Induction of urokinase-type PA (uPA) in chondrocytes by peripheral blood-macrophage-conditioned medium (PB-MCM) stimulation. Chondrocytes were maintained as controls (CL) or stimulated with PB-MCM. Data are the mean ± SEM. *P < 0.05 versus CL chondrocytes. (A) The dose-dependent induction of uPA mRNA expression by PB-MCM. Human chondrocytes were grown as CL or were stimulated with different concentrations of PB-MCM for 2 hours. (B) RNA samples were isolated from human chondrocytes at the indicated times and subjected to real-time PCR analysis. The mRNA data are presented as the fold changes in fluorescent density from CL cells normalized to the 18S rRNA levels. (C) uPA protein secretion in chondrocytes was determined by sandwich ELISA.