FIGURE 4.
Activation of NF-κB is required for K. pneumoniae ompA mutant-induced IL-8 expression. A, activation of a NF-κB luciferase reporter plasmid in A549 cells left untreated (CON) or infected for 8 h with K. pneumoniae strains. Activity is normalized by correction of Renilla expression and is presented relative to the cells untreated (n = 3). *, p < 0.05 (for the indicated comparisons; one-way ANOVA). B, immunoblot analysis showing phospho-p65 and tubulin levels in lysates of A549 infected with K. pneumoniae strains for 90 min IL-1β (20 ng/ml for 30 min) was used as a positive control for NF-κB activation. The results are representative of three independent experiments. C, immunoblots of IκBα and tubulin levels in lysates of A549 cells left untreated (CON; time 0) or infected for different time periods with K. pneumoniae strains. Data are representative of three independent experiments. D, ELISA of IL-8 released by A549 cells left untreated (CON; white bar) or infected for 6 h with 52OmpA2 (gray bars) or 52145-ΔwcaK2ompA (black bars) in the absence or presence of different concentrations of CAPE, an inhibitor of NF-κB, which was added 1 h before infecting the cells and kept until the end of the experiment (n = 3). The data (A and C) are means and S.E. (error bars).