Avian leukosis virus subgroup J in layer chickens, China

Identification and characterization of chicken TRIM45 and its role as a negative regulator of ALV-J replication in vitro

RESEARCH HIGHLIGHTS

Chicken TRIM45 RING domain and protein localization significantly differ from humans.TRIM45 negatively regulates ALV-J replication in vitro.TRIM45 inhibits ALV-J replication by inducing apoptosis in infected cells.

Rapid detection of avian leukemia virus using CRISPR/Cas13a based lateral flow dipstick

Avian leukemia virus (ALV) is one of the main pathogens of poultry tumor diseases, and has caused significant economic losses to the poultry industry since its discovery. Therefore, establishing a rapid detection method is essential to effectively prevent and control the spread of ALV. In this study, specific CRISPR RNA (crRNA) and recombinase-aided amplification (RAA) primers with T7 promoter were designed based on the relatively conserved sequence of avian leukemia virus. When crRNA recognized the target sequence, Cas13a protein was activated to cut the reporting probes, and then the detection results were read by using lateral flow dipstick (LFD). The RAA-CRISPR/Cas13a-LFD reaction system was constructed. The RAA amplification time, Cas13a protein concentration, crRNA concentration and CRISPR reaction time were optimized to evaluate the specificity, sensitivity and reproducibility of the system. Finally, RAA-CRISPR/Cas13a-LFD method was compared with Polymerase chain reaction (PCR)-Agarose electrophoresis method and qPCR method in the detection of clinical samples, and the reliability of RAA-CRISPR/Cas13a-LFD method was evaluated. The results showed that the RAA-CRISPR/Cas13a-LFD method could effectively amplify the target gene at 37°C for 40 min, and the test results could be determined by LFD visual observation. The method had good specificity and no cross-reaction with Marek's disease virus (MDV), Fowl adenovirus (FAdV), Infectious bursal disease virus (IBDV), Newcastle disease virus (NDV), Infectious laryngotracheitis virus (ILTV), and Infectious bronchitis virus (IBV). The minimum detection limit of the method was 100 copies/μL, and it had good repeatability and stability. The coincidence rate of clinical detection reached 97.69% and 99.23%. In summary, this study established a simple, efficient, accurate and visualized ALV detection method, which can be used for the prevention and rapid clinical diagnosis of avian leukosis (AL).

Immunoinformatics, molecular docking and dynamics simulation approaches unveil a multi epitope-based potent peptide vaccine candidate against avian leukosis virus

Lymphoid leukosis is a poultry neoplastic disease caused by avian leukosis virus (ALV) and is characterized by high morbidity and variable mortality rates in chicks. Currently, no effective treatment and vaccination is the only means to control it. This study exploited the immunoinformatics approaches to construct multi-epitope vaccine against ALV. ABCpred and IEDB servers were used to predict B and T lymphocytes epitopes from the viral proteins, respectively. Antigenicity, allergenicity and toxicity of the epitopes were assessed and used to construct the vaccine with suitable adjuvant and linkers. Secondary and tertiary structures of the vaccine were predicted, refined and validated. Structural errors, solubility, stability, immune simulation, dynamic simulation, docking and in silico cloning were also evaluated.The constructed vaccine was hydrophilic, antigenic and non-allergenic. Ramchandran plot showed most of the residues in the favored and additional allowed regions. ProsA server showed no errors in the vaccine structure. Immune simulation showed significant immunoglobulins and cytokines levels. Stability was enhanced by disulfide engineering and molecular dynamic simulation. Docking of the vaccine with chicken's TLR7 revealed competent binding energies.The vaccine was cloned in pET-30a(+) vector and efficiently expressed in Escherichia coli. This study provided a potent peptide vaccine that could assist in tailoring a rapid and cost-effective vaccine that helps to combat ALV. However, experimental validation is required to assess the vaccine efficiency.

N123I mutation in the ALV-J receptor-binding domain region enhances viral replication ability by increasing the binding affinity with chNHE1

The subgroup J avian leukosis virus (ALV-J), a retrovirus, uses its gp85 protein to bind to the receptor, the chicken sodium hydrogen exchanger isoform 1 (chNHE1), facilitating viral invasion. ALV-J is the main epidemic subgroup and shows noteworthy mutations within the receptor-binding domain (RBD) region of gp85, especially in ALV-J layer strains in China. However, the implications of these mutations on viral replication and transmission remain elusive. In this study, the ALV-J layer strain JL08CH3-1 exhibited a more robust replication ability than the prototype strain HPRS103, which is related to variations in the gp85 protein. Notably, the gp85 of JL08CH3-1 demonstrated a heightened binding capacity to chNHE1 compared to HPRS103-gp85 binding. Furthermore, we showed that the specific N123I mutation within gp85 contributed to the enhanced binding capacity of the gp85 protein to chNHE1. Structural analysis indicated that the N123I mutation primarily enhanced the stability of gp85, expanded the interaction interface, and increased the number of hydrogen bonds at the interaction interface to increase the binding capacity between gp85 and chNHE1. We found that the N123I mutation not only improved the viral replication ability of ALV-J but also promoted viral shedding in vivo. These comprehensive data underscore the notion that the N123I mutation increases receptor binding and intensifies viral replication.

3'UTR of ALV-J can affect viral replication through promoting transcription and mRNA nuclear export

IMPORTANCE

3'UTRs can affect gene transcription and post-transcriptional regulation in multiple ways, further influencing the function of proteins in a unique manner. Recently, ALV-J has been mutating and evolving rapidly, especially the 3'UTR of viral genome. Meanwhile, clinical symptoms caused by ALV-J have changed significantly. In this study, we found that the ALV-J strains containing △-r-TM-type 3'UTR are the most abundant. By constructing ALV-J infectious clones and subgenomic vectors containing different 3'UTRs, we prove that 3'UTRs directly affect viral tissue preference and can promote virus replication as an enhancer. ALV-J strain containing 3'UTR of △-r-TM proliferated fastest in primary cells. All five forms of 3'UTRs can assist intron-containing viral mRNA nuclear export, with similar efficiency. ALV-J mRNA half-life is not influenced by different 3'UTRs. Our results dissect the roles of 3'UTR on regulating viral replication and pathogenicity, providing novel insights into potential anti-viral strategies.

The phylogenetic analysis of the new emerging ALV-K revealing the co-prevailing of multiple clades in chickens and a proposal for the classification of ALV-K

Subgroup K avian leukosis virus (ALV-K) is a new subgroup of avian leukosis virus (ALV) that was first defined in 2012 and has been become prevalent in Chinese native chickens in recent years. An in-depth analysis of the genetic diversity of ALV-K was performed in the study. By Blast analysis, the env gene and the sequences of the 25 ALV-K isolates we isolated were found to be closely related to the isolates from Guangdong, Hebei, Jiangsu, and Hubei provinces, China. Further eighty-nine sequences of the gp85 gene of ALV-K strains available were used in the phylogenetic and genetic distance analyses for the classification. ALV-K was divided into two second-order clades (Clades 1.1 and 1.2) and three third-order clades (Clades 1.2.1, 1.2.2, and 1.2.3), indicating that not only 1.1 and 1.2.3, the two old clades which are prevalent in Japan, but also two new clades (1.2.1, 1.2.2), are co-prevalent in China. The representative strains of each clade were defined for the first time. Notably, Clade 1.2.2 was found to have a deletion of an amino acid residue in the gp85 gene, which was obviously different from Clades 1.1, 1.2.1, and 1.2.3. The proposed classification method will facilitate future studies of ALV-K epidemiology and the comparison of sequences obtained across the world. The first global comprehensive molecular epidemiological analysis was accomplished on the emerging ALV-K.

