Epidemiological and pathological studies of subgroup J avian leukosis virus infections in Chinese local “yellow” chickens

C2H2-type zinc-finger protein BCL11B suppresses avian Leukosis virus subgroup J replication by regulating apoptosis

Apoptosis plays a crucial role in host antiviral defense. The avian leukosis virus subgroup J (ALV-J), an avian oncogenic retrovirus, has been shown to suppress apoptosis while promoting its own replication. ALV-J induces myeloid tumors and hemangiomas in chickens resulting in significant economic losses for commercial layer and meat-type chicken production. B-cell lymphoma/leukemia 11B (Bcl11b) encodes a C2H2-type zinc finger protein-BCL11B, that exerts critical functions in cell proliferation, differentiation, and plays an essential role in the immune system. Previous study has been shown that Bcl11b is associated with ALV-J infection. In this study, we further investigated the pathological changes in ALV-J infected cells and examined the role and expression regulation of chicken Bcl11b. Our results demonstrate that Bcl11b, as an interferon-stimulated gene (ISG), encodes C2H2-type zinc finger protein BCL11B that promotes apoptosis to inhibit ALV-J infection. Additionally, gga-miR-1612 and gga-miR-6701-3p regulate apoptosis and are involved in ALV-J infection by targeting Bcl11b, thus revealing immune response strategies between the host and ALV-J. Although the underlying mechanisms require further validation, Bcl11b and its regulatory miRNAs are the first to demonstrate inhibition of ALV-J replication via apoptosis. BCL11B can a valuable target for treating diseases triggered by ALV-J infection.

PMAIP1 promotes J subgroup avian leukosis virus replication by regulating mitochondrial function

Avian leukosis virus Subgroup J (ALV-J) exhibits high morbidity and pathogenicity, affecting approximately 20% of poultry farms. It induces neoplastic diseases and immunosuppression. Phorbol-12-myristate-13-acetate-induced protein 1 (PMAIP1), a proapoptotic mitochondrial protein in the B-cell lymphoma-2 (Bcl-2) family, plays a role in apoptosis in cancer cells. However, the connection between the PMAIP1 gene and ALV-J pathogenicity remains unexplored. This study investigates the potential impact of the PMAIP1 gene on ALV-J replication and its regulatory mechanisms. Initially, we examined PMAIP1 expression using quantitative real-time PCR (qRT-PCR) in vitro and in vivo. Furthermore, we manipulated PMAIP1 expression in chicken fibroblast cells (DF-1) and assessed its effects on ALV-J infection through qRT-PCR, immunofluorescence assay (IFA), and western blotting (WB). Our findings reveal a significant down-regulation of PMAIP1 in the spleen, lung, and kidney, coupled with an up-regulation in the bursa and liver of ALV-J infected chickens compared to uninfected ones. Additionally, DF-1 cells infected with ALV-J displayed a notable up-regulation of PMAIP1 at 6, 12, 24, 48, 74, and 108 h. Over-expression of PMAIP1 enhanced ALV-J replication, interferon expression, and proinflammatory factors. Conversely, interference led to contrasting results. Furthermore, we observed that PMAIP1 promotes virus replication by modulating mitochondrial function. In conclusion, the PMAIP1 gene facilitates virus replication by regulating mitochondrial function, thereby enriching our understanding of mitochondria-related genes and their involvement in ALV-J infection, offering valuable insights for avian leukosis disease resistance strategies.

Immunopathological investigation and genetic evolution of Avian leukosis virus Subgroup-J associated with myelocytomatosis in broiler flocks in Egypt

BACKGROUND

Avian leukosis virus Subgroup-J (ALV-J) is a rapidly oncogenic evolving retrovirus infecting a variety of avian species; causing severe economic losses to the local poultry industry.

METHODS

To investigate ALV-J, a total of 117 blood samples and 57 tissue specimens of different organs were collected for virological, and pathological identification, serological examinations, molecular characterization, and sequencing analysis. To the best of our knowledge, this is the first detailed report recorded in broiler flocks in Egypt. The present study targets the prevalence of a viral tumor disease circulating in broiler flocks in the El-Sharqia, El-Dakahliya, and Al-Qalyubiyya Egyptian governorates from 2021 to 2023 using different diagnostic techniques besides ALV-J gp85 genetic diversity determination.

RESULT

We first isolated ALV-J on chicken embryo rough cell culture; showing aggregation, rounding, and degeneration. Concerning egg inoculation, embryonic death, stunting, and curling were observed. Only 79 serum samples were positive for ALV-J (67.52%) based on the ELISA test. Histopathological investigation showed tumors consist of uniform masses, usually well-differentiated myelocytes, lymphoid cells, or both in the liver, spleen, and kidneys. Immunohistochemical examination showed that the myelocytomatosis-positive signals were in the spleen, liver, and kidney. The PCR assay of ALV-J gp85 confirmed 545 base pairs with only 43 positive samples (75.4%). Two positive samples were sequenced and submitted to the Genbank with accession numbers (OR509852-OR509853). Phylogenetic analysis based on the gp85 gene showed that the ALV-J Dakahlia-2 isolate is genetically related to ALV-EGY/YA 2021.3, ALV-EGY/YA 2021.4, ALV-EGY/YA 2021.14, and ALV-EGY/YA 2021.9 with amino acid identity percentage 96%, 97%; 96%, 96%; respectively. Furthermore, ALV-J Sharqia-1 isolate is highly genetically correlated to ALV-EGY/YA 2021.14, and ALV-EGY/YA 2021.9, ALV-J isolate QL1, ALV-J isolate QL4, ALV-J isolate QL3, ALV-EGY/YA 2021.4 with amino acid identity percentage 97%, 97%; 98%, 97%, 97%, 95%; respectively.

