Interleukin-6 expression after infectious bronchitis virus infection in chickens

Cyclooxygenase-2/prostaglandin E2 pathway orchestrates the replication of infectious bronchitis virus in chicken tracheal explants

In this study, we investigated the localized pathogenesis of infectious bronchitis virus (IBV) in chicken tracheal organ cultures (TOCs), focusing on the role of inducible cyclooxygenase (COX-2). Two divergent IBV strains, respiratory Connecticut (Conn) A5968 and nephropathogenic Delmarva (DMV)/1639, were studied at 6, 12, 24, and 48 hours post-infection (hpi). Various treatments including exogenous prostaglandin (PGE)2, a selective COX-2 antagonist (SC-236), and inhibitors of PGE2 receptors and Janus kinase (JAK) were administered. IBV genome load and antigen expression were quantified using real-time quantitative PCR and immunohistochemistry. COX-2, interferon (IFN)-α, IFN-β, interleukin (IL)-1β, IL-6, and inducible nitric oxide synthase (iNOS) expressions were measured, along with PGE2 and COX-2 concentrations. IBV genome load and protein expression peaked at 12 and 24 hpi, respectively. Conn A5968-infected TOCs exhibited continuous COX-2 expression for up to 24 hpi, extended PGE2 production up to 48 hpi, and reduced inflammatory cytokine expression. In contrast, DMV/1639-infected TOCs displayed heightened inflammatory cytokine expression, brief COX-2 expression, and PGE2 production. Treatment with IFN-γ, SC-236, PGE2 receptor inhibitors, or JAK inhibitors reduced IBV infection and lesion scores, whereas exogenous PGE2 or IFN-γ pretreatment with a JAK-2 inhibitor augmented infection. These findings shed light on the innate immune regulation of IBV infection in the trachea, highlighting the involvement of the COX-2/PGE2 pathway.

IMPORTANCE

Understanding the localized pathogenesis of infectious bronchitis virus (IBV) within the trachea of chickens is crucial for developing effective control strategies against this prevalent poultry pathogen. This study sheds light on the role of inducible cyclooxygenase (COX-2) and prostaglandin (PGE)2 in IBV pathogenesis using chicken tracheal organ culture (TOC) models. The findings reveal distinct patterns of COX-2 expression, PGE2 production, and immune responses associated with different IBV strains, highlighting the complexity of host-virus interactions. Furthermore, the identification of specific inhibitors targeting the COX-2/PGE2 pathway and Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway provides potential therapeutic avenues for mitigating IBV infection in poultry. Overall, this study contributes to our understanding of the innate immune regulation of IBV infection within the trachea, laying the groundwork for the development of targeted interventions to control IBV outbreaks in poultry populations.

The alleviating effect of Phillygenin on the regulation of respiratory microbiota and its metabolites in IBV-infected broilers by inhibiting the TLR7/MyD88/NF-κB axis

Phillygenin (PHI) is an active ingredient derived from the leaf of Forsythia suspensa that has been found to alleviate inflammation and peroxidation response. Avian infectious bronchitis (IB) is a major threat to poultry industry viral respiratory tract disease that infected with infectious bronchitis virus (IBV). This study investigated the protection of PHI to CEK cell and broiler's tracheal injury triggered by avian infectious bronchitis virus (IBV). The results showed that IBV infection did not cause serious clinical symptoms and slowing-body weight in PHI-treated broilers. The expression of virus loads, pro-inflammation factors (IL-6, TNF-α, and IL-1β) in CEK cell, and tracheas were decreased compared to the IBV group, exhibiting its potent anti-inflammation. Mechanistically, the study demonstrated that the inhibition of TLR7/MyD88/NF-κB pathway was mainly involved in the protection effect of PHI to inflammation injury. Interestingly, a higher abundance of Firmicutes and Lactobacillus in respiratory tract was observed in PHI-treated broilers than in the IBV group. Significant differences were observed between the IBV group and PHI-treated group in the Ferroptosis, Tryptophan metabolism, and Glutathione metabolism pathways. PHI exhibited potent protection effect on IBV infection and alleviated inflammation injury, mainly through inhibiting TLR7/MyD88/NF-κB pathway. The study encourages further development of PHI, paving the way to its clinical use as a new candidate drug to relieve IBV-induced respiratory symptoms.

