Interferon regulatory factor 7- (IRF7-) mediated immune response affects Newcastle disease virus replication in chicken embryo fibroblasts

Infectious bronchitis virus nucleocapsid protein suppressed type I interferon production by interfering with the binding of MDA5-dsRNA and interacting with LGP2

The type I interferon (IFN-I) is a critical component of the innate immune responses, and Coronaviruses (CoVs) from both the Alphacoronavirus and Betacoronavirus genera interfere with the IFN-I signaling pathway in various ways. Of the gammacoronaviruses that mainly infect birds, little is known about how infectious bronchitis virus (IBV), evades or interferes with the innate immune responses in avian hosts since few IBV strains have been adapted to grow in avian passage cells. Previously, we reported that a highly pathogenic IBV strain GD17/04 has adaptability in an avian cell line, providing a material basis for further study on the interaction mechanism. In the present work, we describe the suppression of IBV to IFN-I and the potential role of IBV-encoded nucleocapsid (N) protein. We show that IBV significantly inhibits the poly I: C-induced IFN-I production, accordingly the nuclear translocation of STAT1, and the expression of IFN-stimulated genes (ISGs). A detailed analysis revealed that N protein, acting as an IFN-I antagonist, significantly impedes the activation of the IFN-β promoter stimulated by MDA5 and LGP2 but does not counteract its activation by MAVS, TBK1, and IRF7. Further results showed that IBV N protein, verified to be an RNA-binding protein, interferes with MDA5 recognizing double-stranded RNA (dsRNA). Moreover, we found that the N protein targets LGP2, which is required in the chicken IFN-I signaling pathway. Taken together, this study provides a comprehensive analysis of the mechanism by which IBV evades avian innate immune responses.

Targeted knockout of Mx in the DF-1 chicken fibroblast cell line impairs immune response against Newcastle disease virus

Newcastle disease virus (NDV) is an RNA virus taking poultry as the host, and the Newcastle disease (ND) caused by NDV is one of the diseases with serious damage to the health of poultry. Mx encoding by myxovirus resistance gene, induced by type I interferon (IFN), has a wide range of antiviral and GTPase activities in human, mice, and other species via inhibition virus replication. However, the antiviral ability of chicken Mx is still a controversial issue. To explore the effect of chicken Mx post-NDV infection, Mx-knockout DF-1 cells were constructed via CRISPR/Cas9 gene editing system. The number of copies of NDV was detected by RT-qPCR, and the mRNA expression levels of IRF-7, IFN-α, IFN-β, TNF-α, p21, p27, and Bak in DF-1 cells were analyzed after NDV infection. Compared with control cells, virus titers were much higher in Mx-knockout DF-1 cells post-NDV infection. The deficiency of Mx aggravated the cell pathological features post-NDV infection, and promoted the expression levels of IRF-7, IFN-α, IFN-β, and pro-inflammatory cytokine TNF-α in host cells. In addition, cells with Mx deficiency could alleviate the harm from virus by enhancing the expression of p21, p27, and Bak, which related to cell proliferation apoptosis. In conclusion, Mx played an important role in antivirus invasion. In the absence of Mx, cells could alleviate the harm from virus infection via retarding cell proliferation and enhancing cell apoptosis.

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.

Chicken interferon regulatory factor 7 (IRF7) can control ALV-J virus infection by triggering type I interferon production through affecting genes related with innate immune signaling pathway

