Figure 2. Survival of human aortic endothelial cells examined by either clonogenic assay or fold growth following: (a) a 5 h incubation with tumour necrosis factor (TNF) at the indicated doses or (b) exposure to 0.1 Gy, 1 Gy and 2 Gy. Clonogenic assay was performed as described in Materials and methods. Cell viability was determined by the trypan blue dye exclusion method. The data presented are the mean ± standard error of the mean (SEM) of at least four independent experiments. (c) Morphology of endothelial cells. Cells were either untreated or treated with selected concentrations of TNF and stained with acridine orange and ethidium bromide showing the absence of apoptotic cells. Cells incubated with 10 µM staurosporine (positive control) show visible apoptotic cells.