Differential immune-related gene expression in the spleens of duck Tembusu virus-infected goslings

E-M349E and NS2A/2B-P1(T) are compensatory mutations of rDTMUV-NS2AB-P1P1'(AA), which regain virus proliferation by enhancing the virus package and restoring NS2A/2B cleavage

Duck Tembusu virus (DTMUV) belongs to the Flaviviridae family and mainly infects ducks. The genome of DTMUV is translated into a polyprotein, which is further cleaved into several protein by viral NS2B3 protease and host proteases. Crucially, the cleavage of the NS2A/2B precursor during this process is essential for the formation of replication complexes and viral packaging. Previous research has demonstrated that alanine mutations in NS2A/2B (P1P1' (AA)) result in an attenuated strain (rDTMUV-NS2A/2B-P1P1' (AA)) by disrupting NS2A/2B cleavage. In this study, we investigate the effects of the P1P1' (AA) mutation on the viral life cycle and explore compensatory mutations in rDTMUV-NS2A/2B-P1P1' (AA). Infected ducklings exhibit similar body weight gain and viral tissue loads to DTMUV-WT. Compensatory mutations E-M349E and P1(T) emerge, restoring proliferation levels to those of rDTMUV-WT. Specifically, E-M349E enhances viral packaging, while P1(T) reinstates NS2A/2B proteolysis in vitro. Thus, our findings reveal novel compensatory sites capable of restoring the attenuated DTMUV during polyprotein cleavage and packaging.

The topological model of NS4B and its TMD3 in duck TMUV proliferation

Duck Tembusu virus (DTMUV) belongs to the Flaviviridae family and mainly infects ducks. Duck Tembusu virus genome encodes one polyprotein that undergoes cleavage to produce 10 proteins. Among these, NS4B, the largest transmembrane protein, plays a crucial role in the viral life cycle. In this study, we investigated the localization of NS4B and found that it is located in the endoplasmic reticulum, where it co-localizes with DTMUV dsRNA. Subsequently, we confirmed 5 different transmembrane domains of NS4B and discovered that only its transmembrane domain 3 (TMD3) can traverse ER membrane. Then mutations were introduced in the conserved amino acids of NS4B TMD3 of DTMUV replicon and infectious clone. The results showed that V111G, V117G, and I118G mutations enhanced viral RNA replication, while Q104A, T106A, A113L, M116A, H120A, Y121A, and A122G mutations reduced viral replication. Recombinant viruses with these mutations were rescued and studied in BHK21 cells. The findings demonstrated that A113L and H120A mutations led to higher viral titers than the wild-type strain, while Q104A, T106A, V111G, V117G, and Y121A mutations attenuated viral proliferation. Additionally, H120A, M116A, and A122G mutations enhanced viral proliferation. Furthermore, Q104A, T106A, V111G, M116A, V117G, Y121A, and A122G mutants showed reduced viral virulence to 10-d duck embryos. Animal experiments further indicated that all mutation viruses resulted in lower genome copy numbers in the spleen compared to the WT group 5 days postinfection. Our data provide insights into the topological model of DTMUV NS4B, highlighting the essential role of NS4B TMD3 in viral replication and proliferation.

Advancements in Research on Duck Tembusu Virus Infections

Duck Tembusu Virus (DTMUV) is a pathogen of the Flaviviridae family that causes infections in poultry, leading to significant economic losses in the duck farming industry in recent years. Ducks infected with this virus exhibit clinical symptoms such as decreased egg production and neurological disorders, along with serious consequences such as ovarian hemorrhage, organ enlargement, and necrosis. Variations in morbidity and mortality rates exist across different age groups of ducks. It is worth noting that DTMUV is not limited to ducks alone; it can also spread to other poultry such as chickens and geese, and antibodies related to DTMUV have even been found in duck farm workers, suggesting a potential risk of zoonotic transmission. This article provides a detailed overview of DTMUV research, delving into its genomic characteristics, vaccines, and the interplay with host immune responses. These in-depth research findings contribute to a more comprehensive understanding of the virus's transmission mechanism and pathogenic process, offering crucial scientific support for epidemic prevention and control.

Mercury-Modulated Immune Responses in Arctic Barnacle Goslings (Branta leucopsis) upon a Viral-Like Immune Challenge

Historical mining activities in Svalbard (79°N/12°E) have caused local mercury (Hg) contamination. To address the potential immunomodulatory effects of environmental Hg on Arctic organisms, we collected newborn barnacle goslings (Branta leucopsis) and herded them in either a control or mining site, differing in Hg levels. An additional group at the mining site was exposed to extra inorganic Hg(II) via supplementary feed. Hepatic total Hg concentrations differed significantly between the control (0.011 ± 0.002 mg/kg dw), mine (0.043 ± 0.011 mg/kg dw), and supplementary feed (0.713 ± 0.137 mg/kg dw) gosling groups (average ± standard deviation). Upon immune challenge with double-stranded RNA (dsRNA) injection, endpoints for immune responses and oxidative stress were measured after 24 h. Our results indicated that Hg exposure modulated the immune responses in Arctic barnacle goslings upon a viral-like immune challenge. Increased exposure to both environmental as well as supplemental Hg reduced the level of natural antibodies, suggesting impaired humoral immunity. Hg exposure upregulated the expression of proinflammatory genes in the spleen, including inducible nitric oxide synthase (iNOS) and interleukin 18 (IL18), suggesting Hg-induced inflammatory effects. Exposure to Hg also oxidized glutathione (GSH) to glutathione disulfide (GSSG); however, goslings were capable of maintaining the redox balance by de novo synthesis of GSH. These adverse effects on the immune responses indicated that even exposure to low, environmentally relevant levels of Hg might affect immune competence at the individual level and might even increase the susceptibility of the population to infections.

