Platelet-Mediated NET Release Amplifies Coagulopathy and Drives Lung Pathology During Severe Influenza Infection.

The influenza A virus (IAV) causes a respiratory tract infection with approximately 10% of the population infected by the virus each year. Severe IAV infection is characterized by excessive inflammation and tissue pathology in the lungs. Platelet and neutrophil recruitment to the lung are involved in the pathogenesis of IAV, but the specific mechanisms involved have not been clarified. Using confocal intravital microscopy in a mouse model of IAV infection, we observed profound neutrophil recruitment, platelet aggregation, neutrophil extracellular trap (NET) production and thrombin activation within the lung microvasculature in vivo. Importantly, deficiency or antagonism of the protease-activated receptor 4 (PAR4) reduced platelet aggregation, NET production, and neutrophil recruitment. Critically, inhibition of thrombin or PAR4 protected mice from virus-induced lung tissue damage and edema. Together, these data imply thrombin-stimulated platelets play a critical role in the activation/recruitment of neutrophils, NET release and directly contribute to IAV pathogenesis in the lung.

Single stranded (ss)RNA-mediated antiviral response against infectious laryngotracheitis virus infection.

BACKGROUND: Single stranded ribonucleic acid (ssRNA) binds to toll-like receptor (TLR)7 leading to recruitment of immune cells and production of pro-inflammatory cytokines, which has been shown in mammals. In chickens, synthetic ssRNA analog, resiquimod, has been shown to elicit antiviral response against infectious bursal disease virus infection. The objective of this study was to determine the innate host responses activated by the pre-hatch in ovo administration of resiquimod against infectious laryngotracheitis virus (ILTV) infection in chickens post-hatch. RESULTS: First, we observed that in ovo treatment of resiquimod at embryo day (ED) 18 increases macrophage recruitment in respiratory and gastrointestinal tissues of chicken day 1 post-hatch in addition to interleukin (IL)-1ß in lungs. Second, we observed that in ovo treatment of resiquimod reduces ILTV cloacal shedding at 7 days post-infection (dpi) when challenged at day 1 post-hatch coinciding with higher macrophage recruitment. In vitro, we found that resiquimod enhances production of nitric oxide (NO) and IL-1ß and not type 1 interferon (IFN) activity in avian macrophages. Although, the antiviral response against ILTV is associated with the enhanced innate immune response, it is not dependent on any of the innate immune mediators observed as has been shown in vitro using avian macrophage. CONCLUSION: This study provides insights into the mechanisms of antiviral response mediated by resiquimod, particularly against ILTV infection in chicken.

Comparative features of infections of two Massachusetts (Mass) infectious bronchitis virus (IBV) variants isolated from Western Canadian layer flocks.

BACKGROUND: Infectious bronchitis virus (IBV) is one of the leading causes of mortality and morbidity in chickens. There are numerous serotypes and variants, which do not confer cross protection resulting in failure of currently used IBV vaccines. Although variant IBV isolates with major genetic differences have been subjected to comparative studies, it is unknown whether minor genetic differences in IBV variants within a serotype are different in terms of pathogenesis and eliciting host responses. Two Massachusetts (Mass) variant IBV isolates recovered from commercial layer flocks in the Western Canadian provinces of Alberta (AB) and Saskatchewan (SK) were compared genetically and evaluated for their pathogenicity, tissue distribution and ability to recruit and replicate in macrophages. RESULTS: Although whole genome sequencing of these two Mass IBV isolates showed low similarity with the M41 vaccinal strain, they had an identical nucleotide sequence at open reading frames (ORFs) 3a, 3b, envelop (E), matrix (M), 5a and 5b. The rest of the ORFs of these 2 IBV isolates showed 99.9% nucleotide similarity. However, upon experimental infection, we found that the IBV isolate originating from AB was different to the one that originated in SK due to higher tracheal lesion scores and lower lung viral replication and lower genome loads in cecal tonsils. Nevertheless, both IBV isolates elicited host responses characterized by significant macrophage recruitment to the respiratory tract and there was evidence that both IBV isolates replicated within tracheal and lung macrophages. CONCLUSIONS: Overall, this study shows that Mass variant IBV isolates, although possessing minor genetic variations, can lead to significant differences in pathogenicity in young chickens. Further studies are required to investigate the pathogenicity of these two Mass variant IBV isolates in laying hens.

Antiviral response elicited against avian influenza virus infection following activation of toll-like receptor (TLR)7 signaling pathway is attributable to interleukin (IL)-1ß production.

