Intestinal mucosal immune response against virulent duck enteritis virus infection in ducklings

CCCP inhibits DPV infection in DEF cells by attenuating DPV manipulated ROS, apoptosis, and mitochondrial stability

Duck plague virus (DPV) is extremely infectious and lethal, so antiviral drugs are urgently needed. Our previous study shows that DPV infection with duck embryo fibroblast (DEF) induces reactive oxygen species (ROS) changes and promotes apoptosis. In this study, we tested the antiviral effect of the carbonyl cyanide m-chlorophenyl hydrazone (CCCP), a common mitochondrial autophagy inducer. Our results demonstrated a dose-dependent anti-DPV effect of CCCP, CCCP-treatment blocked the intercellular transmission of DPV after infection, and we also proved that CCCP could have an antiviral effect up to 48 hpi. The addition of CCCP reversed the DPV-induced ROS changes, CCCP can inhibit virus-induced apoptosis; meanwhile, CCCP can affect mitochondrial fusion and activate mitophagy to inhibit DPV. In conclusion, CCCP can be an effective antiviral candidate against DPV.

Evaluation of safety and immunogenicity of duck-plague virus gC/gE double gene deletion

Duck plague caused by duck plague virus (DPV) is a highly contagious disease that can cause serious morbidity and death in waterfowl such as ducks and geese, and bring huge economic losses to the duck industry. In this study, on the basis of the duck plague virus gC gene deletion strain CHv-ΔgC, based on the duck plague virus bacterial artificial chromosome (BAC) platform in our laboratory, the gE gene was knocked out using the traceless deletion technology to obtain gC/gE double gene deletion candidate vaccine strain CHv-ΔgC/gE. The double gene deletion strain (CHv-ΔgC/gE) constructed in this study has greatly weakened virulence, no pathogenicity to ducks, and stable genetic characteristics in vitro and in vivo. Ducks immunized with CHv-ΔgC/gE can produce neutralizing antibodies and ELISA antibody levels comparable to those of commercial duck plague attenuated vaccine immunization, and can resist 100 LD₅₀ CHv challenge of ducks, with good immune protection effect. It has the potential to be further developed into duck plague gC/gE double gene deletion, marked attenuated vaccine.

Duck Plague Virus Negatively Regulates IFN Signaling to Promote Virus Proliferation via JNK Signaling Pathway

Duck plague virus (DPV), a member of the alphaherpesvirus subfamily, can cause severe damage and immunosuppression in ducks and geese in China. Since lacking an available cell model, the antiviral signal transduction pathways induction and regulation mechanisms related to DPV infection in duck cells are still enigmatic. Our previous study developed a monocyte/macrophages cell model, which has been applied to study innate immunity with DPV. In the present study, we compared and analyzed transcriptome associated with the DPV infection of CHv (virulent strain) and CHa (avirulent strain) at 48hpi based on the duck monocyte/macrophages cell model and RNA-seq technology. Differentially expressed genes (DEGs) analysis showed 2,909 and 2,438 genes altered in CHv and CHa infected cells compared with control cells. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that the DEGs were mainly involved in biological processes such as metabolic pathways, viral infectious diseases, immune system, and signal transduction. The CHv and CHa virus differentially regulated MAPK, NF-κB, and IFN signaling pathways based on transcriptome sequencing data and RT-qPCR results. The JNK inhibitor SP600125 enhanced the IFN signaling, but potentially reduced the VSV and DPV titers in the cell culture supernatant, indicating that JNK negatively regulates the IFN pathway and the inflammatory pathway to promote virus proliferation. The research results may provide promising information to understand the pathogenesis of DPV and provide a novel mechanism by which DPV modulates antiviral signaling and facilitate virus proliferation through hijacking the JNK pathway, which provides a new means for the prevention and control of DPV infection.

