Mechanisms of protective immunity against asexual blood stages of Plasmodium falciparum in the experimental host Saimiri.

In the Saimiri monkey, an experimental host for human malaria, acquired protection against Plasmodium falciparum blood stages depends on the IgG antibody populations developed. In vivo protective anti-falciparum activity of IgG antibodies is correlated with the in vitro opsonizing activity promoting phagocytosis of parasitized red blood cells. In contrast, non protective antibodies inhibit this mechanism by competing at the target level. A similar phenomenon can be observed in human infection. Anti-cytoadherent and anti-rosette antibodies developed by Saimiri and humans prevent the development of physiopathological events like cerebral malaria which can also occur in this experimental host. Furthermore, transfer to protective human anti-falciparum IgG antibodies into infected Saimiri monkeys exerts an anti parasite activity as efficient as that observed when it is transferred into acute falciparum malaria patients, making the Saimiri an even more attractive host. Studies on the role of immunocompetent cells in the protective immune response are still in their infancy, however the existence of a restricted polymorphism of MHC II class molecules in the Saimiri confers additional theoretical and practical importance to this model.