OBJECTIVE: Single stranded ribonucleic acid (ssRNA) binds to toll-like receptor (TLR)7 leading to recruitment of immune cells and production of pro-inflammatory cytokines, which has been shown in mammals. In chickens, ssRNA has been shown to elicit antiviral response against infectious bursal disease virus infection. The objectives of this study were to determine the pro-inflammatory mediators that are activated downstream of TLR7 signaling pathway in avian macrophages and their roles in antiviral response against avian influenza virus (AIV) infection. RESULTS: In this study, first, we stimulated avian macrophages with the analog of ssRNA, resiquimod, and found that the ssRNA was capable of increasing nitric oxide (NO) and interleukin (IL-1ß) production in avian macrophages. Second, we observed when the avian macrophages were stimulated with ssRNA, it elicits an antiviral response against AIV. Finally, we demonstrated that when we blocked the IL-1ß response using IL-1 receptor antagonist (IL-1Ra) and the NO production using a selective inhibitor of inducible nitric oxide synthase (iNOS), N-([3-(aminomethyl)phenyl]methyl)ethanimidamide dihydrochloride (1400 W), the antiviral response against AIV is attributable to IL-1ß production and not to the NO production. This study provides insights into the mechanisms of antiviral response mediated by ssRNA, particularly against AIV infection.

The In Ovo Delivery of CpG Oligonucleotides Protects against Infectious Bronchitis with the Recruitment of Immune Cells into the Respiratory Tract of Chickens.

The in ovo delivery of cytosine-guanosine (CpG) oligodeoxynucleotides (ODNs) protects chickens against many bacterial and viral infections, by activating the toll-like receptor (TLR)21 signaling pathway. Although the delivery of CpG ODNs in ovo at embryo day (ED) 18 has been shown to reduce infectious bronchitis virus (IBV) loads in embryonic chicken lungs pre-hatch, whether in ovo delivered CpG ODNs are capable of protecting chickens against a post-hatch challenge is unknown. Thus, our objectives were to determine the protective effect of the in ovo delivery of CpG ODNs at ED 18 against IBV infection encountered post-hatch and, then, to investigate the mechanisms of protection. We found significantly higher survival rates and reduced IBV infection in the chickens following the pre-treatment of the ED 18 eggs with CpG ODNs. At 3 days post infection (dpi), we found an increased recruitment of macrophages, cluster of differentiation (CD)8α+ and CD4+ T lymphocytes, and an up-regulation of interferon (IFN)-γ mRNA in the respiratory tract of the chickens. Overall, it may be inferred that CpG ODNs, when delivered in ovo, provide protection against IBV infection induced morbidity and mortality with an enhanced immune response.

Shell-Less Egg Syndrome (SES) Widespread in Western Canadian Layer Operations Is Linked to a Massachusetts (Mass) Type Infectious Bronchitis Virus (IBV) Isolate.

A disease with a sudden drop in egg production and shell-less eggs called, shell-less egg syndrome (SES) has been observed in Western Canada egg layer flocks since 2010. The etiology of this disease is not known. We hypothesize that SES is caused by an infectious bronchitis virus (IBV) strain since it is known that IBV replicates in the shell gland causing various eggshell abnormalities. In this study, we screened egg layer flocks, in the provinces of Alberta (AB) and Saskatchewan (SK), with and without a history of SES for the presence of IBV infection. During 2015⁻2016, a total of 27 egg layer flocks were screened in AB (n = 7) and SK (n = 20). Eighty-one percent of the screened flocks (n = 22) were positive for IBV infection. Thirty of these isolates were successfully characterized using molecular tools targeting the most variable spike (S) 1 gene. IBV isolates from this study clustered into three genotypes based on partial S1 gene variability. The majority of the IBV isolates (70%) were Massachusetts (Mass) type, and the rest were either Connecticut (Conn) type or an uncharacterized genotype with genetic characteristics of Mass and Conn types. Since the majority of the IBV isolates included within the Mass type, we used a Mass type IBV isolate to reproduce SES in specific pathogen free (SPF) white leghorn chickens in lay. Further studies are warranted to investigate whether other IBV isolates can cause SES, to clarify the pathogenesis of SES and to develop a vaccine in order to prevent SES as observed in Western Canadian layer flocks.

Toll-like receptor (TLR)4 signalling induces myeloid differentiation primary response gene (MYD) 88 independent pathway in avian species leading to type I interferon production and antiviral response.

