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‣ Epstein-Barr Virus LMP2A Alters In Vivo and In Vitro Models of B-Cell Anergy, but Not Deletion, in Response to Autoantigen

Swanson-Mungerson, Michelle A.; Caldwell, Robert G.; Bultema, Rebecca; Longnecker, Richard
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /06/2005 Português
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A significant percentage of the population latently harbors Epstein-Barr virus (EBV) in B cells. One EBV-encoded protein, latent membrane protein 2A (LMP2A), is expressed in tissue culture models of EBV latent infection, in human infections, and in many of the EBV-associated proliferative disorders. LMP2A constitutively activates proteins involved in the B-cell receptor (BCR) signal transduction cascade and inhibits the antigen-induced activation of these proteins. In the present study, we investigated whether LMP2A alters B-cell receptor signaling in primary B cells in vivo and in vitro. LMP2A does not inhibit antigen-induced tolerance in response to strong stimuli in an in vivo tolerance model in which B cells are reactive to self-antigen. In contrast, LMP2A bypasses anergy induction in response to low levels of soluble hen egg lysozyme (HEL) both in vivo and in vitro as determined by the ability of LMP2A-expressing HEL-specific B cells to proliferate and induce NF-κB nuclear translocation after exposure to low levels of antigen. Furthermore, LMP2A induces NF-κB nuclear translocation independent of BCR cross-linking. Since NF-κB is required to bypass tolerance induction, this LMP2A-dependent NF-κB activation may complete the tolerogenic signal induced by low levels of soluble HEL. Overall...

‣ Early Alpha/Beta Interferon Production by Myeloid Dendritic Cells in Response to UV-Inactivated Virus Requires Viral Entry and Interferon Regulatory Factor 3 but Not MyD88

Hidmark, Åsa S.; McInerney, Gerald M.; Nordström, Eva K. L.; Douagi, Iyadh; Werner, Kristen M.; Liljeström, Peter; Hedestam, Gunilla B. Karlsson
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /08/2005 Português
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Alpha/beta interferons (IFN-α/β) are key mediators of innate immunity and important modulators of adaptive immunity. The mechanisms by which IFN-α/β are induced are becoming increasingly well understood. Recent studies showed that Toll-like receptors 7 and 8 expressed by plasmacytoid dendritic cells (pDCs) mediate the endosomal recognition of incoming viral RNA genomes, a process which requires myeloid differentiation factor 88 (MyD88). Here we investigate the requirements for virus-induced IFN-α/β production in cultures of bone marrow-derived murine myeloid DCs (mDCs). Using recombinant Semliki Forest virus blocked at different steps in the viral life cycle, we show that replication-defective virus induced IFN-α/β in mDCs while fusion-defective virus did not induce IFN-α/β. The response to replication-defective virus was largely intact in MyD88−/− mDC cultures but was severely reduced in mDC cultures from mice lacking IFN regulatory factor 3. Our observations suggest that mDCs respond to incoming virus via a pathway that differs from the fusion-independent, MyD88-mediated endosomal pathway described for the induction of IFN-α/β in pDCs. We propose that events during or downstream of viral fusion, but prior to replication...

‣ Host Response to the Attenuated Poxvirus Vector NYVAC: Upregulation of Apoptotic Genes and NF-κB-Responsive Genes in Infected HeLa Cells

Guerra, Susana; López-Fernández, Luis A.; Pascual-Montano, Alberto; Nájera, José Luis; Zaballos, Angel; Esteban, Mariano
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /01/2006 Português
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NYVAC has been engineered as a safe, attenuated vaccinia virus (VV) vector for use in vaccination against a broad spectrum of pathogens and tumors. Due to the interest in NYVAC-based vectors as vaccines and current phase I/II clinical trials with this vector, there is a need to analyze the human host response to NYVAC infection. Using high-density cDNA microarrays, we found 368 differentially regulated genes after NYVAC infection of HeLa cells. Clustering of the regulated genes identified six discrete gene clusters with altered expression patterns. Clusters 1 to 3 represented 47.5% of the regulated genes, with three patterns of gene activation kinetics, whereas clusters 4 to 6 showed distinct repression kinetics. Quantitative real-time reverse transcription-PCR analysis of selected genes validated the array data. Upregulated transcripts correlated with genes implicated in immune responses, including those encoding interleukin-1 receptor 2 (IL-1R2), IL-6, ISG-15, CD-80, and TNFSF7. NYVAC upregulated several intermediates of apoptotic cascades, including caspase-9, correlating with its ability to induce apoptosis. NYVAC infection also stimulated the expression of NF-κB1 and NF-κB2 as well as that of NF-κB target genes. Expression of the VV host range K1L gene during NYVAC infection prevented NF-κB activation...

