Susceptibility of primary chicken intestinal epithelial cells for low pathogenic avian influenza virus and velogenic viscerotropic Newcastle disease virus

Immune responses to avian influenza viruses in chickens

Chickens are a key species in both the manifestation of avian influenza and the potential for zoonotic transmission. Avian influenza virus (AIV) infection in chickens can range from asymptomatic or mild disease with low pathogenic AIVs (LPAIVs) to systemic fatal disease with high pathogenic AIVs (HPAIVs). During AIV infection in chickens, Toll-like receptor 7 and melanoma differentiation-associated gene 5 are upregulated to detect the single-stranded ribonucleic acid genomes of AIV, triggering a signaling cascade that produces interferons (IFNs) and pro-inflammatory cytokines. These inflammatory mediators induce the expression of antiviral proteins and recruit immune system cells, such as macrophages and dendritic cells, to the infection site. AIV evades these antiviral responses primarily through its non-structural protein 1, which suppresses type I IFNs, influencing viral pathogenicity. The uncontrolled release of pro-inflammatory cytokines may contribute to the pathogenicity and high mortality associated with HPAIV infections. AIV modulates apoptosis in chicken cells to enhance its replication, with variations in apoptosis pathways influenced by viral strain and host cell type. The presentation of AIV antigens to T and B cells leads to the production of neutralizing antibodies and the targeted destruction of infected cells by CD8+ T cells, respectively, which enhances protection and establishes immunological memory. This review explores the diverse innate and adaptive immune responses in chickens to different AIVs, focusing on the dynamics of these responses relative to protection, susceptibility, and potential immunopathology. By understanding these immune mechanisms, informed strategies for controlling AIV infection and improving chicken health can be developed.

Diversity of genotypes and pathogenicity of H9N2 avian influenza virus derived from wild bird and domestic poultry

Introduction

The H9N2 subtype is a predominant avian influenza virus (AIV) circulating in Chinese poultry, forming various genotypes (A-W) based on gene segment origins. This study aims to investigate the genotypic distribution and pathogenic characteristics of H9N2 isolates from wild birds and domestic poultry in Yunnan Province, China.

Methods

Eleven H9N2 strains were isolated from fecal samples of overwintering wild birds and proximate domestic poultry in Yunnan, including four from common cranes (Grus grus), two from bar-headed geese (Anser indicus), and five from domestic poultry (Gallus gallus). Phylogenetic analysis was conducted to determine the genotypes, and representative strains were inoculated into Yunnan mallard ducks to assess pathogenicity.

Results

Phylogenetic analysis revealed that five isolates from domestic birds and one from a bar-headed goose belong to genotype S, while the remaining five isolates from wild birds belong to genotype A. These bird-derived strains possess deletions in the stalk domain of NA protein and the N166D mutation of HA protein, typical of poultry strains. Genotype S H9N2 demonstrated oropharyngeal shedding, while genotype A H9N2 exhibited cloacal shedding and high viral loads in the duodenum. Both strains caused significant pathological injuries, with genotype S inducing more severe damage to the thymus and spleen, while genotype A caused duodenal muscle layer rupture.

Discussion

These findings suggest that at least two genotypes of H9N2 are currently circulating in Yunnan, and Yunnan mallard ducks potentially act as intermediaries in interspecies transmission. These insights highlight the importance of analyzing the current epidemiological transmission characteristics of H9N2 among wild and domestic birds in China.

Identification of the murine osteoblastic cell MC3T3-E1 as a permissive cell line in response to lumpy skin disease virus

Lumpy skin disease virus (LSDV) is a rapidly emerging pathogen in China. Screening suitable cells for LSDV replication is vital for future research on pathogenic mechanisms and vaccine development. Previous comparative studies have identified that the rodent-derived BHK21 is a highly susceptible cell model to LSDV infection. Using western blot, indirect immune-fluorescence assay, flow cytometry, and transmission electron microscopy methods, this study is the first to identify the murine osteoblastic cell line MC3T3-E1 as a novel permissive cell model for LSDV infection. The establishment of MC3T3-E1 as a suitable infectious cell model enhances our understanding of the species range and cell types of the permissive cells and nonpermissive that support LSDV replication. It is helpful to accelerate future research on the pathogenesis, clinical application, and vaccine development of LSDV.

