Showing papers on "Virus published in 2007"
TL;DR: A novel function of LDs is revealed in the assembly of infectious HCV and a new perspective on how viruses usurp cellular functions is provided.
Abstract: The lipid droplet (LD) is an organelle that is used for the storage of neutral lipids. It dynamically moves through the cytoplasm, interacting with other organelles, including the endoplasmic reticulum (ER). These interactions are thought to facilitate the transport of lipids and proteins to other organelles. The hepatitis C virus (HCV) is a causative agent of chronic liver diseases. HCV capsid protein (Core) associates with the LD, envelope proteins E1 and E2 reside in the ER lumen, and the viral replicase is assumed to localize on ER-derived membranes. How and where HCV particles are assembled, however, is poorly understood. Here, we show that the LD is involved in the production of infectious virus particles. We demonstrate that Core recruits nonstructural (NS) proteins and replication complexes to LD-associated membranes, and that this recruitment is critical for producing infectious viruses. Furthermore, virus particles were observed in close proximity to LDs, indicating that some steps of virus assembly take place around LDs. This study reveals a novel function of LDs in the assembly of infectious HCV and provides a new perspective on how viruses usurp cellular functions.
1,197 citations
TL;DR: Quantitative analysis of serologic memory for multiple antigens in subjects followed longitudinally over the course of more than one decade suggests that peripheral memory B cells and antibody-secreting plasma cells may represent independently regulated cell populations and may play different roles in the maintenance of protective immunity.
Abstract: We performed a longitudinal analysis of antibody titers specific for viral antigens (vaccinia, measles, mumps, rubella, varicella–zoster virus, and Epstein–Barr virus) and nonreplicating antigens (tetanus and diphtheria) in 45 subjects for a period of up to 26 years. In addition, we measured antigen-specific memory B cells by means of limiting-dilution analysis, and we compared memory B-cell frequencies to their corresponding serum antibody levels. Results Antiviral antibody responses were remarkably stable, with half-lives ranging from an estimated 50 years for varicella–zoster virus to more than 200 years for other viruses such as measles and mumps. Antibody responses against tetanus and diphtheria antigens waned more quickly, with estimated half-lives of 11 years and 19 years, respectively. B-cell memory was long-lived, but there was no significant correlation between peripheral memory B-cell numbers and antibody levels for five of the eight antigens tested. Conclusions These studies provide quantitative analysis of serologic memory for multiple antigens in subjects followed longitudinally over the course of more than one decade. In cases in which multiple exposures or repeated vaccinations were common, memory B-cell numbers did not correlate with antibody titers. This finding suggests that peripheral memory B cells and antibody-secreting plasma cells may represent independently regulated cell populations and may play different roles in the maintenance of protective immunity.
1,043 citations
TL;DR: Human TLR3 appears to be redundant in host defense to most microbes but is vital for natural immunity to HSV-1 in the CNS, which suggests that neurotropic viruses have contributed to the evolutionary maintenance ofTLR3.
Abstract: Some Toll and Toll-like receptors (TLRs) provide immunity to experimental infections in animal models, but their contribution to host defense in natural ecosystems is unknown. We report a dominant-negative TLR3 allele in otherwise healthy children with herpes simplex virus 1 (HSV-1) encephalitis. TLR3 is expressed in the central nervous system (CNS), where it is required to control HSV-1, which spreads from the epithelium to the CNS via cranial nerves. TLR3 is also expressed in epithelial and dendritic cells, which apparently use TLR3-independent pathways to prevent further dissemination of HSV-1 and to provide resistance to other pathogens in TLR3-deficient patients. Human TLR3 appears to be redundant in host defense to most microbes but is vital for natural immunity to HSV-1 in the CNS, which suggests that neurotropic viruses have contributed to the evolutionary maintenance of TLR3.
1,038 citations
TL;DR: It is demonstrated that the 1918 virus caused a highly pathogenic respiratory infection in a cynomolgus macaque model that culminated in acute respiratory distress and a fatal outcome, indicating that atypical host innate immune responses may contribute to lethality.
