VEGFR-1–Fc inhibits vascular bed and vascular network formation.

Effects of chimeric proteins containing the extracellular domain of VEGFR-1 or VEGFR-3 in the OP9 coculturing system. Chimeric proteins (20 μg/mL) of the extracellular domain of VEGFR-1 and VEGFR-3 fused to the Fc of human Ig (VEGFR-1–Fc and VEGFR-3–Fc) were added to explant cultures. After 14 days, explants and OP9 cells were stained with the anti-CD31 antibody. CD4-Fc (20 μg/mL) was added as a control (A). Formation of vascular beds and networks was suppressed by 20 μg/mL VEGFR-1–Fc (B) but not by 20 μg/mL VEGFR-3–Fc (C). Addition of VEGF-C (100 ng/mL) rescued only the vascular bed formation of P-Sp explant suppressed by VEGFR-1–Fc (D). Addition of VEGF-A (100 ng/mL) (E) and (200 ng/mL) (F) rescued both vascular beds and network formation of P-Sp explants in the presence of VEGFR-1–Fc. Scale bar indicates 1 mm (low), 0.5 mm (high).