Hemagglutinin-Neuraminidase and fusion genes are determinants of NDV thermostability

Comparative protective efficacy of a newly generated live recombinant thermostable highly attenuated vaccine rK148/GVII-F using a single regimen against lethal NDV GVII.1.1

RESEARCH HIGHLIGHTS

A thermostable, safe, and effective NDV GVII recombinant vaccine was generated.Fusion gene replacement with GVII did not affect GI K148/08 virus thermostability.Strain rK148/GVII-F provided adequate protection against a lethal NDV challenge.Oropharyngeal shedding was significantly reduced on post-challenge days 5 and 7.

Papaverine Enhances the Oncolytic Effects of Newcastle Disease Virus on Breast Cancer In Vitro and In Vivo

Breast cancer is a lethal disease in females worldwide and needs effective treatment. Targeting cancer cells with selective and safe treatment seems like the best choice, as most chemotherapeutic drugs act unselectively. Papaverine showed promising antitumor activity with a high safety profile and increased blood flow through vasodilation. At the same time, it was widely noticed that virotherapy using the Newcastle disease virus proved to be safe and selective against a broad range of cancer cells. Furthermore, combination therapy is favorable, as it attacks cancer cells with multiple mechanisms and enhances virus entrance into the tumor mass, overcoming cancer cells' resistance to therapy. Therefore, we aimed at assessing the novel combination of the AMHA1 strain of Newcastle disease virus (NDV) and nonnarcotic opium alkaloid (papaverine) against breast cancer models in vitro and in vivo. Methods. In vitro experiments used two human breast cancer cell lines and one normal cell line and were treated with NDV, papaverine, and a combination. The study included a cell viability MTT assay, morphological analysis, and apoptosis detection. Animal experiments used the AN3 mouse mammary adenocarcinoma tumor model. Evaluation of the antitumor activity included growth inhibition measurement; the immunohistochemistry assay measured caspase protein expression. Finally, a semiquantitative microarray assay was used to screen changes in apoptotic proteins. In vitro, results showed that the combination therapy induces synergistic cytotoxicity and apoptosis against cancer cells with a negligible cytotoxic effect on normal cells. In vivo, combination treatment induced a significant antitumor effect with an obvious regression in tumor size and a remarkable and significant expression of caspase-3, caspase-8, and caspase-9 compared to monotherapies. Microarray analysis shows higher apoptosis protein levels in the combination therapy group. In conclusion, this study demonstrated the role of papaverine in enhancing the antitumor activity of NDV, suggesting a promising strategy for breast cancer therapy through nonchemotherapeutic drugs.

Biological Significance of Dual Mutations A494D and E495K of the Genotype III Newcastle Disease Virus Hemagglutinin-Neuraminidase In Vitro and In Vivo

As a multifunctional protein, the hemagglutinin-neuraminidase (HN) protein of Newcastle disease virus (NDV) is involved in various biological functions. A velogenic genotype III NDV JS/7/05/Ch evolving from the mesogenic vaccine strain Mukteswar showed major amino acid (aa) mutations in the HN protein. However, the precise biological significance of the mutant HN protein remains unclear. This study sought to investigate the effects of the mutant HN protein on biological activities in vitro and in vivo. The mutant HN protein (JS/7/05/Ch-type HN) significantly enhanced the hemadsorption (HAd) and fusion promotion activities but impaired the neuraminidase (NA) activity compared with the original HN protein (Mukteswar-type HN). Notably, A494D and E495K in HN exhibited a synergistic role in regulating biological activities. Moreover, the mutant HN protein, especially A494D and E495K in HN, enhanced the F protein cleavage level, which can contribute to the activation of the F protein. In vitro infection assays further showed that NDVs bearing A494D and E495K in HN markedly impaired the cell viability. Simultaneously, A494D and E495K in HN enhanced virus replication levels at the early stage of infection but weakened later in infection, which might be associated with the attenuated NA activity and cell viability. Furthermore, the animal experiments showed that A494D and E495K in HN enhanced case fatality rates, virus shedding, virus circulation, and histopathological damages in NDV-infected chickens. Overall, these findings highlight the importance of crucial aa mutations in HN in regulating biological activities of NDV and expand the understanding of the enhanced pathogenicity of the genotype III NDV.

