Galectin, another lectin from Fenneropenaeus merguiensis, contributed in shrimp immune defense.

Numerous lectins act as pattern recognition receptors (PRRs) in the innate immune system of invertebrates. Here, a galectin (FmGal) was isolated from hemocytes of Fenneropenaeus merguiensis. FmGal contained one open reading frame encoding a peptide of 338 amino acids. The primary sequence of FmGal comprised a carbohydrate recognition domain with a specific galactose binding site. The FmGal transcripts were found mostly in hemocytes of healthy shrimp. The expression of FmGal was up-regulated upon challenge with Vibrio parahaemolyticus and white spot syndrome virus (WSSV). Gene-silencing with FmGal double-stranded RNA resulted in extreme down-regulation of FmGal. Knockdown with a co-injection of pathogens reduced the survival rate of shrimp. The recombinantr protein of FmGal (rFmGal) required Ca2+ to agglutinate pathogenic bacteria and exhibited sugar-specificity to galactose, lactose, lipopolysaccharide (LPS) and lipoteichoic acid (LTA). The ELISA-validated binding of rFmGal revealed higher affinity to LTA than LPS. rFmGal did not exhibit antibacterial activity but could enhance the phagocytosis and encapsulation of pathogenic invaders by hemocytes. Encapsulation was suppressed by galactose and lactose. Moreover, rFmGal also promoted the in vivo clearance of V. parahaemolyticus. FmGal, a galectin in F. merguiensis, participated in shrimp immunity, functioning as a PRR which might be involved in certain cellular responses.