Positive TUNEL assay in TRAF1−/− mice treated intratracheally with rmTNF-α. A to E: Liver sections harvested 20 hours after treatment of WT (A, B) and TRAF1−/− (C–E) mice with intratracheal saline (A, C) or rmTNF-α (B, D, E), evaluated by TUNEL assay (red nuclei) and 4,6-diamidino-2-phenylindole counterstain (blue nuclei). F: TRAF1−/− liver 20 hours after intratracheal TNF-α treatment assayed by TUNEL (red), anti-F4/80 antibody immunohistochemistry marking Kupffer cells (blue), and Sytox green nucleic acid counterstain. Arrows indicate TUNEL-positive Kupffer cells (4-μm sections). Original magnifications: ×200 (A–D, F); ×400 (E).