CONCLUSIONS

This study confirmed that ALV-J infection had still been prevalent in broilers in Egypt, and the genetic characteristics of the isolates are diverse.

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.

miR-155 facilitates the synergistic replication between avian leukosis virus subgroup J and reticuloendotheliosis virus by targeting a dual pathway

IMPORTANCE

The synergy of two oncogenic retroviruses is an essential phenomenon in nature. The synergistic replication of ALV-J and REV in poultry flocks increases immunosuppression and pathogenicity, extends the tumor spectrum, and accelerates viral evolution, causing substantial economic losses to the poultry industry. However, the mechanism of synergistic replication between ALV-J and REV is still incompletely elusive. We observed that microRNA-155 targets a dual pathway, PRKCI-MAPK8 and TIMP3-MMP2, interacting with the U3 region of ALV-J and REV, enabling synergistic replication. This work gives us new targets to modulate ALV-J and REV's synergistic replication, guiding future research on the mechanism.

The Emergence, Diversification, and Transmission of Subgroup J Avian Leukosis Virus Reveals that the Live Chicken Trade Plays a Critical Role in the Adaption and Endemicity of Viruses to the Yellow-Chickens

The geographical spread and inter-host transmission of the subgroup J avian leukosis virus (ALV-J) may be the most important issues for epidemiology. An integrated analysis, including phylogenetic trees, homology modeling, evolutionary dynamics, selection analysis and viral transmission, based on the gp85 gene sequences of the 665 worldwide ALV-J isolates during 1988-2020, was performed. A new Clade 3 has been emerging and was evolved from the dominating Clade 1.3 of the Chinese Yellow-chicken, and the loss of a α-helix or β-sheet of the gp85 protein monomer was found by the homology modeling. The rapid evolution found in Clades 1.3 and 3 may be closely associated with the adaption and endemicity of viruses to the Yellow-chickens. The early U.S. strains from Clade 1.1 acted as an important source for the global spread of ALV-J and the earliest introduction into China was closely associated with the imported chicken breeders in the 1990s. The dominant outward migrations of Clades 1.1 and 1.2, respectively, from the Chinese northern White-chickens and layers to the Chinese southern Yellow-chickens, and the dominating migration of Clade 1.3 from the Chinese southern Yellow-chickens to other regions and hosts, indicated that the long-distance movement of these viruses between regions in China was associated with the live chicken trade. Furthermore, Yellow-chickens have been facing the risk of infections of the emerging Clades 2 and 3. Our findings provide new insights for the epidemiology and help to understand the critical factors involved in ALV-J dissemination. IMPORTANCE Although the general epidemiology of ALV-J is well studied, the ongoing evolutionary and transmission dynamics of the virus remain poorly investigated. The phylogenetic differences and relationship of the clades and subclades were characterized, and the epidemics and factors driving the geographical spread and inter-host transmission of different ALV-J clades were explored for the first time. The results indicated that the earliest ALV-J (Clade 1.1) from the United States, acted as the source for global spreads, and Clades 1.2, 1.3 and 3 were all subsequently evolved. Also the epidemiological investigation showed that the early imported breeders and the inter-region movements of live chickens facilitated the ALV-J dispersal throughout China and highlighted the needs to implement more effective containment measures.

New rapid detection by using a constant temperature method for avian leukosis viruses

The avian leukemia virus causes avian leukemia (AL), a severe immunosuppressive disease in chickens (ALV). Since the 1990s, the diversity of ALV subpopulations caused by ALV genome variation and recombination, and the complexity of the infection and transmission, with currently no effective commercial vaccine and therapeutic for ALV, has resulted in severe economic losses to the chicken business in various parts of the world. Therefore, as a key means of prevention and control, an effective, rapid, and accurate detection method is imperative. A new real-time reverse transcription recombinase-aided amplification (RT-RAA) assay for ALV with rapid, highly specific, low-cost, and simple operational characteristics have been developed in this study. Based on the amplification of 114 base pairs from the ALV P12 gene, real-time RT-RAA primers and a probe were designed for this study. The lowest detection line was 10 copies of ALV RNA molecules per response, which could be carried out at 39°C in as fastest as 5 min and completed in 30 min, with no cross-reactivity with Marek's disease virus, avian reticuloendothelial virus, Newcastle disease virus, infectious bronchitis virus, infectious bursal disease virus, infectious laryngotracheitis virus, and avian influenza virus. Furthermore, the kappa value of 0.91 (>0.81) was compared with reverse transcription–polymerase chain reaction (RT-PCR) for 44 clinical samples, and the coefficients of variation were within 5.18% of the repeated assays with three low-level concentration gradients. These results indicate that using a real-time RT-RAA assay to detect ALV could be a valuable method.

