Identification and immune function of the teleost-specific chemokine CCL39 in black rockfish (Sebastes schlegelii)

• Exploring expression pattern of Ss CCL39 post-infection with A. salmonicida . • Ss CCL39 demonstrates chemotaxis to spleen, PB leukocytes in vitro . • Ss CCL39 binds Gram+/− bacteria, microbial ligands (LPS/PGN/LTA), and Poly(I:C). • Ss CCL39 was observed to possess local agglutination effect to different bacteria. • Ss CCL39 was observed to kill bacteria by membrane attack. Chemokines are pivotal regulators of immune cell recruitment in vertebrates. Although teleost-specific chemokines are implicated in immunity, their mechanistic roles remain unclear. In this study, we systematically characterized CCL39, a teleost-specific chemokine, in black rockfish, Sebastes schlegelii ( Ss CCL39), explored its expression patterns following Aeromonas salmonicida infection, and revealed their immune function and antibacterial mechanism. Firstly, Ss CCL39 contained a 309 bp ORF encoding 102 amino acids. Secondly, Ss CCL39 was ubiquitously expressed in all examined tissues, with the highest expression level observed in gill and skin, while the lowest expression level observed in liver. Meanwhile, Ss CCL39 was observed to be significantly up-regulated at most time points in kidney and liver following A. salmonicida infections except the significant down-regulation at the first two time points in the gill. Thirdly, Ss CCL39 was observed to possess chemotaxis to spleen cells and peripheral blood in vitro. In addition, Ss CCL39 was observed to have significant binding ability to Gram-positive, Gram-negative, three examined microbial ligands (LPS, PGN and LTA), and Poly (I:C), which suggested that the pathogen binding ability of r Ss CCL39 might be fulfilled through the recognition of PAMPs on the surface of bacteria. Moreover, Ss CCL39 was observed to possess local agglutination effect to different bacteria, such as Escherichia coli and Staphylococcus aureus . Finally, Ss CCL39 was observed to kill bacteria by membrane attack. Collectively, this study not only indicated the potential vital roles of Ss CCL39 in innate immune responses of teleost species, but also provided insights for the prevention and treatment of bacterial fish diseases.