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

A novel role of ETV6 as a pro-viral factor in host response by inhibiting TBK1 phosphorylation

E26-transforming specific (ETS) variant 6 (ETV6) is a transcription factor regulating the expression of interferon stimulating genes (ISGs) and involved in the embryonic development and hematopoietic regulation, but the role of ETV6 in host response to virus infection is not clear. In this study, we show that ETV6 was upregulated in DF-1 cells with poly(I:C) stimulation or IBDV, AIV and ARV infection via engagement of dsRNA by MDA5. Overexpression of ETV6 in DF-1 cells markedly inhibited IBDV-induced type I interferon (IFN-I) and ISGs expressions. In contrast, knockdown, or knockout of ETV6 remarkably inhibited IBDV replication via promoting IFN-I response. Furthermore, our data show that ETV6 negatively regulated host antiviral response to IBDV infection by interaction with TANK binding kinase 1 (TBK1) and subsequently inhibited its phosphorylation. These results uncovered a novel role of ETV6 as a pro-viral factor in host response by inhibiting TBK1 phosphorylation, furthering our understandings of RNA virus immunosuppression and providing a valuable clue to the development of antiviral reagents for the control of avian RNA virus infection.

RNA-seq reveals role of cell-cycle regulating genes in the pathogenicity of a field very virulent infectious bursal disease virus

Infectious bursal disease virus (IBDV) infection causes highly contagious and immunosuppressive disease in poultry. The thymus, serving as the primary organ for T cell maturation and differentiation, plays an important role in the pathogenicity of IBDV in the infected chickens. However, there are no reports on the molecular pathogenesis of IBDV in the thymus currently. The aim of the study was to elucidate the molecular mechanisms underlying the pathogenicity of a field very virulent (vv) IBDV strain NN1172 in the thymus of SPF chickens using integrative transcriptomic and proteomic analyses. Our results showed that a total of 4,972 Differentially expressed genes (DEGs) in the thymus of NN1172-infected chickens by transcriptomic analysis, with 2,796 up-regulated and 2,176 down-regulated. Meanwhile, the proteomic analysis identified 726 differentially expressed proteins (DEPs) in the infected thymus, with 289 up-regulated and 437 down-regulated. Overall, a total of 359 genes exhibited differentially expression at both mRNA and protein levels, with 134 consistently up-regulated and 198 genes consistently down-regulated, as confirmed through a comparison of the RNA-seq and the proteomic datasets. The gene ontology (GO) analysis unveiled the involvement of both DEGs and DEPs in diverse categories encompassing cellular components, biological processes, and molecular functions in the pathological changes in IBDV-infected thymus. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the host mainly displayed severely disruption of cell survival/repair, proliferation and metabolism pathway, meanwhile, the infection triggers antiviral immune activation with a potential emphasis on the MDA5 pathway. Network inference analysis identified seven core hub genes, which include CDK1, TYMS, MCM5, KIF11, CCNB2, MAD2L1, and MCM4. These genes are all associated with cell-cycle regulating pathway and are likely key mediators in the pathogenesis induced by NN1172 infection in the thymus. This study discovered dominant pathways and genes which enhanced our understanding of the molecular mechanisms underlying IBDV pathogenesis in the thymus.

Pigeon MDA5 inhibits viral replication by triggering antiviral innate immunity

Pigeons are considered less susceptible, and display few or no clinical signs to infection with avian influenza virus (AIV). Melanoma differentiation-associated gene 5 (MDA5), an important mediator in innate immunity, has been linked to the virus resistance. In this study, the pigeon MDA5 (piMDA5) was cloned. The bioinformatics analysis showed that the C-terminal domain (CTD) of MDA5 is highly conserved among species while the N-terminal caspase recruitment domain (CARD) is variable. Upon infection with Newcastle diseases virus (NDV) and AIV, piMDA5 was upregulated in both pigeons and pigeon embryonic fibroblasts (PEFs). Further study found that overexpression of piMDA5 mediated the activation of interferons (IFNs) and IFN-stimulated genes (ISGs) while inhibiting NDV replication. Conversely, the knockdown of piMDA5 promoted NDV replication. Additionally, CARD was found to be essential for the activation of IFN-β by piMDA5. Furthermore, pigeon MDA5, chicken MDA5, and human MDA5 differ in inhibiting viral replication and inducing ISGs expression. These findings suggest that MDA5 contributes to suppressing viral replication by activating the IFN signal pathway in pigeons. This study provides valuable insight into the role of MDA5 in pigeons and a better understanding of the conserved role of MDA5 in innate immunity during evolution.

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.

Role of microRNA-34b-5p in cancer and injury: how does it work?

MicroRNAs (miRNAs or miRs) are a class of noncoding single-stranded RNAs that can regulate gene expression by binding to the untranslated sequences at the 3 ' end of messenger RNAs. The microRNA-34 family is dysregulated in various human diseases. It is considered as a tumor-suppressive microRNA because of its synergistic effect with the well-known tumor suppressor p53. As a member of the miRNA-34 family, miR-34b-5p serves as a powerful regulator of a suite of cellular activities, including cell growth, multiplication, development, differentiation, and apoptosis. It promotes or represses disease occurrence and progression by participating in some important signaling pathways. This review aimed to provide an overview and update on the differential expression and function of miR-34b-5p in pathophysiologic processes, especially cancer and injury. Additionally, miR-34b-5p-mediated clinical trials have indicated promising consequences for the therapies of carcinomatosis and injury. With the application of the first tumor-targeted microRNA drug based on miR-34a mimics, it can be inferred that miR-34b-5p may become a crucial factor in the therapy of various diseases. However, further studies on miR-34b-5p should shed light on its involvement in disease pathogenesis and treatment options.

Interaction between chicken TRIM25 and MDA5 and their role in mediated antiviral activity against IBDV infection

Infectious Bursal Disease Virus (IBDV) is the causative agent of an immunosuppressive disease that affects domestic chickens (Gallus gallus) severely affecting poultry industry worldwide. IBDV infection is characterized by a rapid depletion of the bursal B cell population by apoptosis and the atrophy of this chief lymphoid organ. Previous results from our laboratory have shown that exposure of infected cells to type I IFN leads to an exacerbated apoptosis, indicating an important role of IFN in IBDV pathogenesis. It has been described that recognition of the dsRNA IBDV genome by MDA5, the only known cytoplasmic pattern recognition receptor for viral RNA in chickens, leads to type I IFN production. Here, we confirm that TRIM25, an E3 ubiquitin ligase that leads to RIG-I activation in mammalian cells, significantly contributes to positively regulate MDA5-mediated activation of the IFN-inducing pathway in chicken DF-1 cells. Ectopic expression of chTRIM25 together with chMDA5 or a deletion mutant version exclusively harboring the CARD domains (chMDA5 2CARD) enhances IFN-β and NF-ĸB promoter activation. Using co-immunoprecipitation assays, we show that chMDA5 interacts with chTRIM25 through the CARD domains. Moreover, chTRIM25 co-localizes with both chMDA5 and chMDA5 2CARD, but not with chMDA5 mutant proteins partially or totally lacking these domains. On the other hand, ablation of endogenous chTRIM25 expression reduces chMDA5-induced IFN-β and NF-ĸB promoter activation. Interestingly, ectopic expression of either wild-type chTRIM25, or a mutant version (chTRIM25 C59S/C62S) lacking the E3 ubiquitin ligase activity, restores the co-stimulatory effect of chMDA5 in chTRIM25 knockout cells, suggesting that the E3-ubiquitin ligase activity of chTRIM25 is not required for its downstream IFN-β and NF-ĸB activating function. Also, IBDV-induced expression of IFN-β, Mx and OAS genes was reduced in chTRIM25 knockout as compared to wild-type cells, hence contributing to the enhancement of IBDV replication. Enhanced permissiveness to replication of other viruses, such as avian reovirus, Newcastle disease virus and vesicular stomatitis virus was also observed in chTRIM25 knockout cells. Additionally, chTRIM25 knockout also results in reduced MAVS-induced IFN-β promoter stimulation. Nonetheless, similarly to its mammalian counterpart, chTRIM25 overexpression in wild-type DF-1 cells causes the degradation of ectopically expressed chMAVS.