Role of env gene and LTR sequence in the pathogenesis of subgroup K avian leukosis virus

Avian leukosis virus (ALV) is a retrovirus that induces tumours in infected birds; ALV is divided into different subgroups according to the env gene and cellular tropism. In general, ALV subgroup J (ALV-J) is considered to be the most pathogenic and prevalent subgroup while subgroup K (ALV-K), a newly identified subgroup, only causes mild symptoms. To illuminate the roles of the env viral gene and LTR sequence in pathogenic differences between ALV-J and ALV-K, rescued ALV-J strain rSDAU1005, rescued ALV-K strain rJS11C1, and recombinant strains rENV(J)-LTR(K) and rENV(K)-LTR(J) were characterized and investigated in this study. Among rescued viruses, rSDAU1005 had the highest replication efficiency while rJS11C1 replicated the slowest (replication efficiency rankings were rSDAU1005 >rENV(K)-LTR(J)>rENV(J)-LTR(K)>rJS11 C1). The luciferase reporter gene assay results showed that the promoter activity of ALV-K LTR was lower than that of the ALV-J LTR promoter, which may have accounted for the slower replication efficiency of ALV-K. Pathogenicity of the four rescued viruses was determined via inoculating the yolk sacs of specific-pathogen-free chickens. The results demonstrated that all four viruses were pathogenic; rSDAU1005 caused the most severe growth retardation and immunosuppression. rENV(J)-LTR(K) was more pathogenic when compared to rENV(K)-LTR(J), indicating that env and the LTR sequence play important roles in pathogenicity between ALV-K and ALV-J. Additionally, env seemed to especially play a role in ALV-K pathogenesis. This study provided scientific data and insight to improve detection methods and judgement criteria in ALV clearance and surveillance.

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.

Development and Application of a Reverse-transcription Recombinase-Aided Amplification Assay for Subgroup J Avian Leukosis Virus

Subgroup J Avian leukosis virus (ALV-J) is an important pathogen of poultry tumor diseases. Since its discovery, it has caused significant economic losses to the poultry industry. Thus, the rapid detection of molecular level with strong specificity is particularly important whether poultry are infected with ALV-J. In this study, we designed primers and probe for real-time fluorescent reverse-transcription recombinase-aided amplification assay (RT-RAA) based on the ALV-J gp85 sequence. We had established a real-time fluorescent RT-RAA method and confirmed this system by verifying the specificity and sensitivity of the primers and probe. In addition, repeatability tests and clinical sample regression tests were used for preliminary evaluation of this detection method. The sensitivity of established method was about 10¹ copies/μL, and the repeatability of the CV of the C_T value is 4%, indicating repeatability is good. Moreover, there was no cross-reactivity with NDV, IBV, IBDV, H9N2, MDV, and REV, and other avian leukosis virus subgroups, such as subgroups A, B, C, D, K and E. Importantly, the real-time fluorescent RT-RAA completed the test within 30 min at a constant temperature of 41°C. Forty-two clinical samples with known background were tested, and the test results were coincided with 100%. Overall, these results suggested that the real-time fluorescent RT-RAA developed in this study had strong specificity, high sensitivity, and good feasibility. The method is simple, easy, and portable, that is suitable for clinical and laboratory diagnosis, and provides technical support for the prevention and control of ALV-J.

Antibody profiles of avian leukosis virus subgroups A/B and J In layer flocks suspected to have Marek’s disease in Nigeria

Previous reports indicate high seroprevalence of avian leukosis virus (ALV) p72 antigen in layer flocks suspected to have Marek’s disease (MD) in Kaduna and Plateau States. However, the specific subgroups responsible for ALV infection in layers in the States are still unknown, hence the need for this study. Therefore, the objective of this study was to determine the antibody profiles of ALV subgroups A/B and J in layer flocks suspected to have MD in Kaduna and Plateau States. Sera from 7 and 16 layer flocks suspected to have MD in Kaduna and Plateau States respectively, were screened for the presence of antibodies to ALV subgroups A/B and J using IDEXX enzyme linked immunosorbent assay (ELISA) kits. Out of the seven layer flocks screened in Kaduna State, antibodies to ALV subgroup A/B was detected in six of the flocks (85.7%), while antibodies to ALV subgroup J was detected in only one flock (14.3%). Antibodies to both ALV subgroups A/B and J were detected in one flock (14.3%), which suggests co-infection of the two ALV subgroups. Out of the 16 flocks screened in Plateau State, antibodies to ALV subgroup A/B were detected in 15 flocks (93.8%), while antibodies to ALV subgroup J were detected in six flocks (37.5%). Antibodies to both ALV subgroups A/B and J were detected in five flocks (31.3%). The high detection of antibodies to ALV A/B suggests that ALV infection in layers is mostly due to ALV subgroup A or B in the study areas.

