Intracellular destruction of Leishmania donovani and Leishmania tropica amastigotes by activated macrophages: dissociation of these microbicidal effector activities in vitro.

Resident peritoneal macrophages were exposed to amastigotes of Leishmania donovani and L. tropica and treated with soluble products of antigen or mitogen-stimulated lymphocytes (lymphokines, LK). Macrophages infected with L. donovani were responsive to lower concentrations of LK for elimination of this parasite than cells infected with L. tropica, and the disappearance of L. donovani amastigotes from activated macrophages preceded that of L. tropica by at least 24 hr. That the differential elimination of amastigotes from LK-treated macrophages may reflect different intracellular killing mechanisms for the two parasites is supported by studies with macrophages activated in vivo; macrophages from BCG-treated C3H/HeJ mice that were incapable of eliminating intracellular L. tropica killed amastigotes of L. donovani. Whether the effector mechanism(s) for intracellular destruction of the two Leishmania are qualitatively or only quantitatively different is as yet unknown.