Impairment of the alveolar epithelial barrier is important in the development of ALI. Under physiologic conditions the epithelial barrier is less permeable than the endothelial barrier; thus, destruction of epithelial barrier integrity prompts a progressive influx of protein-rich fluid into the alveoli (95) . On the other hand, the loss of epithelial integrity represents an impairment of physiologic transepithelial fluid transport and further inhibits the reabsorption of alveolar edema (96) . TLRs are critical for airway epithe-lial cell recognition of inhaled pathogens and for innate immune signaling. In cultured human lung epithelial cells, mRNA of all TLRs has been detected (97, 98) . TLR2, TLR3, TLR5 and TLR6 have the highest expression, and the ligands for these TLRs increased IL-8 and vascular endothelial growth factor (VEGF) production in normal human bronchial epithelial cells (99) . TLR2 is a heterodimer with TLR1 and TLR6, and each of these is present on the airway epithelial surface. TLR3, which recognizes dsRNA or poly(I:C), is located in endosomes in unstimulated human bronchial epithelial cells (100) . TLR5 is also present on the airway epithelial surface where it can interact with epidermal growth factor receptor (EGFR). Studies have shown that TLR ligands stimulated IL-8 and VEGF production via EGFR and the downstream signaling that might include MAP kinases and NF-κB (101, 102) . Interestingly, heat shock proteins (Hsp), such as Hsp72 and Hsp90, appear to be intimately involved in the recognition of LPS. Extracellular Hsp72 released from virally infected airway epithelial cells induces IL-8 express in human bronchial epithelial cells, resulting in the recruitment and activation of PMN via TLR4 (103, 104) . Type II alveolar epithelial cells can also be activated by LPS mediated through TLR4 signaling and in turn promote pulmonary inflammatory processes (105, 106) .