Time-course of platelet binding to apoptotic HUVEC. Washed and calcein-loaded nonactivated platelets were allowed to adhere to HUVEC undergoing apoptosis induced either by staurosporine or by keeping cells in suspension with serum-deprivation. After the adhesion assay, HUVEC were permeabilized and stained for DNA with propidium iodide. HUVEC were then assayed by flow cytometry to determine platelet binding and, simultaneously, apoptosis-induced DNA fragmentation. Platelet binding is expressed as the median fluorescence (FL-1-H) of the entire HUVEC population. DNA fragmentation is expressed as percentage of cells with hypodiploid DNA. A representative experiment of three performed is shown.