Host Combats IBDV Infection at Both Protein and RNA Levels

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by infectious bursal disease virus (IBDV). In recent years, with the emergence of IBDV variants and recombinant strains, IBDV still threatens the poultry industry worldwide. It seems that the battle between host and IBDV will never end. Thus, it is urgent to develop a more comprehensive and effective strategy for the control of this disease. A better understanding of the mechanisms underlying virus-host interactions would be of help in the development of novel vaccines. Recently, much progress has been made in the understanding of the host response against IBDV infection. If the battle between host and IBDV at the protein level is considered the front line, at the RNA level, it can be taken as a hidden line. The host combats IBDV infection at both the front and hidden lines. Therefore, this review focuses on our current understanding of the host response to IBDV infection at both the protein and RNA levels.

Advances on Innate Immune Evasion by Avian Immunosuppressive Viruses

Innate immunity is not only the first line of host defense against pathogenic infection, but also the cornerstone of adaptive immune response. Upon pathogenic infection, pattern recognition receptors (PRRs) of host engage pathogen-associated molecular patterns (PAMPs) of pathogens, which initiates IFN production by activating interferon regulatory transcription factors (IRFs), nuclear factor-kappa B (NF-κB), and/or activating protein-1 (AP-1) signal transduction pathways in host cells. In order to replicate and survive, pathogens have evolved multiple strategies to evade host innate immune responses, including IFN-I signal transduction, autophagy, apoptosis, necrosis, inflammasome and/or metabolic pathways. Some avian viruses may not be highly pathogenic but they have evolved varied strategies to evade or suppress host immune response for survival, causing huge impacts on the poultry industry worldwide. In this review, we focus on the advances on innate immune evasion by several important avian immunosuppressive viruses (infectious bursal disease virus (IBDV), Marek’s disease virus (MDV), avian leukosis virus (ALV), etc.), especially their evasion of PRRs-mediated signal transduction pathways (IFN-I signal transduction pathway) and IFNAR-JAK-STAT signal pathways. A comprehensive understanding of the mechanism by which avian viruses evade or suppress host immune responses will be of help to the development of novel vaccines and therapeutic reagents for the prevention and control of infectious diseases in chickens.

GATA3 Inhibits Viral Infection by Promoting MicroRNA-155 Expression

Recognition of viral RNAs by melanoma differentiation associated gene-5 (MDA5) initiates chicken antiviral response by producing type I interferons. Our previous studies showed that chicken microRNA-155-5p (gga-miR-155-5p) enhanced IFN-β expression and suppressed the replication of infectious burse disease virus (IBDV), a double-stranded RNA (dsRNA) virus causing infectious burse disease in chickens. However, the mechanism underlying IBDV-induced gga-miR-155-5p expression in host cells remains elusive. Here, we show that IBDV infection or poly(I:C) treatment of DF-1 cells markedly increased the expression of GATA-binding protein 3 (GATA3), a master regulator for TH2 cell differentiation, and that GATA3 promoted gga-miR-155-5p expression in IBDV-infected or poly(I:C)-treated cells by directly binding to its promoter. Surprisingly, ectopic expression of GATA3 significantly reduced IBDV replication in DF-1 cells, and this reduction could be completely abolished by treatment with gga-miR-155-5p inhibitors, whereas knockdown of GATA3 by RNA interference enhanced IBDV growth, and this enhancement could be blocked with gga-miR-155-5p mimics, indicating that GATA3 suppressed IBDV replication by gga-miR-155-5p. Furthermore, our data show that MDA5 is required for GATA3 expression in host cells with poly(I:C) treatment, so are the adaptor protein TBK1 and transcription factor IRF7, suggesting that induction of GATA3 expression in IBDV-infected cells relies on MDA5-TBK1-IRF7 signaling pathway. These results uncover a novel role for GATA3 as an antivirus transcription factor in innate immune response by promoting miR-155 expression, further our understandings of host response against pathogenic infection, and provide valuable clues to the development of antiviral reagents for public health. IMPORTANCE Gga-miR-155-5p acts as an important antivirus factor against IBDV infection, which causes a severe immunosuppressive disease in chicken. Elucidation of the mechanism regulating gga-miR-155-5p expression in IBDV-infected cells is essential to our understandings of the host response against pathogenic infection. This study shows that transcription factor GATA3 initiated gga-miR-155-5p expression in IBDV-infected cells by directly binding to its promoter, suppressing viral replication. Furthermore, induction of GATA3 expression was attributable to the recognition of dsRNA by MDA5, which initiates signal transduction via TBK1 and IRF7. Thus, it is clear that IBDV induces GATA3 expression via MDA5-TBK1-IRF7 signaling pathway, thereby suppressing IBDV replication by GATA3-mediated gga-miR-155-5p expression. This information remarkably expands our knowledge of the roles for GATA3 as an antivirus transcription factor in host innate immune response particularly at an RNA level and may prove valuable in the development of antiviral drugs for public health.

Differential Modulation of Innate Antiviral Profiles in the Intestinal Lamina Propria Cells of Chickens Infected with Infectious Bursal Disease Viruses of Different Virulence

Infectious bursal disease virus (IBDV) is one of the most important infectious diseases of poultry around the world. Gut-associated lymphoid tissues (GALT) are the first line of defense of the host against the infection. The purpose of this study was to investigate the role of innate immune antiviral signaling triggered by Toll-like receptor 3 (TLR3), as well as macrophage activation and cytokine response in the intestinal lamina propria (ILP) cells after the oral challenge of IBDV in relation to IBDV virulence and disease pathogenesis. The results showed that the expression levels of TLR3, IRF7, IFN-α/β and the corresponding downstream antiviral factors OAS, PKR and Mx were all upregulated in the SPF chicken ILP cells at 8 h post-infection (hpi) and 12 hpi. Similarly, macrophages were activated, with the initial macrophage M1 activation observed at 8 hpi, but then it rapidly shifted to a non-protective M2-type. Both Th1 (IFN-γ, TNF-α, IL-12) and Th2 (IL-4 and IL-10) types of cytokines were differentially upregulated during the early stage of infection; however, the Th1 cytokines exhibited stronger activation before 8 hpi compared to those of the Th2 cytokines. Interestingly, differential regulations of gene expression induced by different IBDV strains with different virulence were detected. The HLJ0504-like very virulent (vv) IBDV strain NN1172 induced stronger activation of TLR3-IFN-α/β pathway, macrophages and the Th1/2 cytokines’ expression, compared to those induced by the attenuated strain B87 at 8 hpi and 12 hpi in the ILP cells. In conclusion, the innate antiviral response mediated by the TLR3-IRF7 pathway, macrophage activation and cytokine expression in the GALT cells at the early stage of IBDV infection was differentially modulated, and the HLJ0504-like vvIBDV strain triggered stronger activation than the attenuated vaccine strain, and that may play an important role in the progression of disease.

