An anti-lipopolysaccharide factor in Litopenaeus vannameiparticipates in the immune defense against WSSV and Vibrio anguillarum

The anti-lipopolysaccharide factors (ALFs) are a group of effector molecules of innate immunity in arthropods, exhibiting binding and neutralizing activities to lipopolysaccharides. In the present paper, an ALF gene from shrimp Litopenaeus vannamei(Boone, 1931) (LvALF) was cloned by rapid amplification of cDNA ends (RACE) technique, which encodes a polypeptide of 122 amino acids with a predicted molecular mass of 13.7 kDa and a theoretical isoelectric point of 9.95. In healthy shrimp, the LvALF mRNA was highly expressed in hemocytes, and moderately in gill and heart, whereas low in muscle, intestine and hepatopancres. While the healthy shrimps were challenged with white spot syndrome virus (WSSV) and Vibrio anguillarum, the LvALF mRNA level in hemocytes was significantly up-regulated and reached peak levels at 6-12 h and then gradually decreased to the control level. Moreover, the LPS-binding activity of recombinant LvALF (r LvALF) was confirmed by ELISA and modified pull-down assay using the polyclonal antibodies against the r LvALF, meanwhile the up-regulated expressions of LvALF in hemocytes after challenges with WSSV or V. anguillarumwere also detected at protein and cellular levels by Western blotting and immunocytochemistry. These results indicated that LvALF was involved in the immune defense against WSSV and V. anguillarum.