Interaction of cytokines and growth factor in the regulation of verotoxin-induced apoptosis in cultured human endothelial cells

The role of CD77, inflammatory cytokines and endothelial cell growth factor (ECGF) in verotoxin (VT)induced apoptosis in human umbilical vein endothel ial cells (HUVECs) was studied. Apoptosis was detected using annexin V and propidium iodide staining. The expression of CD77 antigen was measured on a FACStar flow cytometer using specific monoclonal antibodies. Our experimen ts showed that HUVECs had very low initial levels of CD77 and were resistan t to VT, Treatment with tumour necrosis factor alpha (TNF-alpha) resulted i n a significant upregulation of CD77 expression and sensitized endothelial cells to VT-mediated apoptosis. HUVECs incubated with a combination of cyto kines [TNF-alpha and interferon gamma (IFN-gamma), both 500 U/ml] showed mo re pronounced upregulation of CD77 expression (> sixfold at 48 h) and under went apoptosis, suggesting that TNF-alpha and IFN-gamma have a synergistic effect on CD77 expression in HUVECs and can induce apoptosis without VT. Ce lls pretreated with TNF-alpha and IFN-gamma and incubated with VT showed th e most pronounced (14-fold) increase in CD77 expression. ECGF had a partial protective effect against cytokine- and VT-induced apoptosis. Taken togeth er, our data suggest that CD77 antigen is involved in the regulation of end othelial cell apoptosis.