Increased apoptosis of Sca1⁺B220⁻CD3⁻ and Sca1⁻B220⁻CD3⁻ cells fromFac^−/− mice in response to TNF-α. BM LDMNC from Fac^−/− and Fac^+/+animals were purified by fluorescence cytometry for Sca1⁺B220⁻CD3⁻ and Sca1⁻B220⁻CD3⁻ cells. These two populations of cells were incubated in liquid culture for 24 hours with growth factors alone, growth factors plus TNF-α (1 ng/mL), or TNF-α alone. TUNEL assays were conducted on cytospins of each condition. A total of 100 to 200 cells were evaluated to determine the percentage of apoptotic cells in each condition. Sca1⁺B220⁻CD3⁻ cells in conditions containing TNF-α are depicted. InFac^−/− mice, the percentage of Sca1⁺B220⁻CD3⁻ cells that are apoptotic increases significantly when cultured with TNF-α.