VE-cadherin function-blocking antibody treatment phenocopies vascular anomalies observed in genetic VE-cadherin deficiency. (A-C) Confocal images of PECAM-immunolabeled allantois explants from normal 8.5-dpc embryos following 18 hours of culture in control medium (A), control medium plus BV13 monoclonal antibody (24 μg IgG/mL; B), or BV14 monoclonal antibody (24 μg IgG/mL; C). The interconnected networks of PECAM⁺ cells evident in control explants (A) are absent in the BV13-treated explants (B). Instead, only isolated clusters of PECAM⁺ cells are present. Note that a dose-response series was performed using BV13 IgG and showed a moderate effect at 8 μg IgG/mL and no effect at 3 μg IgG/mL. In contrast to BV13, treatment with BV14 had only a modest effect on allantois explant vascularization (compare panels A and C) when added at concentrations identical to that of BV13 (24 μg IgG/mL) or when added at double the concentration (50 μg IgG/mL) at which BV13 treatment caused the complete dysmorphogenesis of blood vessels. Bars equal 100 μm.