Cyclooxygenase-2/prostaglandin E2 pathway regulates infectious bronchitis virus replication in avian macrophages

Infectious bronchitis virus (IBV) is a significant respiratory pathogen that affects chickens worldwide. As an avian coronavirus, IBV leads to productive infection in chicken macrophages. However, the effects of IBV infection in macrophages on cyclooxygenase-2 (COX-2) expression are still to be elucidated. Therefore, we investigated the role of IBV infection on the production of COX-2, an enzyme involved in the synthesis of prostaglandin E2 (PGE2) in chicken macrophages. The chicken macrophage cells were infected with two IBV strains, and the cells and culture supernatants were harvested at predetermined time points to measure intracellular and extracellular IBV infection. IBV infection was quantified as has been the COX-2 and PGE2 productions. We found that IBV infection enhances COX-2 production at both mRNA and protein levels in chicken macrophages. When a selective COX-2 antagonist was used to reduce the COX-2 expression in macrophages, we observed that IBV replication decreased. When IBV-infected macrophages were treated with PGE2 receptor (EP2 and EP4) inhibitors, IBV replication was reduced. Upon utilizing a selective COX-2 antagonist to diminish PGE2 expression in macrophages, a discernible decrease in IBV replication was observed. Treatment of IBV-infected macrophages with a PGE2 receptor (EP2) inhibitor resulted in a reduction in IBV replication, whereas the introduction of exogenous PGE2 heightened viral replication. Additionally, pretreatment with a Janus-kinase two antagonist attenuated the inhibitory effect of recombinant chicken interferon (IFN)-γ on viral replication. The evaluation of immune mediators, such as inducible nitric oxide (NO) synthase (iNOS), NO, and interleukin (IL)-6, revealed enhanced expression following IBV infection of macrophages. In response to the inhibition of COX-2 and PGE2 receptors, we observed a reduction in the expressions of iNOS and IL-6 in macrophages, correlating with reduced IBV infection. Overall, IBV infection increased COX-2 and PGE2 production in addition to iNOS, NO, and IL-6 expression in chicken macrophages in a time-dependent manner. Inhibition of the COX-2/PGE2 pathway may lead to increased macrophage defence mechanisms against IBV infection, resulting in a reduction in viral replication and iNOS and IL-6 expressions. Understanding the molecular mechanisms underlying these processes may shed light on potential antiviral targets for controlling IBV infection.

Poor body condition is associated with lower hippocampal plasticity and higher gut methanogen abundance in adult laying hens from two housing systems

It is still unclear which commercial housing system provides the best quality of life for laying hens. In addition, there are large individual differences in stress levels within a system. Hippocampal neurogenesis or plasticity may provide an integrated biomarker of the stressors experienced by an individual. We selected 12 adult hens each with good and poor body condition (based on body size, degree of feather cover and redness of the comb) from a multi-tier free range system containing H&N strain hens, and from an enriched cage system containing Hy-Line hens (n = 48 total). Immature neurons expressing doublecortin (DCX) were quantified in the hippocampus, contents of the caecal microbiome were sequenced, and expression of inflammatory cytokines was measured in the spleen. DCX⁺ cell densities did not differ between the housing systems. In both systems, poor condition hens had lower DCX⁺ cell densities, exhibited elevated splenic expression of interleukin-6 (IL6) mRNA, and had a higher relative caecal abundance of methanogenic archea Methanomethylophilaceae. The findings suggest poor body condition is an indicator that individual hens have experienced a comparatively greater degree of cumulative chronic stress, and that a survey of the proportion of hens with poor body conditions might be one way to evaluate the impact of housing systems on hen welfare.

The Genetic Stability, Replication Kinetics and Cytopathogenicity of Recombinant Avian Coronaviruses with a T16A or an A26F Mutation within the E Protein Is Cell-Type Dependent

The envelope (E) protein of the avian coronavirus infectious bronchitis virus (IBV) is a small-membrane protein present in two forms during infection: a monomer and a pentameric ion channel. Each form has an independent role during replication; the monomer disrupts the secretory pathway, and the pentamer facilitates virion production. The presence of a T16A or A26F mutation within E exclusively generates the pentameric or monomeric form, respectively. We generated two recombinant IBVs (rIBVs) based on the apathogenic molecular clone Beau-R, containing either a T16A or A26F mutation, denoted as BeauR-T16A and BeauR-A26F. The replication and genetic stability of the rIBVs were assessed in several different cell types, including primary and continuous cells, ex vivo tracheal organ cultures (TOCs) and in ovo. Different replication profiles were observed between cell cultures of different origins. BeauR-A26F replicated to a lower level than Beau-R in Vero cells and in ovo but not in DF1, primary chicken kidney (CK) cells or TOCs. Genetic stability and cytopathic effects were found to differ depending on the cell system. The effect of the T16A and A26F mutations appear to be cell-type dependent, which, therefore, highlights the importance of cell type in the investigation of the IBV E protein.

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.

Infectious bronchitis virus infection in chicken: viral load and immune responses in Harderian gland, choanal cleft and turbinate tissues compared to trachea

1. The role of the Harderian gland (HG), choanal cleft (CC) and turbinate in terms of IBV M41 viral load compared to the trachea, and immune (innate, cellular and mucosal) responses were studied in 21-day-old commercial broiler chickens.2. After virulent IBV M41 challenge, the antigen concentration detected either by quantitative RT-PCR or immunohistochemistry peaked at 2-3 days post challenge (dpc) in all tissues. Significant increases of lachrymal IBV-specific IgA and IgY levels were found at 4-5 dpc.3. Gene transcription showed a significant up-regulation of TLR3, MDA5, IL-6, IFN-α and IFN-β, where patterns and magnitude fold-change of mRNA transcription were dependent on the gene and tissue type.4. The results demonstrated active IBV M41 replication in the HG, CC and turbinate, comparable to levels of replication found in the trachea. The data on immune related genes in head-associated tissues provides further understanding on the immunobiology of IBV and offers opportunities to identify their use as quantitative biomarkers in pathogenicity and vaccination-challenge studies.

