Figure 4 Significant human cartilage collagen release and increased MMP‐1 and MMP‐13 levels are induced by TNFα (in combination with OSM). HNC was stimulated with TNFα (10 ng/ml) and/or OSM (10 or 50 ng/ml) in serum‐free medium for 21 days, with serum‐free medium only as control. Day 7 and 14 media were collected and replaced with identical test reagents. Collagen release and MMP‐1, MMP‐13, and TIMP‐1 levels were assayed as described in “Materials and methods”. (A) Cumulative collagen release by day 21 is expressed as a percentage of the total. (Bi) Cumulative MMP‐1 levels released by day 21. (Bii) Correlation between cumulative MMP‐1 and cumulative collagen release by day 21. (Ci) Cumulative MMP‐13 levels released by day 21. (Cii) Correlation between cumulative MMP‐13 and cumulative collagen release by day 21. (D) Cumulative TIMP‐1 levels released by day 21. Each bar is the mean (SD) for 4–6 explant cultures for each treatment. The response shown is reproducible and representative of experiments performed with explants from two patients. **p<0.01, ***p<0.001. rs = Spearman's rank correlation coefficient.