Human bocavirus NP1 inhibits IFN-β production by blocking association of IFN regulatory factor 3 with IFNB promoter

B cell immune response to human bocaviruses

BACKGROUND

Human bocaviruses (HBoVs) have been demonstrated in respiratory and gastrointestinal infections; however, the immune response to them has not been studied in detail. In this study, we investigated the B cell immune responses to HBoV1 and HBoV2, representing two different species of bocaviruses in humans.

METHODS

We analyzed the effects of stimulations with HBoV1 and 2 virus-like particles (VLPs) and of co-stimulation with HBoV1-rhinovirus (RV) on cells of the immune system by flow cytometry, transcriptomics, and luminometric immune assays.

RESULTS

Human B cells, and particularly B regulatory cells (Breg cells), showed an increased immune response to HBoV1-VLPs stimulation. These immune responses were also supported by increased IL-1RA and PDL1 expressions in IL-10+ B cells from peripheral blood mononuclear cells (PBMCs) stimulated with HBoV1-VLPs. In addition, increased levels of IL-10 and IL-1RA were determined in the supernatants of PBMCs following HBoV1-VLPs stimulation. HBoV1-VLPs and RV co-stimulation increased the IL-10+ B cell population. Transcriptome analysis by next-generation RNA sequencing showed an increased expression of IL-10 signalling and Breg cell markers in PBMCs stimulated with HBoV1-VLPs. Furthermore, TGF-β and chemoattractants MIP-1α, MIP-1β and IP10 protein levels were high in the supernatants of PBMCs stimulated with HBoV1-VLPs.

CONCLUSIONS

The findings demonstrate that in Breg cells, IL-10 signalling pathways, and anti-inflammatory activity are induced by HBoV1, which can explain the often mild nature of the disease. In addition, the immune regulatory response induced by HBoV1-VLPs may indicate a potential immunomodulatory role of HBoV1 on the immune system and may represent an immune regulatory strategy.

Human bocavirus respiratory infection: Tracing the path from viral replication and virus-cell interactions to diagnostic methods

Human bocaviruses were first described between 2005 and 2010, identified in respiratory and enteric tract samples of children. Screening studies have shown worldwide distribution. Based on phylogenetic analysis, they were classified into four genotypes (HBoV1-4). From a clinical perspective, human bocavirus 1 (HBoV1) is considered the most relevant, since it can cause upper and lower acute respiratory tract infection, mainly in infants, including common cold, bronchiolitis, and pneumonia, as well as wheezing in susceptible patients. However, the specific processes leading to structural, biochemical, and functional changes resulting in the different clinical presentations have not been elucidated yet. This review surveys the interactions between the virus and target cells that can potentially explain disease-causing mechanisms. It also summarises the clinical phenotype of cases, stressing the role of HBoV1 as an aetiological agent of lower acute respiratory infection in infants, together with laboratory tests for detection and diagnosis. By exploring the current knowledge on the epidemiology of HBoV1, insights into the complex scenario of paediatric respiratory infections are presented, as well as the potential effects that changes in the circulation can have on the dynamics of respiratory agents, spotlighting the benefits of comprehensively increase insights into incidence, interrelationships with co-circulating agents and potential control of HBoV1.

Japanese encephalitis virus NS4B inhibits interferon beta production by targeting TLR3 and TRIF

Japanese encephalitis virus (JEV) is a flavivirus transmitted by mosquitoes, causing epidemics of encephalitis in humans and reproductive disorders in pigs. This virus is predominantly distributed in Asian countries and causes tens of thousands of infections in humans annually. Interferon (IFN) is an essential component of host defense against viral infection. Multiple studies have indicated that multifunctional nonstructural proteins of flaviviruses suppress the host IFN response via various strategies to facilitate viral replication. The flaviviruses encoded nonstructural protein 4B (NS4B) is a multifunctional hydrophobic nonstructural protein widely involved in viral replication, pathogenesis and host immune evasion. In this study, we demonstrated that NS4B of JEV suppressed the induction of IFN-β production, mainly through targeting the TLR3 and TRIF (a TIR domain-containing linker that induces IFN-β) proteins in the TLR3 pathway. In a dual-luciferase reporter assay, JEV NS4B significantly inhibited the activation of IFN-β promoter induced by TLR3 and simultaneously treated with poly (I:C). Moreover, NS4B also inhibited the activation of IFN-β promoter triggered by interferon regulatory factor 3 (IRF3)/5D or its upstream molecules in TLR3 signaling pathway. Furthermore, NS4B inhibited the phosphorylation of IRF3 under the stimulation of TLR3 and TRIF molecules. Mechanistically, JEV NS4B interacts with TLR3 and TRIF and confirmed by co-localization and co-immunoprecipitation assay, thereby inhibiting the activation of downstream sensors in the TLR3-mediated pathway. Overall, our results provide a novel mechanism by which JEV NS4B interferes with the host's antiviral response through targeting TLR3 receptor signaling pathway.

Human Bocavirus in Childhood: A True Respiratory Pathogen or a "Passenger" Virus? A Comprehensive Review

Recently, human bocavirus (HBoV) has appeared as an emerging pathogen, with an increasing number of cases reported worldwide. HBoV is mainly associated with upper and lower respiratory tract infections in adults and children. However, its role as a respiratory pathogen is still not fully understood. It has been reported both as a co-infectious agent (predominantly with respiratory syncytial virus, rhinovirus, parainfluenza viruses, and adenovirus), and as an isolated viral pathogen during respiratory tract infections. It has also been found in asymptomatic subjects. The authors review the available literature on the epidemiology of HBoV, the underlying risk factors associated with infection, the virus's transmission, and its pathogenicity as a single pathogen and in co-infections, as well as the current hypothesis about the host's immune response. An update on different HBoV detection methods is provided, including the use of quantitative single or multiplex molecular methods (screening panels) on nasopharyngeal swabs or respiratory secretions, tissue biopsies, serum tests, and metagenomic next-generations sequencing in serum and respiratory secretions. The clinical features of infection, mainly regarding the respiratory tract but also, though rarely, the gastrointestinal one, are extensively described. Furthermore, a specific focus is dedicated to severe HBoV infections requiring hospitalization, oxygen therapy, and/or intensive care in the pediatric age; rare fatal cases have also been reported. Data on tissue viral persistence, reactivation, and reinfection are evaluated. A comparison of the clinical characteristics of single infection and viral or bacterial co-infections with high or low HBoV rates is carried out to establish the real burden of HBoV disease in the pediatric population.

Regulation of cGAS/STING signaling and corresponding immune escape strategies of viruses

Innate immunity is the first line of defense against invading external pathogens, and pattern recognition receptors (PRRs) are the key receptors that mediate the innate immune response. Nowadays, there are various PRRs in cells that can activate the innate immune response by recognizing pathogen-related molecular patterns (PAMPs). The DNA sensor cGAS, which belongs to the PRRs, plays a crucial role in innate immunity. cGAS detects both foreign and host DNA and generates a second-messenger cGAMP to mediate stimulator of interferon gene (STING)-dependent antiviral responses, thereby exerting an antiviral immune response. However, the process of cGAS/STING signaling is regulated by a wide range of factors. Multiple studies have shown that viruses directly target signal transduction proteins in the cGAS/STING signaling through viral surface proteins to impede innate immunity. It is noteworthy that the virus utilizes these cGAS/STING signaling regulators to evade immune surveillance. Thus, this paper mainly summarized the regulatory mechanism of the cGAS/STING signaling pathway and the immune escape mechanism of the corresponding virus, intending to provide targeted immunotherapy ideas for dealing with specific viral infections in the future.