Evaluation of the Safety and Immunogenicity of Duck-Plague Virus gE Mutants

Duck plague (DP) is an acute infectious disease in the duck industry. The duck plague virus (DPV) is the pathogen, a subfamily of alphaherpesvirinae. gE is a type I membrane protein that contains three parts: an extracellular domain, a transmembrane domain, and a cytoplasmic domain. gE is the major virulence determinant of α-herpesvirus. However, the functions of the gE extracellular and cytoplasmic domains have not been reported in DPV. In this study, a gE extracellular domain deletion mutant and a gE cytoplasmic domain deletion mutant were constructed from DPV. Virus replication kinetics showed that the growth titers of both the gE ectodomain-deleted mutant virus and the gE cytoplasmic domain-deleted virus in DEFs were lower than that of the parental virus CHv-50. DPV CHv-gEΔET and DPV CHv-gEΔCT were continuously passed to the 20th passage in DEFs and the 10th in ducklings. The mutant virus DNA after passage was extracted for identification. The results showed that the gE ectodomain and gE cytoplasmic domain deletion mutant viruses have good genetic stability. The ducklings in each group (n=10) were inoculated with the same titers of DPV CHv-gEΔET, DPV CHv-gEΔCT, DPV CHv-ΔgE, and parental CHv-50, respectively. Clinical symptoms and serum antibody levels were detected after inoculation. The results showed that the virulence of DPV CHv-gEΔCT to ducklings was reduced compared with parental CHv-50, while the virulence of DPV CHv-gEΔET to ducklings was significantly reduced. 10⁵ TCID₅₀ DPV CHv-gEΔET or DPV CHv-ΔgE can induce ducklings to produce DPV-specific antibodies, protect the ducklings from virulent CHv challenge. Therefore, DPV CHv-gEΔET may serve as a promising vaccine candidate to prevent and control duck plague.

UL11 Protein Is a Key Participant of the Duck Plague Virus in Its Life Cycle

Tegument protein UL11 plays a critical role in the life cycle of herpesviruses. The UL11 protein of herpesviruses is important for viral particle entry, release, assembly, and secondary envelopment. Lipid raft is cholesterol-rich functional microdomains in cell membranes, which plays an important role in signal transduction and substance transport. Flotillin and prohibition, which are considered to be specific markers of lipid raft. However, little is known about the function of duck plague virus (DPV) UL11 in the life cycle of the viruses and the relationship between the lipid raft and UL11. In this study, an interference plasmid shRNA126 for UL11 was used. Results showed that UL11 is involved in the replication, cell to cell spread, viral particle assembly, and release processes. Furthermore, UL11 was verified that it could interact with the lipid raft through sucrose density gradient centrifugation and that function correlates with the second glycine of the UL11. When the lipid raft was depleted using the methyl-β-cyclodextrin, the release of the DPV was decreased. Moreover, UL11 can decrease several relative viral genes mRNA levels by qRT-PCR and Western blot test. Altogether, these results highlight an important role for UL11 protein in the viral replication cycle.

Duck Enteritis Virus VP16 Antagonizes IFN-β-Mediated Antiviral Innate Immunity

Duck enteritis virus (DEV) can successfully evade the host innate immune responses and establish a lifelong latent infection in the infected host. However, the study about how DEV escapes host innate immunity is still deficient up to now. In this study, for the first time, we identified a viral protein VP16 by which DEV can obviously downregulate the production of IFN-β in duck embryo fibroblast (DEF). Our results showed that ectopic expression of VP16 decreased duck IFN-β (duIFN-β) promoter activation and significantly inhibited the mRNA transcription of IFN-β. Further study showed that VP16 can also obviously inhibit the mRNA transcription of interferon-stimulated genes (ISGs), such as myxovirus resistance protein (Mx) and interferon-induced oligoadenylate synthetase-like (OASL). Furthermore, we found that this anti-interferon activity of VP16 depended on its N-terminus (aa1-200). Coexpression analysis revealed that VP16 selectively blocked duIFN-β promoter activity at the duIRF7 level rather than duIRF1. Based on the results of coimmunoprecipitation analysis (co-IP) and indirect immunofluorescence assay (IFA), VP16 was able to bind to duck IRF7 (duIRF7) directly, but did not interact with duck IRF1 (duIRF1) in vitro.

