Does von Willebrand factor induce platelet aggregation or agglutination?

Von Willebrand factor, which is a glycoprotein that is found in blood plasma, can induce platelet aggregation through interaction with the glycoprotein Ib-IX-V complex (GPIb-IX-V), which is a receptor complex expressed on platelet membranes. However, in the presence of ristocetin or botrocetin, von Willebrand factor can also cause agglutination, due to ristocetin and botrocetin mediating binding of von Willebrand factor to GPIb.