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Phenotype of mice and macrophages deficient in both phagocyte oxidase and inducible nitric oxide synthase
M U Shiloh1, J D MacMicking, S Nicholson
1Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York 10021, USA.
Abstract:
The two genetically established antimicrobial mechanisms of macrophages are production of reactive oxygen intermediates by phagocyte oxidase (phox) and reactive nitrogen intermediates by inducible nitric oxide synthase (NOS2). Mice doubly deficient in both enzymes (gp91(phox-/-)/NOS2(-/-)) formed massive abscesses containing commensal organisms, mostly enteric bacteria, even when reared under specific pathogen-free conditions with antibiotics. Neither parental strain showed such infections. Thus, phox and NOS2 appear to compensate for each other's deficiency in providing resistance to indigenous bacteria, and no other pathway does so fully. Macrophages from gp91(phox-/-)/NOS2(-/-) mice could not kill virulent Listeria. Their killing of S. typhimurium, E. coli, and attenuated Listeria was markedly diminished but demonstrable, establishing the existence of a mechanism of macrophage antibacterial activity independent of phox and NOS2.
Insights
Mice lacking both phagocyte oxidase (phox) and inducible nitric oxide synthase (NOS2) developed severe bacterial infections, indicating these enzymes are crucial for immunity. A compensatory antibacterial mechanism in macrophages exists independently of phox and NOS2.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Macrophages employ reactive oxygen intermediates (phox) and reactive nitrogen intermediates (NOS2) as key antimicrobial mechanisms.
- These two pathways are genetically established and critical for host defense against microbial pathogens.
Purpose of the Study:
- To investigate the compensatory roles of phox and NOS2 in innate immunity against indigenous bacteria.
- To determine if alternative antimicrobial mechanisms exist in macrophages when both phox and NOS2 are absent.
Main Methods:
- Generation of double-knockout mice lacking both gp91(phox) and NOS2 genes.
- Infection models using commensal enteric bacteria and virulent/attenuated Listeria strains.
- Assessment of bacterial load and abscess formation in knockout and parental strains.
Main Results:
- Mice deficient in both phox and NOS2 developed massive abscesses when exposed to commensal organisms, unlike parental strains.
- Macrophages from double-knockout mice showed impaired killing of virulent Listeria but retained some capacity to eliminate S. typhimurium, E. coli, and attenuated Listeria.
- These findings demonstrate a macrophage antibacterial activity independent of phox and NOS2.
Conclusions:
- Phox and NOS2 are essential and largely compensatory for resistance to indigenous bacteria.
- A distinct macrophage-mediated antibacterial pathway exists, offering partial protection when phox and NOS2 are absent.