Escherichia coli hemolysin is a potent inductor of phosphoinositide hydrolysis and related metabolic responses in human neutrophils.

Escherichia coli hemolysin (Hly) is a proteinaceous pore-form- ing exotoxin that probably represents a significant virulence factor in E. coli infections.We investigated its influence on human polymorphonuclear neutrophils (PMN), previously identified as highly susceptible targets.Hly provoked rapid secretion of elastase and myeloperoxidase, generation of super- oxide, and synthesis of platelet-activating factor (PAF) and lyso-PAF.Concomitantly, marked phosphatidylinositol (Ptdlns) hydrolysis with sequential appearance of the inositol- phosphates, inositol triphosphate, diphosphate, and monophos- phate, respectively, and formation of diacylglycerol, occurred.The metabolic responses displayed distinct bell-shaped dose dependencies, with maximum events noted at low toxin concen- trations of 0.1-0.5 hemolytic units per milliliter.Ptdlns hydro- lysis and metabolic responses elicited by Hly exceeded those evoked by optimal concentrations of formylmethionyl-leucyl phenylalanine, PAF, leukotriene B4, A23187, or staphylococ- cal a-toxin.The toxin-induced effects were sensitive toward modulators of PMN stimulus transmission pathways (pertus- sis toxin, the kinase C inhibitor H7, and phorbol myristate acetate "priming").We conclude that the marked capacity of low doses of Hly to elicit degranulation, respiratory burst, and lipid mediator generation in human PMN probably envolves signal transduction via PtdIns hydrolysis.(J.Clin.Invest.1991.88:1531-1539.)Key words: Escherichia coli hemolysin- neutrophil activation * phosphoinositide FMLP, PAF, LTB4, and A23187, Hly emerged as the most potent inductor of PtdIns hydrolysis hitherto described. MethodsMaterials.FMLP, 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (PAF), superoxide dismutase, cytochrome c type IV, diethylene- triaminepentaacetic acid, Hepes, phorbol myristate acetate (PMA), and phospholipids were obtained from Sigma Chemical Co.(Deisen- hofen, FRG); octyl-O-D-glucoside from Behring Diagnostics (Frank- furt, FRG).LT B4 was purchased from Paesel AG (Frankfurt, FRG), purified by high-pressure liquid chromatography (HPLC), and quanti- fied before use as described (33, 34).The PAF receptor antagonist Escherichia coli Hemolysin, NeutrophilActivation, and Phosphoinositide Turnover 1531