Viral double-stranded RNA, cytokines, and the flu

Neuroplasticity elicited by peripheral immune challenge with a viral mimetic

Peripheral viral infections are well known to profoundly alter brain function; however detailed mechanisms of this immune-to-brain communication have not been deciphered. This review focuses on studies of cerebral effects of peripheral viral challenge employing intraperitoneal injection of a viral mimetic, polyinosinic-polycytidylic acid (PIC). In this paradigm, PIC challenge induces the acute phase response (APR) characterized by a transient surge of circulating inflammatory factors, primarily IFNβ, IL-6 and CXCL10. The blood-borne factors, in turn, elicit the generation of CXCL10 by hippocampal neurons. Neurons also express the cognate receptor of CXCL10, i.e., CXCR3 implicating the existence of autocrine/paracrine signaling. The CXCL10/CXCR3 axis mediates the ensuing neuroplastic changes manifested as neuronal hyperexcitability, seizure hypersusceptibility, and sickness behavior. Electrophysiological studies revealed that the neuroplastic changes entail the potentiation of excitatory synapses likely at both pre- and postsynaptic loci. Excitatory synaptic transmission is further augmented by PIC challenge-induced elevation of extracellular glutamate that is mediated by astrocytes. In addition, the hyperexcitability of neuronal circuits might involve the repression of inhibitory signaling. Accordingly, CXCL10 released by neurons activates microglia whose processes invade perisomatic inhibitory synapses, resulting in a partial detachment of the presynaptic terminals, and thus, de-inhibition. This process might be facilitated by the cerebral complement system, which is also upregulated and activated by PIC challenge. Moreover, CXCL10 stimulates the expression of neuronal c-fos protein, another index of hyperexcitability. The reviewed studies form a foundation for full elucidation of the fascinating intersection between peripheral viral infections and neuroplasticity. Because the activation of such pathways may constitute a serious comorbidity factor for neuropathological conditions, this research would advance the development of preventive strategies.

Gene Regulation of Neutrophils Mediated Liver and Lung Injury through NETosis in Acute Pancreatitis

Acute pancreatitis (AP) is one of the most common gastrointestinal emergencies, often resulting in self-digestion, edema, hemorrhage, and even necrosis of pancreatic tissue. When AP progresses to severe acute pancreatitis (SAP), it often causes multi-organ damage, leading to a high mortality rate. However, the molecular mechanisms underlying SAP-mediated organ damage remain unclear. This study aims to systematically mine SAP data from public databases and combine experimental validation to identify key molecules involved in multi-organ damage caused by SAP. Retrieve transcriptomic data of mice pancreatic tissue for AP, lung and liver tissue for SAP, and corresponding normal tissue from the Gene Expression Omnibus (GEO) database. Conduct gene differential analysis using Limma and DEseq2 methods. Perform enrichment analysis using the clusterProfiler package in R software. Score immune cells and immune status in various organs using single-sample gene set enrichment analysis (ssGSEA). Evaluate mRNA expression levels of core genes using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. Validate serum amylase, TNF-α, IL-1β, and IL-6 levels in peripheral blood using enzyme-linked immunosorbent assay (ELISA), and detect the formation of neutrophil extracellular traps (NETs) in mice pancreatic, liver, and lung tissues using immunofluorescence. Differential analysis reveals that 46 genes exhibit expression dysregulation in mice pancreatic tissue for AP, liver and lung tissue for SAP, as well as peripheral blood in humans. Functional enrichment analysis indicates that these genes are primarily associated with neutrophil-related biological processes. ROC curve analysis indicates that 12 neutrophil-related genes have diagnostic potential for SAP. Immune infiltration analysis reveals high neutrophil infiltration in various organs affected by SAP. Single-cell sequencing analysis shows that these genes are predominantly expressed in neutrophils and macrophages. FPR1, ITGAM, and C5AR1 are identified as key genes involved in the formation of NETs and activation of neutrophils. qPCR and IHC results demonstrate upregulation of FPR1, ITGAM, and C5AR1 expression in pancreatic, liver, and lung tissues of mice with SAP. Immunofluorescence staining shows increased levels of neutrophils and NETs in SAP mice. Inhibition of NETs formation can alleviate the severity of SAP as well as the levels of inflammation in the liver and lung tissues. This study identified key genes involved in the formation of NETs, namely FPR1, ITGAM, and C5AR1, which are upregulated during multi-organ damage in SAP. Inhibition of NETs release effectively reduces the systemic inflammatory response and liver-lung damage in SAP. This research provides new therapeutic targets for the multi-organ damage associated with SAP.

Understanding the Variability of Certain Biological Properties of H1N1pdm09 Influenza Viruses

The influenza virus continually evolves because of the high mutation rate, resulting in dramatic changes in its pathogenicity and other biological properties. This study aimed to evaluate the evolution of certain essential properties, understand the connections between them, and find the molecular basis for the manifestation of these properties. To that end, 21 A(H1N1)pdm09 influenza viruses were tested for their pathogenicity and toxicity in a mouse model with a ts/non-ts phenotype manifestation and HA thermal stability. The results demonstrated that, for a strain to have high pathogenicity, it must express a toxic effect, have a non-ts phenotype, and have a thermally stable HA. The ancestor A/California/07/2009 (H1N1)pdm influenza virus expressed the non-ts phenotype, after which the cycling trend of the ts/non-ts phenotype was observed in new strains of A(H1N1)pdm09 influenza viruses, indicating that the ratio of the ts phenotype will increase in the coming years. Of the 21 tested viruses, A/South Africa/3626/2013 had the high pathogenicity in the mouse model. Sequence alignment analysis showed that this virus has three unique mutations in the polymerase complex, two of which are in the PB2 gene and one that is in the PB1 gene. Further study of these mutations might explain the distinguishing pathogenicity.

Intracellular virus sensor MDA5 exacerbates vitiligo by inducing the secretion of chemokines in keratinocytes under virus invasion

Vitiligo is a disfiguring disease featuring chemokines-mediated cutaneous infiltration of autoreactive CD8+ T cells that kill melanocytes. Copious studies have indicated that virus invasion participates in the pathogenesis of vitiligo. IFIH1, encoding MDA5 which is an intracellular virus sensor, has been identified as a vitiligo susceptibility gene. However, the specific role of MDA5 in melanocyte death under virus invasion is not clear. In this study, we first showed that the expression of anti-CMV IgM and MDA5 was higher in vitiligo patients than healthy controls. Then, by using Poly(I:C) to imitate virus invasion, we clarified that virus invasion significantly activated MDA5 and further potentiated the keratinocyte-derived CXCL10 and CXCL16 which are the two vital chemokines for the cutaneous infiltration of CD8+ T cells in vitiligo. More importantly, IFN-β mediated by the MDA5-MAVS-NF-κB/IRF3 signaling pathway orchestrated the secretion of CXCL10 via the JAK1-STAT1 pathway and MDA5-meidiated IRF3 transcriptionally induced the production of CXCL16 in keratinocytes under virus invasion. In summary, our results demonstrate that MDA5 signaling orchestrates the aberrant skin immunity engaging in melanocyte death via mediating CXCL10 and CXCL16 secretion, which supports MDA5 as a potential therapeutic target for vitiligo under virus invasion.