Abstract: The 1918 'Spanish flu' influenza pandemic was unusually severe, causing about 50 million deaths. Why was it so destructive? The lack of antibiotics to fight secondary infections, and socioeconomic factors may be relevant. But experimental infection of nonhuman primates with reconstructed 1918 virus suggests that the lethal nature of the virus itself was a big factor. It is in fact the only influenza virus lethal to experimentally infected nonhuman primates, and the 1918 virus, unlike other strains, suppresses innate immune responses. The H5N1 viruses now circulating cause a severe lung infection similar to that caused by the 1918 virus and also suppress innate immunity, so therapies that protect this type of host immunity might reduce the severity of infection due to these influenza viruses. The 1918 influenza pandemic was unusually severe, resulting in about 50 million deaths worldwide1. The 1918 virus is also highly pathogenic in mice, and studies have identified a multigenic origin of this virulent phenotype in mice2,3,4. However, these initial characterizations of the 1918 virus did not address the question of its pathogenic potential in primates. Here we demonstrate that the 1918 virus caused a highly pathogenic respiratory infection in a cynomolgus macaque model that culminated in acute respiratory distress and a fatal outcome. Furthermore, infected animals mounted an immune response, characterized by dysregulation of the antiviral response, that was insufficient for protection, indicating that atypical host innate immune responses may contribute to lethality. The ability of influenza viruses to modulate host immune responses, such as that demonstrated for the avian H5N1 influenza viruses5, may be a feature shared by the virulent influenza viruses.
912 citations
TL;DR: These findings strongly support the notion that mammalian organisms too, through the interferon system, use cellular miRNAs to combat viral infections.
Abstract: Plants and invertebrates can use RNA silencing as a protective mechanism in viral infection. Now cellular microRNAs (miRNAs) have been found to have an antiviral function in mammalian cells too. Interferon-β is involved in the regulation of a number of cellular miRNAs in human cells, and eight of these are active against sequences on the hepatitis C virus. In addition, modulation of cellular miRNA levels are found to contribute significantly towards the antiviral effects of interferon-β, suggesting that they are a functioning component of the mammalian innate immune response. Plants and invertebrates can use RNA silencing as a protective mechanism in viral infection. Cellular microRNAs can have anti-viral activity also in mammalian cells, in this case by contributing to the antiviral effects of interferon beta against hepatitis C virus. RNA interference through non-coding microRNAs (miRNAs) represents a vital component of the innate antiviral immune response in plants and invertebrate animals; however, a role for cellular miRNAs in the defence against viral infection in mammalian organisms has thus far remained elusive1. Here we show that interferon beta (IFNβ) rapidly modulates the expression of numerous cellular miRNAs, and that eight of these IFNβ-induced miRNAs have sequence-predicted targets within the hepatitis C virus (HCV) genomic RNA. The introduction of synthetic miRNA-mimics corresponding to these IFNβ-induced miRNAs reproduces the antiviral effects of IFNβ on HCV replication and infection, whereas neutralization of these antiviral miRNAs with anti-miRNAs reduces the antiviral effects of IFNβ against HCV. In addition, we demonstrate that IFNβ treatment leads to a significant reduction in the expression of the liver-specific miR-122, an miRNA that has been previously shown to be essential for HCV replication2. Therefore, our findings strongly support the notion that mammalian organisms too, through the interferon system, use cellular miRNAs to combat viral infections.
877 citations
TL;DR: Experimental vector IB vaccines and genetically manipulated IBVs--with heterologous spike protein genes--have produced promising results, including in the context of in ovo vaccination.
Abstract: Infectious bronchitis virus (IBV), the coronavirus of the chicken (Gallus gallus), is one of the foremost causes of economic loss within the poultry industry, affecting the performance of both meat-type and egg-laying birds. The virus replicates not only in the epithelium of upper and lower respiratory tract tissues, but also in many tissues along the alimentary tract and elsewhere e.g. kidney, oviduct and testes. It can be detected in both respiratory and faecal material. There is increasing evidence that IBV can infect species of bird other than the chicken. Interestingly breeds of chicken vary with respect to the severity of infection with IBV, which may be related to the immune response. Probably the major reason for the high profile of IBV is the existence of a very large number of serotypes. Both live and inactivated IB vaccines are used extensively, the latter requiring priming by the former. Their effectiveness is diminished by poor cross-protection. The nature of the protective immune response to IBV is poorly understood. What is known is that the surface spike protein, indeed the amino-terminal S1 half, is sufficient to induce good protective immunity. There is increasing evidence that only a few amino acid differences amongst S proteins are sufficient to have a detrimental impact on cross-protection. Experimental vector IB vaccines and genetically manipulated IBVs - with heterologous spike protein genes - have produced promising results, including in the context of in ovo vaccination.
