Infectious bursal disease virus (IBDV) induces apoptosis in chicken B cells

Exploring Variability: Inflammation Mediator Levels across Tissues and Time in Poultry Experimentally Infected by the G1a and G6 Genogroups of Infectious Bursal Disease Virus (IBDV)

Infectious bursal disease virus (IBDV) is a significant burden for poultry production and market due to both direct disease and induced immunosuppression. In the present study, the expression of different cytokines in the bursa of Fabricius and thymus was evaluated during a 28-day-long experimental infection with two strains classified in the G1a (Classical) and G6 (ITA) genogroups. Although both strains significantly affected and modulated the expression of different molecules, the G6 strain seemed to induce a delayed immune response or suppress it more promptly. A recovery in the expression of several mediators was observed in the G1a-infected group at the end of the study, but not in the G6 one, further supporting a more persistent immunosuppression. This evidence fits with the higher replication level previously reported for the G6 and with the clinical outcome, as this genotype, although subclinical, has often been considered more immunosuppressive. However, unlike other studies focused on shorter time periods after infection, the patterns observed in this paper were highly variable and complex, depending on the strain, tissue, and time point, and characterized by a non-negligible within-group variability. Besides confirming the strain/genogroup effect on immune system modulation, the present study suggests the usefulness of longer monitoring activities after experimental infection to better understand the complex patterns and interactions with the host response.

Advances on adaptive immune responses affected by infectious bursal disease virus in chicken

Infectious bursal disease (IBD) is an acute, highly infectious, and immunosuppressive disease caused by the infectious bursal disease virus (IBDV), which interferes with the immune system, causes hypoimmunity and seriously threatens the healthy development of the poultry industry. Adaptive immune response, an important defense line of host resistance to pathogen infection, is the host-specific immune response mainly mediated by T and B lymphocytes. As an important immunosuppressive pathogen in poultry, IBDV infection is closely related to the injury of the adaptive immune system. In this review, we focus on recent advances in adaptive immune response influenced by IBDV infection, especially the damage on immune organs, as well as the effect on humoral immune response and cellular immune response, hoping to provide a theoretical basis for further exploration of the molecular mechanism of immunosuppression induced by IBDV infection and the establishment of novel prevention and control measures for IBD.

Reduced NR2F2 Expression in the Host Response to Infectious Bursal Disease Virus Infection Suppressed Viral Replication by Enhancing Type I Interferon Expression by Targeting SOCS5

Nuclear receptors are ligand-activated transcription factors that play an important role in regulating innate antiviral immunity and other biological processes. However, the role of nuclear receptors in the host response to infectious bursal disease virus (IBDV) infection remains elusive. In this study, we show that IBDV infection or poly(I·C) treatment of DF-1 or HD11 cells markedly decreased nuclear receptor subfamily 2 group F member 2 (NR2F2) expression. Surprisingly, knockdown, knockout, or inhibition of NR2F2 expression in host cells remarkably inhibited IBDV replication and promoted IBDV/poly(I·C)-induced type I interferon and interferon-stimulated genes expression. Furthermore, our data show that NR2F2 negatively regulates the antiviral innate immune response by promoting the suppressor of cytokine signaling 5 (SOCS5) expression. Thus, reduced NR2F2 expression in the host response to IBDV infection inhibited viral replication by enhancing the expression of type I interferon by targeting SOCS5. These findings reveal that NR2F2 plays a crucial role in antiviral innate immunity, furthering our understanding of the mechanism underlying the host response to viral infection. IMPORTANCE Infectious bursal disease (IBD) is an immunosuppressive disease causing considerable economic losses to the poultry industry worldwide. Nuclear receptors play an important role in regulating innate antiviral immunity. However, the role of nuclear receptors in the host response to IBD virus (IBDV) infection remains elusive. Here, we report that NR2F2 expression decreased in IBDV-infected cells, which consequently reduced SOCS5 expression, promoted type I interferon expression, and suppressed IBDV infection. Thus, NR2F2 serves as a negative factor in the host response to IBDV infection by regulating SOCS5 expression, and intervention in the NR2F2-mediated host response by specific inhibitors might be employed as a strategy for prevention and treatment of IBD.

Chitosan/Calcium-Coated Ginsenoside Rb1 Phosphate Flower-like Microparticles as an Adjuvant to Enhance Immune Responses

Simple Summary

The field-level control over IBD is primarily via vaccination. The development of high effective IBV vaccine has drawing great attentions worldwide. Herein, the GRb1 was encap-sulated into Calcium phosphate and chitosan core-structure nanoparticles microspheres, which con-stitute a novel system for nanoparticle delivery (GRb1/IL-4@CS/Cap). The new nano-adjuvant de-livery system could induce the activation of chicken dendritic cells ( DCs ), with up-regulate the expression of MHC II and CD80, and increase the production of IL-1β and TNF-α. At the same time, it can trigger higher levels of IBDV-specific IgG and higher IgG2a/IgG1 ratio, and promote the production of IFN-γ, TNF-α, IL-4, IL-6, IL-1α, and IL-1βand other cytokines in chicken serum after vaccination, it provides an effective adjuvant system for the development of chicken IBDV attenu-ated vaccine.

Abstract

Infectious bursal disease (IBD) is a highly contagious immunocompromising disorder that caused great economic losses in the poultry industry. The field-level control over IBD is primarily via vaccination. The development of a highly effective IBV vaccine has drawn great attention worldwide. Chitosan/Calcium Phosphate (CS/CaP) nanoparticle was a newly developed effective biological delivery system for drug and antigen. Ginsenoside Rb1 is one of the main bioactive components of ginseng root extract, which has antioxidant, anti-inflammatory and immunological enhancement effects. Until now, the combined effect of CS/CaP and ginsenoside Rb1 on the chicken immune response had remained unknown. In this study, the GRb1 and IL-4 were encapsulated into Calcium phosphate and chitosan core structure nanoparticles microspheres (GRb1/IL-4@CS/CaP), and the effect of a newly developed delivery system on an infectious bursal disease virus (IBDV) attenuated vaccine was further evaluated. The results demonstrated that GRb1/IL-4@CS/CaP treatment could induce the activation of chicken dendritic cells (DCs), with the upregulated expression of MHCII and CD80, and the increased production of IL-1β and TNF-α. Importantly, GRb1/IL-4@CS/CaP could trigger a higher level of IBDV-specific IgG and a higher ratio of IgG2a/IgG1 than the traditional adjuvant groups, promoting the production of cytokine, including IFN-γ, TNF-α, IL-4, IL-6, IL-1α, and IL-1β, in chicken serum after 28 d and 42 d post-vaccine. Taken in all, GRb1/IL-4@CS/CaP could elicit prolonged vigorous immune responses for IBDV attenuated vaccine in chicken, which might provide an effective adjuvant system for avian vaccine development.

