PDGF-BB– and HB-EGF–specific neutralizing antibodies lead to decreased pericyte recruitment to EC tubes and decreased pericyte proliferation. ECs and GFP-pericytes were allowed to coassemble for a period of 72 hours in the presence or absence of neutralizing antibodies to PDGF-BB and HB-EGF. A control neutralizing antibody directed to IL-6 was also used. Each of the antibodies was added at 50 μg/mL. After 72 hours, cultures were fixed for analysis of pericyte recruitment, EC tube width, and pericyte proliferation. (A) Under conditions of either HB-EGF or PDGF-BB neutralization individually, there is a 20%-30% decrease in the number of pericytes associated with EC tubes. When neutralizing antibodies are added to HB-EGF and PDGF-BB in combination, nearly 80% of pericytes are nonassociated with EC tubes. Data are reported as percent pericyte association. (B) EC tube width was measured in conjunction with pericyte association, demonstrating a dramatic width increase of EC tubes in conditions of disrupted pericyte recruitment. (C) Blockade of PDGF-BB and HB-EGF leads to decreased pericyte proliferation, as measured by assessing the total number of GFP-pericytes per high-powered field. n ≥ 5; P ≤ .01. *Significance from control conditions. +Significant from individual factor addition.