Reaction of immune sera with components of the human malarial parasite, Plasmodium falciparum.

Human and monkey sera from individuals exposed to Plasmodium falciparum were characterized by indirect immunofluorescence, in vitro parasite growth inhibition, and immunoprecipitation of 125I-labeled parasite antigens followed by analytical sodium dodecyl-sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In general there was a good correlation between fluorescence titer and the ability of a serum to inhibit parasite growth in vitro. Exceptions were found, however. Some variance was seen in the ability of a given serum to inhibit different strains of the parasite. The significance of this is unknown. The proteins bound by human sera with high and low in vitro inhibitory capacities were compared by SDS-PAGE. The human sera which did not inhibit parasite growth in vitro well differed from those which did by failing to efficiently bind certain parasite components having molecular weights in the range of 200,000, 70,000-85,000, and 45,000.