Plasmid ADAMTS13 containing human full-length cDNA sequence was generously provided by Dr. Jingfei Dong (Baylor College of Medicine, Houston, TX, USA) [24] . Recombinant ADAMTS13 (rADAMTS13) with the C-terminal His-tag was expressed in a stably transfected HeLa cell line. Expression medium was concentrated and purified using a Ni-NTA agarose column (QIAGEN GmbH, Hilden, Germany).