CX3CR1+ monocytes modulate learning and learning-dependent dendritic spine remodeling via TNF-α

Impaired learning and cognitive function often occurs during systemic infection or inflammation. Although activation of the innate immune system has been linked to the behavioral and cognitive effects that are associated with infection, the underlying mechanisms remain poorly understood. Here we mimicked viral immune activation with poly(I:C), a synthetic analog of double-stranded RNA, and longitudinally imaged postsynaptic dendritic spines of layer V pyramidal neurons in the mouse primary motor cortex using two-photon microscopy. We found that peripheral immune activation caused dendritic spine loss, impairments in learning-dependent dendritic spine formation and deficits in multiple learning tasks in mice. These observed synaptic alterations in the cortex were mediated by peripheral-monocyte-derived cells and did not require microglial function in the central nervous system. Furthermore, activation of CX₃CR1^highLy6C^low monocytes impaired motor learning and learning-related dendritic spine plasticity through tumor necrosis factor (TNF)-α-dependent mechanisms. Taken together, our results highlight CX₃CR1^high monocytes and TNF-α as potential therapeutic targets for preventing infection-induced cognitive dysfunction.

Brain Endothelial- and Epithelial-Specific Interferon Receptor Chain 1 Drives Virus-Induced Sickness Behavior and Cognitive Impairment

Sickness behavior and cognitive dysfunction occur frequently by unknown mechanisms in virus-infected individuals with malignancies treated with type I interferons (IFNs) and in patients with autoimmune disorders. We found that during sickness behavior, single-stranded RNA viruses, double-stranded RNA ligands, and IFNs shared pathways involving engagement of melanoma differentiation-associated protein 5 (MDA5), retinoic acid-inducible gene 1 (RIG-I), and mitochondrial antiviral signaling protein (MAVS), and subsequently induced IFN responses specifically in brain endothelia and epithelia of mice. Behavioral alterations were specifically dependent on brain endothelial and epithelial IFN receptor chain 1 (IFNAR). Using gene profiling, we identified that the endothelia-derived chemokine ligand CXCL10 mediated behavioral changes through impairment of synaptic plasticity. These results identified brain endothelial and epithelial cells as natural gatekeepers for virus-induced sickness behavior, demonstrated tissue specific IFNAR engagement, and established the CXCL10-CXCR3 axis as target for the treatment of behavioral changes during virus infection and type I IFN therapy.

Heat stroke

Heat stroke is a life-threatening condition clinically diagnosed as a severe elevation in body temperature with central nervous system dysfunction that often includes combativeness, delirium, seizures, and coma. Classic heat stroke primarily occurs in immunocompromised individuals during annual heat waves. Exertional heat stroke is observed in young fit individuals performing strenuous physical activity in hot or temperature environments. Long-term consequences of heat stroke are thought to be due to a systemic inflammatory response syndrome. This article provides a comprehensive review of recent advances in the identification of risk factors that predispose to heat stroke, the role of endotoxin and cytokines in mediation of multi-organ damage, the incidence of hypothermia and fever during heat stroke recovery, clinical biomarkers of organ damage severity, and protective cooling strategies. Risk factors include environmental factors, medications, drug use, compromised health status, and genetic conditions. The role of endotoxin and cytokines is discussed in the framework of research conducted over 30 years ago that requires reassessment to more clearly identify the role of these factors in the systemic inflammatory response syndrome. We challenge the notion that hypothalamic damage is responsible for thermoregulatory disturbances during heat stroke recovery and highlight recent advances in our understanding of the regulated nature of these responses. The need for more sensitive clinical biomarkers of organ damage is examined. Conventional and emerging cooling methods are discussed with reference to protection against peripheral organ damage and selective brain cooling.

Cerebral Response to Peripheral Challenge with a Viral Mimetic

It has been well established that peripheral inflammation resulting from microbial infections profoundly alters brain function. This review focuses on experimental systems that model cerebral effects of peripheral viral challenge. The most common models employ the induction of the acute phase response via intraperitoneal injection of a viral mimetic, polyinosinic-polycytidylic acid (PIC). The ensuing transient surge of blood-borne inflammatory mediators induces a "mirror" inflammatory response in the brain characterized by the upregulated expression of a plethora of genes encoding cytokines, chemokines and other inflammatory/stress proteins. These inflammatory mediators modify the activity of neuronal networks leading to a constellation of behavioral traits collectively categorized as the sickness behavior. Sickness behavior is an important protective response of the host that has evolved to enhance survival and limit the spread of infections within a population. However, a growing body of clinical data indicates that the activation of inflammatory pathways in the brain may constitute a serious comorbidity factor for neuropathological conditions. Such comorbidity has been demonstrated using the PIC paradigm in experimental models of Alzheimer's disease, prion disease and seizures. Also, prenatal or perinatal PIC challenge has been shown to disrupt normal cerebral development of the offspring resulting in phenotypes consistent with neuropsychiatric disorders, such as schizophrenia and autism. Remarkably, recent studies indicate that mild peripheral PIC challenge may be neuroprotective in stroke. Altogether, the PIC challenge paradigm represents a unique heuristic model to elucidate the immune-to-brain communication pathways and to explore preventive strategies for neuropathological disorders.

Resveratrol inhibits rhinovirus replication and expression of inflammatory mediators in nasal epithelia

Human rhinoviruses (HRV), the cause of common colds, are the most frequent precipitants of acute exacerbation of asthma and chronic obstructive pulmonary disease, as well as causes of other serious respiratory diseases. No vaccine or antiviral agents are available for the prevention or treatment of HRV infection. Resveratrol exerts antiviral effect against different DNA and RNA viruses. The antiviral effect of a new resveratrol formulation containing carboxymethylated glucan was analyzed in H1HeLa cell monolayers and ex vivo nasal epithelia infected with HRV-16. Virus yield was evaluated by plaque assay and expression of viral capsid proteins by Western blot. IL-10, IFN-β, IL-6, IL-8 and RANTES levels were evaluated by ELISA assay. ICAM-1 was assessed by Western blot and immunofluorescence. Resveratrol exerted a high, dose-dependent, antiviral activity against HRV-16 replication and reduced virus-induced secretion of IL-6, IL-8 and RANTES to levels similar to that of uninfected nasal epithelia. Basal levels of IL-6 and RANTES were also significantly reduced in uninfected epithelia confirming an anti-inflammatory effect of the compound. HRV-induced expression of ICAM-1 was reversed by resveratrol. Resveratrol may be useful for a therapeutic approach to reduce HRV replication and virus-induced cytokine/chemokine production.

