Molecular and functional characterisation of a mannose-binding lectin-like gene from Japanese sea bass (Lateolabrax japonicus).

Mannose-binding lectin (MBL) plays an important role in host immune responses against pathogens. LjMBL-like-1 was identified from Japanese sea bass (Lateolabrax japonicas), which has selectivity for galactose. Herein, this lectin might be better designated as galactose-binding lectin (LjGalBL-1). LjGalBL-1 transcripts were detected in all tested tissues, with highest expression in liver. Upon Vibrio harveyi infection, LjGalBL-1 mRNA expression was increased in major immune-related tissues, and protein levels in serum were also upregulated. Recombinant LjGalBL-1 (rLjGalBL-1) bound to monosaccharides and polysaccharides, and both rLjGalBL-1 and native LjGalBL-1 (nLjGalBL-1) agglutinated three Gram-positive bacteria (Staphylococcus aureus, Streptococcus iniae and Micrococcus luteus) and four Gram-negative bacteria (Aeromonas hydrophila, Edwardsiella tarda, Vibrio anguillarum and V. harveyi) in a Ca-dependent manner in vitro. Moreover, rLjGalBL-1 increased the survival rate of V. harveyi-infected fish and decreased bacterial load in liver, spleen, kidney and blood. Thus, LjGalBL-1 protects L. japonicas against V. harveyi infection.