependent manner. Collectively, the data show an active role for virus-infected alveolar epithelium in the regulation of CCL2/CCR2-dependent monocyte transepithelial migration during influenza infection that is essentially dependent on both classical beta(1) and beta(2) integrins but also junctional adhesion molecule pathways.

Hemophagocytic lymphohistiocytosis complicating influenza A infection

During the influenza A (H3N2) season of 2003-2004, several influenza-related complications and deaths were reported in children. Hemophagocytic lymphohistiocytosis complicating influenza A infection is very rare. We report a 3-year-old girl who presented with severe pneumonia and hemophagocytic lymphohistiocytosis associated with influenza A infection. Clinicians should be aware of hemophagocytic syndrome as a serious complication of influenza A infection.

Macrophage-mediated inhibitory effect of Zingiber officinale Rosc, a traditional oriental herbal medicine, on the growth of influenza A/Aichi/2/68 virus

The inhibitory effect of Zingiber officinale Rosc (ZOR), an Oriental traditional herbal medicine, on the growth of influenza A/Aichi/2/68 (Aichi) virus was investigated in Madin-Darby canine kidney (MDCK) cells. Direct addition of ZOR (0.1 approximately 100 microg/ml) to the infected cells did not have any inhibitory effect. However, the ZOR-induced conditioned medium (ZOR-CM) of RAW cells, a murine macrophage (Mphi) cell line, exhibited an apparent inhibitory effect on MDCK cells without cytotoxicity. In accordance with the time-dependent inhibitory effect of ZOR-CM, it has been demonstrated that tumor necrosis factor (TNF)-alpha was gradually accumulated in ZOR-CM by the induction of TNF-alpha mRNA expression in ZOR-stimulated RAW cells. Conversely, the inhibitory effect of ZOR-CM was reduced significantly by the removal of TNF-alpha after the formation of an immune complex with anti-TNF-alpha monoclonal antibody. These data suggested that ZOR itself has no inhibitory effect on the growth of influenza virus, but could exert its effect via macrophage activation leading to production of TNF-alpha.

Adenovirus Infection Dramatically Augments Lipopolysaccharide-Induced TNF Production and Sensitizes to Lethal Shock

We observed a remarkable synergism of adenoviruses and LPS in triggering the production of TNF in intact animals. We found that in mice pre-exposed to adenoviruses, LPS injections generated extremely high levels of TNF with altered kinetics. The elevated TNF synthesis stemmed mostly from posttranscriptional up-regulation of TNF production, although transcription of the TNF gene was also induced. Adenoviruses and LPS exhibited a significant but less dramatic synergism in the induction of IL-6, IFN-gamma, and NO. Only marginal changes were detected in the synthesis of a panel of other cytokines. Different serotypes of the virus showed practically identical effects. As deletion mutants lacking indispensable viral genes or UV inactivated virions exhibited similar activities as the infectious, wild-type virus, it seems unlikely that the viral genome plays any significant role in the phenomenon. Published data indicate that other viruses also show some kind of synergism with LPS, although by different cellular mechanisms. T cells and their IFN-gamma production--crucial in the synergism of influenza viruses and LPS--were dispensable in our experiments. We suggest that the phenomenon is probably a general one: an overlap between different molecular mechanisms detecting bacterial and viral pathogens and inducing mediators of nonspecific cell-mediated host defense. The synergism of viruses and LPS (bacteria) could be a concern in medical practice as well as in gene therapy experiments with high doses of recombinant adenoviruses.

