Characterization of osteoarthritis (OA) tenocytes by flow cytometry. (a) When compared with isotype control staining, analysis for the macrophage lineage marker CD68 showed no surface expression (<1%). (b) Also, no expression of the leucocyte common antigen CD45 was found on the cells (<0.1%). (c) However, fluorescence activated cell sorting analysis with the fibroblast marker AS02 showed positive staining of all the cells (>99%). (d) In addition, more than 99% of the tenocytes stained positive for the fibroblast markers D7-Fib. (e) Intracellular staining for prolyl-4-hydroxylase (>99%) confirmed the fibroblast-like nature of the tenocytes.