表达棒状体蛋白ROP18的核酸疫苗在小鼠体内免疫应答研究

oxoplasma gondii is an obligate intracellular protozoan parasite infecting a large variety of domestic and wild animals and human beings. Rhoptries are major players in T. gondii invasion and host cell interaction, and have been implicated as important virulence factors. In this study, we constructed a DNA vaccine expressing rhoptry protein 18 (ROP18) of T. gondii, and evaluated the immune response it induced in Kunming mice. The gene sequence encoding ROP18 was inserted into the eukaryotic expression vector pVAX I. We immunized Kunming mice intramuscularly. After immunization, we evaluated the immune response using lymphoproliferative assay, cytokine and antibody measurements, and the survival times of mice challenged lethally. The results showed that the group immunized with pVAX-ROP18 developed a high level of specific antibody responses against T. gondii ROP18 expressed in E. coli, a strong lymphoproliferative response, and significant levels of IFN-γ, IL-2, IL-4 and IL-10 production, compared with the other groups immunized with either empty plasmid or phosphate-buffered saline, respectively. These results demonstrate that pVAX-ROP18 induces significant humoral and cellular Th1 immune responses. After lethal challenge, the mice immunized with the pVAX-ROP18 showed a significantly increased survival time (27.9±15.1 days) compared with control mice which died within 7 days of challenge. Our data demonstrate, for the first time, that ROP18 triggered a strong humoral and cellular response against T. gondii, and that the antigen is a promising vaccine candidate against toxoplasmosis, worth further development.