Molecular characterization and protective immunity of rhoptry protein 35 (ROP35) of Toxoplasma gondii as a DNA vaccine

Toxoplasma gondii rhoptry proteins (TgROPs) have been considered the main targets and indicator molecules for immune diagnosis and prophylaxis because they present during the initial process of invasion. The aim of this study was to evaluate the protective effect of a TgROP35 DNA vaccine on experimental mice subjected to T. gondii challenge. The effect of intramuscularly injecting the genetic vaccine pVAX-ROP35 into BALB/c mice was evaluated, by first inserting the TgROP35 sequence into the pVAX I eukaryotic expression vector. The levels of IgG, IgG1 and IgG2a in pVAX-ROP35-vaccinated animals were integrally increased. Cytokine profile analyses revealed that IFN-γ, IL-2 and IL-10 levels were significantly increased, while there were no significant differences in IL-4 expression between the pVAX-ROP35 immunized and control groups. Additionally, we found that immunization with pVAX-ROP35 significantly prolonged the survival time (13.90 ± 1.97 days) of mice after challenge infection with the virulent T. gondii RH strain compared with that in non-vaccinated control animals (mice died within 10 days). Moreover, the number of brain cysts (1450 ± 287) in the animals subjected to pVAX-TgROP35 vaccination decreased remarkably (P <  0.05) compared to that in the blank control mice (2333 ± 473). Furthermore, the size of brain cysts in the pVAX-TgROP35 group was significantly smaller than that in the blank control, PBS and pVAXI groups. The findings indicated that intense cell-mediated and humoural immunity was triggered and that defence mechanisms against T. gondii were partially induced after vaccination by TgROP35.