In order to breed new birds with strong disease resistance, it is necessary to first understand the mechanism of avian antiviral response. Interferon regulatory factor 7 (IRF7) is not only a member of type I interferons (IFNs) regulatory factor (IRFs) family, but also a major regulator of the IFN response in mammals. However, whether IRF7 is involved in the host innate immune response remains unclear in poultry, due to the absence of IRF3. Here, we first observed by HE stains that with the increase of the time of ALV-J challenge, the thymus was obviously loose and swollen, the arrangement of liver cell was disordered, and the bursa of fabricius formed vacuolated. Real-time PCR detection showed that the expression level of IRF7 gene and related immune genes in ALV-J group was significantly higher than that in control group (P < 0.05). To further study the role of chicken IRF7 during avian leukosis virus subgroup J (ALV-J) infection, we constructed an induced IRF7 overexpression and interfered chicken embryo fibroblasts (CEFs) cell and performed in vitro infection using low pathogenic ALV-J and virus analog poly(I:C). In ALV-J and poly(I:C) stimulated CEFs cells, the expression level of STAT1, IFN-α, IFN-β, TLR3 and TLR7 were increased after IRF7 overexpressed, while the results were just the opposite after IRF7 interfered, which indicating that IRF7 may be associated with Toll-like receptor signaling pathway and JAK-STAT signaling pathway. These findings suggest that chicken IRF7 is an important regulator of IFN and is involved in chicken anti-ALV-J innate immunity.

Towards Improved Use of Vaccination in the Control of Infectious Bronchitis and Newcastle Disease in Poultry: Understanding the Immunological Mechanisms

Infectious bronchitis (IB) and Newcastle disease (ND) are two important diseases of poultry and have remained a threat to the development of the poultry industry in many parts of the world. The immunology of avian has been well studied and numerous vaccines have been developed against the two viruses. Most of these vaccines are either inactivated vaccines or live attenuated vaccines. Inactivated vaccines induce weak cellular immune responses and require priming with live or other types of vaccines. Advanced technology has been used to produce several types of vaccines that can initiate prime immune responses. However, as a result of rapid genetic variations, the control of these two viral infections through vaccination has remained a challenge. Using various strategies such as combination of live attenuated and inactivated vaccines, development of IB/ND vaccines, use of DNA vaccines and transgenic plant vaccines, the problem is being surmounted. It is hoped that with increasing understanding of the immunological mechanisms in birds that are used in fighting these viruses, a more successful control of the diseases will be achieved. This will go a long way in contributing to global food security and the economic development of many developing countries, given the role of poultry in the attainment of these goals.

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

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

Newcastle disease virus RNA-induced IL-1β expression via the NLRP3/caspase-1 inflammasome

Newcastle disease virus (NDV) infection causes severe inflammation and is a highly contagious disease in poultry. Virulent NDV strains (GM) induce large quantities of interleukin-1β (IL-1β), which is the central mediator of the inflammatory reaction. Excessive expression of IL-1β exacerbates inflammatory damage. Therefore, exploring the mechanisms underlying NDV-induced IL-1β expression can aid in further understanding the pathogenesis of Newcastle disease. Here, we showed that anti-IL-1β neutralizing antibody treatment decreased body temperature and mortality following infection with virulent NDV. We further explored the primary molecules involved in NDV-induced IL-1β expression from the perspective of both the host and virus. This study showed that overexpression of NLRP3 resulted in increased IL-1β expression, whereas inhibition of NLRP3 or caspase-1 caused a significant reduction in IL-1β expression, indicating that the NLRP3/caspase-1 axis is involved in NDV-induced IL-1β expression. Moreover, ultraviolet-inactivated GM (chicken/Guangdong/GM/2014) NDV failed to induce the expression of IL-1β. We then collected virus from GM-infected cell culture supernatant using ultracentrifugation, extracted the viral RNA, and stimulated the cells further with GM RNA. The results revealed that RNA alone was capable of inducing IL-1β expression. Moreover, NLRP3/caspase-1 was involved in GM RNA-induced IL-1β expression. Thus, our study elucidated the critical role of IL-1β in the pathogenesis of Newcastle disease while also demonstrating that inhibition of IL-1β via anti-IL-1β neutralizing antibodies decreased the damage associated with NDV infection; furthermore, GM RNA induced IL-1β expression via NLRP3/caspase-1.

