We first set out to confirm the role of TLR2 in murine allergic airway disease. WT and TLR2−/− mice were sensitized and challenged with OVA following the protocol showed in Figure 1A. Immunohistochemistry and western blot results showed that TLR2 protein expression was significantly increased in OVA-challenged WT mice in comparison with that of control mice (Figures 1B,C), and TLR2 was expressed on various types of cells, such as epithelial cells and leukocytes. Concomitantly, lung histology showed an increase in leukocyte recruitment to peribronchial and mucous cell metaplasia in OVA-challenged WT mice (Figures 1D–G). In sharp contrast, OVA-challenged TLR2−/− mice showed reductions in inflammatory cells recruitment (Figures 1D,F) and airway PAS+ cells (Figures 1E,G) in comparison with that of OVA-challenged WT mice.