Role of Macrophages in the Pathogenesis of Genotype VII Newcastle Disease Virus in Chickens

Long-term evolution of Newcastle disease virus (NDV) results in substantial alteration in viral pathogenesis. NDVs of genotype VII, a late genotype, show marked tropism to lymphoid tissues, especially to macrophages in chickens. However, the role of macrophages in the pathogenesis of genotype VII NDV is still unclear. Herein, NDV infectivity in macrophages and the role of macrophages in the pathogenesis of genotype VII NDV in chickens were investigated. We reported that NDV strains of genotype VII (JS5/05) and IV (Herts/33) can replicate in the adherent (predominantly macrophages) and non-adherent cells (predominantly lymphocytes) derived from chicken peripheral blood mononuclear cells (PBMCs), and significantly higher virus gene copy was detected in the adherent cells. In addition, JS5/05 had significantly higher infectivity in PBMC-derived adherent cells than Herts/33, correlating with its enhanced tropism to macrophages in the spleen of chickens. Interestingly, the depletion of 68% of macrophages exerted no significant impact on clinical signs, mortality and the systematic replication of JS5/05 in chickens, which may be associated with the contribution of non-depleted macrophages and other virus-supportive cells to virus replication. Macrophage depletion resulted in a marked exacerbation of tissue damage and apoptosis in the spleen caused by JS5/05. These findings indicated that macrophages play a critical role in alleviating tissue damage caused by genotype VII NDV in chickens. Our results unveiled new roles of macrophages in NDV pathogenesis in chickens.

The comparative study revealed that the hTERT-CSF cell line was the most susceptible cell to the Lumpy skin disease virus infection among eleven cells

Lumpy skin disease virus (LSDV) is a rapidly emerging pathogen in Asia, including China. Improving the propagation of LSDV is important for diagnostics and vaccine production. Our study identified and compared the LSDV susceptibility of eleven standard cells using western blot, indirect immune-fluorescence assay, quantitative PCR, and 50% tissue culture infectious dose. Our finding revealed that the LSDV strain could infect five cell lines and show a cytopathic effect. Furthermore, the hTERT-CSF cell line had the highest level of virus in the five cell models, followed by BHK-21, MDBK, Vero, and hTERT-ST. Hence, hTERT-CSF could be used as a candidate cell line for basic and applied research, clinical application, and LSDV vaccine development, providing a vital reference in LSDV and other viruses.

Identification of a Novel Interferon Lambda Splice Variant in Chickens

Type III interferons (IFNLs) have critical roles in the host's innate immune system, also serving as the first line against pathogenic infections of mucosal surfaces. In mammals, several IFNLs have been reported; however, only limited data on the repertoire of IFNLs in avian species is available. Previous studies showed only one member in chicken (chIFNL3). Herein, we identified a novel chicken IFNL for the first time, termed chIFNL3a, which contains 354 bp, and encodes 118 amino acids. The predicted protein is 57.1% amino acid identity with chIFNL. Genetic, evolutionary, and sequence analyses indicated that the new open reading frame (ORF) groups with type III chicken IFNs represent a novel splice variant. Compared to IFNs from different species, the new ORF is clustered within the type III IFNs group. Further study showed that chIFNL3a could activate a panel of IFN-regulated genes and function mediated by the IFNL receptor, and chIFNL3a markedly inhibited the replication of Newcastle disease virus (NDV) and influenza virus in vitro. These data collectively shed light on the repertoire of IFNs in avian species and provide useful information that further elucidate the interaction of the chIFNLs and viral infection of poultry. IMPORTANCE Interferons (IFNs) are critical soluble factors in the immune system, and are composed of 3 types (I, II, and III) that utilize different receptor complexes (IFN-αR1/IFN-αR2, IFN-γR1/IFN-γR2, and IFN-λR1/IL-10R2, respectively). Herein, we identified IFNL from the genomic sequences of chicken and termed it chIFNL3a, located on chromosome 7 of chicken. Phylogenetically clustered with all known types of chicken IFNs, the finding of this IFN is considered a type III IFN. To further evaluate the biological properties of chIFNL3a, the target protein was prepared by the baculovirus expression system (BES), which could markedly inhibit the replication of NDV and influenza viruses. In this study, we uncovered a new interferon lambda splice variant of chicken, termed chIFNL3a, which could inhibit viral replication in cells. Importantly, these novel findings may extend to other viruses, offering a new direction for therapeutic interventions.