Duck enteritis virus UL21 is a late gene encoding a protein that interacts with pUL16

BACKGROUND

pUL21 is a conserved protein of Alphaherpesvirinae that performs multiple important functions. The C-terminus of pUL21 in other members of this subfamily has RNA-binding ability; this domain contributes to pseudorabies virus (PRV) retrograde axonal transport in vitro and in vivo and participates in newly replicated viral DNA packaging and intracellular virus transport. However, knowledge regarding duck enteritis virus (DEV) pUL21 is limited.

RESULTS

We verified that DEV UL21 is a γ2 gene that encodes a structural protein. Moreover, we observed that pUL21 localized to the nucleus and cytoplasm. DEV pUL21 interacted with pUL16 and formed a complex in transfected human embryonic kidney (HEK) 293 T cells and DEV-infected duck embryo fibroblasts (DEFs). These results were further confirmed by CO-IP assays.

CONCLUSIONS

The DEV UL21 gene is a late gene, and pUL21 localizes to the nucleus and cytoplasm. DEV UL21 is a virion component. In addition, pUL21 can interact with pUL16. These findings provide insight into the characteristics of UL21 and the interaction between pUL21 and its binding partner pUL16. Our study enhances the understanding of DEV pUL21.

Ducks induce rapid and robust antibody responses than chickens at early time after intravenous infection with H9N2 avian influenza virus

Background

Compared with chickens, ducks are normally resistant to avian influenza virus without clinical signs while they habor almost all subtypes of influenza A viruses. To date, however the mechanism for duck anti-influenza has not been completely understood. The H9N2 avian influenza virus (AIV) is the most prevalent subtype of influenza A virus that infects chickens and ducks in China. However, H9N2 AIV replication and the host immune response in these domestic birds has not been systematically investigated.

Methods

In the present study, we compared the kinetics and magnitudes of antibody responses in chickens and ducks after infection with H9N2 AIV by the intranasal route or intravenous route. Furthermore, we determined the viral replication and distribution in chickens and ducks after infection with H9N2 AIV by the intravenous route.

Results

Our results revealed that the antibody response was rapid and robust in ducks than in chickens at early time (2-3dpi) after intravenous infection with H9N2 AIVs, while delayed and lower antibody detected in ducks than in chickens after intranasal infection with H9N2 AIVs. The virus was detected in multiple organs tissues in chickens but not in ducks infected by the intravenous route.

Conclusions

Our results provide the evidence that humoral immune response could play a critical role in duck resistance for influenza, which expands our knowledge on duck anti-influenza characteristics.

Duck Plague Virus Promotes DEF Cell Apoptosis by Activating Caspases, Increasing Intracellular ROS Levels and Inducing Cell Cycle S-Phase Arrest

Background: Duck plague virus (DPV) can induce apoptosis in duck embryo fibroblasts (DEFs) and in infected ducks, but the molecular mechanism of DPV-induced apoptosis remains unknown. Methods: We first used qRT-PCR and a Caspase-Glo assay to determine whether the caspase protein family plays an important role in DPV-induced apoptosis. Then, we used an intracellular ROS detection kit and the mitochondrial probe JC-1 to respectively detect ROS levels and mitochondrial membrane potential (MMP). Finally, flow cytometry was used to detect apoptosis and cell cycle progression. Results: In this study, the mRNA levels and enzymatic activities of caspase-3, caspase-7, caspase-8, and caspase-9 were significantly increased during DPV-induced apoptosis. The caspase inhibitors Z-DEVD-FMK, Z-LEHD-FMK, and Q-VD-Oph could inhibit DPV-induced apoptosis and promote viral replication. Subsequently, a significant decrease in MMP and an increase in the intracellular ROS levels were observed. Further study showed that pretreating infected cells with NAC (a ROS scavenger) decreased the intracellular ROS levels, increased the MMP, inhibited apoptosis, and promoted viral replication. Finally, we showed that DPV infection can cause cell cycle S-phase arrest. Conclusions: This study shows that DPV causes cell cycle S-phase arrest and leads to apoptosis through caspase activation and increased intracellular ROS levels. These findings may be useful for gaining an understanding of the pathogenesis of DPV and the apoptotic pathways induced by α-herpesviruses.

