Factors involved in APC-induced EPCR release. (A) HUVECs were incubated with and without APC (100 nM for 2 hours) in the presence and absence of metalloproteinase inhibitors, Ro31-9790 (30 μM) or 1,10-phenanthroline (5 mM), labeled with the EPCR antibody RCR-49, and analyzed by flow cytometry. The effects of the respective metalloproteinase inhibitors are included as is that of IL-1β in the absence and presence of Ro31-9790 (30 μM). (B) HUVECs were incubated for 2 hours with APC (100 nM) alone, APC plus hirudin (6 μM), boiled APC (100 nM), PPACK-APC, and PC (100 nM), and then stained for EPCR with analysis by flow cytometry. Results for both panels A and B are expressed as percentage of EPCR surface expression. Values are mean ± SD and the asterisk indicates P < .005. Data are representative of 3 independent experiments with samples performed in duplicate.