A novel monoclonal antibody efficiently blocks the infection of serotype 4 fowl adenovirus by targeting fiber-2

Evaluation of Tembusu virus single-round infectious particle as vaccine vector in chickens

Orthoflaviviruses are single-stranded RNA viruses characterized by highly efficient self-amplification of RNA in host cells, which makes them attractive vehicles for vaccines. Numerous preclinical and clinical studies have demonstrated the efficacy and safety of orthoflavivirus replicon vectors for vaccine development. In this study, we constructed Tembusu virus (TMUV) replicon-based single-round infectious particles (SRIPs) as vaccine development platform. To evaluate the potential of TMUV SRIPs as vaccines, we generated SRIPs that express the heterologous Fowl adenovirus 4 (FAdV-4) fiber2 protein and fiber2 head domain, named TMUVRP-fiber2 and TMUVRP-fiber2H, respectively. To assess the immunogenicity of the TMUV SRIPs, SPF chicks were intramuscularly inoculated twice. Our results showed that the TMUVRP-fiber2 vaccines elicited high levels of neutralizing antibodies. Challenge experiments showed that TMUVRP-fiber2 provided full protection against virulent FAdV-4 and significantly reduced viral shedding. Moreover, the immunogenicity of TMUVRP-fiber2H was significantly lower than that of TMUVRP-fiber2, which was reflected in the neutralizing antibody titer, survival rate, and virus shedding after challenge. Therefore, our results suggested that TMUV SRIPs are a promising novel platform for the development of vaccines for existing and emerging poultry diseases.

Development of a unique sandwich enzyme-linked immunosorbent assay based on monoclonal antibodies for the specific detection of the egg drop syndrome virus

RESEARCH HIGHLIGHTS

A sandwich ELISA was developed to detect EDSV using the mAbs 5G4 and HRP-6G6.The sandwich ELISA maintained high specificity and sensitivity.The sandwich ELISA had equivalent consistency with real-time PCR assay.

Genetic modification regulates pathogenicity of a fowl adenovirus 4 strain after cell line adaptation (genetic mutation in FAdV-4 lowered pathogenicity)

Fowl adenovirus 4 (FAdV-4) is a major avian virus that induces fatal diseases in chicken such as, hydropericardium and hepatitis. The viral structure consists of hexon, penton, fiber-1, and fiber-2 which are associated with immunopathogenesis. In this study, we investigated the genetic modification of a FAdV-4 strain after continuous passages in a cell line and evaluated the pathogenicity associated with mutations. We used the FadV-4 KNU14061 strain, which was isolated from layers in 2014. The virus went through 80 passages in the Leghorn male hepatoma (LMH) cell line. The full genetic sequence was identified, and we found a frameshift in the fiber-2 amino acid sequence after the initial thirty passages. To examine whether the frameshift in the fiber-2 gene affects the pathogenicity in chicken, we inoculated LMH80 (80 times passaged) and LMH10 (10 times passaged) into 3-day-old chickens and examined the pathogenesis. LMH10 infection via intramuscular route induced fatal pathology, but LMH80 did not. Furthermore, LHM80 pre-treatment protected hosts from the LMH10 challenge. Thus, the genetic modification isolated by serial passage lowered pathogenicity and the resulting virus acted as an attenuated vaccine that can be a FAdV-4 vaccine strain candidate.

Identification of novel B cell epitopes in Fiber-2 protein of duck adenovirus 3 and their application

Duck adenovirus 3 (DAdV-3), a newly emerged duck adenovirus, has resulted in significant economic losses to the duck industry across China since 2014. However, little is known about the B cell epitopes in major antigen of DAdV-3 and the serological approach for detection of DAdV-3 is not available. In this study, four monoclonal antibodies (mAbs) specific to Fiber-2 protein of DAdV-3 were first generated and designated as 2G10, 3D9, 5E6, and 6B12. Indirect immunofluorescence assay (IFA) showed that all of the mAbs reacted with the Fiber-2. Moreover, mAbs 2G10, 5E6, and 6B12 demonstrated good activity with Fiber-2 in Western blot. Notably, the Fiber-2 could be immunoprecipitated efficiently by mAb 3D9. Epitope mapping revealed that mAbs 2G10, 3D9, 5E6, and 6B12 recognized 397-429aa, 463-481aa, 67-99aa, and 1-66aa of Fiber-2, respectively. Besides, a novel sandwich ELISA for efficient detection of DAdV-3 was developed based on mAb 3D9 and horseradish peroxidase (HRP) conjugated mAb 3D9. The sandwich ELISA only reacted with DAdV-3 but not with other duck-associated viruses. The limit of detection of the ELISA was 6.25 × 10³ TCID₅₀/mL. Overall, the mAbs generated laid the foundation for elucidating the critical role of Fiber-2 in mediating infection and pathogenesis, and the sandwich ELISA approach established here provided efficient and rapid serological diagnostic tool for DAdV-3.

