RECOMBINANT TUMOR-NECROSIS-FACTOR-ALPHA AND PLATELET-ACTIVATING-FACTOR SYNERGISTICALLY INCREASE INTERCELLULAR-ADHESION MOLECULE-1 AND E-SELECTIN-DEPENDENT NEUTROPHIL ADHERENCE TO ENDOTHELIUM IN-VITRO

Neutrophil adhesion to microvascular endothelium at sites of acute inf lammation is regulated by both chemotactic peptides and lipid-derived mediators. Tumour necrosis factor-alpha (TNF-alpha) is a pro-inflammat ory peptide that up-regulates endothelial expression of intercellular adhesion molecule-1 (ICAM-1) and endothelial leucocyte adhesion molecu le-1 (E-selectin), while platelet-activating factor (PAF) is a potent lipid mediator that induces vascular changes via an unknown mechanism. Both have been shown to increase leucocyte-endothelial adhesion in va rious in vitro models of acute inflammation; however, the combined eff ects of recombinant TNF-alpha (rTNF-alpha) and PAF on neutrophil-endot helium adhesion have not been well described. In this study, we found rTNF-alpha at 0.5 ng/ml and PAF at 10 mu M acted synergistically to in crease neutrophil adherence to cultured umbilical vein endothelial cel ls 4 hr after stimulation. This increased neutrophil-endothelial adhes ion was, in part, dependent on up-regulated expression of ICAM-1 and E -selectin since application of anti-ICAM1 and anti-E-selectin F(ab')(2 ) fragments markedly diminished adhesion. Cultures stimulated with rTN F-alpha (0.5 ng/ml) or PAF (10 mu M) alone did not show a significant increase in neutrophil adhesion, and neither ICAM-1 nor E-selectin exp ression was up-regulated as determined by flow cytometric analysis of endothelial cells. These results indicate that rTNF-alpha and PAF act synergistically to increase neutrophil-endothelial adhesion by stimula ting endothelial expression of ICAM-1 and E-selectin and, thus, may pl ay important roles in the onset and severity of acute inflammatory rea ctions.