Eradication of avian leukosis virus subgroups J and K in broiler cross chickens by selection against infected birds using multilocus PCR

The avian leukosis virus (ALV) is a serious threat to sustainable and economically viable commercial poultry management world-wide. Active infections can result in more than 20% flock loss, resulting in significant economic damage. ALV detection and elimination from flocks and breeding programs is complicated by high sequence variability and the presence of endogenous virus copies which show up as false positives in assays. Previously-developed approaches to virus detection are either too labor-intensive to implement on an industrial scale or suffer from high false negative or positive rates. We developed a novel multi-locus multiplex quantitative real-time PCR system to detect viruses belonging to the J and K genetic subgroups that are particularly prevalent in our region. We used this system to eradicate ALV from our broiler breeding program comprising thousands of individuals. Our approach can be generalized to other ALV subgroups and other highly genetically diverse pathogens.

Enhanced Antiviral Ability by a Combination of Zidovudine and Short Hairpin RNA Targeting Avian Leukosis Virus

Avian leukosis virus (ALV) causes tumor diseases in poultry and is circulating all over the world, leading to significant economic losses. In addition, mixed infection of ALV with other viruses is very common and is often reported to contaminate live vaccines. At present, there is no effective method to suppress the replication of ALV in vitro, so it is very difficult to remove it in mixed infection. As a retrovirus, the replication of ALV can be limited by reverse transcriptase (RT) inhibitors like zidovudine (AZT), but it also causes nontargeted cytotoxicity. To find the optimal solution in cytotoxicity and inhibition efficiency in vitro culture system, we firstly designed a combination therapy of AZT and short hairpin RNA (shRNA) targeting ALV and then verified its efficiency by multiple biological methods. Results showed that shRNA can effectively inhibit the expression of RT and then limit the replication of ALV. The combination of AZT and shRNA can significantly improve the antiviral efficiency in viral replication, shedding, and provirus assembly under the condition of low cytotoxicity. Overall, in this study, the combination therapy of AZT and shRNA targeting ALV showed excellent antiviral performance against ALV in vitro culture system. This method can be applied to multiple scenarios, such as the removal of ALV in mixed infection or the purification of contaminated vaccine strains.

dPRLR causes differences in immune responses between early and late feathering chickens after ALV-J infection

To understand the differences in immune responses between early feathering (EF) and late feathering (LF) chickens after infection with avian leukosis virus, subgroup J (ALV-J), we monitored the levels of prolactin, growth hormone and the immunoglobulins IgG and IgM in the serum of LF and EF chickens for 8 weeks. Moreover, we analysed the expression of immune-related genes in the spleen and the expression of PRLR, SPEF2 and dPRLR in the immune organs and DF-1 cells by qRT–PCR. The results showed that ALV-J infection affected the expression of prolactin, growth hormone, IgG and IgM in the serum. Regardless of whether LF and EF chickens were infected with ALV-J, the serum levels of the two hormones and two immunoglobulins in EF chickens were higher than those in LF chickens (P  < 0.05). However, the expression of immune-related genes in the spleen of positive LF chickens was higher than that in the spleen of positive EF chickens. In the four immune organs, PRLR and SPEF2 expression was also higher in LF chickens than in EF chickens. Furthermore, the dPRLR expression of positive LF chickens was higher than that of negative LF chickens. After infection with ALV-J, the expression of PRLR in DF-1 cells significantly increased. In addition, overexpression of PRLR or dPRLR in DF-1 cells promoted replication of ALV-J. These results suggested that the susceptibility of LF chickens to ALV-J might be induced by dPRLR.

ACSL1 Inhibits ALV-J Replication by IFN-Ⅰ Signaling and PI3K/Akt Pathway

J subgroup avian leukosis virus (ALV-J) infection causes serious immunosuppression problems, leading to hematopoietic malignancy tumors in chicken. It has been demonstrated that interferon-stimulated genes (ISGs) could limit ALV-J replication; nevertheless, the underlying mechanisms remain obscure. Here, we demonstrate that Long-chain Acyl-CoA synthetase 1 (ACSL1) is an interferon (IFN)-stimulated gene that specifically restricts the replication of ALV-J due to the higher IFN-I production. More importantly, ACSL1 induces primary monocyte-derived macrophages (MDMs) to pro-inflammatory phenotypic states during ALV-J infection, and ACSL1 mediates apoptosis through the PI3K/Akt signaling pathway in ALV-J-infected primary monocyte-derived macrophages (MDMs). Overall, these results provide evidence that ACSL1 contributes to the antiviral response against ALV-J.

The tyrosine phosphatase SHP-2 dephosphorylated by ALV-J via its Env efficiently promotes ALV-J replication

Avian leukosis virus subgroup J (ALV-J) generally induces hemangioma, myeloid leukosis, and immunosuppression in chickens, causing significant poultry industry economic losses worldwide. The unusual env gene of ALV-J, with low homology to other subgroups of ALVs, is associated with its unique pathogenesis. However, the exact molecular basis for the pathogenesis and oncogenesis of ALV-J is still not fully understood. In this study, ALV-J infection and the overexpression of Env could efficiently downregulate the phosphorylation of SHP-2 (pSHP-2) in vitro and in vivo. The membrane-spanning domain (MSD) in Env Gp37 was the functional domain responsible for pSHP-2 downregulation. Moreover, the overexpression of SHP-2 could effectively promote the replication of ALV-J, whereas knockout or allosteric inhibition of SHP-2 could inhibit ALV-J replication. In addition, the knockout of endogenous chicken SHP-2 could significantly increase the proliferation ability of DF-1 cells. All these data demonstrate that SHP-2 dephosphorylated by ALV-J Env could efficiently promote ALV-J replication, highlighting the important role of SHP-2 in the pathogenesis of ALV-J and providing a new target for developing antiviral drugs against ALV-J.

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

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

A Genetically Engineered Commercial Chicken Line Is Resistant to Highly Pathogenic Avian Leukosis Virus Subgroup J

Viral diseases remain a major concern for animal health and global food production in modern agriculture. In chickens, avian leukosis virus subgroup J (ALV-J) represents an important pathogen that causes severe economic loss. Until now, no vaccine or antiviral drugs are available against ALV-J and strategies to combat this pathogen in commercial flocks are desperately needed. CRISPR/Cas9 targeted genome editing recently facilitated the generation of genetically modified chickens with a mutation of the chicken ALV-J receptor Na+/H+ exchanger type 1 (chNHE1). In this study, we provide evidence that this mutation protects a commercial chicken line (NHE1ΔW38) against the virulent ALV-J prototype strain HPRS-103. We demonstrate that replication of HPRS-103 is severely impaired in NHE1ΔW38 birds and that ALV-J-specific antigen is not detected in cloacal swabs at later time points. Consistently, infected NHE1ΔW38 chickens gained more weight compared to their non-transgenic counterparts (NHE1W38). Histopathology revealed that NHE1W38 chickens developed ALV-J typical pathology in various organs, while no pathological lesions were detected in NHE1ΔW38 chickens. Taken together, our data revealed that this mutation can render a commercial chicken line resistant to highly pathogenic ALV-J infection, which could aid in fighting this pathogen and improve animal health in the field.

