ENHANCEMENT BY THE COMPLEMENT MEMBRANE ATTACK COMPLEX OF TUMOR NECROSIS FACTOR-ALPHA-INDUCED ENDOTHELIAL-CELL EXPRESSION OF E-SELECTIN AND ICAM-1

Although TNF-alpha and several products of the activated complement sy stem (e.g., C3b, iC3b, and C5a) are known to modulate endothelial cell function in vitro, relatively little is known about the potential mod ulatory role of the membrane attack complex (MAC) in endothelial cell activation, Using an in vitro neutrophil-endothelial adhesion assay an d a quantitative whole cell ELISA to measure endothelial E-selectin an d intracellular adhesion molecule-1 (ICAM-1) expression, we examined t he modulatory role of the MAC in TNF-alpha-induced neutrophil-endothel ial cell adhesive interactions. Activation of quiescent human umbilica l vein endothelial cells (HUVECs) with TNF-alpha results in a concentr ation-dependent increase in neutrophil adhesion measured at 4 h. Assem bly of sublytic concentrations of the MAC on endothelial cells did not result in changes in neutrophil-HUVEC adhesion measured at 4 h. Activ ation of HUVECs with TNF-alpha followed by assembly of the MAC resulte d in a marked increase in neutrophil binding as compared with that obs erved in cells treated with TNF-alpha alone. Blocking studies of mAb r evealed that in either TNF-alpha-slimulated or TNF-alpha and MAC-activ ated endothelial cells enhanced neutrophil binding was nearly entirely attributable to E-selectin and ICAM-1. This conclusion was further su pported by a whole-cell ELISA, which provided evidence that the MAC au gments TNF-alpha-induced up-regulation of both E-selectin and ICAM-1. This study provides data that support the conclusion that the distal c omplement system (MAC) can enhance TNF-alpha-induced proinflammatory e ndothelial cell functions.