Binding of CXCL12 peptides to HSPG on RA ECs. Rheumatoid arthritis endothelial cells (RA ECs) were incubated with 300 nM biotinylated CXCL12α and, after extensive washing to remove free chemokine, were labeled with fluorescein isothiocyanate-conjugated avidin. Where indicated, RA ECs were simultaneously incubated with soluble sodium heparin (a) or pretreated with heparitinases (b, c) or sodium chlorate (d). In (b), surface heparan sulfate proteoglycan (HSPG) was detected with 10E4 mAb in RA ECs pretreated or not with heparitinases. (e) RA ECs were incubated with 1 μM non-biotinylated wild-type CXCL12α or 2/6 CXCL12α and labelled with K15C mAb. Filled histograms show isotype control IgG. Results are representative of three to five independent experiments with RA ECs from three different donors. (f) Summary of normalized mean fluorescence intensity (MFI) data. Error bars show SD. *p < 0.05.