CD34 and rheumatoid arthritis: While clusters and neo-vessels expressed CD34 (Figures 3B,F) and c-kit (Figures 3C,F), the mesenchymal stem cell marker STRO-1 was detected alongside newly forming vessel sprouts in a predominantly dotty staining pattern (Figures 3D,F), consistent with the perivascular STRO-1 deposition found previously in RA and OA synovial tissue (Rüger et al., 2004; Giurea et al., 2006).