‣ The Leader Proteinase of Foot-and-Mouth Disease Virus Inhibits the Induction of Beta Interferon mRNA and Blocks the Host Innate Immune Response

de los Santos, Teresa; de Avila Botton, Sonia; Weiblen, Rudi; Grubman, Marvin J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /02/2006 Português
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We have previously shown that the leader proteinase (Lpro) of foot-and-mouth disease virus (FMDV) blocks cap-dependent mRNA translation and that a genetically engineered FMDV lacking the leader proteinase coding region (A12-LLV2) is attenuated in cell culture and susceptible animals. The attenuated phenotype apparently is a consequence of the inability of A12-LLV2 to block the expression of type I interferon (IFN-α/β) protein, resulting in IFN-induced inhibition of FMDV replication. Here we show that in addition to preventing IFN-α/β protein synthesis, Lpro reduces the level of immediate-early induction of IFN-β mRNA and IFN-stimulated gene products such as double-stranded RNA-dependent protein kinase R (PKR), 2′,5′-oligoadenylate synthetase, and Mx1 mRNAs in swine cells. Down-regulation of cellular PKR by RNA interference did not affect wild-type virus yield but resulted in a higher yield of A12-LLV2, indicating a direct role of PKR in controlling FMDV replication in the natural host. The observation that Lpro controls the transcription of genes involved in innate immunity reveals a novel role of this protein in antagonizing the cellular response to viral infection.

‣ Functional Genomic Analysis of Herpes Simplex Virus Type 1 Counteraction of the Host Innate Response†

Pasieka, Tracy Jo; Baas, Tracey; Carter, Victoria S.; Proll, Sean C.; Katze, Michael G.; Leib, David A.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /08/2006 Português
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Herpes simplex virus type 1 (HSV-1) mutants lacking the ICP34.5 gene are severely attenuated in mouse models and have a significant growth defect in confluent mouse embryo fibroblasts. Previously, ICP34.5 was demonstrated to have a crucial role in evading the innate immune response to infection by mediating the dephosphorylation of eIF2α, a translation initiation factor phosphorylated by PKR during the antiviral response. To further understand the role of ICP34.5 in evasion of the antiviral response, we used transcriptional profiling to examine host cell gene expression in both wild-type and ICP34.5-null virus-infected mouse embryo fibroblasts over a time course of infection. Our study revealed that cells responded to infection within 3 h through PKR-dependent eIF2α phosphorylation and that the majority of up-regulated genes at 3 h postinfection were involved in the antiviral response. HSV-1 counters this response through early expression of ICP34.5 and dephosphorylation of eIF2α. By 12 h postinfection, the differences between the number and functional classification of genes differentially up- and down-regulated between wild-type and ICP34.5-null virus-infected cells were maximal. Specifically, in wild-type virus-infected cells...

‣ West Nile Virus Differentially Modulates the Unfolded Protein Response To Facilitate Replication and Immune Evasion▿ †

Ambrose, Rebecca L.; Mackenzie, Jason M.
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
Português
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For intracellular survival it is imperative that viruses have the capacity to manipulate various cellular responses, including metabolic and biosynthetic pathways. The unfolded protein response (UPR) is induced by various external and internal stimuli, including the accumulation of misfolded proteins in the endoplasmic reticulum (ER). Our previous studies have indicated that the replication and assembly of the flavivirus West Nile virus strain Kunjin virus (WNVKUN) is intimately associated with the ER. Thus, we sought to determine whether the UPR was induced during WNVKUN infection. WNVKUN induces UPR signaling during replication, which is coordinated with peak replication. Interestingly, signaling is biased toward the ATF6/IRE-1 arm of the response, with high levels of Xbp-1 activation but negligible eukaryotic translation initiation factor 2α phosphorylation and downstream transcription. We show that the PERK-mediated response may partially regulate replication, since external UPR stimulation had a limiting effect on early replication events and cells deficient for PERK demonstrated increased replication and virus release. Significantly, we show that the WNVKUN hydrophobic nonstructural proteins NS4A and NS4B are potent inducers of the UPR...