Diversity of Avian leukosis virus subgroup J in local chickens, Jiangxi, China

Avian leukosis caused by avian leukosis virus (ALV) is one of the most severe diseases endangering the poultry industry. When the eradication measures performed in commercial broilers and layers have achieved excellent results, ALV in some local chickens has gradually attracted attention. Since late 2018, following the re-outbreak of ALV-J in white feather broilers in China, AL-like symptoms also suddenly broke out in some local flocks, leading to great economic losses. In this study, a systematic epidemiological survey was carried out in eight local chicken flocks in Jiangxi Province, China, and 71 strains were finally isolated from 560 samples, with the env sequences of them being successfully sequenced. All of those new isolates belong to subgroup J but they have different molecular features and were very different from the strains that emerged in white feature broilers recently, with some strains being highly consistent with those previously isolated from commercial broilers, layers and other flocks or even isolated from USA and Russian, suggesting these local chickens have been acted as reservoirs to accumulate various ALV-J strains for a long time. More seriously, phylogenetic analysis shows that there were also many novel strains emerging and in a separate evolutionary branch, indicating several new mutated ALVs are being bred in local chickens. Besides, ALV-J strains isolated in this study can be further divided into ten groups, while there were more or fewer groups in different chickens, revealing that ALV may cross propagate in those flocks. The above analyses explain the complex background and future evolution trend of ALV-J in Chinese local chickens, providing theoretical support for the establishment of corresponding prevention and control measures.

Phylogenetic Analysis of ALV-J Associated with Immune Responses in Yellow Chicken Flocks in South China

The aim of this study was to better understand the sequence characteristics and immune responses in avian leukosis virus subgroup J (ALV-J) infected yellow chicken flocks in South China. We isolated four strains of ALV-J virus from these flocks, which were then identified by several methods, including subtype-specific polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and immunofluorescence assay (IFA). All four viruses were sequenced for their complete genomes and named GD19GZ01, GD19GZ02, GD19GZ03, and GD19GZ04. In comparison with the reference sequence, the homology analysis showed that the gag and pol genes were relatively conserved, whereas env contained much variation. Both GD19GZ01 and GD19GZ02 almost entirely lacked the rTM region and E element, while the latter was retained in GD19GZ03 and GD19GZ04. Moreover, the virus replication levels in GD19GZ03 and GD19GZ04were much higher than those in GD19GZ01 and GD19GZ02. And three virus recombination events in GD19GZ01 and GD19GZ02 were revealed by the results of PDR5 and SimPlot software analysis. Additionally, we found that some interferon-stimulating genes (CH25H, MX, PKR, OAS, and ZAP) and inflammatory mediators (IL-4, IL-6, IL-10, IL-12, 1L-18, and TNF-α) were significantly upregulated in the immune system organs of clinical chickens. Taken together, these findings clarify and reveal the sequence characteristics and trends in the variation of ALV-J infection in yellow chicken flocks of South China.

Isolation and Identification of Subgroup J Avian Leukosis Virus Inducing Multiple Systemic Tumors in Parental Meat-Type Chickens

Avian leukosis virus (ALV) continues evolving to obtain new genomic characters to enhance its pathogenicity. In the present study, an ALV-J strain LH20180301 was isolated from broiler breeder chickens that reached the speak of paralyzation before 20-week-old. The necropsy chickens showed subcutaneous and muscular hemorrhage, and developed tumors in multiple organs including bone, liver, spleen, and kidney. The complete provirus was then cloned and sequenced to investigate the molecular characteristics and oncogenicity etiology of this virus associated with the outbreak of disease. The genomic structure of the reported ALV-J strain LH20180301 was highly conservative with other ALVs. Recombination events between the virus with endogenous virus were identified in the viral genome. Compared with the ALV-J original HPRS-103 strain, the major recombination sites of the viral genome with ev-1 were located in 5′ UTR-gag and 3′ UTR regions. Phylogenetic analysis of group specific antigen gp85 encoding protein showed that the LH20180301 branched with ALV-J prevalent in “yellow chickens” of local breeds in South China. Nine amino acids (N58, D60, K70, A71, K108, N112, N113, N121, R272) in the gp85 were highly conserved among ALV-J isolates before 2012, but various mutations were found in the late isolates including LH20180301. In addition, the LH20180301 strain also had the same deletion pattern of 3′ UTR with them. Therefore, LH20180301 might derive from the same ancestor with those viruses and may be the trend of ALV-J evolution in China. The defined new genomic characters in the gp85 and 3′ UTR region of ALV-J might provide the molecular basis for its enhanced oncogenicity.

Targeting the Histone Methyltransferase Disruptor of Telomeric Silencing 1-Like Restricts Avian Leukosis Virus Subgroup J Replication by Restoring the Innate Immune Response in Chicken Macrophages

Avian leukosis virus subgroup J (ALV-J), an oncogenic retrovirus, is known to cause immunosuppression and various types of cancer in chickens. Recent reports have shown that epigenetic changes in DNA and chromatin are widely implicated in the life cycle of diverse viruses, and reversal of these changes in host cells can lead to alterations in the propagation of viruses. In the present study, we found that disruptor of telomeric silencing 1-like (DOT1L), a histone H3 lysine79 (H3K79) methyltransferase, was upregulated during ALV-J infection in chicken macrophage HD11 cells. Subsequently, we show that targeting DOT1L with a specific inhibitor can significantly decrease the ALV-J replication and viral production. By generating of DOT1L-knockout (KO) HD11 cells using the CRISPR/Cas9 system, we show that deletion of the DOT1L led to an increase in the induction of IFNβ and interferon-stimulated genes (ISGs) in HD11 cells in response to ALV-J infection. Importantly, we confirmed that ALV-J infection impaired the activation of the melanoma differentiation-associated protein 5 (MDA5)-mediated-IFN pathway by suppressing the MDA5 expression, and knockout DOT1L rescued the expression of MDA5 and signal transducer and activator of transcription 1 (STAT1), both of which tightly control the antiviral innate immunity. Collectively, it can be deduced from the current data that blocking DOT1L activity or deletion of DOT1L can lead to ALV-J replication inhibition and restoration of the virally suppressed host innate immunity. Thus, we suggest that DOT1L might be a potential drug target for modulating host innate immune responses to combat ALV-J infection.

Molecular characterization of avian leukosis virus subgroup J in Chinese local chickens between 2013 and 2018

Avian leukosis virus subgroup J (ALV-J) was first isolated from broiler chickens in China in 1999; subsequently, it was rapidly introduced into layer chickens and Chinese local chickens. Recently, the incidence of ALV-J in broiler and layer chickens has significantly decreased. However, it has caused substantial damage to Chinese local chickens, resulting in immense challenges to their production performance and breeding safety. To systematically analyze the molecular characteristics and the epidemic trend of ALV-J in Chinese local chickens, 260 clinical samples were collected for the period of 2013–2018; 18 ALV-J local chicken isolates were identified by antigen-capture enzyme-linked immunosorbent assay and subgroup A-, B-, and J-specific multiplex PCR. The whole genomic sequences of 18 isolates were amplified with PCR and submitted to GenBank. Approximately, 55.5% (10/18) of the 18 isolates demonstrated a relatively high homology (92.3–95.4%) with 20 ALV-J early-isolated local strains (genome sequences obtained from GenBank) in gp85 genes clustering in a separated branch. The 3ʹ untranslated region (3ʹ UTR) of the 18 isolates showed a 195–210 and 16–28 base pair deletion in the redundant transmembrane region and in direct repeat 1, respectively; 55.5% (10/18) of the 18 isolates retained the 147 residue E element. The U3 gene of 61.1% (11/18) of the 18 isolates shared high identity (94.6–97.3%) with ALV-J early-isolated local strains. These results implied that the gp85 and U3 of ALV-J local chicken isolates have rapidly evolved and formed a unique local chicken branch. In addition, it was determined that the gene deletion in the 3′UTR region currently serves as a unique molecular characteristic of ALV-J in China. Hence, the obtained results built on the existing ALV-J molecular epidemiological data and further elucidated the genetic evolution trend of ALV-J in Chinese local chickens.

