A key component of the innate defence mecbanisms against infections is represented by the tolllike receptor (TLR) family. We explored the role played by TLR4 in the pathogenesis of chronic obstructive pulmonary disease (COPD). We first assessed TLR4 expression by immunohystochemistry in surgical specimens from current and former smoker COPDs, from healthy smokers and from controls. The expression ofTLR4 was higher in the epithelium ofhealthy smokers and ofcurrent smoker COPDs than in former smoker COPDs and in contro! s. T o clarify the role of ci garette smoke, w e stimulated, in an in vitro mode/, 16-HBE, a bronchial epithelial celi line with cigarette smoke extracts (CSE) an d evaluated the expression ofTLR4 an d the binding of LPS by flow-cytometry. The activation of TLR4 was assessed by evaluating: nuclear translocation of NFkB an d the expression ofphosphorylated ERK 1/2 (western blot analysis); IL-8 release (ELISA) and chemiotactic activity toward neutrophils. CSE were able to up-regulate the TLR4 expression and the LPS binding in a dose dependent manner. CSE alone were able to increase the nuclear translocation of NFkB, the expression of phosphorylated ERK 1/2, the release of IL-8, an d the chemiotactic activity toward neutrophils. The combined exposure of 16HBE to CSE and LPS, further increased ali these phenomena without inducing a further increase ofNFkB nuclear translocation. This study demonstrates that cigarette smoke actively contributes to the pathogenesis of COPD, by upregulating the expression and the activation ofTLR4 receptor. The activation ofthis receptor may in tum promote the release of a chemiotactic activity toward neutrophils, thus contributing to the accumulation ofthese cells within the airways ofsmokers and ofCOPD patients