Platelet string formation on stimulated human endothelial cells. Platelet adhesion to resting and A23187 (30 μM)-stimulated human EA.hy926 endothelial cells during perfusion of calcein-labeled human platelets (20 × 109 platelets/L) in reconstituted blood. (A) Platelet strings form on A23187-stimulated endothelial cells; they are prevented in the presence of the VWF-neutralizing antibody AJvW-2. Objective, 10×/long working distance numerical aperture (B) Mean numbers (± SEM) of platelets adhering per field and of strings formed, before and after endothelial cell stimulation, followed by perfusion with reconstituted blood, supplemented with human plasma, containing anti-ADAMTS13 antibodies (p-IgG; 250 μg/mL) or human TSP-1 at 6 or 3 μg/mL, as indicated. (C) Mean numbers (± SD) of waving strings formed per field after endothelial cell stimulation, followed by perfusion with reconstituted blood containing calcein-labeled human platelets (20 × 109 platelets/L) and subsequent perfusion with human recombinant ADAMTS13 (2 nM) supplemented with human TSP-1 at 3 μg/mL, as indicated. The white arrow (length = 50 μm) represents the direction of the blood flow (*P < .01; #P < .001 vs A23187 stimulation).
