The study of apoptosis, or programmed cell death is of particular interest in the studies of embryogenesis, regulation of immune response, and cell differentiation. Apoptosis is also the mode in which chemo-therapeutic agents and hormones induce tumor cell death. Observable features of apoptosis are chromatin condensation, followed by nuclear fragmentation, cell shrinkage, and distorted morphology. Nuclear fragments are packaged into “apoptotic bodies” which often detach from the cell and are phagocytized by other cells.
Apoptotic cells have a massive number of DNA strand breaks that can be directly labeled with Bromodeoxyuridine triphosphate (BrdUTP) and detected with a fluorochrome-conjugated, anti-Bromodeoxyuridine antibody. Counterstaining with propidium iodide (PI) provides cell cycle information.
Camptothesin treated lymphocytes

Sample Preparation
Human lymphocytes treated with camptothecin (CAM; Sigma, St. Louis, MO) were fixed and labeled with FITC-conjugated BrdUTP and PI according to manufacturer's directions (APO-BRDU; Phoenix Flow Systems, San Diego, CA). Cells were cytocentrifuged onto glass microscope slides and coverslipped with a glycerin-based mounting medium.
LSC Analysis
The slide was analyzed by the Laser Scanning Cytometer using the argon laser operating at 10mW. Cells were identified and selected by contouring on red fluorescence and a minimum cell size, as determined by PI staining. The FITC signal was measured inside the PI contour. Integrated FITC and PI fluorescence of each cell is displayed in the above dot plot. Cells with positive FITC fluorescence were selected by the CompuSort™ process and visualized using the microscope’s epifluorescence illumination with the blue excitation filter. Color digital images of the cells were captured in the LSC's WinCyte™ software and copied to Paint Shop Pro as .bmp images for display.
(Data are from Dr. Elizabeth Bedner, The Cancer Research Institute, Elmhurst, NY.)

See also Apoptosis Analysis with Annexin V and PI.

and APOSCAN: Specifically configured LSC for analyzing apoptotic samples