PSGL-1 mediates a caspase-independent cell death. Mouse T cells at late activation stages were incubated with TAB4 in the presence of caspase inhibitors, Z-VAD-FMK (A) or Z-DEVD-FMK (B) in titrated concentration (0.3-100 μM). Jurkat cells were treated with anti-Fas antibody (CH11) as control (A, bottom panel). Positive Annexin V binding was analyzed by flow cytometry. Error bars indicate standard deviation. (C) Oligonucleosomal DNA fragmentation was checked in cells treated with TAB4 or control antibodies (left). Pulsed-field gel electrophoresis of genomic DNA prepared from TAB4-treated or control cells is shown (right). Similar results were obtained in 3 independent experiments.