Cooperation between antibodies and monocytes that inhibit in vitro proliferation of Plasmodium falciparum.

The cooperative effect between nonsensitized monocytes from normal individuals and malarial antibody in depressing parasite multiplication was investigated in an in vitro assay. The addition of purified normal monocytes to Plasmodium falciparum cultures in the presence of serum from immune individuals markedly inhibited the proliferation of the parasite in vitro: the parasitemia observed was about 22 times lower than that in the presence of immune serum alone. This cooperative effect was found to be effective over a wide range of monocyte/erythrocyte ratios (1:10 to 1:160) and serum concentrations (1/10 to 1/80). Immunoglobulin G extracted on protein A-Sepharose was as effective as total serum in this system. These data suggest that cooperation between nonsensitized cells and immunoglobulins could be an important effector mechanism against P. falciparum parasites in vivo.