810 citations
TL;DR: A broad spectrum of anti-HBV immunity is expressed by patients with chronic HBV infection and this spectrum is proportional to HBV replication levels and can be improved by blocking the PD-1/PD-L1 pathway.
Abstract: Dysfunctional CD8+ T cells present in chronic virus infections can express programmed death 1 (PD-1) molecules, and the inhibition of the engagement of PD-1 with its ligand (PD-L1) has been reported to enhance the antiviral function of these T cells. We took advantage of the wide fluctuations in levels of viremia which are typical of chronic hepatitis B virus (HBV) infection to comprehensively analyze the impact of prolonged exposure to different virus quantities on virus-specific T-cell dysfunction and on its reversibility through the blocking of the PD-1/PD-L1 pathway. We confirm that chronic HBV infection has a profound effect on the HBV-specific T-cell repertoire. Despite the use of a comprehensive panel of peptides covering all HBV proteins, HBV-specific T cells were rarely observed directly ex vivo in samples from patients with chronic infection, in contrast to those from patients with acute HBV infection. In chronic HBV infection, virus-specific T cells were detected mainly in patients with lower levels of viremia. These HBV-specific CD8+ T cells expressed PD-1, and their function was improved by the blocking of PD-1/PD-L1 engagement. Thus, a broad spectrum of anti-HBV immunity is expressed by patients with chronic HBV infection and this spectrum is proportional to HBV replication levels and can be improved by blocking the PD-1/PD-L1 pathway. This information may be useful for the design of immunotherapeutic strategies to complement and optimize available antiviral therapies.
802 citations
TL;DR: This experiment of nature provides a system to advance understanding of immunological homeostasis in humans, illustrating how data obtained from the study of EBV have wider significance to the immunological community.
Abstract: Epstein-Barr virus (EBV) provides a useful model to study cellular immunity to a genetically stable, persistent human virus. Different sets of proteins expressed during EBV's lytic and cell transforming infections induce qualitatively different cellular immune responses. The factors governing immunodominance hierarchies and the biological effectiveness of these different responses are now being revealed. Analysis of infectious mononucleosis (IM), a clinical syndrome that can arise during primary EBV infection, has allowed the evolution of the responses to be tracked over time, giving an understanding of the immune response kinetics and of those determinants affecting selection into memory. Furthermore, following IM, expression of the receptor for the homeostatic cytokine IL-15 on NK and T cells is lost within these individuals. This experiment of nature provides a system to advance understanding of immunological homeostasis in humans, illustrating how data obtained from the study of EBV have wider significance to the immunological community.
736 citations
TL;DR: It is indicated that as with other potentially pathogenic chronic viral infections, the human immune system is able to fully control HIV and prevent HIV-associated disease, at least in some individuals.
723 citations
TL;DR: The presence of multiple instances of the virus in two continents suggests that this virus is geographically widespread in the human population and raises the possibility that the WU virus may be a human pathogen.
Abstract: We report the identification of a novel polyomavirus present in respiratory secretions from human patients with symptoms of acute respiratory tract infection. The virus was initially detected in a nasopharyngeal aspirate from a 3-year-old child from Australia diagnosed with pneumonia. A random library was generated from nucleic acids extracted from the nasopharyngeal aspirate and analyzed by high throughput DNA sequencing. Multiple DNA fragments were cloned that possessed limited homology to known polyomaviruses. We subsequently sequenced the entire virus genome of 5,229 bp, henceforth referred to as WU virus, and found it to have genomic features characteristic of the family Polyomaviridae. The genome was predicted to encode small T antigen, large T antigen, and three capsid proteins: VP1, VP2, and VP3. Phylogenetic analysis clearly revealed that the WU virus was divergent from all known polyomaviruses. Screening of 2,135 patients with acute respiratory tract infections in Brisbane, Queensland, Australia, and St. Louis, Missouri, United States, using WU virus–specific PCR primers resulted in the detection of 43 additional specimens that contained WU virus. The presence of multiple instances of the virus in two continents suggests that this virus is geographically widespread in the human population and raises the possibility that the WU virus may be a human pathogen.