ICP22/IE63 Mediated Transcriptional Regulation and Immune Evasion: Two Important Survival Strategies for Alphaherpesviruses

In the process of infecting the host, alphaherpesviruses have derived a series of adaptation and survival strategies, such as latent infection, autophagy and immune evasion, to survive in the host environment. Infected cell protein 22 (ICP22) or its homologue immediate early protein 63 (IE63) is a posttranslationally modified multifunctional viral regulatory protein encoded by all alphaherpesviruses. In addition to playing an important role in the efficient use of host cell RNA polymerase II, it also plays an important role in the defense process of the virus overcoming the host immune system. These two effects of ICP22/IE63 are important survival strategies for alphaherpesviruses. In this review, we summarize the complex mechanism by which the ICP22 protein regulates the transcription of alphaherpesviruses and their host genes and the mechanism by which ICP22/IE63 participates in immune escape. Reviewing these mechanisms will also help us understand the pathogenesis of alphaherpesvirus infections and provide new strategies to combat these viral infections.

Identification and characterization of a novel bocaparvovirus in tufted deer (Elaphodus cephalophus) in China

We used viral metagenomics and next-generation sequencing to identify a novel strain of bocaparvovirus in the intestinal tract of tufted deer (Elaphodus cephalophus), tentatively named "Elaphodus cephalophus bocaparvovirus" (ECBOV). A nearly complete genome sequence of 5,354 nucleotides was obtained, which had the typical genome organization and protein motifs of a bocaparvovirus. Sequence comparisons and phylogenetic analysis revealed that ECBOV may be a new ungulate bocaparvovirus. The identification and characterization of viruses in wildlife will facilitate our understanding of genetic evolution and cross-species transmission and thus further reduce the potential threat to human and animal health.

Molecular biology and structure of a novel penaeid shrimp densovirus elucidate convergent parvoviral host capsid evolution

The giant tiger prawn (Penaeus monodon) is a decapod crustacean widely reared for human consumption. Currently, viruses of two distinct lineages of parvoviruses (PVs, family Parvoviridae; subfamily Hamaparvovirinae) infect penaeid shrimp. Here, a PV was isolated and cloned from Vietnamese P. monodon specimens, designated Penaeus monodon metallodensovirus (PmMDV). This is the first member of a third divergent lineage shown to infect penaeid decapods. PmMDV has a transcription strategy unique among invertebrate PVs, using extensive alternative splicing and incorporating transcription elements characteristic of vertebrate-infecting PVs. The PmMDV proteins have no significant sequence similarity with other PVs, except for an SF3 helicase domain in its nonstructural protein. Its capsid structure, determined by cryoelectron microscopy to 3-Å resolution, has a similar surface morphology to Penaeus stylirostris densovirus, despite the lack of significant capsid viral protein (VP) sequence similarity. Unlike other PVs, PmMDV folds its VP without incorporating a βA strand and displayed unique multimer interactions, including the incorporation of a Ca²⁺ cation, attaching the N termini under the icosahedral fivefold symmetry axis, and forming a basket-like pentamer helix bundle. While the PmMDV VP sequence lacks a canonical phospholipase A2 domain, the structure of an EDTA-treated capsid, determined to 2.8-Å resolution, suggests an alternative membrane-penetrating cation-dependent mechanism in its N-terminal region. PmMDV is an observed example of convergent evolution among invertebrate PVs with respect to host-driven capsid structure and unique as a PV showing a cation-sensitive/dependent basket structure for an alternative endosomal egress.

Of Keeping and Tipping the Balance: Host Regulation and Viral Modulation of IRF3-Dependent IFNB1 Expression

The type I interferon (IFN) response is a principal component of our immune system that allows to counter a viral attack immediately upon viral entry into host cells. Upon engagement of aberrantly localised nucleic acids, germline-encoded pattern recognition receptors convey their find via a signalling cascade to prompt kinase-mediated activation of a specific set of five transcription factors. Within the nucleus, the coordinated interaction of these dimeric transcription factors with coactivators and the basal RNA transcription machinery is required to access the gene encoding the type I IFN IFNβ (IFNB1). Virus-induced release of IFNβ then induces the antiviral state of the system and mediates further mechanisms for defence. Due to its key role during the induction of the initial IFN response, the activity of the transcription factor interferon regulatory factor 3 (IRF3) is tightly regulated by the host and fiercely targeted by viral proteins at all conceivable levels. In this review, we will revisit the steps enabling the trans-activating potential of IRF3 after its activation and the subsequent assembly of the multi-protein complex at the IFNβ enhancer that controls gene expression. Further, we will inspect the regulatory mechanisms of these steps imposed by the host cell and present the manifold strategies viruses have evolved to intervene with IFNβ transcription downstream of IRF3 activation in order to secure establishment of a productive infection.

Impact of Natural or Synthetic Singletons in the Capsid of Human Bocavirus 1 on Particle Infectivity and Immunoreactivity

Human bocavirus 1 (HBoV1) is a parvovirus that gathers increasing attention due to its pleiotropic role as a pathogen and emerging vector for human gene therapy. Curiously, albeit a large variety of HBoV1 capsid variants has been isolated from human samples, only one has been studied as a gene transfer vector to date. Here, we analyzed a cohort of HBoV1-positive samples and managed to PCR amplify and sequence 29 distinct HBoV1 capsid variants. These differed from the originally reported HBoV1 reference strain in 32 nucleotides or four amino acids, including a frequent change of threonine to serine at position 590. Interestingly, this T590S mutation was associated with lower viral loads in infected patients. Analysis of the time course of infection in two patients for up to 15 weeks revealed a gradual accumulation of T590S, concurrent with drops in viral loads. Surprisingly, in a recombinant vector context, T590S was beneficial and significantly increased titers compared to that of T590 variants but had no major impact on their transduction ability or immunoreactivity. Additional targeted mutations in the HBoV1 capsid identified several residues that are critical for transduction, capsid assembly, or DNA packaging. Our new findings on the phylogeny, infectivity, and immunoreactivity of HBoV1 capsid variants improve our understanding of bocaviral biology and suggest strategies to enhance HBoV1 gene transfer vectors.IMPORTANCE The family of Parvoviridae comprises a wide variety of members that exhibit a unique biology and that are concurrently highly interesting as a scaffold for the development of human gene therapy vectors. A most notable example is human bocavirus 1 (HBoV1), which we and others have recently harnessed to cross-package and deliver recombinant genomes derived from another parvovirus, the adeno-associated virus (AAV). Here, we expanded the repertoire of known HBoV1 variants by cloning 29 distinct HBoV1 capsid sequences from primary human samples and by analyzing their properties as AAV/HBoV1 gene transfer vectors. This led to our discovery of a mutational hot spot at HBoV1 capsid position 590 that accumulated in two patients during natural infection and that lowers viral loads but increases vector yields. Thereby, our study expands our current understanding of HBoV1 biology in infected human subjects and concomitantly provides avenues to improve AAV/HBoV1 gene transfer vectors.