Engagement of toll-like receptor (TLR)4 ligand, lipopolysaccharide (LPS) with TLR4 in mammals activates two downstream intracellular signaling routes; the myeloid differentiation primary response gene (MyD)88 dependent and independent pathways. However, existence of the later pathway leading to production of type I interferons (IFNs) in avian species has been debated due to conflicting observations. The objective of our study was to investigate whether LPS induces type I IFN production in chicken macrophages leading to antiviral response attributable to type I IFN. We found that LPS elicits type I IFN response dominated by IFN-ß production. We also found that reduction in infectious laryngotracheitis virus (ILTV) replication by LPS-mediated antiviral response is attributable to type I IFNs in addition to nitric oxide (NO). Our findings imply that LPS elicits both MyD88 dependent and independent pathways in chicken macrophages consequently eliciting anti-ILTV response attributable to production of both type I IFNs and NO.

Double-Stranded Ribonucleic Acid-Mediated Antiviral Response Against Low Pathogenic Avian Influenza Virus Infection.

Toll-like receptor (TLR)3 signaling pathway is known to induce type 1 interferons (IFNs) and proinflammatory mediators leading to antiviral response against many viral infections. Double-stranded ribonucleic acid (dsRNA) has been shown to act as a ligand for TLR3 and, as such, has been a focus as a potential antiviral agent in many host-viral infection models. Yet, its effectiveness and involved mechanisms as a mediator against low pathogenic avian influenza virus (LPAIV) have not been investigated adequately. In this study, we used avian fibroblasts to verify whether dsRNA induces antiviral response against H4N6 LPAIV and clarify whether type 1 IFNs and proinflammatory mediators such as interleukin (IL)-1ß are contributing to the dsRNA-mediated antiviral response against H4N6 LPAIV. We found that dsRNA induces antiviral response in avian fibroblasts against H4N6 LPAIV infection. The treatment of avian fibroblasts with dsRNA increases the expressions of TLR3, IFN-α, IFN-ß, and IL-1ß. We also confirmed that this antiviral response elicited against H4N6 LPAIV infection correlates, but is not attributable to type 1 IFNs or IL-1ß. Our findings imply that the TLR3 ligand, dsRNA, can elicit antiviral response in avian fibroblasts against LPAIV infection, highlighting potential value of dsRNA as an antiviral agent against LPAIV infections. However, further investigations are required to determine the potential role of other innate immune mediators or combination of the tested cytokines in the dsRNA-mediated antiviral response against H4N6 LPAIV infection.

Potential mediators of in ovo delivered double stranded (ds) RNA-induced innate response against low pathogenic avian influenza virus infection.

BACKGROUND: Toll like receptor (TLR) 3 is a critically important innate pattern recognizing receptor that senses many viral infections. Although, it has been shown that double stranded (ds) RNA can be used for the stimulation of TLR3 signaling pathway in a number of host-viral infection models, it's effectiveness as an antiviral agent against low pathogenic avian influenza virus (LPAIV) needs further investigation. METHODS: In this study, first, we delivered TLR3 ligand, dsRNA, in ovo at embryo day (ED)18 since in ovo route is routinely used for vaccination against poultry viral and parasitic infections and infected with H4N6 LPAIV 24-h post-treatment. A subset of in ovo dsRNA treated and control groups were observed for the expressions of TLR3 and type I interferon (IFN)s, mRNA expression of interleukin (IL)-1ß and macrophage recruitment coinciding with the time of H4N6 LPAIV infection (24 h post-treatment). Additionally, Day 1 chickens were given dsRNA intra-tracheally along with a control group and a subset of chickens were infected with H4N6 LPAIV 24-h post-treatment whereas the rest of the animals were observed for macrophage and type 1 IFN responses coinciding with the time of viral infection. RESULTS: Our results demonstrate that the pre-hatch treatment of eggs with dsRNA reduces H4N6 replication in lungs. Further studies revealed that in ovo delivery of dsRNA increases TLR3 expression, type I IFN production and number of macrophages in addition to mRNA expression of IL-1ß in lung 24-h post-treatment. The same level of induction of innate response was not evident in the spleen. Moreover, we discovered that dsRNA elicits antiviral response against LPAIV correlating with type I IFN activity in macrophages in vitro. Post-hatch, we found no difference in H4N6 LPAIV genome loads between dsRNA treated and control chickens although we observed higher macrophage recruitment and IFN-ß response coinciding with the time of viral infection. CONCLUSIONS: Our findings imply that the TLR3 ligand, dsRNA has antiviral activity in ovo and in vitro but not in chickens post-hatch and dsRNA-mediated innate host response is characterized by macrophage recruitment and expressions of TLR3 and type 1 IFNs.

