PECAM-1^−/− MKs demonstrate increased adhesion mediated by overactivation of the αIIbβ3 integrin. (A) PECAM-1^−/− MKs demonstrate increased adherence to fibronectin (Fn), collagen (Cl), and fibrinogen (Fg) monolayers. This increased adhesion is maintained in the presence of an α5 integrin blocking antibody (α5) however absent in the presence of the αIIbβ3 integrin inhibitor lotrafiban (Lot). Mean of 3 experiments. *P < .05. (Bi) The ratio of Jon/A to CD41 binding on MKs (mean of 3 experiments) presented as geometric mean fluorescence intensity (GMFI) ± SEM. (ii) The ratio of Jon/A to CD41 binding on platelets (mean of 3 experiments) presented as geometric mean fluorescence intensity (GMFI) ± SEM. *P < .05.