TNF and rheumatoid arthritis: Since IL-1β signaling is reported to act both independently or downstream of TNF in RA and SFs (Brennan et al., 1989; Probert et al., 1995; van den Berg et al., 1999; Feldmann, 2002; Zwerina et al., 2007), we treated WT SFs with anakinra (an IL-1 receptor antagonist) and then stimulated them with TNF.