681 citations
TL;DR: The identification of a previously unknown polyomvirus provisionally named KI polyomavirus, which is phylogenetically related to other primatepolyomaviruses in the early region of the genome but has very little homology to known polyomVirus in the late region, illustrates how unbiased screening of respiratory tract samples can be used for the discovery of diverse virus types.
Abstract: We have previously reported on a system for large-scale molecular virus screening of clinical samples. As part of an effort to systematically search for unrecognized human pathogens, the technology was applied for virus screening of human respiratory tract samples. This resulted in the identification of a previously unknown polyomavirus provisionally named KI polyomavirus. The virus is phylogenetically related to other primate polyomaviruses in the early region of the genome but has very little homology (<30% amino acid identity) to known polyomaviruses in the late region. The virus was found by PCR in 6 (1%) of 637 nasopharyngeal aspirates and in 1 (0.5%) of 192 fecal samples but was not detected in sets of urine and blood samples. Since polyomaviruses have oncogenic potential and may produce severe disease in immunosuppressed individuals, continued searching for the virus in different medical contexts is important. This finding further illustrates how unbiased screening of respiratory tract samples can be used for the discovery of diverse virus types.
TL;DR: The sensors involved in coupling recognition of viruses to the induction of the type I IFN genes have only recently been uncovered and include endosomal and cytosolic receptors for RNA and DNA and their properties are reviewed.
TL;DR: It is shown that healthy subjects carry AAV capsid–specific CD8+ T cells and that AAV-mediated gene transfer results in their expansion, and that no such expansion occurs in mice after A AV- mediated gene transfer.
Abstract: Hepatic adeno-associated virus (AAV)-serotype 2 mediatedgene transfer results in transgene product expression that is sustained in experimental animals but not in human subjects. We hypothesize that this is caused by rejection of transduced hepatocytes by AAV capsid–specific memory CD8+ T cells reactivated by AAV vectors. Here we show that healthy subjects carry AAV capsid–specific CD8+ T cells and that AAV-mediated gene transfer results in their expansion. No such expansion occurs in mice after AAV-mediated gene transfer. In addition, we show that AAV-2 induced human T cells proliferate upon exposure to alternate AAV serotypes, indicating that other serotypes are unlikely to evade capsid-specific immune responses.
TL;DR: A deletion-mutant rabies virus encoding EGFP is constructed and found to be an excellent tool for studying detailed morphology and physiology of neurons projecting to injection sites within the mammalian brain.
Abstract: We have constructed a deletion-mutant rabies virus encoding EGFP and find it to be an excellent tool for studying detailed morphology and physiology of neurons projecting to injection sites within the mammalian brain. The virus cannot spread beyond initially infected cells yet, unlike other viral vectors, replicates its core within them. The cells therefore fluoresce intensely, revealing fine dendritic and axonal structure with no background from partially or faintly labeled cells.
TL;DR: The results indicate that, in addition to sequestering dsRNA, the NS1 of influenza A virus binds to RIG-I and inhibits downstream activation of IRF-3, preventing the transcriptional induction of IFN-β.
Abstract: The retinoic acid-inducible gene I product (RIG-I) has been identified as a cellular sensor of RNA virus infection resulting in beta interferon (IFN-β) induction. However, many viruses are known to encode viral products that inhibit IFN-β production. In the case of influenza A virus, the viral nonstructural protein 1 (NS1) prevents the induction of the IFN-β promoter by inhibiting the activation of transcription factors, including IRF-3, involved in IFN-β transcriptional activation. The inhibitory properties of NS1 appear to be due at least in part to its binding to double-stranded RNA (dsRNA), resulting in the sequestration of this viral mediator of RIG-I activation. However, the precise effects of NS1 on the RIG-I-mediated induction of IFN-β have not been characterized. We now report that the NS1 of influenza A virus interacts with RIG-I and inhibits the RIG-I-mediated induction of IFN-β. This inhibition was apparent even when a mutant RIG-I that is constitutively activated (in the absence of dsRNA) was used to trigger IFN-β production. Coexpression of RIG-I, its downstream signaling partner, IPS-1, and NS1 resulted in increased levels of RIG-I and NS1 within an IPS-1-rich, solubilization-resistant fraction after cell lysis. These results suggest that RIG-I, IPS-1, and NS1 become part of the same complex. Consistent with this idea, NS1 was also found to inhibit IFN-β promoter activation by IPS-1 overexpression. Our results indicate that, in addition to sequestering dsRNA, the NS1 of influenza A virus binds to RIG-I and inhibits downstream activation of IRF-3, preventing the transcriptional induction of IFN-β.