Gut microbiota profiles of commercial laying hens infected with tumorigenic viruses

BACKGROUND

Studies have shown that some viral infections cause structural changes in the intestinal microflora, but little is known about the effects of tumorigenic viral infection on the intestinal microflora of chickens.

RESULTS

A 29-week commercial layer flock positive for avian leukosis virus-J (ALV-J), Marek's disease virus (MDV) and avian reticuloendotheliosis virus (REV) was selected, and fresh fecal samples were collected and examined for the composition of the gut microflora by Illumina sequencing of the V3-V4 region of the 16S rRNA gene. The operational taxonomic units (OTUs) of the fecal microbiota differentiated the chickens infected with only ALV-J and those coinfected with ALV-J and MDV or REV from infection-negative chickens. The enrichment and diversity of cloacal microflora in chickens infected with ALV-J alone were slightly different from those in the infection-negative chickens. However, the diversity of cloacal microflora was significantly increased in chickens coinfected with both ALV-J and MDV or REV.

CONCLUSIONS

The intestinal microbiota was more strongly disturbed in chickens after coinfection with ALV-J and MDV or REV than after infection with ALV-J alone, and there may be underlying mechanisms by which the capacity for the stabilization of the intestinal flora was impaired due to viral infection and tumorigenesis.

Isolation and molecular characterization of the first subgroup J avian leukosis virus from chicken in Pakistan

Since subgroup J avian leukosis virus (ALV-J) was first isolated in the United Kingdom in 1988, it has seriously hindered the development of the poultry industry worldwide. Although cases of ALV-J infection have been reported as early as 2001 in Pakistan, there was no further research on the isolation and molecular characteristics of ALVs. In the present study, we first isolated two ALVs from suspicious clinical samples that were collected from a desi chicken farm in Pakistan. The results of multiplex PCR and indirect immunofluorescent antibody assays confirmed that the two isolates (PK19FA01 and PK19SA01) belonged to ALV-J. The complete genomes of the two isolates were amplified, sequenced, and systematically analyzed. We found that gp85 of PK19FA01 was more similar to that of the prototype strain HPRS103, whereas gp85 of PK19SA01 was more similar to that of American strains. The two isolates contained an intact E element of 147 residues and had a unique 135 bp deletion in the redundant transmembrane of the 3' untranslated region. The U3 region of the two isolates was highly homologous to that of American ALV-J strains. To our knowledge, this is the first report of the isolation, complete genome sequencing, and systematic molecular epidemiological investigation of ALV-J in Pakistan. Our findings could enrich epidemiological data and might contributed to more effective measures to prevent and control avian leukosis in Pakistan.

Gp37 Regulates the Pathogenesis of Avian Leukosis Virus Subgroup J via Its C Terminus

Different from other subgroups of avian leukosis viruses (ALVs), ALV-J is highly pathogenic. It is the main culprit causing myeloid leukemia and hemangioma in chickens. The distinctiveness of the env gene of ALV-J, with low homology to those of other ALVs, is linked to its unique pathogenesis, but the underlying mechanism remains unclear. Previous studies show that env of ALV-J can be grouped into three species based on the tyrosine motifs in the cytoplasmic domain (CTD) of Gp37, i.e., the inhibitory, bifunctional, and active groups. To explore whether the C terminus or the tyrosine motifs in the CTD of Gp37 affect the pathogenicity of ALV-J, a set of ALV-J infectious clones containing different C termini of Gp37 or the mutants at the tyrosine sites were tested in vitro and in vivo Viral growth kinetics indicated not only that ALV-J with active env is the fastest in replication and ALV-J with inhibitory env is the lowest but also that the tyrosine sites essentially affected the replication of ALV-J. Moreover, in vivo studies demonstrated that chickens infected by ALV-J with active or bifunctional env showed higher viremia, cloacal viral shedding, and viral tissue load than those infected by ALV-J with inhibitory env Notably, the chickens infected by ALV-J with active or bifunctional env showed significant loss of body weight compared with the control chickens. Taken together, these findings reveal that the C terminus of Gp37 plays a vital role in ALV-J pathogenesis, and change from inhibitory env to bifunctional or active env increases the pathogenesis of ALV-J.IMPORTANCE ALV-J can cause severe immunosuppression and myeloid leukemia in infected chickens. However, no vaccine or antiviral drug is available against ALV-J, and the mechanism for ALV-J pathogenesis needs to be elucidated. It is generally believed that gp85 and LTR of ALV contribute to its pathogenesis. Here, we found that the C terminus and the tyrosine motifs (YxxM, ITIM, and ITAM-like) in the CTD of Gp37 of ALV-J could affect the pathogenicity of ALV-J in vitro and in vivo The pathogenicity of ALV-J with Gp37 containing ITIM only was significantly less than ALV-J with Gp37 containing both YxxM and ITIM and ALV-J with Gp37 containing both YxxM and ITAM-like. This study highlights the vital role of the C terminus of Gp37 in the pathogenesis of ALV-J and thus provides a new perspective to elucidate the interaction between ALV-J and its host and a molecular basis to develop efficient strategies against ALV-J.

Molecular characteristics of the re-emerged avian leukosis virus in China, 2018-2019

Since early 2018, avian leukosis virus (ALV) has re-emerged throughout six provinces in Northeast and East of China and caused huge economic losses. In different farms, there are significant differences in clinical symptoms, including morbidity, mortality and location of tumours, on affected animals, which implies that the present strains may have different origins and molecular characteristics. In this study, a systematic epidemiological investigation was conducted in 21 farms in six provinces. Results showed that the virus strains present in this outbreak are highly consistent but carry different mutations. All the strains shared 97.0%-99.0% identity with each other and were highly similar to the GD14J2 strain isolated previously, while different insertion fragments can be found in the env gene of different strains, suggesting that the strains of ALV in this outbreak may have the same ancestors but have gone through different evolutionary trajectories. This study demonstrated that these viruses may point to multiple sources of infection, and all should be identified and taken seriously in the formulation of control plans.

Development and evaluation of a gp85 protein-based subgroup-specific indirect enzyme-linked immunosorbent assay for the detection of anti-subgroup J avian leukosis virus antibodies

Avian leukosis virus subgroup J (ALV-J) is an important pathogen for various neoplasms and causes significant economic losses in the poultry industry. Serological detection of specific antibodies against ALV-J infection is important for successful clinical diagnosis. Here, a 293F stable cell line was established to stably express gp85 protein. In this cell line, gp85 protein was expressed at approximately 30 mg/L. A subgroup-specific indirect enzyme-linked immunosorbent assay (iELISA) was developed using ALV-J gp85 protein as coated antigen to detect antibodies against ALV-J. The sensitivity of the iELISA (1:51200 diluted in serum) was 16 times more than that of indirect immunofluorescence assay (IFA; 1:3200 diluted in serum). Moreover, there was no crossreactivity with antibodies against other common avian viruses and other avian leukosis virus subgroups, such as subgroups A and B. The practicality of the iELISA was further evaluated by experimental infection and clinical samples. The results from experimental infection indicated that anti-ALV-J antibodies were readily detected by iELISA as early as 4 weeks after ALV-J infection, and positive antibodies were detected until 20 weeks, with an antibody-positive rate of 11.1% to 33.3%. Moreover, analysis of clinical samples showed that 9.49% of samples were positive for anti-ALV-J antibodies, and the concordance rate of iELISA and IFA was 99.24%. Overall, these results suggested that the subgroup-specific iELISA developed in this study had good sensitivity, specificity, and feasibility. This iELISA will be very useful for epidemiological surveillance, diagnosis, and eradication of ALV-J in poultry farms.

