C-type lectin from red swamp crayfish Procambarus clarkii participates in cellular immune response

Lectins are potential immune recognition proteins. In this study, a novel C-type lectin (Pc-Lec1) is reported in freshwater crayfish Procambarus clarkii. Pc-Lec1 encodes a protein of 163 amino acids with a putative signal peptide and a single carbohydrate recognition domain. It was constitutively expressed in various tissues of a normal crayfish, especially in the hepatopancreas and gills. Expressions of Pc-Lec1 were up-regulated in the hepatopancreas and gills of crayfish challenged with Vibrio anguillarum, Staphylococcus aureus, or the white spot syndrome virus. Recombinant mature Pc-Lec1 bound bacteria and polysaccharides (peptidoglycan, lipoteichoic acid, and lipopolysaccharide) but did not agglutinate bacteria. Pc-Lec1 enhanced hemocyte encapsulation of the sepharose beads in vitro, and the blocking of beads by a polyclonal antibody inhibited encapsulation. Pc-Lec1 promoted clearance of V. anguillarum in vivo. These results suggest that Pc-Lec1 is a pattern recognition receptor and participates in cellular immune response. Pc-Lec1 performs its function as an opsonin by enhancing the encapsulation or clearance of pathogenic bacteria.