Cell differentiation studies with CD166+-enriched and -depleted chondrocytes. Isolated osteoarthritis chondrocytes were immunomagnetically enriched (a,c,e) or depleted (b,d,f) for CD166+ cells and subjected to adipogenic, osteogenic, and chondrogenic differentiation. CD166+-enriched as well as CD166+-depleted cell populations differentiate to adipocytes after culture in adipogenic medium, as detected by oil red O staining (a,b). After cultivation with osteogenic medium, both cell populations demonstrate differentiation toward osteoblasts observable as positive alkaline phosphatase activity within the cells (c,d). However, this effect is more pronounced in cells previously enriched for CD166+ chondrocytes (c). Pellet cultures of cells that underwent chondrogenic differentiation are visualized by Alcian blue staining of newly deposited proteoglycans (e,f). Exclusively, the population with CD166+-enriched cells shows a clear chondrogenic phenotype (e).