MDA5 attenuate autophagy in chicken embryo fibroblasts infected with IBDV

1. The role of melanoma differentiation-associated protein 5 (MDA5) in infectious bursal disease virus (IBDV)-induced autophagy was studied in chicken embryos.2. Chicken embryo fibroblasts (CEF) were used as the research model and small interfering RNA (siRNA), western blot, indirect enzyme-linked immunosorbent assay (ELISA), real-time fluorescence quantitative polymerase chain reaction (PCR) and transmission electron microscopy were used to detect autophagy, IBDV replication, CEF damage, and activation of both MDA5 and its signalling pathway.3. The results showed that CEF infected with IBDV activated the intracellular MDA5 signalling pathway and caused autophagy via inactivation of the AKT/mTOR pathway. While autophagy promotes IBDV proliferation, MDA5 weakens IBDV-induced CEF autophagy thus inhibiting IBDV replication and protecting CEF cells.4. The results indicated that chMDA5 can be activated by IBDV and attenuate CEF autophagy caused by IBDV infection, thereby inhibiting IBDV replication. This study provided a foundation for further exploring the relationship between viruses, autophagy and the pathogenic mechanism of the MDA5 pathway involved in IBDV.

DeSUMOylation of Apoptosis Inhibitor 5 by Avibirnavirus VP3 Supports Virus Replication

SUMOylation is a reversible posttranslational modification involved in the regulation of diverse biological processes. Growing evidence suggests that virus infection can interfere with the SUMOylation system. In the present study, we discovered that apoptosis inhibitor 5 (API5) is a SUMOylated protein. Amino acid substitution further identified that Lys404 of API5 was the critical residue for SUMO3 conjugation. Moreover, we found that Avibirnavirus infectious bursal disease virus (IBDV) infection significantly decreased SUMOylation of API5. In addition, our results further revealed that viral protein VP3 inhibited the SUMOylation of API5 by targeting API5 and promoting UBC9 proteasome-dependent degradation through binding to the ubiquitin E3 ligase TRAF3. Furthermore, we revealed that wild-type but not K404R mutant API5 inhibited IBDV replication by enhancing MDA5-dependent IFN-β production. Taken together, our data demonstrate that API5 is a UBC9-dependent SUMOylated protein and deSUMOylation of API5 by viral protein VP3 aids in viral replication.

Role of the chicken oligoadenylate synthase-like gene during in vitro Newcastle disease virus infection

The enzyme 2′-5′ oligoadenylate synthase (OAS) is one of the key interferon-induced antiviral factors that act through inhibition of viral replication. In chickens, there is a single well-characterized OAS gene, oligoadenylate synthase-like (OASL) that has been shown to be upregulated after infection with various viruses. However, a deeper understanding of how chicken OASL acts against viral infection is still necessary. In this study, we tested the hypothesis that OASL short interfering RNA (siRNA)–mediated knockdown would decrease the host gene expression response to the Newcastle disease virus (NDV) by impacting antiviral pathways. To assess our hypothesis, a chicken fibroblast cell line (DF-1) was infected with the NDV (LaSota strain) and OASL expression was knocked down using a specific siRNA. The level of NDV viral RNA in the cells and the expression of interferon response- and apoptosis-related genes were evaluated by quantitative PCR at 4, 8, and 24 h postinfection (hpi). Knockdown of OASL increased the level of NDV viral RNA at 4, 8, and 24 hpi (P < 0.05) and eliminated the difference between NDV-infected and noninfected cells for expression of interferon response- and apoptosis-related genes (P > 0.05). The lack of differential expression suggests that knockdown of OASL resulted in a decreased response to NDV infection. Within NDV-infected cells, OASL knockdown reduced expression of signal transducer and activator of transcription 1, interferon alfa receptor subunit 1, eukaryotic translation initiation factor 2 alpha kinase 2, ribonuclease L, caspase 8 (CASP8) and caspase 9 (CASP9) at 4 hpi, CASP9 at 8 hpi, and caspase 3, CASP8, and CASP9 at 24 hpi (P < 0.05). We suggest that the increased NDV viral load in DF-1 cells after OASL knockdown was the result of a complex interaction between OASL and interferon response- and apoptosis-related genes that decreased host response to the NDV. Our results provide comprehensive information on the role played by OASL during NDV infection in vitro. Targeting this mechanism could aid in future prophylactic and therapeutic treatments for Newcastle disease in poultry.

Different kinetics of chicken interferon-alpha signalling transduction responses following immunization of broiler chickens with different Newcastle disease virus vaccines and infection with virulent genotype VIId strain

Newcastle disease virus (NDV) is a highly contagious and notifiable avian disease leading to grave economic losses in the poultry industry. Although the immune responses against NDV have been widely investigated, little is known regarding the virus interaction with the host innate immune responses. In this study, we tested the effect of different commercially applied Newcastle disease vaccines as well as virulent NDV genotype VIId on the expression pattern of the upstream regulator and downstream effector genes related to chicken interferon-alpha (chIFNα) signalling transduction pathway. Using quantitative real-time PCR analysis, mild transient induction of chIFNα-inducible genes was detected in bird spleen 72 h post-vaccination (hpv) with either live LaSota (respiratory) or VG/GA (enteric) strains. Vaccination with the enteric VG/GA strain led to stimulation of the investigated pathway as early as 24 hpv which continued up to 7 days in bird caecal tonsils. Subcutaneous injection with inactivated LaSota oil adjuvant-based vaccine led to continual stimulation of the investigated pathway up to 7 days post-vaccination (dpv). The recombinant herpesvirus of turkey (rHVT) - NDV vaccine led to remarkable stimulation of all the tested cytokines up to 17 dpv in comparison with LaSota and VG/GA NDV vaccines. Stronger but transient activation of all the tested cytokines was detected in spleens during the first 24 h post-challenge with virulent NDV (vNDV) which reduced gradually and diminished later due to the virus-induced lymphocytic depletion. This study will aid in the discovery of new approaches to control NDV.

Tissue distribution and developmental changes of interferon regulatory factors in chickens and effects of infectious bursal disease virus infection

Interferon regulatory factors (IRFs) are a family of transcription factors that play a role in a variety of biological processes including immune regulation of interferon and expression of inflammatory cytokines. However, the data on IRFs are rather limited in chickens. In the present study, qRT-PCR was used to study the tissue distribution of IRFs in chickens at D15 (the 15th day of raising) and developmental changes of all chIRFs (Chicken interferon regulatory factors) in BF from E15 (the 15th day of incubation) to D15. The effects of IBDV infection with chickens on the transcriptional level of chIRFs were also investigated. The results showed: (1) chIRF1 mRNA was expressed much more abundantly in intestinal tract, chIRF2, chIRF6, chIRF7, chIRF8 and chIRF10 distributed mainly in liver or/and kidney. The expression of chIRF5 was mainly in spleen and chIRF4 distributed uniquely abundantly in BF. (2) The mRNA expression levels of chIRF5, chIRF7, chIRF8 and chIRF10 was low before hatching of chicken and at D1 and increased significantly from D5 till to the experiment end and the fold change of chIRF5 at D10 and chIRF7 at D5 reached 41.0-fold and 15.7-fold compared to that of E15, respectively (P < 0.05). ChIRF4 mRNA level was always high during the whole experiment except for E15 and it was 11.9-fold at the highest time point than that of E15 (the lowest time point). (3) When chicken was infected with IBDV, the expression levels of chIRF2, chIRF7 and chIRF10 mRNA had the tendency of increasing first and then decreasing but they peaked at 1dpi, 2 dpi, and 3dpi, respectively. The expression of chIRF5 mRNA was suppressed obviously during the whole experiment stage in IBDV-infected chicken. And chIRF4 expression was up-regulated transitorily at 1dpi and then was suppressed on a very low level till to the experiment end. Conclusion: The chIRFs were constitutively expressed in different tissues examined and has tissue-specific expression. Of them, chIRF2, chIRF4, chIRF5, chIRF7, chIRF8 and chIRF10 were related closely with the development or immune response of BF, and when chicken was infected with IBDV, some of them were activated, earlier or later on, some of them were suppressed. These findings would help to sieve out a few antiviral chIRF candidate gene to improve the host's innate immune and provide a foundation of the further exploiting a new vaccine adjuvant.