Soluble overexpression and purification of infectious bursal disease virus capsid protein VP2 in Escherichia coli and its nanometer structure observation

As part of the development of an infectious bursal disease virus (IBDV) subunit vaccine, this study was designed to improve the expression of highly soluble VP2-LS3 (Haemophilus parasuis lumazine synthase 3, LS3) protein by using different tagged vectors in E. coli. IBDV VP2-LS3 gene was designed and synthesized. Fusion tags, GST, NusA, MBP, Ppi, γ-crystallin, ArsC, and Grifin were joined to the N-terminus of VP2-LS3 protein. Seven expression plasmids were constructed, and each plasmid was transformed into E. coli BL21 (DE3) competent cells. After induction by IPTG, the solubility and expression levels of the various VP2-LS3 proteins were analyzed by SDS-PAGE and Western Blot analysis. The fusion tag that significantly promoted soluble expression of the VP2-LS3 protein was selected. Recombinant proteins were purified using Ni-NTA affinity chromatography, then cleaved by using TEV protease and detected by using transmission electron microscopy. Gel electrophoresis and sequencing analysis showed that all seven recombinant vectors were successfully constructed. GST, NusA, MBP, Ppi, γ-crystallin, ArsC, and Grifin enhanced the expression and solubility of VP2 protein; however, MBP was more effective for the high-purity production of VP2-LS3. Western Blot analysis confirmed successful generation of VP2-LS3 fusion protein in E. coli. The result of transmission electron microscopy showed that VP2-LS3 formed nano-sized particles with homogeneous shape and relatively uniform size. This study established a method to generate VP2-LS3 recombinant protein, which may lay a foundation for the development and subsequent study of IBDV subunit vaccines.

Folic acid enhances proinflammatory and antiviral molecular pathways in chicken B-lymphocytes infected with a mild infectious bursal disease virus

1. This study evaluated the effect of folic acid (FA) supplementation on the proinflammatory and antiviral molecular pathways of B-lymphocytes infected with a modified live IBDV (ST-12) mild vaccine strain during a timed post-infection analysis.2. A chicken B-lymphocytes (DT-40) cell line was cultured in triplicate at a concentration of 5 × 10⁵ cells per well in 24-well plates; and was divided into three groups: 1: No virus, FA; 2: Virus, no FA; 3: Virus + FA at a concentration of 3.96 mM. The experiment was repeated three times.3. Cells in groups 2 and 3 were infected with a modified live IBDV (ST-12) mild vaccine strain at one multiplicity of infection (MOI: 1). After 1 hour of virus adsorption, samples were collected at 0, 3, 6, 12, 24 and 36 hours post-infection (hpi).4. The modified live IBDV (ST-12) mild vaccine strain triggered a B-lymphocyte specific immune response associated with the upregulation of genes involved in virus recognition (Igß), virus sensing (TLR-2, TLR-3, TLR-4 and MDA5), signal transduction and regulation (TRIF, MyD88 and IRF7), and the antiviral effector molecules (IFN-α, OAS, PKR, and viperin).5. FA supplementation modulated IBDV replication and regulated the proinflammatory and antiviral downstream molecular pathways.6. In conclusion, the low virulent pathotype serotype I modified live IBDV (ST-12) mild vaccine strain was able to trigger and mount an immune response in chicken B-lymphocytes without affecting B-cell viability. FA supplementation modulated B lymphocytes response and improved their innate immune proinflammatory and antiviral response molecular pathways.

Inhibition of Antiviral Innate Immunity by Avibirnavirus VP3 via Blocking TBK1-TRAF3 Complex Formation and IRF3 Activation

Type I interferon plays a critical role in the host response against virus infection, including Avibirnavirus. However, many viruses have developed multiple strategies to antagonize the innate host antiviral immune response during coevolution with the host. In this study, we first identified that K33-linked polyubiquitination of lysine-155 of TRAF3 enhances the interaction with TBK1, which positively regulates the host IFN immune response.

The host innate immune system develops various strategies to antagonize virus infection, and the pathogen subverts or evades host innate immunity for self-replication. In the present study, we discovered that Avibirnavirus infectious bursal disease virus (IBDV) VP3 protein significantly inhibits MDA5-induced beta interferon (IFN-β) expression by blocking IRF3 activation. Binding domain mapping showed that the CC1 domain of VP3 and the residue lysine-155 of tumor necrosis factor receptor-associated factor 3 (TRAF3) are essential for the interaction. Furthermore, we found that the CC1 domain was required for VP3 to downregulate MDA5-mediated IFN-β production. A ubiquitination assay showed that lysine-155 of TRAF3 was the critical residue for K33-linked polyubiquitination, which contributes to the formation of a TRAF3-TBK1 complex. Subsequently, we revealed that VP3 blocked TRAF3-TBK1 complex formation through reducing K33-linked polyubiquitination of lysine-155 on TRAF3. Taken together, our data reveal that VP3 inhibits MDA5-dependent IRF3-mediated signaling via blocking TRAF3-TBK1 complex formation, which improves our understanding of the interplay between RNA virus infection and the innate host antiviral immune response.

IMPORTANCE Type I interferon plays a critical role in the host response against virus infection, including Avibirnavirus. However, many viruses have developed multiple strategies to antagonize the innate host antiviral immune response during coevolution with the host. In this study, we first identified that K33-linked polyubiquitination of lysine-155 of TRAF3 enhances the interaction with TBK1, which positively regulates the host IFN immune response. Meanwhile, we discovered that the interaction of the CC1 domain of the Avibirnavirus VP3 protein and the residue lysine-155 of TRAF3 reduced the K33-linked polyubiquitination of TRAF3 and blocked the formation of the TRAF3-TBK1 complex, which contributed to the downregulation of host IFN signaling, supporting viral replication.

Development and evaluation of a recombinant VP2 neutralizing epitope antigen vaccine candidate for infectious bursal disease virus

Infectious bursal disease (IBD) is one of the most economically important infectious diseases. Currently, vaccination is the most effective method to prevent IBD. Medium-virulence vaccines can damage the bursa of Fabricius and result in immunosuppression. Therefore, it is essential to develop a safe and effective vaccine against infectious bursal disease virus (IBDV). In this study, the five neutralizing epitopes of the IBDV VP2 protein were confirmed by neutralizing single chain variable fragment antibodies. Then, the neutralizing epitopes antigen (NEA) protein was constructed with five neutralizing epitopes and expressed by pET-27b. Furthermore, the immune effect and protective immunity of the NEA protein with the following adjuvants were evaluated in specific-pathogen-free chickens: oil emulsion adjuvant (OEA), double emulsion adjuvant (DEA), granulocyte-macrophage colony-stimulating factor (GM-CSF) adjuvant and complete Freund's adjuvant (CFA). The experimental results demonstrated that chickens immunized with NEA vaccines elicited stronger humoral and/or cellular immune responses and inflammatory responses than those in the NEA protein group. Chickens were protected in OEA, CFA and GM-CSF adjuvant groups, which were challenged with virulent IBDV BC6/85. Furthermore, IBDV RNA was not measured, and there appeared to be little apoptosis in the bursa of Fabricius based on TUNEL histology and the expression of Bax and Bcl-2 in the OEA, CFA and GM-CSF adjuvant groups. Based on the experimental results, the advantages and disadvantages of adjuvants and industrial production methods, GM-CSF was found to be the optimal adjuvant. Therefore, NEA with GM-CSF adjuvant is a promising vaccine candidate against IBDV, and it provides a framework for developing other vaccines against infectious viral diseases.

