Objective:To investigate the homology and cross-reactivity of nucleotide and amino acid sequences of cotton rat surfactant-associated protein D(SP-D)

and to observe the m RNA level and protein expression pattern of SP-D in cotton rat with lung injury induced by lipopolysaccharide(LPS). Methods:Thirty-two cotton rats were randomly divided into normal saline control group and experiment group(also named LPS group;LPS group was subdivided into three subgroups at 24

48 and 96 h after LPS injection;8 cotton rats in each subgroup). Rats in experiment groups were injected with 2 mg/kg LPS while those in control group were given the same amount of normal saline. Total RNA was extracted from lung tissue of cotton rat

SP-D gene was cloned and sequenced after RTPCR

and then the homology and phyletic evolution were analyzed by bioinformatics software. Histopathological changes were observed after HE-staining;the m RNA level of SP-D was measured by q RT-PCR;the protein level of SP-D was determined by Western blot. Results:Cotton rat SP-D was obtained with the size of 1 113 bp encoded 370 amino acids. The SP-D homologies of cotton rat and other animals were shown at 75.64%-90.01% in nucleotide sequences and at 72.68%-88.56% in deduced amino acid sequences. In the phylogenetic analysis

cotton rat and other rodents fell into one of the distinct groups. Histopathological changes in experiment group became more obvious and severe as of the time of LPS injection prolonged. The m RNA and protein levels of SP-D in cotton rat were increased after LPS injection. At the first24 h

SP-D m RNA and protein levels were up-regulated with significant differences(P<0.05)

and reached the peak at the 48 h

then decreased a little at the 96 h

but still kept a high level with extreme significant differences(P<0.01). Conclusion:Cotton rat SP-D shares high level of identity to other species both at nucleotide and amino acid levels

and they show cross-reactivity at protein level.Changes of m RNA and protein expression of SP-D in cotton rat with lung injury are time-dependent. SP-D has close relation with the severity of lung injury and it could be regarded as a valuable biomarker in lung injury.