Flow cytometric analysis. (A) MPs were harvested from the conditioned medium of EPCs at different time points and analyzed by flow cytometry. Note the scarcity of endothelial MPs (CD31⁺CD41⁻), but the abundance of platelet MPs (CD31⁺CD41⁺) in EPC cultures (> 90% of all CD31⁺ MPs). (B) Their decline in the conditioned medium corresponds to the observed uptake by the mononuclear cell population. (C) To evaluate the contribution of platelet MPs to the positivity for “endothelial” markers in EPC cultures, cells were costained for CD31 and integrin αIIb (CD41) on day 1 and day 7. Note that on day 1, CD31 was confined to platelets. By day 7, CD31⁺ cells were present in EPC cultures. However, these cells were also positive for the platelet-specific integrin αIIb. Scale bar represents 25 μm.