Objective To explore whether the amount of lipocalin-2 in the biofluid could reflect the onset of sepsis-induced acute lung injury (ALI) in mice.Methods Lipopolysaccharide (LPS

10 mg/kg) injection or cecal ligation and puncture (CLP) was performed to induce severe sepsis and ALI in C57 BL/6 male mice randomly divided into 5 groups (n=10 in each group): group A (intraperitoneal LPS injection)

group B (intravenous LPS injection via tail vein)

group C (CLP with 25% of the cecum ligated)

group D (CLP with 75% of the cecum ligated)

and the control group (6 sham-operation controls plus 4 saline controls). All the mice received volume resuscitation. Measurements of pulmonary morphological and functional alterations were used to identify the presence of experimental ALI. The expressions of lipocalin-2 and interleukin (IL)-6 in serum

bronchoalveolar lavage fluid (BALF)

and lung tissue were quantified at both protein and mRNA levels. The overall abilities of lipocalin-2 and IL-6 tests to diagnose sepsis-induced ALI were evaluated by generating receiver operator characteristic curves (ROC) and computing area under curve (AUC).Results In both group B and group D

most of the “main features” of experimental ALI were reproduced in mice

while group A and group C showed septic syndrome without definite evidence for the presence of ALI. Compared with septic mice without ALI (group A+group C)

lipocalin-2 protein expression in septic mice with ALI (group B+group D) was significantly up-regulated in BALF (P<0.01) and in serum (P<0.01)

and mRNA expression boosted in lung tissues (all P<0.05). Lipocalin-2 tests performed better than IL-6 tests in recognizing sepsis-induced ALI cases

evidenced by the larger AUC of the former (BALF tests

0.8800 versus 0.6625; serum tests

0.8500 versus 0.7000). Using a dual cutoff system to diagnose sepsis-induced ALI

BALF lipocalin-2 test exhibited the highest positive likelihood ratio (13.000) and the lowest negative likelihood ratio (0.077) among the tests of lipocalin-2 and IL-6 in blood and BALF. A statistically significant correlation was found between lipocalin-2 concentration in BALF and that in serum (Spearman r=0.8803

P<0.0001).Conclusions Lipocalin-2 expression is significantly up-regulated in septic ALI mice compared with those without ALI. Lipocalin-2 tests with a dual cutoff system could be an effective tool in distinguishing experimental ALI cases.