Phagocytosis of Plasmodium falciparum-parasitized erythrocytes by human polymorphonuclear leukocytes.

Polymorphonuclear leukocytes (PMN) from normal blood donors phagocytosed P. falciparum-infected red blood cells (IRBC) to a greater extent than normal RBC under in vitro culture condition. The phagocytic activity of PMN was greatly increased by the addition of sera from individuals living in areas endemic for malaria (immune sera) but not by sera from individuals recovering from a first acute P. falciparum infection. The enhancement of the phagocytic activity was associated with the purified IgG fraction of immune sera and was lost after absorption of IgG on protein A sepharose column of preincubation of the immune sera with IRBC. These experiments suggest that opsonisation of IRBC and their subsequent phagocytosis may be one of the mechanisms involved in the clearance of P. falciparum infection in individuals living in areas endemic for malaria.