Rapid diagnosis of duck Tembusu virus and goose astrovirus with TaqMan-based duplex real-time PCR

The mixed infection of duck Tembusu virus (DTMUV) and goose astrovirus (GoAstV) is an important problem that endangers the goose industry. Although quantitative PCR has been widely used in monitoring these two viruses, there is no reliable method to detect them at the same time. In this study, by analyzing the published genomes of DTMUV and goose astrovirus genotype 2 (GoAstV-2) isolated in China, we found that both viruses have high conservation, showing 96.5 to 99.5% identities within different strains of DTMUV and GoAstV, respectively. Subsequently, PCR primers and TaqMan probes were designed to identify DTMUV and GoAstV-2, and different fluorescent reporters were given to two probes for differential diagnosis. Through the optimization and verification, this study finally developed a duplex TaqMan qPCR method that can simultaneously detect the above two viruses. The lower limits of detection were 100 copies/μL and 10 copies/μL for DTMUV and GoAstV-2 under optimal condition. The assay was also highly specific in detecting one or two viruses in various combinations in specimens, and provide tool for clinical diagnosis of mixed infections of viruses in goose.

Transcriptome analysis of PK-15 cells expressing CSFV NS4A

BACKGROUND

Classical swine fever (CSF) is a severe disease of pigs that results in huge economic losses worldwide and is caused by classical swine fever virus (CSFV). CSFV nonstructural protein 4 A (NS4A) plays a crucial role in infectious CSFV particle formation. However, the function of NS4A during CSFV infection is not well understood.  RESULTS: In this study, we used RNA-seq to investigate the functional role of CSFV NS4A in PK-15 cells. A total of 3893 differentially expressed genes (DEGs) were identified in PK-15 cells expressing NS4A compared to cells expressing the empty vector (NC). Twelve DEGs were selected and further verified by RT‒qPCR. GO and KEGG enrichment analyses revealed that these DEGs were associated with multiple biological functions, including cell adhesion, apoptosis, host defence response, the inflammatory response, the immune response, and autophagy. Interestingly, some genes associated with host immune defence and inflammatory response were downregulated, and some genes associated with host apoptosis and autophagy were upregulated.

CONCLUSION

CSFV NS4A inhibits the innate immune response, and suppresses the expression of important genes associated with defence response to viruses and inflammatory response, and regulates cell adhesion, apoptosis and autophagy.

RNA-Seq analysis of duck embryo fibroblast cells gene expression during duck Tembusu virus infection

Duck Tembusu virus (DTMUV), a member of the family Flaviviridae and an economically important pathogen with a broad host range, leads to markedly decreased egg production. However, the molecular mechanism underlying the host-DTMUV interaction remains unclear. Here, we performed high-throughput RNA sequencing (RNA-Seq) to study the dynamic changes in host gene expression at 12, 24, 36, 48 and 60 h post-infection (hpi) in duck embryo fibroblasts (DEF) infected with DTMUV. A total of 3129 differentially expressed genes (DEG) were identified after DTMUV infection. Gene Ontology (GO) category and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that these DEG were associated with multiple biological functions, including signal transduction, host immunity, virus infection, cell apoptosis, cell proliferation, and pathogenicity-related and metabolic process signaling pathways. This study analyzed viral infection and host immunity induced by DTMUV infection from a novel perspective, and the results provide valuable information regarding the mechanisms underlying host-DTMUV interactions, which will prove useful for the future development of antiviral drugs or vaccines for poultry, thus benefiting the entire poultry industry.

Time-Course Transcriptome Analysis of Lungs From Mice Infected With Hypervirulent Klebsiella pneumoniae via Aerosolized Intratracheal Inoculation

Hypervirulent Klebsiella pneumoniae (hvKp) can cause life-threatening community-acquired infections among healthy young individuals and is thus of concern for global dissemination. In this study, a mouse model of acute primary hvKp pneumonia was established via aerosolized intratracheal (i.t.) inoculation, laying the foundation for conducting extensive studies related to hvKp. Subsequently, a time-course transcriptional profile was created of the lungs from the mouse model at 0, 12, 24, 48 and 60 hours post-infection (hpi) using RNA Sequencing (RNA-Seq). RNA-Seq data were analyzed with the use of Mfuzz time clustering, weighted gene co-expression network analysis (WGCNA) and Immune Cell Abundance Identifier for mouse (ImmuCellAI-mouse). A gradual change in the transcriptional profile of the lungs was observed that reflected expected disease progression. At 12 hpi, genes related to acute phase inflammatory response increased in expression and lipid metabolism appeared to have a pro-inflammatory effect. At 24 hpi, exacerbation of inflammation was observed and active IFN-γ suggested that signaling promoted activation and recruitment of macrophages occurred. Genes related to maintaining the structural integrity of lung tissues showed a sustained decrease in expression after infection and the decrease was especially marked at 48 hpi. TNF, IL-17, MAPK and NF-kB signaling pathways may play key roles in the immunopathogenesis mechanism at all stages of infection. Natural killer (NK) cells consistently decreased in abundance after infection, which has rarely been reported in hvKp infection and could provide a new target for treatment. Genes Saa1 and Slpi were significantly upregulated during infection. Both Saa1, which is associated with lipopolysaccharide (LPS) that elicits host inflammatory response, and Slpi, which encodes an antimicrobial protein, have not previously been reported in hvKp infections and could be important targets for subsequent studies. To t our knowledge, this paper represents the first study to investigate the pulmonary transcriptional response to hvKp infection. The results provide new insights into the molecular mechanisms underlying the pathogenesis of hvKp pulmonary infection that can contribute to the development of therapies to reduce hvKp pneumonia.

