:Δ Live Attenuated Strain Induces Protective Immunity Against Acute and Chronic Toxoplasmosis.

Toxoplasmosis is a zoonotic parasitic disease caused by the obligate intracellular protozoa , which threatens a range of warm-blooded mammals including humans. To date, it remains a challenge to find safe and effective drug treatment or vaccine against toxoplasmosis. In this study, our results found that the development of a mutant strain based on gene disruption of dense granule protein 9 (gra9) in type II PLK strain decreased parasite replication , severely attenuated virulence in mice, and significantly reduced the formation of cysts in animals. Hence, we developed an immunization scheme to evaluate the protective immunity of the attenuated strain of Δ in type II PLK parasite as a live attenuated vaccine against toxoplasmosis in the mouse model. Δ vaccination-induced full immune responses characterized by significantly high levels of pro-inflammatory cytokine interferon gamma (IFN-γ) and interleukin-12 (IL-12), maintained the high -specific immunoglobulin G (IgG) level, and mixed high IgG1/IgG2a levels. Their levels provided the complete protective immunity which is a combination of cellular and humoral immunity in mouse models against further infections of lethal doses of type I RH, type II PLK wild-type tachyzoites, or type II PLK cysts. Results showed that Δ vaccination proved its immunogenicity and potency conferring 100% protection against acute and chronic challenges. Together, Δ vaccination provided safe and efficient immune protection against challenging parasites, suggesting that :Δ is a potentially promising live attenuated vaccine candidate.