Endogenous copper can play an important role in postischemic reperfusion injury, a condition associated with endothelial cell activation and increased interleukin 8 (IL-8) production. Excessive endothelial IL-8 secreted during trauma, major surgery, and sepsis may contribute to the development of systemic inflammatory response syndrome (SIRS), adult respiratory distress syndrome (ARDS), and multiple organ failure (MOF). No previous reports have indicated that copper has a direct role in stimulating human endothelial IL-8 secretion. Increased IL-8 in the culture medium of human umbilical vein (HUVEC), lung microvascular, and iliac artery endothelial cells was observed 24 h after the addition of 10 to 50 microM CuCl2 (cupric ions). HUVEC IL-8 induction by copper was higher than by 50 pg/mL tumor necrosis factor-alpha, whereas 50 pg/mL IL-1beta and 1 ng/mL platelet-activating factor did not stimulate IL-8 production or release. HUVEC IL-8 mRNA increased 3 h after CuCl2 stimulation and remained elevated after 24 h, implying sustained transcriptional activation. Copper did not stimulate HUVECs to secrete other cytokines. Cu(II) appeared to be the primary copper ion responsible for the observed increase in IL-8 because a specific high-affinity Cu(II)-binding peptide, d-Asp-d-Ala-d-His-d-Lys (d-DAHK), completely abolished this effect in a dose-dependent manner. These results suggest that Cu(II) may induce endothelial IL-8 by a mechanism independent of known Cu(I) generation of reactive oxygen species. Furthermore, in vivo studies are warranted to determine if copper is involved in the pathogenesis of systemic inflammation and if Cu(II) chelation can reduce this IL-8-induced endothelial inflammatory response.