The modulatory effect of carvacrol on viral shedding titer and acute phase response in broiler chickens experimentally infected with infectious bronchitis virus

Infectious bronchitis virus (IBV) is one of the major respiratory diseases of broiler causing huge economic losses. The inability to control IBV using different vaccination programs owing to the high mutation rate and recombination ability of the RNA genome generates IBV variants. This study was designed to give a specific perspective of carvacrol effect on early immune response, viral shedding titer, oxidative stress, serum biochemical parameters and clinical consequences in broilers experimentally infected by IBV. One hundred and twenty-one-day old commercial broiler chicks were equally divided into 4 groups. First group was considered as control. Second group was given carvacrol, third group was infected with IBV and fourth group was given carvacrol and infected with IBV. Infection with variant IBV induced significant upregulation of chicken interferon-inducible transmembrane protein 3 (chIFITM3) gene in trachea, elevations in serum levels of Alpha-1 acid glycoprotein (α1-AGP) and Interleukin 6 (IL-6), total leucocytic count (TLC), heterophil/lymphocyte (H/L) ratio and oxidative stress in lung and kidney tissues. Beside, histopathological changes in trachea, lung and kidney induced by IBV, elevation of kidney function tests was detected. The pretreatment with carvacrol significantly reduced viral shedding titer, chIFITM3 gene expression, IL-6 and α1-AGP levels, leucocytic response and H/L ratio with minimization of clinical signs intensity. Also, carvacrol relieved oxidative stress, ameliorated the increased uric acid level and histopathological alterations in kidney and lung caused by viral infection.

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.

Infectious bronchitis virus in Australia: a model of coronavirus evolution - a review

Infectious bronchitis virus (IBV) was first isolated in Australia in 1962. Ongoing surveillance and characterization of Australian IBVs have shown that they have evolved separately from strains found throughout the rest of the world, resulting in the evolution of a range of unique strains and changes in the dominant wild-type strains, affecting tissue tropism, pathogenicity, antigenicity, and gene arrangement. Between 1961 and 1976 highly nephropathogenic genotype GI-5 and GI-6 strains, causing mortalities of 40% to 100%, predominated, while strains causing mainly respiratory disease, with lower mortality rates, have predominated since then. Since 1988, viruses belonging to two distinct and novel genotypes, GIII and GV, have been detected. The genome organization of the GIII strains has not been seen in any other gammacoronavirus. Mutations that emerged soon after the introduction of vaccination, incursion of strains with a novel lineage from unknown sources, recombination between IBVs from different genetic lineages, and gene translocations and deletions have contributed to an increasingly complex IBV population. These processes and the consequences of this variation for the biology of these viruses provide an insight into the evolution of endemic coronaviruses during their control by vaccination and may provide a better understanding of the potential for evolution of other coronaviruses, including SARS-CoV-2. Furthermore, the continuing capacity of attenuated IBV vaccines developed over 40 years ago to provide protection against viruses in the same genetic lineage provides some assurance that coronavirus vaccines developed to control other coronaviruses may continue to be effective for an extended period.

Host immune response to infectious bronchitis virus Q1 in two commercial broiler chicken lines

This study investigated the pathogenesis of infectious bronchitis virus (Gammacoronavirus) strain Q1 in two commercial broiler chicken lines, and the host immune response to infection. Chicks from each line were grouped into either infected or control. Following Q1 infection at day-old, fast (Line-A) and slow (Line-B) growing chicks were monitored for clinical signs and body weights. At 3, 7, 9, 14, 21 and 28 days post infection (dpi), five birds were humanely euthanised, and trachea, kidney and proventriculus tissues were collected for quantitative RT-PCR and histopathology. Blood was collected weekly to determine IBV-specific ELISA antibody titres. Q1 infection significantly reduced the body weights of Line-A chicks at 14 and 21 dpi, but there were no significant differences in Line-B. Through qRT-PCR, significantly higher viral loads were found in the trachea, proventriculus and kidney tissues of Line-A chicks at 7-9 dpi. At day-old and at 28 dpi, the mean antibody titre in Line-B was notably higher than Line-A. Significant IFN-α mRNA expression was noted in the trachea and kidneys of Line-A, whereas no change occurred in Line-B. Chicks in Line-B, compared to those in Line-A, demonstrated a tissue-dependent increase of IFN-β, TLR3, IL-1β and IL-6 and LITAF gene transcription responses to IBV Q1. It appears that the level of maternal antibodies, growth rates, and other inherent host genetic factors could have influenced the differences in viral loads and immune responses.

