Plasmodium falciparum: Immune Pressure inSaimiri sciureusMonkeys Can Select for a Parasite Population Inducing a Protective Immunity That Is Not Controlled by Antibody

Morales-Betoulle, M. E., de la Salmonière, Y.-O. G., Zwetyenga, J., Le Scanf, C., Jouin, H., and Michel, J. C. 1998.Plasmodium falciparum: Immune pressure inSaimiri sciureusmonkeys can select for a parasite population inducing a protective immunity that is not controlled by antibody.Experimental Parasitology90, 49–57. Protective immunity against aPlasmodium falciparumblood infection can be passively transferred by antibodies in humans and in the primate experimental malaria modelSaimiri sciureus.We report here the emergence of a novel virulent parasite population after such passive transfer of hyperimmune serum in splenectomized monkeys. These FUP-2 parasites have been partially genotyped and phenotyped. Although no genotypic variation was detected for four polymorphic loci compared to the original FUP-1 parasite population, FUP-2-infected erythrocytes exhibit little or no detectable surface determinants, including those reacting with antibodies raised against FUP-1 surface antigens. In addition, FUP-2-infected erythrocytes exhibit no rosetting or autoagglutination. Interestingly, althoughSaimirimonkeys control efficiently FUP-2 parasites after repetitive infections, this protection cannot be passively transferred to naive recipients. Our results suggest that antibody-mediated and antibody-independent T-cell-mediated protective responses may cooperate in controllingP. falciparuminfection in splenectomizedSaimirimonkeys.