VARIANT-SPECIFIC AND STRAIN-SPECIFIC IMMUNITY IN SAIMIRI INFECTED WITH PLASMODIUM-FALCIPARUM

Variant- and strain-specific immunity to malaria in Saimiri monkeys in fected with homologous O and R variants of the Pale Alto strain (FUPSP ) of Plasmodium falciparum or by various heterologous divergent strain s were studied. Following homologous reinfections, the primary immune response in monkeys was effective only against the same variant type b ut not against the other variant, which differed only by antigens expo sed at the surface of the infected red blood cell. In contrast, after two successive inoculations with a single variant type, a variant tran scending immunity developed to both O and R parasite populations. The immunity against FUPSP in monkeys repeatedly infected with various com binations of heterologous strains, including Sal I, Tanzania, Camp, FU PCP, FCH4, FVO, and FUPCDC parasites was less effective, resulting at best in protecting the monkey against fulminating infection. However, in several cases, previous or concomitant heterologous infections modi fied the course of virulent infection by FUPSP parasites, indicating a significant degree of cross-protection between the strains. Therefore , in this model, while variant-and strain-specific antigens are import ant components of acquired immunity to malaria, the monkey immune resp onse to infection transcends phenotypic antigenic variation and strain diversity.