The follicle promotes the evolution of variants of avian leukosis virus subgroup J in vertical transmission

Avian leukosis virus (ALV) is one of the main causative agent of tumor development, which brings enormous economic losses to the poultry industry worldwide. ALV can be transmitted horizontally and vertically, and the latter often give rise to more adverse pathogenicity. However, the propagation and evolution of ALV underlying vertical transmission remain not-well understood. Herein, an animal model for the evolution of variants of ALV subgroup J (ALV-J) in the vertical transmission was built and different organs from infected hens and plasma from their ALV-positive progenies were collected, and then three segments in the hypervariable regions of ALV (gp85-A, gp85-B, LTR-C) were amplified and sequenced using conventional Sanger sequencing and MiSeq high-throughput sequencing, respectively. The results showed that the genomic diversity of ALV-J occurred in different organs from ALV-J infected hen, and that the dominant variants in different organs of parental hens, especially in follicle, changed significantly compared with original inoculum strain. Notably, the dominant variants in progenies exhibited higher homologies with variants in parental hens' follicle (88.9%-98.9%) than other organs (85.6%-91.1%), and most consistent mutations in the variants were observed between the progenies and parental hen's follicle. Furthermore, HyPhy analysis indicated that the global selection pressure value (ω) in the follicle is significantly higher than those in other organs. In summary, an animal model for vertical transmission was built and our findings revealed the evolution of variants of ALV in the process of vertical transmission, moreover, the variants were most likely to be taken to the next generation via follicle, which may be related to the higher selection pressure follicle underwent.

Identification and characterization of a novel natural recombinant avian leucosis virus from Chinese indigenous chicken flock

Avian leukosis virus (ALV) caused tremendous economic losses to poultry industry all over the world, especially in China. One natural recombinant ALV strain, designated as HB2015032, was isolated from indigenous chickens with neoplastic diseases in Hubei, China. The complete proviral genome of HB2015032 is 7703 bp in length. Sequence analysis showed that the Env of HB2015032 exhibited 99.3% similarity with that of a ALV subgroup K (ALV-K) isolate JS11C1 at amino acid level. Phylogenetic analysis revealed that both gp85 and gp37 of HB2015032 were clustered in the same branch with JS11C1 and other ALV-K strains isolated from Chinese indigenous chickens in recent years. However, the pol gene, the 3' untranslated region (3' UTR), and the 3' long terminal repeat (3' LTR) of HB2015032 were more closely related to ALV-J prototype HPRS-103, and clustered in the same branch with ALV-J strains. Furthermore, the pol gene of HB2015032 contained a premature stop codon that resulted in a truncated Pol protein with 22 amino acid residues missing, which was a unique feature of the pol gene of ALV-J. 3'UTR of HB2015032 containing entire DR1, E element and U3. E element of HB2015032 contained one base deletion, which resulted in a c-Ets-1 binding site. In addition, U3 region of HB2015032 contains most of the transcription regulatory elements of ALV-J, including two CAAT boxes, Y boxes, CArG boxes, PRE boxes, NFAP-1 boxes, and one TATA box. These results suggest that isolate HB2015032 was a novel recombinant ALV-K containing the ALV-K env gene and the ALV-J backbone and exhibiting high pathogenicity.

MiR-125b Suppression Inhibits Apoptosis and Negatively Regulates Sema4D in Avian Leukosis Virus-Transformed Cells

Subgroup J avian leukosis virus (ALV-J), an oncogenic retrovirus, causes hemangiomas and myeloid tumors in chickens. We previously showed that miR-125b is down-regulated in ALV-J-induced tumors. This study aimed to investigate the possible role of miR-125b in ALV-J-mediated infection and tumorigenesis. Knockdown of miR-125b expression in HP45 cells reduced, whereas over-expression induced late-stage apoptosis. Bioinformatics analysis and luciferase activity assays indicate that miR-125b targets Semaphorin 4D/CD100 (Sema4D) by binding the 3'-untranslated region of messenger RNA (mRNA). Up-regulation of miR-125b in the DF1 cell line suppressed Sema4D expression, whereas miR-125 down-regulation increased Sema4D expression levels. To uncover the function of Sema4D during ALV-J infection, animal infection experiments and in vitro assays were performed and show that Sema4D mRNA levels were up-regulated in ALV-J-infected tissues and cells. Finally, functional experiments show that miR-125 down-regulation and Sema4D over-expression inhibited apoptosis in HP45 cells. These results suggest that miR-125b and its target Sema4D might play an important role in the aggressive growth of HP45 cells induced by avian leukosis viruses (ALVs). These findings improve our understanding of the underlying mechanism of ALV-J infection and tumorigenesis.

The high conserved cellular receptors of avian leukosis virus subgroup J in Chinese local chickens contributes to its wide host range

Avian leukosis virus (ALV) is a tumor-inducing virus that spreads among most chicken species, causing serious financial losses for the poultry industry. Subgroup J avian leukosis virus (ALV-J) is a recombinant exogenous ALV, which shows more extensive host range in comparison with other subgroups, especially in Chinese local chickens. To identify the relationship between ALV-J host range and the polymorphism of its cellular receptors, we performed a wide range epidemiological investigation of current ALV-J infection in Chinese local chickens, and discovered that all the 18 local chicken breeds being investigated from main local chicken breeding provinces were ALV-J positive. Furthermore, we cloned ALV-J cellular receptor genes of chNHE1 and chANXA2 of these 18 chicken breeds. Sequence alignment demonstrated that despite several regular mutations at the nucleotide level, there were no corresponding amino acid mutations for either chNHE1 gene or chANXA2 gene. Additionally, virus entry assay indicated that the level of viral enter into cells is stable among different chicken breeds. Results of this study indicated that the wide host range of ALV-J in Chinese local chickens was partially due to the high conservatism of its cellular receptors, and also provide target sites for drug design of resistance to ALV-J infection.

Outbreak of myelocytomatosis caused by mutational avian leukosis virus subgroup J in China, 2018

Avian leukosis virus subgroup J (ALV-J) was isolated in meat-type breeder chickens for the first time in 1988 in the United Kingdom. Due to the application of an eradication program, there were fewer reports related to myelocytomatosis or ALV-J in China after 2013. However, there was another breakout almost simultaneously in six provinces of China in February 2018. On-site, 15- to 20-week-old broiler breeder chickens showed depression, paralysis and weight loss. Mortality for certain flocks reached 15%. Sick chickens showed numerous yellow-white neoplasms growing in the sternum, rib and lumbar vertebra and had hepatic and renal metastasis. Histopathological observation showed all neoplasms were myelocytomas, and there were massive myelocyte-like tumour cells in the liver, kidney and bone marrow. To explore the aetiology of this re-outbreak of myelocytomatosis in China, we collected tumour-bearing chickens and isolated six strains of ALV-J (GM0209-1 to -6). Phylogenetic analysis of gp85 and gp37 showed GM0209 strains were clearly distinct from the prototype strain of ADOL-7501, HPRS-103 and NX0101, and there was a mutation, R176G, in the conserved region between hr1 and hr2 regions of gp85, which was not found in other 44 ALV-J strains. The 3'UTR nucleotide sequences of GM0209 isolates showed there was a signature deletion of 11 nt that was also present in 3'UTR sequences of SCDY1 and NHH, two isolates that have a reported association with haemangioma, indicating this deletion could not determine the tumour type induced by ALV-J. Although the eradication program of ALV-J has been successfully applied in China, the outbreak of ALV-J still occurred, and the virus strain spread quickly. Thus, the biocharacteristics and pathogenesis of mutational ALV-J should be further studied.

