Gamma Interferon Prevents the Inhibitory Effects of Oxidative Stress on Host Responses toEscherichia coliInfection

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Abstract
Oxidative stress occurs in animals challenged with bacterial endotoxin and can affect the expression of important host inflammatory genes. However, much less is known about the effects of oxidative stress on responses to gram-negative bacteria. The current study compared the effects of redox imbalance on hepatic responses of mice toEscherichia colibacteria versus purified endotoxic lipopolysaccharide (LPS). Oxidative stress induced by glutathione depletion virtually eliminated hepatic tumor necrosis factor alpha responses to bothE. coliand LPS. Inducible NO synthase (iNOS) and intercellular adhesion molecule-1 (ICAM-1) expression was also markedly inhibited by glutathione depletion in LPS-challenged mice, but was unaffected inE. coli-infected animals. Three findings suggested that gamma interferon (IFN-γ) production explained the differences between LPS and bacterial challenge. Glutathione depletion completely inhibited the IFN-γ response to LPS, but only partially inhibited IFN-γ production in infected mice. Exogenous IFN-γ restored iNOS and ICAM-1 responses to LPS in stressed mice. Conversely, IFN-γ-deficient, glutathione-depleted mice showed a marked decrease in iNOS and ICAM-1 expression when challenged withE. coli. These findings indicate that both the nature of the microbial challenge and the production of IFN-γ can be important in determining the effects of redox imbalance during gram-negative bacterial infections.

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