Immunological characterization and expression of lily-type lectin in response to environmental stress in turbot (Scophthalmus maximus)

Abstract Lectins are a superfamily of carbohydrate-binding proteins that are widely distributed throughout living organisms. In earlier work, we identified lily-type lectin ( Sm LTL) in the skin mucus of turbot Scophthalmus maximus , and we characterized the protein in the present study. Results from qRT-PCR indicated that Sm LTL was expressed highly in skin, intestine and gill tissue. Changes in Sm LTL expression occurred in these tissues in response to environmental stressors including ciliate infection, high temperature and salinity. Recombinant Sm LTL purified from Escherichia coli was able to haemagglutinate mouse erythrocytes in the absence of calcium, and was inhibited by d -mannose. In addition, Sm LTL displayed selective binding to bacterial species including Edwardsiella tarda a nd Vibrio anguillarum , and exhibited toxicity towards Philasterides dicentrarchi, with a mortality of over 60% after 24 h at a concentration of only 100 μgml −1 . To investigate this toxicity further, we measured binding of Sm LTL after incubating the ciliate in FITC- Sm LTL solution. Surface fluorescence decreased substantially in the presence of 400 mM d -mannose. Together these results suggest that lily-type lectins serve as the first line of defence against microbial attack and play a pivotal role in the mucosal immune system.