Abstract： Objective To explore the mechanism of protection role of ambroxol against acute lung injury (ALI)by studying the change of cytokine mRNA expression during the course of ALI.Method The study was composed of experiments both in vivo and in vitro. (1)Experiments in vivo were as follows.Twenty-four sprague-Dawley rats were randomly divide into 3 groups,namely,control group(n=8),acute lung injury group(LPS group,n=8)and ambroxol group(LPS+A group,n=8).The rat model of acute lung injury was induced by intraperitoneal injection of 10 mmol/L lipoopolysaccharide(LPS).The pathological alteration of lung tissue and arterial partial pressure of oxygen(PaO2)were observed.Expressions of TNF-α,IL-10 and IL-24 mRNA were determined by using RT-PCR assay. (2)Experiments in vitro were the followings.Alveolar macrophage cells were collected and divided into 3 groups as above mentioned.Cells were treated with normal saline,with LPS,and with LPS plus ambroxolin dose of 180 μmol/L at 0,6,12 and 24 hours after exposure of LPS,respectively,in 3 groups as above stated.The expressions of TNF-α,IL-10 and IL-24 mRNA were also determine by using RT-PCR.Results The pathological changes of could be parially ameliorated by giving ambroxol.Massive hemorrhage along with vascular edema and infiltration occurred in the lungs of ALT rats.The pathological alterations in ALI rats treated with ambroxol were less severe.The expressions of TNF-α,IL-10 and IL-24 mRNA were dramatically increased in ALI rats,and were partially attenuated after treatment of ambroxol.Macrophages oxposed to LPS for 6 hours showed dramatical increase in expressions of TNF-α,IL-10 and IL-24mRNA those remained at high levels afterwards.The expressions of TNF-α,IL-10 and IL-24 mRNA in macrophages after exposure to both LPS and ambroxol were increased less than those exposed to LPS alone.Conclusions Ambroxol can partially ameliorate the expressions of TNF-α,IL-10 and IL-24 mRNA in alveolar macrophage induced by LPS.