A Comparative Study of Pathology and Host Immune Response Induced by Very Virulent Infectious Bursal Disease Virus in Experimentally Infected Chickens of Aseel and White Leghorn Breeds

Indigenous breeds of young chickens in India are believed to be resistant to the classical strain of infectious bursal disease virus (IBDV). However, the mechanism underlying this resistance is obscure. Innate immunity is a key factor in defining the clinical course and pathology of microbial infections. The present study is aimed to compare the pathology of very virulent IBDV (vvIBDV) and immunological host response in experimentally infected - vaccinated and unvaccinated indigenous Aseel and commercial White Leghorn chickens. The viral loads and innate immune gene expression profiles of MDA-5, Mx, IFN-α, and IFN-β in different lymphoid organs were analyzed by quantitative PCR. The histopathological scores in Aseel birds were lower than in White Leghorns despite comparable viral loads. The degrees of histopathological lesions were fewer in vaccinated birds than in unvaccinated birds of both breeds. Analysis of innate immune response genes revealed that the cytoplasmic pattern recognition receptor MDA-5 gene was overexpressed mainly in the cecal tonsils of both vaccinated and nonvaccinated White Leghorn chickens. An increase in the expression of the IFN-α gene was seen in the cecal tonsils of Aseels, and an increase in IFN-β gene expression was seen in the thymuses of White Leghorns following vvIBDV challenge both in vaccinated and nonvaccinated birds. In addition, we observed that the Mx gene plays a minimal role, if any, in vvIBDV infection of the breeds under study. It remains interesting and important that although vvIBDV causes disease in indigenous Aseel birds, the faster clearance and reduced pathology of the virus in Aseel birds compared to White Leghorn chicken indicate some unidentified innate immune factors that are limiting IBDV in this breed. Further studies will be required to correlate kinetics of humoral and cellular immune response in relation to the virus load in different organs to illuminate the mechanism of genetic resistance in native breeds of chicken.

Genetic Analysis of Field Isolates of Infectious Bursal Disease Virus in Iraqi Farms

Sixty samples of bursa of Fabricius were collected from broiler chickens suspected to be infected with infectious bursal disease virus (IBDV) in different areas of Iraq for molecular evaluation. The extracted nucleic acid was amplified using reverse transcriptase polymerase chain reaction (RT-PCR) targeting genes of segment A (Vp2, Vp3, Vp4 and Vp5 genes) and segment B (VP1 genes). The products of amplification were sent to Korea for sequencing using Sanger method. The sequencing analysis of the IBDV from the Iraqi isolates revealed that each gene had different transition and transversion (nonsense and missense of point mutation) compared to reference genes. The phylogenetic tree analysis showed that the VP2 of segment A of the Iraqi samples was similar to that of an Egyptian strain with 96%similarity, the polypeptide VP2-3-4 of segment A of the Iraqi samples was similar to those of a Chinese strain with 99% similarity and the VP5 of segment A was similar to that of Chinese strain with 99% similarity. However, the phylogenetic tree analysis showed that the VP1 of segment B had 95% similarity with that of a Chinese strain.

Targeted Knockout of MDA5 and TLR3 in the DF-1 Chicken Fibroblast Cell Line Impairs Innate Immune Response Against RNA Ligands

The innate immune system, which senses invading pathogens, plays a critical role as the first line of host defense. After recognition of foreign RNA ligands (e.g., RNA viruses), host cells generate an innate immune or antiviral response via the interferon-mediated signaling pathway. Retinoic acid-inducible gene I (RIG-1) acts as a major sensor that recognizes a broad range of RNA ligands in mammals; however, chickens lack a RIG-1 homolog, meaning that RNA ligands should be recognized by other cellular sensors such as melanoma differentiation-associated protein 5 (MDA5) and toll-like receptors (TLRs). However, it is unclear which of these cellular sensors compensates for the loss of RIG-1 to act as the major sensor for RNA ligands. Here, we show that chicken MDA5 (cMDA5), rather than chicken TLRs (cTLRs), plays a pivotal role in the recognition of RNA ligands, including poly I:C and influenza virus. First, we used a knockdown approach to show that both cMDA5 and cTLR3 play roles in inducing interferon-mediated innate immune responses against RNA ligands in chicken DF-1 cells. Furthermore, targeted knockout of cMDA5 or cTLR3 in chicken DF-1 cells revealed that loss of cMDA5 impaired the innate immune responses against RNA ligands; however, the responses against RNA ligands were retained after loss of cTLR3. In addition, double knockout of cMDA5 and cTLR3 in chicken DF-1 cells abolished the innate immune responses against RNA ligands, suggesting that cMDA5 is the major sensor whereas cTLR3 is a secondary sensor. Taken together, these findings provide an understanding of the functional role of cMDA5 in the recognition of RNA ligands in chicken DF-1 cells and may facilitate the development of an innate immune-deficient cell line or chicken model.

Genetic responses of inbred chicken lines illustrate importance of eIF2 family and immune-related genes in resistance to Newcastle disease virus

Newcastle disease virus (NDV) replication depends on the translation machinery of the host cell; therefore, the eukaryotic translation initiation factor 2 (eIF2) gene family is a likely candidate for control of viral replication. We hypothesized that differential expression of host genes related to translation and innate immune response could contribute to differential resistance to NDV in inbred Fayoumi and Leghorn lines. The expression of twenty-one genes related to the interferon signaling pathway and the eIF2 family was evaluated at two- and six-days post infection (dpi) in the spleen from both lines, either challenged by NDV or nonchallenged. Higher expression of OASL in NDV challenged versus nonchallenged spleen was observed in Leghorns at 2 dpi. Lower expression of EIF2B5 was found in NDV challenged than nonchallenged Fayoumis and Leghorns at 2 dpi. At 2 dpi, NDV challenged Fayoumis had lower expression of EIF2B5 and EIF2S3 than NDV challenged Leghorns. At 6 dpi, NDV challenged Fayoumis had lower expression of EIF2S3 and EIF2B4 than NDV challenged Leghorns. The genetic line differences in expression of eIF2-related genes may contribute to their differential resistance to NDV and also to understanding the interaction between protein synthesis shut-off and virus control in chickens.

