Cloning, Expression And Functional Characterization Of Serum Amyloid P Component And Pentraxin-1 Of Cynoglossus Semilaevis

Innate immunity is the first line of defense against pathogens and plays an important role in pathogen clearance in vertebrates. It also affects the activation and orientation of adaptive immunity and the maintenance of tissue integrity and repair. The innate immune system comprises a cellular and a humoral arm, components of the latter including humoral pattern recognition molecules that recognize pathogen associated molecular patterns. As classical humoral pattern recognition molecules, in mammals, Serum amyloid P component(SAP) and pentraxin-1(PTX1), share basic, evolutionarily conserved functions such as opsonization, complement activation, agglutination, neutralization, and regulation of inflammation. However, research on the function of fish SAP and PTX1 is very limited, in particular that concerning immunology. In this study, we cloned the tongue sole SAP(CsSAP) and PTX1(CsPTX1), analyzed their expression and examined the potential of recombinant CsSAP(rCsSAP) and CsPTX1(rCsPTX1) in antibacterial and antiviral immunity.The open reading fream of CsSAP contains 672 bp which encoded a polypeptide of 224 amino acids. CsSAP shares 46%-58% overall sequence identities with known fish SAP and was upregulated in expression by bacterial and viral infection. rCsSAP exhibited differential binding capacities to a wide range of Gram-positive and Gram-negative bacteria and promoted uptake of the bound bacteria by host phagocytes. When introduced in vivo, rCsSAP enhanced host resistance not only to bacterial infection but also to viral infection. Consistently, antibody blockage of CsSAP significantly weakened the ability of tongue sole to clear invading bacteria. These results provide the first evidence that fish SAP contributes significantly to both antibacterial and antiviral immunities.CsPTX1 contains 223 amino acids and shares 38.8%- 49.3% overall sequence identity with other known fish pentraxins. CsPTX1 is expressed in multiple tissues and is upregulated by bacterial and viral infection. CsPTX1 contains a pentraxin domain, which is known to bind extracellular antigens, and recombinant CsPTX1 bound a wide range of Gram-positive and Gram-negative bacteria. rCs PTX1 also agglutinated all the bacteria tested in a Ca2+-dependent manner and the agglutinating capacity of rCsPTX1 was abolished in the absence of calcium. As well as its ability to agglutinate bacterial cells, rCsPTX1 displayed apparent bacteriostatic activity against Pseudomonas fluorescens in vitro by influencing the permeability of the microbial envelope. When introduced in vivo, rCsPTX1 enhanced the host’s resistance to bacterial infection. These results indicate that CsPTX1 is a classic pattern recognition molecule that defends Cynoglossus semilaevis against bacterial infection.