Predominance of Human Bocavirus Genotype 1 and 3 in Outpatient Children with Diarrhea from Rural Communities in South Africa, 2017-2018

Human bocavirus (HBoV) is an emerging virus globally associated with diarrhea in young children. This study aims to investigate the prevalence of HBoV genotypes in children (≤5 years) from rural communities in South Africa (SA) suffering from acute gastroenteritis (AGE). A total of 141 fecal samples of children ≤5 years with acute gastroenteritis (AGE) were collected from rural primary health care facilities in the Vhembe district of SA between June 2017 and July 2018. Clinical symptoms and demographic data were also recorded. A total of 102 (72%) were outpatients, and 39 (28%) were hospitalized patients. Human bocavirus (HBoV) genotypes were determined using real-time multiplex PCR. DNA extracts of positive samples were confirmed by conventional PCR targeting the NS1 gene. Co-infection with other enteric viruses were determined in HBoV-positive samples using real-time PCR. HBoV was detected in eight (5.7%) children with AGE, of which three (37.5%) were HBoV1, three (37.5%) were HBoV3, and two (25%) were HBoV2. The majority of positive cases were identified in outpatients (62%) between the ages of 1 and 24 months. Co-infection in HBoV-positive samples with other enteric viruses included rotavirus (37.5%), adenovirus (37.5%), norovirus (25%), and astrovirus (12.5%). HBoV infections could be seen as a potential emerging diarrheal pathogen in South Africa. However, more studies are needed to understand the role of HBoV infections in children with AGE.

Genomic and transcriptional analyses of novel parvoviruses identified from dead peafowl

To identify potential pathogens responsible for a disease outbreak of cultured peafowls in China in 2013, metagenomic sequencing was conducted. The genomes of two closely related parvoviruses, namely peafowl parvovirus 1 (PePV1) and PePV2, were identified with size of 4428 bp and 4348 bp, respectively. Phylogenetic analysis revealed that both viruses are novel parvoviruses, belonging to the proposed genus Chapparvovirus of Parvoviridae. The transcriptional profile of PePV1 was analyzed by transfecting a nearly complete PePV1 genome into HEK-293T cells. Results revealed that PePV1 employs one promoter and two polyadenylation sites to start and terminate its transcriptions, with one donor site and two acceptor sites for pre-mRNA splicing. PePV1 DNA and structural protein were detected in several tissues of a dead peafowl, which appeared to have suffered enteritis, pneumonia and viremia. These results provide novel information of chapparvoviruses, and call for attention to the potential pathogens.

Novel Chimeric Gene Therapy Vectors Based on Adeno-Associated Virus and Four Different Mammalian Bocaviruses

Parvoviruses are highly attractive templates for the engineering of safe, efficient, and specific gene therapy vectors, as best exemplified by adeno-associated virus (AAV). Another candidate that currently garners increasing attention is human bocavirus 1 (HBoV1). Notably, HBoV1 capsids can cross-package recombinant (r)AAV2 genomes, yielding rAAV2/HBoV1 chimeras that specifically transduce polarized human airway epithelia (pHAEs). Here, we largely expanded the repertoire of rAAV/BoV chimeras, by assembling packaging plasmids encoding the capsid genes of four additional primate bocaviruses, HBoV2–4 and GBoV (Gorilla BoV). Capsid protein expression and efficient rAAV cross-packaging were validated by immunoblotting and qPCR, respectively. Interestingly, not only HBoV1 but also HBoV4 and GBoV transduced pHAEs as well as primary human lung organoids. Flow cytometry analysis of pHAEs revealed distinct cellular specificities between the BoV isolates, with HBoV1 targeting ciliated, club, and KRT5+ basal cells, whereas HBoV4 showed a preference for KRT5+ basal cells. Surprisingly, primary human hepatocytes, skeletal muscle cells, and T cells were also highly amenable to rAAV/BoV transduction. Finally, we adapted our pipeline for AAV capsid gene shuffling to all five BoV isolates. Collectively, our chimeric rAAV/BoV vectors and bocaviral capsid library represent valuable new resources to dissect BoV biology and to breed unique gene therapy vectors.

NSs Protein of Sandfly Fever Sicilian Phlebovirus Counteracts Interferon (IFN) Induction by Masking the DNA-Binding Domain of IFN Regulatory Factor 3

Sandfly fever Sicilian virus (SFSV) is one of the most widespread and frequently identified members of the genus Phlebovirus (order Bunyavirales, family Phenuiviridae) infecting humans. Being transmitted by Phlebotomus sandflies, SFSV causes a self-limiting, acute, often incapacitating febrile disease ("sandfly fever," "Pappataci fever," or "dog disease") that has been known since at least the beginning of the 20th century. We show that, similarly to other pathogenic phleboviruses, SFSV suppresses the induction of the antiviral type I interferon (IFN) system in an NSs-dependent manner. SFSV NSs interfered with the TBK1-interferon regulatory factor 3 (IRF3) branch of the RIG-I signaling pathway but not with NF-κB activation. Consistently, we identified IRF3 as a host interactor of SFSV NSs. In contrast to IRF3, neither the IFN master regulator IRF7 nor any of the related transcription factors IRF2, IRF5, and IRF9 were bound by SFSV NSs. In spite of this specificity for IRF3, NSs did not inhibit its phosphorylation, dimerization, or nuclear accumulation, and the interaction was independent of the IRF3 activation or multimerization state. In further studies, we identified the DNA-binding domain of IRF3 (amino acids 1 to 113) as sufficient for NSs binding and found that SFSV NSs prevented the association of activated IRF3 with the IFN-β promoter. Thus, unlike highly virulent phleboviruses, which either destroy antiviral host factors or sequester whole signaling chains into inactive aggregates, SFSV modulates type I IFN induction by directly masking the DNA-binding domain of IRF3.IMPORTANCE Phleboviruses are receiving increased attention due to the constant discovery of new species and the ongoing spread of long-known members of the genus. Outbreaks of sandfly fever were reported in the 19th century, during World War I, and during World War II. Currently, SFSV is recognized as one of the most widespread phleboviruses, exhibiting high seroprevalence rates in humans and domestic animals and causing a self-limiting but incapacitating disease predominantly in immunologically naive troops and travelers. We show how the nonstructural NSs protein of SFSV counteracts the upregulation of the antiviral interferon (IFN) system. SFSV NSs specifically inhibits promoter binding by IFN transcription factor 3 (IRF3), a molecular strategy which is unique among phleboviruses and, to our knowledge, among human pathogenic RNA viruses in general. This IRF3-specific and stoichiometric mechanism, greatly distinct from the ones exhibited by the highly virulent phleboviruses, correlates with the intermediate level of pathogenicity of SFSV.

The Human Bocavirus 1 NP1 Protein Is a Multifunctional Regulator of Viral RNA Processing

Human bocavirus 1 (HBoV1) encodes a genus-specific protein, NP1, which regulates viral alternative pre-mRNA processing. Similar to NP1 of the related bocavirus minute virus of canine (MVC), HBoV1 NP1 suppressed cleavage and polyadenylation of RNAs at the viral internal polyadenylation site (pA)p. HBoV1 (pA)p is a complex region. It contains 5 significant cleavage and polyadenylation sites, and NP1 was found to regulate only the three of these sites that are governed by canonical AAUAAA hexamer signals. HBoV1 NP1 also facilitated splicing of the upstream intron adjacent to (pA)p. Alternative polyadenylation and splicing of the upstream intron were independent of each other, functioned efficiently within an isolated transcription unit, and were responsive independent of NP1. Characterization of HBoV1 NP1 generalizes its function within the genus Bocaparvovirus, uncovers important differences, and provides important comparisons with MVC NP1 for mechanistic and evolutionary considerations.IMPORTANCE The Parvovirinae are small nonenveloped icosahedral viruses that are important pathogens in many animal species, including humans. The NP1 protein of human bocavirus 1 (HBoV1), similar to NP1 of the bocavirus minute virus of canine (MVC), regulates viral alternative RNA processing by both suppressing polyadenylation at an internal site, (pA)p, and facilitating splicing of an upstream adjacent intron. These effects allow both extension into the capsid gene and splicing of the viral pre-mRNA that correctly registers the capsid gene open reading frame. Characterization of HBoV1 NP1 generalizes this central mode of parvovirus gene regulation to another member of the bocavirus genus and uncovers both important similarities and differences in function compared to MVC NP1 that will be important for future comparative studies.

