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The Journal of Immunology, 2007, 179, 1796 -1802
Copyright © 2007 by The American Association of Immunologists, Inc.
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Early Innate Immune Responses to Sin Nombre Hantavirus Occur Independently of IFN Regulatory Factor 3, Characterized Pattern Recognition Receptors, and Viral Entry1

Joseph B. Prescott*, Pamela R. Hall*, Virginie S. Bondu-Hawkins*, Chunyan Ye* and Brian Hjelle2,*,{dagger},{ddagger}

* Department of Pathology, {dagger} Department of Biology, and {ddagger} Department of Molecular Genetics and Microbiology, Center for Infectious Diseases and Immunity, School of Medicine, University of New Mexico, Albuquerque, NM 87131


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Disclosures
 References
 
Sin Nombre virus (SNV) is a highly pathogenic New World virus and etiologic agent of hantavirus cardiopulmonary syndrome. We have previously shown that replication-defective virus particles are able to induce a strong IFN-stimulated gene (ISG) response in human primary cells. RNA viruses often stimulate the innate immune response by interactions between viral nucleic acids, acting as a pathogen-associated molecular pattern, and cellular pattern-recognition receptors (PRRs). Ligand binding to PRRs activates transcription factors which regulate the expression of antiviral genes, and in all systems examined thus far, IFN regulatory factor 3 (IRF3) has been described as an essential intermediate for induction of ISG expression. However, we now describe a model in which IRF3 is dispensable for the induction of ISG transcription in response to viral particles. IRF3-independent ISG transcription in human hepatoma cell lines is initiated early after exposure to SNV virus particles in an entry- and replication-independent fashion. Furthermore, using gene knockdown, we discovered that this activation is independent of the best-characterized RNA- and protein-sensing PRRs including the cytoplasmic caspase recruitment domain-containing RNA helicases and the TLRs. SNV particles engage a heretofore unrecognized PRR, likely located at the cell surface, and engage a novel IRF3-independent pathway that activates the innate immune response.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Disclosures
 References
 
Microbes are recognized by cells of the innate immune system through their interactions with pattern recognition receptors (PRRs)3 expressed by many cell types including endothelial and epithelial cells. Recognition of pathogen-associated molecular patterns (PAMPs) of viruses by cellular PRRs results in the activation of signaling cascades and transcription factors that modulate the expression of type I IFNs and an array of IFN-stimulated genes (ISGs) that possess diverse antiviral functions. TLRs and the recently discovered caspase recruitment domain-containing cytoplasmic RNA helicases, retinoic acid-inducible gene-I (RIG-I), and myeloid differentiation-associated factor 5 (MDA5), are the best characterized PRRs and their activity is required for the recognition of several pathogenic RNA viruses (1, 2, 3, 4, 5). In the majority of the described systems, viral RNA (vRNA) serves as the PAMP and its binding to specific PRRs, such as TLR3 or RIG-I, results in the activation of transcription factors NF-{kappa}B and IFN regulatory factor 3 (IRF3) via multiple signaling pathways (6). These transcription factors are localized to the cytoplasm and translocate to the nucleus upon activation. Although IRF3 is constitutively expressed, after phosphorylation it forms a homodimer, or a heterodimer with IRF7, and binds IFN-stimulated response elements in the promoter regions of many ISGs, including ISG56 (7, 8, 9, 10, 11). IRF3 also mediates the expression of IFN-beta, although transcription of a subset of ISGs is independent of IFN-beta expression early in viral infection (11, 12, 13, 14). Several groups have shown IRF3 to be indispensable for the expression of ISGs in response to infection by a multitude of RNA viruses (14, 15, 16, 17).

Sin Nombre virus (SNV), an enveloped virus with a genome comprised of three negative-sense RNA segments, is a New World hantavirus (Bunyaviridae: Hantavirus) and is the primary etiologic agent of hantavirus cardiopulmonary syndrome (HCPS) in North America (18, 19). HCPS is characterized by pulmonary edema due to capillary leak, followed by cardiogenic shock. Approximately 453 cases have been reported in the United States since 1993 with a 35% case-fatality ratio (www.cdc.gov/ncidod/diseases/hanta/hps/index.htm). SNV is carried by the deer mouse (Peromyscus maniculatus) and transmitted to humans by inhalation of virus-contaminated urine, feces, and/or saliva (20). Interestingly, infection in the deer mouse is asymptomatic and detectable titers of virus persist for at least many months after experimental inoculation, despite a substantial specific immune response (21). Vascular endothelial cells are thought to be the primary sites of viral replication in humans and infected cells and/or adjacent cells secrete high levels of chemokines and cytokines as a result (22, 23, 24, 25). Despite dysregulation of the vasculature and a strong adaptive immune response, no cytopathic effect is observed in infected tissues. These observations suggest that the inflammatory response in local tissues contributes to the pathogenic process.

We have previously demonstrated that SNV can induce a strong innate immune response in HUVEC even after rendering the virus replication-defective and markedly reducing the titers of vRNA through UV irradiation, suggesting that viral particles themselves contain a PAMP that can induce ISGs independently of the described RNA-recognizing PRRs (26). This, along with the observation that human primary cells infected in vitro mount a robust inflammatory response, indicates that pathology may be due to maladaptive immune responses. One important difference between the hantavirus-human disease model, compared with many other viral disease models, is that humans are an incidental and terminal host for hantaviruses and that neither the virus nor the human immune system have evolved under selective pressures from this host-pathogen interaction. Therefore, we hypothesize that human cells may recognize and signal the activation of innate responses to hantaviruses, such as SNV, differently that those described for other common human pathogenic viruses. Several groups have reported on the innate immune response to hantaviruses, but it has yet to be determined how the human innate immune system recognizes these viruses and how this recognition results in the transcription of innate immunity genes (27, 28, 29, 30, 31). To address these questions, we used well-characterized human hepatoma cell lines to investigate the requirements for viral entry, PRR expression, and the downstream transcription factors in the activation of the innate response to SNV. We found that neither IRF3 nor IRF7 are required for the induction of ISGs in response to replication-defective SNV particles. Furthermore, viral entry and the well-described virus-sensing PRRs are not involved in the initial innate immune response to SNV. These results confirm that some human cells possess an RNA-independent mechanism to detect viruses, distinct from the well-described IRF3-dependent PRR-signaling cascades, which leads to the transcription of ISGs and activation of the innate immune system.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Disclosures
 References
 
Cell culture and treatments with virus or polyinosinic/polycytidylic acid (poly I:C)

We purchased human hepatoma cells (Huh7) and the RIG-I-defective clone Huh7.5 from Apath and grew cells in DMEM (Invitrogen Life Technologies) containing 10% FCS, 1x essential amino acids (Invitrogen Life Technologies), penicillin/streptomycin, and gentamicin.