The Chicken MHC: Insights into Genetic Resistance, Immunity, and Inflammation Following Infectious Bronchitis Virus Infections

The chicken immune system has provided an immense contribution to basic immunology knowledge by establishing major landmarks and discoveries that defined concepts widely used today. One of many special features on chickens is the presence of a compact and simple major histocompatibility complex (MHC). Despite its simplicity, the chicken MHC maintains the essential counterpart genes of the mammalian MHC, allowing for a strong association to be detected between the MHC and resistance or susceptibility to infectious diseases. This association has been widely studied for several poultry infectious diseases, including infectious bronchitis. In addition to the MHC and its linked genes, other non-MHC loci may play a role in the mechanisms underlying such resistance. It has been reported that innate immune responses, such as macrophage function and inflammation, might be some of the factors driving resistance or susceptibility, consequently influencing the disease outcome in an individual or a population. Information about innate immunity and genetic resistance can be helpful in developing effective preventative measures for diseases such as infectious bronchitis, to which a systemic antibody response is often not associated with disease protection. In this review, we summarize the importance of the chicken MHC in poultry disease resistance, particularly to infectious bronchitis virus (IBV) infections and the role played by innate immunity and inflammation on disease outcome. We highlight how future studies focusing on the MHC and non-MHC genes can potentially bring clarity to observed resistance in some chicken B haplotype lines.

The Role of Host Genetic Factors in Coronavirus Susceptibility: Review of Animal and Systematic Review of Human Literature

BACKGROUND

The recent SARS-CoV-2 pandemic raises many scientific and clinical questions. One set of questions involves host genetic factors that may affect disease susceptibility and pathogenesis. New work is emerging related to SARS-CoV-2; previous work has been conducted on other coronaviruses that affect different species.

OBJECTIVES

We aimed to review the literature on host genetic factors related to coronaviruses, with a systematic focus on human studies.

METHODS

We conducted a PubMed-based search and analysis for articles relevant to host genetic factors in coronavirus. We categorized articles, summarized themes related to animal studies, and extracted data from human studies for analyses.

RESULTS

We identified 1,187 articles of potential relevance. Forty-five studies were related to human host genetic factors related to coronavirus, of which 35 involved analysis of specific genes or loci; aside from one meta-analysis on respiratory infections, all were candidate-driven studies, typically investigating small number of research subjects and loci. Multiple significant loci were identified, including 16 related to susceptibility to coronavirus (of which 7 identified protective alleles), and 16 related to outcomes or clinical variables (of which 3 identified protective alleles). The types of cases and controls used varied considerably; four studies used traditional replication/validation cohorts. Of the other studies, 28 involved both human and non-human host genetic factors related to coronavirus, 174 involved study of non-human (animal) host genetic factors related to coronavirus, 584 involved study of non-genetic host factors related to coronavirus, including involving immunopathogenesis, 16 involved study of other pathogens (not coronavirus), 321 involved other studies of coronavirus, and 18 studies were assigned to the other categories and removed.

KEY FINDINGS

We have outlined key genes and loci from animal and human host genetic studies that may bear investigation in the nascent host genetic factor studies of COVID-19. Previous human studies to date have been limited by issues that may be less impactful on current endeavors, including relatively low numbers of eligible participants and limited availability of advanced genomic methods.

Immunologic Pathways in Protective versus Maladaptive Host Responses to Attenuated and Pathogenic Strains of Mycoplasma gallisepticum

Mycoplasmas are small bacterial commensals or pathogens that commonly colonize host mucosal tissues and avoid rapid clearance, in part by stimulating inflammatory, immunopathogenic responses. We previously characterized a wide array of transcriptomic perturbations in avian host tracheal mucosae infected with virulent, immunopathologic Mycoplasma gallisepticum; however, mechanisms delineating these from protective responses, such as those induced upon vaccination, have not been thoroughly explored. In this study, host transcriptomic responses to two experimental M. gallisepticum vaccines were assessed during the first 2 days of infection. Relative to virulent infection, host metabolic and immune gene responses to both vaccines were greatly decreased, including early innate immune responses critical to disease development and subsequent adaptive immunity. These data specify host genes and potential mechanisms contributing to maladaptive versus beneficial host responses-information critical for design of vaccines efficacious in both limiting inflammation and enabling pathogen clearance.

Pathological changes, shedding pattern and cytokines responses in chicks infected with avian influenza-H9N2 and/or infectious bronchitis viruses

Avian influenza H9N2 (AIV-H9N2) and Infectious bronchitis (IB) viruses are the most commonly isolated viruses from poultry flocks suffering from respiratory signs with mortalities. The outcome of co-infection with both viruses hasn't been yet well understood. In this study, eighty 1-day-old specific pathogen free chicks were divided into four distinct groups. Group 1 remained uninfected as negative control group; groups 2, 3 and 4 were inoculated with either AIV-H9N2 or IBV or co infected with AIV-H9N2 followed by IBV three days post inoculation respectively. Chicks were monitored for clinical and pathological changes, virus shedding and both Interleukin-6 (IL6) and Interferon gamma (IFNγ) cytokines immune responses. Clinical signs varied from mild to moderate respiratory signs in all challenged groups but were more severe in group 4 with mortalities in groups 3 and 4. Tracheal shedding of both viruses washigher in group 4 than group 2 and 3. Mean AIV-H9 virus titer in lung and kidney was higher in group 4 than group 2 in all time points. IFNγ mRNA gene expression in lung was significantly lower in groups3 and 4. In conclusion, this study reports that co-infection of chicks with both viruses enhances the pathogenicity, increases both viruses shedding and extend AIV-H9 replication with impairment of IFNγ stimulation in lung.

