Specificity of tie-1 release in endothelial cells. HUVECs were incubated in the absence (blue) or presence of 10 ng/mL TNF (green) or PMA (red) for 1 hour before harvesting. Aliquots of cells were stained for 45 minutes on ice with Abs specific for tie-1, EGF-R, CD31 (PECAM), axl, CD62E (E-selectin), or FGF-R1. Control samples were stained with isotype-matched Abs (black). FACS analysis was performed as described in Materials and Methods.