Rapid Generation of Attenuated Infectious Bursal Disease Virus from Dual-Promoter Plasmids by Reduction of Viral Ribonucleoprotein Activity

Infectious bursal disease virus (IBDV) of the Birnaviridae family leads to immunosuppression of young chickens by destroying B cells in the bursa of Fabricius (BFs). Given the increasing number of variant IBDV strains, we urgently require a method to produce attenuated virus for vaccine development. To accomplish this goal, the dual-promoter plasmids in which the RNA polymerase II and RNA polymerase I (Pol I) promoters were placed upstream of the IBDV genomic sequence, which was followed by mouse Pol I terminator and a synthetic polyadenylation signal, were developed for rapid generation of IBDV. This approach did not require trans-supplementation of plasmids for the expression of VP1 and VP3, the main components of IBDV ribonucleoprotein (RNP). Based on the finding in this study that the IBDV RNP activity was partially retained by VP1-FLAG, we successfully rescued the replication-competent IBDV/1FLAG expressing VP1-FLAG. Compared with its parental counterpart, IBDV/1FLAG formed smaller size plaques in cultured cells and induced the same 100% immune protection in vivo However, neither retarded development nor severe BFs lesion was observed in the IBDV/1FLAG-inoculated chickens. Collectively, this is the first report that viral RNP activity was affected by the addition of an epitope tag on the componential viral proteins. Furthermore, this work demonstrates the rapid generation of attenuated IBDV from dual-promoter plasmids via reducing viral RNP activity by a fused FLAG tag on the C terminus of VP1. This would be a convenient strategy to attenuate epidemic variant IBDV strains for rapid and efficient vaccine development.IMPORTANCE Immunosuppression in chickens as a result of infectious bursal disease virus (IBDV) infection leads to significant economic losses in the poultry industry worldwide every year. Currently, vaccination is still the best way to prevent the prevalence of IBDV. However, with the occurrence of increasing numbers of variant IBDV strains, it is challenging to develop antigen-matched live attenuated vaccine. Here, we first developed a dual-promoter reverse-genetic system for the rapid generation of IBDV. Using this system, the attenuated IBDV/1FLAG expressing VP1-FLAG, which displays the decreased viral RNP activity, was rescued. Moreover, IBDV/1FLAG inoculation induced a similar level of neutralizing antibodies to that of its parental counterpart, protecting chickens against lethal challenge. Our study, for the first time, describes a dual-promoter reverse-genetic approach for the rapid generation of attenuated IBDV while maintaining entire parental antigenicity, suggesting a potential new method to attenuate epidemic variant IBDV strains for vaccine development.

Epigenetic Upregulation of Chicken MicroRNA-16-5p Expression in DF-1 Cells following Infection with Infectious Bursal Disease Virus (IBDV) Enhances IBDV-Induced Apoptosis and Viral Replication

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression posttranscriptionally by silencing or degrading their targets and play important roles in the host response to pathogenic infection. Although infectious bursal disease virus (IBDV)-induced apoptosis in host cells has been established, the underlying molecular mechanism is not completely unraveled. Here, we show that infection of DF-1 cells by IBDV induced gga-miR-16-5p (chicken miR-16-5p) expression via demethylation of the pre-miR-16-2 (gga-miR-16-5p precursor) promoter. We found that ectopic expression of gga-miR-16-5p in DF-1 cells enhanced IBDV-induced apoptosis by directly targeting the cellular antiapoptotic protein B-cell lymphoma 2 (Bcl-2), facilitating IBDV replication in DF-1 cells. In contrast, inhibition of endogenous miR-16-5p markedly suppressed apoptosis associated with enhanced Bcl-2 expression, arresting viral replication in DF-1 cells. Furthermore, infection of DF-1 cells with IBDV reduced Bcl-2 expression, and this reduction could be abolished by inhibition of gga-miR-16-5p expression. Moreover, transfection of DF-1 cells with gga-miR-16-5p mimics enhanced IBDV-induced apoptosis associated with increased cytochrome c release and caspase-9 and -3 activation, and inhibition of caspase-3 decreased IBDV growth in DF-1 cells. Thus, epigenetic upregulation of gga-miR-16-5p expression by IBDV infection enhances IBDV-induced apoptosis by targeting the cellular antiapoptotic protein Bcl-2, facilitating IBDV replication in host cells.IMPORTANCE Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive disease in young chickens, causing severe economic losses to stakeholders across the globe. Although IBD virus (IBDV)-induced apoptosis in the host has been established, the underlying mechanism is not very clear. Here, we show that infection of DF-1 cells by IBDV upregulated gga-miR-16-5p expression via demethylation of the pre-miR-16-2 promoter. Overexpression of gga-miR-16-5p enhanced IBDV-induced apoptosis associated with increased cytochrome c release and caspase-9 and -3 activation. Importantly, we found that IBDV infection induced expression of gga-miR-16-5p that triggered apoptosis by targeting Bcl-2, favoring IBDV replication, while inhibition of gga-miR-16-5p in IBDV-infected cells restored Bcl-2 expression, slowing down viral growth, indicating that IBDV induces apoptosis by epigenetic upregulation of gga-miR-16-5p expression. These findings uncover a novel mechanism employed by IBDV for its own benefit, which may be used as a potential target for intervening IBDV infection.

Alleviation of infectious-bursal-disease-virus-induced bursal injury by betaine is associated with DNA methylation in IL-6 and interferon regulatory factor 7 promoter

Infectious bursal disease virus (IBDV) often infects young chickens and causes severe immunosuppression and inflammatory injury. Betaine is an antiviral and anti-inflammatory ingredient that may exert functions through epigenetic regulation. However, the effects of betaine on an IBDV-induced bursal injury and their underlying mechanisms have not been investigated. In this study, betaine was supplemented to the drinking water of newly hatched commercial broilers for 3 wk. Afterward, the chickens were infected with the IBDV. After 5 D of infection, the bursal lesions were examined. The mRNA expression levels of IBDV VP2 gene, pro-inflammatory cytokines, and interferons were detected. Furthermore, the 5-methylcytosine level of the CpG island in the promoter region of IL-6 and interferon regulatory factor 7 (IRF7) were determined. The IBDV induced the depletion of lymphocytes and inflammation in the bursal follicles. IBDV infection considerably elevated the mRNA levels of VP2, IL-6, types I (IFNα and IFNβ) and II (IFNγ) interferons, and IRF7. The CpG island methylation in the promoter regions of IL-6 and IRF7 were substantially decreased after IBDV infection. Betaine administration attenuated the IBDV-induced bursal lesions. Meanwhile, the IBDV-induced mRNA expression levels of IL-6, IFNβ, and IRF7 were suppressed by betaine consumption. Furthermore, the hypomethylation effects of IBDV infection to the promoter regions of IL-6 and IRF7 genes were eliminated and relieved by betaine administration. Our results indicated that the IBDV-induced expression levels of IL-6 and IRF7 genes are associated with the suppression of methylation in the promoter region. Betaine administration through drinking water may alleviate the IBDV-induced bursal injury via epigenetic regulation.

