TNF-induced functional caspase-1 in rheumatoid arthritis (RA) synovial fibroblasts. RA synovial fibroblasts (2 × 105/well plates; 2 ml/well) were stimulated with TNF in serum-free media for 0 to 48 hours. Caspase-1 expression was assessed at the protein level in cell lysates. Bands shown are specific for active caspase-1. Bars show the mean and standard error of the mean (SEM) from at least six independent experiments using different donors (A). RA synovial fibroblasts (2 × 105/well in 6-well plates; 2 ml/well) were stimulated in RPMI with 10% FBS for 72 hours. IL-18 was detected by western blotting in 10-times concentrated conditioned media. A representative blot of three independent experiments using different donors is shown (B). RA synovial fibroblasts (2 × 105/well in 6-well plates; 2 ml/well) were treated with TNF (20 ng/ml) for 8, 24, and 48 hours in RPMI with 10% FBS. IL-18 protein induction was assessed by ELISA in concentrated conditioned media (C) and cell lysates (D). Results are expressed as the mean of fold induction with SEM. *P < 0.05 versus non stimulated (NS).