We obtained SFs from the human tumor necrosis factor–transgenic (hTNFtg) mouse model of RA and used interleukin (IL)-1 for the induction of intra-articular (IA) cartilage damage because it has been shown to initiate and mediate cartilage degradation in a mouse model of RA without affecting synovial inflammation [14–16]. This evidence concerns the gene IL1B and rheumatoid arthritis.