Soluble tie-1 is released from endothelial cells by inflammatory cytokines or VEGF. Cells were incubated with PMA or the indicated factors (all at 10 ng/mL except for VEGF at 100 ng/mL, LPS at 20 ng/mL, and soluble CD14 at 100 ng/mL) for 1 hour. After treatment, supernatants were collected and assayed for soluble tie-1 by sandwich ELISA as described in Materials and Methods. (A and B) HUVECs release soluble tie in response to PMA, TNF, IL-1β, VEGF, or the combination of LPS and soluble CD14. (C) Soluble tie release by HUVECs was compared with release by microvascular dermal endothelial cells (MDEC) and microvascular lung endothelial cells (MLEC). (□) The basal level of soluble tie release, cells incubated with media alone. Results are expressed as the percentage control (±SD), where 100% control represents soluble tie released by HUVECs in response to PMA (A and C) or TNF (B).