TL;DR: The understanding of the interaction between virus and host response has improved markedly, but there are still no clear surrogate markers for prognosis and there are few treatment options.
Abstract: Human T-lymphotropic virus 1 (HTLV-1) has infected human beings for thousands of years, but knowledge about the infection and its pathogenesis is only recently emerging. The virus can be transmitted from mother to child, through sexual contact, and through contaminated blood products. There are areas in Japan, sub-Saharan Africa, the Caribbean, and South America where more than 1% of the general population is infected. Although the majority of HTLV-1 carriers remain asymptomatic, the virus is associated with severe diseases that can be subdivided into three categories: neoplastic diseases (adult T-cell leukaemia/lymphoma), inflammatory syndromes (HTLV-1-associated myelopathy/tropical spastic paraparesis and uveitis among others), and opportunistic infections (including Strongyloides stercoralis hyperinfection and others). The understanding of the interaction between virus and host response has improved markedly, but there are still no clear surrogate markers for prognosis and there are few treatment options.
TL;DR: These findings confirm an essential role of hemagglutinin receptor specificity for the transmission of influenza viruses among mammals and suggest that a predominant human α-2,6 sialic acid binding preference is essential for optimal transmission of this pandemic virus.
Abstract: The 1918 influenza pandemic was a catastrophic series of virus outbreaks that spread across the globe. Here, we show that only a modest change in the 1918 influenza hemagglutinin receptor binding site alters the transmissibility of this pandemic virus. Two amino acid mutations that cause a switch in receptor binding preference from the human α-2,6 to the avian α-2,3 sialic acid resulted in a virus incapable of respiratory droplet transmission between ferrets but that maintained its lethality and replication efficiency in the upper respiratory tract. Furthermore, poor transmission of a 1918 virus with dual α-2,6 and α-2,3 specificity suggests that a predominant human α-2,6 sialic acid binding preference is essential for optimal transmission of this pandemic virus. These findings confirm an essential role of hemagglutinin receptor specificity for the transmission of influenza viruses among mammals.
TL;DR: It is suggested that rapid induction of neutralizing antibodies during the early phase of infection may contribute to control of HCV infection.
Abstract: In contrast to a detailed understanding of antiviral cellular immune responses, the impact of neutralizing antibodies for the resolution of acute hepatitis C is poorly defined. The analysis of neutralizing responses has been hampered by the fact that patient cohorts as well as hepatitis C virus (HCV) strains are usually heterogeneous, and that clinical data from acute-phase and long-term follow-up after infection are not readily available. Using an infectious retroviral HCV pseudoparticle model system, we studied a cohort of women accidentally exposed to the same HCV strain of known sequence. In this single-source outbreak of hepatitis C, viral clearance was associated with a rapid induction of neutralizing antibodies in the early phase of infection. Neutralizing antibodies decreased or disappeared after recovery from HCV infection. In contrast, chronic HCV infection was characterized by absent or low-titer neutralizing antibodies in the early phase of infection and the persistence of infection despite the induction of cross-neutralizing antibodies in the late phase of infection. These data suggest that rapid induction of neutralizing antibodies during the early phase of infection may contribute to control of HCV infection. This finding may have important implications for understanding the pathogenesis of HCV infection and for the development of novel preventive and therapeutic antiviral strategies.
TL;DR: It is shown that naturally occurring fragments of the abundant semen marker prostatic acidic phosphatase form amyloid fibrils, termed Semen-derived Enhancer of Virus Infection (SEVI), capture HIV virions and promote their attachment to target cells, thereby enhancing the infectious virus titer by several orders of magnitude.
