Dysfunction of lung epithelial cells - a key component of the alveolar-capillary barrier - is central to the development of acute lung injury (ARDS). Cytokines, such as interleukin-1 (IL-1), oxidative stress and FasL are increased in lungs of ARDS patients but their relationship to each other and ARDS is unknown. The sources of oxidative stress in ARDS patients are also unknown but aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR), which is increased in ARDS patients, are intracellular oxygen radical (O2*) generating enzymes whose regulation might be of benefit in ARDS. Our data shows that: 1. Leak and inflammation increased in lungs of rats given IL-1 intratracheally 5h before in vivo. 2. XOR expression, allopurinol-inhibitable 02* production, and apoptosis increased in epithelial cells in lungs of rats given IL-1 intratracheally 24h before in vivo. 3. Inhibition of lung XOR/AOX activity by tungsten feeding decreased epithelial cell apoptosis in lungs of rats given IL-1 intratracheally 24h before in vivo. 4. XOR/AOX expression and allopurinol-inhibitable 02* production, but not apoptosis, increased in lung epithelial cells treated with IL-1 24h before in vitro. 5. IL-1 and 02* increased lung epithelial cell Fas expression in vitro. 6. Lung lavage from rats given IL-1 intratracheally 24h before contained FasL and caused apoptosis of lung epithelial cells in vitro that had increased Fas levels following IL-1 treatment 24h before in vitro. 7. XOR and AOX gene expression was increased in lung epithelial cells treated with IL-1/IL-6 in vitro. Our specific hypothesis is that increased IL-1 increases XOR and/or AOX activity in lung epithelial cells increasing lung epithelial cell O2* production and Fas expression. Concomitant IL-1 dependent increases in lung inflammation increase lung FasL levels and produce epithelial cell apoptosis which contributes to lung injury CARDS). Our specific aims are to determine the mechanisms responsible for IL-1 induced lung epithelial cell XOR and/or AOX expression, 02* production and epithelial cell apoptosis in vivo (Aim 1) and in vitro (Aim 2) and to determine the effect of IL-1 on the regulation of XOR and/or AOX gene expression in lung epithelial cells in vitro (Aim 3). The significance of this approach will be to determine basic physiologic, cellular and molecular aspects regarding XOR and AOX, to gain insight into whether XOR and/or AOX contribute to ARDS, and to evaluate whether inhibiting XOR and/or AOX holds any potential for treating or preventing events that contribute to ARDS.