Knockout of IRF7 Highlights its Modulator Function of Host Response Against Avian Influenza Virus and the Involvement of MAPK and TOR Signaling Pathways in Chicken

Interferon regulatory factor 7 (IRF7) is known as the master transcription factor of the type I interferon response in mammalian species along with IRF3. Yet birds only have IRF7, while they are missing IRF3, with a smaller repertoire of immune-related genes, which leads to a distinctive immune response in chickens compared to in mammals. In order to understand the functional role of IRF7 in the regulation of the antiviral response against avian influenza virus in chickens, we generated IRF7^-/- chicken embryonic fibroblast (DF-1) cell lines and respective controls (IRF7^wt) by utilizing the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) system. IRF7 knockout resulted in increased viral titers of low pathogenic avian influenza viruses. Further RNA-sequencing performed on H6N2-infected IRF7^-/- and IRF7^wt cell lines revealed that the deletion of IRF7 resulted in the significant down-regulation of antiviral effectors and the differential expression of genes in the MAPK (mitogen-activated protein kinase) and mTOR (mechanistic target of rapamycin) signaling pathways. Dynamic gene expression profiling of the host response between the wildtype and IRF7 knockout revealed potential signaling pathways involving AP1 (activator protein 1), NF-κB (nuclear factor kappa B) and inflammatory cytokines that may complement chicken IRF7. Our findings in this study provide novel insights that have not been reported previously, and lay a solid foundation for enhancing our understanding of the host antiviral response against the avian influenza virus in chickens.

IFN-γ establishes interferon-stimulated gene-mediated antiviral state against Newcastle disease virus in chicken fibroblasts

Newcastle disease virus (NDV) causes severe economic losses through severe morbidity and mortality and poses a significant threat to the global poultry industry. Significant efforts have been made to develop novel vaccines and therapeutics; however, the interaction of NDV with the host is not yet fully understood. Interferons (IFNs), an integral component of innate immune signaling, act as the first line of defense against invading viruses. Compared with the mammalian repertoire of IFNs, limited information is available on the antiviral potential of IFNs in chickens. Here, we expressed chicken IFN-γ (chIFN-γ) using a baculovirus expression vector system, characterized its antiviral potential against NDV, and determined its antiviral potential. Priming of chicken embryo fibroblasts with chIFN-γ elicited an antiviral environment in primary cells, which was mainly due to interferon-stimulated genes (ISGs). A genome-wide transcriptomics approach was used to elucidate the possible signaling pathways associated with IFN-γ-induced immune responses. RNA-sequencing (RNA-seq) data revealed significant induction of ISG-associated pathways, activated temporal expression of ISGs, antiviral mediators, and transcriptional regulators in a cascade of antiviral responses. Collectively, we found that IFN-γ significantly elicited an antiviral response against NDV infection. These data provide a foundation for chIFN-γ-mediated antiviral responses and underpin functional annotation of these important chIFN-γ-induced antiviral influencers.

Gga-miR-19b-3p Inhibits Newcastle Disease Virus Replication by Suppressing Inflammatory Response via Targeting RNF11 and ZMYND11

Newcastle disease (ND), an acute and highly contagious avian disease caused by virulent Newcastle disease virus (NDV), often results in severe economic losses worldwide every year. Although it is clear that microRNAs (miRNAs) are implicated in modulating innate immune response to invading microbial pathogens, their role in host defense against NDV infection remains largely unknown. Our prior study indicates that gga-miR-19b-3p is up-regulated in NDV-infected DF-1 cells (a chicken embryo fibroblast cell line) and functions to suppress NDV replication. Here we report that overexpression of gga-miR-19b-3p promoted the production of NDV-induced inflammatory cytokines and suppressed NDV replication, whereas inhibition of endogenous gga-miR-19b-3p expression had an opposite effect. Dual-luciferase and gene expression array analyses revealed that gga-miR-19b-3p directly targets the mRNAs of ring finger protein 11 (RNF11) and zinc-finger protein, MYND-type containing 11 (ZMYND11), two negative regulators of nuclear factor kappa B (NF-κB) signaling, in DF-1 cells. RNF11 and ZMYND11 silencing by small interfering RNA (siRNA) induced NF-κB activity and inflammatory cytokine production, and suppressed NDV replication; whereas ectopic expression of these two proteins exhibited an opposite effect. Our study provides evidence that gga-miR-19b-3p activates NF-κB signaling by targeting RNF11 and ZMYND11, and that enhanced inflammatory cytokine production is likely responsible for the suppression of NDV replication.

