CXCL8 of Scophthalmus maximus: expression, biological activity and immunoregulatory effect

CXCL8, or interleukin-8, is a CXC chemokine that promotes neutrophil migration in response to inflammatory stimuli. In this study, we identified and analyzed a CXCL8 orthologue, SmCXCL8, from turbot (Scophthalmus maximus). The deduced amino acid sequence of SmCXCL8 is 99-residue in length and shares 52-83% overall identities with the lineage 1 CXCL8 of a number of teleost. SmCXCL8 possesses a CXC chemokine domain that contains the conserved CXC motif preceded by the tripeptide sequence EMH. Purified recombinant SmCXCL8 (rSmCXCL8) induced chemotaxis in peripheral blood neutrophils and, to lesser extents, head kidney (HK) lymphocytes and macrophages in a dose-dependent manner. Mutation of the EMH motif by alanine substitution reduced the chemoattractive effect of rSmCXCL8. Expression of SmCXCL8 as determined by quantitative real time RT-PCR (qRT-PCR) was detected mainly in immune organs under normal physiological conditions and was upregulated by experiment challenges with bacterial pathogen and poly(I:C). In addition, SmCXCL8 expression was also induced to significant extents following vaccination of turbot with a subunit vaccine. When rSmCXCL8 was added to the cell cultures of peripheral blood leukocytes and HK lymphocytes and macrophages, it stimulated the proliferation of these cells and enhanced cellular resistance against intracellular bacterial survival. qRT-PCR analysis showed that rSmCXCL8 induced the expression of TNF-α and suppressor of cytokine signaling 3 in HK lymphocytes in different time frames. On the other hand, SmCXCL8 expression was also upregulated by TNF-α. Taken together, these results indicate that SmCXCL8 is a functional CXC chemokine with immunomodulatory effect and plays a role in inflammatory response induced by bacterial infection.