Production of prostaglandin E2 (PGE2) (a), 6-keto-PGF1α (b), and thromboxane (TX)B2 (c) in cytokine-stimulated chondrocytes. Chondrocytes from osteoarthritis patients were incubated for 24 h with interleukin-1β (IL-1β; 0.01–10 ng/ml, filled circles) or tumor necrosis factor-α (0.01–10 ng/ml, open circles). After being washed, the cells were incubated for a further 30 min with 3 μM arachidonic acid; the PGE2, 6-keto-PGF1α (a stable metabolite of PGI2), and TXB2 (a stable metabolite of TXA2) concentrations in the medium were then measured by enzyme-linked immunosorbent assay. Data are means ± SD for triplicate cultures, and representative results from three patients are shown. *P < 0.01 compared with untreated control cells.