TL;DR: This review focuses on recent findings on the importance of glycosylation to viral virulence and immune evasion for several prominent human pathogens.
TL;DR: The demonstration of ISG15 as a novel antiviral molecule with activity against both RNA and DNA viruses provides a target for the development of therapies against important human pathogens.
Abstract: Type I interferons (IFNs) play an essential role in the host response to viral infection through the induction of numerous IFN-stimulated genes (ISGs), including important antiviral molecules such as PKR, RNase L, Mx, and iNOS. Yet, additional antiviral ISGs likely exist. IFN-stimulated gene 15 (ISG15) is a ubiquitin homolog that is rapidly up-regulated after viral infection, and it conjugates to a wide array of host proteins. Although it has been hypothesized that ISG15 functions as an antiviral molecule, the initial evaluation of ISG15-deficient mice revealed no defects in their responses to vesicular stomatitis virus or lymphocytic choriomeningitis virus, leaving open the important question of whether ISG15 is an antiviral molecule in vivo. Here we demonstrate that ISG15 is critical for the host response to viral infection. ISG15−/− mice are more susceptible to influenza A/WSN/33 and influenza B/Lee/40 virus infections. ISG15−/− mice also exhibited increased susceptibility to both herpes simplex virus type 1 and murine gammaherpesvirus 68 infection and to Sindbis virus infection. The increased susceptibility of ISG15−/− mice to Sindbis virus infection was rescued by expressing wild-type ISG15, but not a mutant form of ISG15 that cannot form conjugates, from the Sindbis virus genome. The demonstration of ISG15 as a novel antiviral molecule with activity against both RNA and DNA viruses provides a target for the development of therapies against important human pathogens.
TL;DR: The PVA of low pathogenic avian influenza viruses in human respiratory tract resembled that of H5N1 virus, demonstrating that other properties determine its pathogenicity for humans.
Abstract: Viral attachment to the host cell is critical for tissue and species specificity of virus infections. Recently, pattern of viral attachment (PVA) in human respiratory tract was determined for highly pathogenic avian influenza virus of subtype H5N1. However, PVA of human influenza viruses and other avian influenza viruses in either humans or experimental animals is unknown. Therefore, we compared PVA of two human influenza viruses (H1N1 and H3N2) and two low pathogenic avian influenza viruses (H5N9 and H6N1) with that of H5N1 virus in respiratory tract tissues of humans, mice, ferrets, cynomolgus macaques, cats, and pigs by virus histochemistry. We found that human influenza viruses attached more strongly to human trachea and bronchi than H5N1 virus and attached to different cell types than H5N1 virus. These differences correspond to primary diagnoses of tracheobronchitis for human influenza viruses and diffuse alveolar damage for H5N1 virus. The PVA of low pathogenic avian influenza viruses in human respiratory tract resembled that of H5N1 virus, demonstrating that other properties determine its pathogenicity for humans. The PVA in human respiratory tract most closely mirrored that in ferrets and pigs for human influenza viruses and that in ferrets, pigs, and cats for avian influenza viruses.
TL;DR: The unique phenotype and high degree of polyfunctionality induced by vaccinia virus also extended to inserted HIV gene products of recombinant NYVAC, suggesting that this quality of the CD8+ T cell response may be at least partially responsible for the profound efficacy of these vaccines in protection against smallpox.
Abstract: Vaccinia virus immunization provides lifelong protection against smallpox, but the mechanisms of this exquisite protection are unknown. We used polychromatic flow cytometry to characterize the functional and phenotypic profile of CD8+ T cells induced by vaccinia virus immunization in a comparative vaccine trial of modified vaccinia virus Ankara (MVA) versus Dryvax immunization in which protection was assessed against subsequent Dryvax challenge. Vaccinia virus–specific CD8+ T cells induced by both MVA and Dryvax were highly polyfunctional; they degranulated and produced interferon γ, interleukin 2, macrophage inflammatory protein 1β, and tumor necrosis factor α after antigenic stimulation. Responding CD8+ T cells exhibited an unusual phenotype (CD45RO−CD27intermediate). The unique phenotype and high degree of polyfunctionality induced by vaccinia virus also extended to inserted HIV gene products of recombinant NYVAC. This quality of the CD8+ T cell response may be at least partially responsible for the profound efficacy of these vaccines in protection against smallpox and serves as a benchmark against which other vaccines can be evaluated.
