Immune dysfunction in endotoxicosis: role of nitric oxide produced by inducible nitric oxide synthase.
OBJECTIVE
To investigate whether stimulation with lipopolysaccharide (LPS) alters cytokine production by splenocytes in mice and whether it changes the T-helper 1 (Th1)/Th2 balance. The role of nitric oxide in such immunologic changes was also explored using mice with genetic lack of inducible nitric oxide synthase (iNOS).


METHODS
: Prospective animal study with concurrent controls.


METHODS
University research laboratory.


METHODS
iNOS knockout mice and wild-type littermates.


METHODS
iNOS knockout mice or wild-type mice were injected with LPS or saline with or without anti-interleukin (IL)-6 antibody, and survival was monitored for 7 days.


RESULTS
At 24 and 48 hrs after administration, blood samples and splenocytes were obtained to examine immunologic variables. Cell surface markers and cytokine expression of splenocytes were used to characterize the Th1/Th2 balance and were measured by flow cytometry. At 48 hrs after LPS administration, the Th1/Th2 balance shifted toward Th2 predominance in wild-type mice, irrespective of the IL-6 level, whereas it showed Th1 predominance in iNOS knockout mice, and the increase of IL-6 and IL-10 in response to LPS persisted in these animals. After LPS administration, the mortality rate was significantly higher in iNOS knockout mice than in wild-type mice, irrespective of the IL-6 level.


CONCLUSIONS
These findings suggest that nitric oxide produced by iNOS during endotoxemia may be involved in down-regulation of Th1 cytokines and up-regulation of Th2 cytokines, whereas IL-6 has no such role. The increased lethality of LPS in iNOS knockout mice suggests that nitric oxide may be protective against proinflammatory cytokine-induced damage. Nitric oxide excess may increase susceptibility to nosocomial infections, so-called immunoparalysis.
Miki
Shigeki
S
Department of Emergency and Critical Care Medicine, Kansai Medical University, Osaka, Japan.
Takeyama
Naoshi
N
Tanaka
Takaya
T
Nakatani
Toshio
T
D000818:Animals; D015850:Interleukin-6 / Q000276:immunology / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000172:deficiency / Q000378:metabolism*; D011446:Prospective Studies; D012016:Reference Values; D012772:Shock, Septic / Q000201:enzymology* / Q000276:immunology*; D016019:Survival Analysis; D018417:Th1 Cells / Q000378:metabolism; D018418:Th2 Cells / Q000378:metabolism; D000093242:Interleukin-6 Inhibitors
D015850:Interleukin-6; D008070:Lipopolysaccharides; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D000093242:Interleukin-6 Inhibitors