Interdependent and independent roles of type I interferons and IL-6 in innate immune, neuroinflammatory and sickness behaviour responses to systemic poly I:C

Type I interferons (IFN-I) are expressed in the brain during many inflammatory and neurodegenerative conditions and have multiple effects on CNS function. IFN-I is readily induced in the brain by systemic administration of the viral mimetic, poly I:C (synthetic double-stranded RNA). We hypothesised that IFN-I contributes to systemically administered poly I:C-induced sickness behaviour, metabolic and neuroinflammatory changes. IFN-I receptor 1 deficient mice (IFNAR1(-/-)) displayed significantly attenuated poly I:C-induced hypothermia, hypoactivity and weight loss compared to WT C57BL/6 mice. This amelioration of sickness was associated with equivalent IL-1β and TNF-α responses but much reduced IL-6 responses in plasma, hypothalamus and hippocampus of IFNAR1(-/-) mice. IFN-β injection induced trivial IL-6 production and limited behavioural change and the poly I:C-induced IFN-β response did not preceed, and would not appear to mediate, IL-6 induction. Rather, IFNAR1(-/-) mice lack basal IFN-I activity, have lower STAT1 levels and show significantly lower levels of several inflammatory transcripts, including stat1. Basal IFN-I activity appears to play a facilitatory role in the full expression of the IL-6 response and activation of the tryptophan-kynurenine metabolism pathway. The deficient IL-6 response in IFNAR1(-/-) mice partially explains the observed incomplete sickness behaviour response. Reconstitution of circulating IL-6 revealed that the role of IFNAR in burrowing activity is mediated via IL-6, while IFN-I and IL-6 have additive effects on hypoactivity, but the role of IFN-I in anorexia is independent of IL-6. Hence, we have demonstrated both interdependent and independent roles for IFN-I and IL-6 in systemic inflammation-induced changes in brain function.

Extracellular dsRNA: its function and mechanism of cellular uptake

Double-stranded RNA (dsRNA) is arguably the most potent viral trigger of innate immune signaling. Its activity has been recognized for over 5 decades, first as a toxin, then as a central component of the interferon system, as an efficient activator of antiviral responses and an immunomodulator for therapeutic applications. Nucleic acid sensing is the main basis for antiviral defense systems throughout the diverse forms of life from bacteria to plants and animals. Pattern recognition receptors of the host defense system not only sense viral dsRNA as a pathogen-associated molecular pattern in infected cells, but also recognize circulating endogenous dsRNA, a nonmicrobial signal, as a danger-associated molecular pattern, often leading to autoimmunity. Despite the effects of extracellular viral and host dsRNA associated with infection and autoimmunity, respectively, the understanding of cellular mechanisms for its recognition and uptake has only been appreciated in recent years. This review presents an overview of this unique form of nucleic acid, addressing its roles in infection, autoimmunity, and host sensing mechanisms. The goal of this review is to highlight the novel findings with a focus on extracellular recognition and uptake by the cell.

Central mediators involved in the febrile response induced by polyinosinic-polycytidylic acid: lack of involvement of endothelins and substance P

The present study evaluated the involvement of interleukin(IL)-1β, tumor necrosis factor-α (TNF-α), IL-6, interferon(IFN)-γ, prostaglandins of the E2 series, endothelins, substance P and opioids within the central nervous system in polyinosinic:polycytidylic acid (Poly I:C)-induced fever in rats. Poly I:C injection induced a febrile response which was reduced by intracerebroventricular administration of the antibodies against TNF-α, IL-6, or IFN-γ, or by IL-1 or μ receptor antagonists. Intraperitoneal injection of indomethacin or oral administration of celecoxib also reduced Poly I:C-induced fever. Poly I:C increased prostaglandin E2 levels in the cerebrospinal fluid of the animals which was also reduced by indomethacin. The intracerebroventricular injection of ETB or NK1 receptor antagonists did not alter Poly I:C-induced fever. These data suggest the involvement of IL-1β, TNF-α, IL-6, IFN-γ, prostaglandin E2, and opioids but not endothelins and substance P on Poly I:C-induced fever.

Prenatal infection affects the neuronal architecture and cognitive function in adult mice

Environmental factors such as prenatal infection are involved in the pathogenic processes of neurodevelopmental psychiatric disorders. In the present study, we administered a viral mimic, polyriboinosinic-polyribocytidylic acid (poly I:C, 20 mg/kg, i.p.), to pregnant B6 mice at gestational day 9.5. Neonates born to these poly I:C-treated dams showed an increase of microglia in the hippocampus, indicating an activation of the immune system in the brains. Moreover, a significant increase in the number of dopamine-producing neurons in the ventral tegmental area was observed in adult male poly I:C offspring compared with age-matched saline offspring. Poly I:C offspring also exhibited hypolocomotor activity in a novel open-field arena but did not display signs of anxiety or depression in the elevated plus maze or the forced swim test, respectively. However, the short-term memory of the poly I:C offspring was impaired in a novel object recognition task. Therefore, the dendritic architecture of granule cells in the dentate gyrus (DG) and pyramidal neurons in the medial prefrontal cortex (mPFC) were examined. The dendritic complexity was reduced in the DG granule cells of the poly I:C offspring and exhibited shorter dendritic length compared with the saline offspring. The density of dendritic spines in the DG granule cells was also decreased in the poly I:C offspring. Furthermore, the dendritic complexity and spine density were reduced in layer II/III mPFC pyramidal neurons of the poly I:C offspring. Together, these data demonstrate impaired short-term memory and altered dendritic architecture in adult poly I:C offspring, which validates the prenatal infection paradigm as a model for neurodevelopmental psychiatric disorders.

Digital imprinting of RNA recognition and processing on a self-assembled nucleic acid matrix

The accelerating progress of research in nanomedicine and nanobiotechnology has included initiatives to develop highly-sensitive, high-throughput methods to detect biomarkers at the single-cell level. Current sensing approaches, however, typically involve integrative instrumentation that necessarily must balance sensitivity with rapidity in optimizing biomarker detection quality. We show here that laterally-confined, self-assembled monolayers of a short, double-stranded(ds)[RNA-DNA] chimera enable permanent digital detection of dsRNA-specific inputs. The action of ribonuclease III and the binding of an inactive, dsRNA-binding mutant can be permanently recorded by the input-responsive action of a restriction endonuclease that cleaves an ancillary reporter site within the dsDNA segment. The resulting irreversible height change of the arrayed ds[RNA-DNA], as measured by atomic force microscopy, provides a distinct digital output for each dsRNA-specific input. These findings provide the basis for developing imprinting-based bio-nanosensors, and reveal the versatility of AFM as a tool for characterizing the behaviour of highly-crowded biomolecules at the nanoscale.

