Soluble tie receptor is not released from megakaryocytic UT-7 cells. UT-7 cells were incubated in the absence (blue) or presence of 10 ng/mL PMA (red), TNF (green), IL-1β (pink), or 100 ng/mL VEGF (orange) for 1 hour. After treatment, cells were stained for 45 minutes on ice with phycoerythrin-coupled anti–tie-1 MoAb 42G10. An isotype matched IgG (black) was used as the negative control. FACS analysis was performed as described in Materials and Methods.