‣ The Early Interferon Response to Rotavirus Is Regulated by PKR and Depends on MAVS/IPS-1, RIG-I, MDA-5, and IRF3 ▿

Sen, Adrish; Pruijssers, Andrea J.; Dermody, Terence S.; García-Sastre, Adolfo; Greenberg, Harry B.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /04/2011 Português
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In mouse embryonic fibroblasts (MEFs), the bovine rotavirus (UK strain) but not the simian rhesus rotavirus (RRV) robustly triggers beta interferon (IFN-β) secretion, resulting in an IFN-dependent restriction of replication. We now find that both rotavirus strains trigger antiviral transcriptional responses early during infection and that both transcriptional responses and IFN-β secretion are completely abrogated in MAVS/IPS-1−/− MEFs. Replication of UK virus could be rescued in MAVS/IPS-1−/− MEFs, and synthesis of viral RNA significantly increased early during virus infection. UK virus induced IFN-β secretion and transcription of IFN-stimulated genes (ISGs) in both RIG-I−/− and MDA-5−/− MEFs, and neither receptor was essential by itself for the antiviral response to UK rotavirus. However, when receptors RIG-I and MDA-5 were depleted using RNA interference, we found that both contribute to the magnitude of the IFN response. IRF3 was found to be essential for MAVS/IPS-1-directed ISG transcription and IFN-β secretion during rotavirus infection. Interestingly, absence of the double-stranded RNA-dependent protein kinase PKR led to a profound defect in the capacity of host cells to secrete IFN-β in response to virus. Both PKR and IRF3 restricted the early replication of UK as indicated by significant increases in viral RNA in fibroblasts lacking either gene. Despite the loss in IFN-β secretion in PKR−/− MEFs...

‣ Specific Regulation of the Chemokine Response to Viral Hemorrhagic Septicemia Virus at the Entry Site▿

Montero, Jana; Garcia, Jessica; Ordas, M. Camino; Casanova, Isabel; Gonzalez, Antonia; Villena, Alberto; Coll, Julio; Tafalla, Carolina
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /05/2011 Português
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The fin bases constitute the main portal of rhabdovirus entry into rainbow trout (Oncorhynchus mykiss), and replication in this first site strongly conditions the outcome of the infection. In this context, we studied the chemokine response elicited in this area in response to viral hemorrhagic septicemia virus (VHSV), a rhabdovirus. Among all the rainbow trout chemokine genes studied, only the transcription levels of CK10 and CK12 were significantly upregulated in response to VHSV. As the virus had previously been shown to elicit a much stronger chemokine response in internal organs, we compared the effect of VHSV on the gills, another mucosal site which does not constitute the main site of viral entry or rhabdoviral replication. In this case, a significantly stronger chemokine response was triggered, with CK1, CK3, CK9, and CK11 being upregulated in response to VHSV and CK10 and CK12 being down-modulated by the virus. We then conducted further experiments to understand how these different chemokine responses of mucosal tissues could correlate with their capacity to support VHSV replication. No viral replication was detected in the gills, while at the fin bases, only the skin and the muscle were actively supporting viral replication. Within the skin...

‣ Host Response to Polyomavirus Infection Is Modulated by RNA Adenosine Deaminase ADAR1 but Not by ADAR2▿

George, Cyril X.; Samuel, Charles E.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /08/2011 Português
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Adenosine deaminases acting on RNA (ADARs) catalyze the C-6 deamination of adenosine (A) to produce inosine (I), which behaves as guanine (G), thereby altering base pairing in RNAs with double-stranded character. Two genes, adar1 and adar2, are known to encode enzymatically active ADARs in mammalian cells. Furthermore, two size forms of ADAR1 are expressed by alternative promoter usage, a short (p110) nuclear form that is constitutively made and a long (p150) form that is interferon inducible and present in both the cytoplasm and nucleus. ADAR2 is also a constitutively expressed nuclear protein. Extensive A-to-G substitution has been described in mouse polyomavirus (PyV) RNA isolated late times after infection, suggesting modification by ADAR. To test the role of ADAR in PyV infection, we used genetically null mouse embryo fibroblast cells deficient in either ADAR1 or ADAR2. The single-cycle yields and growth kinetics of PyV were comparable between adar1−/− and adar2−/− genetic null fibroblast cells. While large T antigen was expressed to higher levels in adar1−/− cells than adar2−/− cells, less difference was seen in VP1 protein expression levels between the two knockout MEFs. However, virus-induced cell killing was greatly enhanced in PyV-infected adar1−/− cells compared to that of adar2−/− cells. Complementation with p110 protected cells from PyV-induced cytotoxicity. UV-irradiated PyV did not display any enhanced cytopathic effect in adar1−/− cells. Reovirus and vesicular stomatitis virus single-cycle yields were comparable between adar1−/− and adar2−/− cells...