Design and Identification of a Novel Antiviral Affinity Peptide against Fowl Adenovirus Serotype 4 (FAdV-4) by Targeting Fiber2 Protein

Outbreaks of hydropericardium hepatitis syndrome caused by fowl adenovirus serotype 4 (FAdV-4) with a novel genotype have been reported in China since 2015, with significant economic losses to the poultry industry. Fiber2 is one of the important structural proteins on FAdV-4 virions. In this study, the C-terminal knob domain of the FAdV-4 Fiber2 protein was expressed and purified, and its trimer structure (PDB ID: 7W83) was determined for the first time. A series of affinity peptides targeting the knob domain of the Fiber2 protein were designed and synthesized on the basis of the crystal structure using computer virtual screening technology. A total of eight peptides were screened using an immunoperoxidase monolayer assay and RT-qPCR, and they exhibited strong binding affinities to the knob domain of the FAdV-4 Fiber2 protein in a surface plasmon resonance assay. Treatment with peptide number 15 (P15; WWHEKE) at different concentrations (10, 25, and 50 μM) significantly reduced the expression level of the Fiber2 protein and the viral titer during FAdV-4 infection. P15 was found to be an optimal peptide with antiviral activity against FAdV-4 in vitro with no cytotoxic effect on LMH cells up to 200 μM. This study led to the identification of a class of affinity peptides designed using computer virtual screening technology that targeted the knob domain of the FAdV-4 Fiber2 protein and may be developed as a novel potential and effective antiviral strategy in the prevention and control of FAdV-4.

A novel monoclonal antibody efficiently blocks the infection of duck adenovirus 3 by targeting Fiber-2

Duck adenovirus 3 (DAdV-3), identified as the causative agent of a disease characterized by swelling and hemorrhage of liver and kidney, has caused substantial economic losses to duck industry in China. However, the neutralizing epitopes and the infection mechanism of DAdV-3 have not been extensively elucidated. In this study, a novel monoclonal antibody (mAb) targeting Fiber-2 protein of DAdV-3 was generated and designated as mAb 3E7. Indirect immunofluorescence assay showed that mAb 3E7 specifically reacted with the Fiber-2 in LMH cells transfected with pcDNA3.1-Fiber-2 or infected with DAdV-3. Moreover, mAb 3E7 could immunoprecipitate the Fiber-2 and efficiently inhibit the infection of DAdV-3 in vitro. Further epitope mapping revealed mAb 3E7 recognized the epitope ¹⁰⁸LALGDGLE¹¹⁵ in Fiber-2, which was highly conserved among DAdV-3 strains. These findings not only identified a novel neutralizing epitope in Fiber-2, but also paved the way for further elucidating the vital roles of Fiber-2 in the infection and pathogenesis of DAdV-3.

Fiber-1 of serotype 4 fowl adenovirus mediates superinfection resistance against serotype 8b fowl adenovirus

In recent years, hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH) caused by serotype 4 fowl adenovirus (FAdV-4) and serotype 8b fowl adenovirus (FAdV-8b), respectively, are widely prevalent in China, causing huge economic losses to the poultry industry. Numerous studies have revealed the mechanism of the infection and pathogenesis of FAdV-4. However, little is known about the mechanism of infection with FAdV-8b. Among the major structural proteins of fowl adenoviruses, fiber is characterized by the ability to recognize and bind to cellular receptors to mediate the infection of host cells. In this study, through superinfection resistance analysis and an interfering assay, we found that Fiber-1 of FAdV-4, rather than hexon, penton, and fiber of FAdV-8b, conferred efficient superinfection resistance against the infection FAdV-8b in LMH cells. Moreover, truncation analysis depicted that the shaft and knob domains of FAdV-4 Fiber-1 were responsible for the inhibition. However, knockout of the coxsackie and adenovirus receptor (CAR) in LMH cells inhibited the replication of FAdV-8b only at early time points, indicating that CAR might not be the key cell receptor for FAdV-8b. Overall, our findings give novel insights into the infection mechanism of FAdV-8b and provide a new target for the prevention and control of both FAdV-4 and FAdV-8b.

Oral immunization of recombinant Saccharomyces cerevisiae expressing fiber-2 of fowl adenovirus serotype 4 induces protective immunity against homologous infection

Hydropericardium-hepatitis syndrome (HHS) caused by fowl adenovirus (FAdV) serotype 4 strains is a highly contagious disease that causes significant economic loss to the global poultry industry. However, subunit vaccine against FAdV-4 infection is not yet commercially available to date. This study aims to explore the potential for oral immunization of recombinant Saccharomyces cerevisiae expressing Fiber-2 of FAdV-4 as a subunit vaccine. Here, we constructed recombinant S. cerevisiae (ST1814G/Fiber-2) expressing recombinant Fiber-2 (rFiber-2), which was displayed on the cell surface. To evaluate the immune response and protective effect of live recombinant S. cerevisiae, chickens were orally immunized with the constructed live ST1814G/Fiber-2, three times at 5-day intervals, and then challenged with FAdV-4. The results showed that oral administration of live ST1814G/Fiber-2 could stimulate the production of humoral immunity, enhance the body's antiviral activity and immune regulation ability, improve the composition of gut microbiota, provide protection against FAdV-4 challenge, reduce viral load in the liver, and alleviate the pathological damage of heart, liver, and spleen for chicken. In addition, we found the synergistic effect in combining the ST1814G/Fiber-2 yeast and inactivated vaccine to trigger stronger humoral immunity and mucosal immunity. Our results suggest that oral live ST1814G/Fiber-2 is a potentially safer auxiliary preparation strategy in controlling FAdV-4 infection.

