Killing of Legionella pneumophila by nitric oxide in gamma-interferon-activated macrophages.
The role of nitric oxide (NO) radicals in killing the intracellular bacterial pathogen Legionella pneumophila (Lp) was examined in infected macrophages. Murine (RAW 264.7) and human (HL-60) cell monolayers were treated with 100 U/ml gamma-interferon (IFN) and cocultured with Lp in the presence and absence of NGMMA, a specific inhibitor of NO production. Viable Lp in IFN-treated RAW 264.7 cells decreased from 3.8 to 0.7 +/- 0.12 log CFU/ml after 24 h incubation, whereas in IFN+NGMMA-treated RAW 264.7 cells, viable Lp persisted at 2.2 +/- 0.2 log CFU/ml after 24 h. This increased survival corresponded with an inhibition of NO production (5.65 +/- 2.99 microM with NGMMA vs. 58.6 +/- 5.36 microM without NGMMA). Viable Lp were susceptible to killing, in a dose-dependent fashion, by 0, 2.5, and 5.0 mM sodium nitroprusside, a source of NO radicals. IFN-treated RAW 264.7 cells also had significantly decreased levels of intracellular iron (below assay limit) when compared to IFN+NGMMA-treated cells (72.0 +/- 0.78% of control). Normally permissive HL-60 cells treated with IFN were bacteriostatic rather than bactericidal, and NO production was not detected above background. Thus, NO radicals play a critical role in the bactericidal activity against Lp by IFN-treated RAW 264.7 cells, but the absence of NO production limits IFN-treated HL-60 cells to bacteriostasis.
Summersgill
J T
JT
Department of Medicine, University of Louisville School of Medicine, Kentucky 40292.
Powell
L A
LA
Buster
B L
BL
Miller
R D
RD
Ramirez
J A
JA
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002460:Cell Line; D006801:Humans; D007223:Infant; D007371:Interferon-gamma / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism; D016952:Legionella pneumophila / Q000187:drug effects* / Q000254:growth & development; D015473:Leukemia, Promyelocytic, Acute; D008262:Macrophage Activation; D008264:Macrophages / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009569:Nitric Oxide / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology*; D011994:Recombinant Proteins; D014407:Tumor Cells, Cultured; D019323:omega-N-Methylarginine
D009573:Nitrites; D011994:Recombinant Proteins; D009599:Nitroprusside; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D007371:Interferon-gamma; D001120:Arginine; D007501:Iron