IRF7 Is Involved in Both STING and MAVS Mediating IFN-β Signaling in IRF3-Lacking Chickens

IFN regulatory factor (IRF) 3 has been identified as the most critical regulator of both RNA and DNA virus-induced IFN production in mammals. However, ambiguity exists in research on chicken IRFs; in particular IRF3 seems to be missing in chickens, making IFN regulation in chickens unclear. In this study, we comprehensively investigated the potential IFN-related IRFs in chickens and showed that IRF7 is the most critical IFN-β regulator in chickens. With a chicken IRF7 (chIRF7) knockout DF-1 cell line, we conducted a series of experiments to demonstrate that chIRF7 is involved in both chicken STING (chSTING)- and chicken MAVS (chMAVS)-mediated IFN-β regulation in response to DNA and RNA viral infections, respectively. We further examined the mechanisms of chIRF7 activation by chSTING. We found that chicken TBK1 (chTBK1) is indispensable for chIRF7 activation by chSTING as well as that chSTING interacts with both chIRF7 and chTBK1 to function as a scaffold in chIRF7 activation by chTBK1. More interestingly, we discovered that chSTING mediates the activation of chIRF7 through a conserved SLQxSyS motif. In short, we confirmed that although IRF3 is missing in chickens, they employ IRF7 to reconstitute corresponding IFN signaling to respond to both DNA and RNA viral infections. Additionally, we uncovered a mechanism of chIRF7 activation by chSTING. The results will enrich and deepen our understanding of the regulatory mechanisms of the chicken IFN system.

Cytokine expression in chicken embryo fibroblasts in response to infection with virulent or lentogenic avian avulavirus 1 (AAvV-1)

To investigate cytokine expression in chicken embryo fibroblast (CEF) cells, a virulent avian avulavirus 1 (AAvV-1) strain called SG10 that rapidly causes 100% mortality in its host, and a vaccine strain (La Sota) were characterized. Real-time quantitative PCR was performed on RNA samples from CEF cells, which were collected at 0, 24, 48 and 72 h post-infection. The dynamic expression patterns of ten cytokines (TNF-α, IFN-α, IFN-β, IL-1β, IL-2, IL-6, IL-10, IL-13, IL-15 and IL-18) were investigated. The results showed that infection with lentogenic La Sota induced significantly higher levels of the antiviral cytokines IFN-α and IFN-β, proinflammatory cytokines IL-2, IL-15 and IL-18, and the anti-inflammatory cytokine IL-10, than did infection with virulent SG10. Furthermore, the SG10 strain induced dramatically higher levels of the inflammatory cytokine IL-6 than those observed in cells infected with La Sota. However, the expression patterns of the other cytokines that were tested did not show any obvious trends or statistically significant differences between cells infected with the virulent and avirulent strains. These data show that infection with lentogenic La Sota induced more effective immune responses and anti-viral effects than did infection with virulent SG10 in CEFs. Our data provide distinct expression patterns of IFNs and proinflammatory and anti-inflammatory cytokines to AAvV-1 by virulence in CEF cells.

Chicken interferon regulatory factor 1 (IRF1) involved in antiviral innate immunity via regulating IFN-β production

Interferon regulatory factors (IRFs) is an important family for IFN expression regulating while viral infection. IRF1, IRF3, and IRF7 are the primary regulators that trigger type I IFN response in mammals. However, IRF3, which has been identified as the most critical regulator in mammals, is absent in chickens, and it is unknown whether IRF1 is involved in type I IFN signaling pathways in IRF3-deficient chicken cells. Here, we identified chicken IRF1 (chIRF1) as a critical IFN-β mediator in response to viral infection. Overexpression of chIRF1 activated IFN-β intensively and suppressed AIV and NDV viral replication. Moreover, the mRNA levels of IFN-β and ISGs increased during chIRF1 overexpression. In addition, deletion mutant analysis revealed that the first four domains of chIRF1 are indispensable for IFN-β induction. Together, our studies demonstrate that chIRF1 is an important regulator of IFN-β and is involved in chicken antiviral innate immunity.