Effects of infectious bursal disease virus infection on interferon and antiviral gene expression in layer chicken bursa

Layer chickens were artificially challenged with infectious bursal disease virus (IBDV), and the kinetics of IFN-λ and antiviral genes in the bursa were explored using quantitative real-time PCR. Data showed that after the chickens were infected with IBDV, the virus load in the bursa of the Fabricius peaked at 96 h and gradually decreased. The relative mRNA expression levels of IFN-λ and antiviral genes (zinc-finger antiviral protein [ZAP], interferon alpha-inducible protein 6 [IFI6], laboratory of genetics and physiology 2 [LGP2], virus inhibitory protein [Viperin], and Mx) of the infected group dramatically increased at 24-168 h compared with those of the negative-infected group. Furthermore, the ZAP mRNA expression peaked at 24 h (3.97-fold). The Viperin mRNA transcript level was highest at 48 h (384.60-fold). The mRNA expression levels of IFI6 (96.31-fold), LGP2 (18.29-fold), and Mx (88.85-fold) peaked at 72 h, and that of IFN-λ was most remarkable at 96 h (2978.81-fold). Furthermore, the ZAP change rule was significantly positively correlated with the change rule of the IBDV load. The mRNA expression levels of IFN-λ and antiviral genes (ZAP, IFI6, LGP2, Viperin, and Mx) increased as the virus expression increased and then decreased. These results further corroborated that the IBDV infection seriously interfered with the chicken's innate immune response.

gga-miR-27b-3p enhances type I interferon expression and suppresses infectious bursal disease virus replication via targeting cellular suppressors of cytokine signaling 3 and 6 (SOCS3 and 6)

MicroRNAs are small noncoding RNAs playing an important role in host response to pathogenic infection. Here we show that IBDV infection induced the demethylation of the pre-miR-27 promoter and upregulated gga-miR-27b-3p expression. We found that ectopic expression of miR-27b-3p in DF-1 cells enhanced the expression of chicken IFN-β, IRF3 and NF-κB, via directly targeting cellular suppressors of cytokine signaling 3 and 6 (SOCS3 and 6), inhibiting IBDV replication in host cells, while inhibition of endogenous miR-27b-3p by its inhibitors suppressed the expression of IFN-β, IRF3 and NF-κB, enhancing SOCS3 and 6 expressions and facilitating IBDV replication. Furthermore, transfection of DF-1 cells with miR-27b-3p markedly increased phosphorylation of STAT1 on Tyr701 in cells post chIFN-γ treatment. On the contrary, inhibition of endogenous miR-27b-3p reduced phosphorylation of STAT1 on Tyr701 in cells with chIFN-γ treatment. These findings indicate that gga-miR-27b-3p serves as an inducible antiviral mediator in host response to IBDV infection.

AVIAN INNATE IMMUNITY WITH AN EMPHASIS ON CHICKEN MELANOMA DIFFERENTIATION-ASSOCIATED GENE 5 (MDA5)

Avian species have immune system to fight invading pathogens. The immune system comprises innate and adaptive immunity. Innate immunity relies on pattern recognition receptors to sense particular molecules present in pathogens, i.e. pathogen-associated molecular patterns (PAMPs), or danger signals in the environment, i.e. danger-associated molecular patterns (DAMPs). Cytoplasmic retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) and nucleotide-binding oligomerization domain-like receptors (NLRs) are the sensors recognizing cytoplasmic PAMP and/or DAMP. Among common avian species, chickens do not have RIG-I whereas ducks and finches do. Therefore, the other RLR member, melanoma differentiation-associated gene 5 (MDA5), is believed to play an important role to recognize intracellular pathogens in chickens. Chicken MDA5 has been identified and its function determined. Chicken MDA5 maintains the same domain architecture compared with MDA5 analogs in other animal species. The expression of chicken MDA5 was upregulated when a synthetic double-stranded RNA (dsRNA), polyriboinosinic:polyribocytidylic acids (poly(I:C)), was transfected into chicken cells, whereas that did not change when cells were incubated with poly(I:C). The enhanced expression of chicken MDA5 in chicken cells upregulated the expression of chicken interferon-[Formula: see text] (IFN-[Formula: see text]). The infection of dsRNA infectious bursal disease virus (IBDV) in non-immune cells triggered the activation of chicken MDA5 signaling pathway, leading to the production of IFN-[Formula: see text] and subsequent response of IFN-stimulated genes. Furthermore, in immune cells like macrophages, chicken MDA5 participated in sensing the infection of IBDV by activating downstream antiviral genes and molecules and modulating adaptive immunity.

On the contrary, one of cytoplasmic NLR member, NLR family pyrin domain containing 3 (NLRP3), was cloned and functionally characterized in chicken cells. Chicken NLRP3 conserved the same domain architecture compared with NLRP3 analogs in other animal species. Chicken NLRP3 was highly expressed in kidney, bursa of Fabricius and spleen. The production of mature chicken interleukin 1 [Formula: see text] (IL-1[Formula: see text] in chicken macrophages was stimulated by lipopolysaccharide (LPS) treatment followed by short ATP exposure.

In summary, chicken MDA5 was a cytoplasmic dsRNA sensor that mediated the production of type I IFN upon ligand engagement, whereas NLRP3 sensed danger signals, such as ATP, in the cytoplasm and cleaved pro-IL-1[Formula: see text] to produce mature IL-1[Formula: see text]. Chicken MDA5 was not only involved in the activation of innate immune responses in non-immune and immune cells, but it also participated in modulating adaptive immunity in immune cells. Chicken NLRP3 participated in the production of mature chicken IL-1[Formula: see text] upon ligand engagement.

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.

Cloning, expression and bioinformatics analysis of a putative pigeon melanoma differentiation-associated gene 5

1. Melanoma differentiation-associated gene 5 (MDA5) is a critical member of cytosolic pattern recognition receptors (PRRs) that recognise viral RNA and mediate type I interferon secretion in host cells. 2. The objective of the present study was to identify and characterise the structure and expression of pigeon MDA5. 3. The full-length MDA5 cDNA was cloned from pigeon spleen using RT-PCR and RACE. The distribution and expression level of pigeon MDA5 in different tissues were determined by QRT-PCR. 4. The results showed that the full-length pigeon MDA5 cDNA had 3858 nucleotides (containing a 210-bp 5'-UTR, a 3030-bp open reading frame and a 618-bp 3'-UTR) encoding a polypeptide of 1009 amino acids. The deduced amino acid sequence contained six conserved structural domains typical of RIG-I-like receptor (RLR), including two tandem arranged N-terminal caspase activation and recruitment domains (CARDs), a DEAH/DEAD box helicase domain (DExDc), a helicase superfamily c-terminal domain (HELICc), a type III restriction enzyme (ResIII) and a C-terminal regulatory domain (RD). 5. The pigeon MDA5 showed 84.8%, 87.3%, 87.9% and 87.2% amino acid sequence identities with previously described homologues from chicken, duck, goose and Muscovy ducks, respectively, and phylogenetic analysis revealed a close relationship among these MDA5. 6. Pigeon MDA5 transcript was ubiquitously expressed in all seven tissues tested in healthy pigeons and showed a high level in the thymus gland and kidney. 7. These findings lay the foundation for further research on the function and mechanism of MDA5 in innate immune responses related to vaccinations and infectious diseases in the pigeon.

