Identifying innate immune pathways of the chicken may lead to new antiviral therapies

Recent history of Veterinary Immunology in Australia

This Commentary article reviews the history of veterinary immunology in Australia from the 1980s and discusses the key people and areas of research during this period.

Distribution of importin-α isoforms in poultry species and their tissue- and age-related differences

While importin-α is well studied in mammals, the knowledge in avian species is still limited. In this study, we compared the mRNA expression patterns of five importin-α isoforms in the respiratory tract, liver, and spleen of chickens, turkeys, and pekin ducks in two different age-groups. In addition, we determined the distribution of importin-α in selected tissue of conchae, trachea, and lung of post-hatch chickens at all cellular levels by immunohistochemical staining. Our results indicate that importin-α3 is the most abundant isoform in the respiratory tract of chickens, turkeys, and pekin ducks. Moreover, importin-α is expressed as a gradient with lowest mRNA levels in the conchae and highest levels in the lung. The mRNA expression levels of most isoforms were higher in tissues from post-hatch chickens and turkeys in comparison to the corresponding embryos. In contrast to that, duck embryos mostly show higher mRNA expression levels of importin-α than post-hatch ducks.

Comparative trachea transcriptome analysis in SPF broiler chickens infected with avian infectious bronchitis and avian influenza viruses

Infectious bronchitis virus (IBV) and avian influenza virus (AIV) are two major respiratory infections in chickens. The coinfection of these viruses can cause significant financial losses and severe complications in the poultry industry across the world. To examine transcriptome profile changes during the early stages of infection, differential transcriptional profiles in tracheal tissue of three infected groups (i.e., IBV, AIV, and coinfected) were compared with the control group. Specific-pathogen-free chickens were challenged with Iranian variant-2-like IBV (IS/1494), UT-Barin isolates of H9N2 (A/chicken/Mashhad/UT-Barin/2017), and IBV-AIV coinfection; then, RNA was extracted from tracheal tissue. The Illumina RNA-sequencing (RNA-seq) technique was employed to investigate changes in the Transcriptome. Up- and downregulated differentially expressed genes (DEGs) were detected in the trachea transcriptome of all groups. The Kyoto Encyclopedia of Genes and Genomes pathway and Gene Ontology databases were examined to identify possible relationships between DEGs. In the experimental groups, upregulated genes were higher compared to downregulated genes. A more severe immune response was observed in the coinfected group; further, cytokine-cytokine receptor interaction, RIG-I-like receptor signaling, Toll-like receptor signaling, NOD-like receptor signaling, Janus kinase/signal transducer, and activator of transcription, and apoptotic pathways were important upregulated genes in this group. The findings of this paper may give a better understanding of transcriptome changes in the trachea during the early stages of infection with these viruses.

Interferon Signaling in Chickens Plays a Crucial Role in Inhibiting Influenza Replication in DF1 Cells

Influenza A viruses (IAV) pose a constant threat to human and poultry health. Of particular interest are the infections caused by highly pathogenic avian influenza (HPAI) viruses, such as H5N1, which cause significant production issues. In response to influenza infection, cells activate immune mechanisms that lead to increased interferon (IFN) production. To investigate how alterations in the interferon signaling pathway affect the cellular response to infection in the chicken, we used CRISPR/Cas9 to generate a chicken cell line that lacks a functional the type I interferon receptor (IFNAR1). We then assessed viral infections with the WSN strain of influenza. Cells lacking a functional IFNAR1 receptor showed reduced expression of the interferon stimulated genes (ISG) such as Protein Kinase R (PKR) and Myxovirus resistance (Mx) and were more susceptible to viral infection with WSN. We further investigated the role or IFNAR1 on low pathogenicity avian influenza (LPAI) strains (H7N9) and a HPAI strain (H5N1). Intriguingly, Ifnar-/- cells appeared more resistant than WT cells when infected with HPAI virus, potentially indicating a different interaction between H5N1 and the IFN signaling pathway. Our findings support that ChIFNAR1 is a key component of the chicken IFN signaling pathway and these data add contributions to the field of host-avian pathogen interaction and innate immunity in chickens.

