Different orders for acquisition of apoptotic characteristics by leukocytes.

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 specific hematopoietic cell types, we compared four leukocyte cell types and the following five apoptotic characteristics: MC540 incorporation, annexin V-FITC binding, propidium iodide (PI) labeling of hypodiploid nuclei, DNA fragmentation by a colorimetric assay, and cell membrane permeability to PI. The order for acquisition of these apoptotic 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 activity. In summary, the acquisition of these apoptotic characteristics occurs through caspase-dependent 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.