An Efficient and Rapid Assay for Detecting Neutralizing Antibodies Against Serotype 4 Fowl Adenovirus

Currently, the outbreak of serotype 4 fowl adenovirus (FAdV-4) has spread worldwide and caused tremendous economic loss to the poultry industry. Although inactivated vaccines have been licensed against FAdV-4 in China, a rapid and efficient serological method for measuring the titer of neutralizing antibodies (NAbs) specific for FAdV-4 post-infection or vaccination is rarely reported. Classical virus neutralization test (VNT) is superior in sensitivity and specificity for detecting NAbs but is either time-consuming or laborious. In this study, a recombinant virus FA4-EGFP expressing EGFP-fiber-2 fusion protein, rather than wild type (WT) FAdV-4 was used to develop a novel VNT for detecting FAdV-4 NAbs. Specificity analysis showed that the approach only reacted with the sera against FAdV-4, not with the sera against other avian pathogens tested. The novel VNT was effective in the detection of NAbs against FAdV-4 in sera from both experimentally infected and clinically vaccinated chickens, and had good linear correlation with the classical VNT. Moreover, the novel VNT not only significantly simplifies the procedure for detection of NAbs, but also shortens the timeline to 24 h in comparison with the classical VNT with 3-4 d. All these data demonstrate that the FA4-EGFP based VNT developed here provides an efficient diagnostic method for monitoring the immunological state of the vaccination or diagnosing the clinical infection of FAdV-4 in a quick and funding-saving manner.

Recombinantly Expressed Chimeric Fibers Demonstrate Discrete Type-Specific Neutralizing Epitopes in the Fowl Aviadenovirus E (FAdV-E) Fiber, Promoting the Optimization of FAdV Fiber Subunit Vaccines towards Cross-Protection in vivo

Vaccines against inclusion body hepatitis in chickens are complicated by the involvement of antigenically diverse fowl adenovirus types. Though immunization with fiber protein confers robust protection, type specificity of fiber antibodies is an obstacle for the desired broad coverage. In this study, we utilized information on multiple linear epitopes predicted in the Fowl Aviadenovirus E (FAdV-E) fiber head (knob) to develop chimeric fibers with an exchange between two serotypes’ sequences, each containing proposed epitopes. Two consecutive segments pertaining to amino acid positions 1 to 441 and 442 to 525/523 in the fibers of FAdV-8a and -8b, types of Fowl Aviadenovirus E that cause inclusion body hepatitis, were swapped reciprocally to result in novel chimeras, crecFib-8a/8b and crecFib-8b/8a. crecFib was indistinguishable from monospecific recombinant fibers in its eactivity with different FAdV antisera in Western blotting. However, contrary to the results for monospecific fibers, crecFib induced cross-neutralizing antibodies against both serotypes in chickens. This demonstrates three nonidentical epitopes in the FAdV-E fiber, the conserved epitope detected in Western blotting and at least two epitopes participating in neutralization, being type specific and located opposite residue position 441-442. Furthermore, we supply conformational evidence for a site in the fiber knob with accessibility critical for neutralization. With such an extended neutralization spectrum compared to those of individual fibers, crecFib was anticipated to fulfill and even extend the mechanistic basis of fiber-mediated protection toward bivalent coverage. Accordingly, crecFib, administered as a single-antigen component, protected chickens simultaneously against challenge with FAdV-8a or -8b, demonstrated by up-to-complete resistance to clinical disease, prevention of target organ-related changes, and significant reduction of viral load.

IMPORTANCE The control of inclusion body hepatitis, a disease of economic importance for chicken production worldwide, is complicated by an etiology involving multiple divergent fowl adenovirus types. The fiber protein is principally efficacious in inducing neutralizing and protective antibodies in vaccinated chickens; however, it faces limitations due to its intrinsic type specificity for neutralization. In this study, based on an in silico-guided prediction of multiple epitopes in the fowl adenovirus fiber head’s loops, we designed chimeric proteins, swapping N- and C-distal fiber portions, each containing putative epitopes, between divergent types FAdV-8a and -8b. In in vitro and in vivo studies, the chimeric fiber displayed extended properties compared to those of individual monotype-specific fibers, allowing the number, distribution, functionality, and conformational bearings of epitopes of the fowl adenovirus fiber to be characterized in more detail. Importantly, the chimeric fiber induced cross-neutralizing antibodies and protective responses in chickens against infections by both serotypes, promoting the advancement of broadly protective subunit vaccination strategies against FAdV.

Immunity analysis against Fowl Adenovirus serotype 4 (FAdV-4) based on Fiber-2 trimer Protein with the different virulence

Since June 2015, Fowl adenovirus outbreaks have occurred in China, causing significant economic losses to poultry industry. The FAdV-4 Fiber-2 proteins could induce effective protection, but the precise mechanism of immune protection remains unknown. Here, we have compared the biological characteristics of Fiber-2 protein of the very virulent WZ strain of FAdV-4 (vvFAdV-4) with that of non-virulent ON1 strain. The sequence analysis revealed natural deletions and sequence differences between the classical non-pathogenic strain ON1 and the vvFAdV-4 isolate. These two Fiber-2 proteins successfully expressed in E. coli resemble in structure and function to the native-like trimeric protein. The trimeric structure and bioreactivity of the recombinant Fiber-2 proteins to FAdV-4 specific antibodies were characterized. The immune protection induced by Fiber-2 proteins of FAdV-4 WZ and ON1 strains were compared in SPF chickens. All birds in the WZ-Fiber-2 immunized group generated systemic specific antibodies compared with both ON1-Fiber-2 protein and PBS immunized groups. According to the results of attack mortalities, viral shedding and tissue gross lesion, the WZ Fiber-2 protein induced complete protection at a dose of 2 μg per chicken, whereas the ON1-Fiber-2 protein induced 0 protection at 3 dpc. In view of the characteristics of Fiber-2 proteins of different strains, this study can help us to further understand the mechanism of protective immunity and provide a basis for the prevention and control of FAdV-4 in chickens.