Effect of infectious bursal disease virus infection on energy metabolism in embryonic chicken livers

1. The purpose of this study was to investigate ATP levels and the activities of important enzymes involved in glycolysis and TCA cycle in livers of embryonated chicken eggs infected by infectious bursal disease virus (IBDV).2. Embryonated chicken eggs (9 days) were randomly divided into two groups (50 eggs per group). The first group was inoculated with a very virulent IBDV (vvIBDV) isolate into the chorioallantoic membrane. The second group was maintained as uninfected control eggs and inoculated with physiological saline. Embryo survival was assessed daily, and six embryos were sacrificed at 24, 48, 72, 96, and 120 hpi for examining livers. Viral loads in the livers were evaluated by qRT-PCR. A comparative analysis of markers associated with the regulation of energy metabolism across several functional classes (ATP, pyruvic and lactic acids, mitochondrial protein, NAD+/NADH ratios, and enolase, lactic acid dehydrogenase and the respiratory chain complex I activities) were examined in the context of IBDV infection.3. The results indicated that increases in the enzymatic activities associated with glycolytic metabolism in turn affected the synthesis and cytoplasmic concentrations of ATP at early timepoints in infected chicken embryos. Subsequently, energy metabolism was inhibited through the pathological perturbations of metabolic enzymes and mitochondrial damage, as inferred from reduced ATP generation.4. These results suggested impaired bioenergetics, which may lead to liver dysfunction consequent to IBDV infection, contributing to the disease pathogenesis.

Influence of Marek's disease virus vaccines on chicken melanoma differentiation-associated gene 5-dependent-type I interferon signal transduction pathway with a highlight on their secondary impact on the immune responses post Newcastle disease virus vaccination

Marek's disease virus (MDV) leads to a lytic infection of B-lymphocytes in chickens, and also latently infects T-lymphocytes. Although Marek's disease vaccines have been widely in use, little is known about the innate immune response of this important livestock vaccine. In this study, we tested the effect of different commercially applied Marek's disease vaccines on the expression pattern of selected genes related to chicken interferon-alpha (chIFN-α) (melanoma differentiation associated gene 5 "MDA5″ dependent) signal transduction pathway. Both MDV serotype I (Rispens) and serotype III (Herpesvirus of turkey "HVT") vaccines could stimulate MDA5 dependent-type I interferon response as early as three days post vaccination in a dose-dependent manner. The stimulation continued up to 10 days in the instance of HVT vaccine and declined in the case of Rispens. Surprisingly, increasing the doses of the two vaccines led to dose-dependent down-regulation in the expression pattern of the investigated pathway, five and ten days post vaccination. Additionally, to shed the light on the consequent effect on the immune responses of the other viral vaccine, another experimental model based on Newcastle disease virus (NDV) vaccines was designed using HVT, HVT-VP2 and Rispens MDV vaccines. The three MDV vaccines were found to reduce chicken humoral immune response post NDV vaccination. However, only Rispens and HVT-VP2 had suppressive effects on the expression of MDA5-dependent-chIFN-α related cytokines. Consistent with this finding, the protection rate and NDV- humoral immune response post challenge with virulent NDV strain was lower in case of Rispens and HVT-VP2 vaccines.

Voltage-Dependent Anion Channel Protein 2 (VDAC2) and Receptor of Activated Protein C Kinase 1 (RACK1) Act as Functional Receptors for Lymphocystis Disease Virus Infection

In previous research, a 27.8-kDa protein in flounder Paralichthys olivaceus gill (FG) cells was identified as a putative cellular receptor (27.8R), which mediated lymphocystis disease virus (LCDV) infection via interaction with a 32-kDa viral attachment protein (VAP) of LCDV, and monoclonal antibodies (MAbs) against 27.8R and 32-kDa VAP were developed. In this study, the 27.8R was identified as voltage-dependent anion channel protein 2 (VDAC2) and receptor of activated protein C kinase 1 (RACK1) of flounder. Recombinant VDAC2 (rVDAC2) and RACK1 (rRACK1) were obtained by prokaryotic expression, and rabbit anti-VDAC2/RACK1 polyclonal antibodies were prepared. The rVDAC2, rRACK1, and 27.8-kDa proteins in FG cells were recognized by anti-27.8R MAbs and anti-VDAC2/RACK1 polyclonal antibodies simultaneously. Preincubation of FG cells with anti-VDAC2/RACK1 polyclonal antibodies significantly decreased the percentages of LCDV-infected cells and LCDV copy numbers, blocked virus infection, and delayed the development of cytopathic effect. The mRNA expressions of VDAC2 and RACK1 in FG cells were upregulated to maximum levels 12 h and 48 h after LCDV infection, respectively. VDAC2/RACK1 knockdown through short interfering RNA (siRNA) significantly reduced VDAC2/RACK1 expression and LCDV copy numbers in FG cells compared with negative controls, while VDAC2/RACK1 expression on LCDV-nonpermissive epithelial papillosum cells (EPCs) conferred susceptibility to LCDV infection, indicating the VDAC2 and RACK1 were sufficient to allow LCDV entry and infection. All these results collectively showed that VDAC2 and RACK1 function as receptors for LCDV entry and infection.IMPORTANCE Lymphocystis disease virus (LCDV) is the causative agent of lymphocystis disease in fish, which has caused huge economic losses to the aquaculture industry worldwide, but the molecular mechanism underlying the LCDV-host interaction remains unclear. Here, the 27.8-kDa putative cellular receptor for LCDV was identified as voltage-dependent anion channel protein 2 (VDAC2) and receptor of activated protein C kinase 1 (RACK1), and our results revealed that VDAC2 and RACK1 expression was sufficient to allow LCDV entry and that they are functional receptors that initiate LCDV infection for the first time, which leads to a better understanding of the molecular mechanism underlying LCDV infection and virus-host interactions.