Host Antiviral Responses against Avian Infectious Bronchitis Virus (IBV): Focus on Innate Immunity

Avian infectious bronchitis virus (IBV) is an important gammacoronavirus. The virus is highly contagious, can infect chickens of all ages, and causes considerable economic losses in the poultry industry worldwide. In the last few decades, numerous studies have been published regarding pathogenicity, vaccination, and host immunity-virus interaction. In particular, innate immunity serves as the first line of defense against invasive pathogens and plays an important role in the pathogenetic process of IBV infection. This review focuses on fundamental aspects of host innate immune responses after IBV infection, including identification of conserved viral structures and different components of host with antiviral activity, which could provide useful information for novel vaccine development, vaccination strategies, and intervention programs.

Antiviral responses against chicken respiratory infections: Focus on avian influenza virus and infectious bronchitis virus

Some of the respiratory viral infections in chickens pose a significant threat to the poultry industry and public health. In response to viral infections, host innate responses provide the first line of defense against viruses, which often act even before the establishment of the infection. Host cells sense the presence of viral components through germinal encoded pattern recognition receptors (PRRs). The engagement of PRRs with pathogen-associated molecular patterns leads to the induction of pro-inflammatory and interferon productions. Induced antiviral responses play a critical role in the outcome of the infections. In order to improve current strategies for control of viral infections or to advance new strategies aimed against viral infections, a deep understanding of host-virus interaction and induction of antiviral responses is required. In this review, we summarized recent progress in understanding innate antiviral responses in chickens with a focus on the avian influenza virus and infectious bronchitis virus.

Constitutively elevated levels of SOCS1 suppress innate responses in DF-1 immortalised chicken fibroblast cells

The spontaneously immortalised DF-1 cell line is rapidly replacing its progenitor primary chicken embryo fibroblasts (CEFs) for studies on avian viruses such as avian influenza but no comprehensive study has as yet been reported comparing their innate immunity phenotypes. We conducted microarray analyses of DF-1 and CEFs, under both normal and stimulated conditions using chicken interferon-α (chIFN-α) and the attenuated infectious bursal disease virus vaccine strain PBG98. We found that DF-1 have an attenuated innate response compared to CEFs. Basal expression levels of Suppressor of Cytokine Signalling 1 (chSOCS1), a negative regulator of cytokine signalling in mammals, are 16-fold higher in DF-1 than in CEFs. The chSOCS1 “SOCS box” domain (which in mammals, interacts with an E3 ubiquitin ligase complex) is not essential for the inhibition of cytokine-induced JAK/STAT signalling activation in DF-1. Overexpression of SOCS1 in chIFN-α-stimulated DF-1 led to a relative decrease in expression of interferon-stimulated genes (ISGs; MX1 and IFIT5) and increased viral yield in response to PBG98 infection. Conversely, knockdown of SOCS1 enhanced induction of ISGs and reduced viral yield in chIFN-α-stimulated DF-1. Consequently, SOCS1 reduces induction of the IFN signalling pathway in chicken cells and can potentiate virus replication.

Host genetics determine susceptibility to avian influenza infection and transmission dynamics

Host-genetic control of influenza virus infection has been the object of little attention. In this study we determined that two inbred lines of chicken differing in their genetic background , Lines 0 and C-B12, were respectively relatively resistant and susceptible to infection with the low pathogenicity influenza virus A/Turkey/England/647/77 as defined by substantial differences in viral shedding trajectories. Resistant birds, although infected, were unable to transmit virus to contact birds, as ultimately only the presence of a sustained cloacal shedding (and not oropharyngeal shedding) was critical for transmission. Restriction of within-bird transmission of virus occurred in the resistant line, with intra-nares or cloacal infection resulting in only local shedding and failing to transmit fully through the gastro-intestinal-pulmonary tract. Resistance to infection was independent of adaptive immune responses, including the expansion of specific IFNγ secreting cells or production of influenza-specific antibody. Genetic resistance to a novel H9N2 virus was less robust, though significant differences between host genotypes were still clearly evident. The existence of host-genetic determination of the outcome of influenza infection offers tools for the further dissection of this regulation and also for understanding the mechanisms of influenza transmission within and between birds.

