Isolation and characterization of emerging subgroup J avian leukosis virus associated with hemangioma in egg-type chickens

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.

Avian Leukosis: Will We Be Able to Get Rid of It?

Avian leukosis viruses (ALVs) have been virtually eradicated from commercial poultry. However, some niches remain as pockets from which this group of viruses may reemerge and induce economic losses. Such is the case of fancy, hobby, backyard chickens and indigenous or native breeds, which are not as strictly inspected as commercial poultry and which have been found to harbor ALVs. In addition, the genome of both poultry and of several gamebird species contain endogenous retroviral sequences. Circumstances that support keeping up surveillance include the detection of several ALV natural recombinants between exogenous and endogenous ALV-related sequences which, combined with the well-known ability of retroviruses to mutate, facilitate the emergence of escape mutants. The subgroup most prevalent nowadays, ALV-J, has emerged as a multi-recombinant which uses a different receptor from the previously known subgroups, greatly increasing its cell tropism and pathogenicity and making it more transmissible. In this review we describe the ALVs, their different subgroups and which receptor they use to infect the cell, their routes of transmission and their presence in different bird collectivities, and the immune response against them. We analyze the different systems to control them, from vaccination to the progress made editing the bird genome to generate mutated ALV receptors or selecting certain haplotypes.

TRIM25 participates in the fibrous tissue hyperplasia induced by ALV-J infection in chickens by targeting 14-3-3σ protein

ALV-J-SD1005 strain was subcutaneously inoculated into the necks of 1-day-old HY-Line Brown chickens and caused severe growth retardation, viremia and subcutaneous fibrosarcomas in the necks of all infected chickens from 14 days post inoculation (DPI) to 21 DPI, and also significantly increased the expressions of TRIM25, P53, etc., but significantly decreased the expressions of 14-3-3σ, etc. Overexpression of chicken TRIM25 (chTRIM25) significantly promoted cell proliferation and improved the expressions of P53, CDC2, and CDK2 tumor factors; and significantly inhibited the expression of 14-3-3σ in ALV-J-SD1005-infected DF1 cells; but knockdown of chTRIM25 caused the opposite effects. The results of co-immunoprecipitation (Co-IP) and confocal microscopy confirmed that chTRIM25 can recognize and bind 14-3-3σ protein in ALV-J-SD1005-infected cells, and they were co-located in the cytoplasm. It can be concluded that chTRIM25 participates in the fibrous tissue hyperplasia induced by ALV-J-SD1005 infections in chickens by binding 14-3-3σ protein and regulating the expressions of 14-3-3σ, P53, CDC2, and CDK2.

A study on the infection status and transmission of avian leukosis virus subgroup J in Hy-line brown roosters

Avian leukosis virus subgroup J (ALV-J) is the most prevalent subgroup in chickens and exhibits increased pathogenicity and stronger horizontal and vertical transmission ability among different breeds. Although vertical transmission of ALV-J from infected hens through artificial insemination has been inferred from the detection of the p27 antigen in swabs and serum, there has been no further research on the transmission pattern of ALVs in roosters. In the present study, the positive rate of ALV increased significantly in an indigenous flock after detecting the p27 antigen via enzyme-linked immunosorbent assay (ELISA) and virus isolation in DF-1 cells. Viral sequence comparisons and an indirect fluorescent antibody assay showed that these isolates belonged to the ALV-J subgroup but formed a new branch in a phylogenetic tree when compared to domestic and foreign referential strains. The gp85 gene of the ALV-J isolated from hens and albumen was 94.1-99.7% identical to that in roosters, revealing that these isolates were quite likely transmitted to the hens and their offspring through the semen of ALV-infected roosters by artificial insemination from the Hy-line brown roosters. In addition, we defined four ALV-J infection states in plasma and semen of roosters (P+S+, P-S+, P+S-, and P-S-), which suggests that, in order to eradicate ALV in roosters, it is necessary to perform virus isolation using both semen and plasma. Additionally, ALV detection in semen by ELISA produced false-positive and false-negative results when compared to virus isolation in DF-1 cells. Collectively, our results suggested that an incomplete process of eradication of ALV from ALV-positive roosters led to the sporadic presence of ALV-J in laying hens.

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 CT 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.

