The activation of endothelial cells (EC) and monocyte-macrophages (M phi) by Lipopolysaccharide (LPS) is considered an important element of the vascular injury observed in endotoxemia. Interleukin-1 (IL-1) beta release from M phi in response to LPS, appears to be mediated by the autocrine/paracrine release of ATP via P2X7 receptor activation. In EC, similar nucleotide-mediated signaling pathways may be influenced by high levels of expression of CD39, the vascular nucleoside triphosphate diphosphohydrolase (NTPDase; ENTPD I). To determine whether CD39 modulates ATP-mediated release of IL-1 from EC, we stimulated human EC with LPS and measured levels of ATP secretion and IL-1 release. LPS triggered ATP secretion from EC that was soon followed by IL-1 alpha release. Overexpression of CD39 following infection with recombinant CD39 adenoviral vectors (AdCD39) abrogated the initial phase of ATP secretion and inhibited IL-1 alpha release; comparable results were obtained with soluble NTPDase. These data demonstrate that CD39/NTPDase modulates IL-1 alpha release from LPS stimulated human EC.