Characterization of avian leukosis virus subgroup J isolated between 1999 and 2013 in China

Avian leukosis virus subgroup J (ALV-J) has successively infected white feather chickens, layer hens, cultivated yellow chickens, and indigenous chickens; infection rates and tumorigenicity have attracted increasingly extensive attention in China. To clarify the correlation of the epidemiological phenomenon of ALV-J with the evolution of envelope protein gp85, 140 strains of ALV-J isolated from chickens with different genetic backgrounds from 1999 to 2013 were compared. The homology of the gp85 protein and genetic genealogical relationships between 140 strains of ALV-J and the prototype strain HPRS-103, as well as between the same ALV-J strains and 8 American isolates, were analyzed and compared. The results showed that there was no significant difference in the variation range of homology of the gp85 protein between the prototype HPRS-103 and ALV-J isolates from different genetic backgrounds and different years. However, genetic pedigree analysis showed that virus strains that isolated from the same type of chickens remained close to each other on the phylogenetic tree, which means that there was a correlation between the genetic background of infected chickens and virus strains. Further analysis of amino acid sequences also found similar results and revealed that unique amino acid sites were formed in chickens with different genetic backgrounds, which proved that ALV-J could adapt to the new host through amino acid variation. Genetic sequence phylogenetic tree analysis was more representative than sequence homology comparisons for assessing ALV-J correlations. These conclusions contributed to the control and prevention of ALV infection. ALV-J is still prevalent in Chinese indigenous chickens, more attentions should be given to fulfill the purification.

Development and application of a colloidal gold test strip for detection of avian leukosis virus

Avian leukosis virus (ALV) is an avian oncogenic retrovirus that induces leukemia-like proliferative diseases in chickens. ALV infection can result in the development of immunological tolerance and persistent viremia. Since effective vaccines against ALV are not yet available, its current prevention primarily depends on detection and eradication to establish exogenous ALV-free poultry flocks. In this study, a rapid and simple colloidal gold test strip method, specific for the group-specific antigen, p27 protein, was developed and systematically evaluated for the detection of ALV from different samples. The detection limit of this assay was as low as 6.25 ng/ml for p27 protein and 80 TCID₅₀/ml for different subgroups of ALV. Besides, the test strip showed high specificity in the detection of different subgroups of ALV, including ALV-A, ALV-B, ALV-J, and ALV-K, with no cross-reaction with other avian pathogens. Furthermore, we artificially infected specific pathogen-free (SPF) chickens with ALV-J, collected cloacal swabs, and examined viral shedding using both test strips and ELISA. Results from the test strip were highly consistent with that from ELISA. In addition, 1104 virus isolates from anti-coagulant blood samples, 645 albumen samples, and 4312 meconium samples were tested, and the test strip results agreed with those of ELISA kit up to 97.1%. All the results indicated that the colloidal gold test strip could serve as a simple, rapid, sensitive, and specific diagnostic method for eradication of ALV in poultry farms.

Circular RNA and mRNA profiling reveal competing endogenous RNA networks during avian leukosis virus, subgroup J-induced tumorigenesis in chickens

Avian leukosis virus subgroup J (ALV-J) can induce myeloid tumors and hemangiomas in chickens and causes severe economic losses with commercial layer chickens and meat-type chickens. Here, we generated ribominus RNA sequencing data from three normal chicken spleen tissues and three ALV-J-infected chicken spleen tissues. Structure analysis of transcripts showed that, compared to mRNAs and lncRNAs, chicken circRNAs shared relatively shorter transcripts and similar GC content. Differentially expression analysis showed 152 differentially expressed circRNAs with 106 circRNAs up regulated and 46 circRNAs down regulated. Through comparing differentially expressed circRNA host genes and mRNAs and performed ceRNA network analysis, we found several tumor or immune-related genes, in which, there were four genes existed in both differentially expressed mRNAs and circRNA host genes (Dock4, Fmr1, Zfhx3, Ralb) and two genes (Mll, Aoc3) involved in ceRNA network. We further characterized one exon-intron circRNA derived from HRH4 gene in the ceRNA network, termed circHRH4, which is an abundant and stable circRNA expressed in various tissues and cells in chicken and localizes in cytoplasm. Our results provide new insight into the pathology of ALV-J infection and circRNAs may also mediate tumorigenesis in chicken.

Comprehensive Transcriptome Analysis Reveals Competing Endogenous RNA Networks During Avian Leukosis Virus, Subgroup J-Induced Tumorigenesis in Chickens

Avian leukosis virus subgroup J (ALV-J) is an avian oncogenic retrovirus that induces myeloid tumors and hemangiomas in chickens and causes severe economic losses with commercial layer chickens and meat-type chickens. High-throughput sequencing followed by quantitative real-time polymerase chain reaction and bioinformatics analyses were performed to advance the understanding of regulatory networks associated with differentially expressed non-coding RNAs and mRNAs that facilitate ALV-J infection. We examined the expression of mRNAs, long non-coding RNAs (lncRNAs), and miRNAs in the spleens of 20-week-old chickens infected with ALV-J and uninfected chickens. We found that 1723 mRNAs, 7,883 lncRNAs and 13 miRNAs in the spleen were differentially expressed between the uninfected and infected groups (P < 0.05). Transcriptome analysis showed that, compared to mRNA, chicken lncRNAs shared relatively fewer exon numbers and shorter transcripts. Through competing endogenous RNA and co-expression network analyses, we identified several tumor-associated or immune-related genes and lncRNAs. Along transcripts whose expression levels significantly decreased in both ALV-J infected spleen and tumor tissues, BCL11B showed the greatest change. These results suggest that BCL11B may be mechanistically involved in tumorigenesis in chicken and neoplastic diseases, may be related to immune response, and potentially be novel biomarker for ALV-J infection. Our results provide new insight into the pathology of ALV-J infection and high-quality transcriptome resource for in-depth study of epigenetic influences on disease resistance and immune system.

The emerging novel avian leukosis virus with mutations in the pol gene shows competitive replication advantages both in vivo and in vitro

The avian leukosis virus subgroup K (ALV-K), a novel subgroup in Chinese indigenous chicken breeds, has been difficult to isolate in the past due to its poor replication ability. However, according to the latest monitoring data, the replication ability and isolation rate of ALV-K have clearly increased, and new strains with mutations in the pol gene have also been found. To determine the effects of such mutations on the biological characteristics of ALV-K, a pair of infectious clones were constructed and rescued. The first virus was an ALV-K Chinese isolate with mutations in its pol gene, named rSDAUAK-11. The second virus was a recuperative rSDAUAK-11 from which mutations in the pol gene were recovered according to the corresponding region of the ALV-K prototype virus JS11C1, named rRSDAUAK-11. In addition, two quantitative real-time polymerase chain reaction assays were developed to specifically detect these virus strains. Using such methods, we observed a marked improvement of the reverse transcriptase activity, replication ability and vertical transmission ability of rSDAUAK-11, which also revealed a formidable competitive advantage in mixed infection with rRSDAUAK-11 and corresponded to the differences between the wild strains SDAUAK-11 and JS11C1. Accordingly, our findings not only show that mutations in the pol gene are an important molecular mechanism contributing to corresponding changes in the biological characteristics of the newest ALV-K but also emphasize the potential future eradication of ALV.

