VWF string formation on exocytosis of WPB. BOECs derived from a healthy donor (A) or from the patients heterozygous for a VWF mutation (B-F) were stimulated for 60 minutes with 100 μM histamine at 37°C. Cells were fixed and stained for VWF to visualize the VWF string-like structures (arrowheads). (Scale bars, 20 μm.) All images were taken by Leica SL confocal laser scanning microscopy with a 63×/1.40 NA oil objective.