Molecular characterization of interleukin-6 in the gilthead seabream ( Sparus aurata)

• Published in: Molecular immunology 2008-07, Vol.45 (12), p.3363-3370
• Main Authors: Castellana, Barbara, Iliev, Dimitar B., Sepulcre, M. Pilar, MacKenzie, Simon, Goetz, Frederick W., Mulero, Victoriano, Planas, Josep V.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Cloning, Molecular; Fish; Gene Expression Profiling; Gene Expression Regulation; Interleukin-6; Interleukin-6 - chemistry; Interleukin-6 - genetics; Interleukin-6 - metabolism; Leukocytes; Marine; Molecular Sequence Data; mRNA expression; Phylogeny; RNA, Messenger - genetics; RNA, Messenger - metabolism; Sea Bream - genetics; Sea Bream - microbiology; Sequence Alignment; Sparus aurata; Vibrio; Vibrio anguillarum
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/j.molimm.2008.04.012

A cDNA clone, designated sbIL-6 (seabream interleukin-6), was obtained from a cDNA library of enriched immune-stimulated sequences from gilthead seabream. The deduced sbIL-6 protein corresponds to a 225-amino acid protein with a putative 24-amino acid signal peptide, four conserved alpha helices and one N-linked glycosylation site. At the amino acid level sbIL-6 shares 23–26% identity with mammalian IL-6 sequences and 30–51% identity with other fish IL-6 sequences. The structure of the sbIL-6 gene consisted of 5 exons and 4 introns, spanning 2.4 kb. Healthy fish expressed sbIL-6 in white muscle, skin, spleen, anterior intestine and stomach, while no expression was detected in brain, gill, head kidney, posterior intestine and adipose tissue. A significant up-regulation of sbIL-6 expression was observed after lipopolysaccharide (LPS), Vibrio anguillarum DNA ( VaDNA) and peptidoglycan treatment in cultured seabream head kidney leukocytes. Using purified immune cells, sbIL-6 expression was induced similarly in macrophages and acidophilic granulocytes by VaDNA but LPS was more effective in inducing sbIL-6 expression in acidophilic granulocytes than in macrophages. Furthermore, in vivo infection of seabream with live V. anguillarum caused significant increases in sbIL-6 mRNA expression in the thymus, peritoneal exudate, head kidney and gills. In summary, our study provides further evidence for the existence of distinct IL-6 genes in lower vertebrates and for the strong induction of their expression by immune stimuli, supporting the notion of a potentially important role for this cytokine in fish.