The untranslated regions of classic swine fever virus RNA trigger apoptosis

Classical swine fever virus (CSFV) causes a broad range of disease in pigs, from acute symptoms including high fever and hemorrhages, to chronic disease or unapparent infection, depending on the virus strain. CSFV belongs to the genus Pestivirus of the family Flaviviridae. It carries a single-stranded positive-sense RNA genome. An internal ribosomal entry site (IRES) in the 5' untranslated region (UTR) drives the translation of a single open reading frame encoding a 3898 amino acid long polypeptide chain. The open reading frame is followed by a 3' UTR comprising four highly structured stem-loops. In the present study, a synthetic RNA composed of the 5' and 3' UTRs of the CSFV genome devoid of any viral coding sequence and separated by a luciferase gene cassette (designated 5'UTR-Luc-3'UTR) triggered apoptotic cell death as early as 4 h post-transfection. The apoptosis was measured by DNA laddering analysis, TUNEL assay, annexin-V binding determined by flow cytometry, and by analysis of caspase activation. Contrasting with this, only trace DNA laddering was observed in cells transfected with the individual 5' or 3' UTR RNA; even when the 5' UTR and 3' UTR were co-transfected as separate RNA molecules, DNA laddering did not reach the level induced by the chimeric 5'UTR-Luc-3'UTR RNA. Interestingly, RNA composed of the 5'UTR and of stem-loop I of the 3'UTR triggered much stronger apoptosis than the 5' or 3'UTR alone. These results indicate that the 5' and 3' UTRs act together in cis induce apoptosis. We furthered obtained evidence that the UTR-mediated apoptosis required double-stranded RNA and involved translation shutoff possibly through activation of PKR.

Genome-wide effects of DNA methyltransferase inhibitor on gene expression in double-stranded RNA transfected porcine PK15 cells

Double-stranded RNA (dsRNA) is produced in host cells during viral replication. The effects of DNA demethylation on gene expression in dsRNA transfected swine cells are unclear. The study aims to profile the transcriptome changes which are induced by DNA methyltransferase inhibitor (Aza-CdR) in porcine PK15 cells transfected with viral-like dsRNA (Poly(I:C)). A total of 44, 76 and 952 differentially expressed genes (DEGs) were detected in the cells treated by Poly(I:C) plus Aza-CdR (P+A), Poly(I:C) (P) or Aza-CdR (A) alone compared to the controls (C). Immune response-related pathways are observed in the comparison of A vs. C and P vs. C, and the genes in the pathways were recovered in the comparison of (P+A) vs. C. GO analysis indicated that Aza-CdR has negative regulatory effects on viral reproduction. The results suggest that the stimulant of Poly(I:C) could be regressed by Aza-CdR. These observations provide new insights into the epigenetic regulatory effects on viral replication.

Identification of Host Kinase Genes Required for Influenza Virus Replication and the Regulatory Role of MicroRNAs

Human protein kinases (HPKs) have profound effects on cellular responses. To better understand the role of HPKs and the signaling networks that influence influenza virus replication, a small interfering RNA (siRNA) screen of 720 HPKs was performed. From the screen, 17 HPKs (NPR2, MAP3K1, DYRK3, EPHA6, TPK1, PDK2, EXOSC10, NEK8, PLK4, SGK3, NEK3, PANK4, ITPKB, CDC2L5 (CDK13), CALM2, PKN3, and HK2) were validated as essential for A/WSN/33 influenza virus replication, and 6 HPKs (CDK13, HK2, NEK8, PANK4, PLK4 and SGK3) were identified as vital for both A/WSN/33 and A/New Caledonia/20/99 influenza virus replication. These HPKs were found to affect multiple host pathways and regulated by miRNAs induced during infection. Using a panel of miRNA agonists and antagonists, miR-149* was found to regulate NEK8 expression, miR-548d-3p was found to regulate MAPK1 transcript expression, and miRs -1228 and -138 to regulate CDK13 expression. Up-regulation of miR-34c induced PLK4 transcript and protein expression and enhanced influenza virus replication, while miR-34c inhibition reduced viral replication. These findings identify HPKs important for influenza viral replication and show the miRNAs that govern their expression.

Resveratrol Inhibits respiratory syncytial virus-induced IL-6 production, decreases viral replication, and downregulates TRIF expression in airway epithelial cells

Respiratory syncytial virus (RSV) is the most common pathogen responsible for lower respiratory diseases in children. So far, there is no effective treatment or preventative vaccine available for RSV infection, although ribavirin and dexamethasone are commonly prescribed. Resveratrol has been shown to inhibit the replication of several other viruses, thus the effect of resveratrol on RSV-induced inflammatory mediators in 9HTEo cell cultures was evaluated, and possible mechanisms of action were explored and compared with dexamethasone and ribavirin. Incubation with resveratrol resulted in decreased IL-6 production and partial inhibition of RSV replication. Resveratrol treatment also inhibited virus-induced TIR-domain-containing adapter-inducing interferon-β (TRIF) and TANK binding kinase 1 (TBK1) protein expression. These data demonstrate the ability of resveratrol to inhibit cytokine production by RSV in airway epithelial cells, indicating that it might be a therapeutic agent with both anti-inflammatory and antiviral potential for the treatment of RSV infection.

Olfactory bulb and hypothalamic acute-phase responses to influenza virus: effects of immunization

BACKGROUND

Within hours of intranasal challenge, mouse-adapted H1N1 A/Puerto Rico/8/34 (PR8) influenza genomic RNA is found in the olfactory bulb (OB) and OB pro-inflammatory cytokines are up-regulated. Severing the olfactory tract delays the acute-phase response (APR) and the APR is attenuated by immunization.

OBJECTIVES

To determine if immunization affects OB localization of influenza or the molecular brain mechanisms regulating APR.

METHODS

Male mice were immunized with PR8 influenza, then OB viral RNA, APR, and influenza-related cytokine responses were determined after homologous viral challenge.

RESULTS

Immunization did not prevent influenza OB viral invasion within 24 h of viral challenge. However, it greatly attenuated OB viral RNA 6 days after viral challenge and the APR including hypothermia and body weight loss responses. Within the OB, 24 h after influenza challenge, prior immunization blocked virus-induced up-regulation of toll-like receptor 7 and interferon (IFN) γ mRNAs. At this time, hypothalamic (HT) growth hormone-releasing hormone receptor and tumor necrosis factor-α mRNAs were greatly enhanced in immunized but not in positive control mice. By 6 days after viral challenge, OB and HT mRNAs returned towards baseline values. In the lung, mRNA up-regulation was greater than that in the brain and maximized 6 days after challenge. Lung IFNγ mRNA decreased at 24 h but increased 6 days after challenge in the positive compared to negative controls. Immunization prevented the up-regulation of most of the flu-related mRNAs measured in lungs.

CONCLUSION

Collectively, these data suggest a role for OB and HT involvement in immunization protection against influenza infection.