Regulation of Avian Leukosis Virus Subgroup J Replication by Wnt/β-Catenin Signaling Pathway

Wnt/β-catenin signaling is a highly conserved pathway related to a variety of biological processes in different cells. The regulation of replication of various viruses by Wnt/β-catenin signaling pathway has been reported. However, the interaction between the Wnt/β-catenin pathway and avian leukosis virus is unknown. In the present study, we investigated the effect of modulating the Wnt/β-catenin pathway during avian leukosis virus subgroup J (ALV-J) infection. The activation of the Wnt/β-catenin pathway by GSK-3 inhibitor increased ALV-J mRNA, viral protein expression, and virus production in CEF cells. This increase was suppressed by iCRT14, one of the specific inhibitors of the Wnt/β-catenin signaling pathway. Moreover, treatment with iCRT14 reduced virus titer and viral gene expression significantly in CEF and LMH cells in a dose-dependent manner. Inhibition Wnt/β-catenin signaling pathway by knockdown of β-catenin reduced virus proliferation in CEF cells also. Collectively, these results suggested that the status of Wnt/β-catenin signaling pathway modulated ALV-J replication. These studies extend our understanding of the role of Wnt/β-catenin signaling pathway in ALV-J replication and make a new contribution to understanding the virus–host interactions of avian leukosis virus.

Rapid detection of avian leukosis virus subgroup J by cross-priming amplification

Avian leukosis virus subgroup J (ALV-J) causes oncogenic disease in chickens in China, resulting in great harm to poultry production, and remains widespread in China. Herein, we employed a cross-priming amplification (CPA) approach and a nucleic acid detection device to establish a visual rapid detection method for ALV-J. The sensitivity of CPA, polymerase chain reaction (PCR) and real-time PCR (RT-PCR) was compared, and the three methods were used to detect ALV-J in the cell cultures which inoculated with clinical plasma. The result showed when the amplification reaction was carried out at 60 °C for just 60 min, the sensitivity of CPA was 10 times higher than conventional PCR, with high specificity, which was comparable with RT-PCR, based on detection of 123 cell cultures which inoculated with clinical plasma, the coincidence rate with real-time PCR was 97.3% (71/73). CPA detection of ALV-J does not require an expensive PCR instrument; a simple water bath or incubator is sufficient for complete DNA amplification, and the closed nucleic acid detection device avoids aerosol pollution, making judgment of results more intuitive and objective. The CPA assay would be a promising simple, rapid and sensitive method for identification of ALV-J.

Genetic diversity of avian leukosis virus subgroup J (ALV-J): toward a unified phylogenetic classification and nomenclature system

Avian leukosis virus subgroup J (ALV-J) has infected a variety of birds, causing major economic losses in China. Understanding the comprehensive criteria of classification and nomenclature of ALV-J would be useful for the investigation of the viral evolution and also for the prevention and control of this infection. An in-depth analysis of the genetic diversity of ALV-J was performed in the present study. Four hundred and seventy-five sequences of the gp85 gene, including thirteen of avian endogenous retrovirus designated ev/J and 462 of ALV-J, were used in the phylogenetic and the evolutionary distance analysis for this classification. The study identified that the current ALV-J strains were divided into two first-order clades (Clades 1 and 2) and three second-order clades (Clades 1.1, 1.2 and 1.3). The current Chinese ALV-J strains are predominantly in Clade 1.3, and the Chinese and Egyptian chicken flocks have been facing the emerging Clade 2 viruses. This system pioneers the classification efforts for ALV-J, which uses Pilot tree for rapid classification of the new isolates and also the addition of possible new clades. The proposed unified classification system will facilitate future studies of ALV-J epidemiology and genetic evolution and of the comparison of sequences obtained across the world.

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.

Molecular characteristics of subgroup J avian leukosis virus isolated from yellow breeder chickens in Guangdong, China, during 2016-2019

Since 2005, subgroup J avian leukosis virus (ALV-J) infection has been present in yellow chickens in Guangdong, China, causing severe economic losses to the local poultry industry. ALV-J is a rapidly evolving retrovirus. To investigate the molecular characteristics of ALV-J isolates from yellow breeder chickens in Guangdong, 17 virus strains were isolated from 6549 anticoagulants from clinically healthy birds between 2016 and 2019, and completely sequenced and phylogenetically analyzed. Phylogenetic analysis of the gp85 gene showed that all isolated viruses were divided into three different branches. Notably, 41.2% (7/17) of the isolates shared a novel G2598A nucleotide mutation in the pol gene and caused the stop codon to be advanced by 8 positions. Nearly 200 nucleotides were deleted from the redundant TM (rTM) region in all strains, but all retained an intact direct repeat (DR1). 82.4% (14/17) of isolates contained a complete E element. Additionally, 29.4% (5/17) of isolates detected an 11 bp deletion in U3 region, and the AIB REP1 transcription factor is missing. The study indicated that ALV-J infection had still been prevalent in the yellow breeder chicken farms in Guangdong, and the genetic background of the strains is diverse. This study provides the latest data on the molecular characteristics of ALV-J, which will help to reveal the evolution trend of ALV-J and develop relevant prevention and control measures.