Molecular characteristic and pathogenicity analysis of a novel multiple recombinant ALV-K strain

Avian leukosis virus (ALV) can induce various tumors and cause serious production problems. ALVs isolated from chickens were divided into six subgroups (A-J). In 2012, a strain of a putative novel subgroup of ALVs was isolated from Chinese native chickens in Jiangsu Province and named as ALV-K. In this study, three ALV-K strains (JS14LH01, JS13LH14, and JS15SG01) were isolated from chickens with suspected ALV infection in Jiangsu Province. Their complete genomes were amplified, sequenced, and analyzed systematically. The results showed that JS14LH01 and JS13LH14 were ALV-K and ALV-E recombinant strains. Whereas JS15SG01 is an ALV-K, ALV-E, and ALV-J multiple recombinant strain containing the U3 region of ALV-J. The pathogenicity test of JS15SG01 revealed that, compared with previous ALV-K strains, the viremia and viral shedding level of JS15SG01-infected chickens were significantly increased, reaching 100 % and 59 %, respectively. More important, JS15SG01 induced significant proliferation of gliocytes in the cerebral cortex of infected chickens, accompanied by the neurotropic phenomenon. This is the first report about a multiple recombinant ALV-K strain that could invade and injure the brain tissue of chickens in China. Our findings enriched the epidemiologic data of ALV and helped to reveal the evolution of ALV strains prevalent in chicken fields.

Novel mutation of avian leukosis virus subgroup J from Tibetan chickens

Tibetan chickens are descendants of the ancestral red jungle fowl Gallus gallus. Very little is known about pathogens in Tibetan chickens living in the high-altitude environment. Here, we report for the first time the detection and isolation of avian leukosis virus from Tibetan chickens, with all the avian leukosis virus-positive samples belonging to subgroup J. Phylogenetic analysis of the sequence revealed these viruses were in a new branch compared with previous reports. The 3'-end of the pol gene in the new strains showed 8-amino acid deletion, with 2 strains displaying a large-scale deletion in the hr2 region of gp85 protein. Among all the strains, several mutations in the primer binding site leader sequence and untranslated region, which came from Rous-associated virus, were identified. It is interesting that some of these mutations may have contributed to the competitive advantages to these isolates as observed from their increased replication in vitro. These results indicated that the virus isolates from Tibetan chickens can have competitive advantage over the other strains circulating in the poultry population in future.

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.

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.

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.

Avian leukosis virus contamination in live vaccines: A retrospective investigation in China

Avian leukosis (AL) is one of the most pandemic immunosuppressive diseases and has been widely spread between 2006 and 2009 in China. The contamination of avian leukosis virus (ALV) in attenuated vaccine is considered as one of the possible transmission routes of this disease. Based on a retrospective survey of 918 batches of attenuated vaccine produced before 2010, three of them were identified as ALV-positive and corresponding ALV strains were successfully isolated from a live Fowlpox virus vaccine, a live Newcastle disease virus vaccine and a live Infectious Bursal Disease virus vaccine, respectively, and whole-genome sequencing showed that these three isolates shared the highest homology with ALV-A wild strains isolated in China (97.7%) over the same period, and the phylogenetic analysis based on their gp85 genes further confirmed that they belong to subgroup A. Meanwhile, although these three ALV-A strains isolated from contaminated vaccines shared a close genetic relationship, their U3 region of genome have a relatively low identity, suggesting that these three strains may have different sources. This study reminds us once again that the possibility of ALV infecting chickens through contaminated live vaccines, requiring us to carry out stricter exogenous virus monitoring in vaccines.

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.

Fluctuations in luteinizing hormone, follicle stimulating hormone, and progesterone might affect the disappearance of avian leukosis virus subgroup J viremia in chickens with intermittent viremia

Avian leukosis virus subgroup J (ALV-J) belongs to α-retrovirus genus of retroviridae, causing neoplastic disease, immunosuppression, and other problems in the poultry industry worldwide. The aim of this study was to determine whether the reproductive hormone fluctuation affect the ALV-J viremia at the early egg-laying phase in chicken. Total 8 suspected ALV-J-infected Chinese yellow chickens in the early egg-laying phase were collected from 2 different farms, and further confirmed by PCR and immunofluorescence assay. Plasma samples were collected from experimental chickens for 5 to 10 consecutive weeks at a settled time in each week. ALV-J viremia and reproductive hormone levels were monitored by ELISA or radioimmunoassay. The results showed that fluctuations in luteinizing hormone (LH), follicle stimulating hormone (FSH), and progesterone might have an impact on the disappearance of ALV-J viremia in chickens with intermittent viremia, but not in chickens with persistent viremia. These results suggest that reproductive hormone changes during the early egg-laying phase will affect the detection of positive ALV-J-infected chickens in the ALV-J eradication procedures.

