Reduced efficacy of IFN-γ^−/− LN cells in the induction of BM failure. C.B10 mice were treated with 5 Gy TBI (TBI only; n = 6), TBI plus 5 × 10⁶ B6 LN cells (B6 LN; n = 7), or TBI plus 5 × 10⁶ LN cells from IFN-γ^−/− donors (IFN-γ^−/−LN; n = 10) and were bled and euthanized on day 14 to measure CBC and cellular changes. (A) Recipients of IFN-γ^−/− LN cells had more neutrophils, platelets, and total BM cells than did recipients of B6 LN cells. (B) Marrow cavities appeared to be empty in mice infused with B6 LN cells, had reduced cellularity but contained clusters of hematopoietic cells in mice treated with IFN-γ^−/− LN cells, and had nearly normal cellularity in TBI-only control mice. (C) Proportion and total number of CD4⁺ T cells as well as proportion and total number of CD8⁺ T cells were significantly reduced in the BM of recipients infused with IFN-γ^−/− LN cells than in the BM of recipients infused with B6 LN cells. (D) Total number of FasL⁺CD8 T cells was significantly lower in the BM of recipients infused with IFN-γ^−/− LN cells than in the BM of recipients infused with B6 LN cells. (E) Residual (CD4^–CD8^–) BM cells from mice (n = 4) infused with IFN-γ^−/− LN cells had a lower percentage of annexin V⁺ apoptotic cells than those from mice (n = 3) infused with B6 LN cells. *P < .05; **P < .01; ***P < .001; ****P < .0001.