‣ Increased Susceptibility to DNA Virus Infection in Mice with a GCN2 Mutation

Won, Sungyong; Eidenschenk, Celine; Arnold, Carrie N.; Siggs, Owen M.; Sun, Lei; Brandl, Katharina; Mullen, Tina-Marie; Nemerow, Glen R.; Moresco, Eva Marie Y.; Beutler, Bruce
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /02/2012 Português
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The downregulation of translation through eIF2α phosphorylation is a cellular response to diverse stresses, including viral infection, and is mediated by the GCN2 kinase, protein kinase R (PKR), protein kinase-like endoplasmic reticulum kinase (PERK), and heme-regulated inhibitor kinase (HRI). Although PKR plays a major role in defense against viruses, other eIF2α kinases also may respond to viral infection and contribute to the shutdown of protein synthesis. Here we describe the recessive, loss-of-function mutation atchoum (atc) in Eif2ak4, encoding GCN2, which increased susceptibility to infection by the double-stranded DNA viruses mouse cytomegalovirus (MCMV) and human adenovirus. This mutation was identified by screening macrophages isolated from mice carrying N-ethyl-N-nitrosourea (ENU)-induced mutations. Cells from Eif2ak4atc/atc mice failed to phosphorylate eIF2α in response to MCMV. Importantly, homozygous Eif2ak4atc mice showed a modest increase in susceptibility to MCMV infection, demonstrating that translational arrest dependent on GCN2 contributes to the antiviral response in vivo.

‣ Upregulation of CHOP/GADD153 during Coronavirus Infectious Bronchitis Virus Infection Modulates Apoptosis by Restricting Activation of the Extracellular Signal-Regulated Kinase Pathway

Liao, Ying; Fung, To Sing; Huang, Mei; Fang, Shou Guo; Zhong, Yanxin; Liu, Ding Xiang
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /07/2013 Português
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Induction of the unfolded protein response (UPR) is an adaptive cellular response to endoplasmic reticulum (ER) stress that allows a cell to reestablish ER homeostasis. However, under severe and persistent ER stress, prolonged UPR may activate unique pathways that lead to cell death. In this study, we investigated the activation of the protein kinase R-like ER kinase (PERK) pathway of UPR in cells infected with the coronavirus infectious bronchitis virus (IBV) and its relationship with IBV-induced apoptosis. The results showed moderate induction of PERK phosphorylation in IBV-infected cells. Meanwhile, activating transcription factor 4 (ATF4) was upregulated at the protein level in the infected cells, resulting in the induction in trans of the transcription factor ATF3 and the proapoptotic growth arrest and DNA damage-inducible protein GADD153. Knockdown of PERK by small interfering RNA (siRNA) suppressed the activation of GADD153 and the IBV-induced apoptosis. Interestingly, knockdown of protein kinase R (PKR) by siRNA and inhibition of the PKR kinase activity by 2-aminopurine (2-AP) also reduced the IBV-induced upregulation of GADD153 and apoptosis induction. In GADD153-knockdown cells, IBV-induced apoptosis was suppressed and virus replication inhibited...

