ADAMTS13 is sorted apically in ECV304 and MDCK cells. ADAMTS13 proteases secreted into the apical (AP) and basolateral (BL) domains of untransfected ECV304 (A), stably transfected ECV304 (B), and stably transfected MDCK (C) cells with pcDNA3.1-ADAMTS13-V5-His that were grown on 6-well Transwell filter units (D) were determined by Western blotting with rabbit anti–ADAMTS13 IgG (2 μg/mL) or mouse anti–V5 IgG (2 μg/mL) and SuperSignal ECL reagents. The relative amount of ADAMTS13 in the apical and basolateral domains was determined by densitometry with NIH ImageJ software. The entries represent means ± SD from 3 independent experiments.