Identification of three novel B cell epitopes in ORF2 protein of the emerging goose astrovirus and their application

The outbreak of goose gout disease caused by novel goose astrovirus type 1 (GAstV-1) has resulted in huge economic losses to the goose industry in China since 2017. However, little is known about the B cell epitopes in major antigen of GAstV-1 and the serological approach for detection of GAstV-1 is not available. In this study, three novel monoclonal antibodies (mAbs) against the ORF2 protein were first generated and designated as 3G6, 5H7, and 6C6, respectively. Epitope mapping revealed that mAb 3G6, 5H7, and 6C6 recognized ₆₉₅AVRFEKGGHE₇₀₄, ₆₈₅EKALSAPQAG₆₉₄, and ₆₃₅DDDPLSDVTS₆₄₄ in ORF2, respectively. Sequence alignments found that the three epitopes were highly conserved in GAstV-1 but not in other AAstV members. Moreover, a mAb-based sandwich ELISA for the detection of GAstV-1 was first developed using mAb 6C6. The sandwich ELISA only reacted with GAstV-1 but not with GAstV-2 and the other goose-associated viruses tested. The limit of the detection of the sandwich ELISA reaches 1.58 × 10³ TCID₅₀/mL of GAstV-1. Notably, mAb 6C6 could also efficiently react with the GAstV-1 in tissue frozen sections of the clinical infected goose through IFA. The mAbs generated in this study pave the way for further studying on the role of ORF2 in the infection and pathogenesis of GAstV, and the sandwich ELISA and the tissue frozen section-IFA approaches established here provide efficient and rapid serological diagnostic tools for detection of GAstV-1. KEY POINTS: • Three novel B cell epitopes were identified in ORF2 of GAstV-1. • mAb-based ELISA and IFA for detection of GAstV-1 were developed.

A Novel Fiber-1-Edited and Highly Attenuated Recombinant Serotype 4 Fowl Adenovirus Confers Efficient Protection Against Lethal Challenge

Currently, a fatal disease of hepatitis-hydropericardium syndrome (HHS) caused by serotype 4 fowl adenovirus (FAdV-4) has spread worldwide and resulted in tremendous economic losses to the poultry industry. Various vaccines against FAdV-4 were developed to control the disease; however, few live-attenuated vaccines were available. In this study, we targeted the N-terminal of fiber-1 and rescued a recombinant virus FAdV4-RFP_F1 expressing the fusion protein of RFP and Fiber-1 based on the CRISPR/Cas9 technique. In vitro studies showed that FAdV4-RFP_F1 replicated slower than the wild type FAdV-4, but the peak viral titer of FAdV4-RFP_F1 could still reach 10^7.0 TCID₅₀/ml with high stability in LMH cells. Animal studies found that FAdV4-RFP_F1 not only was highly attenuated to the 2-week-old SPF chickens, but could also provide efficient protection against lethal challenge of FAdV-4. All these demonstrate that the recombinant virus FAdV4-RFP_F1 could be as an efficient live-attenuated vaccine candidate for FAdV-4, and the N-terminal of fiber-1 could be as a potential insertion site for expressing foreign genes to develop FAdV-4-based vaccine.

Identification of a novel immunological epitope on Hexon of fowl adenovirus serotype 4

Fowl adenovirus serotype 4 (FAdV-4), the causative agent of hepatitis-hydropericardium syndrome (HHS), distributed widely in the poultry farms in China. Hexon is one of the major capsid proteins associated with viral species or serotypes. However, the epitopes of Hexon protein remain largely unknown. In this study, a monoclonal antibody (mAb) specific to Hexon protein of FAdV-4, designated as 3G8, was generated. Subsequently, the linear peptide recognized by 3G8 was mapped and identified as ²¹³AYGAYVK²¹⁹ using a series of overlapping peptides generated from Hexon protein. Amino acid sequence analysis revealed that the epitope recognized by 3G8 was highly conserved across all the FAdVs. The epitope was immunogenic and could be recognized by FAdV-4 positive chicken serum samples. These findings will enrich our knowledge regarding the epitope on Hexon and provide valuable information for further characterization of the antigenicity of Hexon protein.

