L. pneumophila -induced IL-8 mRNA expression in epithelial cells. (A) L. pneumophila infection increases IL-8 mRNA expression in A549 cells in a dose-dependent manner. A549 cells were infected with varying concentrations of AA100jm, and the levels of IL-8 mRNA expression were examined by RT-PCR in cells harvested after 8 h. (B) Effect of heat-treatment of L. pneumophila on the ability to induce IL-8 mRNA expression. Expression of IL-8 mRNA in A549 and NCI-H292 cells treated with heat-killed AA100jm was observed at 6 and 24 h after infection. A549 and NCI-H292 cells were infected with the untreated AA100jm at an MOI of 100. β-actin expression served as controls. Representative results of three similar experiments in each panel are shown.