Molecular characterization of duck enteritis virus UL41 protein

BACKGROUND

Duck enteritis virus (DEV) belongs to the subfamily Alphaherpesvirinae, and information on the DEV UL41 gene is limited.

METHODS

The DEV UL41 gene was cloned into the pET32a(+) vector and expressed in a prokaryotic expression system. Antiserum was raised against a bacterially expressed UL41-His fusion protein for further experiments. Transcription was quantified and UL41 protein expression levels were determined in DEV-infected cells at different time points by RT-qPCR and western blotting, respectively. DEV virions were purified by sucrose gradient centrifugation and analyzed by mass spectrometry to identify protein content. We confirmed the DEV UL41 gene kinetic class using a pharmacological test. IFA was used to analyze the intracellular localization of pUL41.

RESULTS

The recombinant expression plasmid, pET-32a(+)-UL41, which highly expresses a 76.0 kDa fusion protein, was constructed and expressed in E. coli BL21 (DE3) after induction with 0.2 mM IPTG at 30 °C for 10 h, generating a specific mouse anti-UL41 protein polyclonal antibody. RT-qPCR and western blot analyses revealed that the UL41 transcript number peaked at 36 hpi, and peak protein expression occurred at 48 hpi. The pharmacological test showed that UL41 was a γ2 gene. Mass spectrometry analysis showed that pUL41 was a virion component. IFA results revealed that pUL41 was localized throughout DEV-infected cells but only localized to the cytoplasm of transfected cells. DEV pUL47 translocated pUL41 to the nuclei of DEF cells; this translocation was dependent on predicted pUL47 NLS signals (40-50 aa and 768-777 aa).

CONCLUSIONS

DEV UL41 is a γ2 gene that encodes a virion structural protein, pUL41 localizes throughout DEV-infected cells but only localizes to the cytoplasm of transfected cells. pUL41 cannot autonomously localize to the nucleus, as this nuclear localization is dependent on predicted DEV pUL47 NLS signals (40-50 aa and 768-777 aa).

RNA-seq comparative analysis of Peking ducks spleen gene expression 24 h post-infected with duck plague virulent or attenuated virus

Duck plague virus (DPV), a member of alphaherpesvirus sub-family, can cause significant economic losses on duck farms in China. DPV Chinese virulent strain (CHv) is highly pathogenic and could induce massive ducks death. Attenuated DPV vaccines (CHa) have been put into service against duck plague with billions of doses in China each year. Researches on DPV have been development for many years, however, a comprehensive understanding of molecular mechanisms underlying pathogenicity of CHv strain and protection of CHa strain to ducks is still blank. In present study, we performed RNA-seq technology to analyze transcriptome profiling of duck spleens for the first time to identify differentially expressed genes (DEGs) associated with the infection of CHv and CHa at 24 h. Comparison of gene expression with mock ducks revealed 748 DEGs and 484 DEGs after CHv and CHa infection, respectively. Gene pathway analysis of DEGs highlighted valuable biological processes involved in host immune response, cell apoptosis and viral invasion. Genes expressed in those pathways were different in CHv infected duck spleens and CHa vaccinated duck spleens. The results may provide valuable information for us to explore the reasons of pathogenicity caused by CHv strain and protection activated by CHa strain.

