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

Current knowledge on the epidemiology and prevention of Avian leukosis virus in China

Avian leukosis virus (ALV) is an enveloped retrovirus with a single-stranded RNA genome, belonging to the genus Alpharetrovirus within the family Retroviridae. The disease (Avian leukosis, AL) caused by ALV is mainly characterized by tumor development and immunosuppression in chickens, which increases susceptibility to other pathogens and leads to significant economic losses in the Chinese poultry industry. The government and poultry industry have made lots of efforts to eradicate ALV, but the threat of which remains not vanished. This review provides a summary of the updated understanding of ALV in China, which mainly focuses on genetic and molecular biology, epidemiology, and diagnostic methods. Additionally, promising antiviral agents and ALV eradication strategies performed in China are also included.

Identification of a New B-Cell Epitope on the Capsid Protein of Avian Leukosis Virus and Its Application

Avian leukosis virus (ALV) is an avian oncogenic retrovirus that can impair immunological function, stunt growth and decrease egg production in avian flocks. The capsid protein (P27) is an attractive candidate for ALV diagnostics. In the present study, a new hybridoma cell (1F8) stably secreting an anti-P27 monoclonal antibody (mAb) was developed. The mAb exhibited a high affinity constant (Ka) of 8.65 × 106.0 L/mol, and it could be used for the detection of ALV-A/B/J/K strains. Moreover, a total of eight truncated recombinant proteins and five synthetic polypeptides were utilized for the identification of the B-cell epitopes present on P27. The results revealed that 218IIKYVLDRQK227 was the minimal epitope recognized by 1F8, which had never been reported before. Additionally, the epitopes could strongly react with different ALV subgroup's specific positive serum and had a complete homology among all the ALV subgroups strains. Finally, a new sandwich ELISA method was created for the detection of ALV antigens, demonstrating increased sensitivity compared to a commercially available ELISA kit. These results offer essential knowledge for further characterizing the antigenic composition of ALV P27 and will facilitate the development of diagnostic reagents for ALV.

Simultaneous Detection of Three Subgroups of Avian Leukosis Virus Using the Nanoparticle-Assisted PCR Assay

Nanoparticle-assisted polymerase chain reaction (nanoPCR) is a novel method for the rapid detection of pathogens. A sensitive and specific multiple nanoPCR assay was developed for simultaneous detection of avian leucosis virus (ALV) subgroups A, B and J. In this study, three pairs of primers were designed, based on the conserved region of the gp85 gene. An exploration of the optimal primer concentration and annealing temperature were carried out, for better performance of the nanoPCR assay. According to the results, the multiple nanoPCR assay amplified 336 pb, 625 bp and 167 bp fragments of ALV-A, -B and -J, respectively, and showed no cross-reactivity with irrelevant pathogens, suggesting the excellent specificity of the assay. The constructed standard DNA templates were used to estimate the limit of detection. As shown by the results, the detection limit of the nanoPCR assay was nearly 10 copies/μL. To further evaluate the detection ability of the assay, 186 clinical samples were detected using the nanoPCR assay, among which, 14 samples were confirmed as ALV positive; the results were further confirmed by sequencing. In conclusion, a highly specific and sensitive nanoPCR assay was successfully developed, which could be a useful tool for clinical diagnosis as well as for the discrimination of ALV-A, -B and -J.

Zambrano-Rodríguez P. The Use of Peptides in Veterinary Serodiagnosis of Infectious Diseases: A Review

Peptides constitute an alternative and interesting option to develop treatments, vaccines, and diagnostic tools as they demonstrate their scope in several health aspects; as proof of this, commercial peptides for humans and animals are available on the market and used daily. This review aimed to know the role of peptides in the field of veterinary diagnosis, and include peptide-based enzyme-linked immunosorbent assay (pELISA), lateral flow devices, and peptide latex agglutination tests that have been developed to detect several pathogens including viruses and bacteria of health and production relevance in domestic animals. Studies in cattle, small ruminants, dogs, cats, poultry, horses, and even aquatic organisms were reviewed. Different studies showed good levels of sensitivity and specificity against their target, moreover, comparisons with commercial kits and official tests were performed which allowed appraising their performance. Chemical synthesis, recombinant DNA technology, and enzymatic synthesis were reviewed as well as their advantages and drawbacks. In addition, we discussed the intrinsic limitations such as the small size or affinity to polystyrene membrane and mention several strategies to overcome these problems. The use of peptides will increase in the coming years and their utility for diagnostic purposes in animals must be evaluated.

Glycosylation of ALV-J envelope protein at sites 17 and 193 is pivotal in the virus replication

Glycans on envelope glycoprotein (Env) of the subgroup J avian leukosis virus (ALV-J) play an essential role in virion integrity and infection process. In this study, we found that among the 13 predicted N-linked glycosylation sites (NGSs) in gp85 of Tibetan chicken strain TBC-J6, N17 and N193/N191 are pivotal in the virus replication. Further research illustrated that mutation at N193 weakened Env-receptor binding in blocking assay of viral entrance, co-immunoprecipitation and ELISA. Our studies also showed that N17 was involved in Env protein processing and later virion incorporation, based on the detection of p27 and Env protein in the supernatant and gp37 in the cell culture. This report is a systematic research on clarifying the biological function of NGSs on ALV-J gp85, which would provide valuable insights in the role of gp85 in ALV life cycle as well as anti-ALV-J strategies. Importance ALV-J is a retrovirus that can cause multiple types of tumors in chickens. Among all the viral proteins, the heavily glycosylated envelope protein is especially crucial. Glycosylation plays a major role in Env protein function, including protein processing, receptor attachment and immune evasion. Notably, viruses isolated recently seem to lose the 6^th and 11^st NGSs, which are proved to be important in receptor binding. In our study, the 1^st (N17) and 8^th (N193) NGS of gp85 of strain TBC-J6 can largely influence the titer of this virus. Deglycosylation at N193 weakened Env-receptor binding, while mutation at N17 influenced Env protein processing. This study systemically analyzed the function of NGSs in ALV-J in different aspects, which may help us to understand the lifecycle of ALV-J and provide antiviral targets for the control of ALV-J.

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

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