Cleavage of HUVEC-anchored VWF strings by HUVEC-released ADAMTS13. HUVECs were stimulated for 2 minutes with 100μM histamine, washed, and incubated statically for 0 to 2 minutes (A-B), 5 minutes (C-D), or 10 to 15 minutes (E-F) in Ca²⁺/Zn²⁺-containing buffer. The cells were fixed and stained with rabbit anti–VWF plus goat anti–rabbit IgG-488 and DAPI. The lengths of VWF strings were measured from microscope fields (201 μm × 150 μm; ×200) after each incubation time (n = 10), and were categorized as follows: lengths > 150 μm; 101 to 150 μm; 51 to 100 μm; 21 to 50 μm; and <20 μm. Representative images and graphs (means ± SD) are shown for each time interval. The arrows on panels C and E indicate cleaved VWF strings. The panels demonstrate that endogenous ADAMTS-13 released from HUVECs progressively cleaved VWF strings anchored to the same and/or nearby cells into smaller forms.