Duck virus enteritis (duck plague) - a comprehensive update

Duck virus enteritis (DVE), also called duck plague, is one of the major contagious and fatal diseases of ducks, geese and swan. It is caused by duck enteritis virus (DEV)/Anatid herpesvirus-1 of the genus Mardivirus, family Herpesviridae, and subfamily Alpha-herpesvirinae. Of note, DVE has worldwide distribution, wherein migratory waterfowl plays a crucial role in its transmission within and between continents. Furthermore, horizontal and/ or vertical transmission plays a significant role in disease spread through oral-fecal discharges. Either of sexes from varying age groups of ducks is vulnerable to DVE. The disease is characterized by sudden death, vascular damage and subsequent internal hemorrhage, lesions in lymphoid organs, digestive mucosal eruptions, severe diarrhea and degenerative lesions in parenchymatous organs. Huge economic losses are connected with acute nature of the disease, increased morbidity and mortality (5%-100%), condemnations of carcasses, decreased egg production and hatchability. Although clinical manifestations and histopathology can provide preliminary diagnosis, the confirmatory diagnosis involves virus isolation and detection using serological and molecular tests. For prophylaxis, both live-attenuated and killed vaccines are being used in broiler and breeder ducks above 2 weeks of age. Since DEV is capable of becoming latent as well as shed intermittently, recombinant subunit and DNA vaccines either alone or in combination (polyvalent) are being targeted for its benign prevention. This review describes DEV, epidemiology, transmission, the disease (DVE), pathogenesis, and advances in diagnosis, vaccination and antiviral agents/therapies along with appropriate prevention and control strategies.

Attenuated Salmonella Typhimurium delivery of a novel DNA vaccine induces immune responses and provides protection against duck enteritis virus

DNA vaccines are widely used to prevent and treat infectious diseases, cancer and autoimmune diseases; however, their relatively low immunogenicity is an obstacle to their use. In this study, we constructed a novel and universal DNA vaccine vector (pSS898) that can be used to build DNA vaccines against duck enteritis virus (DEV) and other viruses that require DNA vaccines to provide protection. This vaccine vector has many advantages, including innate immunogenicity, efficient nuclear trafficking and resistance to attack from nucleases. UL24 and tgB from DEV were chosen as the antigens, and the heat labile enterotoxin B subunit (LTB) from Escherichia coli and the IL-2 gene (DuIL-2) from duck were used as adjuvants for the construction of DNA vaccine plasmids. Ducklings that were orally immunized with S739 (Salmonella Typhimurium Δasd-66 Δcrp-24 Δcya-25) and harboring these DEV DNA vaccines produced strong mucosal and systemic immune responses, and they resisted an otherwise lethal DEV challenge. More importantly, S739 (UL24-LTB) provided 90% protection after a priming-boost immunization. This study shows that our novel and universal DNA vaccine vector can be used efficiently in practical applications and may provide a promising method of orally inoculating ducks with a DEV DNA vaccine delivered by attenuated Salmonella Typhimurium for prevention of DVE.

Immune responses and protection against H5N1 highly pathogenic avian influenza virus induced by the Newcastle disease virus H5 vaccine in ducks

Ducks play an important role in the epidemiology of avian influenza, and there is a need for new avian influenza vaccines that are suitable for mass vaccination in ducks. The immune responses as well as highly pathogenic avian influenza (HPAI) H5N1 protection induced by a Newcastle disease virus (NDV) vector expressing an H5N1 hemagglutinin (rNDV-H5) were investigated in mule ducks, a hybrid between Muscovy (Cairina moschata domesticus) males and Pekin (Anas platyrhynchos domesticus) females. Immunological tools to measure NDV and H5-specific serum antibody, mucosal, and cell-mediated immune (CMI) responses in ducks have been validated after infection with the vector NDV and an H5N1 low pathogenic avian influenza virus. The effect of maternally-derived antibodies (MDAs) to NDV on the humoral and CMI responses after NDV-H5 vaccination was also investigated. Our results showed the rNDV-H5 vaccine elicits satisfactory humoral and cellular responses in 11-day-old ducks correlating with a complete clinical and virological protection against the H5N1 strain. However, vaccination with rNDV-H5 in the presence of NDV MDA induced lower NDV-specific serum antibody, mucosal, and CMI responses than in ducks with no MDA, while interestingly the H5-specific serum antibody and duodenal IgY response were higher in ducks with NDV MDA. To our knowledge, this is the first report of the use of an NDV vector in ducks and of an HPAI H5N1 challenge in mule ducks, which appeared to be as resistant as Pekin ducks.

