Immunohistochemical staining of normal and osteoarthritis (OA) chondrocytes after isolation and initial adherence. Representative images of an OA chondrocyte sample are shown in (a-d); staining results for normal chondrocytes were identical (not shown). Nuclei were visualized with DAPI (4',6-diamidino-2-phenylindole) (a). Cell membranes were double-stained for CD105 by using an Alexa Fluor 488-coupled secondary antibody and for CD166 by using an Alexa Fluor 594-coupled secondary antibody and analyzed by fluorescence microscopy. Co-expression of CD105 and CD166 was identified after computed superimposition of fluorescence signals from both channels. Almost all cells are CD105+ (b), whereas only a few cells express CD166 (c); but in all cases, this is accompanied by the co-expression of CD105 (d). In addition, the results of the quantitative analysis of normal (e) and OA (f) chondrocytes are shown. Magnifications: 100 ×, 400 × (insets). SEM, standard error of the mean.