Role of toll-like receptor 4 in acute neutrophilic lung inflammation induced by intratracheal bacterial products in mice

Abstract

Wakako Yamada1, Sadatomo Tasaka1, Hidefumi Koh1, Mie Shimizu1, Yuko Ogawa1, Naoki Hasegawa1, Taku Miyasho2, Kazuhiro Yamaguchi1, Akitoshi Ishizaka11Division of Pulmonary Medicine, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan; 2Laboratory of Veterinary Biochemistry, School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, JapanBackground: Toll-like receptors (TLRs) represent a conserved family of innate immune recognition receptors. Among TLRs, TLR4 is important for the recognition of Gram-negative bacteria, whereas TLR2 recognizes cell wall constituents of Gram-positive microorganisms, such as peptidoglycan (PGN).Methods: To evaluate the role of TLR4 in the pathogenesis of acute lung injury induced by Escherichia coli endotoxin (lipopolysaccharide; LPS) or PGN, we compared inflammatory cell accumulation in bronchoalveolar lavage (BAL) fluid and lung pathology between C3H/HeJ (TLR4 mutant) and wild-type C3H/HeN mice. The levels of proinflammatory cytokines and chemokines in plasma and BAL fluid and nuclear factor-κB (NF-κB) translocation in the lung were also evaluated.Results: In C3H/HeJ mice, LPS-induced neutrophil emigration was significantly decreased compared with C3H/HeN mice, whereas PGN-induced neutrophil emigration did not differ. Differential cell count in BAL fluid revealed comparable neutrophil recruitment in the alveolar space. In TLR4 mutant mice, LPS-induced upregulation of tumor necrosis factor-alpha (TNF-α), KC, and CXCL10 in plasma and BAL fluid was attenuate, which was not different after PGN. NF-κB translocation in the lung was significantly decreased in C3H/HeJ compared with C3H/HeN mice, whereas PGN-induced NF-κB translocation was not different.Conclusion: These results suggest that TLR4 mediates inflammatory cascade induced by Gram-negative bacteria that is locally administered.Keywords: rodent, TLR4, endotoxin, neutrophils, NF-κB