MPs released by LPS-treated THP-1 cells bind to endothelial cells. MPs were isolated from THP-1 cells left untreated or treated with 5 μg/mL LPS for 24 hours. (A) MPs were stained with annexin V with or without calcium and detected by flow cytometry. (B) Annexin V-positive events per milliliter were calculated using a known concentration of flow count beads. (C) MPs from LPS-treated THP-1 cells were labeled with calcein AM and incubated with HUVECs for the indicated times. Fluorescence intensity was measured using a fluorescent plate reader and shown after the subtraction of the background signal of HUVECs alone. (D) Calcein AM-labeled MPs (green) from LPS-treated THP-1 cells were incubated with calcein orange and 4,6 diamidino-2-phenylindole (blue nuclei)-labeled HUVECs for 4 hours and observed in a 1-μm section by confocal microscopy at room temperature using an Olympus Fluoview 1000 with 40× lens. The image was acquired using Olympus Fluoview Version 2.0 viewer and processed using Image J software. Results are representative of at least 3 independent experiments (n = 3 for panels A and B; n = 6 for panel C). *P < .05 (Student t test).