In ovo CpG DNA delivery increases innate and adaptive immune cells in respiratory, gastrointestinal and immune systems post-hatch correlating with lower infectious laryngotracheitis virus infection.

Cytosine-guanosine deoxynucleotides (CpG) DNA can be delivered in ovo at embryo day (ED)18 for the stimulation of toll-like receptor (TLR)21 signaling pathway that ultimately protects chickens against a number of bacterial and viral infections. There is a dearth of information understanding the mechanisms of protection induced by in ovo delivered CpG DNA. The objective of this study was to determine the immune cell changes post-hatch following in ovo delivery of the TLR21 ligand, CpG DNA. In order to quantify changes of percentage of KUL01+, IgM+ B, cluster of differentiation (CD)4+ and CD8α+ cells, trachea, lung, duodenum, large intestine, spleen and bursa of Fabricius were collected on day 1 post-hatch. We found increased recruitments of KUL01+ cells, in organs of these body systems post-hatch following in ovo delivery of CpG DNA. Although IgM+ B cells, CD4+ and CD8α+ cells were increased in lungs and immune system organs, these cells were not quantifiable from the trachea, duodenum and large intestine immediately following the hatch. Furthermore, when CpG DNA is delivered in ovo and subsequently infected with infectious laryngotracheitis virus (ILTV) post-hatch on day 1, CpG DNA reduces morbidity and mortality resulting from ILTV infection. This study provides insights into the mechanisms of host responses elicited following in ovo delivery of CpG DNA in avian species.

Low pathogenic avian influenza virus infection increases the staining intensity of KUL01+ cells including macrophages yet decrease of the staining intensity of KUL01+ cells using clodronate liposomes did not affect the viral genome loads in chickens.

The effect of depletion of macrophages using clodronate liposomes as well as macrophage response following viral infections have been studied in various mouse-virus infection models, but they have not been extensively studied in chickens relevant to virus infections. When we infected day 6 chickens with H4N6 low pathogenic avian influenza virus (LPAIV), we observed that H4N6 LPAIV infection increased the staining intensity of KUL01+ cells in trachea, lungs and duodenum of chickens at 3 days post-infection. Then, we used clodronate liposomes intra-abdominally in 5 day-old chickens and found significant reduction of staining intensity of KUL01+ cells in trachea and duodenum but not in lungs at 4 days post-treatment. When we infected the clodronate liposome and PBS liposome treated chickens with H4N6 LPAIV intra-nasally at day 6, we found no effect on H4N6 LPAIV genome loads in trachea, lungs and duodenum of chickens. This study indicates that although KUL01+ cell intensity are increased in respiratory and gastrointestinal tissues in chickens following H4N6 LPAIV infection, the decrease of KUL01+ cell intensity using clodronate liposomes did not change the H4N6 LPAIV genome loads in any of the examined tissues suggesting that KUL01+ cells may not be critical during H4N6 LPAIV infection in chicken.

Induction of innate host responses characterized by production of interleukin (IL)-1ß and recruitment of macrophages to the respiratory tract of chickens following infection with infectious bronchitis virus (IBV).

Infectious bronchitis virus (IBV) infection is a major cause of economic losses to the poultry industry. Due to limitations in current control measures, alternative approaches, based on thorough understanding of the host responses are required. As one of the key component of the avian immune system, the innate immune system has a crucial role in limiting virus replication at the initial stage of the infection. As parts of the innate host response, macrophages and cytokines, such as interleukin (IL)-1ß, are critical components as shown in other host-virus infection models. Since information on the importance of macrophages and IL-1ß in IBV infection in chickens is limited, our objective was to determine the association of IL-1ß, originating from avian macrophages and IBV infection in the trachea and lung. Following experimental IBV infection in 6 days old chickens, we found increased production of IL-1ß and increased recruitment of macrophages in the respiratory tract. Towards the end of the study (5 and 7 days following the IBV infection), the recruited macrophages appear to be a significant source IL-1ß. However, only the recruitment of macrophages in the lung correlated with IBV genome loads in this tissue. In conclusion, the present study demonstrates that recruitment of macrophages and the production of IL-1ß originating from macrophages, as well as other sources, occur following IBV infection in the respiratory tract suggesting potential roles of these mediators in the host responses to IBV infection. However, further studies are warranted to elucidate whether macrophages and IL-1ß are the causes of reduced IBV genome loads in the respiratory tract and also to investigate whether immune mediators that were not measured in the current study were involved in reducing IBV genome load in the respiratory tract towards the end of the study.

Hatchery Vaccination Against Poultry Viral Diseases: Potential Mechanisms and Limitations.

