Effects of TNF-α gene deletion and Etanercept administration on apoptosis. Almost no apoptotic cells were detected in the lung from sham-treated (a) tissues collected at 24 hours. At 4 h (bb1) and 24 h (cc1) after the induction of lung inflammation by carrageenan administration, lung tissues demonstrated a marked appearance of dark brown apoptotic cells and intercellular apoptotic fragments. The presence of apoptotic cells or fragments were significantly reduced in the absence of a functional TNF-α R1 gene in TNF-αR1KO mice at 4 h (d) and at 24 hours (e) after carrageenan. Similarly, the treatment of WT mice with Etanercept (5 mg/kg administered sc 2 h prior carrageenan) visibly and significantly reduced the number of apoptotic cells or fragments in the lung tissues collected at 4 h (f) and at 24 hours (g). The graph (h) shows the mean ± SE of percentage TUNEL positive epithelial cells in biopsies from mice in all the experimental groups. *P < 0.01 vs. SHAM; °P < 0.01 vs. carrageenan- WT group ND: not detectable. Figure is representative of at least 3 experiments performed on different experimental days.