GM-CSF-induced priming of human neutrophils for enhanced phagocytosis and killing of asexual blood stages of Plasmodium falciparum: synergistic effects of GM-CSF and TNF.

Granulocyte macrophage-colony stimulation factor (GM-CSF), which is a haematopoietic cytokine generated by activated T lymphocytes and macrophages during infection, was investigated for its effects on human neutrophil-mediated killing of asexual blood forms of Plasmodium falciparum. Pretreatment of neutrophils with human recombinant-GM-CSF markedly increased the parasite killing (measured by a radiometric assay), in the presence of normal serum (containing complement), immune serum (IS), purified IgG (from IS) or heat inactivated IS. GM-CSF pretreatment also enhanced phagocytosis of the parasite by neutrophils and the expression of CR3, Fc gamma RII and Fc gamma RIII receptors. Treatment of neutrophils with a combination of GM-CSF and TNF resulted in a synergistic increase in phagocytosis and killing of the parasite. The findings suggest that GM-CSF is likely to form part of the cytokine network responsible for regulating the antiparasitic activity of the neutrophil in malaria.