Dll4 expression in retrovirally transduced primary human endothelial cells. (A) Flow cytometric measurement of EGFP expression in HUVECs infected 3 days earlier with control retrovirus or Dll4 retrovirus. Representative images from 8 independent infections. (B) Levels of Dll4 expression in HUVECs 3 to 15 days after transduction with control vector or Dll4 retrovirus were evaluated by quantitative RT-PCR relative to GAPDH expression. The results reflect the mean (± SEM) from 14 separate determinations from 8 infections. ^*P = .012. (C) Dll4 and actin expression in HUVECs transduced with control vector or Dll4 retrovirus evaluated by immunoblotting with R3 rabbit anti-Dll4 antibody and reblotting with goat anti-β-actin antibody. (D-F) Immunocytochemical analysis of Dll4 expression in HUVECs transduced with Dll4 (F) or vector only (D) using rabbit anti-Dll4 antibodies; control staining of Dll4-transduced HUVECs with preimmune rabbit serum (E).