Mediator generation and signaling events in alveolar epithelial cells attacked byS. aureusα-toxin

Staphylococcus aureus α-toxin is a pore-forming bacterial exotoxin that has been implicated as a significant virulence factor in human staphylococcal diseases. In primary cultures of rat pneumocyte type II cells and the human A549 alveolar epithelial cell line, purified α-toxin provoked rapid-onset phosphatidylinositol (PtdIns) hydrolysis as well as liberation of nitric oxide and the prostanoids PGE2, PGI2, and thromboxane A2. In addition, sustained upregulation of proinflammatory interleukin (IL)-8 mRNA expression and protein secretion occurred. “Priming” with low-dose IL-1β markedly enhanced the IL-8 response to α-toxin, which was then accompanied by IL-6 appearance. The cytokine response was blocked by the intracellular Ca2+-chelating reagent 1,2-bis(2-aminophenoxy)-ethane- N,N,N′ ,N′-tetraacetic acid, the protein kinase C inhibitor bis-indolyl maleimide I, as well as two independent inhibitors of nuclear factor-κB activation, pyrrolidine dithiocarbamate and caffeic acid phenethyl ester. We conclude that alveolar epithelial cells are highly reactive target cells of staphylococcal α-toxin. α-Toxin pore-associated transmembrane Ca2+flux and PtdIns hydrolysis-related signaling with downstream activation of protein kinase C and nuclear translocation of nuclear factor-κB are suggested to represent important underlying mechanisms. Such reactivity of the alveolar epithelial cells may be relevant for pathogenic sequelae in staphylococcal lung disease.