Characterization, immune response and antibacterial mechanism of CXCL12 in black rockfish (Sebastes schlegelii).

Black rockfish (Sebastes schlegelii) is one of the most important mariculture fish in the Western North Pacific. Although the crucial roles of CXCL12 in immune responses against bacterial infection are well-known, the specific mechanisms underlying its involvement in fish immunity remain poorly understood. In this study, we systematically characterized CXCL12a and CXCL12b in Sebastes schlegelii (SsCXCL12a and SsCXCL12b), Firstly, SsCXCL12a/b were ubiquitously expressed across all seven tissues. Both SsCXCL12a/b were significantly differentially expressed in gill, kidney, liver, and spleen after Aeromonas salmonicida infection. Secondly, both rSsCXCL12a/b were observed to possess chemotactic activity towards spleen and peripheral blood leukocytes. Thirdly, the pathogen binding ability of rSsCXCL12a and rSsCXCL12b might be fulfilled through the recognition of PAMPs (Pathogen-Associated Molecular Patterns) on the surface of bacteria. rSsCXCL12a/b showed local agglutination effect to different bacteria. Subsequently, by detecting the permeability of the cell membrane, it was speculated that membrane attack might be one of the mechanisms by which rSsCXCL12a/b exert antimicrobial effects. Finally, it was speculated that CXCL12a/CXCR4b and CXCL12b/CXCR4a might be the major antimicrobial axes in black rockfish using Dual-Luciferase reporter gene assay system. Overall, the CXCL12/CXCR4 axis is critically involved in the immune response of S. schlegelii against bacterial infection.