Interferon induction by avian reovirus

We have previously shown that the replication of avian reovirus (ARV) in chicken embryo fibroblasts (CEF) is more resistant to the antiviral action of interferon (IFN) than the replication of vesicular stomatitis virus (VSV) or vaccinia virus (VV). In this study we examined the capacity of these three viruses to induce the expression of IFN when infecting avian cells. Efficient expression of both type-α and type-β IFNs, as well as of the double-stranded RNA (dsRNA)-activated protein kinase (PKR), takes place in ARV-infected CEF, but not in cells infected with VSV or VV. PKR expression is not directly induced by ARV infection, but by the IFN secreted by ARV-infected cells. IFN induction in ARV-infected cells requires viral uncoating, but not viral gene expression, a situation similar to that reported for apoptosis induction by ARV-infected cells. However, our results demonstrate that IFN induction by ARV-infected CEF occurs by a caspase-independent mechanism.

Reduction of avian influenza virus shedding by administration of Toll-like receptor ligands to chickens

Avian influenza viruses (AIV) are of concern to the poultry industry. Outbreaks of AIV highlight the urgent need for effective control measures. Prophylactic strategies should be explored that rapidly elicit immunity against the virus. Toll-like receptors (TLRs) are innate immune molecules that can induce anti-viral responses, therefore the application of TLR ligands as prophylactic agents in chickens is gaining more attention. We hypothesized that treatment of chickens with TLR ligands reduces the shedding of AIV from infected birds. In addition, the effects of TLR ligand dose and route of administration on the efficiency of TLR ligands to reduce AIV shedding were examined. Chickens were treated with TLR2, 4, 7 and 21 ligands using different doses and routes of administration, 18h before AIV infection. Moreover, the expression of several candidate genes, such as type I interferons, PKR, OAS, viperin and IFITM3 was quantified at 3, 8 and 18h post-treatment with TLR ligands. The results revealed that route of administration and dosage affect the efficacy of TLR ligands to reduce virus shedding. Furthermore, varying effects were observed when different ligands were applied. Our results demonstrated that all TLR ligand treatments reduced AIV shedding, with the CpG-ODN 1826 being the most efficacious to reduce oral virus shedding, whereas LPS from Escherichia coli 026:B6 resulted in the largest reduction in cloacal virus shedding. Moreover, TLR ligands induced the expression of genes involved in antiviral responses such as type I interferons and interferon-stimulated genes in chicken trachea and cecal tonsils. These results raise the possibility of treatment of chickens with TLR ligands as anti-viral agents.

Interferons and Their Receptors in Birds: A Comparison of Gene Structure, Phylogenetic Analysis, and Cross Modulation

Interferon may be thought of as a key, with the interferon receptor as the signal lock: Crosstalk between them maintains their balance during viral infection. In this review, the protein structure of avian interferon and the interferon receptor are discussed, indicating remarkable similarity between different species. However, the structures of the interferon receptors are more sophisticated than those of the interferons, suggesting that the interferon receptor is a more complicated signal lock system and has considerable diversity in subtypes or structures. Preliminary evolutionary analysis showed that the subunits of the interferon receptor formed a distinct clade, and the orthologs may be derived from the same ancestor. Furthermore, the development of interferons and interferon receptors in birds may be related to an animal’s age and the maintenance of a balanced state. In addition, the equilibrium between interferon and its receptor during pathological and physiological states revealed that the virus and the host influence this equilibrium. Birds could represent an important model for studies on interferon’s antiviral activities and may provide the basis for new antiviral strategies.