TL;DR: A complete genome sequence of each of the three African viruses was obtained and the open reading frames were characterized, indicating that Kedougou virus was close to dengue viruses but nonetheless distinct, while Bagaza virus shared genetic relatedness with West Nile virus in several genomic regions.
Abstract: Many members of the genus Flavivirus are the agents of important diseases of humans, livestock, and wildlife. Currently, no complete genome sequence is available for the three African viruses, Bagaza, Zika, and Kedougou viruses, each representing a distinct virus subgroup according to the latest virus classification. In this study, we obtained a complete genome sequence of each of those three viruses and characterized the open reading frames (ORFs) with respect to gene sizes, cleavage sites, potential glycosylation sites, distribution of cysteine residues, and unique motifs. The sequences of the three viruses were then scanned across the entire length of the ORF against available sequences of other African flaviviruses and selected reference viruses for genetic relatedness. The data collectively indicated that Kedougou virus was close to dengue viruses but nonetheless distinct, while Bagaza virus shared genetic relatedness with West Nile virus in several genomic regions. In the non-coding regions, it was found that a particular organizational pattern of conserved sequences in the 3' terminal region generally correlated with the current virus grouping.
TL;DR: It is concluded that p7 and NS2 function at an early stage of virion morphogenesis, prior to the assembly of infectious virus.
Abstract: Hepatitis C virus (HCV) infection is a global health concern affecting an estimated 3% of the world's population. Recently, cell culture systems have been established, allowing recapitulation of the complete virus life cycle for the first time. Since the HCV proteins p7 and NS2 are not predicted to be major components of the virion, nor are they required for RNA replication, we investigated whether they might have other roles in the viral life cycle. Here we utilize the recently described infectious J6/JFH chimera to establish that the p7 and NS2 proteins are essential for HCV infectivity. Furthermore, unprocessed forms of p7 and NS2 were not required for this activity. Mutation of two conserved basic residues, previously shown to be important for the ion channel activity of p7 in vitro, drastically impaired infectious virus production. The protease domain of NS2 was required for infectivity, whereas its catalytic active site was dispensable. We conclude that p7 and NS2 function at an early stage of virion morphogenesis, prior to the assembly of infectious virus.
TL;DR: Data show that a single amino acid substitution in PB1-F2 can result in increased viral pathogenicity and could be one of the factors contributing to the high lethality seen with the 1918 pandemic virus.
Abstract: The proapoptotic PB1-F2 protein of influenza A viruses has been shown to contribute to pathogenesis in the mouse model. Expression of full-length PB1-F2 increases the pathogenesis of the influenza A virus, causing weight loss, slower viral clearance, and increased viral titers in the lungs. After comparing viruses from the Hong Kong 1997 H5N1 outbreak, one amino acid change (N66S) was found in the PB1-F2 sequence at position 66 that correlated with pathogenicity. This same amino acid change (N66S) was also found in the PB1-F2 protein of the 1918 pandemic A/Brevig Mission/18 virus. Two isogenic recombinant chimeric viruses were created with an influenza A/WSN/33 virus background containing the PB1 segment from the HK/156/97: WH and WH N66S. In mice infected with WH N66S virus there was increased pathogenicity as measured by weight loss and decreased survival, and a 100-fold increase in virus replication when compared to mice infected with the WH virus. The 1918 pandemic strain A/Brevig Mission/18 was reconstructed with a pathogenicity-reducing mutation in PB1-F2 (S66N). The resultant 1918 S66N virus was attenuated in mice having a 3-log lower 50% lethal dose and caused less morbidity and mortality in mice than the wild-type virus. Viral lung titers were also decreased in 1918 S66N–infected mice compared with wild-type 1918 virus–infected mice. In addition, both viruses with an S at position 66 (WH N66S and wt 1918) induced elevated levels of cytokines in the lungs of infected mice. Together, these data show that a single amino acid substitution in PB1-F2 can result in increased viral pathogenicity and could be one of the factors contributing to the high lethality seen with the 1918 pandemic virus.
