Unveiling PoPFP: A short-chain pentraxin involving antibacterial immunity in marine teleost

The pentraxin protein family is a class of evolutionarily conserved proteins that play essential roles in innate immunity. Short-chain pentraxins such as C-reactive protein (CRP) and serum amyloid P component (SAP), act as soluble pattern recognition molecules, exerting effects on the antibacterial immunity. In this study, a short-chain pentraxin protein, i.e., pentraxin fusion protein, was identified in Paralichthys olivaceus, named PoPFP. PoPFP contains a conserved PTX domain in line with that of CRP and SAP, whereas the PoPFP was evolutionarily branched off from the CRP and SAP branches. PoPFP mRNA level and serum PoPFP concentration were obviously responded to bacterial stimulation. In vitro, rPoPFP could bind and agglutinate different types of bacteria, and have bacteriostatic and bactericidal properties. In serum, PoPFP exerted effects on promoting activation of complement. Moreover, rPoPFP interacted with peripheral blood leukocytes (PBLs), leading to the activation of cells including the chemotaxis, proliferation, bacterial phagocytosis, ROS/ACP generation, and immune-related genes generation. Additionally, rPoPFP could attach to NETs released by the rPoPFP-treated neutrophils. Finally, in vivo rPoPFP could help host to defend against bacterial invasion. In conclusion, these findings provide a new cognitive perspective on the immune-antibacterial function of PFP in marine bony fish.