Expression and characterization of hemagglutinin-neuraminidase protein from Newcastle disease virus in Bacillus subtilis WB800

Background

Newcastle disease virus (NDV) belongs to the genus Avaluvirus and Paramyxoviridae family, and it can cause acute, highly contagious Newcastle disease in poultry. The two proteins, haemagglutinin neuraminidase (HN) and Fusion (F), are the main virulence factor of the virus and play an essential role in immunogenicity against the virus. In most paramyxoviruses, the F protein requires HN protein to fuse the membrane, and HN proteins substantially enhance the viruses’ fusion activity.

Results

The present study describes the successful cloning and expression of HN protein from NDV in Bacillus subtilis WB800 using the modified shuttle vector pHT43. HN coding sequence was cloned into the pGet II vector. It was then subcloned into the PHT43 shuttle vector and transferred to Escherichia coli for replication. The recombinant plasmid was extracted from E. coli and used to transform B. subtilis by electroporation. After induction of recombinant B. subtilis by IPTG, total cell protein and the protein secreted into the media were analysed through a time course using SDS-PAGE. The expressed HN protein was purified using cation exchange chromatography followed by metal affinity chromatography, using the 6× His epitope introduced at the carboxyl terminus of the recombinant protein. The accuracy of the PHT43-HN construct was confirmed by sequencing and enzymatic digestion. SDS-PAGE results showed that the recombinant HN protein was successfully expressed and secreted into the medium. Moreover, the purified HN protein showed neuraminidase activity with characteristics similar to the indigenous HN NDV protein. B. subtilis is a free endotoxin host that could be a favourite prokaryotic platform for producing the recombinant HN protein.

Conclusion

The establishment of this expression and purification system has allowed us to explore further the biochemical characteristics of HN protein and obtain material that could be suitable for a new production of NDV candidate vaccine with high immunogenicity.

In Vitro Antiviral Activity of Green Tea Polyphenon-60 against Avian Paramyxoviruses

Avian paramyxoviruses (APMVs) have caused an economically significant drop in global domestic poultry production because of their high morbidity and mortality rates. Polyphenols are the major components of green tea that have great antiviral effects. This study aimed to evaluate the anti-APMV activities of polyphenon-60. Twelve APMV-1 strains representing three different pathotypes, two strains of APMV-2, one strain of APMV-3, and one strain of APMV-7 were propagated in chicken embryos. To determine the cytotoxic effect, chicken embryo fibroblasts were treated with the test compound in various concentrations. To assess the antiviral properties, time-dependent, dose-dependent, and virulence-dependent experiments were conducted in both cell and chicken embryo models. A reduction in virus titers was measured by the hemagglutination test. The inhibitory effect on virus adsorption to the chicken red blood cell (RBC) surface was examined by the hemagglutination inhibition test. The results showed that lentogenic and mesogenic APMV-1 strains, APMV-3 strain, and APMV-7 strain were significantly inhibited ( $p<0.05$ ) by polyphenon-60 at 50 μg/ml, while the 50% cytotoxic concentration of the compound was 345 μg/ml. Polyphenon-60 also exhibited the inhibitory activity against hemagglutination by NDV. Taken together, the results suggest that polyphenon-60 has shown promise as an antiviral agent that has wide safety margins against APMVs, and challenge studies to evaluate its efficacy in chickens are necessary.

Glycyrrhiza polysaccharides can improve and prolong the response of chickens to the Newcastle disease vaccine

Licorice is a medicinal and food plant widely used to treat diseases and produce food additives, because of its unique chemical constituents like polysaccharides, flavones, and saponins. Glycyrrhiza Polysaccharides (GPS-1) are water-soluble neutral polysaccharides extracted from licorice. Currently, GPS-1 is administrated to chickens by gavage every d for 14 d to observe the impact of GPS-1 on the Newcastle disease vaccine. To determine the immunity of these chickens to NDV, blood serum levels of hemagglutinin-inhibition (HI) antibody, and immunoglobulins IgA and IgG were measured. Meanwhile, the expression levels of cytokines IL-2, IL-4, IL-17, and IFN-γ were measured to evaluate the degree of immune booster activity. The chickens' spleen and peripheral blood lymphocytes displayed a significant increase in the proportion of CD4+ and CD8+ T cells after booster treatments with GPS-1. The results indicated that GPS-1 had a significant, dose-dependent, immune-boosting effect which could enhance NDV vaccine immunity in chickens.