A detailed analysis of synonymous codon usage in human bocavirus

Human bocavirus (HBoV) is a recently discovered parvovirus associated with respiratory and gastroenteric infections in children. To date, four distinct subtypes have been identified worldwide. HBoV1 is the most frequently detected bocavirus in clinical samples derived from the respiratory tract. HBoV has a single-stranded DNA genome, which encodes two nonstructural proteins, NS1 and NP1, and two structural proteins, VP1 and VP2. Despite a large number of available HBoV sequences, the molecular evolution of this virus remains enigmatic. Here, we applied bioinformatic methods to measure the codon usage bias in 156 HBoV genomes and analyzed the factors responsible for preferential use of various synonymous codons. The effective number of codons (ENC) indicates a highly conserved, gene-specific codon usage bias in the HBoV genome. The structural genes exhibit a higher degree of codon usage bias than the non-structural genes. Natural selection emerged as dominant factor influencing the codon usage bias in the HBoV genome. Other factors that influence the codon usage include mutational pressure, gene length, protein properties, and the relative abundance of dinucleotides. The results presented in this study provide important insight into the molecular evolution of HBoV and may serve as a primer for HBoV gene expression studies and development of safe and effective vaccines to prevent infection.

Prevalence of Human Bocavirus in Africa and Other Developing Countries between 2005 and 2016: A Potential Emerging Viral Pathogen for Diarrhea

BACKGROUND

Human Bocavirus (HBoV) is an emerging virus discovered in 2005 from individuals suffering gastroenteritis and respiratory tract infections. Numerous studies related to the epidemiology and pathogenesis of HBoV have been conducted worldwide. This review reports on HBoV studies in individuals with acute gastroenteritis, with and without respiratory tract infections in Africa between 2005 and 2016.

MATERIAL AND METHOD

The search engines of PubMed, Google Scholar, and Embase database for published articles of HBoV were used to obtain data between 2005 and 2016. The search words included were as follows: studies performed in Africa or/other developing countries or/worldwide; studies for the detection of HBoV in patients with/without diarrhea and respiratory tract infection; studies using standardized laboratory techniques for detection.

RESULTS

The search yielded a total of 756 publications with 70 studies meeting the inclusion criteria. Studies included children and individuals of all age groups. HBoV prevalence in Africa was 13% in individuals suffering gastroenteritis with/without respiratory tract infection.

CONCLUSION

Reports suggest that HBoV infections are increasingly being recognized worldwide. Therefore, surveillance of individuals suffering from infections in Africa is required to monitor the prevalence of HBoV and help understand the role of HBoV in individuals suffering from gastroenteritis with/without respiratory tract infection.

Impact of RSV Coinfection on Human Bocavirus in Children with Acute Respiratory Infections

OBJECTIVE

The objective of this study was to assess epidemiological and clinical features of human bocavirus (HBoV) coinfection with other viruses.

METHOD

Children coinfected with HBoV between January 2012 and December 2014 were enrolled and retrospectively reviewed.

RESULT

A total of 984 patients were stratified into five groups: HBoV infection alone (n = 249), respiratory syncytial virus (RSV) infection alone (n = 649), HBoV coinfection with RSV (n = 28), with human rhinovirus (HRV) (n = 39) and with other virus (n = 19). Length of hospitalization was longer in HBoV coinfection with RSV group than HBoV (9.0 days vs. 7.0 days, p = 0.001), RSV (9.0 days vs. 8.0 days, p = 0.016) infection alone group. Pneumonia was more common in the HBoV coinfection with RSV group compared with the HBoV, RSV infection alone group, respectively (75.0% vs. 44.2%, 31.3%, p < 0.001). HBoV DNA copy numbers (383 000 copies/ml) were positively correlated with the length of hospitalization (r = 0.334, p < 0.001).

CONCLUSION

HBoV coinfection with RSV increases HBoV infection severity.

Protein A from orange-spotted grouper nervous necrosis virus triggers type I interferon production in fish cell

Family Nodaviridae consists of two genera: Alphanodavirus and Betanodavirus, and the latter is classified into four genotypes, including red-spotted grouper nervous necrosis virus, tiger puffer nervous necrosis virus, striped jack nervous necrosis virus, and barfin flounder nervous necrosis virus. Type I interferons (IFNs) play a central role in the innate immune system and antiviral responses, and the interactions between IFN and NNV have been investigated in this study. We have found that the RNA-dependent RNA polymerase (RdRp) from orange-spotted nervous necrosis virus (OGNNV), named protein A, was capable of activating IFN promoter in fathead minnow (FHM) cells. Transient expression of protein A was found to induce IFN expression and secretion, endowing FHM cells with anti-tiger frog virus ability. Protein A from SJNNV can also induce IFN expression in FHM cells but that from Flock House virus (FHV), a well-studied representative species of genus Alphanodavirus, cannot. RdRp activity and mitochondrial localization were shown to be required for protein A to induce IFN expression by means of activating IRF3 but not NFκB. Furthermore, DsRNA synthesized in vitro transcription and poly I:C activated IFN promoter activity when transfected into FHM cells, and dsRNA were also detected in NNV-infected cells. We postulated that dsRNA, a PAMP, was produced by protein A, leading to activation of innate immune response. These results suggest that protein As from NNV are the agonists of innate immune response. This is the first work to demonstrate the interaction between NNV protein A and innate immune system, and may help to understand pathogenesis of NNV.

Tick-Borne Encephalitis Virus Nonstructural Protein NS5 Induces RANTES Expression Dependent on the RNA-Dependent RNA Polymerase Activity

Tick-borne encephalitis virus (TBEV) is one of the flaviviruses that targets the CNS and causes encephalitis in humans. The mechanism of TBEV that causes CNS destruction remains unclear. It has been reported that RANTES-mediated migration of human blood monocytes and T lymphocytes is specifically induced in the brain of mice infected with TBEV, which causes ensuing neuroinflammation and may contribute to brain destruction. However, the viral components responsible for RANTES induction and the underlying mechanisms remain to be fully addressed. In this study, we demonstrate that the NS5, but not other viral proteins of TBEV, induces RANTES production in human glioblastoma cell lines and primary astrocytes. TBEV NS5 appears to activate the IFN regulatory factor 3 (IRF-3) signaling pathway in a manner dependent on RIG-I/MDA5, which leads to the nuclear translocation of IRF-3 to bind with RANTES promoter. Further studies reveal that the activity of RNA-dependent RNA polymerase (RdRP) but not the RNA cap methyltransferase is critical for TBEV NS5-induced RANTES expression, and this is likely due to RdRP-mediated synthesis of dsRNA. Additional data indicate that the residues at K359, D361, and D664 of TBEV NS5 are critical for RdRP activity and RANTES induction. Of note, NS5s from other flaviviruses, including Japanese encephalitis virus, West Nile virus, Zika virus, and dengue virus, can also induce RANTES expression, suggesting the significance of NS5-induced RANTES expression in flavivirus pathogenesis. Our findings provide a foundation for further understanding how flaviviruses cause neuroinflammation and a potential viral target for intervention.

