Tpl2 knockout (Tpl2Δ/Δ) mice are more susceptible to urethane-induced lung damage, pro-tumorigenic inflammation and tumorigenesis than WT mice. (a) Lung tissues from urethane-treated Tpl2Δ/Δ mice and WT mice. Representative tumors are indicated by arrows. (b) Increased lung tumor multiplicities in urethane-treated Tpl2Δ/Δ mice. Data shown are means ± SD (n ≥ 6; *, p < 0.05). (c) Increased average size of lung tumors in urethane-treated Tpl2Δ/Δ mice. Data shown are means ± SD (n ≥ 5; *, p < 0.05). (d) BrdU labeling showing increased proliferation rate of lung tumors in urethane-treated Tpl2Δ/Δ mice. Scale bar: 20 µm. BrdU-positive cells were also counted and represented as the percentage of total cells. Data shown are means ± SD (n ≥ 5; **, p < 0.01). (e) Real-time PCR assays showing increased expressions of TNF-α and CCL2 in the lungs of urethane-treated Tpl2Δ/Δ mice. Data shown are means ± SD (n ≥ 5; *, p < 0.05). (f) Hema 3 staining assays indicating increase in macrophages and lymphocytes in BALF from urethane-treated Tpl2Δ/Δ mice. Data shown are means ± SD (n ≥ 5; **, p < 0.01). (g) Histological analysis showing severe lung injury in urethane-treated Tpl2Δ/Δ mice. Severe epithelial cell death, protein leak, thickened alveoli, perivascular edema and hemorrhage in the lungs of urethane-treated Tpl2Δ/Δ mice were shown. Scale bar: 50 µm. i, WT mice; ii–iv, Tpl2Δ/Δ mice.