(A through H) illustrates the results of typical two-color flow cytometric analysis of a cell suspension obtained from the Peyer's patch 24 hours after sham-CLP (sham)(A, C, E, G) or CLP (B, D, F, H; simultaneously stained and analyzed). (A and B) represents contour plots of the total cell sample delineated by DAPI fluorescence (FL4-A) versus cell size (width; FL4-W). The primary region (R1) typically established to enclose those cells in the various stages of the cell cycle is also depicted. (C and D) are the cell cycle histograms of cell number versus DNA content (DAPI fluorescent intensity) generated from the R1 gated populations in (A and B). (E and F) are the representative contour plots of these same cell samples assessed by their phenotypic expression, ie, DAPI (FL4-A) versus B220 (FL2-H) fluorescent staining intensity. The nonspecific/negatively (-) stained cells were delineated from the positively stained cells by the use of isotypic antibody controls as indicated in the methods and these regions are indicated as “B220^-” or “B220⁺” regions and the percentage of cells expressing a given phenotype are given. Cell cycle histograms (G and H) of cell number versus DNA content (DAPI fluorescent intensity) produced from each of the phenotypically defined populations in (E and F), respectively, illustrate the typical changes observed in frequency apoptotic cells encountered after CLP in Peyer's patch cells.