Development of an antigen-capture ELISA for beak and feather disease virus

Development of an antigen-capture enzyme-linked immunosorbent assay for diagnosis of Aleutian mink disease virus

Aleutian mink disease (AMD), caused by Aleutian mink disease virus (AMDV), is a very important infectious disease of mink. Currently, elimination of antibody- or antigen-positive animals is the most successful strategy for eradicating AMD, but the claw-cutting method of blood sampling is difficult to perform and painful for the animal. In this study, we aimed to establish an antigen capture enzyme-linked immunosorbent assay (AC-ELISA) method for the efficient detection of AMDV antigens using fecal samples. A purified mouse monoclonal antibody (mAb) was used as the capture antibody, and a rabbit polyclonal antibody (pAb) was used as the detection antibody. The assay was optimized by adjusting a series of parameters. Using a cutoff value of 0.205, the limit of detection of the AC-ELISA for strain AMDV-G antigen was 2 μg/mL, and there was no cross-reaction with other mink viruses. The intra- and inter-assay standard deviations were below 0.046, and the correlation of variance (CV) values were 1.24-7.12% when testing fecal samples. Compared with conventional PCR results, the specificity and sensitivity were 91.5% and 90.6%, respectively, and the concordance rate between the two methods was 91.1%.

Characterization of the nuclear localization sequence of beak and feather disease virus capsid proteins and their assembly into virus-like particles

Beak and feather disease virus (BFDV) is a single-stranded circular DNA icosahedral virus that belongs to the Circoviridae family. This virus is the causative pathogen of beak and feather disease, which leads to feather loss, malformed claws, and immunosuppression of psittacine birds. Our study produced BFDV virus-like particles (VLPs) including capsid proteins, mutant Cap proteins (Cap ΔNLS₅₄, Cap ΔNLS₆₂, Cap C₂₂₈S, and Cap ΔNES) and chimeric Cap proteins carrying the epitope (amino acid residues 64-70) of the replication-associated protein (R-Cap, Cap-R, R-Cap ΔNLS₅₄, and Cap ΔNLS₅₄-R). All of the aforementioned VLPs were observed via transmission electron microscopy and verified through immunogold labeling. The nuclear localization sequence (NLS) of the Cap protein was identified between amino acid residues 55-62. Nuclear export of the Cap protein depended on the nuclear export sequence (NES). All VLPs except Cap ΔNLS₆₂ and Cap ΔNES entered the cells 2 h post-infection (hpi) and were shuttled into the nucleus at 8 hpi. Wheat germ agglutinin (WGA) blocked the nuclear entry of Cap proteins at 8 hpi and the nuclear export of Cap proteins at 16 hpi was inhibited by leptomycin B. The nuclear entry of Cap protein was inhibited by importin α and importin β inhibitors, as well as NLS peptides. Moreover, the interactions of Cap proteins and Cap VLPs with both importin α and importin β were characterized via the GST pull-down and immunofluorescence assays. These interactions were blocked by the presence of importin α and importin β inhibitors, as well as NLS peptides. Therefore, our study is the first to describe the precise position of the NLS of the BFDV Cap protein and the interaction of Cap protein with importin α and importin β in vitro.