IFN Regulatory Factors and Antiviral Innate Immunity: How Viruses Can Get Better

The interferon regulatory factor (IRF) family consists of transcriptional regulators that exert multifaceted and versatile functions in multiple biological processes. Their crucial role as central mediators in the establishment and execution of host immunity in response to pathogen-derived signals downstream pattern recognition receptors (PRRs) makes IRFs a hallmark of the host antiviral response. They function as hub molecules at the crossroad of different signaling pathways for the induction of interferon (IFN) and inflammatory cytokines, as well as of antiviral and immunomodulatory genes even in an IFN-independent manner. By regulating the development and activity of immune cells, IRFs also function as a bridge between innate and adaptive responses. As such, IRFs represent attractive and compulsive targets in viral strategies to subvert antiviral signaling. In this study, we discuss current knowledge on the wide array of strategies put in place by pathogenic viruses to evade, subvert, and/or hijack these essential components of host antiviral immunity.

The 3C protease of enterovirus A71 counteracts the activity of host zinc-finger antiviral protein (ZAP)

Enterovirus A71 (EV-A71) is a positive-strand RNA virus that causes hand-foot-mouth disease and neurological complications in children and infants. Although the underlying mechanisms remain to be further defined, impaired immunity is thought to play an important role. The host zinc-finger antiviral protein (ZAP), an IFN-stimulated gene product, has been reported to specifically inhibit the replication of certain viruses. However, whether ZAP restricts the infection of enteroviruses remains unknown. Here, we report that EV-A71 infection upregulates ZAP mRNA in RD and HeLa cells. Moreover, ZAP overexpression rendered 293 T cells resistant to EV-A71 infection, whereas siRNA-mediated depletion of endogenous ZAP enhanced EV-A71 infection. The EV-A71 infection stimulated site-specific proteolysis of two ZAP isoforms, leading to the accumulation of a 40 kDa N-terminal ZAP fragment in virus-infected cells. We further revealed that the 3C protease (3Cpro) of EV-A71 mediates ZAP cleavage, which requires protease activity. Furthermore, ZAP variants with single amino acid substitutions at Gln-369 were resistant to 3Cpro cleavage, implying that Gln-369 is the sole cleavage site in ZAP. Moreover, although ZAP overexpression inhibited EV-A71 replication, the cleaved fragments did not show this effect. Our results indicate that an equilibrium between ZAP and enterovirus 3Cpro controls viral infection. The findings in this study suggest that viral 3Cpro mediated ZAP cleavage may represent a mechanism to escape host antiviral responses.

The Role of the Human Bocavirus (HBoV) in Respiratory Infections

The human bocavirus is one of the most common respiratory viruses and occurs in all age groups. Because Koch’s postulates have been fulfilled unintendedly, it is currently accepted that the virus is a real pathogen associated with upper and lower respiratory tract infections causing clinical symptoms ranging from a mild common cold to life-threatening respiratory diseases. In order to exclude a viremia, serological analysis should be included during laboratory diagnostics, as acute and chronic infections cannot be differentiated by detection of viral nucleic acids in respiratory specimen alone due to prolonged viral shedding. Besides its ability to persist, the virus appears to trigger chronic lung disease and increases clinical symptoms by causing fibrotic lung diseases. Due to the lack of an animal model, clinical trials remain the major method for studying the long-term effects of HBoV infections.

West Nile Virus NS1 Antagonizes Interferon Beta Production by Targeting RIG-I and MDA5

West Nile virus (WNV) is a mosquito-borne flavivirus that causes epidemics of encephalitis and viscerotropic disease worldwide. This virus has spread rapidly and has posed a significant public health threat since the outbreak in New York City in 1999. The interferon (IFN)-mediated antiviral response represents an important component of virus-host interactions and plays an essential role in regulating viral replication. Previous studies have suggested that multifunctional nonstructural proteins encoded by flaviviruses antagonize the host IFN response via various means in order to establish efficient viral replication. In this study, we demonstrated that the nonstructural protein 1 (NS1) of WNV antagonizes IFN-β production, most likely through suppression of retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) activation. In a dual-luciferase reporter assay, WNV NS1 significantly inhibited the activation of the IFN-β promoter after Sendai virus infection or poly(I·C) treatment. NS1 also suppressed the activation of the IFN-β promoter when it was stimulated by interferon regulatory factor 3 (IRF3)/5D or its upstream molecules in the RLR signaling pathway. Furthermore, NS1 blocked the phosphorylation and nuclear translocation of IRF3 upon stimulation by various inducers. Mechanistically, WNV NS1 targets RIG-I and melanoma differentiation-associated gene 5 (MDA5) by interacting with them and subsequently causing their degradation by the proteasome. Furthermore, WNV NS1 inhibits the K63-linked polyubiquitination of RIG-I, thereby inhibiting the activation of downstream sensors in the RLR signaling pathway. Taken together, our results reveal a novel mechanism by which WNV NS1 interferes with the host antiviral response.IMPORTANCE WNV Nile virus (WNV) has received increased attention since its introduction to the United States. However, the pathogenesis of this virus is poorly understood. This study demonstrated that the nonstructural protein 1 (NS1) of WNV antagonizes the induction of interferon beta (IFN-β) by interacting with and degrading retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5), which are crucial viral sensors in the host innate immune system. Further experiments suggested that NS1-mediated inhibition of the RIG-I-like receptor (RLR) signaling pathway involves inhibition of RIG-I K63-linked polyubiquitination and that the proteasome plays a role in RIG-I degradation. This study provides new insights into the regulation of WNV NS1 in the RLR signaling pathway and reveals a novel mechanism by which WNV evades the host innate immune response. The novel findings may guide us to discover new therapeutic targets and develop effective vaccines for WNV infections.

Mutations in the C-terminus of HBoV NS1 affect the function of NP1

Human bocavirus 1 (HBoV1) is an autonomous parvovirus in the Bocaparvovirus genus. The multifunctional nuclear protein NP1 is involved in viral replication. In the present study, we found that the mutations in the C-terminus of NS1 affected NP1 function in viral replication. Knocking out NP1 expression in the recombinant infectious clone, on which the C-terminus of NS1 was mutated based on the clinical samples from nasopharyngeal aspirates, resulted in different degrees of decreased replication. The result suggested that NP1 facilitated the replication of viral genome but was not necessary, which is different from the minute virus of canines, where NP1 is essential for viral replication. Further studies showed that clinical mutations in the NP1 region did not affect viral genome replication, and UP1 promoted viral DNA replication. Our results suggested that the C-terminus of NS1 is important for viral replication and may be a target for regulating the replication of the viral genome.

Human bocavirus 1 infection of CACO-2 cell line cultures

Human bocavirus 1 (HBoV1) is a parvovirus associated with pneumonia in infants. It has been detected in different tissues, including colorectal tumors. In this study, we investigated whether Caco-2 cell line, derived from human colon cancer, can be utilized as a model for HBoV1 replication. We demonstrate HBoV1 replication in Caco-2 cultures supplemented with DEAE-dextran after inoculation with respiratory material from infected patients presenting with acute respiratory infection. A viral cycle of rapid development is displayed. However, in spite of HBoV1 DNA 4-fold increment in the supernatants and monolayers by day 1, evidencing that the system allows the virus genome replication after the entry occurred, infectious progeny particles were not produced. These results are consistent with an infection that is limited to a single growth cycle, which can be associated to mutations in the NS1 and VP1/VP2 regions of HBoV1 genome. Further research will contribute to fully elucidate these observations.