Molecular cloning, expression and characterization of Pekin duck interferon-λ

Interferons (IFNs) are the first line of defense against viral infections in vertebrates. Type III interferon (IFN-λ) is recognized for its key role in innate immunity of tissues of epithelial origin. Here we describe the identification of the Pekin duck IFN-λ ortholog (duIFN-λ). The predicted duIFN-λ protein has an amino acid identity of 63%, 38%, 37% and 33% with chicken IFN-λ and human IFN-λ3, IFN-λ2 and IFN-λ1, respectively. The duck genome contains a single IFN-λ gene that is comprised of five exons and four introns. Recombinant duIFN-λ up-regulated OASL and Mx-1 mRNA in primary duck hepatocytes. Our observations suggest evolutionary conservation of genomic organization and structural features implicated in receptor binding and antiviral activity. The identification and expression of duIFN-λ will facilitate further study of the role of type III IFN in antiviral defense and inflammatory responses of the Pekin duck, a non-mammalian vertebrate and pathogen host with relevance for human and animal health.

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

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

Contribution of the NS1 gene of H7 avian influenza virus strains to pathogenicity in chickens

Using reverse genetics (rg), we generated two reassortant viruses carrying the NS1 gene of two closely related HPAIV and LPAIV H7N1 variants (designated rgH7N7 HP(HPNS1) and rgH7N7 HP(LPNS1), respectively) in the backbone of the HP H7N7 strain A/Chicken/Netherlands/621557/03 (rgH7N7 HP). Comparison of these reassortants allowed us to determine the effect of amino acid differences in the nuclear export and nucleolar localization sequences of NS1 on pathogenesis in chickens. Compared to rgH7N7 HP(LPNS1), a delay in weight gain and an increase in mortality were observed for rgH7N7 HP(HPNS1). Furthermore, an increase in viral load in brains, lungs, and cloacal swabs, as well as an increased induction of mRNA for type I interferons and pro-inflammatory cytokines in brains, were observed for rgH7N7 HP(HPNS1). Comparison of rgH7N7 HP(LPNS1) with the backbone strain rgH7N7 HP allowed us to examine differences in pathogenesis due to differences in NS1 alleles. rgH7N7 HP, which contained allele A of NS1 showed a higher in vitro replication rate and proved to be more virulent than the isogenic virus carrying allele B of NS1(rgH7N7 HP(LPNS1)). In addition, higher virus accumulation in the lungs and brains, and an increased induction of host gene responses, especially in the brains, were found for rgH7N7 HP compared to rgH7N7 HP(LPNS1). No large differences were observed in type I interferon expression in the lungs of chickens infected with any of the viruses, suggesting that differences in virulence due to differences in NS1 could be related to differences in the induction of pro-inflammatory cytokines in vital organs such as the brains.

Chicken interferons, their receptors and interferon-stimulated genes

The prevalence of pathogenic viruses is a serious issue as they pose a constant threat to both the poultry industry and to human health. To prevent these viral infections an understanding of the host-virus response is critical, especially for the development of novel therapeutics. One approach in the control of viral infections would be to boost the immune response through administration of cytokines, such as interferons. However, the innate immune response in chickens is poorly characterised, particularly concerning the interferon pathway. This review will provide an overview of our current understanding of the interferon system of chickens, including their cognate receptors and known interferon-stimulated gene products.

