Comparison of biological characteristics of H9N2 avian influenza viruses isolated from different hosts

Etiologic characteristics of avian influenza H11 viruses isolated from the live poultry market in southeast coastal region in China

Since it was first identified in 1956, the H11 subvariant influenza virus has been reported worldwide. However, due to the low pathogenicity of the H11 subvariant and the absence of its widespread transmission among humans, there are only a few reports on the etiology of the H11 subvariant influenza virus. Therefore, in the present study, we isolated a strain of the H11N3 avian influenza virus (AIV) from poultry feces from the live poultry market in the southeast coastal region of China. Considering that the H11 subvariant is known to cause infections in humans and to enrich the knowledge of the H11 subvariant of the avian influenza virus, the genetics, pathogenicity, and transmissibility of the isolate were studied. The phylogenetic analysis indicated that the H11N3 isolate was of Eurasian origin and carried genes closely related to duck H7N2 and H4N6. The receptor binding analysis revealed that the H11N3 isolate only acquired a binding affinity for avian-derived receptors. In the respiratory system of mice, the isolate could directly cause infection without adaptation. In addition, the results from transmission experiments and antibody detection in guinea pigs demonstrated that H11N3 influenza viruses can efficiently transmit through the respiratory tract in mammalian models. Direct infection of the H11N3 influenza virus without adaptation in the mouse models and aerosol transmission between guinea pig models confirms its pandemic potential in mammals, underscoring the importance of monitoring rare influenza virus subtypes in future studies.

Influenza A Virus Agnostic Receptor Tropism Revealed Using a Novel Biological System with Terminal Sialic Acid Knockout Cells

Avian or human influenza A viruses bind preferentially to avian- or human-type sialic acid receptors, respectively, indicating that receptor tropism is an important factor for determining the viral host range. However, there are currently no reliable methods for analyzing receptor tropism biologically under physiological conditions. In this study, we established a novel system using MDCK cells with avian- or human-type sialic acid receptors and with both sialic acid receptors knocked out (KO). When we examined the replication of human and avian influenza viruses in these KO cells, we observed unique viral receptor tropism that could not be detected using a conventional solid-phase sialylglycan binding assay, which directly assesses physical binding between the virus and sialic acids. Furthermore, we serially passaged an engineered avian-derived H4N5 influenza virus, whose PB2 gene was deleted, in avian-type receptor KO cells stably expressing PB2 to select a mutant with enhanced replication in KO cells; however, its binding to human-type sialylglycan was undetectable using the solid-phase binding assay. These data indicate that a panel of sialic acid receptor KO cells could be a useful tool for determining the biological receptor tropism of influenza A viruses. Moreover, the PB2KO virus experimental system could help to safely and efficiently identify the mutations required for avian influenza viruses to adapt to human cells that could trigger a new influenza pandemic. IMPORTANCE The acquisition of mutations that allow avian influenza A virus hemagglutinins to recognize human-type receptors is mandatory for the transmission of avian viruses to humans, which could lead to a pandemic. In this study, we established a novel system using a set of genetically engineered MDCK cells with knocked out sialic acid receptors to biologically evaluate the receptor tropism for influenza A viruses. Using this system, we observed unique receptor tropism in several virus strains that was undetectable using conventional solid-phase binding assays that measure physical binding between the virus and artificially synthesized sialylglycans. This study contributes to elucidation of the relationship between the physical binding of virus and receptor and viral infectivity. Furthermore, the system using sialic acid knockout cells could provide a useful tool to explore the sialic acid-independent entry mechanism. In addition, our system could be safely used to identify mutations that could acquire human-type receptor tropism.

Generation of an avian influenza DIVA vaccine with a H3-peptide replacement located at HA2 against both highly and low pathogenic H7N9 virus

A differentiating infected from vaccinated animals (DIVA) vaccine is an ideal strategy for viral eradication in poultry. Here, according to the emerging highly pathogenic H7N9 avian influenza virus (AIV), a DIVA vaccine strain, named rGD4_HALo-mH3-TX, was successfully developed, based on a substituted 12 peptide of H3 virus located at HA2. In order to meet with the safety requirement of vaccine production, the multi-basic amino acid located at the HA cleavage site was modified. Meanwhile, six inner viral genes from a H9N2 AIV TX strainwere introduced for increasing viral production. The rGD4_HALo-mH3-TX strain displayed a similar reproductive ability with rGD4 and low pathogenicity in chickens, suggesting a good productivity and safety. In immuned chickens, rGD4_HALo-mH3-TX induced a similar antibody level with rGD4 and provided 100% clinical protection and 90% shedding protection against highly pathogenic virus challenge. rGD4_HALo-mH3-TX strain also produced a good cross-protection against low pathogenic AIV JD/17. Moreover, serological DIVA characteristics were evaluated by a successfully established competitive inhibition ELISA based on a 3G10 monoclonal antibody, and the result showed a strong reactivity with antisera of chickens vaccinated with H7 subtype strains but not rGD4_HALo-mH3-TX. Collectedly, rGD4_HALo-mH3-TX is a promising DIVA vaccine candidate against both high and low pathogenic H7N9 subtype AIV.

