Objective    To investigate the development of acute lung injury (ALI) of rats at different time phases after injection of different doses of flagellin via caudal vein and to approach the possible mechanism.     Methods    Totally 240 clean female rats were randomized into 4 groups

i.e.

the normal control group and the 1st

2nd and 3rd injury groups. Normal saline was given to the control group

and flagellin was given to 3 injury groups

with dose of 5

50 and 500 μg/kg respectively. Arterial partial pressure of oxygen (PaO

2

)

and ratio of wet

and dry lung tissue (W/D) were determined at 2

4

6

12

24 and 48 h after injection. The histological changes of lung tissue were observed and concentrations of tumor necrosis factor-α (TNF-α)

interleukin-1β (IL-lβ) in peripheral blood and bronchoalveolar lavage fluid (BALF) were  determined at the above-mentioned time points by ELISA.     Results    After injection of flagellin

at the same time points

larger dose of flagllin led to a lower PaO

2

higher W/D of lung tissue

and higher concentrations of TNF-α and IL-lβ in peripheral blood and BALF

and the histological changes of lung were more remarkable. Among all above indexes

there was significant differences between control group and injury groups at every time points (P0.01)

of the 2nd and 3rd injury groups with the control group (P0.01)

more significant differences of the 2nd and 3rd injury groups with the 1st injury group (P0.01). The only significant difference between the 2nd injury group and the 3rd injury group was in TNF-α concentration (P0.01).     Conclusion    Intravenous injection of flagellin may lead to acute lung injury in rats in a dose- and time-dependent manner.