Polymorphisms in pattern recognition receptor genes of indigenous and White Leghorn breeds of chicken

Functional polymorphisms in pattern recognition receptors (PRRs) modulate innate immunity and play a crucial role in resistance or susceptibility to diseases. The present study was carried out to explore polymorphic patterns in the coding sequences of PRR genes TLR3, TLR1LA (TLRs), MDA5, LGP2 (RLRs) and NOD1 (NLR) in chicken breeds of India, namely Ghagus (GH), Nicobari (NB) and the exotic White Leghorn (WLH) breed. Out of 209 SNPs observed in five genes among three breeds, 117 were synonymous (Syn) and 92 were non-synonymous (NS) SNPs. In TLR genes the highest polymorphism was observed in NB (16, 28) compared to GH (14, 16) and WLH (13, 19) breeds. In the MDA5 gene the highest polymorphism was observed in GH (12) compared to NB (eight) and WLH (four) breeds. However, an almost similar level of polymorphism was observed in the LGP2 gene among the three breeds. In the NOD1 gene, the highest polymorphism was observed in NB (27), followed by WLH (11) and GH (10) breeds. The overall highest number of SNPs was observed in NB (90), followed by GH (62) and the WLH (57) breed. With regard to variation in polymorphism among different classes of PRRs, the study revealed the highest polymorphism in TLRs compared to NOD1 and the RLR class of PRRs. Further, the domain locations of various Syn and NS SNPs in each PRR among the three breeds were identified. In silico analysis of NS SNPs revealed that most of them had a neutral effect on protein function. However, two each in TLR1LA and LGP2 and one in the MDA5 gene were predicted to be deleterious to protein function. The present study unravelled extensive polymorphism in the coding sequences of the TLR and NLR class of PRR genes, and the polymorphism was higher in indigenous chicken breeds.

p53 mediated IFN-β signaling to affect viral replication upon TGEV infection

TGEV can induce IFN-β production, which in turn plays a vital role in host antiviral immune responses. Our previous studies showed that TGEV infection activated p53 signaling to induce host cell apoptosis, which might influence virus replication. However, whether there be an interaction between p53 and IFN-β signaling in the process of TGEV infection is unknown. In the present study, we used low dose of TGEV to infect p53 wild-type PK-15 cells (WT PK-15 cells) and p53 deficient cells (p53-/- PK-15 cells), to investigate the modulation of IFN signaling and virus replication by p53. The results showed that the IFN-β expression and production were notably inhibited in p53-/- PK-15 cells compared with that in WT PK-15 cells at early stage of TGEV infection. In addition, TGEV-induced the changes in mRNA levels of TRIF, TRAM, MDA5, RIG-I, IPS-1, IRF9, IRF3, ISG15 and ISG20 were notably hindered in p53-/- PK-15 cells before 36 h post infection (p.i.). Moreover, TGEV genomic RNA and sub genomic mRNA (N gene and ORF7) levels showed significant increase in p53-/- PK-15 cells compared with WT PK-15 cells after TGEV infection. And viral titers were observably enhanced in p53-/- PK-15 cells. Furthermore, exogenous IFN-β and polyinosinic-polycytidylic acid (poly (I:C)) treatment markedly inhibited the mRNA levels of TGEV gRNA, N and ORF7 in WT PK-15 cells and p53-/- PK-15 cells compared to control. Taken together, these results demonstrated that p53 may mediate IFN-β signaling to inhibit viral replication early after TGEV infection.

STAU1 binds to IBDV genomic double-stranded RNA and promotes viral replication via attenuation of MDA5-dependent β interferon induction

Infectious bursal disease virus (IBDV) infection triggers the induction of type I IFN, which is mediated by melanoma differentiation-associated protein 5 recognition of the viral genomic double-stranded RNA (dsRNA). However, the mechanism of IBDV overcoming the type I IFN antiviral response remains poorly characterized. Here, we show that IBDV genomic dsRNA selectively binds to the host cellular RNA binding protein Staufen1 (STAU1) in vitro and in vivo. The viral dsRNA binding region was mapped to the N-terminal moiety of STAU1 (residues 1-468). Down-regulation of STAU1 impaired IBDV replication and enhanced IFN-β transcription in response to IBDV infection, while having little effect on the viral attachment to the host cells and cellular entry. Conversely, overexpression of STAU1 but not the IBDV dsRNA-binding deficient STAU1 mutant (469-702) led to a suppression of IBDV dsRNA-induced IFN-β promoter activity. Moreover, we found that the binding of STAU1 to IBDV dsRNA decreased the association of melanoma differentiation-associated protein 5 but not VP3 with the IBDV dsRNA in vitro. Finally, we showed that STAU1 and VP3 suppressed IFN-β gene transcription in response to IBDV infection in an additive manner. Collectively, these findings provide a novel insight into the evasive strategies used by IBDV to escape the host IFN antiviral response.-Ye, C., Yu, Z., Xiong, Y., Wang, Y., Ruan, Y., Guo, Y., Chen, M., Luan, S., Zhang, E., Liu, H. STAU1 binds to IBDV genomic double-stranded RNA and promotes viral replication via attenuation of MDA5-dependent β interferon induction.

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.

Pattern recognition receptor genes expression profiling in indigenous chickens of India and White Leghorn

Pattern recognition receptors (PRR) such as Toll-like receptors, NOD-like receptors, RIG-I helicase receptors, and C-type lectin receptors play a critical role in innate immunity as a first line of defense against invading pathogens through recognition of pathogen and/or damage-associated molecular patterns. Genetic makeup of birds is known to play a role in resistance or susceptibility to various infectious diseases. Therefore, the present study was carried out to elucidate the differential expression of PRR and some of the cytokine genes in peripheral blood mononuclear cells of indigenous chicken breeds such as Ghagus and Nicobari and an exotic chicken breed, White Leghorn (WLH). The stability of expression of reference genes in peripheral blood mononuclear cells of 3 breeds was first determined using NormFinder and BestKeeper programs. NormFinder determined B2M and G6PDH reference genes as the best combination with stability value of 0.38. Out of total 14 genes studied, expression of ten genes was found to be significantly different among 3 breeds after normalization with these reference genes. Ghagus breed showed higher level of expression of TLR1LB, TLR7, NOD1, NOD5, B-Lec, IFNβ, IL1β, and IL8 genes when compared to Nicobari breed. Further, Ghagus showed higher expression of TLR1LB, MDA5, LGP2, B-Lec, IL1β, and IL8 genes as compared to WLH breed. Higher expression of LGP2 and MDA5 genes was observed in Nicobari compared to the WLH breed while higher expression of TLR7, NOD1, NOD5, and IFNβ genes was observed in WLH as compared to Nicobari breed. No difference was observed in the expression of TLR1LA, TLR3, B-NK, and IFNα genes among 3 breeds. Study revealed significant breed effect in expression profile of PRR and some of the cytokine genes and Ghagus breed seems to have better expression profile of these genes linked to the innate immunity when compared to the WLH and Nicobar breeds.

The down-regulation of casein kinase 1 alpha as a host defense response against infectious bursal disease virus infection

Infectious bursal disease virus (IBDV) is an important immunosuppressive virus of chickens. Although the gene functions of IBDV have been well characterized, the host responses during IBDV infection remain much poor. In the present study, casein kinase 1 alpha (CK1α), a novel VP2-associated protein, was down-regulated during IBDV replication in DF1 cells. Further experiments showed that siRNA-mediated knockdown of CK1α inhibited IBDV replication, while overexpression of CK1α promoted IBDV growth. Finally, we revealed that the effects of CK1α expression level on IBDV replication were involved in the negative regulation of CK1α on type I interferon receptor (IFNAR1), because ubiquitination assay analyses demonstrated that CK1α could promote the ubiquitination of IFNAR1, thereby affecting the stability of this receptor. In conclusion, down-regulation of CK1α during IBDV infection as a host defense response increased abundance of IFNAR1, which in turn enhanced an inhibitory effect on IBDV replication.

