SmCCL19, a CC chemokine of turbot Scophthalmus maximus, induces leukocyte trafficking and promotes anti-viral and anti-bacterial defense

•SmCCL19 is a turbot CC chemokine with conserved DCCL motif.•rSmCCL19 and the mutant rSmCCL19M bearing mutation at the DCCL motif were purified.•rSmCCL19, but not rSmCCL19M, induced migration of head kidney leukocytes.•In vivo administration of rSmCCL19, but not rSmCCL19M, reduced pathogen infection.•rSmCCL19, but not rSmCCL19M, enhanced the expression of immune genes.

Chemokines are classified into several different subfamilies, of which CC chemokines constitute the largest subfamily in teleost. The prominent structural characteristic of CC chemokines is the presence of an Asp-Cys-Cys-Leu (DCCL) motif. To date, cDNA sequences of several CC chemokines have been identified in turbot (Scophthalmus maximus), however, the activity and function of these putative chemokines remain unknown. In this study, we examined the biological effect of the turbot CC chemokine SmCCL19, which has been previously reported as KC70 and shown to be regulated in expression by bacterial infection. To facilitate functional analysis, recombinant SmCCL19 (rSmCCL19) and a mutant form of SmCCL19, SmCCL19M, that bears serine substitutions at the two cysteine residues of the DCCL motif were purified from Escherichia coli. Chemotactic analysis showed that rSmCCL19 induced migration of head kidney leukocytes in a dose-dependent manner, whereas rSmCCL19M caused no apparent cellular migration. To examine the in vivo effect of rSmCCL19, turbot were administered with rSmCCL19 or rSmCCL19M before being inoculated with viral and bacterial pathogens. Subsequent tissue infection analysis showed that the viral and bacterial loads in rSmCCL19-adminsitered fish were significantly reduced, whereas the pathogen loads in rSmCCL19M-adminsitered fish were largely comparable to those in the control fish. Consistent with these observations, significant inductions of immune relevant genes were observed in rSmCCL19-adminsitered fish but not in rSmCCL19M-adminsitered fish. Taken together, these results indicate that SmCCL19 recruits leukocytes and augments host immune defense in a manner that depends on the conserved DCCL motif.