Microscopic images and corresponding FACS analysis of chondrocytes before and after immunomagnetic separation. After incubation with bead-coupled antibodies to the surface antigen CD166, both membrane-bound and free magnetic anti-CD166 particles are visible, as are non-labeled chondrocytes (a1). In the positive fraction after separation, only magnetobead-covered CD166+ cells and free magnetobeads are present (b1). In the negative fraction, only CD166- cells without magnetobeads are present; also, no free magnetobeads are present (c1). These results were confirmed by FACS analysis, demonstrating an enrichment of CD166+ cells from 10% before (a2) to approximately 87% after (b2) separation, whereas the negative fraction contained only a very low percentage of CD166+ cells (c2). FACS, fluorescence-activated cell sorting; FITC, fluorescein isothiocyanate.