Global host immune response: pathogenesis and transcriptional profiling of type A influenza viruses expressing the hemagglutinin and neuraminidase genes from the 1918 pandemic virus

To understand more fully the molecular events associated with highly virulent or attenuated influenza virus infections, we have studied the effects of expression of the 1918 hemagglutinin (HA) and neuraminidase (NA) genes during viral infection in mice under biosafety level 3 (agricultural) conditions. Using histopathology and cDNA microarrays, we examined the consequences of expression of the HA and NA genes of the 1918 pandemic virus in a recombinant influenza A/WSN/33 virus compared to parental A/WSN/33 virus and to an attenuated virus expressing the HA and NA genes from A/New Caledonia/20/99. The 1918 HA/NA:WSN and WSN recombinant viruses were highly lethal for mice and displayed severe lung pathology in comparison to the nonlethal New Caledonia HA/NA:WSN recombinant virus. Expression microarray analysis performed on lung tissues isolated from the infected animals showed activation of many genes involved in the inflammatory response, including cytokine, apoptosis, and lymphocyte genes that were common to all three infection groups. However, consistent with the histopathology studies, the WSN and 1918 HA/NA:WSN recombinant viruses showed increased up-regulation of genes associated with activated T cells and macrophages, as well as genes involved in apoptosis, tissue injury, and oxidative damage that were not observed in the New Caledonia HA/NA:WSN recombinant virus-infected mice. These studies document clear differences in gene expression profiles that were correlated with pulmonary disease pathology induced by virulent and attenuated influenza virus infections.

Fewer CTL, not enhanced NK cells, are sufficient for viral clearance from the lungs of immunocompromised mice

Activation of the aryl hydrocarbon receptor (AhR) causes numerous defects in anti-viral immunity, including suppressed CTL generation and impaired host resistance. However, despite a reduced CTL response, mice that survive infection clear the virus. Therefore, we examined the contribution of NK cells and pro-inflammatory cytokines to viral clearance in influenza virus-infected mice exposed to TCDD, the most potent AhR agonist. Infection caused transient increases in pulmonary TNFalpha, IL-1, and IFNalpha/beta levels, but neither the kinetics nor magnitude of this response was affected by AhR activation. No IL-18 was detected at any time point examined. Exposure to TCDD enhanced NK cell numbers in the lung but did not affect their IFNgamma production. Furthermore, depletion of NK cells did not alter anti-viral cytolytic activity. In contrast, removal of CD8+ T cells ablated virus-specific cytolytic activity. These results demonstrate that the pulmonary CTL response to influenza virus is robust and few CTL are necessary for viral clearance.

Infection of primary human macrophages with hepatitis C virus in vitro: induction of tumour necrosis factor-alpha and interleukin 8

Hepatitis C virus (HCV) has been reported to replicate in monocytes/macrophages in infected patients. However, it is unclear whether macrophages are susceptible to infection in vitro and whether such an infection is consequential. Sera from 26 HCV-infected patients were incubated with primary human macrophages collected from healthy donors. Virus negative strand was detected by a Tth enzyme-based strand-specific assay and virus sequences were analysed by single strand conformation polymorphism (SSCP) and sequencing. Concentrations of the cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1beta, IL-6, IL-8, IL-10 and IL-12p70 were measured in culture supernatants and respective mRNAs were analysed in cell extracts by quantitative RT-PCR. For 15 sera, HCV RNA was detectable in 2- and 3-week cultures from at least one donor. Virus negative strand was detected in 29 % of macrophage samples in this group. In four cases, HCV RNA sequences amplified from macrophages differed from those amplified from sera suggesting evolution during infection. Concentrations of TNF-alpha and IL-8 were found to be significantly higher in supernatants from HCV-infected cultures. In conclusion, these preliminary data suggest that primary human macrophages are susceptible to HCV infection in vitro and this infection is associated with the induction of cytokines TNF-alpha and IL-8.

Procoagulant and inflammatory response of virus-infected monocytes

BACKGROUND

Monocytes play a prominent role in inflammation, coagulation and atherosclerosis by their ability to produce tissue factor (TF) and cytokines. The aim of the present study was to establish whether virus-infected monocytes initiate coagulation. In addition, the production of cytokines by monocytes may accelerate the chronic process of atherosclerosis and may contribute to coronary syndromes by eliciting plaque instability.

MATERIALS AND METHODS

Monocytes were isolated by Vacutainer(R), BD Biosciences, Alphen aan den Rijn, Netherlands and subsequent magnetic cell sorting (MACS(R), Milteny Biotec, Bergish Gladbach, Germany). Coagulation times in normal pooled plasma and Factor VII-deficient plasma were measured after infection with cytomegalovirus (CMV), Chlamydia pneumoniae (Cp) and influenza A\H1N1. Anti-TF antibodies were added to neutralize TF expressed on monocytes. Interleukins (IL) 6, 8 and 10 were measured in the supernatants.

