Attenuation of FVB LN cell-induced BM failure in Fas−/− mice. We infused FVB LN cells into sublethally-irradiated (6.5 Gy TBI) normal B6 mice (B6-BM failure, N=5) or Fasdeficient B6 mice (Fas−/−BM failure, N=4). Relative to TBI only controls (B6-TBI, N=3), B6-BM failure mice showed significant declines in WBCs, RBCs, platelets and total BM cells (A). In contrast, pancytopenia was significantly buffered in Fas−/−BM failure mice in which blood platelets and total BM cells were essentially not different from B6-TBI controls (A). There were significant attenuation in the expansion of CD8 T cells (P<0.05) and CD11a+ CD8 T cells (P<0.05) in Fas−/−BM failure animals, but total FasL+ CD8 T cell number was relatively similar in B6-BM failure and Fas−/−BM failure mice (B).