Recombinant subgroup B avian leukosis virus combined with the subgroup J env gene significantly increases its pathogenicity

The differences among different sub-groups of the avian leukosis virus (ALV) genome are mainly concentrated in the env gene, which binds to cell-specific receptors and determines the characteristics of viral tropism and pathogenicity. In this study, two rescued viruses rGX15MM6-2 (ALV of subgroup J, ALV-J) and rGX14FF03 (ALV of subgroup B, ALV-B) and a recombinant virus rALV-B-Jenv (ALV-B's backbone with ALV-J's env) were generated and tested utilizing both in vitro and in vivo experiments. The results showed that the replication ability of the viruses released in DF-1 cell cultures was listed in order as rGX15MM6-2 > rALV-B-Jenv > rGX14FF03. rGX15MM6-2 caused the most serious suppression of body weight gain, exhibited a significant negative effect on the development of immune organs (P < 0.05) and lower antibody responses to vaccinations with the commercial oil-emulsion vaccines (OEVs) (P<0.05) in the challenged chickens. The viral detection showed that the positive rate in blood from the birds infected with rALV-B-Jenv were respectively higher than those from the birds infected with rGX14FF03 (P < 0.05). At 25 wpi, similar tumors were found in the abdominal cavity of the birds in rGX15MM6-2 and rALV-B-Jenv groups. The results demonstrated that the ALV-J env gene significantly increases the pathogenicity of the recombinant ALV-B. With the increasing incidence of co-infections of different subgroups of ALV in the field, the possibility of viral recombination is increasing and demands further study.

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.

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.

Full-length cDNA sequence analysis of 85 avian leukosis virus subgroup J strains isolated from chickens in China during the years 1988-2018: coexistence of 2 extremely different clusters that are highly dependent upon either the host genetic background or the geographic location

During the process of transmission and spread of avian leukosis virus subgroup J (ALV-J) in chickens worldwide, the viral genome is constantly changing. A comprehensive and systematic study of the evolutionary process of ALV-J in China is needed. In this study, we amplified the full-length viral cDNA sequences of 16 ALV-J isolates of Yellow-chicken origin and analyzed and compared these sequences with another 69 ALV-J strains isolated during the years 1988–2018. These isolates were then sorted into 2 clusters: cluster I included isolates that mainly originated from the layers and White-feather broilers from northern China; cluster II included isolates mainly from the Yellow-chicken, most of them being from southern China. According to the sequence homologies of the whole genome and gag, pol, gp85, and gp37 genes, the ALV-J strains are more likely to randomly change in different directions from the original strain HPRS-103 as time passes. The results of entropy analysis of the sequences of gag, pol, and env revealed that the env gene had the largest variation, and the gag gene nonconserved sites are mainly concentrated in p19, p10, and p12. In addition, 84.71% (72/85) of the isolates had the 205-nucleotide (nt) deletion in the 3′UTR region, and 30.59% (26/85) of the isolates had the 125-nt to 127-nt deletion in the E element. Our study provides evidence for the coexistence of 2 extremely different clusters of ALV-J prevailing in China and in some other countries during the period of 1988–2018 and implies that the clusters are highly dependent on the host genetic background and the geographic location.

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.

Co-infection with avian hepatitis E virus and avian leukosis virus subgroup J as the cause of an outbreak of hepatitis and liver hemorrhagic syndromes in a brown layer chicken flock in China

Hens of a commercial Hy-line brown layer flock in China exhibited increased mortality and decreased egg production at 47 wk of age. From 47 to 57 wk, average weekly mortality increased from 0.11 to 3.0%, and egg production decreased from 10 to 30%, with a peak mortality rate (3.0%) observed at 54 wk of age. Necropsy of 11 birds demonstrated tissue damage that included hepatitis, liver hemorrhage, rupture, and/or enlarged livers. Microscopic liver lesions exhibited hepatocytic necrosis, lymphocytic periphlebitis, and myeloid leukosis. While no bacteria were recovered from liver and spleen samples, avian hepatitis E virus (HEV) RNA was detected in all 11 tested hens by nested reverse transcription-polymerase chain reaction. Of these, subgroup J avian leukosis virus (ALV-J) proviral DNA was detected in 5 hens by PCR. Alignments of partial ORF2 gene sequences obtained here demonstrated shared identity (76 to 97%) with corresponding sequences of other known avian HEV isolates. Env sequences of ALV-J isolates obtained here shared 50.1 to 55% identity with other ALV subgroups and 91.8 to 95.5% identity with other known ALV-J isolates. Phylogenetic tree analysis of selected sequences obtained here grouped an avian HEV sequence with genotype 3 HEV and assigned an ALV-J sequence to a branch separate from known ALV-J subgroups. Immunohistochemical results confirmed the presence of avian HEV and ALV-J in livers. Therefore, these results suggest that avian HEV and ALV-J co-infection caused the outbreak of hepatitis and liver hemorrhagic syndrome observed in the layer hen flock analyzed in this study.

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.

Detection of ALV p27 in cloacal swabs and virus isolation medium by sELISA

BACKGROUND

Avian leukosis (AL), which is caused by avian leukosis virus (ALV), has led to substantial economic losses in the poultry industry. The kit used to detect all ALV-positive chickens in breeder flocks is very important for efficiently controlling AL. However, a new emerging ALV subtype is currently a severe challenge in the poultry industry.

