Protective efficacy of vaccination with Neospora caninum multiple recombinant antigens against experimental Neospora caninum infection.

Protective efficacy of vaccination with Neospora caninum multiple recombinant antigens against N. caninum infection was evaluated in vitro and in vivo. Two major immunodominant surface antigens (NcSAG1 and NcSRS2) and two dense granule proteins (NcDG1 and NcDG2) of N. caninum tachyzoites were expressed in E. coli, respectively. An in vitro neutralization assay using polyclonal antisera raised against each recombinant antigen showed inhibitory effects on the invasion of N. caninum tachyzoites into host cells. Separate groups of gerbils were immunized with the purified recombinant proteins singly or in combinations and animals were then challenged with N. caninum. Following these experimental challenges, the protective efficacy of each vaccination was determined by assessing animal survival rate. All experimental groups showed protective effects of different degrees against experimental infection. The highest protection efficacy was observed for combined vaccination with NcSRS2 and NcDG1. Our results indicate that combined vaccination with the N. caninum recombinant antigens, NcSRS2 and NcDG1, induces the highest protective effect against N. caninum infection in vitro and in vivo.