Attenuated Salmonella typhimurium delivering DNA vaccine encoding duck enteritis virus UL24 induced systemic and mucosal immune responses and conferred good protection against challenge

Orally delivered DNA vaccines against duck enteritis virus (DEV) were developed using live attenuated Salmonella typhimurium (SL7207) as a carrier and Escherichia coli heat labile enterotoxin B subunit (LTB) as a mucosal adjuvant. DNA vaccine plasmids pVAX-UL24 and pVAX-LTB-UL24 were constructed and transformed into attenuated Salmonella typhimurium SL7207 resulting SL7207 (pVAX-UL24) and SL7207 (pVAX-LTB-UL24) respectively. After ducklings were orally inoculated with SL7207 (pVAX-UL24) or SL7207 (pVAX-LTB-UL24), the anti-DEV mucosal and systemic immune responses were recorded. To identify the optimum dose that confers maximum protection, we used different doses of the candidate vaccine SL7207 (pVAX-LTB-UL24) during oral immunization. The strongest mucosal and systemic immune responses developed in the SL7207 (pVAX-LTB-UL24) (10¹¹ CFU) immunized group. Accordingly, oral immunization of ducklings with SL7207 (pVAX-LTB-UL24) showed superior efficacy of protection (60-80%) against a lethal DEV challenge (1000 LD₅₀), compared with the limited survival rate (40%) of ducklings immunized with SL7207 (pVAX-UL24). Our study suggests that the SL7207 (pVAX-LTB-UL24) can be a candidate DEV vaccine.

Development and evaluation of an immunochromatographic strip test based on the recombinant UL51 protein for detecting antibody against duck enteritis virus

Background

Duck enteritis virus (DEV) infection causes substantial economic losses to the worldwide duck-producing areas. The monitoring of DEV-specific antibodies is a key to evaluate the effect of DEV vaccine and develop rational immunization programs. Thus, in this study, an immunochromatographic strip (ICS) test was developed for detecting DEV serum antibodies.

Results

The ICS test is based on membrane chromatography, and uses both the purified recombinant UL51 protein conjugated with colloidal gold and goat anti-rabbit IgG conjugated with colloidal gold as tracers, the purified recombinant UL51 protein as the capture reagent at the test line, and rabbit IgG as the capture reagent at the control line. The specificity of the ICS was evaluated by sera against DEV, Duck hepatitis virus (DHV), Riemerella anatipestifer (RA), Duck E. coli, Muscovy duck parvovirus (MPV), or Duck Influenza viruses (DIV). Only sera against DEV showed the strong positive results. In order to determine the sensitivity of the ICS, anti-DEV serum diluted serially was tested, and the minimum detection limit of 1:128 was obtained. The ICS components, which are provided in a sealed package, require no refrigeration and are stable for 12 months. To evaluate the effect of the ICS, 110 duck serum samples collected from several non-immune duck flocks were simultaneously tested by the ICS test, enzyme-linked immunosorbent assay (ELISA) and neutralization test (NT). The results showed that the sensitivity of the ICS test was almost consistent with ELISA and much higher than NT, has low cost, and is rapid (15 min) and easy to perform with no requirement of specialized equipment, reagent or technicians.

Conclusions

In this work, we successfully developed a simple and rapid ICS test for detecting DEV serum antibodies for the first time. The ICS test was high specific and sensitive for the rapid detection of anti-DEV antibodies, and has great potential to be used for the serological surveillance of DEV infection in the field.