p38 MAPK activity regulates cell death induced by anti-CD95. (a) Total cell death rate for OA chondrocytes quantified by trypan blue exclusion assay after treatment of cells as indicated below. *P < 0.05 versus control. The graph shows the average of three independent experiments. (b) Apoptosis rate of OA chondrocytes quantified by flow cytometry. Chondrocytes were fluorescently labeled by TUNEL assay after treatment of cells as indicated below. The data shown are representative of three OA cartilage samples. Anti-CD95: treatment with a mAb anti-Fas CH 11 (100 ng/ml) in serum-free medium for 17 hours. SB: treatment with SB203580 (10 μmol/l) for 17 hours. SB+Anti-CD95: treatment with SB203580 for 2 hours followed by anti-Fas treatment for 17 hours. Control: cells were treated with DMSO only. (c) Chondrocytes were labeled with Hoechst after treatment of cells as indicated above. Nuclear condensation (indicated by an arrow) was detected in the cells treated with Anti-CD95. DMSO, dimethyl sulfoxide; mAb, monoclonal antibody; MAPK, mitogen-activated protein kinase; OA, osteoarthritis; PI, propidium iodide; TUNEL, terminal dUTP nick-end labeling.