Exacerbated Apoptosis of Cells Infected with Infectious Bursal Disease Virus upon Exposure to Interferon Alpha

Infectious bursal disease virus (IBDV) belongs to the Birnaviridae family and is the etiological agent of a highly contagious and immunosuppressive disease (IBD) that affects domestic chickens (Gallus gallus). IBD or Gumboro disease leads to high rates of morbidity and mortality of infected animals and is responsible for major economic losses to the poultry industry worldwide. IBD is characterized by a massive loss of IgM-bearing B lymphocytes and the destruction of the bursa of Fabricius. The molecular bases of IBDV pathogenicity are still poorly understood; nonetheless, an exacerbated cytokine immune response and B cell depletion due to apoptosis are considered main factors that contribute to the severity of the disease. Here we have studied the role of type I interferon (IFN) in IBDV infection. While IFN pretreatment confers protection against subsequent IBDV infection, the addition of IFN to infected cell cultures early after infection drives massive apoptotic cell death. Downregulation of double-stranded RNA (dsRNA)-dependent protein kinase (PKR), tumor necrosis factor alpha (TNF-α), or nuclear factor κB (NF-κB) expression drastically reduces the extent of apoptosis, indicating that they are critical proteins in the apoptotic response induced by IBDV upon treatment with IFN-α. Our results indicate that IBDV genomic dsRNA is a major viral factor that contributes to the triggering of apoptosis. These findings provide novel insights into the potential mechanisms of IBDV-induced immunosuppression and pathogenesis in chickens.IMPORTANCE IBDV infection represents an important threat to the poultry industry worldwide. IBDV-infected chickens develop severe immunosuppression, which renders them highly susceptible to secondary infections and unresponsive to vaccination against other pathogens. The early dysregulation of the innate immune response led by IBDV infection and the exacerbated apoptosis of B cells have been proposed as the main factors that contribute to virus-induced immunopathogenesis. Our work contributes for the first time to elucidating a potential mechanism driving the apoptotic death of IBDV-infected cells upon exposure to type I IFN. We provide solid evidence about the critical importance of PKR, TNF-α, and NF-κB in this phenomenon. The described mechanism could facilitate the early clearance of infected cells, thereby aiding in the amelioration of IBDV-induced pathogenesis, but it could also contribute to B cell depletion and immunosuppression. The balance between these two opposing effects might be dramatically affected by the genetic backgrounds of both the host and the infecting virus strain.

Surface IgM λ light chain is involved in the binding and infection of infectious bursal disease virus (IBDV) to DT40 cells

Infectious bursal disease virus (IBDV) is an important immunosuppressive virus in chickens. Surface immunoglobulin M (sIgM)-bearing B lymphocytes act as the major targets of IBDV in the bursa of Fabricius, and sIgM may function as one of the membrane binding sites responsible for IBDV infection. Recently, using the virus overlay protein binding assay, the chicken λ light chain of sIgM was identified to specifically interact with IBDV in a virulence-independent manner in vitro. To further investigate sIgM λ light chain-mediated IBDV binding and infection in pre-B cells, the cell line DT40, which is susceptible to both pathogenic and attenuated IBDV, was used. Based on the RNA interference strategy, the DT40 cell line whose λ light chain of sIgM was stably knocked down, herein termed DT40LKD, was generated by the genomic integration of a specific small hairpin RNA and a green fluorescence protein co-expression construct. Flow cytometry analysis indicated that the binding of IBDV to DT40LKD cells was significantly reduced due to the loss of sIgM λ light chain. In particular, reduced viral replication was observed in IBDV-incubated DT40LKD cells, and no viral release into cell culture medium was detected by the IBDV rapid diagnostic strips. In addition, the rescue of sIgM λ light chain expression restored viral binding and replication in DT40LKD cells. These results show that sIgM λ light chain appears to be beneficial for IBDV attachment and infection, suggesting that sIgM acts as a binding site involved in IBDV infection.

Adaptation and Molecular Characterization of Two Malaysian Very Virulent Infectious Bursal Disease Virus Isolates Adapted in BGM-70 Cell Line

Two Malaysian very virulent infectious bursal disease virus (vvIBDV) strains UPM0081 and UPM190 (also known as UPMB00/81 and UPM04/190, respectively) isolated from local IBD outbreaks were serially passaged 12 times (EP12) in specific pathogen free (SPF) chicken embryonated eggs (CEE) by chorioallantoic membrane (CAM) route. The EP12 isolate was further adapted and serially propagated in BGM-70 cell line up to 20 passages (P20). Characteristic cytopathic effects (CPEs) were subtly observed at P1 in both isolates 72 hours postinoculation (pi). The CPE became prominent at P5 with cell rounding, cytoplasmic vacuoles, granulation, and detachment from flask starting from day 3 pi, up to 7 days pi with titers of 10^9.50 TCID₅₀/mL and log10^9.80 TCID₅₀/mL for UPM0081 and UPM190, respectively. The CPE became subtle at P17 and disappeared by P18 and P19 for UPM0081 and UPM190, respectively. However, the presence of IBDV was confirmed by immunoperoxidase, immunofluorescence, and RT-PCR techniques. Phylogenetic analysis showed that these two isolates were of the vvIBDV. It appears that a single mutation of UPM190 and UPM0081 IBDV isolates at D279N could facilitate vvIBDV strain adaptability in CEE and BGM-70 cultures.

VP2 of Infectious Bursal Disease Virus Induces Apoptosis via Triggering Oral Cancer Overexpressed 1 (ORAOV1) Protein Degradation

Infectious bursal disease (IBD) is an acute, highly contagious and immunosuppressive avian disease caused by IBD virus (IBDV). Cell apoptosis triggered by IBDV contributes to the dysfunction of immune system in host. VP2 of IBDV is known to induce cell death but the underlying mechanism remains unclear. Here we demonstrate that VP2 interacts with the oral cancer overexpressed 1 (ORAOV1), a potential oncoprotein. Infection by IBDV or ectopic expression of VP2 causes a reduction of cellular ORAOV1 and induction of apoptosis, so does knockdown of ORAOV1. In contrast, over-expression of ORAOV1 leads to the inhibition of VP2- or IBDV-induced apoptosis, accompanied with the decreased viral release (p < 0.05). Thus, VP2-induced apoptosis during IBDV infection is mediated by interacting with and reducing ORAOV1, a protein that appears to act as an antiapoptotic molecule and restricts viral release early during IBDV infection.

Transcriptional profiles in bursal B-lymphoid DT40 cells infected with very virulent infectious bursal disease virus

Background

Infectious bursal disease virus (IBDV) causes a highly contagious, immunosuppressive disease in chickens. The virus mainly infects immature B lymphocytes in the bursa of Fabricius (BF). Chicken B cell line DT40, an avian leukosis virus-induced B cell line, supports very virulent IBDV (vvIBDV) infection in vitro and thereby serves as a good model for investigating the infection and pathogenesis of this virus. However, a transcriptome-wide understanding of the interaction between vvIBDV and B cells has not yet been achieved. This study aimed to employ time-course DNA microarrays to investigate gene expression patterns in DT40 cells after infection with vvIBDV strain LX.

Results

DT40 cells infected with vvIBDV exhibited alterations in the expression of many important host genes involved in signal transduction pathways, including MAPK signaling, PI3K/mTOR signaling, cell death and survival, BCR signaling, and antigen presentation. The changes in cellular mRNA levels identified by microarray analysis were confirmed for 8 selected genes using real-time reverse transcription-PCR. The upregulation of inflammatory cytokines and Toll-like receptors (TLRs) in the bursa of vvIBDV-infected chickens might involve excessive activation of the innate immune and inflammatory responses and contribute to tissue damage.

Conclusions

The present study is the first to provide a comprehensive differential transcriptional profile of cultured DT40 cells in response to vvIBDV infection and further extends our understanding of the molecular mechanisms underlying vvIBDV infection and pathogenesis.