Regulation of MDA5-dependent anti-Tembusu virus innate immune responses by LGP2 in ducks

Melanoma differentiation associated factor 5 (MDA5), which belongs to the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) family, has been proved to be a key pattern recognition receptor of innate antiviral signaling in duck, which plays an important role in anti-Tembusu virus (TMUV) infection. However, laboratory of genetics and physiology 2 (LGP2), the third member of RLRs family, the regulatory function on antiviral innate immunity of MDA5 is currently unclear. In this study, we investigated the subcellular localization of duck LGP2 (duLGP2) and confirmed that it is an important regulator of the duMDA5-mediated host innate antiviral immune response. The present experimental data demonstrate that the overexpression of duLGP2 inhibits duMDA5 downstream transcriptional factor (IRF-7, IFN-β, and NF-κB) promoter activity, and duMDA5-mediated type I IFNs and ISGs expression were significantly suppressed by duLGP2 regardless of viral infection in vitro. The inhibition of duLGP2 on the antiviral activity of duMDA5 ultimately leads to an increase in viral replication. However, the overexpression of duLGP2 promotes expression of mitochondrial antiviral-signaling protein (MAVS) and duMDA5-mediated proinflammatory cytokines. This study provides a new rationale support for the duLGP2 regulates duMDA5-mediated anti-viral immune signaling pathway theory in duck.

The E3 Ubiquitin Ligase TRIM25 Inhibits Tembusu Virus Replication in vitro

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that has caused significant economic losses to the duck industry in China since 2010 due to egg production losses and neurological dysfunction. DTMUV is a public health concern because the infection spreads rapidly among birds. Retinoic acid-inducible gene-I (RIG-I)serves as an innate immune sensor and plays a key role in host antiviral defenses. Tripartite motif-containing protein 25 (TRIM25), an E3 ubiquitin ligase, is pivotal for RIG-I ubiquitination and activation. In addition, TRIM25 acts as an interferon-stimulated gene and mediates the antiviral activity. However, the effect of duck TRIM25 on DTMUV has not been assessed. Herein, we reportthe antiviral function of TRIM25 against DTMUV. First, we constructed the pcDNA3.1-c-myc-duTRIM25 plasmid. TRIM25 has a 2052 bp open reading frame that encodes a predicted 684 amino acid protein consisting of a RING finger domain, a B-box domain, a coiled-coil domain, and a PRY/SPRY domain. The protein sequence identity with chicken, mouse, and human TRIM25 is 69.7, 47.8, and 48.3%, respectively. TRIM25 was upregulated in BHK-21 cells, duck embryo fibroblasts, and 293T cellsupon DTMUV infection. The expression of viral RNA and proteins was significantly lower in cells over expressing TRIM25 than in control cells. Furthermore, siRNA-mediated silencing of TRIM25 increased the production of viral progeny. These results help elucidate the molecular mechanisms underlying the host response to DTMUV infection and suggest potential control measures for DTMUV outbreaks.

Morphologic Study on Lymphocyte Homing in Duck Tembusu Virus-Infected Duck Spleen

The present study was designed to analyze the histologic and cytologic changes of lymphocyte homing in noninfected and duck Tembusu virus (DTMUV)-infected duck spleens. At first, we investigated the noninfected structure that facilitates lymphocyte homing. Under light and electron microscopy, results showed that sheath capillaries were located in the white pulp of the spleen, and the endothelial cells of sheath capillaries were cuboidal in shape, which is a typical characteristic of high endothelial venules. To monitor the lymphocyte homing, 5,6-carboxy fluoresceindiacetate succinimidyl ester (CFSE)-labeled lymphocytes that were intravenously injected into noninfected ducks appeared in the periellipsoidal sheaths (PELS), which proved that lymphocytes can return to the spleen through sheath capillaries. Furthermore, proteoglycans (PGs) associated with homing factors were positively observed in sheath capillaries and PELS by colloidal iron staining. This suggests that PGs are associated with lymphocyte homing. The results of the DTMUV infection experiment showed that PELS appeared vacuolized at 3 dpi. The spleen tissue gradually recovered at 5 and 7 dpi. In addition, the lymphocytes increased around sheath capillaries, and the expression of PGs in sheath capillaries increased after virus infection. Meanwhile, the gaps between endothelial cells were enlarged, and the lymphocytes were mainly in the lumen and basement membrane. In conclusion, lymphocytes could recruit into the spleen through sheath capillaries, and PGs participated and promoted the lymphocyte homing, suggesting that the unique high endothelial capillaries favor lymphocyte homing, which promotes tissue repair and antigen clearance in the duck.

