We have shown that platelet-activating factor (PAF) primes neutrophil (PMN) responses and enhances their ability to damage endothelial cells. Furthermore, thrombin-stimulated endothelial cells which produce PAF can augment and prime PMN superoxide production, elastase release and adhesion to endothelium. We wondered whether these marginated neutrophils (PMN) themselved, or their release products, might feedback and further amplify endothelial cell activation. To measure cellular activation, we assessed changes in endothelial cell intracellular celcium ([Ca2+]i) in endothelial monolayers loaded with Fura-2, and PAF production by [3H] acetate incorporation into phospholipid. Resting PMNs induced no change in [Ca2+]i, while N-formyl-L-methionine-L-luceyl-L-phenylalan ine stimulated PMN and their lysosomal products caused a 25% increase in endothelial cell calcium. Sonicates of PMN produced a much larger increase in [Ca2+]i than activated PMN; the effect of PMN sonicates could in part be reduced by the serine protease inhibitor, α1 antitrypsin. In contrast, purified neutrophil elastase did not alter endothelial cell [Ca2+]i. Despite hydrogen peroxide's ability to increase [Ca2+]i, catalase failed to inhibit the PMN-induced rise in [Ca2+]i. Since polyanionic heparin inhibited the PMN sonicate rise in calcium, a cationic protein released by PMN was thought to be responsible. The cationic primary granule enzyme, cathepsin G, duplicates the rise in [Ca2+]i seen with PMN sonicates. Furthermore, PAF production increased threefold in response to neutrophil sonicates. Thus, during inflammation, when coagulation and inflammatory cells are activated the endothelium responds by priming PMNs and promoting margination. This priming may be a physiological response to contain infection, but in certain clinical states (such as septic shock) this amplification of the inflammatory response might lead to capillary leak due to perturbation of endothelial cell integrity.
|Original language||English (US)|
|Journal||Journal of Lipid Mediators|
|State||Published - Jan 1 1990|