Enhanced Plasmodium falciparum merozoite phagocytosis by monocytes from immune individuals

Phagocytosis of merozoites and schizont-infected erythrocytes prepared from continuous cultures by peripheral blood monocytes from patients with falciparum malaria was investigated with an in vitro assay. Monocytes do ingest merozoites of Plasmodium falciparum, but rarely phagocytose parasitized or nonparasitized erythrocytes in the absence of immune serum. The monocytes from hyperimmune subjects were significantly more efficient in the ingestion of merozoites than were those obtained from sensitized or noninfected subjects. These data indicate, first, that the merozoite rather than the parasitized erythrocyte is the specific target for blood phagocytic cells in human falciparum malaria and, second, that the phagocytosis of merozoites by peripheral blood monocytes increases depending on the level of specific immunity.