Process Development for Newcastle Disease Virus-Vectored Vaccines in Serum-Free Vero Cell Suspension Cultures

The ongoing COVID-19 pandemic drew global attention to infectious diseases, attracting numerous resources for development of pandemic preparedness plans and vaccine platforms—technologies with robust manufacturing processes that can quickly be pivoted to target emerging diseases. Newcastle Disease Virus (NDV) has been studied as a viral vector for human and veterinary vaccines, but its production relies heavily on embryonated chicken eggs, with very few studies producing NDV in cell culture. Here, NDV is produced in suspension Vero cells, and analytical assays (TCID₅₀ and ddPCR) are developed to quantify infectious and total viral titer. NDV-GFP and NDV-FLS (SARS-CoV-2 full-length spike protein) constructs were adapted to replicate in Vero and HEK293 suspension cultures using serum-free media, while fine-tuning parameters such as MOI, temperature, and trypsin concentration. Shake flask productions with Vero cells resulted in infectious titers of 1.07 × 10⁸ TCID₅₀/mL for NDV-GFP and 1.33 × 10⁸ TCID₅₀/mL for NDV-FLS. Production in 1 L batch bioreactors also resulted in high titers in culture supernatants, reaching 2.37 × 10⁸ TCID₅₀/mL for NDV-GFP and 3.16 × 10⁷ TCID₅₀/mL for NDV-FLS. This shows effective NDV production in cell culture, building the basis for a scalable vectored-vaccine manufacturing process that can be applied to different targets.

Carboxymethylated and acetylated xerogel derivatives of Plectranthus esculentus starch protect Newcastle disease vaccines against cold chain failure

Developing vaccine stabilizers from local natural sources is desirable especially if the stabilizer would enhance the ability of the antigen to withstand frequent failures in cold chains. The study was undertaken to formulate immunogenic live Newcastle Disease (ND) LaSota vaccines stabilized with modified native starches for use at cold and ambient temperatures and to assess the immunogenicity of the starch stabilized vaccines in vaccinated chickens. Native starch extracted from the tubers of Plectranthus esculentus (Family, Lamiaceae) was modified by carboxymethylation and acetylation/xerogel formation and used as vaccine stabilizers of ND LaSota virus with/without buffers/bulking excipients. Cold Chain Failure (CCF) was simulated by storing the vaccines at 5 ± 2 °C for one month then at 37 ± 1 °C for 96 h. The stability of the samples were evaluated in comparison with peptone stabilized ND vaccines using pH, residual moisture, XRD, reconstitution time, mean embryo infective dose (EID50) and haemagglutination (HA) tests. Haemagglutination inhibition was used to evaluate the efficacy of the vaccines in conferring positive serum antibody titers (≥2³ log₂) in vaccine-naïve 2-week old broilers that were orally administered a single dose of the vaccines kept at 37 ± 1 °C for 96 h and bled weekly over four weeks. Temperature, pH, moisture content and amorphousness impacted vaccine stability. Peptone stabilized vaccines were significantly less stable and most affected by temperature changes with 1.2log₁₀EID50 loss while buffered/bulked trehalose, carboxymethylated and acetylated/xerogelized starch stabilized vaccines were most stable (0.2-0.5log₁₀EID50 loss in titer) after 96 h in CCF. Buffered trehalose stabilized vaccine (TVB) had lower HA titres than peptone and starch stabilized vaccines containing D-mannitol and Na₂HPO₄. Antibody titres of vaccinated broilers were between 3.3 ± 1.398 and 8.35 ± 2.678. All the vaccines were immunogenic (HI ≥ 2³) and developed HI titres (≥2⁴) considered to be protective. Carboxymethylated and acetylated/xerogel derivatives of P. esculentus starch have a great potential as vaccine stabilizers especially in areas prone to CCF.

The Expression of Hemagglutinin by a Recombinant Newcastle Disease Virus Causes Structural Changes and Alters Innate Immune Sensing

Recombinant Newcastle disease viruses (rNDV) have been used as bivalent vectors for vaccination against multiple economically important avian pathogens. NDV-vectored vaccines expressing the immunogenic H5 hemagglutinin (rNDV-H5) are considered attractive candidates to protect poultry from both highly pathogenic avian influenza (HPAI) and Newcastle disease (ND). However, the impact of the insertion of a recombinant protein, such as H5, on the biological characteristics of the parental NDV strain has been little investigated to date. The present study compared a rNDV-H5 vaccine and its parental NDV LaSota strain in terms of their structural and functional characteristics, as well as their recognition by the innate immune sensors. Structural analysis of the rNDV-H5 demonstrated a decreased number of fusion (F) and a higher number of hemagglutinin-neuraminidase (HN) glycoproteins compared to NDV LaSota. These structural differences were accompanied by increased hemagglutinating and neuraminidase activities of rNDV-H5. During in vitro rNDV-H5 infection, increased mRNA expression of TLR3, TLR7, MDA5, and LGP2 was observed, suggesting that the recombinant virus is recognized differently by sensors of innate immunity when compared with the parental NDV LaSota. Given the growing interest in using NDV as a vector against human and animal diseases, these data highlight the importance of thoroughly understanding the recombinant vaccines’ structural organization, functional characteristics, and elicited immune responses.

