Different orders for acquisition of apoptotic characteristics by leukocytes

Abstract: Apoptotic leukocytes undergo cellular changes that are used as markers for “early ” versus “late ” stages of apoptosis. To ascertain if the order for acquisition of these changes is unique to spe-cific hematopoietic cell types, we compared four leukocyte cell types and the following five apo-ptotic characteristics: MC540 incorporation, an-nexin V-FITC binding, propidium iodide (PI) label-ing of hypodiploid nuclei, DNA fragmentation by a colorimetric assay, and cell membrane permeabil-ity to PI. The order for acquisition of these apo-ptotic characteristics was significantly different for each of the leukocyte cell types and for the mode of induction of apoptosis. It is interesting that the nuclear changes but not the membrane changes studied in mouse spleen cells required caspase ac-tivity. In summary, the acquisition of these apo-ptotic characteristics occurs through caspase-de-pendent and caspase-independent mechanisms, and importantly, the order for acquisition of the characteristics is specific for the cell type and for the mode of induction of apoptosis. J. Leukoc