EphrinB phosphorylation and extracellular matrix-dependent cord formation by HUVEC and MSC. (A) Cell lysates from unstimulated or EphB4-Fc–stimulated HUVEC and MSC were immunoblotted with specific antibodies. (B) HUVEC marked by a green fluorescent dye (CellTrace CFSE) and MSC marked by a red fluorescent dye (PKH26) were incubated (37°C for 18 hours) individually or together (ratio 2:1) onto solidified Matrigel. Representative images from inverted fluorescence microscopy (original magnification ×4) showing time-dependent network formation.