CD11b/CD18 (Mac-1) is a novel surface receptor for extracellular double-stranded RNA to mediate cellular inflammatory responses

During viral infection, extracellular dsRNA is a potent signaling molecule that activates many innate immune cells, including macrophages. TLR3 is a well-known receptor for extracellular dsRNA, and internalization of extracellular dsRNA is required for endosomal TLR3 activation. Preserved inflammatory responses of TLR3-deficient macrophages to extracellular dsRNA strongly support a TLR3-independent mechanism in dsRNA-mediated immune responses. The present study demonstrated that CD11b/CD18 (Mac-1 [macrophage-1 Ag]), a surface integrin receptor, recognized extracellular dsRNA and induced macrophage immune responses. CD11b deficiency reduced inflammatory cytokine induction elicited by polyinosinic:polycytidylic acid (poly I:C; a synthetic dsRNA) in mouse sera and livers, as well as in cultured peritoneal macrophages. dsRNA-binding assay and confocal immunofluorescence showed that Mac-1, especially the CD11b subunit, interacted and colocalized with poly I:C on the surface of macrophages. Further mechanistic studies revealed two distinct signaling events following dsRNA recognition by Mac-1. First, Mac-1 facilitated poly I:C internalization through the activation of PI3K signaling and enhanced TLR3-dependent activation of IRF3 in macrophages. Second, poly I:C induced activation of phagocyte NADPH oxidase in a TLR3-independent, but Mac-1-dependent, manner. Subsequently, phagocyte NADPH oxidase-derived intracellular reactive oxygen species activated MAPK and NF-κB pathways. Our results indicate that extracellular dsRNA activates Mac-1 to enhance TLR3-dependent signaling and to trigger TLR3-independent, but Mac-1-dependent, inflammatory oxidative signaling, identifying a novel mechanistic basis for macrophages to recognize extracellular dsRNA to regulate innate immune responses. This study identifies Mac-1 as a novel surface receptor for extracellular dsRNA and implicates it as a potential therapeutic target for virus-related inflammatory diseases.

Cd14 SNPs regulate the innate immune response

CD14 is a monocytic differentiation antigen that regulates innate immune responses to pathogens. Here, we show that murine Cd14 SNPs regulate the length of Cd14 mRNA and CD14 protein translation efficiency, and consequently the basal level of soluble CD14 (sCD14) and type I IFN production by murine macrophages. This has substantial downstream consequences for the innate immune response; the level of expression of at least 40 IFN-responsive murine genes was altered by this mechanism. We also observed that there was substantial variation in the length of human CD14 mRNAs and in their translation efficiency. sCD14 increased cytokine production by human dendritic cells (DCs), and sCD14-primed DCs augmented human CD4T cell proliferation. These findings may provide a mechanism for exploring the complex relationship between CD14 SNPs, serum sCD14 levels, and susceptibility to human infectious and allergic diseases.

Phosphatidylinositol-3-kinase (PI3K) is activated by influenza virus vRNA via the pathogen pattern receptor Rig-I to promote efficient type I interferon production

The phosphatidylinositol-3-kinase (PI3K) was identified to be activated upon influenza A virus (IAV) infection. An early and transient induction of PI3K signalling is caused by viral attachment to cells and promotes virus entry. In later phases of infection the kinase is activated by the viral NS1 protein to prevent premature apoptosis. Besides these virus supporting functions, it was suggested that PI3K signalling is involved in dsRNA and IAV induced antiviral responses by enhancing the activity of interferon regulatory factor-3 (IRF-3). However, molecular mechanisms of activation remained obscure. Here we show that accumulation of vRNA in cells infected with influenza A or B viruses results in PI3K activation. Furthermore, expression of the RNA receptors Rig-I and MDA5 was increased upon stimulation with virion extracted vRNA or IAV infection. Using siRNA approaches, Rig-I was identified as pathogen receptor necessary for influenza virus vRNA sensing and subsequent PI3K activation in a TRIM25 and MAVS signalling dependent manner. Rig-I induced PI3K signalling was further shown to be essential for complete IRF-3 activation and consequently induction of the type I interferon response. These data identify PI3K as factor that is activated as part of the Rig-I mediated anti-pathogen response to enhance expression of type I interferons.

The ribonucleotide reductase R1 subunits of herpes simplex virus 1 and 2 protect cells against poly(I · C)-induced apoptosis

We recently provided evidence that the ribonucleotide reductase R1 subunits of herpes simplex virus types 1 and 2 (HSV-1 and -2) protect cells against tumor necrosis factor alpha- and Fas ligand-induced apoptosis by interacting with caspase 8. Double-stranded RNA (dsRNA) is a viral intermediate known to initiate innate antiviral responses. Poly(I · C), a synthetic analogue of viral dsRNA, rapidly triggers caspase 8 activation and apoptosis in HeLa cells. Here, we report that HeLa cells after HSV-1 and HSV-2 infection were quickly protected from apoptosis caused by either extracellular poly(I · C) combined with cycloheximide or transfected poly(I · C). Cells infected with the HSV-1 R1 deletion mutant ICP6Δ were killed by poly(I · C), indicating that HSV-1 R1 plays a key role in antiapoptotic responses to poly(I · C). Individually expressed HSV R1s counteracted caspase 8 activation by poly(I · C). In addition to their binding to caspase 8, HSV R1s also interacted constitutively with receptor-interacting protein 1 (RIP1) when expressed either individually or with other viral proteins during HSV infection. R1(1-834)-green fluorescent protein (GFP), an HSV-2 R1 deletion mutant protein devoid of antiapoptotic activity, did not interact with caspase 8 and RIP1, suggesting that these interactions are required for protection against poly(I · C). HSV-2 R1 inhibited the interaction between the Toll/interleukin-1 receptor domain-containing adaptor-inducing beta interferon (IFN-β) (TRIF) and RIP1, an interaction that is essential for apoptosis triggered by extracellular poly(I · C) plus cycloheximide or TRIF overexpression. TRIF silencing reduced poly(I · C)-triggered caspase 8 activation in mock- and ICP6Δ-infected cells, confirming that TRIF is involved in poly(I · C)-induced apoptosis. Thus, by interacting with caspase 8 and RIP1, HSV R1s impair the apoptotic host defense mechanism prompted by dsRNA.

Identifying innate immune pathways of the chicken may lead to new antiviral therapies

Zoonotic viruses, such as highly pathogenic avian influenza (HPAI), present a significant threat to both the poultry industry and public health. The present method of controlling avian influenza (AI) relies on good farming practice with limited use of vaccination in some countries. However, new ways to control disease outbreaks might be possible with additional knowledge of the natural host response to virus. Moreover, manipulation of the innate immune system in mammals improves the outcomes following viral infection. A similar approach might be applied to the chicken, nevertheless, a greater knowledge of the chicken innate immune system is required. This review outlines important mammalian antiviral mechanisms that have been modulated to strengthen viral immunity and highlights the potential application of these strategies in the chicken, especially in regards, to AI.

Age exacerbates sickness behavior following exposure to a viral mimetic

Poly I:C, a viral mimetic, is a synthetic double-stranded RNA that is known to cause activation of the innate immune system, resulting in the emergence of sickness behaviors in otherwise healthy adult mice. However, the way in which such effects of poly I:C manifest themselves in aged mice are not currently known. We hypothesized that poly I:C administration would lead to burrowing deficits, but that these deficits would be exaggerated in aged subjects (19-months old) compared to young subjects (4-months old) that received the same dose. In order to associate these behavioral decrements with inflammatory factors, we measured mRNA expression of IL-1β and IL-6 in the hippocampus and parietal cortex and peripheral protein expression of IL-6, TNF-α, MCP-1, MIP-1α, and IL-1β in the serum. After exposure to poly I:C, aged subjects demonstrated significant impairments in their burrowing behavior, compared to younger subjects administered the same dose. These behavioral decrements coincided with increased expression of IL-6 among animals exposed to poly I:C and increased expression of IL-1β among aged animals in the hippocampus and cortex. Furthermore, we observed an increase in peripheral poly I:C-induced IL-6, TNF-α, MCP-1, and MIP-1α, but not IL-1β. These results indicate that virus-mediated immune activation in the aging body can lead to increased sickness behavior. Furthermore, these data indicated a possible dissociation between the effects of poly I:C on sickness behaviors in aged mice, with central expression of IL-1β potentially playing a role in age-related impairments.

