Endotoxin and interferon-gamma inhibit the caspase-activity in neutrophilsthrough a tyrosine kinase dependent mechanism

Aim/Background: Reduced apoptosis of neutrophils (PMN) leads to an accumula tion of PMN during sepsis. Intracellular cysteine-proteases (caspases) are important for the regulation of PMN-apoptosis. The aim of this study was to investigate the activity and regulation of caspases in PMN during sepsis. Methods: Isolated PMN of 8 healthy volunteers and 8 patients with severe se psis were isolated by density gradient centrifugation and were incubated du ring 16 hrs with or without endotoxin (LPS, 1 mu g/ml), interferon-gamma (I FN-gamma, 10 ng/ml), or the tyrosine kinase inhibitor herbimycin (1 mu mol/ ml). PMN-apoptosis was measured by propidium iodide using flow cytometry. T he activity of caspases was analyzed by caspase 3-like protease activity-as say. Results: In parallel to reduced PMN-apoptosis (31.3 +/- 3.0 %) the caspase- activity in PMN from septic patients (564 +/- 88 pmol/min x mg) was signifi cantly decreased compared to the control group (caspase-activity: 1217 +/- 213 pmol/min x mg; apoptosis: 67.9 +/- 0.1%). LPS and IFN-gamma reduced (p < 0.05) the apoptotic rate of PMN as well as the caspase activity in both g roups. The effect by LPS and INF-gamma on PMN apoptosis and caspase-activit y could be antagonized by herbimycin. Conclusion: The regulation of caspase-activity in PMN by endotoxin and IFN- gamma depends on the tyrosine kinase pathway. The reduced activity of caspa ses in PMN seems to play an important role for prolonged lifespan of those cells during sepsis.