Eukaryotic translational initiation factor 4AII reduces the replication of infectious bursal disease virus by inhibiting VP1 polymerase activity

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). Although an interaction between eukaryotic translational initiation factor 4AII (eIF4AII) of the host and viral protein 1 (VP1), the RNA-dependent RNA polymerase (RdRp) of IBDV, has been established, the underlying effects of this interaction on IBDV and the molecular mechanism remain unclear. We here report that interaction of the host eIF4AII with VP1 inhibits the RNA polymerase activity of IBDV to reduce its replication in host cells. We found that ectopically expressed eIF4AII markedly inhibited IBDV growth in DF1 cells, and knockdown of eIF4AII by small interfering RNA significantly enhanced viral replication in CEF cells. Furthermore, IBDV infection led to an increase in host eIF4AII expression, suggesting a feedback mechanism between the host and virus infection both in vitro and in vivo, which further confirmed the involvement of the host eIF4AII in the IBDV life cycle. Thus, via the interaction with VP1, eIF4AII plays a critical role in the IBDV life cycle, by inhibiting viral RNA polymerase activity, leading to a reduction of IBDV replication in cells.

The C-terminal amyloidogenic peptide contributes to self-assembly of Avibirnavirus viral protease

Unlike other viral protease, Avibirnavirus infectious bursal disease virus (IBDV)-encoded viral protease VP4 forms unusual intracellular tubule-like structures during viral infection. However, the formation mechanism and potential biological functions of intracellular VP4 tubules remain largely elusive. Here, we show that VP4 can assemble into tubules in diverse IBDV-infected cells. Dynamic analysis show that VP4 initiates the assembly at early stage of IBDV infection, and gradually assembles into larger size of fibrils within the cytoplasm and nucleus. Intracellular assembly of VP4 doesn't involve the host cytoskeleton, other IBDV-encoded viral proteins or vital subcellular organelles. Interestingly, the last C-terminal hydrophobic and amyloidogenic stretch (238)YHLAMA(243) with two "aggregation-prone" alanine residues was found to be essential for its intracellular self-assembly. The assembled VP4 fibrils show significantly low solubility, subsequently, the deposition of highly assembled VP4 structures ultimately deformed the host cytoskeleton and nucleus, which was potentially associated with IBDV lytic infection. Importantly, the assembly of VP4 significantly reduced the cytotoxicity of protease activity in host cells which potentially prevent the premature cell death and facilitate viral replication. This study provides novel insights into the formation mechanism and biological functions of the Avibirnavirus protease-related fibrils.

The association of receptor of activated protein kinase C 1(RACK1) with infectious bursal disease virus viral protein VP5 and voltage-dependent anion channel 2 (VDAC2) inhibits apoptosis and enhances viral replication

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). Our previous report indicates that IBDV VP5 induces apoptosis via interaction with voltage-dependent anion channel 2 (VDAC2). However, the underlying molecular mechanism is still unclear. We report here that receptor of activated protein kinase C 1 (RACK1) interacts with both VDAC2 and VP5 and that they could form a complex. We found that overexpression of RACK1 inhibited IBDV-induced apoptosis in DF-1 cells and that knockdown of RACK1 by small interfering RNA induced apoptosis associated with activation of caspases 9 and 3 and suppressed IBDV growth. These results indicate that RACK1 plays an antiapoptotic role during IBDV infection via interaction with VDAC2 and VP5, suggesting that VP5 sequesters RACK1 and VDAC2 in the apoptosis-inducing process.

Chicken melanoma differentiation-associated gene 5 (MDA5) recognizes infectious bursal disease virus infection and triggers MDA5-related innate immunity

The objective of the present study was to determine if chicken melanoma differentiation-associated gene 5 (MDA5) senses infectious bursal disease virus (IBDV) infection to initiate and amplify an innate immune response in the chicken MDA5 (chMDA5) signaling pathway. Chicken embryo fibroblast DF-1 cells were infected with IBDV LP1 at a multiplicity of infection (MOI) of 0.5 or 10. In addition, knockdown and overexpression of chMDA5 were performed by transfecting DF-1 cells with chMDA5-targeting small interfering RNA (siRNA) or chMDA5-expressing DNA. The transfected cells were infected with IBDV LP1 at an MOI of 10. Cell culture supernatants and lysates were collected at 2, 8, 16 and 24 hours postinfection (hpi) for IBDV titer determination and RNA extraction, respectively. IBDV RNA loads and mRNA expression levels of chicken MDA5, interferon-β (IFN-β) promoter stimulator 1 (IPS-1), interferon regulatory factor-3 (IRF-3), IFN-β, double-stranded RNA-dependent protein kinase (PKR), 2′,5′-oligoadenylate synthetase (OAS), myxovirus resistance gene (Mx), and major histocompatibility complex class I (MHC class I) were determined by real-time RT-PCR. The IBDV titer increased up to 1.4 × 10⁷ plaque-forming units (PFU)/mL at 24 hpi, and the IBDV RNA load reached 464 ng/μL at 24 hpi. The mRNA expression levels of chicken MDA5, IRF-3, IFN-β, PKR, OAS, Mx and MHC class I in IBDV-infected DF-1 cells exhibited significant (p < 0.05) upregulation up to 906-, 199-, 26,310-, 12-, 66,144-, 64,039- and 33-fold, respectively. Expressed chMDA5 from transfection and double-stranded RNA from IBDV infection were localized or colocalized in the cytoplasm of DF-1 cells at 16 hpi. When chMDA5 was knocked down in DF-1 cells, IBDV titers and RNA loads were significantly higher (p < 0.05) than those in DF-1 cells without chMDA5 knockdown at 24 hpi. The expression levels of chicken MDA5, IRF-3, IFN-β and MHC class I in chMDA5-knockdown DF-1 cells were significantly lower (p < 0.05) at 16 and 24 hpi. DF-1 cells overexpressing chMDA5 by transfection with chMDA5 expressing DNA had significantly lower (p < 0.05) IBDV titers and RNA loads at 16 and 24 hpi and showed significantly higher (p < 0.05) expression of chicken MDA5, IRF-3, IFN-β, PKR, OAS, Mx and MHC class I at 2 hpi. The results indicated that chicken MDA5 recognized IBDV infection and that this interaction resulted in the activation of chMDA5-related innate immune genes and upregulation of chicken MHC class I.

Avian Immunosuppressive Diseases and Immunoevasion

Subclinical immunosuppression in chickens is an important but often underestimated factor in the subsequent development of clinical disease. Immunosuppression can be caused by pathogens such as chicken infectious anemia virus, infectious bursal disease virus, reovirus, and some retroviruses (e.g., reticuloendotheliosis virus). Mycotoxins and stress, often caused by poor management practices, can also cause immunosuppression. The effects on the innate and acquired immune responses and the mechanisms by which mycotoxins, stress and infectious agents cause immunosuppression are discussed. Immunoevasion is a common ploy by which viruses neutralize or evade immune responses. DNA viruses such as herpesvirus and poxvirus have multiple genes, some of them host-derived, which interfere with effective innate or acquired immune responses. RNA viruses may escape acquired humoral and cellular immune responses by mutations in protective antigenic epitopes (e.g., avian influenza viruses), while accessory non-structural proteins or multi-functional structural proteins interfere with the interferon system (e.g., Newcastle disease virus).