RESULTS

In this paper, we compared different enzyme-linked immunosorbent assay (ELISA) kits for detecting p27 of ALV in the same batch of meconium samples. Different positive samples were further analyzed by PCR or virus isolation. The results showed that 36 positive samples among the 1812 chicken meconium samples could be detected by a sandwich ELISA (sELISA) kit, but only 17 positive samples could be identified by a commercial kit. To verify this result, cloacal swabs and viruses isolated from the positive chickens (2 days old) were used to detect the presence of p27. The results showed that the positive rate of p27 was 100% for the swabs and 40% for virus isolation. Surprisingly, PCR and sequence analysis revealed that the env gene of ALV in these positive samples belonged to the novel subgroup K (ALV-K).

CONCLUSION

These data not only demonstrate the relatively high sensitivity of the sELISA kit but also highlight the challenge of controlling ALV-K.

Oral Immunization of Chickens With Recombinant Lactobacillus plantarum Vaccine Against Early ALV-J Infection

In this study, a novel oral vaccine of recombinant Lactobacillus plantarum (L. plantarum) containing the gp85 protein was explored, and the effects of this vaccine on the prevention of subgroup J Avian Leukosis Virus (ALV-J) infection were assessed. In the current study, the gp85 protein of ALV-J was expressed on the surface of L. plantarum with the surface-display motif, pgsA, by constructing a shuttle vector pMG36e:pgsA:gp85. Surface localization of the fusion protein was verified by western blotting and flow cytometry. Subsequently, Specific Pathogen Free Hy-Line Brown layer chickens were orally vaccinated with the recombinant L. plantarum and presented with high levels of serum immunoglobulin G (IgG) and secretory immunoglobulin A (sIgA) titers in bile and duodenal-mucosal fluid. After challenged with ALV-J of a 3 × 10³ 50% tissue culture infective dose (TCID50), serum samples of the chickens were collected and viremia was analyzed. Results showed that, compared to the L. plantarum and PBS control group, the recombinant L. plantarum group showed a significant rise in antibody levels after inoculation, and provide improved protection against ALV-J according to viremia detection. These results indicate that oral immunization with the recombinant L. plantarum provided an effective means for eliciting protective immune response against early ALV-J infection.

Geese not susceptible to virulent subgroup J avian leukosis virus isolated from chickens

To determine whether geese are susceptible to infection by avian leukosis virus (ALV), 702 serum samples from domestic and foreign goose breeds were screened for p27 antigen as well as being inoculated into DF-1 cell cultures to isolate ALV. Although 5.7% of samples were positive for p27 antigen, reactivity appeared to be non-specific because no ALV was detected in the corresponding DF-1 cultures. To further determine whether geese are susceptible to ALV-J isolated from chickens, ALV-J strain JS09GY7 was artificially inoculated into 10-day-old goose embryos, with one-day-old hatched goslings then screened for p27 antigen and the presence of ALV. In all cases, the results of both tests were negative. Liver tissues from the 1-day-old goslings were screened using a polymerase chain reaction-based assay, which failed to amplify ALV-J gene fragments from any of the samples. Further, no histopathological damage was observed in the liver tissues. ALV-J was further inoculated intraperitoneally into one-day-old goslings, with cloacal swabs samples and plasma samples then collected every 5 days for 30 days. All samples were again negative for the presence of p27 antigen and ALV, and liver tissues from the challenged geese showed no histopathological damage and were negative for the presence of ALV-J gene fragments. Furthermore, p27 antigen detection, PCR-based screening, and indirect immunofluorescence assays were all negative following the infection of goose embryo fibroblasts with ALV-J. Together, these results confirm that virulent chicken-derived ALV-J strains cannot infect geese, and that p27 antigen detection in goose serum is susceptible to non-specific interference.

Expression patterns of novel circular RNAs in chicken cells after avian leukosis virus subgroup J infection

Avian leukosis virus subgroup J (ALV-J) is an oncogenic retrovirus that causes severe economic losses to the poultry industry worldwide. Circular RNAs (circRNAs) are a class of non-coding RNAs that has been described in various biological systems and pathogenic processes. However, the immune mechanisms in response to circRNAs remain unknown. In this study, high-throughput transcriptome sequencing was used to detect circRNAs present in chicken macrophage (HD11) and chick embryo fibroblast (CEF) cells infected with ALV-J. We identified 7684 circRNAs from diverse genomic locations in CEF and HD11 after ALV-J infection, these RNAs showed complex expression patterns that differed based on the cells type and infection time. In total, 302 differentially expressed (DE) circRNAs and 164 DE circRNAs were identified in CEF and HD11 after ALV-J infection, respectively. CircRNA7419-associated with KDM4C- and circRNA6679 and circRNA6680-associated with TNFAIP6- were involved in the immune response upon ALV-J infection in CEF. Host genes were analyzed through further bioinformatics analysis. The result confirmed that a large number of DE circRNAs corresponded to several immune-associated or tumor-associated terms and pathways, such as Mucin type O-Glycan biosynthesis, MAPK signaling pathway, B cell receptor signaling, and Wnt signaling pathway in CEF, as well as Jak-STAT signaling pathway, apoptosis, and MAPK signaling pathway in HD11. CircRNAs related to the B cell receptor signaling pathway in CEF, and the Jak-STAT signaling pathway in HD11, were selected for circRNA-miRNA interaction network analyses. Our study indicates that circRNAs expression was altered by ALV-J infection in both CEF and HD11, and may play a key role in the progression of ALV-J infection.

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.

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.