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.

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.

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.

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.

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.

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.

Phylogenetic Analysis and Pathogenicity Assessment of the Emerging Recombinant Subgroup K of Avian Leukosis Virus in South China

In recent years, cases of avian leukosis virus (ALV) infection have become more frequent in China. We isolated 6 ALV strains from yellow feather broiler breeders in south China from 2014 to 2016. Their full genomes were sequenced, compared, and analyzed with other reference strains of ALV. The complete genomic nucleotide sequences of GD150509, GD160403, GD160607, GDFX0601, and GDFX0602 were 7482 bp in length, whereas GDFX0603 was 7480 bp. They shared 99.7% to 99.8% identity with each other. Homology analysis showed that the gag, pol, long terminal repeats (LTRs), and the transmembrane region (gp37) of the env genes of the 6 viruses were well conserved to endogenous counterpart sequences (>97.8%). However, the gp85 genes displayed high variability with any known chicken ALV strains. Growth kinetics of DF-1 cells infected with the isolated ALV showed viral titers that were lower than those infected with the GD13 (ALV-A), CD08 (ALV-B), and CHN06 (ALV-J) on day 7 post-infection. The infected Specific-pathogen-free (SPF) chickens could produce continuous viremia, atrophy of immune organs, growth retardation and no tumors were observed. These subgroup ALVs are unique and may be common in south China. The results suggested that updating the control and eradication program of exogenous ALV for yellow feather broiler breeders in south China needs to be considered because of the emergence of the new subgroup viruses.

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.

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.

ALV-J infection induces chicken monocyte death accompanied with the production of IL-1β and IL-18

Immunosuppression induced by avian leukosis virus subgroup J (ALV-J) causes serious reproduction problems and secondary infections in chickens. Given that monocytes are important precursors of immune cells including macrophages and dendritic cells, we investigated the fate of chicken monocytes after ALV-J infection. Our results indicated that most monocytes infected with ALV-J including field or laboratory strains could not successfully differentiate into macrophages due to cells death. And cells death was dependent upon viral titer and accompanied with increased IL-1β and IL-18 mRNA levels. In addition, ALV-J infection up-regulated caspase-1 and caspase-3 activity in monocytes. Collectively, we found that ALV-J could cause cell death in chicken monocytes, especially pyroptosis, which may be a significant reason for ALV-J induced immunosuppression.

The construction and application of a cell line resistant to novel subgroup avian leukosis virus (ALV-K) infection

A novel avian leukosis viruses (ALV) subgroup named ALV-K was recently isolated from Chinese indigenous chickens which is different from the subgroups (A to E and J) that have previously been reported to infect chickens. More and more ALV-K strains have recently been isolated from local breeds of Chinese chickens. However, there are no more effective diagnostic methods for ALV-K other than virus isolation followed by envelope gene sequencing and comparison. Viral infection can be blocked through expression of the viral receptor-binding protein. In this study, we have engineered a cell line, DF-1/K, that expresses ALV-K env protein and thereby confers resistance to ALV-K infection. DF-1/K can be used in combination with the ALV-K susceptible cell line DF-1 as a specific diagnostic tool for ALV-K and provides a good tool for further research into the molecular mechanisms of interaction between ALV-K env protein and the host cell receptor.

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.