Infectious Bursal Disease: a complex host-pathogen interaction

Infectious Bursal Disease (IBD) is caused by a small, non-enveloped virus, highly resistant in the outside environment. Infectious Bursal Disease Virus (IBDV) targets the chicken's immune system in a very comprehensive and complex manner by destroying B lymphocytes, attracting T cells and activating macrophages. As an RNA virus, IBDV has a high mutation rate and may thus give rise to viruses with a modified antigenicity or increased virulence, as emphasized during the last decades. The molecular basis of pathogenicity and the exact cause of clinical disease and death are still poorly understood, as it is not clearly related to the severity of the lesions and the extent of the bursal damage. Recent works however, pointed out the role of an exacerbated innate immune response during the early stage of the infection with upregulated production of promediators that will induce a cytokine storm. In the case of IBDV, immunosuppression is both a direct consequence of the infection of specific target immune cells and an indirect consequence of the interactions occurring in the immune network of the host. Recovery from disease or subclinical infection will be followed by immunosuppression with more serious consequences if the strain is very virulent and infection occurs early in life. Although the immunosuppression caused by IBDV is principally directed towards B-lymphocytes, an effect on cell-mediated immunity (CMI) has also been demonstrated therefore increasing the impact of IBDV on the immunocompetence of the chicken. In addition to its zootechnical impact and its role in the development of secondary infections, it may affect the immune response of the chicken to subsequent vaccinations, essential in all types of intensive farming. Recent progress in the field of avian immunology has allowed a better knowledge of the immunological mechanisms involved in the disease but also should give improved tools for the measurement of immunosuppression in the field situation. Although satisfactory protection may be provided by the induction of high neutralizing antibody titres, interference from parental antibodies with vaccination has become the most important obstacle in the establishment of control programs. In this context, recombinant HVT and immune complex vaccines show promising results.

Spatiotemporal Phylogenetic Analysis and Molecular Characterisation of Infectious Bursal Disease Viruses Based on the VP2 Hyper-Variable Region

Background

Infectious bursal disease is a highly contagious and acute viral disease caused by the infectious bursal disease virus (IBDV); it affects all major poultry producing areas of the world. The current study was designed to rigorously measure the global phylogeographic dynamics of IBDV strains to gain insight into viral population expansion as well as the emergence, spread and pattern of the geographical structure of very virulent IBDV (vvIBDV) strains.

Methodology/Principal Findings

Sequences of the hyper-variable region of the VP2 (HVR-VP2) gene from IBDV strains isolated from diverse geographic locations were obtained from the GenBank database; Cuban sequences were obtained in the current work. All sequences were analysed by Bayesian phylogeographic analysis, implemented in the Bayesian Evolutionary Analysis Sampling Trees (BEAST), Bayesian Tip-association Significance testing (BaTS) and Spatial Phylogenetic Reconstruction of Evolutionary Dynamics (SPREAD) software packages. Selection pressure on the HVR-VP2 was also assessed. The phylogeographic association-trait analysis showed that viruses sampled from individual countries tend to cluster together, suggesting a geographic pattern for IBDV strains. Spatial analysis from this study revealed that strains carrying sequences that were linked to increased virulence of IBDV appeared in Iran in 1981 and spread to Western Europe (Belgium) in 1987, Africa (Egypt) around 1990, East Asia (China and Japan) in 1993, the Caribbean Region (Cuba) by 1995 and South America (Brazil) around 2000. Selection pressure analysis showed that several codons in the HVR-VP2 region were under purifying selection.

Conclusions/Significance

To our knowledge, this work is the first study applying the Bayesian phylogeographic reconstruction approach to analyse the emergence and spread of vvIBDV strains worldwide.

New insight into the structure, development, functions and popular disorders of bursa Fabricii

Humoral immune responses in birds, contrary to mammals, depend on the normal functioning of bursa Fabricii. Recent studies have delivered new information about the structure, development and origin of cells that compose the bursa environment. Several viral infections affect bursa, causing lymphocyte depletion or excessive proliferation. This review summarizes data on the development and histology of healthy bursa and introduces some common disorders that affect this organ.

Critical roles of glucocorticoid-induced leucine zipper in infectious bursal disease virus (IBDV)-induced suppression of type I Interferon expression and enhancement of IBDV growth in host cells via interaction with VP4

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). Although IBDV-induced immunosuppression has been well established, the underlying exact molecular mechanism for such induction is not very clear. We report here the identification of IBDV VP4 as an interferon suppressor by interaction with the glucocorticoid-induced leucine zipper (GILZ) in host cells. We found that VP4 suppressed the expression of type I interferon in HEK293T cells after tumor necrosis factor alpha (TNF-α) treatment or Sendai virus (SeV) infection and in DF-1 cells after poly(I·C) stimulation. In addition, the VP4-induced suppression of type I interferon could be completely abolished by knockdown of GILZ by small interfering RNA (siRNA). Furthermore, knockdown of GILZ significantly inhibited IBDV growth in host cells, and this inhibition could be markedly mitigated by anti-alpha/beta interferon antibodies in the cell cultures (P < 0.001). Thus, VP4-induced suppression of type I interferon is mediated by interaction with GILZ, a protein that appears to inhibit cell responses to viral infection.

Protective vaccination against infectious bursal disease virus with whole recombinant Kluyveromyces lactis yeast expressing the viral VP2 subunit

Here we report on vaccination approaches against infectious bursal disease (IBD) of poultry that were performed with complete yeast of the species Kluyveromyces lactis (K. lactis). Employing a genetic system that enables the rapid production of stably transfected recombinant K. lactis, we generated yeast strains that expressed defined quantities of the virus capsid forming protein VP2 of infectious bursal disease virus (IBDV). Both, subcutaneous as well as oral vaccination regiments with the heat-inactivated but otherwise untreated yeast induced IBDV-neutralizing antibodies in mice and chickens. A full protection against a subsequent IBDV infection was achieved by subcutaneous inoculation of only milligram amounts of yeast per chicken. Oral vaccination also generated protection: while mortality was observed in control animals after virus challenge, none of the vaccinees died and ca. one-tenth were protected as indicated by the absence of lesions in the bursa of Fabricius. Recombinant K. lactis was thus indicated as a potent tool for the induction of a protective immune response by different applications. Subcutaneously applied K. lactis that expresses the IBDV VP2 was shown to function as an efficacious anti-IBD subunit vaccine.

An overview of infectious bursal disease

Infectious bursal disease (IBD) is a viral immunosuppressive disease of chickens attacking mainly an important lymphoid organ in birds [the bursa of Fabricius (BF)]. The emergence of new variant strains of the causative agent [infectious bursal disease virus (IBDV)] has made it more urgent to develop new vaccination strategies against IBD. One of these strategies is the use of recombinant vaccines (DNA and viral-vectored vaccines). Several studies have investigated the host immune response towards IBDV. This review will present a detailed background on the disease and its causative agent, accompanied by a summary of the most recent findings regarding the host immune response to IBDV infection and the use of recombinant vaccines against IBD.

