BACKGROUND: In sepsis, activation of inflammatory cells and excessive production of proinflammatory cytokines leads to tissue injury, multiple organ failure, and death. We postulated that attenuation but not complete abrogation of hyperinflammation is of clinical benefit in sepsis. Because pentoxifylline (PTX) is known to decrease tumor necrosis factor (TNF)-alpha production and to increase anti-inflammatory cytokine synthesis, we tested the hypothesis that PTX treatment would change the pro- and anti-inflammatory balance and decrease mortality in a murine model of acute endotoxemia. In addition, we investigated the effects of PTX on nuclear factor (NK)-kappaB activation using lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (PBMCs) as a model. METHODS: Sprague-Dawley rats were treated with intravenous saline (sham), LPS (lipopolysaccharide, Escherichia coli serotype 0111:B4, 5 mg/kg), and concomitant injection of LPS + PTX (25 mg/kg). Four- and 24-hour plasma TNF-alpha and interleukin (IL)-10 levels, 4-hour white cell count, and 24-hour mortality rates were assessed. The IL-10/TNF-alpha ratio was also calculated. Human PBMCs were stimulated with LPS (10 microg/mL) and exposed to PTX (20 mM) concomitantly or 15 minutes after LPS stimulation. I-kappaB phosphorylation by Western blot and NF-kappaB nuclear translocation by electrophoretic mobility shift assay were assessed. RESULTS: PTX markedly down-regulates TNF-alpha production. IL-10 levels at 4 hours were up-regulated in both LPS and PTX + LPS-treated animals; however, levels were higher in the LPS groups, which paralleled high TNF-alpha levels. In contrast, IL-10 levels at 4 and 24 hours in PTX + LPS-treated animals remained constant, whereas in LPS-treated animals, IL-10 levels at 24 hours were markedly decreased. A shift in the internal milieu balance toward anti-inflammatory activity was confirmed by the calculation of the IL-10/TNF-alpha ratio. These changes were not related to changes in the number of circulating leukocytes. The 24-hour mortality rate was 50% in the LPS group and nil in PTX-treated animals. In LPS-stimulated PBMCs, PTX markedly decreases I-kappaB phosphorylation and NF-kappaB nuclear translocation. CONCLUSION: PTX enhances anti-inflammatory activity and decreases mortality in acute endotoxemia. PTX may be an important adjunct to therapies aiming to modulate the inflammatory response in sepsis.