Avian leukosis virus subgroup J promotes cell proliferation and cell cycle progression through miR-221 by targeting CDKN1B

Avian leukosis virus subgroup J (ALV-J), a highly oncogenic retrovirus, causes leukemia-like proliferative diseases in chickens. microRNAs post-transcriptionally suppress targets and are involved in the development of various tumors. We previously showed that miR-221 is upregulated in ALV-J-induced tumors. In this study, we analyzed the possible function of miR-221 in ALV-J tumorigenesis. The target validation system showed that CDKN1B is a target of miR-221 and is downregulated in ALV-J infection. As CDKN1B arrests the cell cycle and regulates its progression, we analyzed the proliferation of ALV-J-infected DF-1 cells. ALV-J-infection-induced DF1 cell derepression of G1/S transition and overproliferation required high miR-221 expression followed by CDKN1B downregulation. Cell cycle pathway analysis showed that ALV-J infection induced DF-1 cell overproliferation via the CDKN1B-CDK2/CDK6 pathway. Thus, miR-221 may play an important role in ALV-J-induced aggressive growth of DF-1 cells; these findings have expanded our insights into the mechanism underlying ALV-J infection and tumorigenesis.

A chicken liver cell line efficiently supports the replication of ALV-J possibly through its high level viral receptor and efficient protein expression system

In this study, we identified a chicken liver cell line (LMH) which could strongly support the replication of ALV-J (Subgroup J of avian leukosis virus) with high viral titer. Notably, ALV-J was efficiently detected by ELISA in LMH cells 1 day before DF1 cells. In comparison with DF1 cells, LMH cells not only expressed higher levels of ALV-J receptor chNHE-1, but also possessed a more efficient protein expression system for foreign genes. Thus, LMH cells could be a novel tool to shorten the ALV-J eradication approach and accelerate studies on the pathogenesis and oncogenesis of ALV-J.

Preparation of the Secretory Recombinant ALV-J gp85 Protein Using Pichia pastoris and Its Immunoprotection as Vaccine Antigen Combining with CpG-ODN Adjuvant

This study focuses on preparing the secretory recombinant J subgroup of avian leukosis virus (ALV-J) gp85 protein using Pichia pastoris and evaluating its immunoprotection as vaccine antigen combining with CpG-ODN adjuvant. The secretory recombinant plasmid pPIC9-gp85 containing ALV-J gp85 gene was designed and was transfected into the genome of P. pastoris (GS115) cells. The recombinant plasmid was expressed under the induction of methanol. The expressed products in the medium of the cells were purified and identified with endoglycosidase digestion assay and western blot mediated with monoclonal antibody (MAb) JE9. The purified product combining with CpG-ODN adjuvant was inoculated intramuscularly into 7-day-old chickens and three booster inoculations were performed on 21 days post first inoculation (dpfi), 42, and 56 dpfi. The antibody responses and cellular immune responses were detected, and the protective effects were analyzed after challenge with ALV-J. The results showed that the secretory pPIC9-gp85 plasmid was successfully constructed and could be stably expressed in GS115 cells. The expressed products were N-acetylglucosylated and could specifically combine with MAb (JE9). The secreted gp85 protein combining with CpG-ODN adjuvant could induce higher antibody response and spleen lymphocyte proliferation response and IFN-γ-inducing response, and could protect all the inoculated chickens against the viremia and the immunosuppressive lesions caused by ALV-J challenge. The results of neutralizing test in vitro suggested that the antisera with some ALV-J antibody titers could neutralize ALV-J strain and inhibit the growth of virus in vitro. The result of IFA showed that IgG antibody in the antisera could specifically combine with ALV-J strain in cells. It can be concluded that the secretory recombinant gp85 protein, as a new acetylglucosylated gp85 protein, was successfully prepared and combining with CpG-ODN adjuvant could protect the inoculated chickens against ALV-J infection. This study first reported the methods on preparing the secretory recombinant ALV-J gp85 protein using P. pastoris and evaluated its immunoprotection.

Characterization of subgroup J avian Leukosis virus isolated from Chinese indigenous chickens

Background

In spite of the purification of the laying hens and broilers of avian leukosis virus (ALV) has made remarkable achievements, the infection of ALV was still serious in Chinese indigenous chickens.

Methods

In order to assess the epidemic state of avian leukosis virus in indigenous chickens in China, 10 novel strains of ALV subgroup J (ALV-J), named JS16JH01 to JS16JH10, were isolated and identified by virus isolation and immunofluorescence antibody assays from a Chinese local breed farm with a sporadic incidence of tumors. To understand their virological characteristics further, the proviral genome of ENV-LTR was sequenced and compared with the reference strains.

Results

The homology of the gp85 gene between the ten ALV-J strains and NX0101 was in the range from 89.7–94.8% at the nuclear acid level. In addition, their gp85 genes were quite varied, with identities of 92–98% with themselves at the nuclear acid level. There were several snp and indel sites in the amino acid sequence of gp85 genes after comparison with other reference strains of ALV. Interestingly, a novel insertion in the gp85 region was found in two strains, JS16JH01 and JS16JH07, compared with NX0101 and HPRS-103.

Discussion

At present, owing to the large-scale purification of ALV in China, laying hens and broiler chickens with ALV infection are rarely detected, but ALVs are still frequently detected in the local chickens, which suggests that more efforts should be applied to the purification of ALV from indigenous chickens.

Avian leukosis virus subgroup J induces VEGF expression via NF-κB/PI3K-dependent IL-6 production

Avian leukosis virus subgroup J (ALV-J) is an oncogenic virus causing hemangiomas and myeloid tumors in chickens. Interleukin-6 (IL-6) is a multifunctional pro-inflammatory interleukin involved in many types of cancer. We previously demonstrated that IL-6 expression was induced following ALV-J infection in chickens. The aim of this study is to characterize the mechanism by which ALV-J induces IL-6 expression, and the role of IL-6 in tumor development. Our results demonstrate that ALV-J infection increases IL-6 expression in chicken splenocytes, peripheral blood lymphocytes, and vascular endothelial cells. IL-6 production is induced by the ALV-J envelope protein gp85 and capsid protein p27 via PI3K- and NF-κB-mediated signaling. IL-6 in turn induced expression of vascular endothelial growth factor (VEGF)-A and its receptor, VEGFR-2, in vascular endothelial cells and embryonic vascular tissues. Suppression of IL-6 using siRNA inhibited the ALV-J induced VEGF-A and VEGFR-2 expression in vascular endothelial cells, indicating that the ALV-J-induced VEGF-A/VEGFR-2 expression is mediated by IL-6. As VEGF-A and VEGFR-2 are important factors in oncogenesis, our findings suggest that ALV-J hijacks IL-6 to promote tumorigenesis, and indicate that IL-6 could potentially serve as a therapeutic target in ALV-J infections.

Noncoding RNAs in Retrovirus Replication

Although a limited percentage of the genome produces proteins, approximately 90% is transcribed, indicating important roles for noncoding RNA (ncRNA). It is now known that these ncRNAs have a multitude of cellular functions ranging from the regulation of gene expression to roles as structural elements in ribonucleoprotein complexes. ncRNA is also represented at nearly every step of viral life cycles. This chapter will focus on ncRNAs of both host and viral origin and their roles in retroviral life cycles. Cellular ncRNA represents a significant portion of material packaged into retroviral virions and includes transfer RNAs, 7SL RNA, U RNA, and vault RNA. Initially thought to be random packaging events, these host RNAs are now proposed to contribute to viral assembly and infectivity. Within the cell, long ncRNA and endogenous retroviruses have been found to regulate aspects of the retroviral life cycle in diverse ways. Additionally, the HIV-1 transactivating response element RNA is thought to impact viral infection beyond the well-characterized role as a transcription activator. RNA interference, thought to be an early version of the innate immune response to viral infection, can still be observed in plants and invertebrates today. The ability of retroviral infection to manipulate the host RNAi pathway is described here. Finally, RNA-based therapies, including gene editing approaches, are being explored as antiretroviral treatments and are discussed.