Pathologic Mechanisms of the Newcastle Disease Virus

Newcastle disease (ND) has been a consistent risk factor to the poultry industry worldwide. Its pathogen, Newcastle disease virus (NDV), is also a promising antitumor treatment candidate. The pathogenic mechanism has intrigued the great curiosity of researchers, and advances in the last two decades have been summarized in this paper. The NDV’s pathogenic ability is highly related to the basic protein structure of the virus, which is described in the Introduction of this review. The overall clinical signs and recent findings pertaining to NDV-related lymph tissue damage are then described. Given the involvement of cytokines in the overall virulence of NDV, cytokines, particularly IL6 and IFN expressed during infection, are reviewed. On the other hand, the host also has its way of antagonizing the virus, which starts with the detection of the pathogen. Thus, advances in NDV’s physiological cell mechanism and the subsequent IFN response, autophagy, and apoptosis are summarized to provide a whole picture of the NDV infection process.

Pattern Recognition Receptor Signaling and Innate Responses to Influenza A Viruses in the Mallard Duck, Compared to Humans and Chickens

Mallard ducks are a natural host and reservoir of avian Influenza A viruses. While most influenza strains can replicate in mallards, the virus typically does not cause substantial disease in this host. Mallards are often resistant to disease caused by highly pathogenic avian influenza viruses, while the same strains can cause severe infection in humans, chickens, and even other species of ducks, resulting in systemic spread of the virus and even death. The differences in influenza detection and antiviral effectors responsible for limiting damage in the mallards are largely unknown. Domestic mallards have an early and robust innate response to infection that seems to limit replication and clear highly pathogenic strains. The regulation and timing of the response to influenza also seems to circumvent damage done by a prolonged or dysregulated immune response. Rapid initiation of innate immune responses depends on viral recognition by pattern recognition receptors (PRRs) expressed in tissues where the virus replicates. RIG-like receptors (RLRs), Toll-like receptors (TLRs), and Nod-like receptors (NLRs) are all important influenza sensors in mammals during infection. Ducks utilize many of the same PRRs to detect influenza, namely RIG-I, TLR7, and TLR3 and their downstream adaptors. Ducks also express many of the same signal transduction proteins including TBK1, TRIF, and TRAF3. Some antiviral effectors expressed downstream of these signaling pathways inhibit influenza replication in ducks. In this review, we summarize the recent advances in our understanding of influenza recognition and response through duck PRRs and their adaptors. We compare basal tissue expression and regulation of these signaling components in birds, to better understand what contributes to influenza resistance in the duck.

A within-host mathematical model of H9N2 avian influenza infection and type-I interferon response pathways in chickens

Chickens infected with avian influenza virus (AIV) transmit the virus via respiratory and cloacal shedding. While previous mathematical models have shown that the innate immune response is necessary for the early suppression of virus production in infected respiratory cells, the different pathways by which the innate immune response can affect cloacal viral shedding have not been studied in chickens. The present study aims to evaluate the sensitivity of H9N2 low pathogenic AIV shedding in chicken gastrointestinal cells to different type-I interferon (IFN) response pathways, and to determine the impact of a cellular eclipse phase (latent period) on the time to peak virus shedding using a mathematical model describing within host viral kinetics. Our model results demonstrate that a mechanistic model that incorporates 1) the intracellular antiviral effects of type-I IFN on virus production, 2) destruction of infected cells by type-I IFN activated Natural Killer cells, and 3) an eclipse phase is most consistent with experimental cloacal virus shedding data. These results provide a potential mechanistic explanation for the delay to peak cloacal virus shedding observed in experimental studies conducted in chickens, as well as an improved understanding of the primary type-I IFN pathways involved in the control of cloacal virus shedding, which may lead to the development of more targeted vaccine candidates.