‣ CD4 T Cell Help Is Limiting and Selective during the Primary B Cell Response to Influenza Virus Infection

Alam, Shabnam; Knowlden, Zackery A. G.; Sangster, Mark Y.; Sant, Andrea J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /01/2014 Português
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Influenza virus vaccination strategies are focused upon the elicitation of protective antibody responses through administration of viral protein through either inactivated virions or live attenuated virus. Often overlooked in this strategy is the CD4 T cell response: how it develops into memory, and how it may support future primary B cell responses to heterologous infection. Through the utilization of a peptide-priming regimen, this study describes a strategy for developing CD4 T cell memory with the capacity to robustly expand in the lung-draining lymph node after live influenza virus infection. Not only were frequencies of antigen-specific CD4 T cells enhanced, but these cells also supported an accelerated primary B cell response to influenza virus-derived protein, evidenced by high anti-nucleoprotein (NP) serum antibody titers early, while there is still active viral replication ongoing in the lung. NP-specific antibody-secreting cells and heightened frequencies of germinal center B cells and follicular T helper cells were also readily detectable in the draining lymph node. Surprisingly, a boosted memory CD4 T cell response was not sufficient to provide intermolecular help for antibody responses. Our study demonstrates that CD4 T cell help is selective and limiting to the primary antibody response to influenza virus infection and that preemptive priming of CD4 T cell help can promote effective and rapid conversion of naive B cells to mature antibody-secreting cells.

‣ Expression of Mosquito MicroRNA Aae-miR-2940-5p Is Downregulated in Response to West Nile Virus Infection To Restrict Viral Replication

Slonchak, Andrii; Hussain, Mazhar; Torres, Shessy; Asgari, Sassan; Khromykh, Alexander A.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /08/2014 Português
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West Nile virus (WNV) is an enveloped virus with a single-stranded positive-sense RNA genome from the Flaviviridae family. WNV is spread by mosquitoes and able to infect humans, causing encephalitis and meningitis that can be fatal; it therefore presents a significant risk for human health. In insects, innate response to RNA virus infection mostly relies on RNA interference and JAK/SAT pathways; however, some evidence indicates that it can also involve microRNAs (miRNAs). miRNAs are small noncoding RNAs that regulate gene expression at posttranscriptional level and play an important role in a number of processes, including immunity and antiviral response. In this study, we focus on the miRNA-mediated response to WNV in mosquito cells. We demonstrate that in response to WNV infection the expression of a mosquito-specific miRNA, aae-miR-2940, is selectively downregulated in Aedes albopictus cells. This miRNA is known to upregulate the metalloprotease m41 FtsH gene, which we have also shown to be required for efficient WNV replication. Correspondingly, downregulation of aae-miR-2940 reduced the metalloprotease level and restricted WNV replication. Thus, we have identified a novel miRNA-dependent mechanism of antiviral response to WNV in mosquitoes.

‣ Coinfection with Streptococcus pneumoniae Modulates the B Cell Response to Influenza Virus

Wolf, Amaya I.; Strauman, Maura C.; Mozdzanowska, Krystyna; Whittle, James R. R.; Williams, Katie L.; Sharpe, Arlene H.; Weiser, Jeffrey N.; Caton, Andrew J.; Hensley, Scott E.; Erikson, Jan
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /10/2014 Português
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Pathogen-specific antibodies (Abs) protect against respiratory infection with influenza A virus (IAV) and Streptococcus pneumoniae and are the basis of effective vaccines. Sequential or overlapping coinfections with both pathogens are common, yet the impact of coinfection on the generation and maintenance of Ab responses is largely unknown. We report here that the B cell response to IAV is altered in mice coinfected with IAV and S. pneumoniae and that this response differs, depending on the order of pathogen exposure. In mice exposed to S. pneumoniae prior to IAV, the initial virus-specific germinal center (GC) B cell response is significantly enhanced in the lung-draining mediastinal lymph node and spleen, and there is an increase in CD4+ T follicular helper (TFH) cell numbers. In contrast, secondary S. pneumoniae infection exaggerates early antiviral antibody-secreting cell formation, and at later times, levels of GCs, TFH cells, and antiviral serum IgG are elevated. Mice exposed to S. pneumoniae prior to IAV do not maintain the initially robust GC response in secondary lymphoid organs and exhibit reduced antiviral serum IgG with diminished virus neutralization activity a month after infection. Our data suggest that the history of pathogen exposures can critically affect the generation of protective antiviral Abs and may partially explain the differential susceptibility to and disease outcomes from IAV infection in humans.

