Abstract: Objective To study the immune response elicited by the recombinant protein vaccine and DNA vaccine of the complex antigen ROP2-SAG1 from Toxoplasma gondii. Methods Sixty female BALB/c mice were randomly divided into 4 groups （15 per group）. Mice in rROP2-SAG1 group were immunized subcutaneously with 2.5 μg rROP2-SAG1 protein formulated in Freund′s adjuvant. Mice in control group received only adjuvant emulsified with normal saline. Mice in recombinant plasmid pcROP2-SAG1 and control plasmid pcDNA3.1 groups were each injected intramuscularly with 100 μg of pcROP2-SAG1 and pcDNA3.1, respectively. All the mice received three immunizations at 2-week intervals. Serum samples were collected at 25, 45, and 70 days after immunization for determining antibody IgG, and at 2 weeks after the last immunization IgG1 and IgG2a were detected all by ELISA. Cell counting kit-8 （CCK-8） was used to determine the splenocyte proliferation, and the supernatant of cultured splenocytes was collected for the detection of IFN-γ by ELISA. Results The level of IgG continued to rise in rROP2-SAG1 group after immunization, and similarly in pcROP2-SAG1 group. At 2 weeks after the last immunization, level of IgG1 （1.538±0.183） was higher than that of IgG2a （0.618±0.122）（P＜0.05） in rROP2-SAG1 group. Whereas no significant difference between IgG1 （1.107±0.137） and IgG2a （0.830±0.185） was observed in pcROP2-SAG1 group （P＞0.05）. Compared with the pcROP2-SAG1 group （A₄₅₀=0.123±0.018）, more significant proliferation response of splenocytes was observed in rROP2?-SAG1 group （0.348±0.042） （P＜0.05）. There was no significant difference（P＞0.05） of IFN-γ and IL-2 in the supernatant of cultured splenocytes between the groups of rROP2-SAG1 and pcROP2-SAG1. Conclusion The antibody level and splenocyte proliferation have been significantly higher in mice immunized with recombinant protein rROP2-SAG1 than those with recombinant plasmid pcROP2-SAG1.

Key words: Toxoplasma gondii, Rhoptry protein 2, Major surface protein 1, Vaccine