Antibody-mediated elimination of malaria parasites (plasmodium berghei) in vivo.

An infective preparation of extracellular blood forms (FP) of Plasmodium berghei was used to study some aspects of the interaction between protective antibodies and malaria parasites. FP but not infected erythrocytes (IRBC) were shown by the fluorescent antibody technique to be coated by antibodies after in vitro incubation with immune serum. Preincubation of both FP and IRBC with immune serum followed by their washing did not result in enhanced elimination of the parasites in vivo. However, FP preincubated with immune serum and subsequently washed were eliminated more efficiently than FP preincubated with normal serum if the preparations were injected with some immune serum. Such an increase in the efficiency of elimination was not detected with similarly pretreated IRBC. It is thus probable that protective antibodies acted in vivo against extracellular parasites rather than against parasites in erythrocytes. The interaction between parasites and antibodies may be of a highly reversible nature, and washing of the in vitro-treated parasites may cause elution of antibody from the sensitized parasites so that the amount of antibody on the parasite falls below the critical level required for in vivo elimination.