Isolation, identification and genetic characterization analysis of a fowl aviadenovirus serotype 4 strain from Tianjin, China

A fowl aviadenovirus serotype 4 (FAdV-4), Y17215-1, was isolated from the liver of chickens with Hydropericardium-hepatitissyndrome(HHS) in a chicken farm of Tianjin, China. Obvious cytopathic effects were observed in the infected chicken liver hepatocellular carcinoma cell line (LMH cells) at 24 h post infection (hpi), which consisted of enlarger and rounder shape of cells. The typical and specific green fluorescence was observed by indirect immunofluorescence assay (IFA). Tissue Culture Infectious Dose50 (TCID₅₀) of it measured after five stable passage in LMH cells reached 10^6.5TCID₅₀/0.1 mL. The strain was inoculated through allantoic membrane of 10-day specific pathogen free(SPF) Chick embryos, the thicker allantoic membranes were observed at 120 hpi. 7-day-old SPF chickens were inoculated with the strain via intramuscular (i.m.) or intranasal (i.n.) injection which resulted in 100% mortality of test chickens. Additionally, the sickness and death of cohabitation chickens in the test group were observed which indicated that the virus can infect healthy chickens by horizontal transmission. The sick chickens showed depression, anorexia and diarrhea with green watery feces. Y17215-1-inoculated chickens mainly presented swollen liver with blood spot, and the enhancement of effusion or yellow gel like effusion that were observed in the pericardium through necropsy. Histopathological examination showed focal necrosis of hepatocytes and characteristic eosinophilic inclusion bodies in the cytoplasm. The results showed that the Y17215-1 isolate had high pathogenicity to SPF chickens. The phylogenetic analysis of the major structural proteins including hexon, fiber-1 and fiber-2 revealed that Y17215-1 strain belongs to C species of fowl aviadenovirus of aviadenovirus family, and has high homology with other Chinese strains isolated in recent years, but was distinct from ON1、MX-SHP95、KR5 and other foreign isolates. This study laid a foundation for further study of epidemiological investigation, pathogenic mechanism as well as the diagnosis and control technology of FAdV-4.

Development of a subunit vaccine based on fiber2 and hexon against fowl adenovirus serotype 4

Hepatitis-hydropericardium syndrome (HHS) is widespread in China and causes high chicken mortality that results in great economic losses. A safe and effective vaccine is needed, and a subunit vaccine has potential for development. In this study, a truncated region of the FAdV-4 fiber 2 fused with coding sequence of one epitope of hexon was expressed in a prokaryotic expression system, and the immune protective effects of different doses of recombinant fiber 2 subunit vaccine on SPF chickens were compared. The recombinant fiber2 (Gly275- Pro479 aa)-hexon (Met21-Val51 aa) protein (rFH) obtained in Escherichia coli showed good solubility. The chicken survival rate at the lowest dose (2.5 μg/bird) was 75% (6/8), and at higher doses (≥5 μg/bird) was 100% (8/8) in challenge experiment. Two chickens in the 2.5 μg/bird treatment showed severe lesions, while birds in the higher dose treatments showed no obvious tissue damage as determined by histopathologic analysis of liver and spleen. Absolute quantitative real-time PCR showed no viral load in the ≥5 μg/bird treatments, but two chickens in the 2.5 μg/bird treatment had high viral loads. The challenge experience demonstrated that the rFH vaccine provided 100% protection at ≥5 μg/bird. These results suggested that rFH protein as an effective vaccine to protect against FAdV-4 and provided a new idea for the development of vaccine against HHS.

Oral Immunization of Recombinant Lactococcus lactis and Enterococcus faecalis Expressing Dendritic Cell Targeting Peptide and Hexon Protein of Fowl Adenovirus 4 Induces Protective Immunity Against Homologous Infection

Hepatitis-hydropericardium syndrome (HPS) causes severe economic losses in the global poultry industry. The present study aims to explore oral immunization of recombinant Lactococcus lactis and Enterococcus faecalis expressing Hexon protein of fowl adenovirus 4 (FAdV-4). The bacteria L. lactis NZ9000 and E. faecalis MDXEF-1 were, respectively, modified as host strain to deliver truncated Hexon protein (ΔHexon) or ΔHexon protein fusing with dendritic cell (DC) targeting peptide (DC-ΔHexon) on the surface of bacteria. The expression of target protein in L. lactis NZ9000 and E. faecalis MDXEF-1 were detected by western blot. To evaluate the immune responses and protective efficacies provided by the live recombinant bacteria, chickens were immunized with the constructed ΔHexon-expressing bacteria three times at 2-week intervals, then experimentally challenged with hypervirulent FAdV-4/GX01. The results showed that oral immunizations with the four ΔHexon-expressing bacteria (NZ9000/ΔHexon-CWA, NZ9000/DC-ΔHexon-CWA, MDXEF-1/ΔHexon-CWA, and MDXEF-1/DC-ΔHexon-CWA), especially the two bacteria carrying DC-targeting peptide, stimulated higher levels of ΔHexon-specific sera IgG and secretory IgA (sIgA) in jejunal lavage fluid, higher proliferation of peripheral blood lymphocytes (PBLs) and higher levels of Th1/Th2-type cytokines, along with significantly decreased virus loads in liver and more offered protective efficacies against FAdV infection compared with PBS and empty vector control groups (p < 0.01). For chickens in the group MDXEF-1/DC-ΔHexon-CWA, the levels of aspartate transaminase (AST), alanine transaminase (ALT) and lactate dehydrogenase (LDH) in sera, and the virus loads in livers were significantly decreased vs. the other three ΔHexon-expressing bacteria (p < 0.01). The pathological changes in the hearts, livers, spleens and kidneys of chickens in MDXEF-1/DC-ΔHexon-CWA group were relatively slight compared to infection control group and other three ΔHexon-expressing bacteria groups. The rate of protection in MDXEF-1/DC-ΔHexon-CWA group was 90%. The present work demonstrated that cell surface-displayed target protein and immune enhancers in L. lactis and E. faecalis might be a promising approach to enhance immunity and immune efficacy against pathogen FAdV-4 infection.