Influenza a virus antagonizes type I and type II interferon responses via SOCS1-dependent ubiquitination and degradation of JAK1

Background

Although influenza A virus (IAV) employs diverse strategies to evade IFN responses by inhibiting the synthesis of IFN, how IAV regulates signaling downstream of IFN is incompletely understood.

Methods

In this study, we used Western blot-based protein analysis coupled with RT-qPCR, overexpression and RNA interference to investigate the regulation of JAK1 by IAV infection.

Results

The results indicated that JAK1 was ubiquitinated and degraded, resulting in inhibition of type I and type II IFN responses, demonstrating that IAV antagonizes the IFN-activated JAK/STAT signaling pathway by inducing the degradation of JAK1. Furthermore. IAV infection upregulated the suppressor of cytokine signaling (SOCS) protein SOCS1, and SOCS1 mediated the ubiquitination and degradation of JAK1.

Conclusion

Collectively, our findings suggest that IAV infection induces SOCS1 expression to promote JAK1 degradation, which in turn inhibits host innate immune responses.

Genetic, Molecular, and Pathogenic Characterization of the H9N2 Avian Influenza Viruses Currently Circulating in South China

The prevalence and variation of the H9N2 avian influenza virus (AIV) pose a threat to public health. A total of eight viruses isolated from farmed poultry in South China during 2017–2018 were selected as representative strains for further systematic study. Phylogenetic analyses indicated that these prevalent viruses belong to the Y280-like lineage and that the internal genes are highly similar to those of recently circulating human H7N9 viruses. The receptor-binding assay showed that most of the H9N2 isolates preferentially bound to the human-like receptor, increasing the risk of them crossing the species barrier and causing human infection. Our in vitro, multi-step growth curve results indicate these viruses can effectively replicate in mammalian cells. Infection in mice showed that three viruses effectively replicated in the lung of mice. Infection in swine revealed that the viruses readily replicated in the upper respiratory tract of pig and effectively induced viral shedding. Our findings suggested that the H9N2 AIVs circulating in poultry recently acquired an enhanced ability to transmit from avian to mammalians, including humans. Based on our findings, we propose that it is essential to strengthen the efforts to surveil and test the pathogenicity of H9N2 AIVs.

Sequential DNA immunization of chickens with bivalent heterologous vaccines induce highly reactive and cross-specific antibodies against influenza hemagglutinin

Vaccines against avian influenza are mostly based on hemagglutinin (HA), which is the main antigen of this virus and a target for neutralizing antibodies. Traditional vaccines are known to be poorly efficient against newly emerging strains, which is an increasing worldwide problem for human health and for the poultry industry. As demonstrated by research and clinical data, sequential exposure to divergent influenza HAs can boost induction of universal antibodies which recognize conserved epitopes. In this work, we have performed sequential immunization of laying hens using monovalent or bivalent compositions of DNA vaccines encoding HAs from distant groups 1 and 2 (H5, H1, and H3 subtypes, respectively). This strategy gave promising results, as it led to induction of polyclonal antibodies against HAs from both groups. These polyclonal antibodies showed cross-reactivity between different HA strains in ELISA, especially when bivalent formulations were used for immunization of birds. However, cross-reactivity of antibodies induced against H3 and H5 HA subtypes was rather limited against each other after homologous immunization. Using a cocktail of HA sequences and/or sequential DNA vaccination with different strains presents a good strategy to overcome the limited effectiveness of vaccines and induce broader immunity against avian influenza. Such a strategy could be adapted for vaccinating laying hens or parental flocks of different groups of poultry.

