Expression of Plasmodium falciparum surface antigens in Escherichia coli.

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Abstract
The asexual blood stages of the human malarial parasite Plasmodium falciparum produce many antigens, only some of which are important for protective immunity. Most of the putative protective antigens are believed to be expressed in schizonts and merozoites, the late stages of the asexual cycle. With the aim of cloning and characterizing genes for important parasite antigens, late-stage P. falciparum mRNA was used to construct a library of c[complementary]DNA sequences inserted in the Escherichia coli expression vector pUC8. Nine thousand clones from the expression library were immunologically screened in situ with serum from Aotus monkeys immune to P. falciparum, and 95 clones expressing parasite antigens were identified. Mice were immunized with lysates from 49 of the bacterial clones that reacted with Aotus sera, and the mouse sera were tested for their reactivity with parasite antigens by indirect immunofluorescence, immunoprecipitation and immunoblotting assays. Several different P. falciparum antigens were identified by these assays. Indirect immunofluorescence studies of extracellular merozoites showed that 3 of these antigens appear to be located on the merozoite surface. cDNA clones to 3 different P. falciparum antigens were identified that may be important in protective immunity.