An inflammatory CC chemokine of Cynoglossus semilaevis is involved in immune defense against bacterial infection

Chemokines are a family of small cytokines that regulate leukocyte migration. Based on the arrangement of the first two cysteine residues, chemokines are classified into four groups called CXC(alpha), CC(beta), C, and CX3C. In this study, we identified a CC chemokine, C5CCK1, from half-smooth tongue sole (Cynoglossus semilaevis) and analyzed its biological activity. The deduced amino acid sequence of CsCCK1 contains 111 amino acid residues and is phylogenetically belonging to the CCL19/21/25 group of CC chemokines. CsCCK1 possesses a DCCL motif that is highly conserved among CC chemokines. Quantitative real time RT-PCR analysis showed that the expression of CsCCK1 was relatively abundant in immune organs under normal physiological conditions and was upregulated by experimental infection of a bacterial pathogen. Purified recombinant CsCCK1 (rC5CCK1) induced chemotaxis in peripheral blood leukocytes (PBL) of both tongue sole and turbot (Scophthalmus maximus) in a dose-dependent manner. Mutation of the CC residues in the DCCL motif by serine substitution completely abolished the biological activity of rC5CCK1. When rC5CCK1, but not the mutant protein, was added to the cell culture of PBL, it enhanced cellular resistance against intracellular bacterial infection. Taken together, these results indicate that C5CCK1 is a functional CC chemokine whose biological activity depends on the DCCL motif and that C5CCK1 plays a role in host immune defense against bacterial infection. (C) 2011 Elsevier Ltd. All rights reserved.