Critical role for voltage-dependent anion channel 2 in infectious bursal disease virus-induced apoptosis in host cells via interaction with VP5

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). Although IBDV-induced host cell apoptosis has been established, the underlying molecular mechanism is still unclear. We report here that IBDV viral protein 5 (VP5) is a major apoptosis inducer in DF-1 cells by interacting with the voltage-dependent anion channel 2 (VDAC2) in the mitochondrion. We found that in DF-1 cells, VP5-induced apoptosis can be completely abolished by 4,4'-diisothiocyanatostibene-2,2'-disulfonic acid (DIDS), an inhibitor of VDAC. Furthermore, knockdown of VDAC2 by small interfering RNA markedly inhibits IBDV-induced apoptosis associated with decreased caspase-9 and -3 activation and cytochrome c release, leading to increased IBDV growth in host cells. Thus, VP5-induced apoptosis during IBDV infection is mediated by interacting with VDAC2, a protein that appears to restrict viral replication via induction of cell death.

Surface IgM on DT40 cells may be a component of the putative receptor complex responsible for the binding of infectious bursal disease virus

To investigate the host-pathogen interactions between infectious bursal disease virus (IBDV) and target B-lymphocytic cells, a cDNA T7 phage display library from the chicken bursa of Fabricius was constructed and screened for virus binding. Surface immunoglobulin M (sIgM) was isolated as a putative candidate binding site and its interactions with IBDV were further investigated using a chicken bursal lymphoma-derived cell line DT40. The results showed that the λ light chain of sIgM specifically interacted with IBDV in a virulence-independent manner in vitro, and most of the binding of IBDV to DT40 cells was inhibited by sIgM-specific monoclonal antibodies. Further, the infectivity of IBDV in vitro was reduced by sIgM-specific monoclonal antibodies. Our data provided evidence that sIgM may participate as one of the putative membrane binding sites responsible for IBDV infection.

Effective inhibition of replication of infectious bursal disease virus by miRNAs delivered by vectors and targeting the VP2 gene

RNA interference (RNAi) is a potent mechanism against a variety of viral infections. Infectious bursal disease virus (IBDV) causes an important disease economically in chickens, which is difficult to control. As part of the development of viral vector-mediated RNAi strategy against the disease, five anti-VP2 small interference RNAs were selected for construction of microRNA (miRNA) expression vectors tailored for avian cells. Transfection of DF-1 cells with the five vectors resulted in significant inhibition of VP2-EGFP reporter gene expression. More effective miVP2A and miVP2E were selected for further study using single or double miRNA expression vectors. After demonstration of specific miRNA expression, the gene silencing effects were determined in the vector-transfected and IBDV-infected cells. Reverse transcriptase PCR and virus titration showed inhibition rates from 76 to 82% on VP2 expression and significant decreases in virus titer by individual and co-expressed miVP2A and miVP2E. The inhibitory effects lasted for at least 120 h after infection with IBDV. These data suggest that the miRNAs targeting the VP2 can inhibit efficiently replication of IBDV.

Pivotal role of ChIFNgamma in the pathogenesis and immunosuppression of infectious bursal disease

This study investigates the pivotal role of chicken interferon-gamma (ChIFNgamma) in the pathogenesis and immunosuppression of infectious bursal disease virus (IBDV) infection and is divided into in vivo, ex vivo and in vitro experiments. Two-week-old specific pathogen free chickens were inoculated with the 849VB very virulent strain of IBDV. The levels of systemic ChIFNgamma and chicken interleukin-6 in the serum were followed for 2 weeks during in vivo experiments. Then, splenocytes and bursal cells from infected chickens were analysed for their immunocompetence after mitogenic activation in ex vivo experiments. Finally, in vitro experiments were conducted to assess the direct immunosuppressive effect of ChIFNgamma on splenocytes and peripheral blood lymphocytes from non-inoculated specific pathogen free chickens. Our results reveal that the acute phase of infectious bursal disease coincides, on one hand, with high levels of systemic ChIFNgamma and chicken interleukin-6 and, on the other hand, with a strong inhibition of proliferation and activation of mitogen-stimulated splenocytes from infected chickens, as measured by ChIFNgamma production. Two weeks after viral inoculation, T lymphocytes infiltrating the bursa of Fabricius had recovered their activation capability. Finally, an in vitro study showed that the proliferation of naïve splenocytes and peripheral blood lymphocytes was directly and specifically inhibited by ChIFNgamma. In conclusion, a ChIFNgamma dysregulation occurs in chickens infected with IBDV and the overproduction of ChIFNgamma by T lymphocytes plays a key role in the pathogenesis and immunosuppression induced by this virus.

Reduction of infectious bursal disease virus replication in cultured cells by proteasome inhibitors

Infectious bursal disease virus (IBDV) is the etiological agent of a highly contagious disease in chickens. In a recent report, proteasome inhibitor MG132 has been shown to completely inhibit IBDV-induced apoptosis. This raises the possibility that the ubiquitin–proteasome pathway may be used by the virus to promote viral replication. In this study, we examined the interplay between IBDV replication and the ubiquitin–proteasome pathway in cultured cells. Treatment of DF-1 cells with the proteasome inhibitors MG132 or lactacystin significantly decreased virus release in the supernatant and prevented virus-induced cytopathic effect. Inhibition of the ubiquitin–proteasome pathway did reduce markedly viral RNA transcription and protein translation but not affect virus internalization. We also demonstrated that IBDV activates caspase pathway via triggering the efflux of cytochrome c in mitochondria into cytosol of infected cells. This activity was dose-dependently reduced by proteasome inhibitor treatment. Taken together, our data suggest that proteasome inhibitor reduces IBDV replication through inhibition of viral RNA transcription and protein synthesis, and thus preventing IBDV-induced apoptosis.

Transcriptional profiling reveals a possible role for the timing of the inflammatory response in determining susceptibility to a viral infection

Using a novel cDNA microarray prepared from sources of actively responding immune system cells, we have investigated the changes in gene expression in the target tissue during the early stages of infection of neonatal chickens with infectious bursal disease virus. Infections of two lines of chickens previously documented as genetically resistant and sensitive to infection were compared in order to ascertain early differences in the response to infection that might provide clues to the mechanism of differential genetic resistance. In addition to major changes that could be explained by previously described changes in infected tissue, some differences in gene expression on infection, and differences between the two chicken lines, were observed that led to a model for resistance in which a more rapid inflammatory response and more-extensive p53-related induction of apoptosis in the target B cells might limit viral replication and consequent pathology. Ironically, the effect in the asymptomatic neonatal infection is that more-severe B-cell depletion is seen in the more genetically resistant chicken. Changes of expression of many chicken genes of unknown function, indicating possible roles in the response to infection, may aid in the functional annotation of these genes.