Commercial broiler and layer chickens are heavily vaccinated against economically important viral diseases with a view of preventing morbidity, mortality, and production impacts encountered during short production cycles. Hatchery vaccination is performed through in ovo embryo vaccination prehatch or spray and subcutaneous vaccinations performed at the day of hatch before the day-old chickens are being placed in barns with potentially contaminated environments. Commercially, multiple vaccines (e.g., live, live attenuated, and viral vectored vaccines) are available to administer through these routes within a short period (embryo day 18 prehatch to day 1 posthatch). Although the ability to mount immune response, especially the adaptive immune response, is not optimal around the hatch, it is possible that the efficacy of these vaccines depends partly on innate host responses elicited in response to replicating vaccine viruses. This review focuses on the current knowledge of hatchery vaccination in poultry and potential mechanisms of hatchery vaccine-mediated protective responses and limitations.

Infectious bronchitis corona virus establishes productive infection in avian macrophages interfering with selected antimicrobial functions.

Infectious bronchitis virus (IBV) causes respiratory disease leading to loss of egg and meat production in chickens. Although it is known that macrophage numbers are elevated in the respiratory tract of IBV infected chickens, the role played by macrophages in IBV infection, particularly as a target cell for viral replication, is unknown. In this study, first, we investigated the ability of IBV to establish productive replication in macrophages in lungs and trachea in vivo and in macrophage cell cultures in vitro using two pathogenic IBV strains. Using a double immunofluorescent technique, we observed that both IBV Massachusetts-type 41 (M41) and Connecticut A5968 (Conn A5968) strains replicate in avian macrophages at a low level in vivo. This in vivo observation was substantiated by demonstrating IBV antigens in macrophages following in vitro IBV infection. Further, IBV productive infection in macrophages was confirmed by demonstrating corona viral particles in macrophages and IBV ribonucleic acid (RNA) in culture supernatants. Evaluation of the functions of macrophages following infection of macrophages with IBV M41 and Conn A5968 strains revealed that the production of antimicrobial molecule, nitric oxide (NO) is inhibited. It was also noted that replication of IBV M41 and Conn A5968 strains in macrophages does not interfere with the induction of type 1 IFN activity by macrophages. In conclusion, both M41 and Con A5968 IBV strains infect macrophages in vivo and in vitro resulting productive replications. During the replication of IBV in macrophages, their ability to produce NO can be affected without affecting the ability to induce type 1 IFN activity. Further studies are warranted to uncover the significance of macrophage infection of IBV in the pathogenesis of IBV infection in chickens.

Toll-like receptor (TLR)21 signalling-mediated antiviral response against avian influenza virus infection correlates with macrophage recruitment and nitric oxide production.

Cytosine-guanosinedeoxynucleotide (CpG) DNA can be used for the stimulation of the toll-like receptor (TLR)21 signalling pathway in avian species which ultimately leads to up-regulation of gene transcription for pro-inflammatory molecules including nitric oxide and recruitment of innate immune cells. The objective of this study was to determine the antiviral effect of NO, produced in response to in ovo delivery of CpG DNA, against avian influenza virus (AIV) infection. We found that when CpG DNA is delivered at embryo day (ED)18 in ovo and subsequently challenged with H4N6 AIV at ED19 pre-hatch and day 1 post-hatching, CpG DNA reduces H4N6 AIV replication associated with enhanced NO production and macrophage recruitment in lungs. In vitro, we showed that NO originating from macrophages is capable of eliciting an antiviral response against H4N6 AIV infection. This study provides insights into the mechanisms of CpG DNA-mediated antiviral response, particularly against AIV infection in avian species.

Activation of toll-like receptor signaling pathways leading to nitric oxide-mediated antiviral responses.

Toll-like receptors (TLRs), well-characterized pattern-recognizing receptors of the innate arm of the immune system, are vital in detecting pathogen-associated molecular patterns (PAMPs). The TLR-PAMP interaction initiates an intracellular signaling cascade, predominantly culminating in upregulation of antiviral components, including inducible nitric oxide synthase (iNOS). After activation, various TLR pathways can promote iNOS production via the myeloid differentiation primary response-88 (MyD-88) adapter protein. Subsequently, iNOS facilitates production of nitric oxide (NO), a highly reactive and potent antiviral molecule that can inhibit replication of RNA and DNA viruses. Furthermore, NO can diffuse freely across cell membranes and elicit antiviral mechanisms in various ways, including direct and indirect damage to viral genomes. This review emphasizes current knowledge of NO-mediated antiviral responses elicited after activation of TLR signaling pathways.