AbstractThe aim of this study has been to elucidate how different oxygen levels impact the effects of Interleukin‐17 (IL‐17) on angiogenic properties of endothelial cells. Two endothelial cell lines, mouse MS‐1 and human EA.hy 926, were grown in 20% and 3% O2 and their angiogenic abilities analyzed after IL‐17 treatment: proliferation, apoptosis, migration and tubulogenesis. Expression of endothelial nitric oxide synthase (eNOS) and cyclooxygenase‐2 (Cox‐2) was also measured. Considering EA.hy 926 cell line, hypoxia alone reduced proliferation, survival and migration, but not their ability to form tubules. When cultured at 20% O2, IL‐17 stimulated proliferation, migration and tubulogenesis, whereas a hypoxic environment did not affect their migration and proliferation, but increased their survival and tubulogenic properties. Expression of eNOS and Cox‐2 increased by both IL‐17 and hypoxia, as well as with their combination. With the MS‐1 cell line hypoxia did not affect proliferation, survival, migration and tubule formation. At 20% O2, IL‐17 did not alter their proliferation,but inhibited migration and stimulated tubule formation. At 3% O2, only the stimulating effect of IL‐17 on tubulogenesis was evident. The constitutive expression of eNOS was unaffected by oxygen concentrations or IL‐17 supplementation, whereas both IL‐17 and hypoxia upregulated Cox‐2 expression. Thus the effects of IL‐17 on the angiogenic properties of endothelial cells depend on both the cell line used and the oxygen concentration.