Phylogenetic analysis and pathogenicity assessment of pigeon paramyxovirus type 1 circulating in China during 2007-2019

Pigeon paramyxovirus type 1 (PPMV-1) is an antigenic variant of Newcastle disease virus (NDV) which is mainly associated with infections of pigeons and has the potential to result in disease in chickens. In this study, we characterised 21 PPMV-1 isolates from diseased pigeons in China during 2007-2019. Phylogenetic analysis revealed that all isolates belonged to genotype VI. Among them, most isolates belonged to sub-genotype VI.2.1.1.2.2, suggesting that VI.2.1.1.2.2 has become a prevalent genotype in pigeons in China. The results showed that all PPMV-1 isolates were mesogenic in nature according to the mean death time (MDT) and intracerebral pathogenicity index (ICPI). In vitro and in vivo studies demonstrated that two genetically closely related isolates (Pi-11 and Pi-10) both of which belonged to sub-genotype VI.2.1.1.2.2 had similar replication kinetics in cells derived from pigeons, while the replication titre of Pi-11 was significantly higher than that of Pi-10 in cells derived from chickens. Pi-11 and Pi-10 could contribute to morbidity and mortality in pigeons. Remarkably, although the two viruses resulted in no apparent disease symptom in chickens, Pi-11 could cause more severe histopathological lesions and had a stronger replication ability in chickens compared to Pi-10. Moreover, chickens infected with Pi-11 had higher shedding efficiency than chickens infected with Pi-10. Additionally, several mutations within important functional regions of the fusion (F) and haemagglutinin-neuraminidase (HN) proteins might be associated with different pathogenicity of the two viruses in chickens. Collectively, these results indicated that the Pi-11-like virus of pigeon origin has the potential to induce severe outbreaks in chicken flocks. These findings will help us better understand the epidemiology and evolution of PPMV-1 in China and serve as a foundation for the further investigation of the mechanism underlying the pathogenic difference of PPMV-1 isolates in chickens.

Accurate detection of Newcastle disease virus using proximity-dependent DNA aptamer ligation assays

Detecting viral antigens at low concentrations in field samples can be crucial for early veterinary diagnostics. Proximity ligation assays (PLAs) in both solution and solid‐phase formats are widely used for high‐performance protein detection in medical research. However, the affinity reagents used, which are mainly poly‐ and monoclonal antibodies, play an important role in the performance of PLAs. Here, we have established the first homogeneous and solid‐phase proximity‐dependent DNA aptamer ligation assays for rapid and accurate detection of Newcastle disease virus (NDV). NDV is detected by a pair of extended DNA aptamers that, upon binding in proximity to proteins on the envelope of the virus, are joined by enzymatic ligation to form a unique amplicon that can be sensitively detected using real‐time PCR. The sensitivity, specificity, and reproducibility of the assays were validated using 40 farm samples. The results demonstrated that the developed homogeneous and solid‐phase PLAs, which use NDV‐selective DNA aptamers, are more sensitive than the sandwich enzymatic‐linked aptamer assay (ELAA), and have a comparable sensitivity to real‐time reverse transcription PCR (rRT‐PCR) as the gold standard detection method. In addition, the solid‐phase PLA was shown to have a greater dynamic range with improved lower limit of detection, upper‐ and lower limit of quantification, and minimal detectable dose as compared with those of ELAA and rRT‐PCR. The specificity of PLA is shown to be concordant with rRT‐PCR.

