Neutralization of HIF-2α inhibits sVEGFR-1, but not VEGF, production. (A) Bone marrow-derived macrophages from wild-type mice were transfected with a control siRNA or a HIF-2α–specific siRNA cocktail and stimulated with GM-CSF for 48 hours at ambient O₂ or at 0.5% O₂. Transfection resulted in an approximate 35% decrease in HIF-2α transcript levels by real-time PCR, whereas HIF-1α was unaffected. (B) Cell-free culture supernatants were assessed for sVEGFR-1 after 48 hours. Levels of (C) sVEGFR-1 and (D) VEGF were also assessed via real-time PCR. Data are mean ± SEM of 5 mice per group.