[Investigation of inflammatory responses of alveolar epithelial cells induced by lipopolysaccharide and mechanism].

Objective: Lipopolysaccharide (LPS) can activate alveolar epithelial cells (AECs) and induce inflammatory injury. Toll-like receptor-4 (TLR-4) is integrally involved in LPS signaling and has a requisite role in the activation of NF-κB. NF-κB is a key intercellular signaling event that mediates cell inflammatory responses. The aim of the study is to investigate in an in vitro model the inflammatory responses of AECs induced by LPS and the probable mechanism underlined the observed inflammatory responses. So cytokines of ICAM-1, TNF-α and IL-8 secreted by LPS-activated AECs were observed. And the initial signal molecule (the expression of TLR-4 mRNA) and the key intracellular steps (the activation of NF-κB) were studied in detail.

Methods: The study was performed on A549 cells (Human lung adenocarcinoma cell line). A549 cells were divided into two groups: control, and LPS interference group. Proinflammatory cytokines ICAM-1, TNF-α and IL-8 were detected by ELISA or radioimmunological methods. The expression of TLR-4 mRNA was detected by real time PCR. The activation of NF-κB was detected by Western blot (proteins of I-κBα and NF-κB p65).

Results: Compared with control group, ICAM-1 and TNF-α of LPS-stimulated group were significantly higher and peaked after 2h before gradually declining at 6 and 12 h; IL-8 was higher after 2 h, which continued up to 12 h. The expression of TLR-4 mRNA of LPS group was significantly higher and peaked after 2 h and gradually declining at 6 and 12 h. Meanwhile, NF-κB was activated after 0.5, 2, 6 and 12 h indicated by the significant degradation of IκB-α and the significant release of NF-κB P65 and its subsequent translocation into the nucleus approximately synchronized.

Conclusion: Taken together, the results demonstrate that LPS can induce AECs inflammatory injury via activating TLR-4 and subsequently activating NF-κB.