Transcriptome analysis reveals new insight of duck Tembusu virus (DTMUV)-infected DF-1 cells

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that has caused huge economic losses to the duck industry in China since 2010. Moreover, the infection has spread rapidly, resulted in a potential public health concern. To improve our understanding of the host cellular responses to virus infection and the pathogenesis of DTMUV infection, we used RNA-Seq to detect the gene changes in DF-1 cells infected and mock-infected with DTMUV. A total of 663 differentially-expressed genes (DEGs) were identified in DTMUV-infected compared with mock-infected DF-1 cells at 24 h post-infection (hpi), among which 590 were up regulated and 73 were down regulated. Gene Ontology analysis indicated that the DEGs were mainly involved in cellular process, immune system processes, metabolic processes, and signal-organism process. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the DEGs were mainly involved in several signaling pathways such as Toll-like receptor signaling, Jak-STAT signaling, RIG-I-like receptor signaling and AGE-RAGE signaling pathway. Moreover, some selected DEGs were further confirmed by real-time PCR and the results were consistent with the sequencing data. To our knowledge, this study is the first to analyze the transcriptomic change in DF-1 cells following DTMUV infection. We believe that our research provides useful information in better understanding the host response to DTMUV infection and the inherent mechanism of DTMUV replication and pathogenicity.

Transcriptome Profiles of Highly Pathogenic Pure Avian H7N9 Virus-Infected Lungs of BALB/c Mice

Avian influenza A (H7N9) viruses emerged in China in 2013 and caused a zoonotic disease associated with a high case-fatality ratio of more than 30%. Transcriptional profiles obtained using animal models reveal host responses to the disease, thereby providing insights into disease pathogenesis. Therefore, we aimed to characterize the host responses of the H7N9 virus infected-mouse lungs in this study. First, we isolated an avian-originated H7N9 strain, which was shown to be highly pathogenic to both chickens and mice. Genomic analysis results suggested that a 12-nucleotide-insertion was present at the hemagglutinin cleavage site, and both the hemagglutinin and neuraminidase genes belonged to the Yangtze River Delta lineage. RNA sequencing results revealed 566 differentially expressed genes in the H7N9-infected lungs. Moreover, transcriptome analysis revealed that over-activated antiviral signals and intense interferon-stimulated gene products possibly contributed to the high virulence of the virus in mice. Importantly, lung concentrations of inflammatory cytokines, including interleukin-1β and interleukin-6, interferon-β, and tumor necrosis factor-α, were upregulated in response to H7N9 virus infection. Overall, the present study provided a comprehensive understanding of H7N9 virus pathogenicity and correlated host immune responses.

Transcriptome analysis of duck embryo fibroblasts for the dynamic response to duck tembusu virus infection and dual regulation of apoptosis genes

Duck Tembusu virus (DTMUV) is an emerging pathogenic flavivirus that has caused enormous economic losses in Southeast Asia. However, the pathogenic mechanism and host's responses after DTMUV infection remain poorly understood. During this study, total mRNA sequencing (RNA-Seq) analysis was used to detect the global gene expression in DEFs at various time points after DTMUV infection. We identified 326 genes altered significantly at all time points, and these genes were dynamically enriched in multifarious biological processes, including apoptosis, innate immune response, DNA replication, cell cycle arrest and DNA repair. Next, the results showed that apoptosis was induced and the proportion of apoptosis increased with time, and pro-apoptotic molecules caspases were activated. The RNA-seq data analysis further revealed that most pro-apoptosis and anti-apoptosis genes were early continually responsive, and the genes involved in both intrinsic and extrinsic apoptotic pathways were initiated. Further, the considerably enriched immune-relevant pathways were involved in apoptosis process, and protein-protein interactions (PPIs) analysis showed that IL6, STAT1, TNFAIP3, CFLAR and PTGS2 may be key regulators of DEFs apoptosis. In conclusion, this study not only contributes to understanding the underlying mechanism of DEFs infection with DTMUV, but also provides new insights into targets screening for antiviral therapy.

Transcriptomic Analysis and Functional Characterization Reveal the Duck Interferon Regulatory Factor 1 as an Important Restriction Factor in the Replication of Tembusu Virus

Duck Tembusu virus (DTMUV) infection has caused great economic losses to the poultry industry in China, since its first discovery in 2010. Understanding of host anti-DTMUV responses, especially the innate immunity against DTMUV infection, would be essential for the prevention and control of this viral disease. In this study, transcriptomic analysis of duck embryonic fibroblasts (DEFs) infected with DTMUV reveals that several innate immunity-related pathways, including Toll-like, NOD-like, and retinoic acid-inducible gene I (RIG-I)-like receptor signaling pathways, are activated. Further verification by RT-qPCR confirmed that RIG-I, MAD5, TLR3, TLR7, IFN-α, IFN-β, MX, PKR, MHCI, MHCII, IL-1β, IL-6, (IFN-regulatory factor 1) IRF1, VIPERIN, IFIT5, and CMPK2 were up-regulated in cells infected with DTMUV. Through overexpression and knockdown/out of gene expression, we demonstrated that both VIPERIN and IRF1 played an important role in the regulation of DTMUV replication. Overexpression of either one significantly reduced viral replication as characterized by reduced viral RNA copy numbers and the envelope protein expression. Consistently, down-regulation of either one resulted in the enhanced replication of DTMUV in the knockdown/out cells. We further proved that IRF1 can up-regulate VIPERIN gene expression during DTMUV infection, through induction of type 1 IFNs as well as directly binding to and activation of the VIPERIN promoter. This study provides a genome-wide differential gene expression profile in cells infected with DTMUV and reveals an important function for IRF1 as well as several other interferon-stimulated genes in restricting DTMUV replication.