Differential innate immune responses induced by classical and variant infectious bronchitis viruses in specific pathogen free chicks

Avian infectious bronchitis virus (IBV) continues to cause serious economic losses in global chicken production. Concurrent circulation of both classic and variant IBVs have been identified in most parts of the world, raising major challenges to global prevention and control efforts. Therefore, immunopathogenesis, particularly early host responses, needs to be better understood for effective control of diseases caused by different strains of IBVs. We investigated differing immunopathogenesis in chickens following infection with IS/885/00-like (885), QX-like (QX) and M41 IBV strains. We confirmed that the histopathological changes, proinflammatory and innate immune gene responses were induced to different magnitudes, depending on the IBV strain. Results indicated that upregulation of proinflammatory cytokines (such as IL-6 and IL-1β) and lipopolysaccharide-induced tumor necrosis factor-alpha factor (LITAF) expression is induced by IBV M41 in the trachea and by IBV 885 and QX in the kidney, which mainly coincides with tracheal and renal histopathological lesions respectively caused by these strains. In addition, elevated levels of TLR3, MDA5 and IFN-β expression occurred concurrently with greater lesion severity in IBV infected trachea and kidney tissues. Overall, this study reports marked differences in the activation of early host responses by pathogenic IBV strains.

Early immune responses and development of pathogenesis of avian infectious bronchitis viruses with different virulence profiles

Avian infectious bronchitis virus (IBV) primarily replicates in epithelial cells of the upper respiratory tract of chickens, inducing both morphological and immune modulatory changes. However, the association between the local immune responses induced by IBV and the mechanisms of pathogenesis has not yet been completely elucidated. This study compared the expression profile of genes related to immune responses in tracheal samples after challenge with two Brazilian field isolates (A and B) of IBV from the same genotype, associating these responses with viral replication and with pathological changes in trachea and kidney. We detected a suppressive effect on the early activation of TLR7 pathway, followed by lower expression levels of inflammatory related genes induced by challenge with the IBV B isolate when compared to the challenge with to the IBV A isolate. Cell-mediated immune (CMI) related genes presented also lower levels of expression in tracheal samples from birds challenged with B isolate at 1dpi. Increased viral load and a higher percentage of birds with relevant lesions were observed in both tracheal and renal samples from chickens exposed to challenge with IBV B isolate. This differential pattern of early immune responses developed after challenge with IBV B isolate, related to the downregulation of TLR7, leading to insufficient pro-inflammatory response and lower CMI responses, seem to have an association with a most severe renal lesion and an enhanced capability of replication of this isolate in chicken.

Outbreaks of Virulent Infectious Bursal Disease in Flocks of Battery Cage Brooding System of Commercial Chickens

Clinical and pathological investigations were conducted on outbreaks of infectious bursal disease (IBD) in pullets under brooding using the battery cage system in a commercial poultry farm in Kaduna, Nigeria. Two consecutive outbreaks of IBD on the same farm were studied. The onset of the disease and morbidity and mortality rates were recorded. Postmortem examinations were conducted and gross lesions recorded. Tissues were collected and fixed in 10% buffered formalin and processed for histopathological examinations. In the first outbreak, 80 to 100% of the chicks were affected at the age of 4 to 5 weeks and mortality rate was 95.8% and lasted for 9 days. In the second outbreak, the mortality rate was 43.3% and it also lasted for 9 days. At the onset of the disease, the birds were also 4-week-old like in case 1. The disease was diagnosed based on clinical signs, pathology, and agar gel immunodiffusion test (AGID). Clinical signs, gross lesions, and histopathological findings were characteristic of virulent infectious bursal disease. After the first outbreak (case 1) the house was disinfected using polidine® (iodophor compound), V-ox® (inorganic peroxygen compounds), CID₂₀® (quaternary ammonium chloride, aldehydes, and alcohol), terminator III® (phenols), and glutasan® (aldehyde and quaternary ammonium chloride). But they failed to eliminate the IBD virus from the poultry pen.

Small interfering RNA expression inhibits avian infectious bronchitis virus replication and inflammatory response

BACKGROUND

Avian infectious bronchitis virus (IBV) is a major cause of poor weight gain and mortality among chicks.