RESULTS

Chlamydia pneumoniae- and CMV-infected monocytes decreased the clotting time by 60%, and influenza-infected monocytes by 19%, as compared to uninfected monocytes. Procoagulant activity was absent when Factor VII-deficient plasma or anti-TF antibodies were used. Monocytes produced both IL-6 and IL-8 after infection with CMV (317 pg mL-1 and 250 pg mL-1) or Cp (733 pg mL-1 and 268 pg mL-1). Similar results were obtained for influenza virus-infected monocytes, but the levels of both cytokines were 3-5-fold higher (1797 pg mL-1 and 725 pg mL-1). Interleukin-10 was not produced by infected monocytes.

CONCLUSION

The procoagulant activity of virus-infected monocytes is TF-dependent. Although influenza infection did not generate a significant reduction in clotting time, the pronounced expression of IL-6 and IL-8 may induce local and/or systemic inflammatory reactions, which may be associated with plaque rupture and atherosclerosis. The lack of production of the anti-inflammatory cytokine IL-10 may even accelerate these processes.

Tumor necrosis factor alpha exerts powerful anti-influenza virus effects in lung epithelial cells

Previous studies have associated influenza virus-induced expression of inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), with influenza pathogenesis in the human respiratory tract and have suggested that alpha and beta interferons are the first cytokines recruited to counteract such infection. However, we report here that TNF-alpha has powerful anti-influenza virus activity. When infected with influenza virus, cultured porcine lung epithelial cells expressed TNF-alpha in a dose-dependent manner. Expression of TNF-alpha was induced only by replicating virus. TNF-alpha showed strong antiviral activity against avian, swine, and human influenza viruses, and the antiviral effect of TNF-alpha was greater than that of gamma or alpha interferon. These findings suggest that TNF-alpha serves as the first line of defense against influenza virus infection in the natural host.

Expression of tumour necrosis factor-alpha is associated with apoptosis in lungs of pigs experimentally infected with porcine reproductive and respiratory syndrome virus

Expression of tumour necrosis factor (TNF)-alpha and its association with apoptosis was examined in lungs from pig experimentally inoculated with porcine reproductive and respiratory syndrome virus (PRRSV). The TNF-alpha nucleic acid was detected in PRRSV-infected alveolar macrophages by reverse transcription-polymerase chain reaction (RT-PCR). The TNF-alpha antigen was detected in alveolar macrophages by immunohistochemisty. DNA fragmentation in apoptotic cells was detected by in situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL). A double-labelling procedure using immunohistochemisty for the detection of PRRSV and the in situ TUNEL assay for the detection of apoptosis demonstrated that a majority of labelled cells were infected with PRRSV or apoptotic, but not both. Apoptotic cells were more abundant than PRRSV-infected cells in all lungs examined. A double-labelling procedure using immunohistochemisty for the detection of TNF-alpha and the in situ TUNEL assay for the detection of apoptosis demonstrated that a majority of labelled cells were apoptotic or for TNF-alpha, but not both. These data suggested that TNF-alpha released from macrophages after infection by PRRSV may induce apoptosis in uninfected bystander cells.

Pathology of fatal human infection associated with avian influenza A H5N1 virus

Eighteen cases of human influenza A H5N1 infection were identified in Hong Kong from May to December 1997. Two of the six fatal cases had undergone a full post-mortem which showed reactive hemophagocytic syndrome as the most prominent feature. Other findings included organizing diffuse alveolar damage with interstitial fibrosis, extensive hepatic central lobular necrosis, acute renal tubular necrosis and lymphoid depletion. Elevation of soluble interleukin-2 receptor, interleukin-6 and interferon-gamma was demonstrated in both patients, whereas secondary bacterial pneumonia was not observed. Virus detection using isolation, reverse transcription-polymerase chain reaction and immunostaining were all negative. It is postulated that in fatal human infections with this avian subtype, initial virus replication in the respiratory tract triggers hypercytokinemia complicated by the reactive hemophagocytic syndrome. These findings suggest that the pathogenesis of influenza A H5N1 infection might be different from that of the usual human subtypes H1-H3.

