DLL4 blockade facilitated proliferation of HUVECs in vitro. (A) Expression of DLL4, Notch1, and Notch4 in HUVECs and HMVECs was examined by RT-PCR. (B) The change of DLL4 expression was examined before or after VEGF stimulation by flow cytometry. The gray histogram shows the background staining with control mouse IgG1. (C) The dotted histogram shows the binding of Notch1-Fc after preincubation of the indicated cells with control IgG. The bold histogram shows the binding of Notch1-Fc after preincubation of the indicated cells with MHD4-46. Thin histogram shows the background staining. (D) HUVECs and HMVECs were treated with VEGF, MHD4-46, or both, and proliferation was determined by WST assay. The values represent mean plus or minus SE of triplicate wells repeated twice. *P < .05 versus control, ¶ and §P < .05 versus VEGF, †P < .05 versus MHD4-46 by 1-way ANOVA with Fisher least-significant-difference test.