Temporal changes of microRNA gga-let-7b and gga-let-7i expression in chickens challenged with subgroup J avian leukosis virus

Two important microRNAs, gga-let-7b and gga-let-7i were examined for the relative expression in liver and bone marrow tissues from specific pathogen free chickens that were challenged either with GD1109 or NX0101 strain of subgroup J avian leukosis virus (ALV-J). The GD1109 strain of ALV-J reportedly causes hemangioma (HE) and NX0101 reportedly causes myeloma (ML) in susceptible chickens. Temporal changes of both gga-let-7b and gga-let-7i expression in ALV-J infected chickens were observed in contrast to its counterpart of a non-infected negative control group of chickens (P < 0.05 or P < 0.01) during the first 120 days post infection. Use of the web-based computational DIANA-mirPath software (available at http://microrna.gr/mirpath ), it was predicted that both gga-let-7b and gga-let-7i were involved in multiple pathways including signaling pathways, such as MAPK, TGF-beta, Notch, Wnt, mTOR, Cell cycle, P53 and Jak-STAT. Combining our experimental data with reports on the microRNAs, we suggest that both gga-let-7i and gga-let-7b may also act as tumor suppressors in chicken, especially play a critical role in tumorigenesis induced by ALV-J.

Growth retardation induced by avian leukosis virus subgroup J associated with down-regulated Wnt/β-catenin pathway

Avian leukosis virus subgroup J (ALV-J), an oncogenic retrovirus, induces growth retardation and neoplasia in chickens, leading to enormous economic losses in poultry industry. Increasing evidences showed several signal pathways involved in ALV-J infection. However, what signaling pathway involved in growth retardation is largely unknown. To explore the possible signaling pathway, we tested the cell proliferation and associated miRNAs in ALV-J infected CEF cells by CCK-8 and Hiseq, respectively. The results showed that cell proliferation was significantly inhibited by ALV-J and three associated miRNAs were identified to target Wnt/β-catenin pathway. To verify the Wnt/β-catenin pathway involved in cell growth retardation, we analyzed the key molecules of Wnt pathway in ALV-J infected CEF cells. Our data demonstrated that protein expression of β-catenin was decreased significantly post ALV-J infection compared with the normal (P < 0.05). The impact of this down-regulation caused low expression of known target genes (Axin2, CyclinD1, Tcf4 and Lef1). Further, to obtain in vivo evidence, we set up an ALV-J infection model. Post 7 weeks infection, ALV-J infected chickens showed significant growth retardation. Subsequent tests showed that the expression of β-catenin, Tcf1, Tcf4, Lef1, Axin2 and CyclinD1 were down-regulated in muscles of growth retardation chickens. Taken together, all data demonstrated that chicken growth retardation caused by ALV-J associated with down-regulated Wnt/β-catenin signaling pathway.

Immunity to Avian Leukosis Virus: Where Are We Now and What Should We Do?

Avian leukosis virus (ALV) is an avian oncogenic retrovirus causing enormous economic losses in the global poultry industry. Although ALV-related research has lasted for more than a century, there are no vaccines to protect chickens from ALV infection. The interaction between chickens and ALV remains not fully understood especially with regard to the host immunity. The current review provides an overview of our current knowledge of innate and adaptive immunity induced by ALV infection. More importantly, we have pointed out the unknown area involved in ALV-related studies, which is worthy of our serious exploring in future.

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.

Inhibition of ERK/MAPK suppresses avian leukosis virus subgroup A and B replication

We have previously shown that the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway contributes to subgroup J avian leukosis virus (ALV-J) replication and tumorigenicity. However, a role for ERK/MAPK signaling in ALV-A and ALV-B replication is unknown. In this study we successfully constructed and recovered a recombinant form of ALV-A strain GD13-1 which showed similarities in growth to the parental wild type virus in vitro. ALV subgroups J, A or B all triggered ERK2 activation in primary CEF cells. ERK/MAPK inhibition markedly suppressed ALV-A and ALV-B replication as shown by extremely low levels of viral transcription and virus protein production. This finding provides evidence that ERK/MAPK signaling responses play important roles in ALV replication and may represent novel drug targets for therapeutic intervention strategies.