Compatibility between haemagglutinin and neuraminidase drives the recent emergence of novel clade 2.3.4.4 H5Nx avian influenza viruses in China

Genetic reassortments between highly pathogenic avian influenza (HPAI) H5 subtype viruses with different neuraminidase (NA) subtypes have increased in prevalence since 2010 in wild birds and poultry from China. The HA gene slightly evolved from clade 2.3.4 to clade 2.3.4.4, raising the question of whether novel clade 2.3.4.4 HA broke the balance with N1 but is matched well with NAx to drive viral epidemics. To clarify the role of compatibility between HA and NA on the prevalence of H5Nx subtypes, we constructed 10 recombinant viruses in which the clade 2.3.4 or clade 2.3.4.4 HA genes were matched with different NA (N1, N2 and N8) genes and evaluated viral characteristics and pathogenicity. Combinations between clade 2.3.4 HA and N1 or between clade 2.3.4.4 HA and NAx, but not between clade 2.3.4.4 HA and N1, or between clade 2.3.4 HA and NAx, promoted viral growth, NA activity, thermostability, low-pH stability and pathogenicity in chicken and mice. These findings suggest that both clade 2.3.4 HA/N1 and clade 2.3.4.4 HA/NAx displayed a better match, which could promote the increased prevalence of clade 2.3.4 H5N1 AIV (prior to 2010) and clade 2.3.4.4 H5Nx AIV (since 2010) in China, respectively.

Dynamic analysis of expression of chemokine and cytokine gene responses to H5N1 and H9N2 avian influenza viruses in DF-1 cells

H5N1 and H9N2 are the most important causes of avian influenza in China. Chemokines and cytokines play important roles in inflammatory response that clearly differ between H5N1 and H9N2 infection. To investigate whether chemokines and cytokines are differentially regulated following H5N1 and H9N2 AIVs infection, dynamic expression of chemokines and cytokines, including IL8L1, IL8L2, CX3CL1, CCL5, CCL20, K203, SCYA4, XLC1, CCLi10, CCL19, IFN-α, IFN-β, IL-1β, IL-6 and TNF-α, were analyzed by real-time quantitative RT-PCR in DF-1 cells. It was found that IL8L1, IL8L2, CX3CL1, CCL5, CCL20, K203, SCYA4, IFN-α, IFN-β, IL-1β, IL-6 and TNF-α increased significantly after induction of H5N1 or H9N2 AIV infection, whereas no expression of XCL1, CCLi10 or CCL19 was detected. H9N2 AIV infection was associated with much stronger chemokine responses than infection with H5N1, whereas the cytokines showed opposite results. It was found that K203 is a constant chemotactic factor independent of subtype of AIVs and infectious dose, CCL20 and IL-1β are constant regardless of the infectious dose but depend on the subtype of AIV, chemotactic factors IL8L1, IL8L2 and CCL5 are dependent both on subtype of AIVs and infectious dose, and K203, CX3CL1, SCYA4, CCL20, IFN-α, IL-1β and TNF-α are specific to responses to H5N1 AIV infection whereas K203, CCL20, IFN-β, IL-1β and IL-6 are specific to H9N2 infection. These results provide basic data for explaining differences in inflammation and phenotypes of histopathological changes caused by H5N1 and H9N2 and add new information on the roles of chemokines and cytokines in virulence of AIVs.

Efficacy of Live-Attenuated H9N2 Influenza Vaccine Candidates Containing NS1 Truncations against H9N2 Avian Influenza Viruses

H9N2 avian influenza virus is a zoonotic agent with a broad host range that can contribute genetic information to H5 or H7N9 subtype viruses, which are significant threats to both humans and birds. Thus, there is a great need for a vaccine to control H9N2 avian influenza. Three mutant viruses of an H9N2 virus A/chicken/Taixing/10/2010 (rTX-NS1-73, rTX-NS1-100, and rTX-NS1-128) were constructed with different NS1 gene truncations and confirmed by western blot analysis. The genetic stability, pathogenicity, transmissibility, and host immune responses toward these mutants were evaluated. The mutant virus rTX-NS1-128 exhibited the most attenuated phenotype and lost transmissibility. The expression levels of interleukin 12 in the nasal and tracheal tissues from chickens immunized with rTX-NS1-128 were significantly upregulated on day 3 post-immunization and the IgA and IgG antibody levels were significantly increased on days 7, 14, and 21 post-immunization when compared to chickens that received an inactivated vaccine. rTX-NS1-128 also protected chickens from challenge by homologous and heterologous H9N2 avian influenza viruses. The results indicate that rTX-NS1-128 can be used as a potential live-attenuated vaccine against H9N2 avian influenza.

