Effect of IgG from a patient with TTP on VWF-mediated and activation-independent platelet thrombus formation under flow. Whole blood containing 93 μM PPACK as anticoagulant and 10 μM PG E₁ to inhibit platelet activation was supplemented with 2 mg/mL IgG purified from the plasma of a healthy individual (control IgG) or 2 mg/mL IgG purified from the plasma of a patient with function-blocking antibodies against ADAMTS13 (patient IgG) and then perfused over immobilized VWF. The images shown are single frames from a real-time recording. The timeline (black horizontal bar) shows at what moment during the experiment a given image was taken as well as the wall shear rate during different periods of perfusion, as explained in the Figure 1 legend (A, 120 seconds, 13 000 s^-1; B, 540 seconds, 13 000 s^-1). The bar graph shows the average count, length, and area of all the platelet aggregates present in a field of view after 2 and 9 minutes of perfusion in the presence of control or patient IgG, as indicated.