The production of bioactive IL-1β in vivo. The level of mature IL-1β in peritoneal cavity of WT C57BL/6, caspase-1-deficient, cathepsin C-deficient, caspase-1 and cathepsin C double-deficient mice after 4 hours i.p. injection of 0.5 mg of silica crystal. Functional IL-1β activities were measured using MRC-5 fibroblast bioassay, which the MRC-5 fibroblasts produce IL-8 in response to IL-1. The data are combined results of 3 experiments and represented as means ± SEM (n = total number of mice from the multiple experiments for each group). *P<0.05, NS, not significant versus WT groups using ANOVA with Dunnett's multiple comparison tests. Bkg, background level in IL-1β deficient mice.