ADAMTS13 and thrombotic thrombocytopenic purpura: The microvessels were stimulated in the absence or presence of recombinant ADAMTS13 at a concentration of 1 μg ml−1 (a physiologic enzyme concentration, Fig. 4a and Supplementary Fig. 4), or in the presence of normal human plasma (Fig. 6a) or plasma from a TTP patient with <5% ADAMTS13 activity (Fig. 6b).