For SNV treatment, we seeded cells in 48- or 24-well plates at a density to achieve 90–95% confluent after overnight incubation at 37°C, 5% CO2. We previously described the isolation of SNV strain SN77734 from a deer mouse and its propagation and titration in Vero E6 cells under strict standard operating procedures using biosafety level 3 facilities and practices (CDC registration number C20041018-0267; Centers for Disease Control) (32). Treatment was done essentially as described previously (26). Briefly, the cell culture medium was removed and we then added SNV at a multiplicity of infection equivalent to 1.0 (after 15 s inactivation by 254 nm UV light, ~5 mW/cm2) to the cell cultures. SNV-treated cells were then incubated for 1 h at 37°C in a 5% CO2 atmosphere. We then removed the virus-containing medium and replaced it with fresh medium and incubated the cells as above for the amount of time indicated.

For Sendai virus treatment, we exposed cells to Sendai virus (SeV) (Cantell strain; Charles River Laboratories) at a final concentration of 150 hemagglutinin units/ml in serum-free DMEM. We incubated this mixture at 37°C, 5% CO2 for 2 h, followed by the addition of an equal volume of DMEM containing 20% FCS to the cells and incubated them for an additional 14 h. For poly I:C treatment, we seeded cells as above and at the time of infection, and exposed cells to 10% DMEM containing 20 µg/ml poly I:C (Sigma-Aldrich).

RNA silencing

We seeded Huh7 cells in 48-well plates at a density to achieve 50% confluency after overnight incubation. We then transfected these cells for 64 h with the specified siRNA (siGENOME gene-specific pool or siCONTROL nontargeting siRNA pool from Dharmacon) at a final concentration of 100 nM/well along with 0.6 µl/well of DharmaFect 1 transfection reagent as per Dharmacon’s protocol. Control cells were treated in parallel with transfection reagent only. We then exposed cells to UV-SNV or poly I:C, or live SeV as described above. After treatment, we extracted total RNA from cells using the RNeasy kit (Qiagen) and used this RNA in quantitative RT-PCR (qRT-PCR) assays.

Blocking by neutralizing antisera

We used heat-inactivated (56°C, 30 min) serum with a known focus-reduction neutralization titers of 1/1600/ml, to neutralize live or UV-killed SNV (1.5 x 106 foci-forming units/ml) at a 1:40 ratio of serum to virus and incubated this for 30 min at room temperature. We then treated Huh7 with this mixture or with the virus alone for 1 h, removed the supernatant, and added fresh medium. Six hours after treatment with UV-SNV, or 24 h after incubation with live virus, we harvested total cellular RNA and quantitated viral S-segment RNA and ISGs as above. As controls, we used the plasma of two SNV-seronegative individuals as well as serum from a rabbit with Abs raised against rSNV N Ag which is known to lack any neutralizing activity.

Plasmid transfections

We seeded Huh7.5 cells in 48-well plates at a density to achieve 50% confluency after an overnight incubation. We then transfected these cells for 64 h with the indicated amounts of pNiFTy-secreted alkaline phosphatase (SEAP) (Invivogen), pEGFP, pTLR3 (a gift from G. Sen, Lerner Research Institute, Cleveland, OH (33)), or pRIG-I (a gift from M. Gale, University of Texas Southwestern, Dallas, TX (34)) using 4 µl/well effectene (Qiagen) as per the Qiagen transfection protocol. We then removed the medium and treated cells as described above for the amount of time indicated in the experiments.

NF-{kappa}B-SEAP assay

We cotransfected Huh7.5 cells seeded in 48-well plates with 100 ng of pNiFTy and 100 ng of either pEGFP or pTLR3 for 48 h using Effectene as above. After transfection, we exposed cells to ligands followed by the collection of cell supernatants, and heat inactivated the endogenous alkaline phosphatases for 30 min in a 65°C water bath before performing the assay. To perform the phosphatase assay, we added 40 µl of each supernatant to 20 µl of 0.05% CHAPS/PBS (Sigma-Aldrich) and added this to 100 µl of equal parts BluePhos A and B solutions (KPL) in 96-well plates. After a 20-min incubation, we read the 96-well plate using an ELISA plate reader at 630 nm. We calculated the fold change of SEAP by subtracting the OD of control wells and comparing the sample ODs to a standard curve generated using serial dilutions of a sample known to have a high concentration of SEAP.

Real-time SYBR Green and TaqMan RT-PCR

For SYBR Green RT-PCR, we performed reverse transcription using 2 µg of total RNA extracted from cell cultures using the RNeasy kit (Qiagen) and random hexamer primers in 50-µl reactions using the Applied Biosystems TaqMan Reverse Transcription Reagents kit. For PCR, we used the Applied Biosystems Power SYBR Green Reagents kit to perform reactions in triplicate using 3 µl of cDNA and a 0.4 µM final concentration of each primer in a 25 µl total reaction volume. The primers we used were: beta-actin, sense (5'-ccatcatgaagtgtgacgtgg-3') and antisense (5'-gtccgcctagaagcatttgcg-3'); IFN promoter stimulator-1 (IPS-1), sense (5'-agcaagagaccaggatcgactg-3') and antisense (5'-cgcaatgaagtactccaccca-3'); IRF7, sense (5'-taccatctacctgggcttcg-3') and antisense (5'-agggttccagcttcacca-3'); ISG56, sense (5'-tctcagaggagcctggctaag-3') and antisense (5'-ccacactgtatttggtgtctagg-3'); MDA5, sense (5'-cagaaggaagtgtcagctgcttag-3') and antisense (5'-tgctgccacattctcttcatct-3'); myxovirus resistance A (MxA), sense (5'-tgatccagctgctgcatccc-3') and antisense (5'-ggcgcaccttctcctcatac-3'); MyD88, sense (5'-agcattgaggaggattgcca-3') and antisense (5'-gtccgtgggacactgctgt-3'); RIG-I, sense (5'-gactggacgtggcaaaacaa-3') and antisense (5'-ttgaatgcatccaatatacacttctg-3'); Toll/IL-1R domain-containing adaptor protein inducing IFN-beta (TRIF), sense (5'-ccagatgcaacctccactgg-3') and antisense (5'-ctgttccgatgatgattcc-3'). We incubated the reactions at 50°C for 2 min, then 95°C for 10 min followed by 40 cycles of 95°C for 15 s and 60°C for 1 min using an Applied Biosystems Prism 7000 Sequence Detection System. We subjected the reactions to dissociation curve analysis to exclude the possibility of nonspecific amplification and then calculated the fold-change for each gene using the mean of the change in cycle threshold (CT) values ({Delta}CT) normalized to the CT values of GAPDH for each sample (2–{Delta}{Delta}CT).

