Peritoneal macrophages from C57BL/6 mice orally immunized withToxoplasma gondiiantigens in association with cholera toxin possess an enhanced ability to inhibit parasite multiplication

Abstract

Gamma-interferon (IFN-gamma) has been reported to be a major mediator of resistance to toxoplasma infection, mainly through macrophage activation. Cholera toxin used as oral adjuvant induces enhanced protection. Following oral immunization of C57BL/6 mice with a Toxoplasma gondii sonicate (TSo), in association with either cholera toxin (CT) or its B subunit (CTB), the ability of primed sensitized peritoneal macrophages (PM phi) to prevent T. gondii intracellular proliferation in vitro was examined both with and without rIFN-gamma activation. Under these conditions, the inhibition of T. gondii multiplication was greatly enhanced in PM phi from mice immunized with a TSo and CT as an oral adjuvant. In contrast, PM phi from mice immunized with a TSo in association with CTB showed a decrease in their microbiostatic activity towards T. gondii. This negative effect on IFN-gamma-treated PM phi was cancelled out by the addition of a small amount of CT in association with TSo and CTB in the immunization regimen. These data suggest that CT could act as an oral adjuvant in vaccination against toxoplasmosis by increasing the microbiostatic activity of M phi activated with IFN-gamma. Further studies, using intestinal effector cells such as enterocytes, are needed to confirm the value of CT for enhancing this major mechanism of protection against T. gondii infection.