Integrin activation induced by GP Ib-IX-V. Washed platelets from ADAP^+/+ (A-C) or ADAP^−/− (D-F) mice were allowed to settle on dmA1A2 VWF. The activation state of αIIbβ3 was reported by the binding of soluble FITC-fibrinogen (green). A noninhibitory antibody to αIIbβ3 was used to view the cell outline (red). (A and D) Platelets were on dmA1A2 VWF in the presence of a cocktail of inhibitors against ADP and thromboxane A2. (B and E) As in panels A and D, with the addition of EDTA. (C and F) Platelets were on dmA1A2 VWF and activated with PMA without inhibitors. Results shown are representative of at least 3 experiments with similar results. (G-H) Quantification of specific, activation-dependent FITC-fibrinogen (G) or POW-2 Fab (H) binding to αIIbβ3 in response to GP Ib-IX-V ligation, as shown in panels A to F for FITC-fibrinogen. Results for ADAP^−/− (white bars) are depicted as a percentage of the soluble ligand that is specifically bound by ADAP^+/+ platelets (black bars) ± SEM. Data represent a summary of 4 experiments.