ENDOTOXIN INFUSION IN ANESTHETIZED SHEEP IS ASSOCIATED WITH INTRAPULMONARY SEQUESTRATION OF LEUKOCYTES THAT IMMUNOHISTOCHEMICALLY EXPRESS TUMOR-NECROSIS-FACTOR-ALPHA

Plasma levels of tumor necrosis factor-alpha (TNF-alpha) peak between 2 and 4 h during a 12-h continuous infusion of endotoxin in awake shee p. We hypothesized that a source of this TNF-alpha is the pool of leuk ocytes that accumulate in the pulmonary circulation, To test this hypo thesis, we physiologically monitored six anesthetized sheep during bas eline and 4-h endotoxin infusion periods (10 ng/kg x min), We obtained open-lung biopsies at baseline and at 20 min and 2 and 4 h during the endotoxin infusion period for immunohistochemical localization of TNF -alpha. The plasma concentration of TNF-alpha increased from an averag e baseline concentration of 0.06 +/- 0.03 ng/ml (mean +/- SD) to a pea k of 1.40 +/- 0.28 ng/ml at 2 h of the endotoxin infusion, We observed increased cytoplasmic TNF-alpha immunoreactivity in situ among neutro phils and intravascular mononuclear phagocytes during the endotoxin in fusion compared with baseline. Also, the number of immunopositive leuk ocytes increased in the pulmonary circulation during the continuous in fusion of endotoxin, We conclude that TNF-alpha-producing leukocytes a ccumulate in the pulmonary circulation during endotoxemia, These cells probably contribute to both the rise in the circulating levels of TNF -alpha and the development of acute lung injury.