Molecular characterization and pathogenicity of a fowl adenovirus serotype 4 isolated from peacocks associated with hydropericardium hepatitis syndrome

In September 2019, a highly prevalent infectious disease caused severe hydropericardium hepatitis syndrome (HHS) in a peacock farm in Central China. The disease showed high mortality of 78.6% in 28-42 day-old peacocks. In this study, one strain of highly pathogenic fowl adenovirus serotype 4 (FAdV-4) was isolated from peacocks and designated as HN19. Molecular characterization of amino acid revealed that HN19 contains the same deletions as the dominate strains in chickens in China recently. Phylogenetic analyses revealed that HN19 showed higher homology with other FAdV-4 strains isolated from China, indicating that HN19 might originate from previously FAdV-4 predecessor in China. Experimental infection of the HN19 strain via intramuscular injection led to 100% mortality rate in 21-day-old specific pathogenic-free (SPF) chickens. To our knowledge, this represents the first report on the prevalence of FAdV-4 in peacocks. These results suggested that the potential risk of cross-species transmission of FAdV-4 from chickens to peacocks, highlighting the need for implementing strict biosecurity measures to avoid the mixing of different bird species.

A Peptide-Based Enzyme-Linked Immunosorbent Assay for Detecting Antibodies Against Avian Infectious Bronchitis Virus

Infectious bronchitis virus (IBV) causes substantial loss to the poultry industry despite extensive vaccination. Assessing the antibody response is important for the development and evaluation of effective vaccines. We have developed an enzyme-linked immunosorbent assay (ELISA) for the detection of IBV-specific antibodies, using a synthetic peptide based on a conserved sequence in the IBV spike protein. This peptide-based ELISA (pELISA) specifically detects antibodies to different genotypes of IBV but not antibodies against other common chicken viruses. This assay could detect IBV-specific antibody response on as early as day 7 postinfection. In the testing with field serum samples collected from chickens administered with IBV vaccines, the sensitivity, specificity, and accuracy of pELISA were 98.30, 94.12, and 98.8%, respectively, relative to indirect immunofluorescence assay. Our data demonstrate that the pELISA is of value for the detection of IBV antibody and the evaluation of IBV vaccines.

Fiber-1, Not Fiber-2, Directly Mediates the Infection of the Pathogenic Serotype 4 Fowl Adenovirus via Its Shaft and Knob Domains

Recently, the disease of hepatitis-hydropericardium syndrome (HPS) caused by serotype 4 fowl adenovirus (FAdV-4) has spread widely and resulted in huge economic losses to the poultry industry. Although the genome of FAdV-4 has two fiber genes (fiber-1 and fiber-2), the exact role of the genes in the infection of FAdV-4 is barely known. In this study, through superinfection resistance analysis and an interfering assay, we found that fiber-1, but not fiber-2, was the key factor for directly triggering the infection of FAdV-4. The truncation analysis further revealed that both of the shaft and knob domains of fiber-1 were required for the infection. Moreover, the sera against the knob domain were able to block FAdV-4 infection, and the knob-containing fusion protein provided efficient protection against the lethal challenge of FAdV-4 in chickens. All the data demonstrated the significant roles of fiber-1 and its knob domain in directly mediating the infection of FAdV-4, which established a foundation for identifying the receptor of FAdV-4 and developing efficient vaccines against FAdV-4.IMPORTANCE Among 12 serotypes of fowl adenovirus (FAdV), FAdV-1, FAdV-4, and FAdV-10 all carry two fiber genes (i.e., fiber-1 and fiber-2), whereas other serotypes have only one. As important viral surface proteins, the fibers play vital roles in the infection and pathogenesis of FAdV. However, the importance of the fibers to the infection and pathogenesis of FAdV may be different from each other. Recent studies reveal that fiber-2 is identified as a determinant of virulence, but which fiber triggers the infection of FAdV-4 remains unknown. In this study, fiber-1 was identified as a key factor for directly mediating the infection of FAdV-4 through its shaft and knob domains, whereas fiber-2 did not play a role in triggering FAdV-4 infection. The results suggest that fiber-1 and its knob domain may serve as a target for identifying the receptor of FAdV-4 and developing efficient drugs or vaccines against FAdV-4.

