Preliminary study on expression and functions of Toxoplasma gondii SRS67 and SRS20A proteins

Toxoplasma gondii surface proteins play critical roles in parasite invasion, proliferation, and host immune modulation, and represent promising targets for anti-toxoplasmosis intervention. SRS67 and SRS20A are poorly characterized surface proteins of T. gondii, and their biological functions and host regulatory effects remain largely unclear.

In the present study, we prepared recombinant SRS67 and SRS20A proteins and generated corresponding polyclonal antibodies to explore their functional characteristics and protective potentials.

Immunofluorescence analysis localized both proteins as punctate signals surrounding the parasite membrane, indicating their involvement in surface-associated biological processes. In vitro phenotypic assays demonstrated that the prepared polyclonal antibodies significantly inhibited host cell invasion and intracellular proliferation of T. gondii. In vivo animal experiments further showed that antibody treatment effectively alleviated T. gondii-caused pathological injuries in mice. In the acute RH infection model, single or combined protein immunization increased the survival rate of mice by approximately 60%, and combined immunization delayed mortality by 1-2 days. In chronic PRU infection, antibody intervention reduced brain cyst burden by over 85% and markedly attenuated meningeal thickening and neuronal necrosis. Mechanistically, SRS67 upregulated the expression of Th1 cytokines (TNF-α, IL-18) during acute infection, while both proteins downregulated IFN-γ to limit excessive immune-mediated tissue damage. The elevated glutathione (GSH) level suggested the participation of these proteins in antioxidant regulation. During chronic infection, combined immunization synergistically enhanced superoxide dismutase (SOD) activity to resist oxidative stress, and decreased IFN-γ expression contributed to the maintenance of immune homeostasis.

Collectively, this study systematically characterizes the biological functions of SRS67 and SRS20A, and demonstrates that their polyclonal antibodies exert potent inhibitory effects against T. gondii infection by directly blocking parasite biological behaviors and indirectly regulating host immune responses and antioxidant status. Our findings provide novel insights into the functional mechanisms of SRS family proteins and support the development of SRS-targeted anti-Toxoplasma strategies.