Development of a Recombinant Thermostable Newcastle Disease Virus (NDV) Vaccine Express Infectious Bronchitis Virus (IBV) Multiple Epitopes for Protecting against IBV and NDV Challenges

Newcastle disease (ND) and infectious bronchitis (IB) are two highly contagious diseases that severely threaten the poultry industry. The goal of this study is to prevent these two diseases and reduce the vaccine costs during storage and transportation. In this study, we design a thermostable recombinant Newcastle disease virus (NDV) candidate live vaccine strain designated as rLS-T-HN-T/B, which expresses the multiple epitope cassette of the identified infectious bronchitis virus (IBV) (S-T/B). The rLS-T-HN-T/B strain was found to possess similar growth kinetics, passage stability, morphological characteristics, and virulence to the parental LaSota strain. After incubation at 56 °C at the indicated time points, the rLS-T-HN-T/B strain was determined by the hemagglutination (HA), and 50% embryo infectious dose (EID₅₀) assays demonstrated that it accords with the criteria for thermostability. The thermostable rLS-T-HN-T/B and parental LaSota vaccines were stored at 25 °C for 16 days prior to immunizing the one-day-old specific pathogen-free (SPF) chicks. Three weeks postimmunization, the virus challenge results suggested that the chicks vaccinated with the rLS-T-HN-T/B vaccine were protected by 100% and 90% against a lethal dose of NDV and IBV, respectively. Furthermore, the trachea ciliary activity assay indicated that the mean ciliostasis score of the chicks vaccinated with thermostable rLS-T-HN-T/B vaccine was significantly superior to that of the LaSota and PBS groups (p < 0.05). The rLS-T-HN-T/B vaccine stored at 25 °C for 16 days remained capable of eliciting the immune responses and protecting against IBV and NDV challenges. However, the same storage conditions had a great impact on the parental LaSota strain vaccinated chicks, and the NDV challenge protection ratio was only 20%. We conclude that the thermostable rLS-T-HN-T/B strain is a hopeful bivalent candidate vaccine to control both IB and ND and provides an alternative strategy for the development of cost-effective vaccines for village chickens, especially in the rural areas of developing countries.

Residues 315 and 369 in HN Protein Contribute to the Thermostability of Newcastle Disease Virus

Thermostable Newcastle disease virus (NDV) vaccines have been widely used in areas where a “cold-chain” is not reliable. However, the molecular mechanism of NDV thermostability remains poorly understood. In this work, we constructed chimeric viruses by exchanging viral fusion (F) and/or hemagglutinin-neuraminidase (HN) genes between the heat-resistant strain HR09 and thermolabile strain La Sota utilizing a reverse genetic system. The results showed that only chimeras with HN derived from the thermostable virus exhibited a thermostable phenotype at 56°C. The hemagglutinin (HA) and neuraminidase (NA) activities of chimeras with HN derived from the HR09 strain were more thermostable than those containing HN from the La Sota strain. Then, we used molecular dynamics simulation at different temperatures (310 K and 330 K) to measure the HN protein of the La Sota strain. The conformation of an amino acid region (residues 315–375) was observed to fluctuate. Sequence alignment of the HN protein revealed that residues 315, 329, and 369 in the La Sota strain and thermostable strains differed. Whether the three amino acid substitutions affected viral thermostability was investigated. Three mutant viruses based on the thermolabile strain were generated by substituting one, two or three amino acids at positions 315, 369, and 329 in the HN protein. In comparison with the parental virus, the mutant viruses containing mutations S315P and I369V possessed higher thermostablity and HA titers, NA and fusion activities. Taken together, these data indicate that the HN gene of NDV is a major determinant of thermostability, and residues 315 and 369 have important effects on viral thermostability.

Rapid Development of an Effective Newcastle Disease Virus Vaccine Candidate by Attenuation of a Genotype VII Velogenic Isolate Using a Simple Infectious Cloning System

Genotype-matched vaccines provide ideal protection against infection caused by new Newcastle disease virus (NDV) genotypes or variants even in the vaccinated chickens. In this study, we report a protocol for attenuation and rapid development of a velogenic NDV isolate as an effective vaccine candidate, using a simple and reliable infectious cloning platform. Based on DHN3, a genotype VII velogenic NDV isolate, recombinant rDHN3 was rescued by co-transfection of plasmids expressing the genomic RNA, NDV proteins NP, P and L, and the T7 polymerase without using a helper virus. Subsequently, an attenuated strain rDHN3-mF was produced by substitution of residues from amino acids 112 to 117 in the DHN3 F protein with the corresponding sequence from the LaSota strain. Both rDHN3 and rDHN3-mF are genetically stable during propagation in cell culture and chicken embryos. Further characterization through determination of EID₅₀, MDT and clinical assessments confirmed that rDHN3 is velogenic and rDHN3-mF lentogenic. Vaccination of one-week-old SPF chicks with inactivated rDHN3-mF produced much higher anti-DHN3 antibody response and better protection against live DHN3 challenge than did the commercial LaSota vaccine, providing 100% protection and much earlier viral clearance. This attenuated NDV isolate would merit further development into a vaccine product.