METHODS

A lentivirus vector was used to generate transgenic chickens expressing small interfering RNA (siRNA) targeting the M protein of IBV. Offspring of generation 0 (G0) were screened to identify G1 transgenic chickens (Tg). Monocytes from G1 Tg were stimulated with IBV in vitro.

RESULTS

Monocytes producing siRNA efficiently inhibit IBV replication. Expression of inflammatory cytokines, Mx protein and nitric oxide levels were lower in early IBV infection in Tg. In vivo experiments show that siRNA expression inhibits IBV replication, significantly decreases mortality and increases weight gain. Inflammatory responses and oxidative damage were significantly decreased, yielding minimal tissue injury. The inflammatory responses indicate that the cellular immune response is most effective during the initial stage, while the humoral immune response is more significant in later stages of infection.

CONCLUSIONS

Small interfering RNA expression inhibits avian IBV replication and inflammatory response.

The early immune response to infection of chickens with Infectious Bronchitis Virus (IBV) in susceptible and resistant birds

Background

Infectious Bronchitis is a highly contagious respiratory disease which causes tracheal lesions and also affects the reproductive tract and is responsible for large economic losses to the poultry industry every year. This is due to both mortality (either directly provoked by IBV itself or due to subsequent bacterial infection) and lost egg production. The virus is difficult to control by vaccination, so new methods to curb the impact of the disease need to be sought. Here, we seek to identify genes conferring resistance to this coronavirus, which could help in selective breeding programs to rear chickens which do not succumb to the effects of this disease.

Methods

Whole genome gene expression microarrays were used to analyse the gene expression differences, which occur upon infection of birds with Infectious Bronchitis Virus (IBV). Tracheal tissue was examined from control and infected birds at 2, 3 and 4 days post-infection in birds known to be either susceptible or resistant to the virus. The host innate immune response was evaluated over these 3 days and differences between the susceptible and resistant lines examined.

Results

Genes and biological pathways involved in the early host response to IBV infection were determined andgene expression differences between susceptible and resistant birds were identified. Potential candidate genes for resistance to IBV are highlighted.

Conclusions

The early host response to IBV is analysed and potential candidate genes for disease resistance are identified. These putative resistance genes can be used as targets for future genetic and functional studies to prove a causative link with resistance to IBV.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0575-6) contains supplementary material, which is available to authorized users.

Immune Responses to Virulent and Vaccine Strains of Infectious Bronchitis Viruses in Chickens

Infectious bronchitis (IB) is an acute and highly contagious chicken viral disease, causing severe economic losses to poultry producers worldwide. In the last few decades, infectious bronchitis virus (IBV) has been extensively studied, but knowledge of immune responses to virulent or vaccine strains of IBVs remains limited. This review focuses on fundamental aspects of immune responses against IBV, including the role of pattern recognition receptors (PRRs) in identification of conserved viral structures and the role of different components of innate immunity (e.g., heterophils, macrophages, dendritic cells, acute phase protein, and cytokines). Studies on adaptive immune activation and the role of humoral and cellular immunity in IBV clearance are also reviewed. Multiple interlinking immune responses are essential for protection against virulent IBVs, including passive, innate, adaptive, and effector T cells active at mucosal surfaces. Although the development of approaches for chicken transcriptome and proteome analyses have greatly helped the understanding of the underlying genetic mechanisms for immunity, there are still major knowledge gaps, such as the role of mucosal and cellular responses to IBVs. In view of recent reports of emergent IBV variants in many countries, there is renewed interest in a more complete understanding of poultry immune responses to both virulent and vaccine strains of IBVs. This will be critical for developing new vaccine or vaccination strategies and other intervention programs.

Increased expression of Interleukin-6 related to nephritis in chickens challenged with an Avian infectious bronchitis virus variant

A Brazilian field isolate (IBV/Brazil/PR05) of avian infectious bronchitis virus (IBV), associated with development of nephritis in chickens, was previously genotyped as IBV variant after S1 gene sequencing. The aim of this study was to evaluate the levels of IL-6 in kidneys and trachea of birds vaccinated and challenged with IBV/Brazil/PR05 strain, correlating these results with scores of microscopic lesions, specific IBV antigen detection and viral load. The up-regulation of IL-6 and the increased levels of viral load on renal and tracheal samples were significantly correlated with scores of microscopic lesions. Reduced levels of viral load were detected in kidneys of birds previously vaccinated and challenged, compared to non-vaccinated challenged group, although markedly microscopic lesions were observed for both groups. The expression of IL-6, present both in the kidney and in the tracheas, was dependent on the load of the virus present in the tissue, and the development of lesions was related with IL-6 present in the tissues. These data suggest that variant IBV/Brazil/PR05 can induce the expression of proinflammatory cytokines in a manner correlated with viral load and increased IL-6 is involved in the tissue with the influx of inflammatory cells and subsequent nephritis. This may contribute with a model to the development of immunosuppressive agents of IL-6 to prevent acute inflammatory processes against infection with IBV and perhaps other coronaviruses, as well as contribute to the understanding of the immunopathogenesis of IBV nephropatogenic strains.

