Integrin α_vβ₃ is important for VWF string adhesion. (A) Confluent HUVECs in a flow chamber were perfused at a shear stress of 2.5 dyne/cm² using medium 199 supplemented with 100 μM histamine, 2% BSA, and the indicated concentration of fibronectin CS-1 peptide or RGDS peptide, and the number of VWF strings formed was quantified by immunofluorescence microscopy. (B) Perfusion assays were performed similarly with the indicated concentrations of mouse IgG (mIgG) or anti-integrin α_vβ₃ antibody LM609, which blocks ligand binding. (C) Perfusion assays were performed similarly without (Ctrl) or with 10 μg/mL anti-integrin α_vβ₃ antibody LM609 or function blocking anti-integrin α5 antibody CBL497. (D) Perfusion assays were conducted without (Ctrl) or with 10 μg/mL anti-integrin α_vβ₃ antibody LM609 (which blocks ligand binding) or LM142 (which does not block ligand binding). (E,F) Cells were perfused with Ca²⁺- and Mg²⁺-free DPBS (E) without (No Agonist) or with 100 μM histamine in the absence (Ctrl) or presence of RGDS peptide (40 μg/mL), or (F) without (Ctrl) or with anti-integrin α_vβ₃ antibody LM609 (10 μg/mL), and total VWF strings (■) and platelet-decorated VWF strings (□) were quantitated. Results are shown as the mean plus or minus SEM from 10 fields per experiment. Each experiment was performed 3 times.