TNF-alpha controls intracellular mycobacterial growth by both inducible nitric oxide synthase-dependent and inducible nitric oxide synthase-independent pathways.
The role of TNF-alpha in the control of mycobacterial growth in murine macrophages was studied in vitro. Infection of macrophages from TNF-alpha gene disrupted (TNF-knockout (KO)) mice with recombinant Mycobacterium bovis bacillus Calmette Guérin (BCG) expressing the vector only (BCG-vector) resulted in logarithmic growth of the intracellular bacilli. Infection with BCG-secreting murine TNF-alpha (BCG-TNF) led to bacillary killing. Killing of BCG-TNF was associated with rapid accumulation of inducible NO synthase (iNOS) protein and the production of nitrite. The uncontrolled growth of BCG-vector was associated with low iNOS expression but no nitrite production. Thus, iNOS expression appears to be TNF-alpha independent but iNOS generation of NO requires TNF-alpha. In cultures of TNF-KO macrophages infected with BCG-TNF, inhibition of iNOS by aminoguanidine (AMG) abolished the killing of the bacilli. However, the growth of the organisms was still inhibited, suggesting an iNOS-independent TNF-alpha-mediated growth inhibition. To confirm this, macrophages from iNOS-KO mice were infected with either BCG-vector or BCG-TNF. As expected, no nitrite was detected in the culture medium. TNF-alpha was detected only when the cells were infected with BCG-TNF. In the iNOS-KO macrophages, the growth of BCG was inhibited only in the BCG-TNF infection. These results suggest that in the absence of iNOS activity, TNF-alpha stimulates macrophages to control the growth of intracellular BCG. Thus, there appears to be both a TNF-alpha-dependent-iNOS-dependent killing pathway as well as a TNF-alpha-dependent-iNOS-independent growth inhibitory pathway for the control of intracellular mycobacteria in murine macrophages.
Bekker
L G
LG
Laboratory of Cellular Physiology and Immunology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Freeman
S
S
Murray
P J
PJ
Ryffel
B
B
Kaplan
G
G
D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000235:genetics / Q000276:immunology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005822:Genetic Vectors / Q000276:immunology / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology; D007371:Interferon-gamma / Q000502:physiology; D007424:Intracellular Fluid / Q000201:enzymology* / Q000276:immunology / Q000382:microbiology*; D017737:Macrophages, Peritoneal / Q000201:enzymology / Q000276:immunology / Q000382:microbiology / Q000648:ultrastructure; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009163:Mycobacterium bovis / Q000235:genetics / Q000254:growth & development* / Q000276:immunology* / Q000648:ultrastructure; D009569:Nitric Oxide / Q000096:biosynthesis / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II; D009573:Nitrites / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
D004791:Enzyme Inhibitors; D006146:Guanidines; D009573:Nitrites; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; C004479:pimagedine