The strings were formed by tethering platelets to ultralarge VWF multimers via GP Ibα of the GP Ib-X complex.

The formation of strings with adherent platelets was blocked by monoclonal antibodies against either VWF (6G1; A) or GP Ibα (AK2; B) but not by a control mouse IgG (C). Original magnifications × 400. The platelet strings did not form above the surface of endothelial cells incapable of VWF synthesis (ECV304; D). Polystyrene beads coated with a polyclonal anti-VWF antibody also adhered in strings on activated HUVECs (E). Each figure is representative of 4 to 6 separate experiments.