Residues 28 to 39 of the Extracellular Loop 1 of Chicken Na+/H+ Exchanger Type I Mediate Cell Binding and Entry of Subgroup J Avian Leukosis Virus

Chicken Na⁺/H⁺ exchanger type I (chNHE1), a multispan transmembrane protein, is a cellular receptor of the subgroup J avian leukosis virus (ALV-J). To identify the functional determinants of chNHE1 responsible for the ALV-J receptor activity, a series of chimeric receptors was created by exchanging the extracellular loops (ECL) of human NHE1 (huNHE1) and chNHE1 and by ECL replacement with a hemagglutinin (HA) tag. These chimeric receptors then were used in binding and entry assays to map the minimal ALV-J gp85-binding domain of chNHE1. We show that ECL1 of chNHE1 (chECL1) is the critical functional ECL that interacts directly with ALV-J gp85; ECL3 is also involved in ALV-J gp85 binding. Amino acid residues 28 to 39 of the N-terminal membrane-proximal region of chECL1 constitute the minimal domain required for chNHE1 binding of ALV-J gp85. These residues are sufficient to mediate viral entry into ALV-J nonpermissive cells. Point mutation analysis revealed that A30, V33, W38, and E39 of chECL1 are the key residues mediating the binding between chNHE1 and ALV-J gp85. Further, the replacement of residues 28 to 39 of huNHE1 with the corresponding chNHE1 residues converted the nonfunctional ALV-J receptor huNHE1 to a functional one. Importantly, soluble chECL1 and huECL1 harboring chNHE1 residues 28 to 39 both could effectively block ALV-J infection. Collectively, our findings indicate that residues 28 to 39 of chNHE1 constitute a domain that is critical for receptor function and mediate ALV-J entry.IMPORTANCE chNHE1 is a cellular receptor of ALV-J, a retrovirus that causes infections in chickens and serious economic losses in the poultry industry. Until now, the domains determining the chNHE1 receptor function remained unknown. We demonstrate that chECL1 is critical for receptor function, with residues 28 to 39 constituting the minimal functional domain responsible for chNHE1 binding of ALV-J gp85 and efficiently mediating ALV-J cell entry. These residues are located in the membrane-proximal region of the N terminus of chECL1, suggesting that the binding site of ALV-J gp85 on chNHE1 is probably located on the apex of the molecule; the receptor-binding mode might be different from that of retroviruses. We also found that soluble chECL1, as well as huECL1 harboring chNHE1 residues 28 to 39, effectively blocked ALV-J infection. These findings contribute to a better understanding of the ALV-J infection mechanism and also provide new insights into the control strategies for ALV-J infection.

Discovery of novel long non-coding RNAs induced by subgroup J avian leukosis virus infection in chicken

Avian leukosis virus subgroup J (ALV-J) is an avian oncogenic retrovirus that has led to severe economic losses in the poultry industry in China in recent decades. Here, using high throughput transcriptome sequencing of HD11 and CEF cells infected with ALV-J, a set of 4804 novel long non-coding transcripts and numerous differentially expressed long non-coding RNAs (lncRNAs) were identified. We also found that they share relatively shorter transcripts and fewer exon numbers compared to mRNA. Correlation analysis suggested that many lncRNAs may activate gene expression in an enhancer-like manner other than through transcriptional regulation. Expression level analyses in vivo showed that three lncRNAs (NONGGAT001975.2, NONGGAT005832.2 and NONGGAT009792.2) may be associated with immune response regulation and could function as novel biomarkers for ALV-J infection. Our findings provides new insight into the pathological process of ALV-J infection and should serve as a high-quality resource for further research on epigenetic influences on disease-resistance breeding as well as immune system and genomic studies.

Human-Aided Movement of Viral Disease and the Archaeology of Avian Osteopetrosis

The term avian osteopetrosis is used to describe alterations to the skeletal elements of several species of domestic bird, most typically the chicken, Gallus gallus domesticus (L. 1758). Such lesions are routinely identified in animal bones from archaeological sites due to their distinctive appearance, which is characterised by proliferative diaphyseal thickening. These lesions are relatively uncomplicated for specialists to differentially diagnose and are caused by a range of avian leucosis viruses in a series of subgroups. Only some avian leucosis viruses cause the development of such characteristic lesions in osteological tissue. Viraemia is necessary for the formation of skeletal pathology, and avian osteopetrosis lesions affect skeletal elements at different rates. Lesion expression differs by the age and sex of the infected individual, and environmental conditions have an impact on the prevalence of avian leucosis viruses in poultry flocks. These factors have implications for the ways in which diagnosed instances of avian osteopetrosis in archaeological assemblages are interpreted. By integrating veterinary research with archaeological evidence for the presence of avian leucosis viruses across Western Europe, this paper discusses the nature of these pathogens, outlines criteria for differential diagnosis, and offers a fresh perspective on the human-aided movement of animal disease in the past through investigation of the incidence and geographic distribution of avian osteopetrosis lesions from the first century BC to the post-medieval period.

Vertical transmission of avian leukosis virus subgroup J (ALV-J) from hens infected through artificial insemination with ALV-J infected semen

Background

Avian leukosis virus (ALV) is one of the main causes of tumour development within the poultry industry in China. The subgroup J avian leukosis viruses (ALV-J), which induce erythroblastosis and myelocytomatosis, have the greatest pathogenicity and transmission ability within this class of viruses. ALV can be transmitted both horizontally and vertically; however, the effects of ALV infection in chickens—especially roosters—during the propagation, on future generations is not clear. Knowing the role of the cock in the transmission of ALV from generation to generation might contribute to the eradication programs for ALV.

Results

The results showed that two hens inseminated with ALV-J-positive semen developed temporary antibody responses to ALV-J at 4–5 weeks post insemination. The p27 antigen was detected in cloacal swabs of six hens, and in 3 of 26 egg albumens at 1–6 weeks after insemination. Moreover, no viremia was detected at 6 weeks after insemination even when virus isolation had been conducted six times at weekly intervals for each of the 12 females. However, ALV-J was isolated from 1 of their 34 progeny chicks at 1 week of age, and its gp85 had 98.4%–99.2% sequence identity with the gp85 of ALV-J isolated from semen samples of the six cocks.

Conclusions

Our findings indicated that females that were late horizontally infected with ALV-J by artificial insemination might transmit the virus to progeny through eggs, which amounts to vertical transmission.

Dynamic Co-evolution and Interaction of Avian Leukosis Virus Genetic Variants and Host Immune Responses

Subgroup J avian leukosis virus (ALV-J), a typical retrovirus, is characterized of existence of a cloud of diverse variants and considerable genetic diversity. Previous studies describing the evolutionary dynamics of ALV-J genetic variants mainly focused on the early infection period or few randomly selected clones. Here, we inoculated 30 specific-pathogen-free chickens with the same founder ALV-J stock of known genetic background. Six (three antibody positive and three antibody negative) chickens were selected among 15 chickens with viremia. Viruses were serially isolated in 36 weeks and then sequenced using MiSeq high-throughput sequencing platform. This produced the largest ALV-J dataset to date, composed of more than three million clean reads. Our results showed that host humoral immunity could greatly enhance the genetic diversity of ALV-J genetic variants. In particular, selection pressures promoted a dynamic proportional changes in ALV-J genetic variants frequency. Cross-neutralization experiment showed that along with the change of the dominant variant, the antibody titers specific to infectious clones corresponding to the most dominant variants in weeks 12 and 28 have also changed significantly in sera collected in weeks 16 and 32. In contrast, no shift of dominant variant was observed in antibody-negative chickens. Moreover, we identified a novel hypervariable region in the gp85 gene. Our study reveals the interaction between ALV-J and the host, which could facilitate the development of vaccines and antiviral drugs.