The collectin subfamily member 11 (Ca-Colec11) from Qihe crucian carp (Carassius auratus) agglutinates and inhibits Aeromonas hydrophila and Staphylococcus aureus

The collectin subfamily member 11 (Colec11), plays an important role in innate immunity as a pattern recog-nition molecule. In the present study, a colec11 homolog was identified and characterised from Qihe crucian carp, namely, Ca-colec11. The full-length cDNA of Ca-colec11 was composed of 1129 bp, with a 99 bp 5 '-un-translated region (UTR), 816 bp open reading frame (ORF) encoding a 271-aa protein and 214 bp 3 '-UTR with a polyadenylation signal sequence (aataaa) and a poly(A) tail. The deduced amino acid sequence of Ca-Colec11 contained a si gnal peptide, collagen domain, neck region and carbohydrate-recognition domain (CRD), which had four conserved cysteine residues (Cys170-Cys256 and Cys242-Cys264) and an EPN/WND motif required for carbohydrate-binding specificity. Tissue expression profile analysis by quantitative real-time polymerase chain reaction (RT-qPCR) showed that Ca-colec11 was ubiquitously distributed in the tested tissues and highly expressed in the liver. The gene expression levels of Ca-colec11 were evidently up-regulated in the liver, spleen, kidney and head kidney after infection with A. hydrophila and S. aureus. The recombinant Ca-Colec11 (rCa-Colec11) purified from Escherichia coli BL21 (DE3) could agglutinate A. hydrophila and S. aureus, and it possessed haemagglutination activity against rabbit erythrocytes, which was inhibited by various carbohydrates, including D-Mannose, N-Acetyl-D-mannosamine, L-Fucose, D-Glucose, N-Acetyl-D-glucosamine, D-Galactose, LPS and PGN. Furthermore, rCa-Colec11 could inhibit the growth of A. hydrophila and S. aureus. These findings collectively demonstrated that Ca-Colec11, as a PRR, could play a role in the immune defence of Qihe crucian carp.