Interleukin (IL)-1β is the major factor underlying peripheral blood-macrophage-conditioned medium (PB-MCM)-induced urokinase-type PA (uPA) expression in chondrocytes. RNA samples were then isolated and subjected to real-time PCR analysis. The mRNA data are presented as the fold changes in fluorescent intensities compared with control (CL) chondrocytes normalized to the 18S rRNA levels. (A) Chondrocytes were untreated (CL) or stimulated with PB-MCM for 2 hours. Before culturing under control conditions (CL) or stimulation with PB-MCM, the PB-MCM and chondrocytes were preincubated with PBS, IL-1ra, isotype-matched IgG, or neutralizing antibody against TNF-α (TNF Ab) individually for 2 hours. *P < 0.05 versus CL. #P < 0.05 versus PBS, IgG-, or TNF Ab-treated cells under PB-MCM stimulation. (B) Chondrocytes cultured as unstimulated CL, or stimulated with different doses of IL-1b or TNF-a for 2 hours. *P < 0.01 versus CL.