TGF-β1 levels are reduced in serum and chondrocytes of Spon1^−/− mice.

Total (latent + active) TGF-β1 levels in protein extracts isolated from (A) serum (n = 14-16) or (B) indicated organs (n = 4–5) of 6 month old WT and Spon1^−/− mice. TGF-β1 was measured by ELISA. (C) Total and active TGF-β levels in conditioned media of rib chondrocyte cultures (n = 4) isolated from costal cartilage of 5 day old WT, HET and KO littermates. Total TGF-β levels were determined by ELISA, active TGF-β levels were measured using MLEC bioassays. Corresponding Spon1 mRNA levels, determined by QPCR, are shown for each group (WT = 100%). Statistically significant differences in total TGF-β level to WT group are indicated by *(P<0.05). Statistically significant difference in active TGF-β level to WT group is indicated by # (P<0.05).