AS and IB3-1 cells were pretreated with parthenolide or vehicle (Placebo) for 1 h and then stimulated with IL-1β and/or TNFα for the indicated time. Total cells protein extracts were prepared then analyzed for phosphorylated MAPK pERK, MAPK pJNK and the MAPK pp38 in AS cells (A/B, C/D and E/F, respectively) and in IB3-1 cells (G/H, I/J and K/L respectively). Summary graph of data for phosphorylated MAPKs determined by image analysis of densitometry from autoradiograph. Data show mean ± SEM of scan area of MAPK ERK, JNK and p38 expression (n = 5 to 8 for each time point and condition) corrected for scan area of β-actin in the same gel lane. In both cell lines Parthenolide inhibited cytokine-induced phosphorylation of ERK, but stabilized the phosphorylation of JNK and p38. Solid bar, placebo; open bar, parthenolide-treated cells.