Flow cytometric characterization of SP cells. (A) Bovine synovial cells were stained with Hoechst 33342, and excited by a UV laser. Populations including SP cells were determined by live/dead evaluation using PI, single/doublet cells evaluation using FSC-A/SSC-A and microscopic evaluation (B). SP patterns were visible after Hoechst 33342 staining in population 3 (P3). P1 and P2 consisted of small, non-adherent cells.