Effects of TNF-α gene deletion and Etanercept administration on carrageenan-induced accumulation of polymorphonuclear cells in pleural cavity (a) and neutrophils infiltration in the lung tissues (b). A significant polymorphonuclear cells infiltration (a) was observed in pleural cavity of WT mice at 4 h and 24 h after carrageenan administration. The absence of TNF-α receptor 1 gene in mice (TNF-αR1KO) as well as the treatment of WT mice with Etanercept significantly reduced the number of inflammatory cells in the pleural cavity (a) at 4 and 24 hours after carrageenan injection. In addition, at 4 and 24 hrs, the neutrophils infiltration by measurement of the activity of myeloperoxidase. Myeloperoxidase activity was significantly elevated at 4 h and 24 h after carrageenan administration in WT mice. In TNF-αR1KO mice lung myeloperoxidase activity was significantly reduced at 4 h and at 24 hours. Similarly, the treatment of WT mice with Etanercept (5 mg/kg administered s.c. 2 h prior carrageenan) significantly reduced the neutrophils infiltration in the lung tissues at 4 h and at 24 hours after carrageenan administration. Data are means ± SEM of 10 mice for each group. *P < 0.01 vs. SHAM; °P < 0.01 vs. carrageenan- WT group.