Involvement of nitric oxide in the inhibition of angiogenesis by interleukin‐2

Interleukin-2 (IL-2), an immunoregulatory cytokine possessing antitumour activity, is an inducer of nitric oxide (NO) synthesis in mice and man. In this study, the possibility that IL-2 possesses antiangiogenic properties that account for its antitumour effects in vivo was examined. IL-2 caused a dose-dependent inhibition of angiogenesis in the chick embryo chorioallantoic membrane (CAM). This inhibition was completely reversed by the NO synthase inhibitor NG-nitro-L-arginine methylester (L-NAME). Furthermore, IL-2 was capable of stimulating NO synthase activity in the CAM in vitro and this effect was suppressed by L-NAME. Addition of IL-2 to human umbilical vein endothelial cells (HUVECs) in culture, had no effect on their growth characteristics. These results suggest that IL-2 may be an important antiangiogenic molecule causing its effect via nitric oxide synthesis. The antiangiogenic activity of IL-2 may be, at least in part, responsible for its antitumour properties.