Transcription profiles of the responses of chicken bursae of Fabricius to IBDV in different timing phases

Background

Infectious bursal disease virus (IBDV) infection causes immunosuppression in chickens and increases their susceptibility to secondary infections. To explore the interaction between host and IBDV, RNA-Seq was applied to analyse the transcriptional profiles of the responses of chickens’ bursas of Fabricius in the early stage of IBDV infection.

Results

The results displayed that a total of 15546 genes were identified in the chicken bursa libraries. Among the annotated genes, there were 2006 and 4668 differentially expressed genes in the infection group compared with the mock group on day 1 and day 3 post inoculation (1 and 3 dpi), respectively. Moreover, there were 676 common up-regulated and 83 common down-regulated genes in the bursae taken from the chickens infected with IBDV on both 1 and 3 dpi. Meanwhile, there were also some characteristic differentially expressed genes on 1 and 3 dpi. On day 1 after inoculation with IBDV, host responses mainly displayed immune response processes, while metabolic pathways played an important role on day three post infection. Six genes were confirmed by quantitative reverse transcription-PCR.

Conclusions

In conclusion, the differential gene expression profile demonstrated with RNA-Seq might offer a better understanding of the molecular interactions between host and IBDV during the early stage of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0757-x) contains supplementary material, which is available to authorized users.

Chemokine receptor CCR5 and CXCR4 might influence virus replication during IBDV infection

Both CCR5 and CXCR4 are important chemokine receptors and take vital role in migration, development and distribution of T cells, however, whether they will influence the process of T cell infiltration into bursa of Fabricius during infectious bursal disease virus (IBDV) infection is unclear. In the current study, CCR5 and CXCR4 antagonists, Maraviroc and AMD3100, were administrated into chickens inoculated with IBDV, and the gene levels of IBDV VP2, CCR5, CXCR4 and related cytokines were determined by real-time PCR. The results showed that large number of T cells began to migrate into the bursae on Day 3 post infection with IBDV and the mRNA of chemokine receptors CCR5 and CXCR4 began to increase on Day 1. Moreover, antagonist treatments have increased the VP2, CCR5 and CXCR4 gene transcriptions and influenced on the gene levels of IL-2, IL-6, IL-8, IFN-γ, TGF-β4, MHC-I and MDA5. In conclusion, the chemokine receptors CCR5 and CXCR4 might influence virus replication during IBDV infection and further study would focus on the interaction between chemokine receptors and their ligands.

MiR-34b-5p Suppresses Melanoma Differentiation-Associated Gene 5 (MDA5) Signaling Pathway to Promote Avian Leukosis Virus Subgroup J (ALV-J)-Infected Cells Proliferaction and ALV-J Replication

Avian leukosis virus subgroup J (ALV-J) is an oncogenic retrovirus that has a similar replication cycle to multiple viruses and therefore can be used as a model system for viral entry into host cells. However, there are few reports on the genes or microRNAs (miRNAs) that are responsible for the replication of ALV-J. Our previous miRNA and RNA sequencing data showed that the expression of miR-34b-5p was significantly upregulated in ALV-J-infected chicken spleens compared to non-infected chicken spleens, but melanoma differentiation-associated gene 5 (MDA5) had the opposite expression pattern. In this study, a dual-luciferase reporter assay showed that MDA5 is a direct target of miR-34b-5p. In vitro, overexpression of miR-34b-5p accelerated the proliferation of ALV-J-infected cells by inducing the progression from G2 to S phase and it promoted cell migration. Ectopic expression of MDA5 inhibited ALV-J-infected cell proliferation, the cell cycle and cell migration, and knockdown of MDA5 promoted proliferation, the cell cycle and migration. In addition, during ALV-J infections, MDA5 can detect virus invasion and it triggers the MDA5 signaling pathway. MDA5 overexpression can activate the MDA5 signaling pathway, and thus it can inhibit the mRNA and protein expression of the ALV-J env gene and it can suppress virion secretion. In contrast, in response to the knockdown of MDA5 by small interfering RNA (siRNA) or an miR-34b-5p mimic, genes in the MDA5 signaling pathway were significantly downregulated (P < 0.05), but the mRNA and protein expression of ALV-J env and the sample-to-positive ratio of virion in the supernatants were increased. This indicates that miR-34b-5p is able to trigger the MDA5 signaling pathway and affect ALV-J infections. Together, these results suggest that miR-34b-5p targets MDA5 to accelerate the proliferation and migration of ALV-J-infected cells, and it promotes ALV-J replication, via the MDA5 signaling pathway.

gga-miR-2127 downregulates the translation of chicken p53 and attenuates chp53-mediated innate immune response against IBDV infection

Infectious bursal disease (IBD) is characterized by the immune suppression of infected birds. The molecular mechanism by which IBD virus (IBDV) suppresses the host immune system remains to be elucidated. The tumor suppressor protein p53 can inhibit the replication of various viruses, but its effect on IBDV remains unknown. This study established an in vitro infection model based on DF-1 cells (chicken embryo fibroblast cell line) to investigate the antiviral effects of chicken p53 (chp53) on IBDV infection. The expression level and activity of chp53 remarkably increased in IBDV-infected DF-1 cells. The overexpression of chp53 inhibited IBDV replication and upregulated the expression of multiple chicken antiviral innate immunity genes (IPS-1, IRF3, PKR, OAS, and Mx), whereas the suppression of chp53 led to the opposite effect. This result indicates that chp53 activates the antiviral innate immune response of chickens to IBDV infection. Bioinformatics analysis and dual-luciferase reporter assay showed that gga-miR-2127 targeted the 3'UTR of chp53. qRT-PCR and western blot revealed that gga-miR-2127 overexpression in DF-1 cells not only downregulated the expression levels of chp53 and of the antiviral innate immunity genes in chickens but also promoted IBDV replication. Our results suggest that gga-miR-2127 downregulates chp53 mRNA translation by targeting its 3'UTR and attenuates chp53-mediated antiviral innate immune response against IBDV.

Avian Tembusu virus infection effectively triggers host innate immune response through MDA5 and TLR3-dependent signaling pathways

Avian Tembusu virus (ATMUV) is a newly emerged flavivirus that belongs to the Ntaya virus group. ATMUV is a highly pathogenic virus causing significant economic loss to the Chinese poultry industry. However, little is known about the role of host innate immune mechanism in defending against ATMUV infection. In this study, we found that ATMUV infection significantly up-regulated the expression of type I and type III interferons (IFN) and some critical IFN-stimulated genes (ISG) in vivo and in vitro. This innate immune response was induced by genomic RNA of ATMUV. Furthermore, we observed that ATMUV infection triggered IFN response mainly through MDA5 and TLR3-dependent signaling pathways. Strikingly, shRNA-based disruption of IPS-1, IRF3 or IRF7 expression significantly reduced the production of IFN in the 293T cell model. Moreover, NF-κB was shown to be activated in both chicken and human cells during the ATMUV infection. Inhibition of NF-κB signaling also resulted in a clear decrease in expression of IFN. Importantly, experiments revealed that treatment with IFN significantly impaired ATMUV replication in the chicken cell. Consistently, type I IFN also exhibited promising antiviral activity against ATMUV replication in the human cell. Together, these data indicate that ATMUV infection triggers host innate immune response through MDA5 and TLR3-dependent signaling that controls IFN production, and thereby induces an effective antiviral immunity.