We performed TaqMan RT-PCR for viral S-segment RNA as previously described (21). Briefly, we extracted vRNA from cells using the RNeasy kit as above. We then reverse-transcribed 3 µl of RNA using an S-segment-specific sense primer (5'-agcacattacagagcagacgggc-3') and subjected 5 µl of the resulting cDNA to PCR with S-segment-specific primers, sense (5'-gcagacgggcagctgtg-3') and antisense (5'-agatcagccagttcccgct-3') and a fluorescently labeled TaqMan probe 5'-(FAM)-tgcattggagaccaaactcggagaactt-(TAMRA)-3' in triplicate PCRs using an Applied Biosystems Prism 7000 Sequence Detection System. We quantitated the vRNA using a standard curve generated using S-segment templates of known copy number.

Western blotting

We cultured Huh7 cells in 24-well plates and transfected them with the indicated small-interfering RNA (siRNA) or transfection reagent only. At 64 h posttreatment, we washed the cells once with ice-cold PBS and made whole cell extracts using 100 µl of a buffer containing 1% Triton X-100, 10 mM Na2HPO4, 150 mM NaCl, 2 mM EDTA, 1% sodium deoxycholate, 0.25% SDS, 1 mM PMSF, and complete mini protease inhibitor (Roche). We then separated equal volumes of lysates on 12.5% SDS-PAGE gels and electrophoretically transferred the proteins to nitrocellulose membranes for 1 h at 100 v. We blocked the membranes in 1% BSA-PBS for 1 h and then probed them with a primary rabbit anti-CD61 (AB1932; Chemicon International) or anti-IRF3 (SC-9082; Santa Cruz Biotechnology) or anti-actin Ab (Cruz SC-1616-R; Santa Cruz Biotechnology) overnight at a dilution of 1/750, 1/200 and 1/2000, respectively. We then washed the membranes three times for 5 min each in Western wash, and incubated them with a phosphatase-labeled anti-rabbit IgG secondary Ab for 1 h. To visualize the proteins, we washed the membranes again and developed using the colorimetric substrate NBT-5-bromo-4-chloro-3-indolyl phosphate.

For N protein detection, we heated supernatants containing virus particles with 5x sample loading buffer containing SDS to 95°C for 5 min before electrophoresis and transfer as above. We then blocked the membranes for 1 h with 5% milk-PBS and then incubated them with a polyclonal rabbit-anti SNV-N Ab (1/1000) for 1 h in 5% milk-PBS. After the primary incubation, we washed the membranes three times for 5 min each in Western wash, and incubated them with a peroxidase-labeled anti-rabbit IgG secondary Ab (1/1000) for 1 h. After an additional washing step, we visualized the proteins using ECL and Kodak BioMax MR film.

Density gradient purification of SNV

We added 10 ml of UV-SNV to a 2-ml cushion of a 50% solution of Optiprep (iodixanol, 5,5'-[(2-hydroxy-1–3 propanediyl)-bis(acetylamino)] bis [N,N'-bis (2,3dihydroxypropyl-2,4,6-triiodo-1,3-benzenecarboxamide]) (Sigma-Aldrich) contained in a 14 x 89 polyallomer centrifuge tube (Beckman). This was placed in a TH641 swing bucket rotor (Sorvall) and centrifuged at 40,000 rpm for 3 h at 4°C. After centrifugation, we collected 4 ml of solution from the bottom of the tube and mixed it with 1 ml of a 50% Optiprep solution. We added this to a 5-ml Optiseal (Bechman) tube and centrifuged at 65,000 rpm for 5 h at 4°C in a NVT90 rotor. We then collected 100-µl fractions from the bottom of the tube and determined the location and concentration of the virus proteins by Western blot (data not shown). Fractions that contained the viral particles were pooled and used in experiments.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Disclosures
 References
 
Replication-defective SNV particles induce ISG transcription in human hepatoma cells

We previously demonstrated that live SNV, or SNV treated with a minimal dose of UV irradiation (UV-SNV) that renders the virus unable to replicate and express N protein, can nonetheless induce ISG expression in primary endothelial cells (26). In an effort to investigate ISG transcription in a tractable and well-studied cell line, we exposed the human hepatoma line Huh7 to UV-inactivated UV-SNV obtained from Vero E6 cell cultures or, as a control, supernatants from uninfected Vero cells. We then measured ISG expression at early time points after such treatment (Fig. 1A). We found that ISG56 and MxA were both up-regulated by 1 h postexposure to supernatants from SNV-infected Vero cell cultures, while Vero-conditioned medium did not elicit a response.


Figure 1
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  		FIGURE 1. Huh7 cells respond to UV-SNV and purified UV-SNV by expression of ISGs. A, Confluent Huh7 were treated with medium (Con), uninfected Vero-conditioned cell culture supernatants (SN), or UV-SNV grown on Vero E6 cells. At the indicated time points posttreatment, ISG56 and MxA expression was analyzed by real-time qRT-PCR. B, UV-SNV was density-purified in Optiprep and equal volumes of UV-SNV stock or purified UV-SNV, or the indicated amounts of recombinant N were used in an anti-N Western blot. C, Huh7 were treated as in (A) with UV-SNV or the indicated ratio of purified UV-SNV relative to N concentration and 6 h posttreatment ISG56 and MxA mRNA levels were determined as above. Results are representative of several individual experiments. Real-time qRT-PCR results are reported as the mean ± SEM from duplicate experiments.

 
SNV is propagated on Vero E6 cells which lack the ability to express type I IFNs (35, 36). Despite this, we sought to confirm that the observed ISG responses are due to factors associated with the virus and not soluble mediators released by these cells into the culture supernatants. We compared responses elicited by UV-SNV obtained directly from Vero cultures as above to those elicited by Optiprep-purified UV-SNV. Purification of virus stocks resulted in an ~6- to 8-fold concentration of the virus as determined by Western blotting of N protein isolated from those fractions that contained high concentrations of viral proteins (Fig. 1B). Treatment of Huh7 with either UV-SNV or purified UV-SNV preparations at similar concentrations of N protein resulted in comparable ISG inductions and stimulation with purified virus was dose dependent, further supporting the hypothesis that the PAMP activity was associated with the viral particle (Fig. 1C).

