Prolonged expression of IFN gamma induced by protective blood-stage immunization against Plasmodium yoelii malaria

Mice vaccinated with whole blood-stage antigens of Plasmodium yoelii develo p protective, antibody-mediated immune responses to homologous challenge in fection. In this model the level of protection induced by whole parasite an tigen vaccination is dependent on antibody isotype, which can be influenced by adjuvant formulations. In this study the ability adjuvant formulations to affect cytokine production and protection against P. yoelii blood-stage infection was investigated. Survival of mice in groups vaccinated with P, y oelii antigens in an aqueous mix of copolymer P1005 + RaLPS was 100%. Mice vaccinated with either P. yoelii antigens alone or combined with a water-in -oil emulsion of copolymer P1005 + RaLPS demonstrated 83 or 50% survival, r espectively. The fully protective aqueous vaccine group produced higher lev els of interferon gamma (IFN gamma) and interleukin 4 (IL-4) than the water -in-oil vaccine group following a live parasite challenge infection. Furthe rmore, mice vaccinated with the aqueous vaccine displayed prolonged IFN gam ma and IL-4 response as compared to mice that received the same antigens wi thout adjuvants. These data support the hypothesis that both the Th1 cytoki ne IFN gamma, and the Th2 cytokine IL-4 are modulated by the vaccine vehicl e and adjuvant used for vaccination, thus possibly affecting expression of protective immune responses. However, it is the long-lasting IFN gamma resp onse following blood-stage P. yoelii parasite challenge that is associated with enhanced survival. Published by Elsevier Science Ltd.