Effectiveness of Gamma Rays in Attenuation of Toxoplasma gondii Pathogenicity and Eliciting Immune Response in Mice

Gamma irradiation was applied to the tachyzoites Toxoplasma gondii virulent strain at doses of 0.25, 0.5, 1, 1.5 and 2 KGy. Radiation's effects were assessed both in vivo and in vitro. In vitro, the modest dosage of radiation, 0.25 KGy, showed 97% tachyzoites viability with only slight surface abnormalities and a normal crescent form using a scanning electron microscope. Protein analysis by SDS-PAGE demonstrated that while higher doses of radiation altered the protein banding profile, the 0.25 KGy irradiated tachyzoites showed no significant changes compared to the control (non-irradiated tachyzoites). While, tachyzoites exposed to the higher dose of irradiation (1, 1.5 and 2 KGy) resulted in the appearance of a new protein band as the molecular weights detected were 60, 30 and 10 kDa for antigens prepared from tachyzoites exposed to 1 kDa, and 1.5 and 60, 28 kDa for antigen prepared from tachyzoites exposed to 2 KGy. The immunogenicity of the tachyzoites exposed to radiation did not reveal any significant change in comparison with no irradiated tachyzoites when tested by ELISA using sheep-infected sera. A study conducted in vivo evaluated the infectivity of irradiation tachyzoites by inoculating mice with a 2500 tachyzoites virulent strain/mouse. There are six groups of mice, each with twelve animals, for the six doses of radiation. Mice harbouring irradiation tachyzoites remained viable until 40 days post-inoculation. On the other hand, the mice of control group had a mean survival time of 6.5 ± 0.22 days, and none of them survived past 7 dpi. Comparing the attenuated T. gondii tachyzoites at 0.25 KGy to the control group and other groups injected with irradiated tachyzoites, the results showed statistically significant increases in total IgG. Compared to other irradiation groups, the group injected with 0.25 KGy irradiated tachyzoites had a considerably higher level of IFN γ and IL17 (p < 0.000001). The groups which received 0.25 and 0.5 KGy irradiated tachyzoites as an injection showed no discernible variation in their higher levels of IL12. The findings imply that gamma irradiation was successful in reducing the pathogenicity of the T. gondii virulent strain while preserving the potential of the irradiated tachyzoites to induce an immunological reaction. An investigation into this immune response's immunoprotective potential is advised.