Figure 4.

Effect of IL-15 on GAG release and tissue GAG content in vitro. (A) Cartilage explants (n = 7 experiments) were exposed to 100 ng/ml rhIL-15 (blue squares) or left unstimulated (control black circles) as described. Exposure to TNFα and Oncostatin M (TNF-OSM, 100 ng/ml each, red triangles) served as a positive control for proteoglycan release. The cumulative GAG content of the media collected every 2 days for up to 10 days is depicted over 10 days in culture. IL-15 had no significant effect on GAG loss from explants compared to unstimulated control cultures. (B) GAG content of cartilage explants (n = 3 separate experiments) collected at day 0 (fresh) and after 14 days of culture was measured as described. IL-15 had no effect on cartilage tissue GAG content after 14 days compared to control unstimulated explants. TNF/OSM led to net loss (p = ns) of cartilage GAG content as expected. (C) The total GAG content of the culture system (explants + media aliquots) after 14 days in vitro was calculated to evaluate GAG synthesis and subsequent release. Total GAG content was increased at 14 days compared to baseline in unstimulated controls, indicating a net synthesis of GAGs in the explants. This was not further impacted by exposure to IL-15. *p < 0.05 compared to day 14 unstimulated explants.