Construction of an Adenovirus Vaccine Expressing the Cross-reactive Antigen AMA1 for Neospora caninum and Toxoplasma gondii and Its Immune Response in an Animal Model

Background: We aimed to construct an adenovirus expressing a cross-reactive fragment of the apical membrane antigen 1 (AMA1) antigen and evaluated the concomitant immune response in BABL/c mice, allowing protection against N. caninum and T. gondii infection.

Methods: The study was conducted in Agricultural College of Yanbian University, Yanji, Jilin, China In 2015-2016. Primers were designed using the AMA1 gene sequences of N. caninum (AB265823.1) and T. gondii (AF010264.1). After linearization of the plasmid ADV4-NcAMA1 and the framework plasmid pacAd5, a total of 293T cells were cotransfected and Ad5-NcAMA1 recombinant adenovirus were packed. BALB/c mice were inoculated. Simultaneously serum IgG antibody levels and IFN-γ and IL-4 cytokine levels were determined by ELISA. After immunization three times in two weeks, each group of BABL/c mice were divided into two groups, respectively given intraperitoneal inoculation by the Neospora tachyzoite and Toxoplasma tachyzoite. Then we observed the clinical symptoms and statistical survival rate of mice.

Results: The level of IgG in BABL/c mice immunized with Ad5-NcAMA1 was significantly increased when compared with that of pVAX1-NcAMA1 and PBS groups (P<0.01). At the same time, the cytokine levels of IFN-γ and IL-4 were also higher in the Ad4-NcAMA1 group than in the control groups (P<0.01). Moreover, BABL/c mice immunized with Ad5-NcAMA1, pVAX1-NcAMA1, and PBS showed survival rates of 75%, 45% and 20% after N. caninum infection, and 45%, 10% and 0% after T. gondii infection, respectively.

Conclusion: The adenovirus vaccineAd5-NcAMA1 could provide protective immunity against N. caninum and T. gondii infection.