Apoptotic cells in wt and Fas^lpr mice. (A) Flow cytometry analysis for the presence of apoptotic cells in the spleens and MLNs of wt and Fas^lpr mice by FITC-VAD-FMK staining is shown. Representative histograms for wt and Fas^lpr spleen cells are shown (top). Each histogram is gated on lymphocytes and the percent VAD-FMK⁺ is provided. The graph below shows the average ± SEM of percent apoptotic lymphocytes in the spleen and MLN of mice at 2 months and 3 months of age (n = 3). **A significant difference with wt (P < .01). (B) TUNEL-positive cell distributions in spleen and MLN of both wt and Fas^lpr mice. Both low (× 10) and high (× 40) magnifications are shown. Boxes indicate the areas of higher magnification. WP indicates white pulp; RP, red pulp; GC, germinal center; and F, follicle. (C) Macrophages from wt, Fas^lpr, MRL/Fas^lpr, and Mer^kd mice were incubated with apoptotic thymocytes for 60 minutes, and the percent of phagocytized thymocytes was determined by fluorescent microscopy. Controls are the percentage of live thymocytes (nonapoptotic) phagocytized. The graph is representative of 4 experiments and shows the average ± SEM of 3 mice per strain at both 2 months and 3 months of age. *P < .05, compared with wt.