Exogenous TNF-α accelerates BM destruction and promotes T-cell IFN-γ secretion in TNF-α^−/−mice. (A) TNF-α^−/− mice received 6.5 Gy TBI and infusion of 5 × 10⁶ FVB LN cells were either untreated (n = 4), or were injected with recombinant TNF-α protein at 100 ng per day IV for 7 days (n = 5). Mice were euthanized and analyzed on day 10. Injection of recombinant TNF-α to LN-cell–infused TNF-α^−/− mice reduced BM cellularity (n = 4; original magnification ×200; hematoxylin and eosin stain) (B), significantly increased intracellular IFN-γ levels in BM CD4⁺ and CD8⁺ T cells (C), but did not change intracellular TNF-α levels in BM CD4⁺ and CD8⁺ T cells (D), when compared with LN-cell–infused TNF-α^−/− mice without TNF-α injection. *P < .05; **P < .01.