Innate immune responses to duck Tembusu virus infection

The disease caused by duck Tembusu virus (DTMUV) is characterized by severe egg-drop in laying ducks. Currently, the disease has spread to most duck-raising areas in China, leading to great economic losses in the duck industry. In the recent years, DTMUV has raised some concerns, because of its expanding host range and increasing pathogenicity, as well as the potential threat to public health. Innate immunity is crucial for defending against invading pathogens in the early stages of infection. Recently, studies on the interaction between DTMUV and host innate immune response have made great progress. In the review, we provide an overview of DTMUV and summarize current advances in our understanding of the interaction between DTMUV and innate immunity, including the host innate immune responses to DTMUV infection through pattern recognition receptors (PRRs), signaling transducer molecules, interferon-stimulated genes (ISGs), and the immune evasion strategies employed by DTMUV. The aim of the review is to gain an in-depth understanding of DTMUV pathogenesis to facilitate future studies.

pUC18-CpG Is an Effective Adjuvant for a Duck Tembusu Virus Inactivated Vaccine

Duck Tembusu virus (DTMUV) is an emerging pathogenic flavivirus responsible for massive economic losses in the duck industry. However, commercially inactivated DTMUV vaccines have been ineffective at inducing protective immunity in ducks. The widely used adjuvant cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) reportedly improve humoral and cellular immunities in animal models. However, its effectiveness in DTMUV vaccines requires validation. Here, we assessed the protective efficacy of pUC18-CpG as an adjuvant in an inactivated live DTMUV vaccine in ducks. Our results revealed that the serum hemagglutination inhibition (HI) antibody titers, positive rates of anti-DTMUV antibodies, the concentration of serum cytokines, and protection efficacy were significantly increased in ducks immunized with pUC18-CpG compared to that in the control group. Moreover, ducks immunized with a full vaccine dose containing a half dose of antigen supplemented with 40 μg of pUC18-CpG exhibited the most potent responses. This study suggests that pUC18-CpG is a promising adjuvant against DTMUV, which might prove effective in treating other viral diseases in waterfowl.

Host Innate Immune Response of Geese Infected with Clade 2.3.4.4 H5N6 Highly Pathogenic Avian Influenza Viruses

Since 2014, highly pathogenic avian influenza (HPAI) H5N6 viruses have circulated in waterfowls and caused human infections in China, posing significant threats to the poultry industry and the public health. However, the genetics, pathogenicity and innate immune response of H5N6 HPAIVs in geese remain largely unknown. In this study, we analyzed the genetic characteristic of the two H5N6 viruses (GS38 and DK09) isolated from apparently healthy domestic goose and duck in live poultry markets (LPMs) of Southern China in 2016. Phylogenetic analysis showed that the HA genes of the two H5N6 viruses belonged to clade 2.3.4.4 and were clustered into the MIX-like group. The MIX-like group viruses have circulated in regions such as China, Japan, Korea, and Vietnam. The NA genes of the two H5N6 viruses were classified into the Eurasian sublineage. The internal genes including PB2, PB1, PA, NP, M, and NS of the two H5N6 viruses derived from the MIX-like. Therefore, our results suggested that the two H5N6 viruses were reassortants of the H5N1 and H6N6 viruses and likely derived from the same ancestor. Additionally, we evaluated the pathogenicity and transmission of the two H5N6 viruses in domestic geese. Results showed that both the two viruses caused serious clinical symptoms in all inoculated geese and led to high mortality in these birds. Both the two viruses were transmitted efficiently to contact geese and caused lethal infection in these birds. Furthermore, we found that mRNA of pattern recognition receptors (PRRs), interferons (IFNs), and stimulated genes (ISGs) exhibited different levels of activation in the lungs and spleens of the two H5N6 viruses-inoculated geese though did not protect these birds from H5N6 HPAIVs infection. Our results suggested that the clade 2.3.4.4 waterfowl-origin H5N6 HPAIVs isolated from LPMs of Southern China could cause high mortality in geese and innate immune-related genes were involved in the geese innate immune response to H5N6 HPAIVs infection. Therefore, we should pay more attention to the evolution, pathogenic variations of these viruses and enhance virological surveillance of clade 2.3.4.4 H5N6 HPAIVs in waterfowls in China.

