Effect of PC and APC on MP-associated EPCR release. (A) HUVECs and (B) monocytes were incubated with concentrations of PC (dark gray bars) or APC (light gray bars) ranging from 6.25 nM to 100 nM for 24 hours and stained with RCR-49 for flow cytometric analysis; data are expressed as percentage of EPCR surface expression and are the mean value of 3 experiments ± SD with the asterisk indicating P < .005. Panels C and D show the corresponding quantitation of MPs isolated from the media after HUVEC and monocyte treatment, respectively, with PC or APC. These were then captured for EPCR and quantified by chromogenic S2366 for the APC bound (nM) and separately for EPCR detected (ng/mL).