Endothelium Down-Regulates Fas,TNF,and TRAIL-Induced Neutrophil Apoptosis

Abstract

Background

: Neutrophil (PMN) apoptosis regulates PMN functional longevity and is integral to the resolution of inflammation. We have recently shown that PMN contact with an endothelial monolayer down-regulates spontaneous PMN apoptosis. We sought to explore endothelial-mediated down-regulation of PMN apoptosis following mediator-induced apoptosis. We tested the three known membrane-initiated, receptor-ligand apoptotic pathways: Fas, tumor necrosis factor-α (TNF), and TNF-related apoptosis inducing ligand (TRAIL).

Methods

: PMNs were isolated from peripheral venous blood of healthy volunteers. PMNs were co-cultured in the absence and presence of a human coronary artery endothelial cell (HCAEC) monolayer for 4 h. PMNs were then stimulated with the pro-apoptotic agonists (agonistic anti-Fas IgM, TNF, and TRAIL) for one hour, followed by an assessment of apoptosis after 5 h. PMN apoptosis was measured using an acridine orange/ethidium bromide in situ fluorescent microscopy assay. Caspase 3 activity was assessed using a spectrophotometric assay.

Results

: In addition to spontaneous PMN apoptosis, endothelial co-culture resulted in significant increases in the percentages of normal cells and decreased percentages of apoptotic cells after stimulation with agonistic anti-Fas IgM, TNF and TRAIL. Endothelial co-culture did not alter PMN caspase 3 activity.

Conclusion

: Endothelial-mediated down-regulation of PMN apoptosis is conferred after 4 h of co-culture. In addition to spontaneous apoptosis, endothelial contact down-regulated the three known membrane-initiated PMN apoptotic pathways: Fas, TNF, and TRAIL. These data imply that endothelial-mediated down-regulation of PMN apoptosis may involve defects in each apoptotic pathway or a single defect in a distal transduction or effector event common to all three pathways. Alterations in the activity of caspase 3 did not appear to serve as a mechanism for endothelial-mediated down-regulation of PMN apoptosis.