Macrophage protection caused by an apoptotic cell-derived soluble factor. (A-C) Caspase-3 activity in etoposide-treated (8 hours, 250 μM) THP-1 macrophages normalized to untreated controls. Cells and media were preincubated for 16 hours. Data are presented as the mean ± SD from 3 independent experiments. Statistical differences between samples are marked with an asterisk (P < .05). (A) Cells remained untreated or were treated with apoptotic cells alone or in combination with 2 μM cytochalasine D. (B) Cells remained untreated or were treated with conditioned media from macrophages cocultured with apoptotic cells (ACCM), necrotic cells (NCCM), or conditioned medium from apoptotic cells (ACM). (C) Cells remained untreated or were pre-exposed to apoptotic cells in transwell inserts for 16 hours prior to stimulation with etoposide.