IL-1β is activated by the P. aeruginosa LasB protease. (a) Relative IL-1 signalling by caspase-1/11−/− BMM 2 h post-infection by PAO1 that were previously incubated 1 h with the indicated protease inhibitors classes (Aspartyl, Pepstatin; Cysteine, E64; Metallo, Phosphoramidon; Serine, PMSF; Tryptic, Benzamidine). (b) Visualisation of bacterial proteolytic activity by decreased media opacity on LB agarose plates containing casein. (c) Relative IL-1 signalling by caspase-1/11−/− BMM 2 h post-infection with isogenic mutant strains of PAO1. (d) Relative IL-1 signalling by caspase-1/11−/− BMM 2 h post-infection by PAO1, ΔlasB, or plasmid-complemented ΔlasB. (e) il1a and il1b expression by real-time quantitative PCR and (f) secretion by ELISA. Error bars show mean ± s.d, n = 4, and represent at least 3 independent experiments. Statistical analysis by ANOVA with Tukey post-test, *P < 0.05, **P < 0.005, ***P < 0.0005.