Viral entry is not required for UV-SNV-mediated ISG inductions

ISG expression is initiated by 1 h following exposure to UV-SNV (Fig. 1A) and this activation is more rapid than that elicited by poly I:C, a synthetic dsRNA that activates the innate response (our unpublished observations), suggesting that early events, perhaps preceding viral entry, may signal the transcription of ISGs. Therefore, we sought to examine viral entry requirements in the context of ISG inductions by silencing CD61, the beta3 integrin receptor for pathogenic hantaviruses, including SNV (37). A panel of siRNAs directed against CD61 mRNA specifically decreased beta3 integrin protein levels in Huh7 as demonstrated by Western blotting (Fig. 2A). To determine whether receptor knockdown can effectively inhibit viral entry, we exposed CD61-silenced Huh7 to live SNV and measured the abundance of viral S-segment genomic RNA 24 and 72 h postinfection. As expected, CD61 knockdown resulted in a 60% decrease in accumulation of vRNA at both time points, showing that viral entry was indeed inhibited by silencing this receptor (Fig. 2B). Despite this inhibition, Huh7 in which CD61 had been silenced responded by up-regulation of ISG mRNAs 6 h after exposure to UV-SNV, and ISG expression was higher, rather than reduced, in those cells than in cells transfected with control siRNAs (Fig. 2C). To assess the effects of neutralizing Abs, we exposed Huh7 to SNV that had been pretreated with human convalescent sera known to contain high titers of neutralizing Abs (38) and measured the abundance of S-segment vRNA 24 h postinfection with live SNV, and ISG expression 6 h posttreatment with UV-SNV. Virus neutralization resulted in a 56–66% decrease in vRNA titers (Fig. 2D). This neutralization did not inhibit ISG responses to UV-SNV (Fig. 2E).


Figure 2
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  		FIGURE 2. Blocking SNV entry does not inhibit ISG responses. A–C, Huh7 were transfected with the indicated siRNAs for 64 h. A, Equal amounts of total cell lysates, or soluble CD61 (lane 3), were used for Western blots which were probed with either anti-CD61 (top panel) or anti-actin (bottom panel). B, Cells were infected with live SNV and at the indicated time points, total cellular RNA was extracted and used for quantitation of viral S-segment by TaqMan assays. Results are reported as the mean ± SEM from triplicate experiments. C, Gene-silenced cells were exposed to UV-SNV and 6 h posttreatment total RNA was extracted and used to determine the expression of ISG56 and MxA by real-time qRT-PCR. Results are reported as the mean ± SEM from duplicate experiments. D and E, SNV (D) or UV-SNV (E) was incubated with serum samples from two convalescent HCPS patients +(a) and +(b) or two control sera -(c) and -(d), or anti-N Abs for 1 h. Huh7 were then exposed to virus samples as above and S-segment vRNA (D) was quantitated 24 h postinfection or ISG56 and MxA mRNA abundances (E) were determined 6 h postexposure.

 
IRF3 and IRF7 are not required for ISG responses to SNV viral particles

Transcription of ISGs is mediated by binding of the IRF family of transcription factors to the promoters of these genes. Signals generated from virus binding to specific, identified PRRs, most of which require viral entry, results in the activation of IRF3, and at later time points, IRF7. IRF3 is activated early and controls the expression of a subset of ISGs, including ISG56 and the initial transcription of IFN-beta. IRF7 is subsequently activated and mediates the expression of IFN-{alpha} (39). In this system, we observe ISG responses that occur independently of viral entry and we have previously reported that SNV particles do not induce IFN-{alpha}/IFN-beta expression in primary endothelial cells. Other investigators have shown the lack of early induction of IFN expression by hantaviruses (28). Based on these observations, we hypothesized that SNV activates a novel entry-independent pathway that results in the transcription of ISGs and that this mechanism is likely to be IRF3 and 7 independent. To determine whether either molecule is required for ISG transcription, we used siRNAs to knock down their expression in Huh7 and measured ISG inductions mediated by UV-SNV or control ligands. Western blotting of IRF3 protein and real-time qRT-PCR of IRF7 mRNAs confirmed effective knockdown of these genes (Fig. 3, A and B). As expected, silencing of IRF3 almost completely inhibited ISG56 and MxA transcriptional responses to poly I:C and SeV, which activate ISGs in an IRF3-dependent fashion (40, 41), but induction of ISGs following exposure to UV-SNV was not attenuated (Fig. 3C). Silencing of IRF7 partially inhibited poly I:C-mediated ISG responses, but again, responses to UV-SNV were not inhibited (Fig. 3C).


Figure 3
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  		FIGURE 3. IRF3 and IRF7 are not required for ISG responses to UV-SNV. A–C, Huh7 were transfected with the indicated siRNAs for 64 h. A, Equal amounts of total cell lysates were used for anti-IRF3 (top panel) or anti-actin (bottom panel) Western blots. B, Total cellular RNA was extracted from cells and used to determine IRF7 mRNA levels by real-time qRT-PCR. C, Total cellular RNA from cells treated with medium, UV-SNV, poly I:C, or SeV, as in Materials and Methods was used to determine ISG56 and MxA mRNA expression levels by real-time qRT-PCR. Results are reported as the mean ± SEM from triplicate experiments.

 
ISG responses to UV-SNV in human hepatoma cells does not require engagement of TLR3 and RIG-I

The lack of involvement of IRF3 and IRF7 in induction of ISGs by SNV suggested to us the well-described viral nucleic acid-sensing PRRs, TLR3 and RIG-I, might not be the molecules that detect the SNV PAMP. To confirm or refute this hypothesis, we exposed Huh7 or Huh7.5 cells, which do not express TLR3 and possess a defective form of RIG-I (34), to UV-SNV and measured the induction of ISG mRNAs. Exposure to UV-SNV induced ISG56 and MxA in both cell lines at 6 h posttreatment, although ISGs were induced slightly better in Huh7 than in Huh7.5 (Fig. 4A). As positive controls to assess the function of TLR3 and RIG-I pathways in our cultures, we used poly I:C presented in the medium and replication-competent SeV, respectively. As expected, Huh7.5 cells did not respond to either treatment, confirming the expected deficiencies, whereas Huh7 cells responded well to both treatments. Both SeV and poly I:C induced ISG56 transcription much better than MxA transcription in responsive Huh7, results opposite that seen when UV-SNV was used as the stimulus.


