ICAM-2 protects endothelial cells from apoptosis. (A) Serum starvation-induced apoptosis. Cells were maintained in DMEM with 1% BSA for 24 or 48 hours. Apoptosis was quantified by FACS analysis using the annexin V (AnxV) and propidium iodide (PI) method (A, inset) and shown as fold increase of the AnxV (+)/PI (–) cells compared with control. (B) Anti-Fas–induced apoptosis. MCECs were treated with 100 ng/mL IFN-γ for 16 hours followed by 10 μg/mL anti-Fas Ab for 24 or 48 hours. Data are shown as fold increase of the AnxV (+)/PI (–) cells compared with control. (C) Staurosporine-induced apoptosis. MCECs were incubated with 20 nM staurosporine for 3 or 6 hours. Apoptosis was measured by acridine orange staining (C, inset) and pyknotic nuclei count. Image was acquired as in Figure 1A. Data are shown as average percentage of apoptotic cells/200 × field. Scale bar equals 20 μm. With all 3 stimuli, MCECs from ICAM-2^–/– mice were significantly more susceptible to apoptosis compared with WT MCECs. *Comparison with WT cells at the same time point. †Comparison with ICAM-2^–/– cells at 24 hours. *P < .05; ***P < .001; †P < 0.05, ‡P < .01, ANOVA. n = 3. (A-C) Error bars indicate mean ± SEM.