LPS induces bioactive IL-1β in primary monocytes. (A) Human PBMCs, purified CD14⁺ monocytes, or the CD14⁻ lymphocytes were incubated with 10 ng/mL LPS, and the IL-1β concentrations were measured in the supernatant by specific ELISA after 24-hour incubation. (B) CD14⁺ monocytes were stimulated with various stimuli for the induction of IL-1β. (C) Human PBMCs were incubated with 10 ng/mL LPS and the levels of mature and precursor IL-1β or were measured in the supernatant by specific ELISA after 24-hour incubation. (Inset) Western blot of IL-1β and pro-IL-1β the supernatant derived from PBMCs stimulated with LPS (100 ng/mL) or MDP (10 μg/mL). (D) Dose-response of caspase-1 inhibitor ZVAD-fmk on the 24-hour levels of LPS-induced IL-1β from PBMCs. (E,F) The inhibitory effects of the caspase-1 inhibitor (20 μM) and of IL-1Ra (10 μg/mL) on the induction of IL-6 (E) and intracellular IL-1α measured in cell lysates (F) by 10 ng/mL LPS. Data from all 4 panels are presented as mean plus or minus SEM of cells harvested from 6 volunteers. *P < .05 compared with LPS stimulation alone.