Endogenous Retrovirus ev21 Dose Not Recombine with ALV-J and Induces the Expression of ISGs in the Host

Avian leukosis virus subgroup J (ALV-J) infection can cause tumors and immunosuppression. Endogenous viruses integrate into host genomes and can recombine with exogenous avian leukosis virus (ALV). In this study, we analyzed the interaction of endogenous retrovirus 21 (ev21) with the ALV-J in late-feathering Chinese yellow chicken. Two ALV-J strains M180 and K243 were isolated from late-feathering and fast-feathering Chinese yellow chicken flocks, respectively. The env gene of the two strains showed 94.2-94.8% nucleotide identity with reference ALV-J strains. Compared with the env gene and the LTR of ev21 and M180, the nucleotide identity of LTR was 69.7% and env gene was 58.4%, respectively, especially the amino acid identity of env gene as low as 14.2%. Phylogenetic analysis of the nucleotide sequence of the env gene and the 3'LTR showed that M180 was closely related to ALV-J, and was located in a distinct group with ev21 in the phylogenetic tree. Using co-immunoprecipitation (co-IP), we next demonstrate that the envelope protein of ev21 does not interact with the M180 envelope protein. We further show that the envelope protein of ev21 cannot activate ALV-J LTR promoter activity using luciferase-reporter assays. qPCR and western blot analysis revealed that envelope protein of endogenous ev21 can facilitate the expression of PKR at 6h post ALV-J infection (hpi) and facilitate the expression of ISG12 and CH25H at 24 hpi. However, the expression of the env gene of M180 strain was not significantly at 6 and 24 hpi. We conclude that there is no evidence of recombination between endogenous retrovirus ev21 and ALV-J strain M180 in late-feathering Chinese yellow chicken, and envelope protein of ev21 can affect the expression of host ISGs, but appears not to influence the replication of ALV-J strain M180. This is the first report of interaction among the endogenous retrovirus ev21, ALV-J and the late-feathering chicken.

Rescue of avian leukosis subgroup-J-associated acutely transforming viruses carrying different lengths of the v-fps oncogene and analysis of their tumorigenicity

In our previous study, six subgroup J strains of avian leukosis virus (ALV-J)-associated acutely transforming viruses carrying different lengths of the v-fps oncogene, designated as Fu-J and Fu-J1-5, were isolated and characterized from fibrosarcomas in ALV-J-infected chickens. In the present study, the oncogenic potential of Fu-J and Fu-J1-5 was investigated using a reverse genetics technique. Six replication-defective viruses, named rFu-J and rFu-J1-5, were rescued with the replication-competent rescued ALV-J strain rSDAU1005 as a helper virus by co-transfection of chicken embryo fibroblast monolayers with infectious clone plasmids. Experimental bird studies were performed, demonstrating that only the rescued rFu-J virus carrying the complete v-fps oncogene with rSDAU1005 as the helper virus could induce acute fibrosarcoma after inoculation in specific-pathogen-free (SPF) chickens. These results provide direct evidence that the replication-defective acutely transforming Fu-J virus, with the complete v-fps oncogene, was associated with acute fibrosarcoma in chickens infected with ALV-J in the field, as reported previously.

Cutaneous Hemangiosarcoma in a Pacific Parrotlet (Forpus coelestis)

A 2-month-old Pacific parrotlet (Forpus coelestis) was presented for assessment following a traumatic injury to the right wing that resulted in persistent swelling and inflammation. Six weeks postinjury the bird underwent surgical resection of a large hemorrhagic cavitated mass that had formed at the site of the original injury and a second, smaller mass on the body in direct contact with the wing mass. Histopathology of the wing mass confirmed a diagnosis of hemangiosarcoma. While commonly diagnosed in domestic species, hemangiosarcoma is uncommonly reported in avian species. To the authors' knowledge, this is the first report of hemangiosarcoma in a Pacific parrotlet and describes the development of hemangiosarcoma in a psittacine bird following trauma-induced inflammation.

Identification of a linear B-cell epitope on the avian leukosis virus P27 protein using monoclonal antibodies

Avian leukosis virus (ALV) is an avian oncogenic retrovirus that can induce various clinical tumors. The capsid protein P27 is the group-specific antigen of ALV and has many viral antigen sites that are easy to detect. In this study, we produced a monoclonal antibody (mAb), 3A9, that is specific for the P27 protein. A series of partially overlapping peptides were screened to define (181)PPSAR(185) as the minimal linear epitope recognized by mAb 3A9. The identified epitope could be recognized by chicken anti-ALV and mouse anti-ALV P27 sera. The epitope was highly conserved among a number of ALV-A, ALV-B and ALV-J strains. MAb 3A9 might be a valuable tool for the development of new immunodiagnostic approaches for ALV, and the defined linear epitope might help further our understanding of the antigenic structure of the P27 protein.