Inflammatory and cell-mediated immune responses in the respiratory tract of chickens to infection with avian infectious bronchitis virus

Tracheal mucosa is the primary site of replication of avian infectious bronchitis virus (IBV), which leads to both morphologic and immune modulatory changes in this organ. To increase the understanding of the mechanisms involved in these processes, we focused on the evaluation of local inflammatory and cell-mediated immune responses after challenge with the M41 strain of IBV, associating these responses with pathologic changes in the tracheal mucosa. At 24 h post-infection, inflammatory cytokines related genes were significantly upregulated, including peaks of TNFSF15 and TGFβ mRNA production, although no tracheal microscopic alterations were observed and only a slightly increase in viral load occurred. At 3 days post-infection (dpi), we observed that the highest upregulation of IL6, IL1β, and IFNγ coincided with highest scores of viral load and microscopic lesions, suggesting a role of both these cytokines and virus load on the development of tracheal lesions. Later, at 7 dpi, the most prominent increases of CD8αα mRNA and Granzyme homolog A mRNA were followed by a significant decrease of scores of tracheal lesions and viral load. In conclusion, an early upregulation of expression of proinflammatory cytokines such as IL6, IL1β, and IFNγ induced by the M41 strain of IBV may be partially implicated in the viral pathogenicity on trachea tissues of nonimmune challenged chickens, in addition to a late induction of a putative protective immune responses by this virus through upregulation of CD8αα and Granzyme homolog A genes in this organ.

Altered pro-inflammatory cytokine mRNA levels in chickens infected with infectious bronchitis virus

Infectious bronchitis virus (IBV) replicates primarily in the respiratory tract and grows in various organs in chickens, with or without pathological effects. The diversity of this virus has been verified by sequence analysis of the S1 glycoprotein gene, but this method must be supplemented with further analysis for characterization of the agent. To increase our understanding of the pathogenesis of the disease caused by this virus, we investigated the response of chickens to 2 IBV with different genotypes, KIIa and ChVI. The clinical signs induced by the viruses were observed. In addition, the mRNA levels of the pro-inflammatory cytokines, IL-6, IL-1β, and lipopolysaccharide-induced tumor necrosis factor-α factor and the serum levels of α₁-acid glycoprotein, which is a major acute phase protein, were measured. The KIIa genotype (Kr/ADL110002/2011) induced clinical signs accompanied by the excessive production of pro-inflammatory cytokines and a higher viral load. In chickens infected with this isolate, simultaneous peaks in the viral copy number and cytokine production were observed at 7 dpi in the trachea and 9 d postinoculation in the kidney. On the other hand, the chickens infected with the ChVI genotype (Kr/ADL120003/2012) did not show a response other than a mild upregulation of cytokines at 1 d postinoculation, which appears to indicate the invasion of the virus. In summary, we confirmed a differential innate response following infection with distinct IBV. We hypothesize that an excessive innate response contributes to the scale of the pathophysiologic effect in chickens.

An assessment of opportunities to dissect host genetic variation in resistance to infectious diseases in livestock

This paper reviews the evidence for host genetic variation in resistance to infectious diseases for a wide variety of diseases of economic importance in poultry, cattle, pig, sheep and Atlantic salmon. Further, it develops a method of ranking each disease in terms of its overall impact, and combines this ranking with published evidence for host genetic variation and information on the current state of genomic tools in each host species. The outcome is an overall ranking of the amenability of each disease to genomic studies that dissect host genetic variation in resistance. Six disease-based assessment criteria were defined: industry concern, economic impact, public concern, threat to food safety or zoonotic potential, impact on animal welfare and threat to international trade barriers. For each category, a subjective score was assigned to each disease according to the relative strength of evidence, impact, concern or threat posed by that particular disease, and the scores were summed across categories. Evidence for host genetic variation in resistance was determined from available published data, including breed comparison, heritability studies, quantitative trait loci (QTL) studies, evidence of candidate genes with significant effects, data on pathogen sequence and on host gene expression analyses. In total, 16 poultry diseases, 13 cattle diseases, nine pig diseases, 11 sheep diseases and three Atlantic salmon diseases were assessed. The top-ranking diseases or pathogens, i.e. those most amenable to studies dissecting host genetic variation, were Salmonella in poultry, bovine mastitis, Marek's disease and coccidiosis, both in poultry. The top-ranking diseases or pathogens in pigs, sheep and Atlantic salmon were Escherichia coli, mastitis and infectious pancreatic necrosis, respectively. These rankings summarise the current state of knowledge for each disease and broadly, although not entirely, reflect current international research efforts. They will alter as more information becomes available and as genome tools become more sophisticated for each species. It is suggested that this approach could be used to rank diseases from other perspectives as well, e.g. in terms of disease control strategies.

