Abstract: Objective To examine the immune response in BALB/c mice induced by oral mixed Toxoplasma gondii DNA vaccine delivered by live attenuated Salmonella typhimurium. Methods Gene fragments SAG1 and SAG2 were amplified from the genomic DNA of T. gondii RH strain by PCR and were subcloned into pcDNA3.1(±) eukaryotic expression vector. The positive recombinant plasmid was transformed into aroA- and aroD-attenuated Salmonella typhimurium BRD509 (BRD509/pSAG1/SAG2). After screened by PCR, restrictive enzyme digestion and sequencing, recombinant Salmonella strain was used to immunize BALB/c mice by i.g. route, three times at 2-week interval. Humoral and cellular responses were assayed using ELISA for determining antibody, IFN-γ and IL-4. MTT assay was used to detect the proliferation activity of T lymphocytes and the activity of NK killers. FCM was also used to sort the lymphocyte subsets of spleen cells. All mice were then infected with highly virulent RH tachyzoites of T. gondii intraperitoneally. Results Significant increase of specific IgG level was observed in immunized mice with a titer of 1∶100. Proliferation activity of specific NK cells and T lymphocytes was highly enhanced in BRD509/ pSAG1/SAG2 vaccinated mice： the killing activity of NK cells was 85%±7%， the proliferation SI of T lymphocytes was 2.83， which resulted in a 5 days longer survival time than mice in control group after challenge infection. Conclusion The oral mixed DNA vaccine delivered by attenuated Salmonella typhimurium shows an immunoprotection against T. gondii in mice.

Key words: Toxoplasma gondii, Attenuated Salmonella BRD509, SAG1/SAG2, Mixed DNA immunization