Collectin-11(CcCL-11) with broad microbe binding and agglutination activities participates in antibacterial innate immunity of Yellow River carp (Cyprinus carpio haematopterus).

Collectin-11 (CL-11) is a multifunctional lectin that binds carbohydrates on pathogens and inhibits infection through direct neutralization, agglutination, opsonization and killing pathogens, playing an important role in innate immunity. In the present study, a homolog of collectin-11 (CL-11), designated as CcCL-11, was identified and functionally characterized from Yellow River carp (Cyprinus carpio haematopterus). Its expression profile and agglutination activity were systematically analyzed. The full-length cDNA of CcCL-11 was 834 bp and it contained an open reading frame (ORF) of 831 bp that encoded 277 amino acids. The amino acid sequence of CcCL-11 contains signal peptide, collagen-like region (CLR), α-helical neck region and carbohydrate recognition domain (CRD). Tissue expression profiling analysis showed that CcCL-11 was ubiquitously distributed in the tested tissues and was highly expressed in the liver. Furthermore, CcCL-11 expression was significantly upregulated in the liver and intestine after challenge with a Gram-positive bacterial pathogen (Staphylococcus aureus) and a Gram-negative bacterial pathogen (Aeromonas hydrophila). The recombinant CcCL-11 (rCcCL-11) is able to agglutinate and bind to Aeromonas hydrophila, Aeromonas veronii, Escherichia coli, Klebsiella pneumoniae, Micrococcus lysodeikticus, Bacillus subtilis and Staphylococcus aureus and it possessed haemagglutination activity against C. carpio erythrocytes. In addition, rCcCL-11 showed concentration-dependent binding to major bacterial cell wall components such as lipopolysaccharide (‌LPS) and peptidoglycan (PGN). Competition ELISA analysis showed that certain concentrations of carbohydrates can inhibit the binding of rCcCL-11 to bacteria. These findings confirm the biological activity of CcCL-11 and suggest that it plays an important role in pattern recognition. In vivo experiments demonstrated that rCcCL-11 could promote the clearance of A. hydrophila in the liver, kidney, and spleen of C. carpio, and enhance the survival rate of the fish. In summary, the results of this study indicate that CcCL-11 has obvious agglutination and binding effects on pathogenic bacteria and may serve as a pattern recognition receptor (PRR) to participate in the natural immune response of C. carpio against bacterial infection.