•

HBoV1 replicates within 24 h in standard and differentiated Caco-2 cells.

•

DNA is detected in attached cell and supernatant medium.

•

Immunofluorescence tests evidences HBoV1 infection.

•

DNA replication occurred but infectious progeny particles were not produced.

•

The viral genome presents deleterious mutations at NS1 and VP1/VP2 regions.

Evolutionary and genetic analysis of human bocavirus genotype-1 strains reveals an evidence of intragenomic recombination

PURPOSE

Human bocavirus (HBoV) exsits in four genotypes: 1 to 4, with HBoV-1 being the most prevalent genotype. The aim of the current study was to genetically analyze the full-length genome of the HBoV-1 of recently detected Egyptian strains.

METHODOLOGY

Seven overlapping sets of primers were developed to amplify an almost complete HBoV-1 genome from the clinical samples. The primer sets were tested on three recently identified Egyptian HBoV-1 strains with viral loads ≥105 ml-1. Sequencing was conducted using the same sets of primers. HBoV-1 virus strains were genetically analyzed based on the sequences of their complete genomes and the individual ORFs.

RESULTS

The new sets of primers successfully amplified the three tested strains. Sequence analysis of the full-length genome of the HBoV-1 revealed a considerable level of genetic heterogenicity between different strains. Based on the full genome and VP1 ORF, HBoV-1 viruses were clustered into three main lineages, A to C, and lineage A was further subdivided into three sublineages, A1-A3. The Egyptian strains were clustered within two sublineages, A1 and A2. New amino acid substitutions were detected in NS1 and VP1/VP2 proteins. Both inter- and intragenomic recombination events were detected among the Egyptian strains.

CONCLUSION

The existence of both intragenomic recombination event and multiple amino acid substitutions in the examined Egyptian HBoV-1 strains elucidates considerable level of genetic alterations among bocaviruses. Their possible effects on the virus virulence and multiplication efficiency need to be investigated.

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

Porcine bocavirus NP1 protein suppresses type I IFN production by interfering with IRF3 DNA-binding activity

Type I interferon (IFN) and the IFN-induced cellular antiviral responses are the primary defense mechanisms against viral infection; however, viruses always evolve various mechanisms to antagonize this host's IFN responses. Porcine bocavirus (PBoV) is a newly identified porcine parvovirus. In this study, we found that the nonstructural protein NP1 of PBoV inhibits Sendai virus-induced IFN-β production and the subsequent expression of IFN-stimulating genes (ISGs). Ectopic expression of NP1 significantly impairs IRF3-mediated IFN-β production; however, it does not affect the expression, phosphorylation, and nuclear translocation of IRF3, the most important transcription factor for IFN synthesis. Coimmunoprecipitation and Chromatin immunoprecipitation assays suggested that NP1 interacts with the DNA-binding domain of IRF3, which in turn blocks the association of IRF3 with IFN-β promoter. Together, our findings demonstrated that PBoV encodes an antagonist inhibiting type I IFN production, providing a better understanding of the PBoV immune evasion strategy.

Molecular epidemiology and clinical severity of Human Bocavirus (HBoV) 1-4 in children with acute gastroenteritis from Pune, Western India

Although acute gastroenteritis is a major public health problem worldwide, ∼40% of the cases remain undiagnosed for any etiological agent. Human Bocavirus (HBoV) has been detected frequently in feces of diarrhoeic children suggesting its possible etiological involvement in the disease. HBoV has not been reported in association with acute gastroenteritis from India. Fecal samples (n = 418) collected from children (age ≤5 years) hospitalized with acute gastroenteritis, between January 2009 and December 2011, from three local hospitals were examined for presence of HBoV using PCR targeting the partial VP1/VP2 capsid region (∼575 bp) followed by phylogenetic analysis. HBoV was detected in 24/418 (5.7%) cases. Co-infection was observed in 5/24 (21%) cases. HBoV infections occurred in children ≤12 months of age. Peak HBoV activity was observed in monsoon and post monsoon season. All four HBoV genotypes were detected in the study region. Major clinical symptoms of HBoV mono infections included diarrhoea (100%), fever (90%), dehydration (74%), and vomiting (58%). Dehydration was observed in all of the HBoV2-4 cases and in 50% of the HBoV1 cases. Clinical severity varied with genotype (HBoV2 > HBoV1 > HBoV3 > HBoV4). HBoV2 cases recorded severe and very severe infections. The study illustrates prevalence and vast genetic diversity of HBoVs in acute gastroenteritis. It highlights the clinical features of HBoV1-4 infections and sheds light on clinical impact of HBoV genotypes in gastroenteritis. J. Med. Virol. 89:17-23, 2017. © 2016 Wiley Periodicals, Inc.

Human Bocavirus NS1 and NS1-70 Proteins Inhibit TNF-α-Mediated Activation of NF-κB by targeting p65

Human bocavirus (HBoV), a parvovirus, is a single-stranded DNA etiologic agent causing lower respiratory tract infections in young children worldwide. Nuclear factor kappa B (NF-κB) transcription factors play crucial roles in clearance of invading viruses through activation of many physiological processes. Previous investigation showed that HBoV infection could significantly upregulate the level of TNF-α which is a strong NF-κB stimulator. Here we investigated whether HBoV proteins modulate TNF-α–mediated activation of the NF-κB signaling pathway. We showed that HBoV NS1 and NS1-70 proteins blocked NF-κB activation in response to TNF-α. Overexpression of TNF receptor-associated factor 2 (TRAF2)-, IκB kinase alpha (IKKα)-, IκB kinase beta (IKKβ)-, constitutively active mutant of IKKβ (IKKβ SS/EE)-, or p65-induced NF-κB activation was inhibited by NS1 and NS1-70. Furthermore, NS1 and NS1-70 didn’t interfere with TNF-α-mediated IκBα phosphorylation and degradation, nor p65 nuclear translocation. Coimmunoprecipitation assays confirmed the interaction of both NS1 and NS1-70 with p65. Of note, NS1 but not NS1-70 inhibited TNF-α-mediated p65 phosphorylation at ser536. Our findings together indicate that HBoV NS1 and NS1-70 inhibit NF-κB activation. This is the first time that HBoV has been shown to inhibit NF-κB activation, revealing a potential immune-evasion mechanism that is likely important for HBoV pathogenesis.

Respiratory infections of the human bocavirus

The human bocavirus is one of the most common respiratory viruses and occurs in all age groups. It is associated with upper and lower respiratory tract infections, and causes clinical symptoms from the mild common cold to life threatening respiratory diseases. Besides its ability to persist the virus appears to trigger chronic lung disease and increase the clinical symptoms, while being a putative trigger for fibrotic lung diseases.

Laboratory diagnostics should include serological diagnostics in order to rule out a viremia because due to prolonged viral shedding acute and chronic infections cannot be differentiated on the detection of viral nucleic acids in respiratory specimen alone.

Although Koch’s postulates cannot be formally fulfilled due to the lack of an animal model and the chance for clinical trials with volunteers are limited due to the long term effects of HBoV infections, there is no doubt that the virus is a serious pathogen and requires attention.

The aim of the chapter is to present an overview of our current knowledge on respiratory infections with the human bocavirus, and to provide basic and essential information on clinical features, molecular diagnostics, and epidemiologic challenges arising with this pathogen.