Synthetic double-stranded RNA polyinosinic-polycytidylic acid augments morphine-induced conditioned place preference in rats

Three experiments were performed to study the effects of immune challenge on the rewarding properties of opiates. Intraperitoneal injection of polyinosinic-polycytidylic acid (Poly I:C, 1 mg/kg) was used to trigger an immune challenge. Conditioned place preference (CPP) in rats trained with alternating subcutaneous injections of morphine (5 mg/kg) and saline was used to assess the rewarding effect of morphine. Poly I:C administered before CPP training had no effects on CPP acquisition. Poly I:C administered during CPP training enhanced CPP acquisition. Poly I:C administered after morphine-induced CPP acquisition retarded CPP extinction. These results show that the immune challenge by Poly I:C augmented morphine CPP in rats depending on the onset time of the challenge. The findings suggest that immune challenge may enhance the rewarding properties of opiates.

Activation of interferon response through toll-like receptor 3 impacts viral pathogenesis and pulmonary toll-like receptor expression during respiratory syncytial virus and influenza infections in the cotton rat Sigmodon hispidus model

Interferon (IFN) therapy in humans often causes flu-like symptoms by an unknown mechanism. Poly ICLC is a synthetic dsRNA and a Toll-like receptor 3 (TLR3) agonist with a strong IFN-inducing ability. In this work, we analyzed the effect of poly ICLC on pulmonary responses to influenza and respiratory syncytial virus (RSV) infections in the cotton rat (Sigmodon hispidus) model. Viral replication, pulmonary inflammation, and expression of IFN, TLR, and chemokines were monitored and compared. Antiviral effect of poly ICLC against influenza virus and RSV was best achieved at high poly ICLC concentrations that, in the absence of virus infection, induced a strong IFN response. The antiviral doses of poly ICLC, however, also increased lung inflammation, an unexpected finding because of the reported poly ICLC safety in BALB/c mice. Similarly, in contrast to murine model, pathology of RSV infection was increased in cotton rats treated with poly ICLC. Augmented lung inflammation was accompanied by an earlier induction of IFN and TLR responses and a stronger chemokine expression. Overall, these findings indicate significant association between antiviral IFN action and pulmonary inflammation and highlight important animal model-specific variations in the potential of IFN to cause pathology.

dsRNA and the innate antiviral immune response

Innate immunity is the first line of defense against viral infections. It is based on a mechanism of sensing pathogen-associated molecular patterns through host germline-encoded pattern recognition receptors. dsRNA is arguably the most important viral pathogen-associated molecular pattern due to its expression by almost all viruses at some point during their replicative cycle. Viral dsRNA has been studied for over 55 years, first as a toxin, then as a type I interferon inducer, a viral mimetic and an immunomodulator for therapeutic purposes. This article will focus on dsRNA, its structure, generation (both endogenous and viral), host sensing mechanisms and induction of type I interferons. The possible therapeutic applications of these findings will also be discussed. The goal of this article is to give an overview of these mechanisms, highlighting novel findings, while providing a historical perspective.

An accessory to the 'Trinity': SR-As are essential pathogen sensors of extracellular dsRNA, mediating entry and leading to subsequent type I IFN responses

Extracellular RNA is becoming increasingly recognized as a signaling molecule. Virally derived double stranded (ds)RNA released into the extracellular space during virus induced cell lysis acts as a powerful inducer of classical type I interferon (IFN) responses; however, the receptor that mediates this response has not been identified. Class A scavenger receptors (SR-As) are likely candidates due to their cell surface expression and ability to bind nucleic acids. In this study, we investigated a possible role for SR-As in mediating type I IFN responses induced by extracellular dsRNA in fibroblasts, a predominant producer of IFNbeta. Fibroblasts were found to express functional SR-As, even SR-A species thought to be macrophage specific. SR-A specific competitive ligands significantly blocked extracellular dsRNA binding, entry and subsequent interferon stimulated gene (ISG) induction. Candidate SR-As were systematically investigated using RNAi and the most dramatic inhibition in responses was observed when all candidate SR-As were knocked down in unison. Partial inhibition of dsRNA induced antiviral responses was observed in vivo in SR-AI/II(-/-) mice compared with WT controls. The role of SR-As in mediating extracellular dsRNA entry and subsequent induced antiviral responses was observed in both murine and human fibroblasts. SR-As appear to function as 'carriers', facilitating dsRNA entry and delivery to the established dsRNA sensing receptors, specifically TLR3, RIGI and MDA-5. Identifying SR-As as gatekeepers of the cell, mediating innate antiviral responses, represents a novel function for this receptor family and provides insight into how cells recognize danger signals associated with lytic virus infections. Furthermore, the implications of a cell surface receptor capable of recognizing extracellular RNA may exceed beyond viral immunity to mediating other important innate immune functions.

Attenuation of the influenza virus sickness behavior in mice deficient in Toll-like receptor 3

Certain sickness behaviors occur consistently in influenza-infected humans and mice. These include body temperature changes, somnolence, and anorexia. Several cytokines serve as mediators of the influenza acute phase response (APR), including these sickness behaviors, and one likely inducer of these cytokines is dsRNA produced during viral replication. TLR3 is known to be one of the host cellular components capable of recognizing dsRNA and activating cytokine synthesis. To determine the role of TLR3-detected viral dsRNA in the causation of viral symptoms, TLR3-deficient mice (TLR3 knockouts, or KOs) were infected with a marginally-lethal dose of mouse-adapted X-31 influenza virus. TLR3 KOs and their wild-type (WT) controls were monitored for baseline body temperature, locomotor activity, and sleep profiles prior to infection. Both mouse strains were then infected and monitored for changes in these sickness behaviors plus body weight changes and mortality for up to 14days post-infection. Consistent with the observations that influenza pathology is reduced in TLR3 KOs, we showed that hypothermia after post-infection day 5 and the total loss of body weight were attenuated in the TLR3 KOs. Sleep changes characteristic of this infection model [particularly increased non-rapid-eye-movement sleep (NREMS)] were also attenuated in TLR3 KOs and returned to baseline values more rapidly. Locomotor activity suppression was similar in both strains. Therefore virus-associated dsRNA detected by TLR3 appears to play a substantial role in mediating several aspects of the influenza syndrome in mice.

Activation of the Antiviral Kinase PKR and Viral Countermeasures

The interferon-induced double-stranded (ds)RNA-dependent protein kinase (PKR) limits viral replication by an eIF2α-mediated block of translation. Although many negative-strand RNA viruses activate PKR, the responsible RNAs have long remained elusive, as dsRNA, the canonical activator of PKR, has not been detected in cells infected with such viruses. In this review we focus on the activating RNA molecules of different virus families, in particular the negative-strand RNA viruses. We discuss the recently identified non-canonical activators 5′-triphosphate RNA and the vRNP of influenza virus and give an update on strategies of selected RNA and DNA viruses to prevent activation of PKR.