Evaluation of the Protective Efficacy of Poly I:C as an Adjuvant for H9N2 Subtype Avian Influenza Inactivated Vaccine and Its Mechanism of Action in Ducks

Current commercial H9 avian influenza vaccines cannot provide satisfactory protective immunity against antigenic variant influenza viruses in ducks. Poly I:C, when used as an adjuvant, improves humoral and cellular immunity in many animals but has not been tested in ducks. In this study, we investigated the protective efficacy of Poly I:C as an adjuvant for an inactivated H9N2 Avian influenza vaccine in ducks. We found that an H9N2 vaccine administered with poly I:C (H9-PIC vaccine) induced a significantly more rapid response with higher anti-influenza antibody titers than those of the vaccine alone (H9 vaccine). Moreover, virus shedding was reduced in ducks immunized with the H9-PIC vaccine after challenge with an H9 subtype antigenic variant viruses. IFN-α, IFN-γ, IL-6 and MHC-II mRNA levels were all elevated in ducks receiving the H9-PIC vaccine. In addition, lower expression level of MHC-I may be a reason for inefficient protective ability against heterologous influenza viruses in H9-PIC vaccination of ducks. In conclusion, poly I:C adjuvant enhanced both humoral and cellular immune responses in ducks induced by immunization of inactivated H9N2 vaccine.

Weighing serological evidence of human exposure to animal influenza viruses - a literature review

Assessing influenza A virus strains circulating in animals and their potential to cross the species barrier and cause human infections is important to improve human influenza surveillance and preparedness. We reviewed studies describing serological evidence of human exposure to animal influenza viruses. Comparing serological data is difficult due to a lack of standardisation in study designs and in laboratory methods used in published reports. Therefore, we designed a scoring system to assess and weigh specificity of obtained serology results in the selected articles. Many studies report reliable evidence of antibodies to swine influenza viruses among persons occupationally exposed to pigs. Most avian influenza studies target H5, H7 and H9 subtypes and most serological evidence of human exposure to avian influenza viruses is reported for these subtypes. Avian influenza studies receiving a low grade in this review often reported higher seroprevalences in humans compared with studies with a high grade. Official surveillance systems mainly focus on avian H5 and H7 viruses. Swine influenza viruses and avian subtypes other than H5 and H7 (emphasising H9) should be additionally included in official surveillance systems. Surveillance efforts should also be directed towards understudied geographical areas, such as Africa and South America.

Biological Characteristics of H9N2 Avian Influenza Viruses from Healthy Chickens in Shanghai, China

Background

H9N2 avian influenza viruses that circulate in domestic poultry in eastern China pose challenges to human health. However, few studies have compared the biological characteristics of H9N2 viruses isolated from healthy chickens in Shanghai.

Material/Methods

Three H9N2 viruses – CK/SH/Y1/07, CK/SH/Y1/02, and CK/SH/23/13 – isolated from healthy chickens in Shanghai between 2002 and 2013, were selected and their biological characteristics were determined.

Results

All 3 H9N2 viruses showed a preference for both the avian- and human-like receptors, and they replicated well in MDCK and A549 cells. All H9N2 viruses were non-pathogenic to mini-pigs and were detected in the trachea and lung tissues. The CK/SH/Y1/07 and CK/SH/Y1/02 viruses were transmitted to mini-pigs through direct-contact or respiratory droplet exposure, but CK/SH/23/13 virus was not.

Conclusions

These results suggest that H9N2 viruses isolated from healthy chickens in Shanghai efficiently replicate and transmit among pigs and other mammals.

Antigenic mapping of an H9N2 avian influenza virus reveals two discrete antigenic sites and a novel mechanism of immune escape

H9N2 avian influenza virus is a major cause of poultry production loss across Asia leading to the wide use of vaccines. Efficacy of vaccines is often compromised due to the rapid emergence of antigenic variants. To improve the effectiveness of vaccines in the field, a better understanding of the antigenic epitopes of the major antigen, hemagglutinin, is required. To address this, a panel of nine monoclonal antibodies were generated against a contemporary Pakistani H9N2 isolate, which represents a major Asian H9N2 viral lineage. Antibodies were characterized in detail and used to select a total of 26 unique 'escape' mutants with substitutions across nine different amino acid residues in hemagglutinin including seven that have not been described as antigenic determinants for H9N2 viruses before. Competition assays and structural mapping revealed two novel, discrete antigenic sites "H9-A" and "H9-B". Additionally, a second subset of escape mutants contained amino acid deletions within the hemagglutinin receptor binding site. This constitutes a novel method of escape for group 1 hemagglutinins and could represent an alternative means for H9N2 viruses to overcome vaccine induced immunity. These results will guide surveillance efforts for arising antigenic variants as well as evidence based vaccine seed selection and vaccine design.