Proteinase 3 is the major target antigen of antineutrophil cytoplasmic autoantibodies (ANCA) in Wegener's granulomatosis and is contained in the azurophilic granules of polymorphonuclear neutrophils, the dominant cell type in vascular lesions during the early stages of systemic vasculitis. This study questioned whether neutrophil lysosomal enzymes, once released at the site of inflammation, are able to potentiate the influx of additional neutrophils by enhancing the production of the chemotactic cytokine interleukin-8 (IL-8) by endothelial cells. Therefore, human umbilical vein endothelial cells in culture were incubated with varying concentrations of highly purified proteinase 3, human neutrophil elastase, and cathepsin G for different time periods. The supernatants were subsequently assessed for IL-8 antigen by using a sandwich ELISA. The presence of both proteinase 3 and elastase resulted in an increased production of IL-8, up to 15.6- and 4.2-fold, respectively, in a dose- and time-dependent fashion. Cathepsin G did not influence IL-8 production. Although the addition of an alpha 1-proteinase inhibitor completely abrogated elastase-mediated IL-8 production, it did not significantly influence the effect of proteinase 3. Both proteinase 3-and elastase-mediated production of IL-8 was inhibited by cycloheximide, indicating de novo synthesis. This was supported by the finding of increased IL-8 mRNA levels in proteinase 3-treated human umbilical vein endothelial cells by using Northern blot analysis. Taken together, the neutrophil lysosomal enzymes proteinase 3 and human neutrophil elastase may contribute to a self-perpetuating process of neutrophil recruitment in acute inflammation by increasing de novo synthesis of IL-8 by endothelial cells. The studies presented here also show that proteinase 3 mediates its effect independently of its enzymatic activity, indicating a hitherto unknown mode of action on endothelial cells.