Thrombospondin-1 (TSP1 or THBS1) is increased by chondroitin sulfate. Overexpression values of thrombospondin-1(TSP1) were determined by (A) real-time PCR and (B) western blot (WB) analysis of both IL-1β-stimulated and unstimulated human articular chondrocytes, and by (C) immunohistochemical analysis of cartilage shavings as described in Materials and methods. Each condition was tested in duplicate. Results are expressed as the mean ± standard error of the mean of three independent experiments. Representative images of western blot and immunohistochemical assays are shown. *P < 0.05, CS-treated group was significantly different from IL-1β-stimulated group. CS, chondroitin sulfate; CTL, control.