Platelets are required for the formation of NETs under flow in whole-blood samples of acute iTTP. (A-B) Representative images illustrate adhered neutrophils and platelets on a collagen-coated surface following perfusion of a whole blood sample from patients with iTTP on admission and after therapy, respectively, with or without DNase I (200 IU/mL) as indicated. (C-D) The rate of thrombus formation as a function of time (mean ± SEM, n = 6) following perfusion of iTTP blood samples collected on admission and after therapy, respectively, with or without DNase I (200 IU/mL) as indicated. (E-F) Final platelets, leukocytes, and DNA strings on a collagen surface following perfusion, fixation, and restained with anti-CD41 APC and SytoxGreen with or without DNase I as indicated. (Ei-Fi) Enlarged (5×) areas of the bottom images in E and F, respectively, indicate the extracellular DNA strings, platelets (PLT), and neutrophils (N). (G-H) The number of DNA strings formed on a collagen surface following perfusion of blood samples collected from patients with iTTP on admission and during remission, respectively, with or without DNase I. Data are shown as median (bar) and IQR. Mann-Whitney test was used to determine differences. N, neutrophil; PLT, platelet; n.s. and ∗∗ indicate P > .05 and P < .01, respectively.