Complement activation and regulator expression after anoxic injury of human endothelial cells

Complement activation is involved in the ischemia-reperfusion injury of var ious organs, but the mechanisms leading to activation of the complement sys tem are incompletely understood. In this study we show that EA.hy 926 human endothelial cells cultured under anoxic conditions (24 or 48 h) become act ivators of the homologous complement system. Flow cytometric analysis indic ated that Clq, C3c, C3d, C4, C5, C9 components of complement are deposited on anoxic but not on normoxic cells after incubation with normal human seru m. Cell membrane-associated regulators of complement, membrane cofactor pro tein (CD46), decay-accelerating factor (CD55) and protectin (CD59) were exp ressed on EA.hy 926 cells grown under normal oxygen tension. Under anoxic c onditions the expression of protectin was clearly decreased, whereas the ex pression of CD46 and CD55 diminished only slightly. Our results suggest tha t anoxia can convert human endothelial cells to activators of the complemen t system. The diminished expression of protectin, CD46 and CD55 can sensiti ze the cells to complement-mediated damage. Activation of the complement sy stem due to the anoxic injury of human endothelial cells might be an import ant triggering mechanism in the pathogenesis of ischemia-reperfusion injury of human heart.