Figure 4
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  		FIGURE 4. ISG responses to UV-SNV do not require intact TLR3 or RIG-I signaling pathways. A, Confluent Huh7 and Huh7.5 were treated with either medium, UV-SNV, SeV, or poly I:C as described in Materials and Methods. Six hours posttreatment with UV-SNV or poly I:C, and 16 h after SeV infection, total cellular RNA was used to quantitate ISG56 and MxA mRNA expression by real-time qRT-PCR. Results are representative of several individual experiments. B, Huh7.5 were cotransfected with pNiFTy and either pTLR3 or pEGFP. Sixty-four hours posttransfection, cells were treated with medium, UV-SNV, or poly I:C. At the indicated time points, duplicate samples of cell supernatants were collected and used in phosphatase assays as described in Materials and Methods. C, Huh7.5 were transfected with either pEGFP or pRIG-I for 64 h. Cells were then treated with either medium, UV-SNV, or SeV. Six hours postinfection with UV-SNV and 16 h postinfection with SeV, total cellular RNA was used to determine ISG56 and MxA mRNA abundance by qRT-PCR. Results are reported as the mean ± SEM from triplicate experiments.

 
To further examine any possible involvement by TLR3 or RIG-I, we expressed TLR3 and RIG-I in Huh7.5 and measured the responses elicited by UV-SNV or control ligands. Ligand binding to TLR3 results in the activation of NF-{kappa}B, as well as IRF3 (42). We cotransfected Huh7.5 with a NF-{kappa}B reporter construct (pNiFTy-SEAP) and either pTLR3, or a control plasmid (pEGFP) before addition of each ligand. As expected, TLR3 expression conferred NF-{kappa}B-mediated responsiveness to poly I:C, but did not enhance UV-SNV-mediated responses (Fig. 4B). Likewise, transfection of a RIG-I expression plasmid into Huh7.5 conferred responsiveness to SeV, but inductions of MxA and ISG56 mRNAs following UV-SNV exposure were unaffected (Fig. 4C).

SNV-mediated ISG transcription does not require known candidate PRRs

TLR family members other than TLR3, and another described caspase recruitment domain (CARD)-RNA helicase, MDA5, have been shown to recognize viral PAMPs. Therefore, we used gene silencing to inhibit members of these signaling pathways in responsive Huh7 and measured ISG transcription elicited by UV-SNV or control ligands. We transfected Huh7 with panels of siRNAs directed against RIG-I or MDA5, or the downstream adaptor molecule for both helicases, IPS-1, and demonstrated diminished steady-state levels of these mRNAs as determined by real-time qRT-PCR studies (Fig. 5A). As expected, responses to SeV were almost completely inhibited by knockdown of both RIG-I and IPS-1. However, ISG induction by UV-SNV was unaffected by silencing of RIG-I and only slightly inhibited by IPS-1 silencing (Fig. 5B). Knockdown of MDA5 had no effect on UV-SNV-mediated ISG responses (Fig. 5C). To examine TLR-dependent pathways, we successfully silenced both TRIF and MyD88, molecules used by all identified TLRs. Silencing of MyD88 had no effect on UV-SNV-mediated ISG inductions despite decreased MyD88 mRNA levels (Fig. 5, A and C). Silencing of TRIF, which can be used by TLR4, but is the sole adaptor molecule for TLR3, inhibited ISG inductions by poly I:C as expected, but only slightly inhibited UV-SNV-mediated ISG inductions (Fig. 5, A and C).


Figure 5
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  		FIGURE 5. TLRs and CARD-RNA helicases are not necessary for ISG responses to UV-SNV. A–C, Huh7 were transfected with the indicated siRNAs for 64 h. A, Total cellular RNA was extracted and used in qRT-PCR with beta-actin and the specified gene-specific primers. B and C, siRNA-transfected Huh7 were treated with medium, UV-SNV, SeV or poly I:C as in Materials and Methods and total RNA used to determine ISG56 and MxA mRNA expression levels by qRT-PCR. PCR was performed in triplicate for duplicate biological experiments. All results are reported as the mean ± SEM from triplicate experiments.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Disclosures
 References
 
In this study, using a pathogenic hantavirus, we provide the first description of a pathway that is independent of the transcription factors IRF3 and IRF7, that nonetheless leads to the activation of ISG transcription. IRF3 is activated early upon infection by several viruses and is responsible for the transcription of a subset of ISGs, including ISG56, in a type I IFN-independent fashion (10). IRF3 also directs the transcription of IFN-beta, which subsequently acts to amplify the ISG response and stimulates the expression of additional ISGs. Here, we demonstrate that this normally critical transcription factor is dispensable for the innate immune response to SNV in human cell lines and that ISG56 is nonetheless transcribed quickly following exposure to hantavirus particles. Cells of the innate immune system generally detect RNA viruses through recognition of nucleic acids, although there are a limited number of reports where viral proteins are detected by TLRs expressed on the cell surface (43, 44, 45, 46). In this system, we show that vRNA is unlikely to be the PAMP and the protein-sensing TLRs are not responsible for ISG responses to SNV.

Others groups have demonstrated that viruses are able to induce ISG expression following UV treatment and recently it has been discovered that enveloped viruses can induce ISGs following interactions with the cell surface independent of the commonly implicated virus-sensing PRRs (14, 16). IRF3 activity is required in these systems for the transcription of ISGs. The results we report here support the findings that viral entry and these PRRs are not essential for the initial response to virus; however, the new finding that the innate immune system is able to detect and respond to SNV independent of IRF3 suggests the existence of an alternate signaling pathway that nonetheless leads to ISG transcription. It is not surprising that the innate immune system has evolved redundant transcriptional pathways to detect viral infection. Several recent studies have focused on the discovery of virally encoded proteins that modulate the antiviral program and a number of molecules within the recently described PRR-IRF signaling pathways, including IRF3 itself, are targeted for antagonism by viral proteins (47). The existence of these viral defense pathways confirms the importance of the PRR-IRF pathway, but also provides selective pressures that favor the evolution of alternative recognition mechanisms to sense invading microbes. It is possible that our use of a pathogen that is non-native to human cells as a probe facilitated our discovery of this novel antiviral sensing system.

Individual viruses interact with multiple cell surface receptors and use a wide array of receptor classes to gain entry into cells including cellular adhesion molecules, integrins, extracellular matrix molecules, growth factor receptors, and complement cascade proteins, and many of these receptors modulate cellular functions with possible innate immunity implications (48). Although CD61 has been described as an entry receptor for hantaviruses, and possibly is an important mediator of vascular dysregulation in the context of the pathogenic process, it is likely that other cellular receptors participate in virus-cell interactions (29, 37, 49). SNV may interact with additional plasma membrane receptors, such as coreceptors for tethering or entry, and interaction with one or more of these molecules may initiate the observed ISG transcriptional response. We show here that CD61 is not required for the activation of ISGs, although its role in entry was confirmed.

