Ultrastructural characteristics of PSGL-1–mediated cell death. Activated T cells were incubated with TAB4 or control antibodies for 6 hours. Semithin sections (1 μm) were obtained and stained with Toluidine blue (A, R anti-H; B, HIg; C, TAB4; D, anti-CD3). Cells with dark-stained nuclei were then prepared for the electronic microscopy (E, HIg; F, anti-CD3; G-H, TAB4). Arrowhead indicates apoptotic body; arrow, peripheral condensation; scale bar, 5 μm in Figure 5D.