Role of IFN-alpha during the acute stage of a swine influenza virus infection

Cytokines, especially interferon-alpha (IFN-alpha) are important in controlling influenza virus infections. To investigate the role of IFN-alpha in influenza, the swine IFN-alpha neutralizing monoclonal antibody (Ab) K9 was applied in a swine model of influenza A virus infection. First, the optimal dose and route for administration of the IFN-alpha neutralizing Abs was determined. Based on those results, the effect of the Abs on a swine influenza virus infection was investigated. Pigs were inoculated intratracheally with 10(6.0) mean egg infectious dose (EID(50)) A/Swine/Belgium/1/98 (H1N1) virus. At the time of challenge and 18 h later, they were injected intratracheally and intraperitoneally with a high dose of IFN-alpha neutralizing Abs or control Abs. The animals were euthanized at 0, 24, 30, 48 and 72 h after inoculation. At 24 and 30 h, IFN-alpha levels in broncho-alveolar lavage fluid of K9 recipient animals were strongly suppressed, and this coincided with reduced IL-6 and IL-12 levels. TNF-alpha and IL-1 levels were unaffected compared to those in the control Ab treated group. Importantly, the onset and peak of clinical symptoms in IFN-alpha neutralizing Abs treated animals were delayed by 24h, simultaneously with the suppression of IFN-alpha, but there was no obvious effect on virus replication and lung pathology. These results suggest an important role for IFN-alpha in IL-6 and IL-12 induction and a role of all three cytokines in the symptoms of swine influenza.

Comparison of anorexia, lethargy, and fever induced by bacterial and viral mimetics in rats

Although it has been established that some acute phase responses present differently depending on whether a virus or bacteria activates the innate immune system, it has not yet been established whether fever and sickness behaviors, such as anorexia and lethargy, present differently. We therefore investigated the effects of administering lipopolysaccharide (LPS) and polyinosinic : polycytidylic acid (poly I:C) on body temperature, food intake, body mass, and activity (cage activity and wheel running). Male Sprague-Dawley rats were randomly assigned to receive an intraperitoneal injection of one of LPS (75 microg/kg or 250 microg/kg), poly I:C (3000 microg/kg or 4000 microg/kg), or saline. Administration of LPS or poly I:C induced fever, anorexia, and lethargy. Although voluntary wheel running and cage activity were both significantly reduced after administration of LPS or poly I:C, they were not affected equally. Indeed voluntary wheel running was decreased on average by approximately 30% more than cage activity regardless of the dose or type of mimetic administered. Our results indicate that poly I:C is less effective at inducing anorexia, lethargy, and fever in rats than is LPS, and that avoidance of exercise in animals and humans during infection is likely to be a more prominent feature of illness than is avoidance of routine daily activity.

Influenza B virus ribonucleoprotein is a potent activator of the antiviral kinase PKR

Activation of the latent kinase PKR is a potent innate defense reaction of vertebrate cells towards viral infections, which is triggered by recognition of viral double-stranded (ds) RNA and results in a translational shutdown. A major gap in our understanding of PKR's antiviral properties concerns the nature of the kinase activating molecules expressed by influenza and other viruses with a negative strand RNA genome, as these pathogens produce little or no detectable amounts of dsRNA. Here we systematically investigated PKR activation by influenza B virus and its impact on viral pathogenicity. Biochemical analysis revealed that PKR is activated by viral ribonucleoprotein (vRNP) complexes known to contain single-stranded RNA with a 5′-triphosphate group. Cell biological examination of recombinant viruses showed that the nucleo-cytoplasmic transport of vRNP late in infection is a strong trigger for PKR activation. In addition, our analysis provides a mechanistic explanation for the previously observed suppression of PKR activation by the influenza B virus NS1 protein, which we show here to rely on complex formation between PKR and NS1's dsRNA binding domain. The high significance of this interaction for pathogenicity was revealed by the finding that attenuated influenza viruses expressing dsRNA binding-deficient NS1 proteins were rescued for high replication and virulence in PKR-deficient cells and mice, respectively. Collectively, our study provides new insights into an important antiviral defense mechanism of vertebrates and leads us to suggest a new model of PKR activation by cytosolic vRNP complexes, a model that may also be applicable to other negative strand RNA viruses.

Upon viral infection of vertebrate cells, a vigorous innate defense response is initiated via the recognition of viral double-stranded (ds) RNA by the protein kinase PKR, resulting in the cessation of protein synthesis and subsequent blockage of viral propagation. The activation of PKR's potent antiviral response against influenza and other viruses with a negative strand RNA genome has presented a conundrum, however, as previous attempts failed to detect dsRNA in cells infected with these viruses. Here, we identify genomic RNA within the ribonucleoprotein (RNP) of influenza viruses as a non-canonical activator of the latent kinase PKR. Cell biological examinations revealed that the transfer of viral RNP from the nucleus to the cytoplasm provides a strong stimulus for PKR activation. Moreover, we provide insight into mechanisms of pathogenesis by showing PKR and the NS1 protein of influenza B virus forms a complex in infected cells, which inhibits PKR activation. This interaction seems to be crucial for viral pathogenicity, as a strong attenuation of NS1 mutant viruses was largely rescued in PKR-deficient mice and cells. Taken together, these findings suggest a new model for the induction and inhibition of PKR by influenza virus that may also apply to viruses with a similar genome structure.

Molecular cloning, expression, and characterization of chicken IFN -lambda

Interferons (IFN) provide a critical first line of defense against viral infection in vertebrates. Moreover, IFN-lambda, a recently identified group of mammalian IFN, has demonstrated antiviral potential in the treatment of mammalian viruses. With the growing concern over such diseases as avian influenza (AI), there is a pressing need for new antiviral strategies to manage problem viruses in poultry. Furthermore, the use of immune molecules, such as IFN-lambda, provides an attractive option for treating poultry by augmenting the host response to virus. With this in mind, we report here the first cloning, expression, and analysis of biologic activity of chicken IFN-lambda (ChIFN-lambda). We compared the similarity of ChIFN-lambda to those identified in other species and demonstrate that ChIFN-lambda has antiviral properties similar to those of human IFN-lambda (HuIFN-lambda). Our results demonstrate that in the chicken, as in human, the antiviral activity demonstrated by ChIFN-lambda supports its inclusion in therapeutic strategies directed against viral infections.

