T-bet^−/− LN-cell malfunction in vivo in the induction of BM failure. Lymph node (LN) cells from normal B6 or T-bet^−/− donors were used as effectors to induce bone marrow (BM) failure in sublethally irradiated (5 Gy) CByB6F1 recipient mice. Data were pooled from 4 different experiments showing as means with SEs for animals that received the following treatments: (1) TBI only (5 Gy TBI, n = 11), (2) B6 LN (5 Gy TBI + 5 × 10⁶ B6 LN, n = 13), (3) T-bet^−/− LN (5 Gy TBI + 5 × 10⁶ T-bet^−/− LN, n = 16), (4) T-bet^−/− LN-H (5 Gy TBI + 10 × 10⁶ T-bet^−/− LN, n = 8). Total BM cells were calculated assuming that bilateral tibia and femurs contain 25% of total marrow cells. Infusion of B6 LN cells, but not T-bet^−/− LN cells, caused significant decreases in WBCs (P < .01, panel A), neutrophils (P < .01, panel A), platelets (P < .01, panel A), and total BM cells (P < .01, panel B).