Fas deficiency leads to decreased spontaneous apoptosis and accumulation of lymphocytes and myeloid cells in vivo in mice. (A) Phenotype of Fas^lpr mice. Shown are lymph nodes of WT and of Fas^lpr mice. The arrows point to the lymph nodes. Ruler in mm scale. (B-E) Spleens were collected from WT (n = 3) and Fas^lpr (n = 3) mice. Cells were stained with Annexin V and PI and analyzed by flow cytometry. PI⁺ cells were gated (B) and quantified as total cell death (C). Annexin V⁺ and PI⁺ cells were gated (D) and quantified for apoptotic cell death (E). (F) Thymuses, LNs, and spleens were collected from WT (n = 3) and Fas^lpr (n = 3) mice. Cells were stained with the indicated cell surface marker–specific antibodies and analyzed by flow cytometry.