High level expression of ISG12(1) promotes cell apoptosis via mitochondrial-dependent pathway and so as to hinder Newcastle disease virus replication

Newcastle disease (ND), caused by virulent Newcastle disease virus (NDV), poses a considerable risk for the poultry industry. A comprehensive understanding of the interaction between NDV and its host is therefore critical for control of this disease. Previously, we found that chicken ISG12(1) was among the significantly upregulated interferon-stimulated genes (ISGs) in embryos and the bursa of Fabricius of chickens infected by NDV, based on transcriptome sequencing. However, its antiviral effects and function were poorly understood. In this study, we aimed to determine the effects of chicken ISG12(1) on NDV replication. First, we confirmed that NDV infection stimulated high level expression of chicken ISG12(1) in vivo and in vitro based on RT-qPCR. Next, through overexpression and knockdown experiments, the antiviral activity of ISG12(1) was investigated. As expected, this protein was found to hinder NDV replication. In addition, we showed that ISG12(1) localized to the mitochondria; promoted the redistribution of Bax, a proapoptotic protein causing irreversible loss of mitochondrial function, from the cytoplasm to the mitochondria; and therefore induced cell apoptosis. In conclusion, elucidation of the role of chicken ISG12(1) in combatting NDV infection contributes to our understanding of the responses of poultry to viruses and may facilitate the generation of more efficient vaccines to control ND.

Avian parvovirus: classification, phylogeny, pathogenesis and diagnosis

Poultry parvoviruses identified during the early 1980s are found worldwide in intestines from young birds with enteric disease syndromes as well as healthy birds. The chicken parvovirus (ChPV) and turkey parvovirus (TuPV) belong to the Aveparvovirus genus within the subfamily Parvovirinae. Poultry parvoviruses are small, non-enveloped, single-stranded DNA viruses consisting of three open reading frames, the first two encoding the non-structural protein (NS) and nuclear phosphoprotein (NP) and the third encoding the viral capsid proteins 1 (VP1 and VP2). In contrast to other parvoviruses, the VP1-unique region does not contain the phospholipase A2 sequence motif. Recent experimental studies suggested the parvoviruses to be the candidate pathogens in cases of enteric disease syndrome. Current diagnostic methods for poultry parvovirus detection include PCR, real-time PCR, enzyme linked immunosorbent assay using recombinant VP2 or VP1 capsid proteins. Moreover, sequence-independent amplification techniques combined with next-generation sequencing platforms have allowed rapid and simultaneous detection of the parvovirus from affected and healthy birds. There is no commercial vaccine; hence, the development of an effective vaccine to control the spread of infection should be of primary importance. This review presents the current knowledge on poultry parvoviruses with emphasis on taxonomy, phylogenetic relationship, genomic analysis, epidemiology, pathogenesis and diagnostic methods.

Broad-spectrum antiviral functions of duck interferon-induced protein with tetratricopeptide repeats (AvIFIT)

Mammalian interferon-induced proteins with tetratricopeptide repeats (IFITs) play important roles in many cellular processes and host innate immune response to viruses. However, the functions of IFIT proteins in birds are largely unknown. Here, we first describe that the only one avian IFIT protein is orthologous to ancestor of mammalian IFITs. We find that the predicted structure of duck AvIFIT protein is similar to that of human IFIT5. We also find that duck AvIFIT protein shows antiviral activity to a broad range of specific RNA and DNA viruses like mammalian IFIT proteins. Further analysis indicates that overexpression of duck AvIFIT protein in DF1 cells leads to a remarkable accumulation of cells at G1/S transition associated with growth arrest and may promote apoptosis. Moreover, duck AvIFIT binds to nucleoprotein (NP) of H5N1 influenza virus and upregulates the expression of genes involving the IFN pathway in DF1 cells. In summary, our findings support that duck AvIFIT protein plays critical role in host immune response to viruses, at least H5N1 virus, through affecting function of viral NP protein, magnifying the IFN signaling and arresting cell growth.