Human bocaviruses: Possible etiologic role in respiratory infection

Four species of human bocaviruses (HBoV) are currently included in the Bocavirus genus. There is satisfactory evidence demonstrating an association between HBoV1 and respiratory disease in children, and there is evidence that HBoV2 (and possibly the HBoV3 and HBoV4 species) are associated with gastroenteritis. In particular, HBoV1 has been associated with a prolonged period of persistence in the mucosa of the respiratory tract. Virus persistence does play a role in the high frequency of co-infections with proper pathogens of the upper and lower respiratory tracts. The high detection rate of multiple respiratory viruses in up to 83% of respiratory specimens and the presence of asymptomatic HBoV1 infections complicate the elucidation of the pathogenic role of the agent. Overall, a large amount of data are available concerning HBoV1, whereas little information is available about other bocavirus species. High viral loads are often associated with symptoms, and viremia may be associated with systemic manifestations such as encephalopathy. The effects and mechanisms of latency, persistence, reactivation, and reinfection are poorly understood. Thus, particularly in co-infections, the pathogenic contribution of the detected bocavirus species cannot be accurately stated. This review summarizes the current knowledge of HBoV species and provides perspectives for future clinical studies.

Porcine bocavirus NP1 negatively regulates interferon signaling pathway by targeting the DNA-binding domain of IRF9

To subvert host antiviral immune responses, many viruses have evolved countermeasures to inhibit IFN signaling pathway. Porcine bocavirus (PBoV), a newly identified porcine parvovirus, has received attention because it shows clinically high co-infection prevalence with other pathogens in post-weaning multisystemic wasting syndrome (PWMS) and diarrheic piglets. In this study, we screened the structural and non-structural proteins encoded by PBoV and found that the non-structural protein NP1 significantly suppressed IFN-stimulated response element (ISRE) activity and subsequent IFN-stimulated gene (ISG) expression. However, NP1 affected neither the activation and translocation of STAT1/STAT2, nor the formation of the heterotrimeric transcription factor complex ISGF3 (STAT1/STAT2/IRF9). Detailed analysis demonstrated that PBoV NP1 blocked the ISGF3 DNA-binding activity by combining with the DNA-binding domain (DBD) of IRF9. In summary, these results indicate that PBoV NP1 interferes with type I IFN signaling pathway by blocking DNA binding of ISGF3 to attenuate innate immune responses.

•

Porcine bocavirus (PBoV) NP1 interferes with the IFN α/β signaling pathway.

•

PBoV NP1 does not prevent STAT1/STAT2 phosphorylation and nuclear translocation.

•

PBoV NP1 inhibits the DNA-binding activity of ISGF3.

•

PBoV NP1 interacts with the DNA-binding domain of IRF9.

Detection and characterisation of novel bocavirus (genus Bocaparvovirus) and gastroenteritis viruses from asymptomatic pigs in Ireland

Background

Livestock animals have been the assumed source of several human epidemics in recent years, for example, influenza H1N1, rotavirus G8/G9, and MERS-CoV. Surveillance of novel viruses in animals is essential to evaluate the risk to human and animal health and to determine any economic impact, for example, failure to thrive. There is a paucity of data regarding detection and characterisation of gastroenteritis viruses, particularly novel viruses, in porcines in Ireland. Recently, a number of small novel porcine DNA viruses have emerged globally, for example, torque teno sus virus, porcine bocavirus, and parvoviruses 2 & 4, and little is known about the biology and potential pathogenicity of these viruses. Bocaparvovirus is a genetically distinct group of viruses which has been recently detected in humans and animals.

Methods

In this study, the presence of gastroenteritis viruses (rotavirus A, porcine circovirus, adenovirus, and porcine bocavirus) was investigated in a selection of archived faecal samples from asymptomatic piglets from a commercial farm in Ireland. A total of 104 specimens were pooled and screened using conventional molecular techniques (PCR and RT-PCR), a subset of specimens (n=44) were then examined individually. Viral diversity was then investigated using statistical and phylogenetic techniques.

Results

Initial screening showed a high prevalence of PBoV in this farm, with the formation of three distinct groups in phylogenetic analysis. Other viruses were also investigated in this study with the first report of PCV, PAdV and lineage I G5 RVA in Ireland. Some specimens contained >1 virus, with statistical analysis indicating a strong correlation for mixed infections of PBoV and PAdV on this farm.

Conclusion

Investigating the diversity of circulating enteric viruses on Irish porcine farms is important to improve the prophylactic tools available and to facilitate the early detection of changes in circulating viruses.

HSV-2 immediate-early protein US1 inhibits IFN-β production by suppressing association of IRF-3 with IFN-β promoter

HSV-2 is the major cause of genital herpes, and its infection increases the risk of HIV-1 acquisition and transmission. After initial infection, HSV-2 can establish latency within the nervous system and thus maintains lifelong infection in humans. It has been suggested that HSV-2 can inhibit type I IFN signaling, but the underlying mechanism has yet to be determined. In this study, we demonstrate that productive HSV-2 infection suppresses Sendai virus (SeV) or polyinosinic-polycytidylic acid-induced IFN-β production. We further reveal that US1, an immediate-early protein of HSV-2, contributes to such suppression, showing that US1 inhibits IFN-β promoter activity and IFN-β production at both mRNA and protein levels, whereas US1 knockout significantly impairs such capability in the context of HSV-2 infection. US1 directly interacts with DNA binding domain of IRF-3, and such interaction suppresses the association of nuclear IRF-3 with the IRF-3 responsive domain of IFN-β promoter, resulting in the suppression of IFN-β promoter activation. Additional studies demonstrate that the 217-414 aa domain of US1 is critical for the suppression of IFN-β production. Our results indicate that HSV-2 US1 downmodulates IFN-β production by suppressing the association of IRF-3 with the IRF-3 responsive domain of IFN-β promoter. Our findings highlight the significance of HSV-2 US1 in inhibiting IFN-β production and provide insights into the molecular mechanism by which HSV-2 evades the host innate immunity, representing an unconventional strategy exploited by a dsDNA virus to interrupt type I IFN signaling pathway.

Porcine bocavirus: achievements in the past five years

Porcine bocavirus is a recently discovered virus that infects pigs and is classified within the Bocavirus genus (family Parvoviridae, subfamily Parvovirinae). The viral genome constitutes linear single-stranded DNA and has three open reading frames that encode four proteins: NS1, NP1, VP1, and VP2. There have been more than seven genotypes discovered to date. These genotypes have been classified into three groups based on VP1 sequence. Porcine bocavirus is much more prevalent in piglets that are co-infected with other pathogens than in healthy piglets. The virus can be detected using PCR, loop-mediated isothermal amplification, cell cultures, indirect immunofluorescence, and other molecular virology techniques. Porcine bocavirus has been detected in various samples, including stool, serum, lymph nodes, and tonsils. Because this virus was discovered only five years ago, there are still many unanswered questions that require further research. This review summarizes the current state of knowledge and primary research achievements regarding porcine bocavirus.

Human bocavirus in patients with encephalitis, Sri Lanka, 2009-2010

We identified human bocavirus (HBoV) DNA by PCR in cerebrospinal fluid from adults and children with encephalitis in Sri Lanka. HBoV types 1, 2, and 3 were identified among these cases. Phylogenetic analysis of HBoV1 strain sequences found no subclustering with strains previously identified among encephalitis cases in Bangladesh.