Synergy of subgroup J avian leukosis virus and Eimeria tenella to increase pathogenesis in specific-pathogen-free chickens

To investigate the effects of co-infections of subgroup J avian leukosis virus (ALV-J) and Eimeria tenella on the pathogenesis in specific-pathogen-free (SPF) white leghorn chickens, groups of chickens were infected with ALV-J strain NX0101 at one day of age or with E. tenella at 14 days of age or both. The control group was left uninfected and was mock-inoculated with phosphate buffer saline (PBS). Mortality rates, body weights, cecal lesions, and viremia of infected chickens in each group were evaluated. Immune status was evaluated by measuring several parameters: immune organ weight/body weight index, specific humoral responses to inactivated NDV vaccine and to inoculated E. tenella, proportions of blood CD3+CD4+ and CD3+CD8α+ lymphocytes and transcriptional levels of cytokines in blood and cecal tonsils. The results show that co-infections of ALV-J and E. tenella induced a higher mortality rate and a lower body weight in SPF chickens compared to single-pathogen infection. In co-infected chickens, ALV-J accelerated the disease symptoms induced by E. tenella, and the E. tenella extended the ALV-J viremia. Thymus atrophy, decrease in the humoral response levels to pathogens and the NDV vaccine, modifications in the blood lymphocyte sub-populations and transcriptional cytokine disorders were found in co-infected chickens compared to chickens infected with one pathogen alone and to controls. We underline a synergy between ALV-J and E. tenella that results in increasing pathogenesis in SPF chickens.

Innate Immune Responses in ALV-J Infected Chicks and Chickens with Hemangioma In Vivo

Avian leukosis virus subgroup J (ALV-J) infection can cause tumors and immunosuppression. Since the precise mechanism of the innate immune response induced by ALV-J is unknown, we investigated the antiviral innate immune responses induced by ALV-J in chicks and chickens that had developed tumors. Spleen levels of interleukin-6 (IL-6), IL-10, IL-1β, and interferon-β (IFN-β) were not significantly different between the infected chick groups and the control groups from 1 day post hatch to 7 days post hatch. However, IL-6, IL-1β, and IFN-β protein levels in the three clinical samples with hemangiomas were dramatically increased compared to the healthy samples. In addition, the anti-inflammatory cytokine IL-10 increased sharply in two of three clinical samples. We also found a more than 20-fold up-regulation of ISG12-1 mRNA at 1 day post infection (d.p.i.) and a twofold up-regulation of ZC3HAV1 mRNA at 4 d.p.i. However, there were no statistical differences in ISG12-1 and ZC3HAV1 mRNA expression levels in the tumorigenesis phase. ALV-J infection induced a significant increase of Toll-like receptor 7 (TLR-7) at 1 d.p.i. and dramatically increased the mRNA levels of melanoma differentiation-associated gene 5 (MDA5) in the tumorigenesis phase. Moreover, the protein levels of interferon regulatory factor 1 (IRF-1) and signal transducer and activator of transcription 1 (STAT1) were decreased in chickens with tumors. These results suggest that ALV-J was primarily recognized by chicken TLR7 and MDA5 at early and late in vivo infection stages, respectively. ALV-J strain SCAU-HN06 did not induce any significant antiviral innate immune response in 1 week old chicks. However, interferon-stimulated genes were not induced normally during the late phase of ALV-J infection due to a reduction of IRF1 and STAT1 expression.

Identification of ALV-J associated acutely transforming virus Fu-J carrying complete v-fps oncogene

Transduction of oncogenes by ALVs and generation of acute transforming viruses is common in natural viral infections. In order to understand the molecular basis for the rapid oncogenicity of Fu-J, an acutely transforming avian leukosis virus isolated from fibrosarcomas in crossbreed broilers infected with subgroup J avian leukosis virus (ALV-J) in China, complete genomic structure of Fu-J virus was determined by PCR amplification and compared with those of Fu-J1, Fu-J2, Fu-J3, Fu-J4, and Fu-J5 reported previously. The results showed that the genome of Fu-J was defective, with parts of gag gene replaced by the complete v-fps oncogene and encoded a 137 kDa Gag-fps fusion protein. Sequence analysis revealed that Fu-J and Fu-J1 to Fu-J5 were related quasi-species variants carrying different lengths of v-fps oncogenes generated from recombination between helper virus and c-fps gene. Comparison of virus carrying v-fps oncogene also gave us a glimpse of the molecular characterization and evolution process of the acutely transforming ALV.