Cytochrome P450 inactivation by serum from humans with a viral infection and serum from rabbits with a turpentine-induced inflammation: the role of cytokines

Serum from humans with an acute upper respiratory viral infection and from rabbits with turpentine-induced inflammation reduce the catalytic activity of hepatic cytochrome P450 (P450). The aim of this study was to identify the serum mediators responsible for the decrease in P450 activity. Rabbit and human sera were fractionated by size exclusion chromatography and the fractions tested for their ability to reduce the activity and amount of P450 after 4 h of incubation with hepatocytes from turpentine-treated rabbits (H(INF)). Rabbit and human sera decreased P450 activity by around 40% without any change in the amount of CYP1A1 and 1A2 apoproteins. In rabbit serum, the fraction containing proteins of M(r) 23-15 kDa decreased P450 content by 41%, but did not alter the amount of the apoproteins. Anti-IL-6 antibody added to the M(r) 23-15 kDa fraction restored P450 content to 97% of control values, while anti-IL-1beta, TNF-alpha and IFN-gamma antibodies had no effect. Supporting the role of IL-6, incubation of H(INF) in the presence of IL-6 for 4 h reduced P450 content by 40%. In human serum, the fraction containing proteins of M(r) >95 kDa lowered P450 content by 43% without modifying the amounts of CYP1A1/2. Neutralization experiments showed that IFN-gamma, IL-6, and IL-1beta contributed to the decrease in P450 content. In conclusion, the present results demonstrate that IL-6, and IFN-gamma, IL-6 and IL-1beta are the serum mediators released in vivo by a turpentine-induced inflammatory reaction in the rabbit and an upper respiratory viral infection in humans, respectively, inactivating hepatic P450.

Tumor necrosis factor (TNF)-alpha and TNF receptors in viral pathogenesis

Tumor necrosis factor-alpha (TNF-alpha) and TNF receptors (TNFR) are members of the growing TNF ligand and receptor families that are involved in immune regulation. The present report will focus on the role of the prototypic ligand TNF and its two receptors, TNFR1 and TNFR2, in viral pathogenesis. Although TNF was reported years ago to modulate viral infections, recent findings on the molecular pathways involved in TNFR signaling have allowed a better understanding of the molecular interactions between cellular and viral factors within the infected cell. The interactions of viral proteins with intracellular components downstream of the TNFR have highlighted at the molecular level how viruses can manipulate the cellular machinery to escape the immune response and to favor the spread of the infection. We will review here the role of TNF and TNFR in immune response and the role of TNF and TNFR signaling in viral pathogenesis.

Local and systemic cytokine responses during experimental human influenza A virus infection. Relation to symptom formation and host defense

To further understand the role of cytokine responses in symptom formation and host defenses in influenza infection, we determined the levels of IL-1beta, IL-2, IL-6, IL-8, IFN-alpha, TGF-beta, and TNF-alpha in nasal lavage fluid, plasma, and serum obtained serially from 19 volunteers experimentally infected with influenza A/Texas/36/91 (H1N1) and correlated these levels with various measures of infection and illness severity. We found that IL-6 and IFN-alpha levels in nasal lavage fluids peaked early (day 2) and correlated directly with viral titers, temperature, mucus production, and symptom scores. IL-6 elevations were also found in the circulation at this time point. In contrast, TNF-alpha responses peaked later (day 3 in plasma, day 4 in nasal fluids), when viral shedding and symptoms were subsiding. Similarly, IL-8 peaked late in the illness course (days 4-6) and correlated only with lower respiratory symptoms, which also occurred late. None of IL-1beta, IL-2, or TGF-beta levels increased significantly. These data implicate IL-6 and IFN-alpha as key factors both in symptom formation and host defense in influenza.