Innate antiviral immune signaling, viral evasion and modulation by HIV-1

The intracellular innate antiviral response in human cells is an essential component of immunity against virus infection. As obligate intracellular parasites, all viruses must evade the actions of the host cell's innate immune response in order to replicate and persist. Innate immunity is induced when pathogen recognition receptors of the host cell sense viral products including nucleic acid as "non-self". This process induces downstream signaling through adaptor proteins to activate latent transcription factors that drive the expression of genes encoding antiviral and immune modulatory effector proteins that restrict virus replication and regulate adaptive immunity. The interferon regulatory factors (IRFs) are transcription factors that play major roles in innate immunity. In particular, IRF3 is activated in response to infection by a range of viruses including RNA viruses, DNA viruses and retroviruses. Among these viruses, human immunodeficiency virus type 1 (HIV-1) remains a major global health problem mediating chronic infection in millions of people wherein recent studies show that viral persistence is linked with the ability of the virus to dysregulate and evade the innate immune response. In this review, we discuss viral pathogen sensing, innate immune signaling pathways and effectors that respond to viral infection, the role of IRF3 in these processes and how it is regulated by pathogenic viruses. We present a contemporary overview of the interplay between HIV-1 and innate immunity, with a focus on understanding how innate immune control impacts infection outcome and disease.

Herpes simplex virus 1 serine/threonine kinase US3 hyperphosphorylates IRF3 and inhibits beta interferon production

Viral infection initiates a series of signaling cascades that lead to the transcription of interferons (IFNs), finally inducing interferon-stimulated genes (ISGs) to eliminate viruses. Viruses have evolved a variety of strategies to modulate host IFN-mediated immune responses. Herpes simplex virus 1 (HSV-1) US3, a Ser/Thr kinase conserved in alphaherpesviruses, was previously reported to counteract host innate immunity; however, the molecular mechanism is elusive. In this study, we report that US3 blocks IFN-β production by hyperphosphorylating IFN regulatory factor 3 (IRF3). Ectopic expression of US3 protein significantly inhibited Sendai virus (SeV)-mediated activation of IFN-β and IFN-stimulated response element (ISRE) promoters and the transcription of IFN-β, ISG54, and ISG56. US3 was also shown to block SeV-induced dimerization and nuclear translocation of IRF3. The kinase activity was indispensable for its inhibitory function, as kinase-dead (KD) US3 mutants K220M and D305A could not inhibit IFN-β production. Furthermore, US3 interacted with and hyperphosphorylated IRF3 at Ser175 to prevent IRF3 activation. Finally, the US3 KD mutant viruses were constructed and denoted K220M or D305A HSV-1, respectively. Cells and mice infected with both mutant viruses produced remarkably larger amounts of IFN-β than those infected with wild-type HSV-1. For the first time, these findings provide convincing evidence that US3 hyperphosphorylates IRF3, blocks the production of IFN-β, and subverts host innate immunity.

Human bocavirus VP2 upregulates IFN-β pathway by inhibiting ring finger protein 125-mediated ubiquitination of retinoic acid-inducible gene-I

Precise regulation of innate immunity is crucial for maintaining optimal immune responses against infections. Whereas positive regulation of IFN signaling elicits rapid type I IFNs, negative regulation is equally important in preventing the production of superfluous IFNs that can be hazardous to the host. The positive regulators of IFN pathway are known to be the main targets of viruses to antagonize the innate immune system. Whether viruses target the negative regulators of IFN pathway remains to be fully investigated. In this study, we report that the structural protein VP2 of human Bocavirus modulates IFN pathway by targeting the ring finger protein 125 (RNF125), a negative regulator of type I IFN signaling, which conjugates Lys(48)-linked ubiquitination to retinoic acid-inducible gene-I (RIG-I) and subsequently leads to the proteasome-dependent degradation of RIG-I. VP2 not only upregulated Sendai virus (SeV)-induced IFNB promoter activity, but also enhanced SeV-induced IFN-β production at both mRNA and protein levels. In agreement, the level of Ser(396)-phosphorylated IFN regulatory factor 3 stimulated by SeV was enhanced in the presence of VP2. Furthermore, VP2 was demonstrated to physically interact with RNF125, resulting in the reduction of RNF125-mediated ubiquitination and proteasome-dependent degradation of RIG-I. Additional study indicated that endogenous RIG-I degradation was decreased in VP2-expressing cells. Our study delineates a unique phenomenon for aberrant activation of IFN regulatory factor 3 pathway and may represent a new mechanism underlying viral manipulation of the host immune system.

Identification and characterization of complex dual nuclear localization signals in human bocavirus NP1: identification and characterization of complex dual nuclear localization signals in human bocavirus NP1

Human bocavirus (HBoV), closely related to canine minute virus (MVC) and bovine parvovirus (BPV), is a new member of the Bocavirus genus within the Parvoviridae family. The non-structural protein NP1 of HBoV is a nuclear localized protein and plays an important role in DNA replication as well as in the evasion of host innate immunity. In the current study, we provide the first evidence that NP1 possesses a non-classical nuclear localization signal (ncNLS) (amino acids 7-50). Embedded within this ncNLS is a classical bipartite nuclear localization signal (cNLS) (amino acids 14-28), capable of transporting a heterologous cytoplasmic protein β-galactosidase fusion protein (β-gal-EGFP) to the nucleus via the classical importin α/β1-mediated pathway. Amino acids 7-50 containing the cNLS and the ncNLS of NP1 or full-length NP1 interact with importin α1, importin β1 and importin β1Δ, which lacks the importin α binding domain, indicating that the nuclear import of NP1 is through both conventional importin α/β1 heterodimer- and non-classical importinß1-mediated pathways. Given that the arrangement of a cNLS embedded within an ncNLS is unusual in viral proteins, our data together reveal a novel molecular mechanism underlying the nuclear import of HBoV NP1, providing a basis for further understanding its biological function.

Human bocavirus: lessons learned to date

Human bocavirus (HBoV) was identified as the second human parvovirus with pathogenic potential in 2005 in respiratory samples from children suffering from viral respiratory infections of unknown etiology. Since its first description, a large number of clinical studies have been performed that address the clinical significance of HBoV detection and the molecular biology of the virus. This review summarizes the most important steps taken in HBoV research to date and addresses open questions that need to be answered in the future to provide a better understanding of the role of a virus that is difficult to grow in cell culture and is suspected to be a pathogen, although it has not yet fulfilled Koch’s postulates.

Correlation between nucleotide mutation and viral loads of human bocavirus 1 in hospitalized children with respiratory tract infection

The human bocavirus 1 (HBoV1) parvovirus causes respiratory disease and primarily affects children. Despite its worldwide prevalence, the mechanisms of HBoV1 replication and pathogenesis remain largely undefined. In this study of 846 children hospitalized at the Children's Hospital of Chongqing Medical University in China for respiratory tract infection between June 2009 and May 2011, HBoV1 was detected in 112 (13.2%) by real-time quantitative PCR. The median age of HBoV1-positive patients was 10 months old. Forty-five (40.2%) of the HBoV1 cases were monoinfections, and 67 (59.8%) were viral co-infections. Genotyping of all 112 HBoV1-positive cases yielded 27 full HBoV1 sequences, as well as two NS1 gene sequences, 15 NP1 gene sequences and 10 VP1/VP2 gene sequences harbouring 24, 10 and 43 mutations, respectively. Statistical analysis revealed no relationship between genetic mutations and clinical manifestations of HBoV1-positive patients. However, the viral loads were significantly lower in samples with mutations G236A or A447G in NP1, or G1461A in VP1/VP2, than in samples with wild-type HBoV1. Future studies should investigate whether these mutations in the HBoV1 gene may represent useful markers of disease pathogenesis.