Molecular characterization and pathogenicity of highly pathogenic fowl adenovirus serotype 4 isolated from laying flock with hydropericardium-hepatitis syndrome

Hydropericardium-hepatitis syndrome (HHS) is an important emerging disease responsible for huge economic losses to the poultry industry in China. HHS primarily affects 20 to 60-day-old broilers and rarely occurs in laying flock. In this study, the highly pathogenic fowl adenovirus (FAdV) strain, AH-F19, was isolated from the liver samples of 120-day-old laying flock with HHS and its phylogenetic information, genetic mutations, and pathogenicity was evaluated. The phylogenetic analysis revealed that AH-F19 belonged to the FAdV serotype 4 (FAdV-4) cluster, however, 100K differs from the other FAdV-4 strains and is divided into different branches. Amino acid variations in fiber-2 for pathogenic isolates and non-pathogenic isolates indicated that D219, T300, and T380 may not be responsible for virulence. Animal experiments revealed AH-F19 to be a highly pathogenic isolate that can cause 100% mortality in three-week-old specific pathogen-free (SPF) chickens, which exhibited typical hydropericardium and hepatitis. Microscopically, the presence of basophilic intranuclear inclusion bodies in hepatocytes, fractured heart muscle fibers, as well as kidney degeneration and necrosis was observed. Collectively, these findings enriched our understanding of FAdV-4 pathogenicity and provided a reference for further exploration into its pathogenicity.

Isolation and Characterization of A Novel Fowl Adenovirus Serotype 8a Strain from China

Since 2012, the clinical cases of inclusion body hepatitis showed an increasing trend in China, causing considerable economic losses to the poultry industry. In this study, a fowl adenovirus strain CH/GDLZ/201801 was isolated from a chicken flock experiencing inclusion body hepatitis and analyzed by complete genome sequencing. The pathogenicity of the new virus strain was examined by experimental infection of specific pathogen free chickens. The isolate was identified by immunofluorescence and the virions presented typical icosahedral particles under transmission electron microscopy. The full genome of the isolate was 44,329 nucleotides in length with 58% G+C content. Phylogenetic analysis, based on the whole genome, revealed that the new isolate was closest to serotype 8a from the species Fowl aviadenovirus E (FAdV-E). Recombination analysis and phylogenetic analysis showed that the new isolate is a recombinant strain between FAdV-8a and FAdV-8b. In infection experiments, three infected chickens showed clinical signs and one chicken died on day 7 post infection, corresponding to 5% mortality. Macroscopic and microscopic lesions in the liver were observed, and viral antigen could be detected in the livers by immunohistochemical staining and TEM. Taken together, our study describes the genomic characteristics and pathogenicity of a FAdV-8a strain in China. It would lay a solid foundation for further study of the pathogenic mechanism and vaccine development of the virus.

Identification of novel B cell epitopes in the fiber protein of serotype 8 Fowl adenovirus

In recent years, hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH) caused by fowl adenovirus (FAdV) infection have resulted in significant economic losses to the poultry industry worldwide. Epidemiological analysis revealed that serotype FAdV-8 is one of the major pathogenic FAdVs currently prevalent in domestic flocks. Although the fiber protein of FAdV plays vital roles in viral infection and pathogenesis, the B cell epitope in the fiber protein is less known. In this study, two monoclonal antibodies (mAbs) specific to fiber protein of FAdV-8, designated as 4D9 and 5F10, were prepared. Although the mAb 4D9 and 5F10 could not neutralize FAdV-8 infection, 4D9 and 5F10 showed good activities of indirect immunofluorescence, western blot and immunoprecipitation. Epitope analysis revealed that mAb 5F10 recognized 187-219aa in the fiber whereas mAb 4D9 recognized 113-149aa in the fiber. Sequence analysis showed that the epitope recognized by mAb 5F10 was conserve across serotypes FAdV-7, 8a and 8b whereas that for mAb 4D9 was only conserve in FAdV-8b. The generation of mAbs specific to fiber of FAdV-8 and the identification of the novel B cell epitopes here lay the foundation for further studying the antigenicity of the fiber and developing specific diagnosis for FAdV-8.

Two novel monoclonal antibodies against fiber-1 protein of FAdV-4 and their application in detection of FAdV-4/10

BACKGROUND

Recently, serotype 4 fowl adenovirus (FAdV-4) has spread widely and caused huge economic loss to poultry industry. However, little is known about the molecular pathogenesis of FAdV-4. Fiber protein is thought to be vital for its infection and pathogenesis.

RESULTS

Two novel monoclonal antibodies (mAbs) targeting the fiber-1 protein of FAdV-4 were generated, designated as mAb 3B5 and 6H9 respectively. Indirect immunofluorescence assay (IFA) showed that both mAbs only reacted with the FAdV-4 and FAdV-10, not with other serotypes including FAdV-1, FAdV-5, FAdV-6, FAdV-7, FAdV-8 and FAdV-9 tested. Although both mAbs did not recognize the linear epitopes, they could efficiently immunoprecipitate the fiber-1 protein in LMH cells either infected with FAdV-4 or transfected with pcDNA3.1-Fiber-1. Moreover, mAb 3B5 as a capture antibody and HRP-conjugated mAb 6H9 as a detection antibody, a novel sandwich ELISA for efficient detection of FAdV-4 was generated. The limit of detection of the ELISA could reach to 1000 TCID₅₀/ml of FAdV-4 and the ELISA could be efficiently applied to detect FAdV-4 in the clinical samples.

CONCLUSION

The two mAbs specific targeting fiber-1 generated here would pave the way for further studying on the role of fiber-1 in the infection and pathogenesis of FAdV-4, and the established mAb based sandwich ELISA would provide an efficient diagnostics tool for detection of FAdV-4/10.

