Effect of a LECT2 on the immune response of peritoneal lecukocytes against Vibrio anguillarum in roughskin sculpin

Leukocyte cell-derived chemotaxin 2 (LECT2) is a multi-functional protein that is mainly synthesized by the liver. However, its role in roughskin scalping is less known. Here, we cloned a leukocyte cell-derived chemotaxin 2 (TfLECT2) genes in the liver of roughskin scalping, Trachidermus fasciatus, and studied its possible role involved in the immune response against Vibrio anguillarum (V. anguillarum) of peritoneal lecukocytes under in vivo conditions. The cDNA sequence of TfLECT2 is 566 bp in size. Its deduced amino acid (aa) sequence comprises 151 residues, of which the first 16 residues form a putative signal peptide and 101 residues compose a typical peptidase M23 domain in the C-terminal region. The domain structure is conserved in all LECT2 proteins, which suggests a close phylogenetic relationship between TfLECT2 and LECT2 in other fish species. Real-time quantitative PCR analysis revealed that TfLECT2 gene expression was dramatically increased in liver after V. anguillarum stimulation. Subsequently, TfLECT2 was prokaryotic expressed and purified to prepare anti-TfLECT2 antibody. After V. anguillarum challenge, leukocytes recruitment and LECT2 levels in peritoneal exudates were increased, and positively correlated with each other. Moreover, recombinant TfLECT2 administration significantly improved immune responses after infection, principally in stimulating the recruitment, phagocytosis and respiratory burst of leukocytes at the site of infection; however, anti-TfLECT2 treatment neutralized these abilities. Therefore, TfLECT2 may trigger the early immune events of peritoneal leukocytes and it will be useful to induce innate immune response of fish.