Overexpression of Chicken IRF7 Increased Viral Replication and Programmed Cell Death to the Avian Influenza Virus Infection Through TGF-Beta/FoxO Signaling Axis in DF-1

During mammalian viral infections, interferon regulatory factor 7 (IRF7) partners with IRF3 to regulate the type I interferon response. In chickens, however, it is still unclear how IRF7 functions in the host innate immune response, especially given that IRF3 is absent. To further elucidate the functional role of chicken IRF7 during avian influenza virus (AIV) infection, we generated inducible IRF7 overexpression DF-1 cell lines and performed in vitro infection using low pathogenic AIVs (LPAIVs). Overexpression of IRF7 resulted in higher viral replication of H6N2 and H10N7 LPAIVs compared to empty vector control cells regardless of IRF7 expression level. In addition, a high rate of induced cell death was observed due to elevated level of IRF7 upon viral infection. RNA-seq and subsequent transcriptome analysis of IRF7 overexpression and control cells discovered candidate genes possibly controlled by chicken IRF7. Functional annotation revealed potential pathways modulated by IRF7 such as TGF-beta signaling pathway, FoxO signaling pathway and cell structural integrity related pathways. Next, we analyzed the host response alteration due to the IRF7 overexpression and additionally discovered the possible connection of chicken IRF7 and JAK-STAT signaling pathway. These findings suggest that chicken IRF7 could modulate a wide range of cellular processes in the host innate immune response thus meticulous control of IRF7 expression is crucial to the host in response to AIV infection.

Duck interferon regulatory factor 7 (IRF7) can control duck Tembusu virus (DTMUV) infection by triggering type I interferon production and its signal transduction pathway

Human interferon regulatory factor 7 (IRF7) plays an important role in the innate antiviral immune response. To date, the characteristics and functions of waterfowl IRF7 have not been clarified. This study reports the cDNA sequence, tissue distribution, and antiviral function of duck IRF7. The duck IRF7 gene has a 1536-bp open read frame (ORF) and encodes a 511-amino acid polypeptide. IRF7 is highly expressed in the blood and pancreas of 5-day-old ducklings and in the small intestine, large intestine and liver of 60-day-old adult ducks. Indirect immunofluorescence assay (IFA) showed that over-expressed duck IRF7 was located in both the cytoplasm and nucleus of transfected duck embryo fibroblasts (DEFs), which was also observed in poly(I:C)-stimulated or duck Tembusu virus (DTMUV)-infected DEFs. Titres and copies of DTMUV were significantly reduced in DEFs overexpressing IRF7. Moreover, overexpression of duck IRF7 significantly induced IFNα/β, but not IFNγ, mRNA expression, and transcription of downstream interferon-stimulated genes (ISGs), such as MX, OASL and IL-6, which were significantly induced by poly(I:C) co-stimulation, was enhanced. Additionally, duck IRF7 overexpression can significantly activate the IFNβ promoter in DEFs. Collectively, duck IRF7 plays an important role in host anti-DTMUV immune regulation, which depends on type I interferons and associated signal transduction pathway(s).

Avian Interferons and Their Antiviral Effectors

Interferon (IFN) responses, mediated by a myriad of IFN-stimulated genes (ISGs), are the most profound innate immune responses against viruses. Cumulatively, these IFN effectors establish a multilayered antiviral state to safeguard the host against invading viral pathogens. Considerable genetic and functional characterizations of mammalian IFNs and their effectors have been made, and our understanding on the avian IFNs has started to expand. Similar to mammalian counterparts, three types of IFNs have been genetically characterized in most avian species with available annotated genomes. Intriguingly, chickens are capable of mounting potent innate immune responses upon various stimuli in the absence of essential components of IFN pathways including retinoic acid-inducible gene I, IFN regulatory factor 3 (IRF3), and possibility IRF9. Understanding these unique properties of the chicken IFN system would propose valuable targets for the development of potential therapeutics for a broader range of viruses of both veterinary and zoonotic importance. This review outlines recent developments in the roles of avian IFNs and ISGs against viruses and highlights important areas of research toward our understanding of the antiviral functions of IFN effectors against viral infections in birds.

