The important character of acute lung injury (ALI) is alveolar capillary membrane damage caused by different diseases, such as sepsis, trauma and shock. One of the important pathological stages is the varying degrees of interstitial fibrosis and semi-permeable alveolar membrane fibrosis. It has been proved that CXCL12/SDF-1 (stromal cell-derived factor-1) induces fibrocyte migration, and promotes fibrosis progression. Study indicated that inhibition of TLR4 receptor signaling pathway improves fibrosis progression induced by ALI, however, the role of fibrocyte in ALI is still unclear. The fibrocytes was significantly increased in asthmatic patients with pulmonary fibrosis, which companies with increased CTGF expression. Therefore, this project assumes that fibrocyte will differentiation to fibroblast/myofibroblast in patient with acute lung injury, which in turn leads to progression of fibrosis. The central hypothesis of this project is that peripheral progenitor cell fibrocytes play an important role in alveolitis caused by acute lung injury. The overall objective of this project is to study the role of fibrocytes in acute lung injury.