Variability of Integrin a 2 / 31 Activity on Human Platelets

The activity and surface antigenicity of az& on platelets from 27 normal subjects were found to vary significantly. A fourfold range of surface antigen correlates with a 20fold variation in the ability of nonactivated, washed platelets to adhere to type I collagen and a fivefold variation in the adhesion of platelets to type Ill collagen. These differences in surface receptor are reflected in significant variation in the lag time required for type I collagen-induced platelet aggregation in platelet-rich plasma. Among the same individuals, no difference was observed in surface levels or activities of two other platelet integrins, the fibronectin receptor a& and the fibrinogen receptor all&. In all cases studied, we observed complimentary differences in the incorporation of lZ6l into surface adl , in quantity of surface azBl antigens, and in adl collagen receptor activ-