DEF Cell-Derived Exosomal miR-148a-5p Promotes DTMUV Replication by Negative Regulating TLR3 Expression

Duck tembusu virus (DTMUV) is a single-stranded, positive-polarity RNA flavivirus that has caused considerable economic losses in China in recent years. Innate immunity represents the first line of defense against invading pathogens and serves as an important role in resisting viral infections. In this study, we found that the infection of ducks by DTMUV triggers Toll-like receptors (TLRs) and (RIG-I)-like receptors (RLRs) signaling pathways and inducing abundant of pro-inflammatory factors and type I interferons (IFNs), in which melanoma differentiation-associated gene 5 (MDA5) and Toll-like receptor 3 (TLR3) play important immunity roles, they can inhibit the replication process of DTMUV via inducing type I IFNs. Moreover, we demonstrated that type I IFNs can inhibit the DTMUV replication process in a time- and dose-dependent manner. Exosomes are small membrane vesicles that have important roles in intercellular communication. MicroRNAs (miRNAs) are small non-coding RNAs that can modulate gene expression and are common substances in exosomes. In our experiment, we successfully isolated DEF cells derived exosome for the first time and explored its function. Firstly, we found the expression of miR-148a-5p is significantly decreased following DTMUV infect. Then we found miR-148a-5p can target TLR3 and down-regulate the expression of TLR3, serving as a negative factor in innate immunity. Unfortunately, we cannot find miRNAs with different expression changes that can target MDA5. Lastly, our experimental results showed that TLR3 was one of the causes of miR-148a-5p reduction, suggesting that the high level of TLR3 after DTMUV infect can both trigger innate immunity and suppress miR-148a-5p to resist DTMUV.

Binding of the Duck Tembusu Virus Protease to STING Is Mediated by NS2B and Is Crucial for STING Cleavage and for Impaired Induction of IFN-β

Duck Tembusu virus (DTMUV) is a newly emerged causative agent of avian disease. The protease-dependent immune evasion of flaviviruses has been reported; however, the molecular details of this process are unclear. In this study, we found that DTMUV nonstructural protein 2B-3, a NS2B3 protease, can inhibit IFN-β production. DTMUV NS2B3 inhibited RIG-I-, MDA5-, MAVS-, and STING-directed IFN-β transcription, but not TBK1- and IRF7-mediated induction of IFN-β. Further analysis showed that DTMUV NS2B3 could cleave duck STING (duSTING); the cleavage was dependent on the protease activity of NS2B3. Moreover, the STING cleavage event occurred in a not-strictly-species-specific manner. The scissile bond of duSTING cleaved by NS2B3 was mapped between the R84 and G85 residues. The ability of NS2B3 to reduce duSTING cleavage-resistant mutant-mediated IFN-β, and ISG production was significantly reduced, demonstrating that duSTING cleavage is essential for NS2B3-induced suppression of type I IFN responses. Remarkably, the binding of NS2B3 to duSTING, which is a prerequisite for cleavage, was found to depend on NS2B, but not NS3, the cofactor of the enzyme. Unexpectedly, we found that the region between aa residues 221-225 of duSTING, distal from the site of the scissile bond, was essential for the binding of NS2B3 to duSTING and/or the cleavage of duSTING by NS2B3. Thus, we identified the molecular mechanism by which DTMUV subverts the host innate immunity using its protease. More importantly, our study provides insight into NS2B3-mediated STING cleavage events in general.

Genetically stable reporter virus, subgenomic replicon and packaging system of duck Tembusu virus based on a reverse genetics system

Duck Tembusu virus (DTMUV) is a novel flavivirus that has caused an outbreak of severe duck egg-drop syndrome since 2010. It has spread rapidly to other avian species, causing enormous economic loss. In the present study, we generated a reporter virus expressing NanoLuc luciferase, which was stable after 10 rounds of continuous propagation without reporter gene deletion. Moreover, we generated two types of replicons driven by the T7 promoter or CMV promoter, both of which worked well in BHK21 cells. Furthermore, we developed the first packaging system for DTMUV by co-transfection into BHK21 cells of a replicon (containing mature C) and a plasmid encoding C₁₆-prM-E, which resulted in the production of single round infectious particles (SRIPs). We also generated a packaging cell line for DTMUV to produce SRIPs. We believe that these multicomponent platform tools are important for DTMUV pathogenesis research and novel vaccine development.

RNA-Seq analysis of duck embryo fibroblast cell gene expression during the early stage of egg drop syndrome virus infection

Egg drop syndrome virus (EDSV), a member of the family Adenoviridae and an economically important pathogen with a broad host range, leads to markedly decreased egg production. However, the molecular mechanism underlying the host-EDSV interaction remains unclear. Here, we performed high-throughput RNA sequencing (RNA-Seq) to study the dynamic changes in host gene expression at 6, 12, and 24 hours post-infection in duck embryo fibroblasts (DEFs) infected with EDSV. Atotal of 441 differentially expressed genes (DEGs) were identified after EDSV infection. Gene Ontology category and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that these DEGs were associated with multiple biological functions, including signal transduction, host immunity, virus infection, cell apoptosis, cell proliferation, and pathogenicity-related and metabolic process signaling pathways. We screened and identified 12 DEGs for further examination by using qRT-PCR. The qRT-PCR and RNA-Seq results were highly consistent. This study analyzed viral infection and host immunity induced by EDSV infection from a novel perspective, and the results provide valuable information regarding the mechanisms underlying host-EDSV interactions, which will prove useful for the future development of antiviral drugs or vaccines for poultry, thus benefiting the entire poultry industry.

