To examine the interactions of autologous leukocytes with activated platelets at arterial flow conditions, we perfused blood from control subjects and 3 unrelated patients with Glanzmann thrombasthenia (lacking platelet integrin αIIbβ3) at a wall shear rate of 1000 s−1 over a collagen surface, using a previously described microfluidics setup.31 Representative bright-field and fluorescence microscopic images after 4 minutes of flow with control blood showed the presence of large thrombi, with aggregated platelets showing high fibrinogen binding and CD62P expression (Figure 1A and 1B). Here, SELP is linked to Glanzmann thrombasthenia 1.