VWF string formation depends on integrin α_v expression. HUVECs were infected with control shRNA lentivirus (shLuc) or integrin α_v shRNA lentivirus (sh1129) and cultured for 2 weeks under selection with puromycin. (A) Fluorescence-activated cell sorter analysis was performed with control antibody on cells treated with shLuc (black trace) or with anti-integrin α_vβ₃ antibody LM609 on cells treated with shLuc (blue trace) or sh1129 (red trace). The level of integrin α_vβ₃ was reduced 70% in sh1129 cells. (B) Lentivirus-infected HUVECs were stimulated with histamine and exposed to fluid shear stress of 2.5 dyne/cm² (■) or 7.5 dyne/cm² (□). VWF strings were stained in situ with fluorescent anti-VWF antibody and counted. Values represent the mean plus or minus SEM from 10 fields per experiment. (C) Representative images are shown. Flow direction is from bottom left to top right. Bars represent 20 μm.