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.

Proteomic investigation and understanding on IgY purification and product development

An increasing demand for the development of immunoglobin Y (IgY) illustrates the necessity of the component analysis in the process of conduction and quality control. This study investigated the proteomic changes in crude IgY extracts and purified IgY products obtained by sequential polyethylene glycol precipitation (PEG) of egg yolks followed by human mycoplasma protein-based affinity chromatography compared with intact egg yolks. After confirming the extraction efficiency and purity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, liquid chromatography tandem-mass spectrometry (LC-MS/MS) was performed with samples including fresh yolk, IgY extracted product and purified product. A total of 348 proteins were identified, with 36 proteins deleted and 209 newly detected proteins in the purified product compared to the intact egg yolk. The significantly decreased proteins mainly included phosvitin, albumin, and apolipoprotein B whereas the significantly increased proteins were mainly IgY-related proteins. GO analysis showed that the purified IgY product had ATPase activity and purine ribonucleoside triphosphate binding activity, and was mainly involved in purine and nucleic acid metabolism. This study will inevitably fasten the commercial application of IgY antibodies and is of greater significance for promotion, development and approval for new antibody derived drug products.

J Subgroup Avian Leukosis Virus Strain Promotes Cell Proliferation by Negatively Regulating 14-3-3σ Expressions in Chicken Fibroblast Cells

This study focuses on clarifying the regulation of chicken 14-3-3σ protein on the fibrous histiocyte proliferation caused by ALV-J-SD1005 strain infection. DF-1 cells were inoculated with 10² TCID₅₀ of ALV-J-SD1005 strain; the cell proliferation viability was dramatically increased and 14-3-3σ expressions were dramatically decreased within 48 h after inoculation. Chicken 14-3-3σ over-expression could significantly decrease the cell proliferation and the ratio of S-phase cells, but increase the ratio of G2/M-phase cells in ALV-J-infected DF-1 cells; by contrast, chicken 14-3-3σ knockdown expression could cause the opposite effects. Additionally, chicken 14-3-3σ over-expression could also dramatically down-regulate the expressions of CDK2/CDC2, but up-regulate p53 expressions in the DF-1 cells; in contrast, the knockdown expression could significantly increase the expressions of CDK2/CDC2 and decrease p53 expressions. It can be concluded that chicken 14-3-3σ can inhibit cell proliferation and cell cycle by regulating CDK2/CDC2/p53 expressions in ALV-J-infected DF1 cells. ALV-J-SD1005 strain can promote cell proliferation by reducing 14-3-3σ expressions. This study helps to clarify the forming mechanism of acute fibrosarcoma induced by ALV-J infection.

Advances on genetic and genomic studies of ALV resistance

Avian leukosis (AL) is a general term for a variety of neoplastic diseases in avian caused by avian leukosis virus (ALV). No vaccine or drug is currently available for the disease. Therefore, the disease can result in severe economic losses in poultry flocks. Increasing the resistance of poultry to ALV may be one effective strategy. In this review, we provide an overview of the roles of genes associated with ALV infection in the poultry genome, including endogenous retroviruses, virus receptors, interferon-stimulated genes, and other immune-related genes. Furthermore, some methods and techniques that can improve ALV resistance in poultry are discussed. The objectives are willing to provide some valuable references for disease resistance breeding in poultry.

A20 Enhances the Expression of the Proto-Oncogene C-Myc by Downregulating TRAF6 Ubiquitination after ALV-A Infection

Hens infected with avian leukosis virus subgroup A (ALV-A) experience stunted growth, immunosuppression, and potentially, lymphoma development. According to past research, A20 can both promote and inhibit tumor growth. In this study, DF-1 cells were infected with ALV-A rHB2015012, and Gp85 expression was measured at various time points. A recombinant plasmid encoding the chicken A20 gene and short hairpin RNA targeting chicken A20 (A20-shRNA) was constructed and transfected into DF-1 cells to determine the effect on ALV-A replication. The potential signaling pathways of A20 were explored using bioinformatics prediction, co-immunoprecipitation, and other techniques. The results demonstrate that A20 and ALV-A promoted each other after ALV-A infection of DF-1 cells, upregulated A20, inhibited TRAF6 ubiquitination, and promoted STAT3 phosphorylation. The phosphorylated-STAT3 (p-STAT3) promoted the expression of proto-oncogene c-myc, which may lead to tumorigenesis. This study will help to further understand the tumorigenic process of ALV-A and provide a reference for preventing and controlling ALV.

The role of ATF6 in Cr(VI)-induced apoptosis in DF-1 cells

Hexavalent chromium (Cr(VI)) is a common heavy metal pollutant in environment and has been proved possessing the cytotoxicity. In this study, we aimed to investigate the role of activating transcription factor 6 (ATF-6) in apoptosis of chicken embryo fibroblasts cell line (DF-1) induced by Cr(VI). Firstly, DF-1 cells were exposed to Cr(VI) to establish the cytotoxicity model, then the cell apoptosis and ATF-6 protein level were analyzed. By silencing ATF-6 gene, changes of the apoptosis rate and apoptotic proteins were examined. To further explore the regulatory mechanism of ATF-6, endoplasmic reticulum (ER) stress, mitochondrial function, reactive oxygen species (ROS) level, as well as the related pathway were evaluated. Results showed that Cr(VI) can result in DF-1 cell apoptosis, along with mitochondrial membrane potential (MMP) reducing and ER stress. Meanwhile, ATF-6 silencing lowered the apoptosis rate and ER stress level, showing with the decrease of XBP-1, PERK, GRP78, Caspase-12, Cleaved Caspase-3 and the increase of Bcl-2. Further analysis found that ATF-6 silencing down-regulated ROS and caused MMP loss, suggesting that ATF-6 silencing inhibited Cr(VI)-induced mitochondrial damage. In conclusion, this study indicate that ATF-6 plays an important regulatory role in Cr(VI)-induced DF-1 cell apoptosis through the ER stress and mitochondrial pathway.

