Murine TLR4 Is Implicated in Cigarette Smoke-Induced Pulmonary Inflammation

Abstract

Background: Chronic obstructive pulmonary disease (COPD) is associated with an abnormal inflammatory response of the lungs to noxious particles or gases. We investigated whether Toll-like receptor 4 (TLR4) is implicated in cigarette smoke (CS)-induced pulmonary inflammation in a murine model of COPD. Methods: C3H/HeOuJ (Tlr4^WT) and C3H/HeJ (Tlr4^defective) mice were exposed to air or CS for 5 weeks (subacute) and 26 weeks (chronic), and pulmonary inflammation was evaluated. Results: In Tlr4^WT mice, subacute and chronic CS exposure induced a substantial pulmonary infiltration of macrophages, neutrophils, lymphocytes and dendritic cells (DCs), that was absent in air-exposed mice. CS exposure increased the costimulatory marker expression on DCs, the levels of monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-α (TNF-α) in bronchoalveolar lavage (BAL) fluid and induced the pulmonary expression of matrix metalloproteinase-12 (MMP-12), TLR4 and TLR2. In contrast, after subacute CS exposure, Tlr4^defective mice showed a limited (5-fold lower) increase of DCs and lymphocytes in BAL fluid, lower costimulatory marker expression on DCs and lower MCP-1 and TNF-α levels in BAL fluid compared to Tlr4^WT animals. After chronic CS exposure, however, the difference in pulmonary inflammation between Tlr4^WT and Tlr4^defective mice was less pronounced and both strains showed similar MCP-1 and TNF-α levels in BAL and similar pulmonary MMP-12, TLR4 and TLR2 expression. Conclusions: We demonstrated that the TLR4 mutation in C3H/HeJ mice is protective against CS-induced pulmonary influx of neutrophils, DCs and lymphocytes upon subacute CS exposure. However, TLR4 is only of minor importance in chronic CS-induced inflammation in mice.