Activated macrophages destroy intracellular Leishmania major amastigotes by an L-arginine-dependent killing mechanism.
Macrophages infected with amastigotes of Leishmania major and treated with IFN-gamma in vitro develop potent antimicrobial activities that eliminate the intracellular parasite. This antileishmanial activity was suppressed in a dose dependent fashion by NG-monomethyl-L-arginine (NGMMLA), a competitive inhibitor of nitrite, nitrate, nitric oxide and L-citrulline synthesis from L-arginine. Excess L-arginine added to infected macrophage cultures reversed the inhibitory effects of NGMMLA. Addition of arginase to culture media inhibited intracellular killing by IFN-gamma-treated cells. Similar effects were seen with macrophages obtained from BCG-infected C3H/HeN mice. Increased levels of nitrite, an oxidative product of the L-arginine-dependent effector mechanism, was measured in cultures of infected IFN gamma-treated macrophages as well as infected BCG-activated macrophages. Nitrite production correlated with development of antileishmanial activity. Nitrite production and microbicidal activity both decreased when in vivo or in vitro-activated macrophages were cultured in the presence of either arginase or NGMMLA. Nitric oxide synthesized from a terminal guanidino nitrogen atom of L-arginine and a precursor of the nitrite measured, may disrupt Fe-dependent enzymatic pathways vital to the survival of amastigotes within macrophages.
Green
S J
SJ
Department of Cellular Immunology, Walter Reed Army Institute of Research, Washington, D.C. 20307.
Meltzer
M S
MS
Hibbs
J B
JB
Nacy
C A
CA
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology*; D003602:Cytotoxicity, Immunologic; D007111:Immunity, Cellular; D007371:Interferon-gamma / Q000494:pharmacology; D007895:Leishmania tropica / Q000276:immunology*; D008262:Macrophage Activation; D008264:Macrophages / Q000276:immunology* / Q000469:parasitology; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D019323:omega-N-Methylarginine
D009573:Nitrites; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D007371:Interferon-gamma; D001120:Arginine