A novel monoclonal antibodies-based sandwich ELISA for detection of serotype 4 fowl adenovirus

As a major causative agent for hepatitis-hydropericardium syndrome (HPS) in chickens, serotype 4 fowl adenovirus (FAdV-4) has caused huge economic losses in the poultry industry globally. However, there is no commercial diagnostic test for FAdV-4 antigens. To generate a rapid approach for specific detection of FAdV-4, a monoclonal antibodies (mAbs)-based sandwich ELISA was developed. In this ELISA, a purified mAb 4A3 and a HRP-labelled mAb 3C2 specific to the fiber-2 of FAdV-4 were used as the capture antibody and detection antibody respectively. Specificity assay revealed the ELISA only reacted with FAdV-4, not with other avian viruses tested. Sensitivity assay showed the limit of detection of the ELISA was 1000 TCID₅₀/ml and 12.5 ng/ml for the FAdV-4 and the purified GST-Fiber2 protein respectively. Moreover, the ELISA could be efficiently applied in detecting the FAdV-4 in tissue samples from a clinically-diseased chicken flock. All these data demonstrated that the ELISA developed here provides a promising tool for rapid and efficient diagnosis of clinical infection with FAdV-4.

Pathogenicity and molecular characterization of a fowl adenovirus 4 isolated from chicken associated with IBH and HPS in China

Background

Since July in 2015, an emerging infectious disease, Fowl adenovirus (FAdV) species C infection with Hepatitis-Hydropericardium syndrome was prevalent in chicken flocks in China. In our study, one FAdV strain was isolated from commercial broiler chickens and was designated as SDSX1.The phylogenetic information, genetic mutations and pathogenicity of SDSX1 were evaluated.

Results

The phylogenetic analysis indicated that SDSX1 is a strain of serotype 4, FAdV-C. The amino acid analysis of fiber-2 showed that there were more than 20 mutations compared with the non-virulent FAdV-C strains. The pathogenic evaluation of SDSX1 showed that the mortality of one-day-old chickens inoculated SDSX1 was 100%. The typical histopathological changes of SDSX1 were characterized by the presence of basophilic intranuclear inclusion bodies in hepatocytes. The virus copies in different tissues varied from10⁷ to 10¹¹ per 100 mg tissue and liver had the highest virus genome copies.

Conclusion

In conclusion, the isolate SDSX1, identified as FAdV-4, could cause one-day-old chicks’ typical inclusion body hepatitis (IBH) and hepatitis-hydropericardium syndrome (HHS) with 100% mortality. The virus genome loads were the highest in the liver. Molecular analysis indicated that substitutions in fiber-2 proteins may contribute to the pathogenicity of SDSX1.

A novel linear epitope crossing Group 1 and Group 2 influenza A viruses located in the helix A of HA2 derived from H7N9

In this research, four monoclonal antibodies (mAbs) were first generated as an immunogen by using the GST fusion protein that carries the fusion peptide and helix A derived from H7N9 influenza A virus (IAV). These mAbs could react with HA of H7N9, H3N2, and H9N2 with neutralizing activity. A novel linear epitope recognized by these mAbs was identified by peptide-based ELISA, and this epitope was located in TAADYKSTQSAIDQITGKLN at the C terminus of the helix A of H7N9. 3 A11, which is one of the four mAbs, could efficiently recognize the corresponding epitopes derived from H9, H7, H5, H3, and H1. Analysis of sera against the corresponding epitope from different HAs revealed that the C terminus of helix A in H9, H7, and H3 possessed dominant B cell epitopes that cross both Group 1 and Group 2 IAV, whereas the C terminus of helix A in H5 possessed only dominant B cell epitopes that cross subtypes in Group 1 virus. All these results demonstrated that the linear epitope identified in the helix A of H7N9 could be a novel target for developing broad-spectrum influenza diagnostics or vaccine candidates.

Identification of two novel fowl adenovirus C-specific B cell epitopes using monoclonal antibodies against the capsid hexon protein

The diseases associated with fowl adenovirus (FAdV) infection, such as inclusion body hepatitis (IBH), hepatitis-hydropericardium syndrome (HPS), and gizzard erosion (GE), were first reported in Pakistan in 1987, and subsequent outbreaks have been reported worldwide, especially in China, where severe outbreaks of HPS with high mortality from 30 to 100% were recently reported and resulted in significant economic losses to the poultry industry. The diagnosis methods of FAdVs were mostly limited to the nucleotide sequence of hexon by PCR and DNA sequencing. The aim of this study was to generate B cell epitope maps of the species- and serotype-specific hexon L1 using monoclonal antibodies (mAbs) and bioinformatics tools for the development of novel diagnostic methods. In this study, the hexon L1 (230 amino acids) was expressed and used to generate 10 mAb-expressing hybridoma cell lines against the relative protein peptide. Subsequently, we defined the linear peptide epitopes recognized by these mAbs using a series of partially overlapping peptides derived from the FAdV-C hexon protein amino acid sequence to map mAbs reactivity. Finally, a common B cell epitope (₃₁PLAPKESMFN₄₀) for all species FAdVs and two FAdV-C-specific epitopes (₇₉KISGVFPNP₈₇ and ₁₈₁DYDDYNIGTT₁₉₀) were identified. These mAbs and their defined epitopes may support the development of the universal or species-specific differential diagnostic methods of FAdVs.