Generation and evaluation of a genetically attenuated Newcastle disease virus rGM-VIIm as a genotype-matched vaccine

Despite intensive vaccination campaigns, outbreaks of Newcastle disease (ND) have been frequently reported in China, especially of genotype VII that first emerged in the late 1990s. Given the dire need for vaccines against the circulating genotype VII virus, we developed an alternative method to recover a highly virulent recombinant GM (rGM) virus that involves a T7 system with a hammerhead ribozyme sequence introduced downstream of the T7 promoter. By changing the F₀ polybasic cleavage site RRQKR↓F to the monobasic GRQGR↓L, we generated a mutant virus (rGM-VIIm) that was found to be highly attenuated in chickens. The rGM-VIIm virus not only produced fourfold higher hemagglutination assay (HA) titers than the parental virus, but also exhibited genetic stability after 15 continuous passages in specific-pathogen-free (SPF) embryonated eggs. Whether live or inactivated, rGM-VIIm and LaSota vaccines can protect vaccinated birds from GM challenge infection. However, live and inactivated rGM-VIIm vaccines reduced virus shedding of the homologous challenge virus significantly better than the LaSota virus vaccine did. Altogether, our results suggest that rGM-VIIm vaccines could aid in the control of ND in China.

Phylogenetic and Pathotypic Characterization of Newcastle Disease Viruses Circulating in South China and Transmission in Different Birds

Although Newcastle disease virus (NDV) with high pathogenicity has frequently been isolated in poultry in China since 1948, the mode of its transmission among avian species remains largely unknown. Given that various wild bird species have been implicated as sources of transmission, in this study we genotypically and pathotypically characterized 23 NDV isolates collected from chickens, ducks, and pigeons in live bird markets (LBMs) in South China as part of an H7N9 surveillance program during December 2013–February 2014. To simulate the natural transmission of different kinds of animals in LBMs, we selected three representative NDVs—namely, GM, YF18, and GZ289—isolated from different birds to evaluate the pathogenicity and transmission of the indicated viruses in chickens, ducks, and pigeons. Furthermore, to investigate the replication and shedding of NDV in poultry, we inoculated the chickens, ducks, and pigeons with 10⁶ EID₅₀ of each virus via intraocular and intranasal routes. Eight hour after infection, the naïve contact groups were housed with those inoculated with each of the viruses as a means to monitor contact transmission. Our results indicated that genetically diverse viruses circulate in LBMs in South China's Guangdong Province and that NDV from different birds have different tissue tropisms and host ranges when transmitted in different birds. We therefore propose the continuous epidemiological surveillance of LBMs to support the prevention of the spread of these viruses in different birds, especially chickens, and highlight the need for studies of the virus–host relationship.

S1PR1 expression correlates with inflammatory responses to Newcastle disease virus infection

Newcastle disease virus (NDV) is the causative agent of Newcastle disease, which is characterized by inflammatory pathological changes in the organs of chickens. The inflammatory response to this disease has not been well characterized. Previous reports showed that the sphingosine-1-phosphate-1 receptor (S1PR1), a G protein-coupled receptor, is important to the activation of inflammatory responses. To understand better the viral pathogenesis and host inflammatory response, we analyzed S1PR1 expression during NDV infection. We observed a direct correlation between chicken embryo fibroblast (CEF) cellular inflammatory responses and S1PR1 expression. Virulent NDV-infected CEF cells also had elevated levels of pro-inflammatory cytokines (IL-1β, IL-6 and IL-18). When S1PR1 was inhibited by using the specific antagonist W146, pro-inflammatory cytokine production declined. Overexpression of S1PR1 resulted in increased virus-induced IL-1β production. S1PR1 expression levels did not impact significantly NDV replication. These findings highlight the important role of S1PR1 in inflammatory responses in NDV infection.