VEGF attenuates IFN-α signaling and requires IFNAR1 degradation for efficient angiogenesis. (A) Immunoblot analysis of levels and phosphorylation of STAT1 (Tyr701 and Ser727) and STAT3 (Ser727) in HUVECs left untreated or treated with VEGF (100 ng/mL for 2 hours) before treatment with the indicated dose of IFN-α (for 15 minutes). (B) Cell surface levels of IFNAR1 in untreated (blue line) or murine VEGF-treated (red line) CD31-positive bone marrow cells from indicated mice. Green line indicates control Ig. (C) In vivo angiogenesis assay in mice of indicated genotype was carried out as outlined in “Methods.” Pictures of retrieved plugs and a graph that depicts measurement of hemoglobin (mean ± SEM). *P < .01 between genotypes for VEGF-induced values. (D) Immunohistochemical analysis of Matrigel plugs retrieved from mice of indicated genotype (untreated or treated with VEGF) was carried out using anti-CD31 antibody and H&E staining. Images were taken using an Olympus BX600 microscope (40×) and a SPOT FIEX camera.