PRETREATMENT WITH PHORBOL-MYRISTATE ACETATE INHIBITS MACROPHAGE ACTIVITY AGAINST INTRACELLULAR PROTOZOA

Abstract

To further document the role of toxic O2 intermediates in mononuclear phagocyte antiprotozoal activity, microbicidal [mouse peritoneal] macrophages were depleted of the capacity to generate the superoxide anion (O2-) and H2O2 by pretreatment with phorbol myristate acetate (PMA), a soluble agent which triggers a macrophage respiratory burst. Treating cells for 90 min with 200 ng/ml of PMA inhibited the extracellular release of both O2- and H2O2 by 90% upon subsequent restimulation with either PMA or opsonized zymosan. This effect persisted for 48 h, and could not be reversed by the addition of lymphokine. Intracellular nitroblue tetrazolium reduction by PMA-treated cells was also inhibited by 66-95% upon rechallenge with either PMA or inert or viable particulate agents. In parallel, PMA pretreatment abolished or markedly impaired the ability of normal, lymphokine-stimulated, and in vivo activated macrophages to kill 3 different Protozoa-Toxoplasma gondii, Leishmania donovani and Trypanosoma cruzi. These studies illustrate an additional technique for investigating the antiprotozoal effects of macrophage-derived O2- and H2O2, and reemphasize the importance of an intact respiratory burst mechanism in the killing of intracellular parasites.