Promoter structures and differential responses to viral and non-viral inducers of chicken melanoma differentiation-associated gene 5

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A 2.5 kb chicken MDA5 promoter fragment was cloned and characterized (Accession number KT335979).

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The activity of the promoter is extremely low under basal conditions.

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Viral (IBDV) and non-viral (IFN-β or poly (I:C) inducers could activate the promoter.

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Gene expression driven by exogenous MDA5 promoter is in accordance with endogenous MDA5.

Melanoma differentiation-associated gene 5 (MDA5) is a member of the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) family and plays a pivotal role in the anti-viral innate immune response. As RIG-I is absent in chickens, MDA5 is hypothesized to be important in detecting viral nucleic acids in the cytoplasm. However, the molecular mechanism of the regulation of chicken MDA5 (chMDA5) expression has yet to be fully elucidated. With this in mind, a ∼2.5 kb chMDA5 gene promoter region was examined and PCR amplified to assess its role in immune response. A chMDA5 promoter reporter plasmid (piggybac-MDA5-DsRed) was constructed and transfected into DF-1 cells to establish a Piggybac-MDA5-DsRed cell line. The MDA5 promoter activity was extremely low under basal condition, but was dramatically increased when cells were stimulated with polyinosinic: polycytidylic acid (poly I:C), interferon beta (IFN-β) or Infectious Bursal Disease Virus (IBDV). The DsRed mRNA level represented the promoter activity and was remarkably increased, which matched the expression of endogenous MDA5. However, Infectious Bronchitis Virus (IBV) and Newcastle disease virus (NDV) failed to increase the MDA5 promoter activity and the expression of endogenous MDA5. The results indicated that the promoter and the Piggybac-MDA5-DsRed cell line could be utilized to determine whether a ligand regulates MDA5 expression. For the first time, this study provides a tool for testing chMDA5 expression and regulation.

Infectious bursal disease virus in poultry: current status and future prospects

Infectious bursal disease virus (IBDV) affects immature B lymphocytes of the bursa of Fabricius and may cause significant immunosuppression. It continues to be a leading cause of economic losses in the poultry industry. IBDV, having a segmented double-stranded RNA genome, is prone to genetic variation. Therefore, IBDV isolates with different genotypic and phenotypic diversity exist. Understanding these features of the virus and the mechanisms of protective immunity elicited thereof is necessary for developing vaccines with improved efficacy. In this review, we highlighted the pattern of virus evolution and new developments in prophylactic strategies, mainly the development of new generation vaccines, which will continue to be of interest for research as well as field application in the future.

Role of chicken melanoma differentiation-associated gene 5 in induction and activation of innate and adaptive immune responses to infectious bursal disease virus in cultured macrophages

The objective of the present study was to determine if chicken melanoma-differentiation-associated gene 5 (MDA5) senses infectious bursal disease virus infection to induce innate immunity that bridges to adaptive immunity. During IBDV infection in HD11 cells, IBDV titers and RNA loads increased up to 3.4 × 10(7) plaque-forming units (PFU)/mL and 1114 ng/µL, respectively, at 24 hours postinfection (hpi). IBDV infection in HD11 cells induced significantly upregulated (p < 0.05) expression levels of chicken MDA5 (59-fold), interferon-β (IFN-β) (693-fold), dsRNA-dependent protein kinase (PKR) (4-fold), 2', 5'-oligoadenylate synthetase (OAS) (286-fold), myxovirus resistance gene (Mx) (22-fold), interleukin-1β (IL-1β) (5-fold), IL-6 (146-fold), IL-8 (4-fold), IL-10 (4-fold), inducible nitric oxide synthase (iNOS) (15-fold), and major histocompatibility complex class I (MHC class I) (4-fold). Nitric oxide production in the culture supernatants increased significantly (p < 0.05) up to 6.5 μM at 24 hpi. The expressed chMDA5 and IBDV-derived dsRNA were localized in the cytoplasm of HD11 cells during IBDV infection. ChMDA5-knockdown HD11 cells had significantly higher (p < 0.05) IBDV RNA loads at 24 hpi and significantly lower (p < 0.05) nitric oxide production and expression levels of chicken MDA5, IFN-β, PKR, OAS, Mx, IL-1β, IL-6, IL-8, IL-12(p40), IL-18, IL-10, iNOS, MHC class I and CD86 at 24 hpi. In addition, chMDA5 overexpression in HD11 cells resulted in significantly reduced (p < 0.05) IBDV titers and RNA loads and significantly increased (p < 0.05) nitric oxide production at 16 and 24 hpi. It also resulted in significantly higher (p < 0.05) expression levels of chicken MDA5, IFN-β, PKR, OAS, Mx, IL-1β, IL-6, IL-8, IL-12(p40), IL-10 and iNOS at 2 hpi. In conclusion, the results indicate that chMDA5 senses IBDV infection in chicken macrophages, and this is associated with IBDV-induced expression of IFN-β and initiation of an innate immune response that in turn activates the adaptive immune response and limits IBDV replication.

Pigeon RIG-I Function in Innate Immunity against H9N2 IAV and IBDV

Retinoic acid-inducible gene I (RIG-I), a cytosolic pattern recognition receptor (PRR), can sense various RNA viruses, including the avian influenza virus (AIV) and infectious bursal disease virus (IBDV), and trigger the innate immune response. Previous studies have shown that mammalian RIG-I (human and mice) and waterfowl RIG-I (ducks and geese) are essential for type I interferon (IFN) synthesis during AIV infection. Like ducks, pigeons are also susceptible to infection but are ineffective propagators and disseminators of AIVs, i.e., “dead end” hosts for AIVs and even highly pathogenic avian influenza (HPAI). Consequently, we sought to identify pigeon RIG-I and investigate its roles in the detection of A/Chicken/Shandong/ZB/2007 (H9N2) (ZB07), Gansu/Tianshui (IBDV TS) and Beijing/CJ/1980 (IBDV CJ-801) strains in chicken DF-1 fibroblasts or human 293T cells. Pigeon mRNA encoding the putative pigeon RIG-I analogs was identified. The exogenous expression of enhanced green fluorescence protein (EGFP)-tagged pigeon RIG-I and caspase activation and recruitment domains (CARDs), strongly induced antiviral gene (IFN-β, Mx, and PKR) mRNA synthesis, decreased viral gene (M gene and VP2) mRNA expression, and reduced the viral titers of ZB07 and IBDV TS/CJ-801 virus strains in chicken DF-1 cells, but not in 293T cells. We also compared the antiviral abilities of RIG-I proteins from waterfowl (duck and goose) and pigeon. Our data indicated that waterfowl RIG-I are more effective in the induction of antiviral genes and the repression of ZB07 and IBDV TS/CJ-801 strain replication than pigeon RIG-I. Furthermore, chicken melanoma differentiation associated gene 5(MDA5)/ mitochondrial antiviral signaling (MAVS) silencing combined with RIG-I transfection suggested that pigeon RIG-I can restore the antiviral response in MDA5-silenced DF-1 cells but not in MAVS-silenced DF-1 cells. In conclusion, these results demonstrated that pigeon RIG-I and CARDs have a strong antiviral ability against AIV H9N2 and IBDV in chicken DF-1 cells but not in human 293T cells.