Background Lipopolysaccharide （LPS） forms outer membrane of the wall of Gram-negative cells.LPS can directlycause damage to epithelia of respiratory tract and is the major factor responsible for the chronic inflammation ofrespiratory passage.The mitogen-activated protein kinase （MAPK） signal transduction pathway of the airway epithelia isintimately associated with the action of LPS.The chronic inflammation of respiratory tract and smoking are interrelatedand entwined in the development and progression of chronic lung diseases.This study was designed to examine theeffects of cigarette smoke extract （CSE） and LPS on MAPK signal transduction pathway in order to further understandthe roles CSE and LPS play in chronic lung inflammation.Methods Cultured primary human epithelial cells of airway were divided into four groups according to the stimulantsused:blank control group,LPS-stimulation group,CSE-stimulation group and CSE plus LPS group.Western blotting wasemployed for the detection of phosphorylation level of extracellular-signal-regulated-kinase (ERK),p38 MAPK andc-Jun N-terminal kinase （JNK）.The expression of cytokines of MAPK transduction pathway (granulocyte-macrophagecolony stimulating factor （GM-CSF） and mRNA of IL-8) in the primary epithelial cells of respiratory tract was alsodetermined.Results Western blotting revealed that the phosphorylation levels of ERK,p38 MAPK and JNK were low and 2 hoursafter the LPS stimulation,the phosphorylation of ERK,p38 MAPK and JNK were all increased.There was a significantdifference in the phosphorylation between the LPS-stimulation group and blank control group （P<0.05）;no significantdifference was found between CSE-stimulation group and blank control group （P>0.05）;there was a significant differencebetween CSE + LPS group and blank control group and between CSE + LPS group and LPS group （P<0.05）.Thephosphorylation of CSE-LPS group was higher than that of blank control group but lower than that of LPS group.In blankcontrol group,the expression of IL-8 and GM-CSF mRNA was low in the epithelial cells of airway and the release of IL-8and GM-CSF was also at a low level.One hour after LPS stimulation,the level of IL-8 mRNA increased （P<0.05） andreached a peak after 2 hours.On the other hand,GM-CSF mRNA level increased 2 hours after the stimulation （P<0.05）and reached the highest level 4 hours after the stimulation.Two hours after LPS stimulation,IL-8 and GM-CSF proteinlevel began to rise （P<0.05）,and the level was the highest 8 hours after the stimulation （P<0.01）.Stimulation with CSEalone had no effect on the release of IL-8 and GM-CSF and expression of IL-8 mRNA （P>0.05）,but pre-treatment withCSE could delay the LPS-induced release of IL-8 and GM-CSF and the expression of IL-8 mRNA and its peak was lower.Conclusions LPS stimulation can significantly increase the phosphorylation of ERK,p38 MAPK and JNK in theepithelial cells of airway and activate the MAPK transduction pathway,thereby can activate the downstream signaltransduction pathway,and can ultimately result in the release of cytokines by the epithelial cells of airway.CSE canpartially abolish the LPS-induced activation of MAPK signal transduction pathway and the expression of cytokines of thepathway,which might contribute to the development and progression of the inflammatory reactions in COPD patients.Chin Med J 2007;120（12）:1075-1081
