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

Molecular characteristics and pathogenicity of a Tibet-origin mutant avian leukosis virus subgroup J isolated from Tibetan chickens in China

Tibetan chicken is found in China Tibet (average altitude; ˃4500 m). However, little is known about avian leukosis virus subgroup J (ALV-J) found in Tibetan chickens. ALV-J is a typical alpharetrovirus that causes immunosuppression and myelocytomatosis and thus seriously affects the development of the poultry industry. In this study, Tibet-origin mutant ALV-J was isolated from Tibetan chickens and named RKZ-1-RKZ-5. A Myelocytomatosis outbreak occurred in a commercial Tibetan chicken farm in Shigatse of Rikaze, Tibet, China, in March 2022. About 20% of Tibetan chickens in the farm showed severe immunosuppression, and mortality increased to 5.6%. Histopathological examination showed typical myelocytomas in various tissues. Virus isolation and phylogenetic analysis demonstrated that ALV-J caused the disease. Gene-wide phylogenetic analysis showed the RKZ isolates were the original strains of the previously reported Tibetan isolates (TBC-J4 and TBC-J6) (identity; 94.5% to 94.9%). Furthermore, significant nucleotide mutations and deletions occurred in the hr1 and hr2 hypervariable regions of gp85 gene, 3'UTR, Y Box, and TATA Box of 3'LTR. Pathogenicity experiments demonstrated that the viral load, viremia, and viral shedding level were significantly higher in RKZ-1-infected chickens than in NX0101-infected chickens. Notably, RKZ-1 caused more severe cardiopulmonary damage in SPF chickens. These findings prove the origin of Tibet ALV-J and provide insights into the molecular characteristics and pathogenic ability of ALV-J in the plateau area. Therefore, this study may provide a basis for ALV-J prevention and eradication in Tibet.

Chicken CH25H inhibits ALV-J replication by promoting cellular autophagy

Autophagy plays an important role in host antiviral defense. The avian leukosis virus subgroup J (ALV-J) has been shown to inhibit autophagy while promoting viral replication. The underlying autophagic mechanisms, however, are unknown. Cholesterol 25-hydroxylase (CH25H) is a conserved interferon-stimulated gene, which converts cholesterol to a soluble antiviral factor, 25-hydroxycholesterol (25HC). In this study, we further investigated the autophagic mechanism of CH25H resistance to ALV-J in chicken embryonic fibroblast cell lines (DF1). Our results found that overexpression of CH25H and treatment with 25HC promoted the autophagic markers microtubule-associated protein 1 light chain 3 II (LC3II) and autophagy-related gene 5(ATG5), while decreased autophagy substrate p62/SQSTM1 (p62) expression in ALV-J infection DF-1 cells. Induction of cellular autophagy also reduces the levels of ALV-J gp85 and p27. ALV-J infection, on the other hand, suppresses autophagic marker protein LC3II expression. These findings suggest that CH25H-induced autophagy is a host defense mechanism that aids in ALV-J replication inhibition. In particular, CH25H interacts with CHMP4B and inhibits ALV-J infection in DF-1 cells by promoting autophagy, revealing a novel mechanism by which CH25H inhibits ALV-J infection. Although the underlying mechanisms are not completely understood, CH25H and 25HC are the first to show inhibiting ALV-J infection via autophagy.

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.

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.

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.

Chicken telomerase reverse transcriptase promotes the tumorigenicity of avian leukosis virus subgroup J by regulating the Wnt/β-catenin signaling pathway

This research aimed to analyze the regulatory effect of chicken telomerase reverse transcriptase (chTERT) on the Wnt/β-catenin signaling pathway and its effect on the tumorigenicity of avian leukosis virus subgroup J (ALV-J) through in vivo experiments. The chTERT eukaryotic expression plasmid and its recombinant lentivirus particles were constructed for in vivo transfection of chTERT to analyze the effect of chTERT continuously overexpressed in chickens on the tumorigenicity of ALV-J. During 156 days of the artificial ALV-J tumor-inducing process, 7 solid tumors developed in 3 chickens in the chTERT-overexpression group (n = 26*2) and no tumors developed in the control group (n = 26*2). Another 18 tumors induced by ALV-J were confirmed and collected from breeding poultry farms. And we confirmed that chTERT was significantly highly expressed in ALV-J tumors. The ELISA data suggested that the protein levels of β-catenin and c-Myc in the chicken plasma of the chTERT-overexpressing group with ALV-J infected were consistently and significantly higher than those of the control group. Compared with that of the tumor-adjacent tissues, the activity of the Wnt/β-catenin signaling pathway and expression of the c-Myc was significantly increased in ALV-J tumors. And the percentage of apoptosis in ALV-J tumors significantly lower than that in tumor-adjacent tissues. Immunohistochemistry, Western blot and RT-qPCR suggested that the replication level of ALV-J in tumors was significantly higher than that in tumor-adjacent tissues. This study suggests that chTERT plays a critical role in the tumorigenicity of ALV-J by enhancing the Wnt/β-catenin signaling pathway, which will contribute to further elucidating the tumor-inducing mechanism of ALV-J.

SOCS3 Promotes ALV-J Virus Replication via Inhibiting JAK2/STAT3 Phosphorylation During Infection

Avian leukosis virus subgroup J (ALV-J) is an oncogenic retrovirus that causes immunosuppression and neoplastic diseases in poultry. Cytokine signal-transduction inhibitor molecule 3 (SOCS3) is an important negative regulator of the JAK2/STAT3 signaling pathway and plays certain roles in ALV-J infection. It is of significance to confirm the roles of SOCS3 in ALV-J infection and study how this gene affects ALV-J infection. In this study, we assessed the expression of the SOCS3 gene in vivo and in vitro, and investigated the roles of SOCS3 in ALV-J infection using overexpressed or interfered assays with the SOCS3 in DF-1 cells. The results showed that the SOCS3 expression of ALV-J infected chickens was different from uninfected chickens in the spleen, thymus and cecal tonsil. Further, SOCS3 is mainly expressed in the nucleus as determined by immunofluorescence assay. Overexpression of SOCS3 in DF-1 cells promoted the replication of ALV-J virus, and the expression of interferons (IFNα and INFβ), inflammatory factors (IL-6 and TNFα) along with interferon-stimulating genes (CH25H, MX1, OASL, and ZAP). Conversely, interference of SOCS3 showed the opposite results. We also observed that SOCS3 promoted ALV-J virus replication by inhibiting JAK2/STAT3 phosphorylation. In conclusion, SOCS3 promotes ALV-J replication via inhibiting the phosphorylation of the JAK2/STAT3 signaling pathway. These results would advance further understanding of the persistent infection and the viral immune evasion of the ALV-J virus.