Side population in normal cartilage. (a) FACS image of the gated side population (SP) and non-SP (NSP) cells isolated via cell sorting. (b) Expression level of ABCG2 in SP and NSP cells. The three-fold higher expression of ABCG2 indicates successful isolation of the cartilage SP.
Grogan et al. Arthritis Research & Therapy 2009 11:R85 doi:10.1186/ar2719