Defense genes missing from the flight division

Birds have a smaller repertoire of immune genes than mammals. In our efforts to study antiviral responses to influenza in avian hosts, we have noted key genes that appear to be missing. As a result, we speculate that birds have impaired detection of viruses and intracellular pathogens. Birds are missing TLR8, a detector for single-stranded RNA. Chickens also lack RIG-I, the intracellular detector for single-stranded viral RNA. Riplet, an activator for RIG-I, is also missing in chickens. IRF3, the nuclear activator of interferon-beta in the RIG-I pathway is missing in birds. Downstream of interferon (IFN) signaling, some of the antiviral effectors are missing, including ISG15, and ISG54 and ISG56 (IFITs). Birds have only three antibody isotypes and IgD is missing. Ducks, but not chickens, make an unusual truncated IgY antibody that is missing the Fc fragment. Chickens have an expanded family of LILR leukocyte receptor genes, called CHIR genes, with hundreds of members, including several that encode IgY Fc receptors. Intriguingly, LILR homologues appear to be missing in ducks, including these IgY Fc receptors. The truncated IgY in ducks, and the duplicated IgY receptor genes in chickens may both have resulted from selective pressure by a pathogen on IgY FcR interactions. Birds have a minimal MHC, and the TAP transport and presentation of peptides on MHC class I is constrained, limiting function. Perhaps removing some constraint, ducks appear to lack tapasin, a chaperone involved in loading peptides on MHC class I. Finally, the absence of lymphotoxin-alpha and beta may account for the observed lack of lymph nodes in birds. As illustrated by these examples, the picture that emerges is some impairment of immune response to viruses in birds, either a cause or consequence of the host-pathogen arms race and long evolutionary relationship of birds and RNA viruses.

The differential antiviral activities of chicken interferon α (ChIFN-α) and ChIFN-β are related to distinct interferon-stimulated gene expression

Chicken interferon α (ChIFN-α) and ChIFN-β are type I IFNs that are important antiviral cytokines in the innate immune system. In the present study, we identified the virus-induced expression of ChIFN-α and ChIFN-β in chicken fibroblast DF-1 cells and systematically evaluated the antiviral activities of recombinant ChIFN-α and ChIFN-β by cytopathic-effect (CPE) inhibition assays. We found that ChIFN-α exhibited stronger antiviral activity than ChIFN-β in terms of inhibiting the replication of vesicular stomatitis virus, Newcastle disease virus and avian influenza virus, respectively. To elucidate the mechanism of differential antiviral activities between the two ChIFNs, we measured the relative mRNA levels of IFN-stimulated genes (ISGs) in IFN-treated DF-1 cells by real-time PCR. ChIFN-α displayed greater induction potency than ChIFN-β on several ISGs encoding antiviral proteins and MHC-I, whereas ChIFN-α was less potent than ChIFN-β for inducing ISGs involved in signaling pathways. In conclusion, ChIFN-α and ChIFN-β presented differential induction potency on various sets of ISGs, and the stronger antiviral activity of ChIFN-α is likely attributed to the greater expression levels of downstream antiviral ISGs.

The 9th International Veterinary Immunology Symposium

This special issue of Veterinary Immunology and Immunopathology summarizes the Proceedings of the 9th International Veterinary Immunology Symposium (9th IVIS) held August 2010, in Tokyo, Japan. Over 340 delegates from 30 countries discussed research progress analyzing the immune systems of numerous food animals and wildlife, probing basic immunity and the influence of stress, genetics, nutrition, endocrinology and reproduction. Major presentations addressed defense against pathogens and alternative control and prevention strategies including vaccines, adjuvants and novel biotherapeutics. A special Organisation for Economic Co-operation and Development (OECD) Co-operative Research Programme Sponsored Conference on "Vaccination and Diagnosis for Food Safety in Agriculture" highlighted the particular issue of "Immunology in Bovine Paratuberculosis". In April 2010 there was an outbreak of foot-and-mouth disease (FMD) in the southern part of Japan. This stimulated a special 9th IVIS session on FMD, sponsored by the World Organization for Animal Health (OIE) and the Ministry of Agriculture, Forestry and Fisheries (MAFF) of Japan, to discuss improvements of FMD vaccines, their use in FMD control, and risk assessment for decision management. The 9th IVIS was supported by the Veterinary Immunology Committee (VIC) of the International Union of Immunological Societies (IUIS) and included workshops for its MHC and Toolkit Committees. Finally VIC IUIS presented its 2010 Distinguished Service Award to Dr. Kazuya Yamanouchi for "outstanding contributions to the veterinary immunology community" and its 2010 Distinguished Veterinary Immunologist Award to Dr. Douglas F. Antczak for "outstanding research on equine immunology".