Regulatory effects of chicken TRIM25 on the replication of ALV-A and the MDA5-mediated type I interferon response

This study focuses on the immunoregulatory effects of chicken TRIM25 on the replication of subgroup A of avian leukosis virus (ALV-A) and the MDA5-mediated type I interferon response. The ALV-A-SDAU09C1 strain was inoculated into DF1 cells and 1-day-old SPF chickens, and the expression of TRIM25 was detected at different time points after inoculation. A recombinant overexpression plasmid containing the chicken TRIM25 gene (TRIM25-GFP) was constructed and transfected into DF1 cells to analyse the effects of the overexpression of chicken TRIM25 on the replication of ALV-A and the expression of MDA5, MAVS and IFN-β. A small interfering RNA targeting chicken TRIM25 (TRIM25-siRNA) was prepared and transfected into DF1 cells to assess the effects of the knockdown of chicken TRIM25 on the replication of ALV-A and the expression of MDA5, MAVS and IFN-β. The results showed that chicken TRIM25 was significantly upregulated at all time points both in ALV-A-infected cells and in ALV-A-infected chickens. Overexpression of chicken TRIM25 in DF1 cells dramatically decreased the antigenic titres of ALV-A in the cell supernatant and upregulated the relative expression of MDA5, MAVS and IFN-β induced by ALV-A or by poly(I:C); in contrast, knockdown of chicken TRIM25 significantly increased the antigenic titres of ALV-A and downregulated the relative expression of MDA5, MAVS and IFN-β. It can be concluded that chicken TRIM25 can inhibit the replication of ALV-A and upregulate the MDA5 receptor-mediated type I interferon response in chickens. This study can help improve the understanding of the antiviral activities of chicken TRIM25 and enrich the knowledge of antiviral responses in chickens.

Identification of a novel epitope specific for Gp85 protein of avian leukosis virus subgroup K

During the past two decades, avian leukosis virus (ALV) caused tremendous economic losses to poultry industry in China. ALV-K as a newly found subgroup in recent years, which made the control and eradication of ALV more difficult as they were originated from the recombination of different subgroups. To date, specific rapid detection methods refer to ALV-K are still missing. Gp85 is the main structural protein of the virus, which mediates the invasion of host cells by the virus and determinates the classification of subgroups. In this study, we prepared a monoclonal antibody (Mab) named Km3 against Gp85 of ALV-K. Immunofluorescence assay showed that Km3 specifically recognized the strains of ALV-K rather than the strains of ALV-A or ALV-J. To explain the subgroups specificity of Km3, the epitope cognized by the Mab was identified by Western blotting using 15 overlapping fragments spanning the Gp85. Finally, the peptide ¹²⁹AFGPRSIDTLSDWSRPQ¹⁴⁵ was identified as the minimal linear epitope recognized by Km3. Alignment of Gp85 from different subgroups showed that the epitope was highly conserved among ALV-K strains, which was quite different from that of the strains from ALV -A, -B and -J. In conclusion, the Mab Km3 may serve as a useful reagent for ALV-K detection and diagnosis in the future.

Difference in pathogenicity of 2 strains of avian leukosis virus subgroup J in broiler chicken

Avian leukosis virus subgroup J has been found to infect many types of chickens with various genetic backgrounds. The ALV-J strain NX0101, which was isolated from broiler breeders in 2001, mainly induces the formation of myeloid cell tumors. However, strain HN10PY01, which was recently isolated from laying hens, mainly induces the formation of myeloid cell tumors and hemangioma. In order to determine the difference in pathogenicity of the 2 strains in broiler chickens, 2 groups of chicken embryos were infected with NA0101 and HN10PY01 separately. A comparison was made of the mortality, oncogenicity, body weights, indexes for immune organs, levels of ALV group-specific antigen p27, and mRNA expression levels of the tumor-related gene, p53, in ALV-J-infected birds and immune organs of theses chickens in response to Newcastle Disease Virus (NDV) and avian influenza virus subtype H9 (AIV-H9) vaccination. The results indicated that strain NX0101 was highly pathogenic in broiler chickens and led to a 30% mortality rate and 45% oncogenicity, compared with the HN10PY01-infected birds. Weight of chickens was also significantly lower after 15 wk (P < 0.05). In addition, the mRNA expression levels of tumor-related p53 in medulla, liver, and lung in broilers infected with strain NX0101 were significantly higher than those infected with strain HN10PY01 (P < 0.05). These results indicated that strain NX0101 had a higher replication ability in broiler chickens. The findings of this study will contribute to further elucidating the mechanisms underlying host susceptibility and tumor classification in ALV-J-infected chickens.

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

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