Proinflammatory VWF strings. Hypothetical mechanism through which ADAMTS13 deficiency promotes leukocyte adhesion and extravasation. (1) Endothelial cells at atherosclerosis-prone sites become activated and induce the release of UL-VWF from Weibel-Palade bodies (green). (2) A proportion of the UL-VWF that is secreted remains attached to the endothelium, where it unravels and tethers platelets. (3) Retention of platelets over the endothelial surface promotes the release of a variety of different chemokines that (4) act on the endothelium, thereby inducing the expression of adhesion molecules like P-selectin (blue). (5) P-selectin promotes rolling and adhesion of circulating leukocytes, which in turn can (6) extravasate into the subendothelial layers. In the presence of ADAMTS13 (purple), VWF strings are rapidly proteolysed from the endothelial surface to prevent this proinflammatory sequence.