Differences in genetic background influence the induction of innate and acquired immune responses in chickens depending on the virulence of the infecting infectious bursal disease virus (IBDV) strain

Previous studies and field observations have suggested that genetic background influences infectious bursal disease virus (IBDV) pathogenesis. However, the influence of the virulence of the infecting IBDV strain and the mechanisms underlying the differences in susceptibility are not known. In the present study IBDV pathogenesis was compared between specific-pathogen-free layer-type (LT) chickens, which are the most susceptible chicken for IBDV and have been used as the model for pathogenesis studies, and broiler-type (BT) chickens, which are known to be less susceptible to clinical infectious bursal disease (IBD). The innate and acquired immune responses were investigated after inoculation of an intermediate (i), virulent (v) or very virulent (vv) strain of IBDV. IBDV pathogenesis was comparable among genetic backgrounds after infection with iIBDV. After infection with vIBDV and vvIBDV, LT birds showed severe clinical disease and mortality, higher bursal lesion scores and IBDV-antigen load relative to BT birds. Circulating cytokine induction varied significantly in both timing and quantity between LT and BT birds and among virus strains (P<0.05). Evaluation of different immune cell populations by flow-cytometric analysis in the bursa of Fabricius provided circumstantial evidence of a stronger local T cell response in BT birds vs. LT birds after infection with the virulent strain. On the other hand, LT birds showed a more significant increase in circulating macrophage-derived immune mediators such as total interferon (IFN) and serum nitrite than BT birds on days 2 and 3 post-vIBDV infection (P<0.05). Stronger stimulation of innate immune reactions especially after vIBDV infection in the early phase may lead to faster and more severe lesion development accompanied by clinical disease and death in LT chickens relative to BT chickens. Interestingly, no significant differences were seen between genetic backgrounds in induction of the IBDV-specific humoral response: timing of IBDV-antibody induction and antibody levels were comparable between BT and LT birds. This study clearly demonstrates a significant influence of chickens' genetic background on disease outcome. The difference between backgrounds in IBDV susceptibility is further influenced by the virulence of the infecting virus strain.

Effects of stress, mimicked by administration of corticosterone in drinking water, on the expression of chicken cytokine and chemokine genes in lymphocytes

In this study, we identify molecular mediators that participate in the regulation of the immune response during corticosterone-induced stress in chickens. At 7 weeks of age, 120 chickens were exposed for 1 week to corticosterone treatment. Cytokine and chemokine mRNA expression levels were evaluated in peripheral blood and splenic lymphocytes. Expression levels of interleukin (IL)-1beta, IL-6, IL-18 and transforming growth factor (TGF)-beta4 mRNA were significantly up-regulated in lymphocytes 3 h after first treatment with corticosterone. TGF-beta4 and IL-18 remained elevated 1 week post-initial treatment. Compared with controls, corticosterone-treated birds showed greater expression levels of chemokine (CC) mRNA, particularly for CCLi2, CCL5 (RANTES), CCL16 and CXCLi1, in peripheral and splenic lymphocytes 3 h post-initial exposure. CCLi2 mRNA was highly expressed in splenocytes at all time-points. Administration of corticosterone significantly increased circulating corticosterone concentrations and decreased total lymphocyte counts at 3, 24 h and 1 week post-initiation of corticosterone treatment. There was a positive correlation between plasma corticosterone concentrations and CCL5 and CCL16 mRNA at 3 h post-initial administration. At 1 week post-initial treatment, corticosterone concentrations correlated positively with CCL5 and negatively with IL-18 mRNA level. Conditions associated with significant changes in corticosterone levels might therefore affect the immune response by increasing pro-inflammatory responses, leading to potential modulation of the Th1/Th2 balance.

Mouse hepatitis virus liver pathology is dependent on ADP-ribose-1''-phosphatase, a viral function conserved in the alpha-like supergroup

Viral infection of the liver can lead to severe tissue damage when high levels of viral replication and spread in the organ are coupled with strong induction of inflammatory responses. Here we report an unexpected correlation between the expression of a functional X domain encoded by the hepatotropic mouse hepatitis virus strain A59 (MHV-A59), the high-level production of inflammatory cytokines, and the induction of acute viral hepatitis in mice. X-domain (also called macro domain) proteins possess poly-ADP-ribose binding and/or ADP-ribose-1''-phosphatase (ADRP) activity. They are conserved in coronaviruses and in members of the "alpha-like supergroup" of phylogenetically related positive-strand RNA viruses that includes viruses of medical importance, such as rubella virus and hepatitis E virus. By using reverse genetics, we constructed a recombinant murine coronavirus MHV-A59 mutant encoding a single-amino-acid substitution of a strictly conserved residue that is essential for coronaviral ADRP activity. We found that the mutant virus replicated to slightly reduced titers in livers but, strikingly, did not induce liver disease. In vitro, the mutant virus induced only low levels of the inflammatory cytokines tumor necrosis factor alpha and interleukin-6 (IL-6). In vivo, we found that IL-6 production, in particular, was reduced in the spleens and livers of mutant virus-infected mice. Collectively, our data demonstrate that the MHV X domain exacerbates MHV-induced liver pathology, most likely through the induction of excessive inflammatory cytokine expression.