Expression of dysregulated miRNA in vivo in DF-1 cells during the course of subgroup J avian leukosis virus infection

Aberrant expression of microRNAs (miRNAs) is known to be involved in cancer progression caused by subgroup J avian leukosis virus (ALV-J) in liver tissues. To advance our understanding of the related pathological mechanisms and virus-host interactions, seven previously reported miRNAs were selected for a comparative analysis of miRNA expression between infected and uninfected DF-1 cells, including six miRNAs related to tumorigenesis (let-7b/7i, miR-221/222, miR-125b, miR-375 and miR-2127. The results showed that six of the seven miRNAs except gga-miR-375 were upregulated in cells infected with NX0101 (caused myeloma (ML)) and GD1109 (caused hemangioma (HE)) at 1 h post infection. On day 2 post-infection, all seven miRNAs were upregulated in infected DF-1 cells. On day 6 post-infection, gga-let-7b, gga-miR-125b, and gga-miR-375 were downregulated whereas gga-miR-221 and gga-miR-222 were upregulated in DF-1 cells infected with the two ALV-J strains of different phenotypes. However, expression of gga-let-7i was reduced in DF-1 cells infected with NX0101 and was increased in those infected with GD1109; gga-miR-2127 expression showed no significant difference between infected and uninfected cells. This study is the first to report the changes in the miRNA expression levels in DF-1 cells during the course of ALV-J infection, and suggests a relationship between its pathological mechanisms and miRNAs.

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.

Isolation and characterization of subgroup J Avian Leukosis virus associated with hemangioma in commercial Hy-Line chickens

There was an outbreak of hemangioma associated with avian leukosis virus subgroup J (ALV-J) between 2006 and 2010 in China in commercial layer chickens. Recently, severe hemangiomas broke out in Hy-Line layer chickens on a poultry farm in 2017 where ALV was eradicated earlier. Six isolates of ALV-J, named SDAU1701-SDAU1706, were characterized by virus isolation and sequence analysis of the complete proviral genomes. Avian leukosis virus subgroup J was identified by an immunofluorescence assay with monoclonal antibody JE9, whereas Marek's disease virus or reticuloendotheliosis virus was not detected. Sequence analysis of the complete proviral genome revealed that there was 96.0-99.6% identity between each other and had a homology of 94.6-96.0% when compared with the reference strain. The six isolates formed one distinct lineage separate from the reference sequences in a phylogenetic-tree, which suggested that there were several genetic differences between these groups. Homology analysis of the env, pol, and gag genes of the six isolates showed that the env gene was more variable, especially the gp85 protein, which shared only 88.2-91.9% identity with the reference strains. Sequence comparisons of the gp85 protein indicated that 19 sites were different from those in the NX0101 and HPRS-103 strains inducing myeloid leukosis; among our strains, five mutations were identical to those in the viruses causing hemangioma. Four other distinctive mutations were detected in our six isolates. This study reminds us that the surveillance of viral eradication should be conducted continuously on a farm where ALVs were eradicated. To prevent the prevalence of ALVs, more attention should be paid to daily monitoring.

Identification of novel B-cell epitope in gp85 of subgroup J avian leukosis virus and its application in diagnosis of disease

Background

The gp85 is the main envelope protein of avian leukosis subgroup J (ALV-J) involved in virus neutralization. Here, we mapped the epitope in ALV-J gp85 by ELISA using synthetic peptides and developed epitope based diagnostic methods for ALV-J infection.

Results

The results revealed that monoclonal antibody (mAb) JE9 recognized ⁸³WDPQEL⁸⁸ motif, which was highly conserved in gp85 among different ALV-J strains by homology analysis. Moreover, after evaluation with two hundred and forty sera samples obtained from different chicken farms, the epitope-based peptide ELISA had much higher sensitivity than commercial ELISA kit for antibody detection of ALV-J.

Conclusions

A novel B-cell epitope recognized by the mAb JE9 was identified. The developed peptide-ELISA based on this novel B-cell epitope could be useful in laboratory viral diagnosis, routine surveillance in chicken farms, and also in understanding the pathogenesis 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.

Baicalin is an inhibitor of subgroup J avian leukosis virus infection

Avian leukosis virus subgroup J (ALV-J) can cause great economic losses to the poultry industry worldwide. Baicalin, one of the flavonoids present in S.baicalensis Georgi, has been shown to have antiviral activities. To investigate whether baicalin has antiviral effects on the infection of ALV-J in DF-1 cells, the cells were treated with baicalin at different time points. We found that baicalin could inhibit viral mRNA, protein levels and overall virus infection in a dose- and time-dependent manner using a variety of assays. Baicalin specifically targeted virus internalization and reduced the infectivity of ALV-J particles, but had no effect on the levels of major ALV-J receptor and virus binding to DF-1 cells. Collectively, these results suggest that baicalin might have potential to be developed as a novel antiviral agent for ALV-J infection.

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.