‣ Analysis of the Early Immune Response to Infection by Infectious Bursal Disease Virus in Chickens Differing in Their Resistance to the Disease

Smith, Jacqueline; Sadeyen, Jean-Remy; Butter, Colin; Kaiser, Pete; Burt, David W.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em 10/12/2014 Português
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Chicken whole-genome gene expression arrays were used to analyze the host response to infection by infectious bursal disease virus (IBDV). Spleen and bursal tissue were examined from control and infected birds at 2, 3, and 4 days postinfection from two lines that differ in their resistance to IBDV infection. The host response was evaluated over this period, and differences between susceptible and resistant chicken lines were examined. Antiviral genes, including IFNA, IFNG, MX1, IFITM1, IFITM3, and IFITM5, were upregulated in response to infection. Evaluation of this gene expression data allowed us to predict several genes as candidates for involvement in resistance to IBDV.

‣ Frequent and Strong Antibody-Mediated Natural Killer Cell Activation in Response to HIV-1 Env in Individuals with Chronic HIV-1 Infection

Thobakgale, Christina F.; Fadda, Lena; Lane, Kimberly; Toth, Ildiko; Pereyra, Florencia; Bazner, Suzane; Ndung'u, Thumbi; Walker, Bruce D.; Rosenberg, Eric S.; Alter, Galit; Carrington, Mary; Allen, Todd M.; Altfeld, Marcus
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /06/2012 Português
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Natural killer (NK) cells play a critical role in the control of HIV-1 infection, and NK cells that respond to HIV-1 peptides have been recently described. However, the mechanisms by which NK cells recognize HIV-1 antigens are not fully understood. We investigated NK cell activation in response to HIV-1 peptides during early and chronic HIV-1 clade B infection using a whole-blood assay and multiparameter flow cytometry. Antibody-mediated NK cell activation in response to HIV-1 peptides was not detected in HIV-1-uninfected individuals. In contrast, 79% of individuals with chronic infection and 22% of individuals with early infection had detectable gamma interferon (IFN-γ) NK cell responses to HIV-1 antigens (P < 0.00001). IFN-γ- and tumor necrosis factor alpha (TNF-α)-producing NK cells most frequently targeted Env gp120 (median of 4% and range of 0 to 31% of all NK cells). NK cells rarely targeted other HIV-1 proteins such as Gag, Pol, and Nef. Antibody-mediated NK cell responses to peptides mapped predominantly to Env protein, required the presence of plasma or plasma IgG, and resulted in lower CD16 expression on NK cells, suggesting an antibody-mediated activation of NK cells. Further studies are needed to assess the consequences of these antibody-mediated NK cell responses for HIV-1 disease progression and vaccine-induced protection from infection.

‣ Establishment and Maintenance of the Innate Antiviral Response to West Nile Virus Involves both RIG-I and MDA5 Signaling through IPS-1▿ †

Fredericksen, Brenda L.; Keller, Brian C.; Fornek, Jamie; Katze, Michael G.; Gale, Michael
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
Português
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RIG-I and MDA5, two related pathogen recognition receptors (PRRs), are known to be required for sensing various RNA viruses. Here we investigated the roles that RIG-I and MDA5 play in eliciting the antiviral response to West Nile virus (WNV). Functional genomics analysis of WNV-infected fibroblasts from wild-type mice and RIG-I null mice revealed that the normal antiviral response to this virus occurs in two distinct waves. The initial response to WNV resulted in the expression of interferon (IFN) regulatory factor 3 target genes and IFN-stimulated genes, including several subtypes of alpha IFN. Subsequently, a second phase of IFN-dependent antiviral gene expression occurred very late in infection. In cells lacking RIG-I, both the initial and the secondary responses to WNV were delayed, indicating that RIG-I plays a critical role in initiating innate immunity against WNV. However, another PRR(s) was able to trigger a response to WNV in the absence of RIG-I. Disruption of both MDA5 and RIG-I pathways abrogated activation of the antiviral response to WNV, suggesting that MDA5 is involved in the host's defense against WNV infection. In addition, ablation of the function of IPS-1, an essential RIG-I and MDA5 adaptor molecule, completely disabled the innate antiviral response to WNV. Our data indicate that RIG-I and MDA5 are responsible for triggering downstream gene expression in response to WNV infection by signaling through IPS-1. We propose a model in which RIG-I and MDA5 operate cooperatively to establish an antiviral state and mediate an IFN amplification loop that supports immune effector gene expression during WNV infection.

