Regulation of lipopolysaccharide-induced NO synthase expression in the major organs in a mouse model. The roles of endogenous interferon-gamma, tumornecrosis factor-alpha and interleukin-10

Elevated NO production mediated by activation of the enzyme iNOS is thought to play a central role in the development of tissue damage observed during septic shock. IFN-gamma, TNF-alpha and IL-10 have been shown to be involve d in the regulation of LPS-induced serum levels of the NO-oxidation product s nitrate and nitrite. Therefore, in the present study, we investigated the role of endogenous IFN-gamma, TNF-alpha and IL-10 in the regulation of LPS -induced tissue iNOS expression in the major organs. To this end, mice were pre-treated with anti-IFN-gamma, anti-TNF-alpha, anti-IL-10 monoclonal ant ibodies, or combinations of these, two hours before intraperitoneal LPS-cha llenge. Immunohistochemical staining for iNOS and determination of iNOS act ivity indicated that iNOS expression was mainly upregulated in the small in testine, lung and heart, and that IFN-gamma, TNF-alpha as well as IL-10 are involved in the regulation of iNOS expression and enzyme activity. Whereas blocking either IFN-gamma or TNF-alpha did not affect iNOS expression, iNO S enzymatic activity seems to be inhibited. In contrast, blocking both medi ators nearly completely prevents iNOS expression after LPS challenge, sugge sting that the presence of either IFN-gamma or TNF-alpha is essential for L PS-induced iNOS expression in these organs. Combined treatment of these mon oclonal antibodies revealed that whereas on the one hand IL-10 inhibits LPS -induced iNOS expression, on the other hand IL-10 or an IL-10 inducible fac tor is also involved in the upregulation of iNOS expression after LPS chall enge.