A key role for Toll-like receptor-3 in disrupting the hemostasis balance on endothelial cells

Various virus infections cause dysfunctional hemostasis and in some instances lead to the development of viral hemorrhagic fever syndrome. How do diverse viruses induce the expression of tissue factor on vascular cells? We hypothesize that a direct stimulation of pattern recognition receptors (PRR) by viral nucleic acids may be the key. Double-stranded RNA (dsRNA) is produced by many viruses and is recognized by various PRR, including Toll-like receptor-3 (TLR3). We have investigated whether poly I:C, a model for viral dsRNA, can influence cellular hemostasis. Poly I:C could up-regulate tissue factor and down-regulate thrombomodulin expression on endothelial cells but not on monocytes. The response to poly I:C was diminished upon small interfering RNA (siRNA)-mediated inhibition of TLR3, but not other PRR. In vivo, application of poly I:C induced similar changes in the aortic endothelium of mice as determined by enface microscopy. D-dimer, a circulating marker for enhanced coagulation and fibrinolysis, and tissue fibrin deposition was elevated. All the hemostasis-related responses to poly I:C, but not cytokine secretion, were blunted in TLR3(-/-) mice. Hence, the activation of TLR3 can induce the procoagulant state in the endothelium, and this could be relevant for understanding the mechanisms of viral stimulation of hemostasis.

Inflammation activates the interferon signaling pathways in taste bud cells

Patients with viral and bacterial infections or other inflammatory illnesses often experience taste dysfunctions. The agents responsible for these taste disorders are thought to be related to infection-induced inflammation, but the mechanisms are not known. As a first step in characterizing the possible role of inflammation in taste disorders, we report here evidence for the presence of interferon (IFN)-mediated signaling pathways in taste bud cells. IFN receptors, particularly the IFN-gamma receptor IFNGR1, are coexpressed with the taste cell-type markers neuronal cell adhesion molecule and alpha-gustducin, suggesting that both the taste receptor cells and synapse-forming cells in the taste bud can be stimulated by IFN. Incubation of taste bud-containing lingual epithelia with recombinant IFN-alpha and IFN-gamma triggered the IFN-mediated signaling cascades, resulting in the phosphorylation of the downstream STAT1 (signal transducer and activator of transcription protein 1) transcription factor. Intraperitoneal injection of lipopolysaccharide or polyinosinic:polycytidylic acid into mice, mimicking bacterial and viral infections, respectively, altered gene expression patterns in taste bud cells. Furthermore, the systemic administration of either IFN-alpha or IFN-gamma significantly increased the number of taste bud cells undergoing programmed cell death. These findings suggest that bacterial and viral infection-induced IFNs can act directly on taste bud cells, affecting their cellular function in taste transduction, and that IFN-induced apoptosis in taste buds may cause abnormal cell turnover and skew the representation of different taste bud cell types, leading to the development of taste disorders. To our knowledge, this is the first study providing direct evidence that inflammation can affect taste buds through cytokine signaling pathways.

Cutting Edge: Influenza A virus activates TLR3-dependent inflammatory and RIG-I-dependent antiviral responses in human lung epithelial cells

Influenza A virus (IAV) triggers a contagious acute respiratory disease that causes considerable mortality annually. Recently, we established a role for the pattern-recognition TLR3 in the response of lung epithelial cells to IAV-derived dsRNA. However, additional nucleic acid-recognition proteins have lately been implicated as key viral sensors, including the RNA helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene (MDA)-5. In this study, we investigated the respective role of TLR3 vs RIG-I/MDA-5 signaling in human respiratory epithelial cells infected by IAV using BEAS-2B cells transfected with vectors encoding either a dominant-negative form of TLR3 or of mitochondrial antiviral signaling protein (MAVS; a signaling intermediate of RIG-I and MDA-5), or with plasmids overexpressing functional RIG-I or MDA-5. We demonstrate that the sensing of IAV by TLR3 primarily regulates a proinflammatory response, whereas RIG-I (but not MDA-5) mediates both a type I IFN-dependent antiviral signaling and a proinflammatory response.

The sickness behaviour and CNS inflammatory mediator profile induced by systemic challenge of mice with synthetic double-stranded RNA (poly I:C)

Poly inosinic:poly cytidylic acid (poly I:C) is a synthetic double-stranded RNA and is a ligand for the Toll like receptor-3. This receptor is involved in the innate immune response to viral infection and poly I:C has been used to mimic the acute phase of a viral infection. The effects of TLR3 activation on brain function have not been widely studied. In the current study we investigate the spectrum of sickness behavioural changes induced by poly I:C in C57BL/6 mice and the CNS expression of inflammatory mediators that may underlie this. Poly I:C, at doses of 2, 6 and 12 mg/kg, induced a dose-responsive sickness behaviour, decreasing locomotor activity, burrowing and body weight, and caused a mild hyperthermia at 6h. The 12 mg/kg dose caused significant hypothermia at later times. The Remo400 remote Telemetry system proved a sensitive measure of this biphasic temperature response. The behavioural responses to poly I:C were not significantly blunted upon a second poly I:C challenge either 1 or 3 weeks later. Plasma concentrations of IL-6, TNF-alpha and IFN-beta were markedly elevated and IL-1 beta was also detectable. Cytokine synthesis within the CNS, as determined by quantitative PCR, was dominated by IL-6, with lesser inductions of IL-1 beta, TNF-alpha and IFN-beta and there was a clear activation of cyclooxygenase-2 at the brain endothelium. These findings demonstrate clear CNS effects of peripheral TLR3 stimulation and will be useful in studying aspects of the effects of systemic viral infection on brain function in both normal and pathological situations.

Interferon type I receptor-deficient mice have altered disease symptoms in response to influenza virus

The role of type I interferons (IFNs) in mediation of acute viral symptoms (fever, somnolence, anorexia, etc.) is unknown. To determine the role of type I IFN in selected symptom development, body temperature and sleep responses to a marginally lethal dose of X-31 influenza virus were examined in mice with a targeted mutation of the IFN receptor type I (IFN-RI knockouts) and compared to wild-type 129 SvEv control mice. Mice were monitored for 48 h to determine baseline temperature and sleep profiles prior to infection, and then for 9 days following infection. Hypothermic responses to virus were perceptible beginning at 64 h post-infection (PI) and were more marked in KO mice until 108 h, when hypothermia became more exaggerated in wild-type controls. Temperatures of wild-type mice continued to decline through day 9 while temperatures in IFN-RI KO mice stabilized. Time spent in non-rapid eye movement sleep (NREMS) increased in KO mice when hypothermia was marked and then returned to baseline levels, while NREMS continued to increase in wild-type mice through day 9. Other sleep parameters [time spent in rapid eye movement sleep (REMS), relative NREMS EEG slow wave activity, NREMS EEG power density] were all reduced in wild-type mice compared to KOs from days 3 to 8 while REMS low frequency EEG power density increased in wild-type relative to KOs. In conclusion, our results indicate that the presence of functional type I IFN slightly ameliorates disease symptoms early in the X-31 infection while exacerbating disease symptoms later in the infection.

Exploited defense: how influenza viruses take advantage of antiviral signaling responses

Influenza virus infection results in the activation of a variety of intracellular signaling responses. With regard to the function of these responses, the overall picture that has emerged suggests that most of the signaling events are initiated as a cellular response to defend the invading pathogen. While on the one hand influenza viruses have evolved strategies to keep these responses in a tolerable limit, there is accumulating evidence that the virus has also acquired the capability to exploit the remaining activities to ensure efficient replication. Here we will summarize the current knowledge on influenza virus-induced signaling processes and how these pathogens take advantage of some of these activities within the infected cell to support its propagation.