‣ Epstein-Barr Virus-Encoded Poly(A)− RNA Confers Resistance to Apoptosis Mediated through Fas by Blocking the PKR Pathway in Human Epithelial Intestine 407 Cells

Nanbo, Asuka; Yoshiyama, Hironori; Takada, Kenzo
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /10/2005 Português
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Our recent findings demonstrated that the Epstein-Barr virus-encoding small nonpolyadenylated RNA (EBER) confers resistance to various apoptotic stimuli and contributes to the maintenance of malignant phenotypes in Burkitt's lymphoma. In this study we investigated the role of EBER in the human epithelial Intestine 407 cell line, which is known to be susceptible to Fas (Apo1/CD95)-mediated apoptosis. Fas, a member of the tumor necrosis factor receptor family, transduces extracellular signals to the apoptotic cellular machinery, leading to cell death. Transfection of the EBER gene into Intestine 407 cells significantly protected the cells from Fas-mediated apoptosis, whereas EBER-negative cell lines underwent apoptosis after Fas treatment. EBER bound double-stranded RNA-dependent protein kinase R (PKR), an interferon-inducible serine/threonine kinase, and abrogated its kinase activity. Moreover, expression of the catalytically inactive dominant-negative PKR provided resistance to Fas-induced apoptosis. Expression of EBER or dominant-negative PKR also inhibited the cleavage of poly(ADP-ribose) polymerase, a mediator of the cellular response to DNA damage, downstream of the Fas-mediated apoptotic pathway. These results in combination indicate that EBER confers resistance to Fas-mediated apoptosis by blocking PKR activity in Intestine 407 cells...

‣ Flavivirus Infection Activates the XBP1 Pathway of the Unfolded Protein Response To Cope with Endoplasmic Reticulum Stress▿

Yu, Chia-Yi; Hsu, Yun-Wei; Liao, Ching-Len; Lin, Yi-Ling
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Português
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The unfolded protein response (UPR) is a coordinated change in gene expression triggered by perturbations in functions of the endoplasmic reticulum (ER). XBP1, a key transcription factor of the UPR, is activated by an IRE1-mediated splicing event, which results in a frameshift and encodes a protein with transcriptional activity. Here, we report that XBP1 was activated during flaviviral infection, as evidenced by XBP1 mRNA splicing and protein expression, as well as induction of the downstream genes ERdj4, EDEM1, and p58(IPK) in Japanese encephalitis virus (JEV)- and dengue virus serotype 2 (DEN-2)-infected cells. Reporter systems based on IRE1-mediated XBP1 splicing were established, and several flaviviral proteins associated with the ER, including glycoproteins and small hydrophobic membrane-anchored proteins, were found to trigger the splicing event. Notably, nonstructural protein NS2B-3 of DEN-2, but not of JEV, was a potent inducer of XBP1 splicing through an unclear mechanism(s). Reduction of XBP1 by a small interfering RNA had no effect on cells' susceptibility to the two viruses but exacerbated the flavivirus-induced cytopathic effects. Overall, flaviviruses trigger the XBP1 signaling pathway and take advantage of this cellular response to alleviate virus-induced cytotoxicity.

‣ IRF-3 Activation by Sendai Virus Infection Is Required for Cellular Apoptosis and Avoidance of Persistence▿

Peters, Kristi; Chattopadhyay, Saurabh; Sen, Ganes C.
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
Português
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Here, we report that specific manipulations of the cellular response to virus infection can cause prevention of apoptosis and consequent establishment of persistent infection. Infection of several human cell lines with Sendai virus (SeV) or human parainfluenza virus 3, two prototypic paramyxoviruses, caused slow apoptosis, which was markedly accelerated upon blocking the action of phosphatidylinositol 3-kinases (PI3 kinases) in the infected cells. The observed apoptosis required viral gene expression and the action of the caspase 8 pathway. Although virus infection activated PI3 kinase, as indicated by AKT activation, its blockage did not inhibit JNK activation or IRF-3 activation. The action of neither the Jak-STAT pathway nor the NF-κB pathway was required for apoptosis. In contrast, IRF-3 activation was essential, although induction of the proapototic protein TRAIL by IRF-3 was not required. When IRF-3 was absent or its activation by the RIG-I pathway was blocked, SeV established persistent infection, as documented by viral protein production and infectious virus production. Introduction of IRF-3 in the persistently infected cells restored the cells' ability to undergo apoptosis. These results demonstrated that in our model system...