Figure 1: Human adult synovial fibroblasts (Asterand plc, Detroit, MI, USA) and BMSCs (Lonza Group Ltd., Switzerland) were characterized for their multi-lineage differentiation capacities. Human synovial fibroblasts were positively stained for alkaline phosphatase (ALP), adipose drops [Oil Red O (ORO) staining], GAG (Alcian blue staining) and collagen II (immunostaining), indicating they are hSDSCs. After incubation in osteogenic medium for two weeks, hBMSCs were intensively stained with calcium matrix [stained by Alizarin Red S (ARS)] and ALP, indicating that, compared to hSDSCs, hBMSCs are tissue-specific stem cells for osteogenesis. There was nondetectable ARS staining and comparable ALP staining in hSDSCs, suggesting that there was less osteogenic potential for the hSDSC group. After incubation in chondrogenic medium for two weeks, hSDSCs exhibited intensive staining of GAG and collagen II compared to hBMSCs, suggesting that hSDSCs had more chondrogenic differentiation capacity than hBMSCs. The scale bar is 800 Ám.