[Immune response elicited by the recombinant protein and plasmid DNA of complex antigen ROP2-SAG1 from Toxoplasma gondii].

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-SAGI group were immunized subcutaneously with 2.5 microg 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 microg 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-gamma 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-gamma and IL-2 in the supematant 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.