Binding of CXCL12 to synovial osteoarthritis (OA) and rheumatoid arthritis (RA) ECs and cytokine-treated HUVECs. Endothelial cells (ECs) were incubated with 300 nM biotinylated CXCL12α and, after extensive washing to remove free chemokine, were labeled with fluorescein isothiocyanate-conjugated avidin. Human umbilical-vein endothelial cells (HUVECs) were treated with tumor necrosis factor-α (TNF-α; top) or lymphotoxin α1β2 (LT-αβ; middle) for 16 hours before CXCL12α binding as indicated. Filled histograms show isotype control IgG. The bottom panel shows a summary of normalized mean fluorescence intensity (MFI) data. Error bars show SD. Results are representative of three to five independent experiments in three RA EC, four OA EC and three HUVEC lines. *p < 0.05 compared with HUVECs, **p < 0.05 compared with cytokine-untreated HUVECs.