Radiation effects on <i>Toxoplasma</i> antigens: different immune responses of irradiated intact tachyzoites or soluble antigens in experimental mice models

<b>Purpose:</b> Purpose: Protein irradiation causes aggregation, chain breakage, and oxidation, enhancing its uptake by antigen-presenting cells. To evaluate if irradiated proteins participate on the protection, we studied the immune response induced in mice immunized with irradiated soluble extracts of <i>T. gondii</i> tachyzoites (STag) or irradiated intact <i>T. gondii</i> RH tachyzoites (RH^{0.25 kGy}). <b>Material and Methods:</b> Soluble extracts of <i>Toxoplasma gondii</i> tachyzoites (STag) were irradiated at different dose by Cobalt-60 source. By polyacrylamide gel electrophoresis (SDS-Page) we evaluated the effects on primary structures of protein STags induced by irradiation. By Enzyme-linked Immunosorbent Assay (ELISA) we evaluated the difference between humoral immune response induced by irradiated STag or RH tachyzoites in immunized mice from the detection of specific immunoglobulin G (IgG) antibodies in the serum of immunized mice. From challenge with viable RH strain of <i>T. gondii</i> we evaluated the protection induced in the immunized animals. By cytometry we performed the phenotyping of T and B lymphocytes in the peripheral blood of the immunized animals. <b>Results:</b> Irradiation dose of 1.5 kGy induced minimal changes in most proteins, without affecting their antigenicity or immunogenicity. Immunization showed saturation at the dose of 10 µg/mice, with worst response at higher doses. STag irradiated at 1.5 kGy (STag^{1.5 kGy}) induced higher survival and protection similar to <i>T. gondii</i> RH strain irradiated at 0.25 kGy (RH^{0.25 kGy}), with higher serum levels of high affinity IgG compared to STag native. Blood immune memory cells of mice immunized with STag^{1.5 kGy} had higher proportions of CD19⁺ (cluster of differentiation 19) and CD4⁺ (cluster of differentiation 14) cells, whereas mice RH^{0.25 kGy} had high proportion of memory CD8⁺ (cluster of differentiation 8) cells. <b>Conclusions:</b> Our data suggest that major histocompatibility complex type I (MHCI) pathway, appears seem to be used by RH^{0.25 kGy} to generate cytotoxic cells while STag1.5 kGy uses a major histocompatibility complex type II (MHCII) pathway for B-cell memory, but both induce sufficient immune response for protection in mice without any adjuvant. Irradiation of soluble protein extracts enhances their immune response, allowing similar protection against <i>T. gondii</i> in mice as compared to irradiated intact parasites.