A long-lasting protective immunity against chronic toxoplasmosis in mice induced by recombinant rhoptry proteins encapsulated in poly (lactide-co-glycolide) microparticles.

Toxoplasma gondii infection in humans and animals is a worldwide zoonosis. Prevention and control of toxoplasmosis based on vaccination is one of the promising strategies. In the present study, recombinant T. gondii rhoptry proteins 38 and 18 (TgROP38 and TgROP18) were encapsulated into poly (lactide-co-glycolide) (PLG) (1:1), respectively, to obtain the stable water-in-oil-in-water double emulsion. Female Kunming mice were then immunized with the protein vaccines twice at a 2-week interval. Eight weeks after the second immunization, 10 mice from each group were challenged with T. gondii PRU strain (genotype II). The entrapment rates of PLG-rROP38 and PLG-rROP18 ranged from 65.5 to 77.7% and 58.1 to 72.3%, respectively. Immunization of mice with rROP38 and rROP18 proteins encapsulated into PLG microparticles elicited strongly humoral and cell-mediated responses against T. gondii, associated with relatively high levels of total IgG, IgG2a isotype, and IFN-γ, as well as the mixed Th1/Th2 immunity responses. Immunization with various protein vaccines induced significant reduction of the brain cysts after chronic infection with the T. gondii PRU strain, and the most effective protection was achieved in the PLG-rROP38-rROP18-immunized mice, with a cyst reduction of 81.3%. The findings of the present study indicated that recombinant rhoptry antigens encapsulated in PLG could maintain the protein immunogenicity in an extended period and elicit effective protection against chronic T. gondii infection, which has implications for the development of long-lasting vaccines against chronic toxoplasmosis in animals.