Use of PECAM-1 and αvβ3 coexpression to delineate the endothelial origin of MPs: in vitro setup and ex vivo detection. For in vitro studies, the release of MPs in EC supernatants was induced by TNF, as described. (a) Setup of PECAM-1 and αvβ3 double labeling of MPs generated in vitro. (b) SDS-PAGE and Western blot analysis of HUVECs (E) and MP lysates (M) under nonreducing conditions, revealed with control isotype mAb, PECAM-1, and αvβ3. Ex vivo, double labeling of MPs was performed in normal human plasma (c–f). (c) Labeling with isotype control mAb’s, allowing the setting of the background noise position on the subsequent cytograms. (d) Positive double labeling of plasma MPs with FITC–anti-αvβ3 and either PE–anti-PECAM-1, PE–anti-CD41 (e), or PE–anti-CD14 (f).