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  • Title: Protective effect of a DNA vaccine delivered in attenuated Salmonella typhimurium against Toxoplasma gondii infection in mice.
    Author: Qu D, Wang S, Cai W, Du A.
    Journal: Vaccine; 2008 Aug 18; 26(35):4541-8. PubMed ID: 18590785.
    Abstract:
    Infection with the intracellular protozoan parasite Toxoplasma gondii causes serious public health problems and is of great economic importance worldwide. The T. gondii surface antigen protein SAG1 is a significant candidate vaccine against toxoplasmosis. In this study, we evaluated safety, stability of ZJ111/pcDNA3-SAG1, a DNA vaccine delivered in attenuated Salmonella typhimurium, and immune responses induced by immunizing ICR mice orally with ZJ111/pcDNA3-SAG1 of different doses. Mice had no significant differences in body weight between the groups before immunization and at week 4 after the booster immunization. The ZJ111/pcDNA3-SAG1 was eventually eliminated from the spleen and liver on week 6 post-immunization. The plasmid pcDNA3-SAG1 was stably maintained over 90% of the attenuated S. typhimurium population after 100 generations of growth in antibiotic-free media. Oral immunization of mice with ZJ111/pcDNA3-SAG1 elicited specific humoral responses and stimulated proliferation of splenocytes (P<0.05). The cellular immune response was associated with the production of IFN-gamma, indicating that a Th-1 type response was elicited, which was confirmed by the production of large amounts of IgG2a (P<0.01). Mice immunized with ZJ111/pcDNA3-SAG1 displayed significant protection against an intraperitoneally challenge with 500 tachyzoite forms of T. gondii RH strain. Vaccination at 10(7) and 10(8)CFU per mice provided a 20% and 10% survival rate comparing 100% mortality of the non-immunized mice, exhibiting longer living time and better survival rate. These results confirmed a DNA vaccine delivered in attenuated S. typhimurium, ZJ111/pcDNA3-SAG1, can elicit specific immune response as well as provide effective protection against T. gondii infection, and the dosage of 10(7)CFU was a most considerate one.
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