Gut microbiota modulates type I interferon and antibody-mediated immune responses in chickens infected with influenza virus subtype H9N2

Commensal gut microbes play a critical role in shaping host defences against pathogens, including influenza viruses. The current study was conducted to assess the role and mechanisms of action of commensal gut microbiota on the innate and antibody-mediated responses of layer chickens against influenza virus subtype H9N2. A total of 104 one-day-old specific pathogen free chickens were assigned to either of the four treatments, which included two levels of antibiotics treatment (ABX- and ABX+) and two levels of H9N2 virus infection (H9N2- and H9N2+). At day 17 of age, chickens in the H9N2+ group were infected via the oral-nasal route with 400 μl of 107 TCID₅₀/ml (200 μl/each route). Oropharyngeal and cloacal swabs at days 1, 3, 5, 7 and 9 post-infection (p.i.) for virus shedding, tissue samples at 12 h, 24 h and 36 h p.i. for mRNA measurement, and serum samples at days 7 and 14 p.i. for hemagglutination inhibition (HI) assay and IgG antibodies were collected. Virus shedding analysis showed that antibiotic treated (depleted)-H9N2 virus infected chickens showed a significantly higher oropharyngeal virus shedding at all time points, and cloacal shedding at days 3 and 5 p.i. compared to control treated (undepleted)-H9N2 infected chickens. Analysis of mRNA expression showed that infection of depleted chickens with H9N2 virus resulted in significantly down-regulated type I interferon responses both in the respiratory and gastrointestinal tracts compared to undepleted-H9N2 infected chickens. However, antibody-mediated immune response analysis showed a significantly higher HI antibody titre and IgG levels in the serum of chickens depleted with antibiotics and infected with H9N2 virus compared to undepleted-H9N2 infected chickens. In conclusion, findings from the current study suggest that the gut microbiota of chickens plays an important role in the initiation of innate responses against influenza virus infection, while the antibody-mediated immune response remains unaffected.

The Bacterial Species Campylobacter jejuni Induce Diverse Innate Immune Responses in Human and Avian Intestinal Epithelial Cells

Campylobacter remain the major cause of human gastroenteritis in the Developed World causing a significant burden to health services. Campylobacter are pathogens in humans and chickens, although differences in mechanistic understanding are incomplete, in part because phenotypic strain diversity creates inconsistent findings. Here, we took Campylobacter jejuni isolates (n = 100) from multi-locus sequence typed collections to assess their pathogenic diversity, through their inflammatory, cytotoxicity, adhesion, invasion and signaling responses in a high-throughput model using avian and human intestinal epithelial cells. C. jejuni induced IL-8 and CXCLi1/2 in human and avian epithelial cells, respectively, in a MAP kinase-dependent manner. In contrast, IL-10 responses in both cell types were PI 3-kinase/Akt-dependent. C. jejuni strains showed diverse levels of invasion with high invasion dependent on MAP kinase signaling in both cell lines. C. jejuni induced diverse cytotoxic responses in both cell lines with cdt-positive isolates showing significantly higher toxicity. Blockade of endocytic pathways suggested that invasion by C. jejuni was clathrin- and dynamin-dependent but caveolae- independent in both cells. In contrast, IL-8 (and CXCLi1/2) production was dependent on clathrin, dynamin, and caveolae. This study is important because of its scale, and the data produced, suggesting that avian and human epithelial cells use similar innate immune pathways where the magnitude of the response is determined by the phenotypic diversity of the Campylobacter species.

Interferon-Lambda: A Potent Regulator of Intestinal Viral Infections

Interferon-lambda (IFN-λ) is a recently described cytokine found to be of critical importance in innate immune regulation of intestinal viruses. Endogenous IFN-λ has potent antiviral effects and has been shown to control multiple intestinal viruses and may represent a factor that contributes to human variability in response to infection. Importantly, recombinant IFN-λ has therapeutic potential against enteric viral infections, many of which lack other effective treatments. In this mini-review, we describe recent advances regarding IFN-λ-mediated regulation of enteric viruses with important clinical relevance including rotavirus, reovirus, and norovirus. We also briefly discuss IFN-λ interactions with other cytokines important in the intestine, and how IFN-λ may play a role in regulation of intestinal viruses by the commensal microbiome. Finally, we indicate currently outstanding questions regarding IFN-λ control of enteric infections that remain to be explored to enhance our understanding of this important immune molecule.