Characterization of a C-type lectin (PcLec2) as an upstream detector in the prophenoloxidase activating system of red swamp crayfish

C-type lectins are abundantly found in crustaceans. They function in the immune system by recognizing, opsonizing, or agglutinating. Some of them also feature anti-microbial activity. In this study, we identify a hepatopancreas-specific C-type lectin (PcLec2) that responds significantly to immune challenges in red swamp crayfish (Procambarus clarkii). Recombinant PcLec2 shows no agglutinating or anti-microbial activity. It can bind to lipopolysaccharides and bacterial cells in the absence of calcium, and its binding to Gram-negative bacteria is stronger than that to Gram-positive ones. Moreover, the protein can stimulate the activation of prophenoloxidase both in vitro and in vivo. We conclude that this C-type lectin may be an upstream detector of the prophenoloxidase activating system in crayfish.