Avian thrombocytes spread less efficiently than platelets and express low levels of α_2bβ₃ integrins. Platelet and thrombocyte spreading on collagen was measured over 10 minutes with RICM. (A) The fold increase in surface area covered by adherent platelets and thrombocytes is shown. (B) The absolute area covered by adherent platelets and thrombocytes is shown. Mean ± SEM is shown; n = 25 for each group. (C) Levels of α_2bβ₃ integrin expression on washed human platelets and washed chicken thrombocytes were determined by staining with FITC-conjugated AP-2 mAb staining and analyzed by flow cytometry. The forward and side scatter of values of cells in platelet-rich plasma (PRP) and thrombocyte-rich plasma (TRP) are shown, and gates denote platelets and thrombocytes, respectively. Staining of human platelets and chicken thrombocytes for the α_2bβ₃ integrin with the use of AP-2 mAb binding is shown. (D) The histogram depicts the mean fluorescence intensity (MFI) of AP-2 binding for platelets and thrombocytes. Error bars indicate SD; n = 3 in each group. (E) Scanning electron microscopy images are shown after perfusion of human and chicken blood over collagen at a shear rate of approximately 1300 seconds⁻¹. The α_2bβ₃ integrin antagonist eptifibatide was added at 10μM. Scale bars indicate 10 μm. Shown are representative images from 3 and 5 human and chicken flow experiments, respectively.