Degradation of Polysaccharides from Grateloupia filicina and Their Antiviral Activity to Avian Leucosis Virus Subgroup J

In this study, polysaccharides from Grateloupia filicinia (GFP) were extracted and several low molecular weight (Mw) G. filicina polysaccharides (LGFPs) were prepared by the hydrogen peroxide (H₂O₂) oxidation method. Additionally, the effect of different experimental conditions on the degradation of GFP was determined. Results showed that the GFP degradation rate was positively related to H₂O₂ concentration and temperature, and negatively related to pH. Chemical analysis and Fourier transform infrared spectra (FT-IR) of GFP and LGFPs showed that the degradation caused a slight decrease of total sugar and sulfate content. However, there was no obvious change for monosaccharide contents. Then, the anti-ALV-J activity of GFP and LGFPs were determined in vitro. Results revealed that all of the samples could significantly inhibit ALV-J and lower Mw LGFPs exhibited a stronger suppression, and that the fraction LGFP-3 with Mw 8.7 kDa had the best effect. In addition, the reaction phase assays showed that the inhibition effect was mainly because of the blocking virus adsorption to host cells. Moreover, real-time PCR, western-blot, and IFA were further applied to evaluate the blocking effects of LGFP-3. Results showed that the gene relative expression and gp85 protein for LGFPS-3 groups were all reduced. Data from IFA showed that there was less virus infected cells for 1000 and 200 μg/mL LGFPS-3 groups when compared to virus control. Therefore, lower Mw polysaccharides from G. filicina might supply a good choice for ALV-J prevention and treatment.

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.

Genomic diversity of the Avian leukosis virus subgroup J gp85 gene in different organs of an infected chicken

The genomic diversity of Avian leukosis virus subgroup J (ALV-J) was investigated in an experimentally infected chicken. ALV-J variants in tissues from four different organs of the same bird were re-isolated in DF-1 cells, and their gp85 gene was amplified and cloned. Ten clones from each organ were sequenced and compared with the original inoculum strain, NX0101. The minimum homology of each organ ranged from 96.7 to 97.6%, and the lowest homology between organs was only 94.9%, which was much lower than the 99.1% homology of inoculum NX0101, indicating high diversity of ALV-J, even within the same bird. The gp85 mutations from the left kidney, which contained tumors, and the right kidney, which was tumor-free, had higher non-synonymous to synonymous mutation ratios than those in the tumor-bearing liver and lungs. Additionally, the mutational sites of gp85 gene in the kidney were similar, and they differed from those in the liver and lung, implying that organ- or tissue-specific selective pressure had a greater influence on the evolution of ALV-J diversity. These results suggest that more ALV-J clones from different organs and tissues should be sequenced and compared to better understand viral evolution and molecular epidemiology in the field.

A deep sequencing reveals significant diversity among dominant variants and evolutionary dynamics of avian leukosis viruses in two infectious ecosystems

Background

As a typical retrovirus, the evolution of Avian leukosis virus subgroup J (ALV-J) in different infectious ecosystems is not characterized, what we know is there are a cloud of diverse variants, namely quasispecies with considerable genetic diversity. This study is to explore the selection of infectious ecosystems on dominant variants and their evolutionary dynamics of ALV-J between DF1 cells and specific-pathogen-free (SPF) chickens. High-throughput sequencing platforms provide an approach for detecting quasispecies diversity more fully.

Results

An average of about 20,000 valid reads were obtained from two variable regions of gp85 gene and LTR-U3 region from each sample in different infectious ecosystems. The top 10 dominant variants among ALV-J from chicken plasmas, DF1 cells and liver tumor were completely different from each other. Also there was a difference of shannon entropy and global selection pressure values (ω) in different infectious ecosystems. In the plasmas of two chickens, a large portion of quasispecies contained a 3-peptides “LSD” repeat insertion that was only less than 0.01% in DF1 cell culture supernatants. In parallel studies, the LTR-U3 region of ALV-J from the chicken plasmas demonstrated more variants with mutations in their transcription regulatory elements than those from DF1 cells.

Conclusions

Our data taken together suggest that the molecular epidemiology based on isolated ALV-J in cell culture may not represent the true evolution of virus in chicken flocks in the field. The biological significance of the “LSD” insert and mutations in LTR-U3 needs to be further studied.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0902-6) contains supplementary material, which is available to authorized users.

gp85 protein vaccine adjuvanted with silica nanoparticles against ALV-J in chickens

This study focused on the effect of silica nanoparticles as adjuvant for vaccine applications comprised of gp85, a dominating structural protein of J Subgroup Avian Leukosis Virus (ALV-J), and which was evaluated by comparing with the responsiveness induced by that emulsified in Freund adjuvant. Thirty-six chickens were inoculated twice with gp85 adjuvanted with the silica nanoparticles or Freund's adjuvant at the 2nd and 3rd week old. Two weeks later, the inoculated chickens were challenged with a 10^2.2 50% tissue culture infective dose (TCID50) of ALV-J. The blood samples were collected weekly to detect the serum antibodies and viremia. Results showed that positive serum antibodies (S/P value>0.6) against gp85 emerged at the third week in the inoculated chickens, while the antibodies level persisted longer in silica nanoparticles adjuvanted-group to Freund's adjuvanted-group. Furthermore, viremia in silica nanoparticles adjuvanted-group was recovered more quickly compared with Freund's adjuvanted-group. Hence our study revealed that silica nanoparticles can effectively improve the protection of gp85 vaccine against ALV-J and present a better performance than Freund's adjuvant.