[Toxoplasma gondii: perspectives for a vaccine].

To date no single vaccine has been commercialized in the field of human parasitology, and therefore a practical approach to a potential Toxoplasma vaccine in the field can only be discussed theoretically. The aim of such a vaccine would consist either in inhibiting endogenous parasite multiplication (tachyzoite formation) and thus dissemination, or in preventing the final formation of Toxoplasma cysts (bradyzoite formation). Immune protectivity should confer resistance to disease and parasite dissemination in pregnant women, in order to prevent congenital toxoplasmosis in the unborn infant, and prevent cyst formation in order to avoid reactivation in case of future immunosuppression of the individual. The establishment of a successful protective immunity was elucidated in the mouse model: the number of formed Toxoplasma cysts is primarily regulated by the function of Toxoplasma-specific CD8(+)-T-cells. Direct effector functions of cytotoxic CD8+ lymphocytes directly depend on local periparasitic gamma-interferon- and TNF alpha-concentrations. Immunological aberrance occurs if locally (cerebral) synthesized Il-10 and Il-6 induce anergistic immunosuppression. An experimental vaccine in the mouse demonstrated primary dependence of a protective immune response on CD8+ and CD4+ (Th) cells. Experimental vaccines within domestic animals concentrate mainly on the development of temperature-sensitive mutants of the T. gondii RH-strain, which will protect animals from disease but not from infection and cyst formation.(ABSTRACT TRUNCATED AT 250 WORDS)