It remains unclear whether the antiviral response described herein contributes to SNV pathogenesis. Of potential interest in this regard is our inability to elicit an ISG response to UV-SNV using murine embryonic fibroblasts as targets (our unpublished observations), in light of the inability of SNV to cause disease in murine models (32). Furthermore, several differences in the response to SNV are observed between our previous experiments in primary endothelial cells, and the cell lines used here, that indicate that some mechanistic heterogeneity may be present in detection of SNV by human cells. Although both cell types can be infected by SNV, neutralizing Abs block ISG responses in endothelial cells (26), but not in Huh7 cells, and ISG expression is activated more rapidly in Huh7. These data indicate that either a divergent PAMP is detected by these cells, or differences in PRR expression, context or localization, allow unique requirements for engagement and signaling by the same PAMP. We have recently investigated SNV-mediated ISG transcription in a number of diverse cell lines that support or do no support SNV replication, including those that lack expression of CD61 and that nonetheless respond by increasing the expression of ISG mRNAs. The PRRs used by these cell lines generate responses similar to that of Huh cells (our unpublished observations), indicating that these responses are not unique to the widely used Huh cell lines. These results differ from what we have previously reported in HUVEC, although additional primary cells have not been examined. In support of the findings described here is our previous observation that HUVEC exposed to either UV-SNV or live SNV do not transcribe IFN-{alpha}/IFN-beta, even at late time points posttreatment. Because IRF3 controls the initial expression of IFN-beta, these data suggest that IRF3 may not be essential for the immunologic recognition of SNV by endothelial cells. Although others have shown that IRF3 and IRF7 are activated in endothelial cells upon infection with hantaviruses at later time points than those examined here, it was not determined whether these transcription factors were required for the observed transcription of ISGs in those systems (30, 50).

In summary, SNV particles can induce the expression of ISGs rapidly without a requirement for IRF3 or IRF7. To our knowledge, this is the first demonstration of the activation of the innate immune response that does not require these transcription factors to respond to a viral infection. Because viral entry is not required for the initiation of ISG transcriptional activation, the cellular responses to the virus particle are transduced directly from the plasma membrane. Furthermore, activation is independent of the TLR and CARD-containing RNA helicase families of receptors commonly identified as important for these responses. Considered together, these results suggest that a heretofore-undefined PAMP-PRR pathway is engaged by SNV that can induce expression of ISGs without the need for IRF3 or IRF7. The SNV PAMP offers a useful instrument through which the identity of this alternative PAMP-PRR axis can be dissected.


   Acknowledgments
 
We thank Ganes Sen from the Lerner Research Institute for providing the TLR3 expression clone and for helpful discussion, and Michael Gale from the University of Texas Southwestern for providing the RIG-I expression clone.


   Disclosures
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Disclosures
References
 
The authors have no financial conflict of interest.


   Footnotes
 
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

1 This work was supported by U.S. Public Services Grants U01 AI56618 and U01 AI054779. J.B.P. was supported by National Institute of Allergy and Infectious Disease Grant 1 T32 AI07583. Back

2 Address correspondence and reprint requests to Dr. Brian L. Hjelle, Department of Pathology, University of New Mexico, 329CRF (MSC08 4640), 1 University of New Mexico, Albuquerque, NM 87131-0001. E-mail address: bhjelle{at}salud.unm.edu Back

3 Abbreviations used in this paper: PRR, pattern recognition receptor; PAMP, pathogen-associated molecular pattern; ISG, IFN-stimulated gene; RIG-I, retinoic acid-inducible gene I; MDA5, myeloid differentiation-associated factor 5; IRF, IFN regulatory factor; vRNA, viral RNA; SNV, Sin Nombre virus; HCPS, hantavirus cardiopulmonary syndrome; TRIF, Toll/IL-1R domain-containing adaptor protein inducing IFN-beta; siRNA, small-interfering RNA; qRT-PCR, quantitative RT-PCR; MxA, myxovirus resistance A; poly I:C, polyinosinic/polycytidylic acid; IPS-1, IFN promoter stimulator-1; SeV, Sendai virus; CT, cycle threshold; SEAP, secreted alkaline phosphatase; CARD, caspase recruitment domain. Back

Received for publication January 19, 2007. Accepted for publication May 14, 2007.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Disclosures
 References
 