Identification of determinants that mediate binding between Tembusu virus and the cellular receptor heat shock protein A9

Heat shock protein A9 (HSPA9), a member of the heat shock protein family, is a putative receptor for Tembusu virus (TMUV). By using Western blot and co-immunoprecipitation assays, E protein domains I and II were identified as the functional domains that facilitate HSPA9 binding. Twenty-five overlapping peptides covering domain I and domain II sequences were synthesized and analyzed by using an HSPA9 binding assay. Two peptides showed the capability of binding to HSPA9. Dot blot assay of truncated peptides indicated that amino acid residues 19 to 22 and 245 to 252 of E protein constitute the minimal motifs required for TMUV binding to HSPA9. Importantly, peptides harboring those two minimal motifs could effectively inhibit TMUV infection. Our results provide insight into TMUV-receptor interaction, thereby creating opportunities for elucidating the mechanism of TMUV entry.

Comparative proteomic analysis revealed complex responses to classical/novel duck reovirus infections in the spleen tissue of Cairna moschata

Duck reovirus (DRV), a member of the genus Orthoreovirus in the family Reoviridae, was first isolated from Muscovy ducks. The disease associated with DRV causes great economic losses to the duck industry. However, the responses of duck (Cairna moschata) to the classical/novel DRV (C/NDRV) infections are largely unknown. To reveal the relationship of pathogenesis and immune response, the proteomes of duck spleen cells under the control and C/NDRV infections were compared. In total, 5986 proteins were identified, of which 5389 proteins were quantified. The different accumulated proteins (DAPs) under the C/NDRV infections showed displayed various biological functions and diverse subcellular localizations. The proteins related to the serine protease system were siginificantly changed, suggesting that the activated serine protease system may play an important role under the C/NDRV infections. Furthermore, the differences in the responses to the C/NRDV infections between the duck liver and spleen tissues were compared. Only a small number of common DAPs were identified in both liver and spleen tissues, suggesting diversified pattern involved in the responses to the C/NRDV infections. However, the changes in the proteins involved in the serine protease systems were similar in both liver and spleen cells. Our data may give a comprehensive resource for investigating the responses to C/NDRV infections in ducks. SIGNIFICANCE: A newly developed MS/MS-based method involving isotopomer labels and 'tandem mass' has been applied to protein accurate quantification in current years. However, no studies on the responses of duck (Cairna moschata) spleen tissue to the classical/novel DRV (C/NDRV) infections have been performed. As a continued study of our previous report on the responses of duck liver tissue to the C/NDRV infections, the current study further compared the differences in the responses to the C/NRDV infections between the duck liver and spleen tissues. Our results will provide an opportunity to reveal the relationship of pathogenesis and immune response and basic information on the pathogenicity of C/NDRV in ducks.

Evolution of Tembusu Virus in Ducks, Chickens, Geese, Sparrows, and Mosquitoes in Northern China

Tembusu virus (TMUV) is a contagious pathogen from fowl that mainly infects ducks and geese, causing symptoms of high fever, loss of appetite, retarded growth, neurological symptoms, severe duck-drop syndrome, and even death. During an epidemiological investigation of TMUV in Northern China, we isolated 11 TMUV strains from ducks, chickens, geese, sparrows, and mosquitoes (2011–2017). Phylogenetic analysis of the open-reading frames of genes revealed that these strains clustered into Chinese strains II. The nucleotide and amino acid homologies of NS1 of the strains ranged between 85.8–99.8% and 92.5–99.68%, respectively, which were lower than those of E (86.7–99.9% and 96.5–99.9%, respectively), NS3 (87.6–99.9% and 98.2–99.8%, respectively), and NS5 (86.5–99.9% and 97.8–99.9%, respectively). Predictions of the tertiary structure of the viral proteins indicated that NS1 in 4 of 11 strains had a protein structure mutation at ¹⁸⁰TAV¹⁸² that changed a random crimp into an alpha helix. The protein of 6 of 11 strains had a glycosylation site mutation from NTTD to NITD. Furthermore, epidemiological data suggested that TMUV has been circulating in half of China’s provinces (17 of 34). Our findings, for the first time, have identified the NS1 protein as a potential hypervariable region for genetic evolution. Additionally, the territorial scope of the virus has expanded, requiring strict bio-security measures or a multivalent vaccine to control its spread.

Comparative Transcriptomic Analysis of Immune-Related Gene Expression in Duck Embryo Fibroblasts Following Duck Tembusu Virus Infection

Duck is a major waterfowl species in China, providing high-economic benefit with a population of up to 20–30 billion per year. Ducks are commonly affected by severe diseases, including egg-drop syndrome caused by duck Tembusu virus (DTMUV). The immune mechanisms against DTMUV invasion and infection remain poorly understood. In this study, duck embryo fibroblasts (DEFs) were infected with DTMUV and harvested at 12 and 24 h post-infection (hpi), and their genomes were sequenced. In total, 911 (764 upregulated and 147 downregulated genes) and 3008 (1791 upregulated and 1217 downregulated) differentially expressed genes (DEGs) were identified at 12 and 24 hpi, respectively. Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that DEGs were considerably enriched in immune-relevant pathways, including Toll-like receptor signaling pathway, Cytosolic DNA-sensing pathway, RIG-I-like receptor signaling pathway, Chemokine signaling pathway, NOD-like receptor signaling pathway, and Hematopoietic cell lineage at both time points. The key DEGs in immune system included those of the cytokines (IFN α2, IL-6, IL-8L, IL-12B, CCR7, CCL19, and CCL20), transcription factors or signaling molecules (IRF7, NF-κB, STAT1, TMEM173, and TNFAIP3), pattern recognition receptors (RIG-I and MDA5), and antigen-presenting proteins (CD44 and CD70). This suggests DTMUV infection induces strong proinflammatory/antiviral effects with enormous production of cytokines. However, these cytokines could not protect DEFs against viral attack. Our data revealed valuable transcriptional information regarding DTMUV-infected DEFs, thereby broadening our understanding of the immune response against DTMUV infection; this information might contribute in developing strategies for controlling the prevalence of DTMUV infection.

