The PB subunit vaccine evokes immune response against fox encephalitis

Canine adenovirus type 1 (CAdV-1) is an important pathogen for fox encephalitis, and posing a severe threat to the global fox farming industry. Although live CAdV-2 vaccines are currently available, its defect remains a considerable challenge. It is vital to develop a safe subunit vaccine. This study aimed to evaluate the immunogenicity and safety of the penton base (PB) subunit vaccine in fox with CAdV-1, for which little is known. Bioinformatics methods were used to design a recombinant protein vaccine based on conserved regions of protein consensus sequences in PB protein. The E.coli prokaryotic expression system was utilized to enhance protein expression, solubility and immunogenicity. After the PB proteins of CAdV-1 were successfully expressed, the mice and silver foxes were immunized. The specific antibody, neutralizing antibody titters, T lymphocyte proliferation, cytokine, tissue histopathology, virus shedding, and the survival rate were investigated. The results showed that the PB subunit vaccine induced the production of antibodies in mice at 7, 14, 21, 30, 60 d post-vaccination (dpv). Moreover, the neutralizing antibody level of the PB group was higher than that in the Knob group at 21 and 28 dpv. It indicates that PB subunit vaccine elicits immunity. In the silver fox, PB subunit vaccine induced the production of antibodies at 30 dpv. Moreover, the neutralizing antibody level in PB group was higher than that in the CAdV-2 vaccine group at 30 dpv. PB subunit vaccine conferred complete protection in fox against CAdV-1. The tissue histopathology suggested that the PB subunit vaccine was more effective in blocking the pathogenicity of CAdV-1. In addition, the PB subunit vaccine further reduced the virus shedding in silver foxes than the CAdV-2 vaccine. The results suggest that this vaccine could be a promising candidate for preventing CAdV-1 in foxes.