Cytokine-activated TEC are sensitive to anti-Fas–induced apoptosis. TEC subcultured after 10 to 13 days of primary culture were incubated in the presence of 1 ng/mL IL-1-β, 10 ng/mL TNF-, and 500 U/mL IFN-γ, alone or in combination, for 48 hours. After two washes, various concentrations of agonistic anti-Fas antibody or control IgM were added. After 24 hours, cells were collected by trypsin treatment and labeled with annexin-V–FITC and propidium iodide. Dead cells, ie, cells incorporating propidium iodide, were excluded from the analysis. A representative analysis is shown. (A) The proportion of annexin-V–positive cells among total living cells is expressed as a function of the concentration of IgM or anti-Fas. Increasing concentrations of IgM were inactive, whereas Fas-mediated apoptosis was concentration-dependent. (B) The analysis of annexin-V–FITC binding in TEC previously activated by cytokines and incubated with 0.5 μg/mL anti-Fas CH-11 or IgM is presented.