Tumor necrosis factor enhances neutrophil-mediated killing of Plasmodium falciparum.

We developed a radiometric assay by which the antiplasmodial effects of phagocytic cells can be quantitated. This assay was used to examine the effects of recombinant human tumor necrosis factor alpha (TNF-alpha) on the killing of Plasmodium falciparum by human neutrophils. Data presented demonstrated that neutrophils engulf and destroy P. falciparum, but substantial killing of parasites required the presence of either heat-labile or heat-stable opsonins. While recombinant TNF-alpha at concentrations of 5 to 50,000 U/ml showed no direct effects on the parasite, this cytokine augmented the antimalarial activity of neutrophils at doses of 20 to 250 U/10(6) neutrophils. The results suggest that TNF-alpha is an important component of the immune phagocytic effector mechanisms which are involved in destruction of the malarial parasite.