Matrilin-3 MATN3) enhances IL-1Ra expression by chondrocytes. Recombinant human (rh) MATN3 protein enhances the gene expression of IL-1Ra in a dose-dependent manner at 12 hours post cell culture treatment as seen here in C28/I2 cells (A). Recombinant MATN3 also enhances IL-1Ra expression in primary mouse chondrocytes after 24 hours of treatment (B). MATN3-induced IL-1Ra gene expression is evident in primary human chondrocytes (PHCs) at 24 hours post treatment in both the presence and absence of IL-1β (C). PHCs treated with both MATN3 and IL-1β for 24 hours exhibit significantly higher concentrations of IL-1Ra protein in their cell media, relative to the media of cells treated with IL-1β alone (D). In these experiments, rh MATN3 protein is used at one of two concentrations: lower dose (+) of 100 ng/ml, or higher dose (++) of 200 ng/ml. Rh IL-1β protein treatment is always 5.0 ng/ml. *Significant differences (P ≤ 0.05) from the untreated control group; #significant differences (P ≤ 0.05) from the IL-1β only treated group. Data are representative of three individual experiments.