  1. Yoneyama, M., M. Kikuchi, K. Matsumoto, T. Imaizumi, M. Miyagishi, K. Taira, E. Foy, Y. M. Loo, M. Gale, Jr, S. Akira, et al 2005. Shared and unique functions of the DExD/H-box helicases RIG-I, MDA5, and LGP2 in antiviral innate immunity. J. Immunol. 175: 2851-2858. [Abstract/Free Full Text]
  2. Kato, H., O. Takeuchi, S. Sato, M. Yoneyama, M. Yamamoto, K. Matsui, S. Uematsu, A. Jung, T. Kawai, K. J. Ishii, et al 2006. Differential roles of MDA5 and RIG-I helicases in the recognition of RNA viruses. Nature 441: 101-105. [Medline]
  3. Kato, H., S. Sato, M. Yoneyama, M. Yamamoto, S. Uematsu, K. Matsui, T. Tsujimura, K. Takeda, T. Fujita, O. Takeuchi, S. Akira. 2005. Cell type-specific involvement of RIG-I in antiviral response. Immunity 23: 19-28. [Medline]
  4. Sen, G. C., S. N. Sarkar. 2005. Transcriptional signaling by double-stranded RNA: role of TLR3. Cytokine Growth Factor Rev. 16: 1-14. [Medline]
  5. Takeda, K., S. Akira. 2004. TLR signaling pathways. Semin. Immunol. 16: 3-9. [Medline]
  6. Maniatis, T., J. V. Falvo, T. H. Kim, T. K. Kim, C. H. Lin, B. S. Parekh, M. G. Wathelet. 1998. Structure and function of the interferon-beta enhanceosome. Cold Spring Harb. Symp. Quant. Biol. 63: 609-620. [Medline]
  7. Lin, R., C. Heylbroeck, P. M. Pitha, J. Hiscott. 1998. Virus-dependent phosphorylation of the IRF-3 transcription factor regulates nuclear translocation, transactivation potential, and proteasome-mediated degradation. Mol. Cell Biol. 18: 2986-2996. [Abstract/Free Full Text]
  8. Guo, J., K. L. Peters, G. C. Sen. 2000. Induction of the human protein P56 by interferon, double-stranded RNA, or virus infection. Virology 267: 209-219. [Medline]
  9. Yang, H., G. Ma, C. H. Lin, M. Orr, M. G. Wathelet. 2004. Mechanism for transcriptional synergy between interferon regulatory factor (IRF)-3 and IRF-7 in activation of the interferon-beta gene promoter. Eur. J. Biochem. 271: 3693-3703. [Medline]
  10. Peters, K. L., H. L. Smith, G. R. Stark, G. C. Sen. 2002. IRF-3-dependent, NF{kappa}B- and JNK-independent activation of the 561 and IFN-beta genes in response to double-stranded RNA. Proc. Natl. Acad. Sci. USA 99: 6322-6327. [Abstract/Free Full Text]
  11. Grandvaux, N., M. J. Servant, B. tenOever, G. C. Sen, S. Balachandran, G. N. Barber, R. Lin, J. Hiscott. 2002. Transcriptional profiling of interferon regulatory factor 3 target genes: direct involvement in the regulation of interferon-stimulated genes. J. Virol. 76: 5532-5539. [Abstract/Free Full Text]
  12. Wathelet, M. G., P. M. Berr, G. A. Huez. 1992. Regulation of gene expression by cytokines and virus in human cells lacking the type-I interferon locus. Eur. J. Biochem. 206: 901-910. [Medline]
  13. Bandyopadhyay, S. K., G. T. Leonard, Jr, T. Bandyopadhyay, G. R. Stark, G. C. Sen. 1995. Transcriptional induction by double-stranded RNA is mediated by interferon-stimulated response elements without activation of interferon-stimulated gene factor 3. J. Biol. Chem. 270: 19624-19629. [Abstract/Free Full Text]
  14. Collins, S. E., R. S. Noyce, K. L. Mossman. 2004. Innate cellular response to virus particle entry requires IRF3 but not virus replication. J. Virol. 78: 1706-1717. [Abstract/Free Full Text]
  15. tenOever, B. R., M. J. Servant, N. Grandvaux, R. Lin, J. Hiscott. 2002. Recognition of the measles virus nucleocapsid as a mechanism of IRF-3 activation. J. Virol. 76: 3659-3669. [Abstract/Free Full Text]
  16. Paladino, P., D. T. Cummings, R. S. Noyce, K. L. Mossman. 2006. The IFN-independent response to virus particle entry provides a first line of antiviral defense that is independent of TLRs and retinoic acid-inducible gene I. J. Immunol. 177: 8008-8016. [Abstract/Free Full Text]
  17. Fredericksen, B. L., M. Smith, M. G. Katze, P. Y. Shi, M. Gale, Jr. 2004. The host response to West Nile virus infection limits viral spread through the activation of the interferon regulatory factor 3 pathway. J. Virol. 78: 7737-7747. [Abstract/Free Full Text]
  18. Elliott, L. H., T. G. Ksiazek, P. E. Rollin, C. F. Spiropoulou, S. Morzunov, M. Monroe, C. S. Goldsmith, C. D. Humphrey, S. R. Zaki, J. W. Krebs. 1994. Isolation of the causative agent of hantavirus pulmonary syndrome. Am. J. Trop. Med. Hyg. 51: 102-108. [Abstract/Free Full Text]
  19. Childs, J. E., T. G. Ksiazek, C. F. Spiropoulou, J. W. Krebs, S. Morzunov, G. O. Maupin, K. L. Gage, P. E. Rollin, J. Sarisky, R. E. Enscore. 1994. Serologic and genetic identification of Peromyscus maniculatus as the primary rodent reservoir for a new hantavirus in the southwestern United States. J. Infect. Dis. 169: 1271-1280. [Medline]
  20. Schmaljohn, C. S.. 1996. Bunyaviridae: the viruses and their replication. B. N. Fields, Jr, and D. M. Knipe, Jr, and P. M. Howley, Jr, eds. Fields Virology 1447-1471. Lippincott-Raven, Philadelphia.
  21. Botten, J., K. Mirowsky, D. Kusewitt, C. Ye, K. Gottlieb, J. Prescott, B. Hjelle. 2003. Persistent Sin Nombre virus infection in the deer mouse (Peromyscus maniculatus) model: sites of replication and strand specific expression. J. Virol. 77: 1540-1550. [Medline]
  22. Nolte, K. B., R. M. Feddersen, K. Foucar, S. R. Zaki, F. T. Koster, D. Madar, T. L. Merlin, P. J. McFeeley, E. T. Umland, R. E. Zumwalt. 1995. Hantavirus pulmonary syndrome in the United States: a pathological description of a disease caused by a new agent. Hum. Pathol. 26: 110-120. [Medline]
  23. Mori, M., A. L. Rothman, I. Kurane, J. M. Montoya, K. B. Nolte, J. E. Norman, D. C. Waite, F. T. Koster, F. A. Ennis. 1999. High levels of cytokine-producing cells in the lung tissues of patients with fatal hantavirus pulmonary syndrome. J. Infect. Dis. 179: 295-302. [Medline]
  24. Zaki, S. R., P. W. Greer, L. M. Coffield, C. S. Goldsmith, K. B. Nolte, K. Foucar, R. M. Feddersen, R. E. Zumwalt, G. L. Miller, A. S. Khan. 1995. Hantavirus pulmonary syndrome: pathogenesis of an emerging infectious disease. Am. J. Pathol. 146: 552-579. [Abstract]
  25. Pober, J. S., M. S. Kluger, J. S. Schechner. 2001. Human endothelial cell presentation of antigen and the homing of memory/effector T cells to skin. Ann. NY Acad. Sci. 941: 12-25. [Medline]
