HUMAN MONOCYTES CULTURED WITH AND WITHOUT INTERFERON-GAMMA INHIBIT PLASMODIUM-FALCIPARUM PARASITE GROWTH IN-VITRO VIA SECRETION OF REACTIVENITROGEN INTERMEDIATES

Adherent cells from human peripheral blood were studied for their inte raction with asexual blood forms of Plasmodium falciparum in vitro. Fr eshly isolated monocytes only showed weak anti-parasitic effects. Howe ver, an enhancement of this anti-parasitic activity was apparent when monocytes were allowed to mature in vitro. Monocytes activated with IF N-gamma for two or three days had an enhanced anti-parasitic effect. I n contrast, the inhibition mediated by cells incubated for five days w as the same with or without IFN-gamma treatment. There was no evidence of toxicity when IFN-gamma at high concentrations was added directly to P. falciparum cultures. The anti-parasitic activity of the activate d cells seemed to be due to nitric oxide since incubation of macrophag es with L-NMMA reduced the level of inhibition. However, inhibition wa s only partial suggesting that other factors also were involved in inh ibition of parasite growth.