The 125th Lys and 145th Thr Amino Acids in the GTPase Domain of Goose Mx Confer Its Antiviral Activity against the Tembusu Virus

The Tembusu virus (TMUV) is an avian pathogenic flavivirus that causes a highly contagious disease and catastrophic losses to the poultry industry. The myxovirus resistance protein (Mx) of innate immune effectors is a key antiviral “workhorse” of the interferon (IFN) system. Although mammalian Mx resistance against myxovirus and retrovirus was witnessed for decades, whether or not bird Mx has anti-flavivirus activity remains unknown. In this study, we found that the transcription of goose Mx (goMx) was obviously driven by TMUV infection, both in vivo and in vitro, and that the titers and copies of TMUV were significantly reduced by goMx overexpression. In both primary (goose embryo fibroblasts, GEFs) and passaged cells (baby hamster kidney cells, BHK21, and human fetal kidney cells, HEK 293T), it was shown that goMx was mainly located in the cytoplasm, and sporadically distributed in the nucleus. The intracellular localization of this protein is attributed to the predicted bipartite nuclear localization signal (NLS; 30 residues: the 441st–471st amino acids of goMx). Intuitively, it seems that the cells with a higher level of goMx expression tend to have lower TMUV loads in the cytoplasm, as determined by an immunofluorescence assay. To further explore the antiviral determinants, a panel of variants was constructed. Two amino acids at the 125th (Lys) and 145th (Thr) positions in GTP-binding elements, not in the L4 loop (40 residues: the 532nd–572nd amino acids of goMx), were vital for the antiviral function of goMx against TMUV in vitro. These findings will contribute to our understanding of the functional significance of the antiviral system in aquatic birds, and the development of goMx could be a valuable therapeutic agent against TMUV.

Establishment of a reverse genetics system for duck Tembusu virus to study virulence and screen antiviral genes

Recently, a newly emerged avian flavivirus, duck Tembusu virus (TMUV), was identified as the causative agent of a serious duck viral disease in Asia. Its rapid spread and expanded host range have raised substantial concerns regarding its potential threat to non-avian hosts, including humans. In this study, we report an infectious cDNA clone for a clinical strain CQW1 isolated from Southwest China, which is representative of the disease outbreak in the Chinese mainland. We generated a full-length cDNA clone pACYC FL-TMUV, which is infectious, and this cDNA clone-derived recombinant TMUV (rTMUV) showed comparative growth kinetics in both BHK21 cells and DEF cells compared with parental TMUV (pTMUV). In addition, rTMUV also showed the same high virulence in 9-day-old duck embryos as that in pTMUV, suggesting that rTMUV possessed similar properties to the natural virus both in vitro and in vivo. Based on the cDNA-clone, we first generated a reporter TMUV (TMUV-RLuc) carrying a Renilla luciferase (RLuc) gene. The luciferase kinetics of TMUV-RLuc were determined both in BHK21 and DEF cells. It seems that TMUV-RLuc grew well in vitro; however, the insertion of the RLuc gene attenuated viral replication in vitro. The higher viral titres of TMUV-RLuc were observed in BHK21 compared with that in DEF cells. The antiviral effects of exogenous-expressed duck RIG-I, MDA5, STING, MAVS, TBK1, IFNα and IFNγ were studied in vitro by using TMUV-RLuc. Our reverse genetics system will provide a multicomponent platform for the pathogenesis study of duck TMUV and the development of molecular countermeasures against duck TMUV infection.

A Novel Diagnostic Method to Detect Duck Tembusu Virus: A Colloidal Gold-Based Immunochromatographic Assay

Duck Tembusu virus (DTMUV) is an emerging pathogenic flavivirus that has resulted in large economic losses to the duck-rearing industry in China since 2010. Therefore, an effective diagnostic approach to monitor the spread of DTMUV is necessary. Here, a novel diagnostic immunochromatographic strip (ICS) assay was developed to detect DTMUV. The assay was carried out using colloidal gold coated with purified monoclonal antibody A12D3 against envelope E protein. Purified polyclonal C12D1 antibodies from BALB/c mice against the envelope E protein were used as the capture antibody. Goat anti-mouse IgG was used to detect DTMUV, which was also assembled on the ICS. Results showed that the ICS could specifically detect DTMUV within 10 min. It also could be stored 25 and 4°C for 4 and 6 months, respectively. The sensitivity of the ICS indicated that the dilution multiples of positive allantoic fluid of DTMUV (LD50: 10^4.33/0.2 ml) was up to 200. Its specificity and sensibility showed no significant change under the above storage situations. Fifty clinical samples were simultaneously detected by ICS and reverse-transcription polymerase chain reaction with a 93.9% coincidence rate between them. It proved that the ICS in the present study was highly specific, sensitive, repeatable, and more convenient to rapidly detect DTMUV in clinical samples.