Molecular cloning, expression and functional analysis of interleukin-8 (IL-8) in South African clawed frog ( Xenopus laevis)

► An IL-8 homologue has been cloned and identified from Xenopus laevis. ► The expression pattern of IL-8 gene is investigated in various tissues. ► The expression of IL-8 mRNA in monocytes is up-regulated by LPS stimulation. ► We also describe the expression and bioactivity analysis of IL-8 protein. In this study, an IL-8 homologue has been cloned and identified from South African clawed frog Xenopus laevis (designated XlIL-8). The open reading frame (ORF) of XlIL-8 consists of 312 bases encoding a protein of 103 amino acids. The chemokine CXC domain, which contained Glu-Leu-Arg (ELR) motif and four cysteine residues, was well conserved in South African clawed frog IL-8. By quantitative real-time PCR, mRNA transcript of XlIL-8 was detectable in all the examined tissues with higher level in spleen and kidney. The temporal expression of XlIL-8 mRNA in the monocytes was up-regulated by lipopolysaccharide (LPS) stimulation and reached the maximum level at about 6 h post-stimulation. Recombinant soluble XlIL-8 (XlsIL-8) was fused with a small ubiquitin-related modifier gene (SUMO) to enhance the soluble expression level in Escherichia coli BL21 (DE3). The fusing protein SUMO-XlsIL-8 was purified using metal chellate affinity chromatography (Ni-NTA) and cleaved by a SUMO-specific protease, then confirmed by SDS-PAGE and Western blotting analysis. Chemotaxis assays showed that lymphocytes but not monocytes could be recruited toward SUMO-XlsIL-8 or XlsIL-8 protein in a dose-dependent manner in vitro. The present study may be useful for understanding the anti-bacteria immunity in amphibian and gives the potential to use the recombinant proteins to manipulate the immune response.