Establishment of reverse transcription recombinase-aided amplification-lateral-flow dipstick and real-time fluorescence-based reverse transcription recombinase-aided amplification methods for detection of the Newcastle disease virus in chickens

Newcastle disease is an acute and highly contagious disease of poultry caused by Newcastle disease virus infection, which does great harm to the poultry industry all over the world. To diagnose the disease simply and quickly, 2 detection methods were established based on reverse transcription recombinase-aided amplification (RT-RAA) technology. One is reverse transcription recombinase-aided amplification-lateral flow dipstick (RT-RAA-LFD) that is to combine RT-RAA with lateral flow dipstick; the other is real-time fluorescence-based reverse transcription recombinase-aided amplification (RF-RT-RAA) that is the combination of RT-RAA and exo probe. In this study, the reaction conditions such as reaction temperature and reaction time of the 2 methods were optimized, and their specificity and sensitivity were tested. The results showed that the RT-RAA-LFD method could be used to complete reaction within 23 min, and its lowest detectable limit was 10² copies/μL, 10 times higher than that of the conventional PCR method (10³ copies/μL); the RF-RT-RAA method could be used to complete reaction within 26 min, and its lowest detectable limit was 10 copies/μL, 100 times higher than that of conventional PCR method (10³ copies/μL), and it was as sensitive as real-time fluorescence-based quantitative PCR (10 copies/μL). The 2 methods had no cross reaction to the nucleic acid of other avian pathogens and showed good specificity. A total of 86 clinical samples suspected of the Newcastle disease virus were tested by conventional PCR, real-time fluorescence-based quantitative PCR, RT-RAA-LFD, and RF-RT-RAA. Based on the commonly used conventional PCR method, the other 3 detection methods had a coincidence rate of higher than 93%. In summary, RT-RAA-LFD and RF-RT-RAA had high specificity, sensitivity, and efficiency, which were suitable for clinical and laboratory diagnosis, respectively, and provided technical support for the prevention and control of Newcastle disease.

Application of Newcastle disease virus in the treatment of colorectal cancer

Colorectal cancer (CRC) is one of the main reasons of tumor-related deaths worldwide. At present, the main treatment is surgery, but the results are unsatisfactory, and the prognosis is poor. The majority of patients die due to liver or lung metastasis or recurrence. In recent years, great progress has been made in the field of tumor gene therapy, providing a new treatment for combating CRC. As oncolytic viruses selectively replicate almost exclusively in the cytoplasm of tumor cells and do not require integration into the host genome, they are safer, more effective and more attractive as oncolytic agents. Newcastle disease virus (NDV) is a natural RNA oncolytic virus. After NDV selectively infects tumor cells, the immune response induced by NDV’s envelope protein and intracellular factors can effectively kill the tumor without affecting normal cells. Reverse genetic techniques make NDV a vector for gene therapy. Arming the virus by inserting various exogenous genes or using NDV in combination with immunotherapy can also improve the anti-CRC capacity of NDV, and good results have been achieved in animal models and clinical treatment trials. This article reviews the molecular biological characteristics and oncolytic mechanism of NDV and discusses in vitro and in vivo experiments on NDV anti-CRC capacity and clinical treatment. In conclusion, NDV is an excellent candidate for cancer treatment, but more preclinical studies and clinical trials are needed to ensure its safety and efficacy.

The Ntail region of nucleocapsid protein is associated with the pathogenicity of pigeon paramyxovirus type 1 in chickens

The nucleoprotein (NP) of pigeon paramyxovirus type 1 (PPMV-1) and other paramyxoviruses plays an important role in virus proliferation. A previous study found that NP is associated with the low pathogenicity of PPMV-1 strains in chickens. Here, we investigated which domain of NP is responsible for regulating the pathogenicity of PPMV-1. We found that the Ntail sequences were more diverse for different viral genotypes compared to Ncore sequences. The chimeric rBJ-SG10Ntail strain caused more severe clinical symptoms than the parental rBJ strain, increased the viral copy number in sampled tissues and induced higher IFN-γ gene expression. This demonstrated that the Ntail sequence plays a role in regulating viral virulence. These findings increase our understanding of the Ntail of NP protein and the virulence factors associated with PPMV-1.