A CCL21 chemokine of tongue sole (Cynoglossus semilaevis) promotes host resistance against bacterial infection

Chemokines are a large family of chemotactic cytokines. Based on the arrangement of the first two cysteine residues, chemokines are divided into four groups, one of which is the CC chemokine group. In this study, we characterized a CC chemokine, CsCCL21, from half-smooth tongue sole (Cynoglossus semilaevis), and analyzed its activity. CsCCL21 contains two conserved N-terminal cysteine residues in a NCCL motif and is phylogenetically related to the CCL19/21/25 subgroup of CC chemokines. CsCCL21 was constitutively expressed in nine tissues and significantly upregulated by bacterial and viral infection. The recombinant CsCCL21 (rCsCCL21) induced migration of peripheral blood leukocytes. When the two conserved cysteine residues in the NCCL motif were mutated, the chemotactic activity of rCsCCL21 was abolished. rCsCCL21 enhanced the resistance of tongue sole against bacterial infection, but the mutant protein with NCCL mutation lacked this antibacterial effect. Taken together, these results suggest that CsCCL21 is a functional CC chemokine with the ability to recruit leukocytes and is involved in antibacterial immunity in a manner that requires the conserved NCCL motif.