TL;DR: The capacity of FLUAV NS1 to suppress the antiviral host defense at multiple levels is demonstrated and the existence of strain-specific differences that may modulate virus pathogenicity is demonstrated.
Abstract: The replication and pathogenicity of influenza A virus (FLUAV) are controlled in part by the alpha/beta interferon (IFN-α/β) system. This virus-host interplay is dependent on the production of IFN-α/β and on the capacity of the viral nonstructural protein NS1 to counteract the IFN system. Two different mechanisms have been described for NS1, namely, blocking the activation of IFN regulatory factor 3 (IRF3) and blocking posttranscriptional processing of cellular mRNAs. Here we directly compare the abilities of NS1 gene products from three different human FLUAV (H1N1) strains to counteract the antiviral host response. We found that A/PR/8/34 NS1 has a strong capacity to inhibit IRF3 and activation of the IFN-β promoter but is unable to suppress expression of other cellular genes. In contrast, the NS1 proteins of A/Tx/36/91 and of A/BM/1/18, the virus that caused the Spanish influenza pandemic, caused suppression of additional cellular gene expression. Thus, these NS1 proteins prevented the establishment of an IFN-induced antiviral state, allowing virus replication even in the presence of IFN. Interestingly, the block in gene expression was dependent on a newly described NS1 domain that is important for interaction with the cleavage and polyadenylation specificity factor (CPSF) component of the cellular pre-mRNA processing machinery but is not functional in A/PR/8/34 NS1. We identified the Phe-103 and Met-106 residues in NS1 as being critical for CPSF binding, together with the previously described C-terminal binding domain. Our results demonstrate the capacity of FLUAV NS1 to suppress the antiviral host defense at multiple levels and the existence of strain-specific differences that may modulate virus pathogenicity.
TL;DR: It is shown that the interferon-induced protein viperin inhibits influenza A virus release from the plasma membrane of infected cells, suggesting that targeting the release stage of the life cycle may affect the replication of many enveloped viruses.
TL;DR: The biological, medical, and neurological aspects of acute, latent, and reactivated infections with the neurotropic herpes viruses are reviewed.
Abstract: Summary Herpes simplex viruses types 1 and 2 (HSV1 and HSV2) and varicella-zoster virus (VZV) establish latent infection in dorsal root ganglia for the entire life of the host. From this reservoir they can reactivate to cause human morbidity and mortality. Although the viruses vary in the clinical disorders they cause and in their molecular structure, they share several features that affect the course of infection of the human nervous system. HSV1 is the causative agent of encephalitis, corneal blindness, and several disorders of the peripheral nervous system; HSV2 is responsible for meningoencephalitis in neonates and meningitis in adults. Reactivation of VZV, the pathogen of varicella (chickenpox), is associated with herpes zoster (shingles) and central nervous system complications such as myelitis and focal vasculopathies. We review the biological, medical, and neurological aspects of acute, latent, and reactivated infections with the neurotropic herpes viruses.
TL;DR: The replication characteristics of recent clinical CHIKV strains are described, indicating that viral entry occurs through pH-dependent endocytosis and general insight is provided into the interaction between chikungunya virus and its mammalian host.
Abstract: An unprecedented epidemic of chikungunya virus (CHIKV) infection recently started in countries of the Indian Ocean area, causing an acute and painful syndrome with strong fever, asthenia, skin rash, polyarthritis, and lethal cases of encephalitis. The basis for chikungunya disease and the tropism of CHIKV remain unknown. Here, we describe the replication characteristics of recent clinical CHIKV strains. Human epithelial and endothelial cells, primary fibroblasts and, to a lesser extent, monocyte-derived macrophages, were susceptible to infection and allowed viral production. In contrast, CHIKV did not replicate in lymphoid and monocytoid cell lines, primary lymphocytes and monocytes, or monocyte-derived dendritic cells. CHIKV replication was cytopathic and associated with an induction of apoptosis in infected cells. Chloroquine, bafilomycin-A1, and short hairpin RNAs against dynamin-2 inhibited viral production, indicating that viral entry occurs through pH-dependent endocytosis. CHIKV was highly sensitive to the antiviral activity of type I and II interferons. These results provide a general insight into the interaction between CHIKV and its mammalian host.