  26. Prescott, J., C. Ye, G. Sen, B. Hjelle. 2005. Induction of innate immune response genes by Sin Nombre hantavirus does not require viral replication. J. Virol. 79: 15007-15015. [Abstract/Free Full Text]
  27. Khaiboullina, S. F., A. A. Rizvanov, V. M. Deyde, S. C. St. Jeor. 2005. Andes virus stimulates interferon-inducible MxA protein expression in endothelial cells. J. Med. Virol. 75: 267-275. [Medline]
  28. Khaiboullina, S. F., A. A. Rizvanov, E. Otteson, A. Miyazato, J. Maciejewski, S. St. Jeor. 2004. Regulation of cellular gene expression in endothelial cells by Sin Nombre and Prospect Hill viruses. Viral Immunol. 17: 234-251. [Medline]
  29. Geimonen, E., S. Neff, T. Raymond, S. S. Kocer, I. N. Gavrilovskaya, E. R. Mackow. 2002. Pathogenic and nonpathogenic hantaviruses differentially regulate endothelial cell responses. Proc. Natl. Acad. Sci. USA 99: 13837-13842. [Abstract/Free Full Text]
  30. Sundstrom, J. B., L. K. McMullan, C. F. Spiropoulou, W. C. Hooper, A. A. Ansari, C. J. Peters, P. E. Rollin. 2001. Hantavirus infection induces the expression of RANTES and IP-10 without causing increased permeability in human lung microvascular endothelial cells. J. Virol. 75: 6070-6085. [Abstract/Free Full Text]
  31. Kraus, A. A., M. J. Raftery, T. Giese, R. Ulrich, R. Zawatzky, S. Hippenstiel, N. Suttorp, D. H. Kruger, G. Schonrich. 2004. Differential antiviral response of endothelial cells after infection with pathogenic and nonpathogenic hantaviruses. J. Virol. 78: 6143-6150. [Abstract/Free Full Text]
  32. Botten, J., K. Mirowsky, D. Kusewitt, M. Bharadwaj, J. Yee, R. Ricci, R. M. Feddersen, B. Hjelle. 2000. Experimental infection model for Sin Nombre hantavirus in the deer mouse (Peromyscus maniculatus). Proc. Natl. Acad. Sci. USA 97: 10578-10583. [Abstract/Free Full Text]
  33. Sarkar, S. N., H. L. Smith, T. M. Rowe, G. C. Sen. 2003. Double-stranded RNA signaling by Toll-like receptor 3 requires specific tyrosine residues in its cytoplasmic domain. J. Biol. Chem. 278: 4393-4396. [Abstract/Free Full Text]
  34. Sumpter, R., Jr, Y. M. Loo, E. Foy, K. Li, M. Yoneyama, T. Fujita, S. M. Lemon, M. Gale, Jr. 2005. Regulating intracellular antiviral defense and permissiveness to hepatitis C virus RNA replication through a cellular RNA helicase, RIG-I. J. Virol. 79: 2689-2699. [Abstract/Free Full Text]
  35. Emeny, J. M., M. J. Morgan. 1979. Regulation of the interferon system: evidence that Vero cells have a genetic defect in interferon production. J. Gen. Virol. 43: 247-252. [Abstract/Free Full Text]
  36. Mosca, J. D., P. M. Pitha. 1986. Transcriptional and posttranscriptional regulation of exogenous human beta interferon gene in simian cells defective in interferon synthesis. Mol. Cell Biol. 6: 2279-2283. [Abstract/Free Full Text]
  37. Gavrilovskaya, I. N., M. Shepley, R. Shaw, M. H. Ginsberg, E. R. Mackow. 1998. beta3 integrins mediate the cellular entry of hantaviruses that cause respiratory failure. Proc. Natl. Acad. Sci. USA 95: 7074-7079. [Abstract/Free Full Text]
  38. Bharadwaj, M., R. Nofchissey, D. Goade, F. Koster, B. Hjelle. 2000. Humoral immune responses in the hantavirus cardiopulmonary syndrome. J. Infect. Dis. 182: 43-48. [Medline]
  39. Levy, D. E., I. Marie, A. Prakash. 2003. Ringing the interferon alarm: differential regulation of gene expression at the interface between innate and adaptive immunity. Curr. Opin. Immunol. 15: 52-58. [Medline]
  40. Li, K., Z. Chen, N. Kato, M. Gale, Jr, S. M. Lemon. 2005. Distinct poly(I-C) and virus-activated signaling pathways leading to interferon-beta production in hepatocytes. J. Biol. Chem. 280: 16739-16747. [Abstract/Free Full Text]
  41. Elco, C. P., J. M. Guenther, B. R. Williams, G. C. Sen. 2005. Analysis of genes induced by Sendai virus infection of mutant cell lines reveals essential roles of interferon regulatory factor 3, NF-{kappa}B, and interferon but not Toll-like receptor 3. J. Virol. 79: 3920-3929. [Abstract/Free Full Text]
  42. Alexopoulou, L., A. C. Holt, R. Medzhitov, R. A. Flavell. 2001. Recognition of double-stranded RNA and activation of NF-{kappa}B by Toll-like receptor 3. Nature 413: 732-738. [Medline]
  43. Compton, T., E. A. Kurt-Jones, K. W. Boehme, J. Belko, E. Latz, D. T. Golenbock, R. W. Finberg. 2003. Human cytomegalovirus activates inflammatory cytokine responses via CD14 and Toll-like receptor 2. J. Virol. 77: 4588-4596. [Abstract/Free Full Text]
  44. Bieback, K., E. Lien, I. M. Klagge, E. Avota, J. Schneider-Schaulies, W. P. Duprex, H. Wagner, C. J. Kirschning, V. M. Ter, S. Schneider-Schaulies. 2002. Hemagglutinin protein of wild-type measles virus activates Toll-like receptor 2 signaling. J. Virol. 76: 8729-8736. [Abstract/Free Full Text]
  45. Dolganiuc, A., S. Oak, K. Kodys, D. T. Golenbock, R. W. Finberg, E. Kurt-Jones, G. Szabo. 2004. Hepatitis C core and nonstructural 3 proteins trigger Toll-like receptor 2-mediated pathways and inflammatory activation. Gastroenterology 127: 1513-1524. [Medline]
  46. Kurt-Jones, E. A., L. Popova, L. Kwinn, L. M. Haynes, L. P. Jones, R. A. Tripp, E. E. Walsh, M. W. Freeman, D. T. Golenbock, L. J. Anderson, R. W. Finberg. 2000. Pattern recognition receptors TLR4 and CD14 mediate response to respiratory syncytial virus. Nat. Immunol. 1: 398-401. [Medline]
  47. Haller, O., G. Kochs, F. Weber. 2006. The interferon response circuit: induction and suppression by pathogenic viruses. Virology 344: 119-130. [Medline]
  48. Baranowski, E., C. M. Ruiz-Jarabo, E. Domingo. 2001. Evolution of cell recognition by viruses. Science 292: 1102-1105. [Abstract/Free Full Text]
  49. Gavrilovskaya, I. N., T. Peresleni, E. Geimonen, E. R. Mackow. 2002. Pathogenic hantaviruses selectively inhibit beta3 integrin directed endothelial cell migration. Arch. Virol. 147: 1913-1931. [Medline]
  50. Spiropoulou, C. F., C. G. Albarino, T. G. Ksiazek, P. E. Rollin. 2007. Andes and Prospect Hill hantaviruses differ in early induction of interferon although both can down-regulate interferon signaling. J. Virol. 81: 2769-2776. [Abstract/Free Full Text]



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