Avian leukosis virus subgroup J induces its receptor--chNHE1 up-regulation

Background

Avian leukosis virus subgroup J (ALV-J) is an oncogenic retrovirus which causes immunosuppression and neoplasia in meat-type and egg-type chickens. ALV-J infects host cells via specific interaction between the viral Env and the cell surface receptor —chicken sodium hydrogen exchanger type 1 (chNHE1). NHE1 involved in altering the cellular pH and playing a critical role in tumorigenesis. However, little is known about the other relationship between ALV-J and chNHE1.

Methods and results

In ALV-J infected DF-1 cells, the mRNA level of chNHE1 was up-regulated with time-dependent manner tested by real time PCR, and accordingly, intracellular pH was increased tested by spectrofluorometer. In vivo, the mRNA level of chNHE1 was determined by real time PCR in ALV-J infected experimental chickens and field cases. The result showed that the mRNA level of chNHE1 was up-regulated after virus shedding, especially in continuous viremic shedders (CS group). However, no significant difference was found between non-shedding group (NS group) and control group. In field cases, mRNA level of chNHE1 was positively correlated with increasing ALV-J load in tumor bearing and immune tolerance chickens. Furthermore, immunohistochemistry results showed that the protein expression of chNHE1 was up-regulated in different organs of both experimental chickens and tumor bearing chickens compared with the control.

Conclusion

Taken together, we conclude that ALV-J induces chNHE1 up-regulation in viremia and neoplasia chickens.

Identification of avian leukosis virus subgroup J-associated acutely transforming viruses carrying the v-src oncogene in layer chickens

To elucidate the molecular basis for the rapid oncogenicity of an acutely transforming avian leukosis virus (ALV), isolated from fibrosarcomas in Hy-Line Brown commercial layer chickens infected with ALV subgroup J (ALV-J), the complete genomic structure of the provirus was determined. In addition to ALV-J replication-complete virus SDAU1102, five proviral DNA genomes, named SJ-1, SJ-2, SJ-3, SJ-4 and SJ-5, carrying different lengths of the v-src oncogene were amplified from original tumours and chicken embryo fibroblasts (CEFs) infected with viral stocks. The genomic sequences of the SJ-1-SJ-5 provirus were closely related to that of SDAU1102 but were defective. The results of Western blot analysis and immunohistochemical staining also showed overexpression of the p60v-src protein in infected CEFs and tumour tissue. To the best of our knowledge, this is the first report of the isolation and identification of acutely transforming viruses carrying the v-src oncogene with ALV-J as the helper virus. It also offers insight into the generation of acutely transforming ALVs carrying the v-src oncogene.

Lamivudine Inhibits the Replication of ALV-J Associated Acutely Transforming Virus and its Helper Virus and Tumor Growth In vitro and In vivo

To study the antiviral effects of lamivudine on avian leukosis virus subgroup J (ALV-J) and its inhibitory effect on the growth of fibrosarcomas caused by acute transforming avian leukosis virus, a series of experiments were performed in chicken embryo fibroblast cultures and 1-day-old chickens inoculated with an acutely transforming viral stock Fu-J (SDAU1005). This stock was prepared from an acutely fibrosarcoma of field cases in chicken farms and contained both the replication-defective virus Fu-J carrying v-fps oncogene and its helper virus ALV-J strain SDAU1005. The results from three different assays in cell cultures demonstrated the significant inhibitory effect of lamivudine on the replication of both SDAU1005 and Fu-J viruses. Furthermore, the effect was dose dependent in the concentration range of 1–4 μg/ml. In chicken experiments, lamivudine could decrease the viral loads of SDAU1005 and Fu-J in the plasma of inoculated chickens, delay the appearance of acute sarcomas, and decrease chicken mortality in the early stage. This model may be used to directly evaluate the inhibitory effects of lamivudine on such tumors and to understand the relationship between the replication-defective virus and its helper virus while also assessing tumor processes.