Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/devcompimm The biological effects of rainbow trout (Oncorhynchus mykiss) recombinant interleukin-8 Nor Omaima Harun a , Jun Zou a , Yang-An Zhang a,b , Pin Nie b , Chris J. Secombes a,Ã a Scottish Fish Immunology Research Centre, University of Aberdeen, School of Biological Sciences, Tillydrone Avenue, Aberdeen AB24 2TZ, UK b Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, PR China Received 28 February 2007; received in revised form 8 October 2007; accepted 10 October 2007 Available online 18 December 2007 KEYWORDS Rainbow trout; Recombinant protein; Interleukin-8; Biological activity; Migration; Respiratory burst Summary In this report, recombinant interleukin-8 (rIL-8) was produced and its activity tested for the first time in fish. The rainbow trout rIL-8 was produced in Escherichia coli and purified using a 6xHis tag at the N-terminus. The rIL-8 induced a dose-dependent migration of head kidney leukocytes at concentrations from 0.1 to 10 ng/ml, with a peak response at 1 ng/ml. Trout rIL-8 also had a significant effect on superoxide production by head kidney cells, with maximal activity at 0.1 and 1 ng/ml. When injected intraperitoneally into trout, rIL-8 had a clear effect on total leukocyte number in the peritoneal cavity, with increasing doses (up to 5 mg) eliciting more cells. Of three leukocyte types distinguished, neutrophils were the dominant cell type, especially at higher rIL-8 concentrations. In contrast, the proportion of macrophages and lymphocytes decreased with rIL-8 administration, suggesting that they were not attracted at the same rate as neutrophils. & 2007 Elsevier Ltd. All rights reserved. 1. Introduction Phagocytes are known to be important cells in the non- specific defense against infections [1,2]. In addition to their direct effector functions, including phagocytosis of microbes and release of antimicrobial compounds, phagocytes can release a variety of pro-inflammatory mediators that control the acute phase response and that affect multiple events leading to activation of the cellular and humoral defenses [3,4]. Amongst these mediators are a number of pro- inflammatory cytokines, such as tumor necrosis factor a (TNF-a), interleukin-1b (IL-1b), IL-6 and the chemokine IL-8 [5]. IL-8, or CXCL8, belongs to the CXC family of chemokines, so called because of the arrangement of the first two cysteine residues that have an amino acid residue (X) between them [6]. It was first purified as a chemotactic factor for neutrophils and is viewed as a potent pro- inflammatory mediator in mammals and a marker of inflammation. IL-8 is synthesized as a precursor with a ARTICLE IN PRESS 0145-305X/$ - see front matter & 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.dci.2007.10.005 Ã Corresponding author. Tel.: +441224 272872; fax: +44 1224 272396. E-mail address: c.secombes@abdn.ac.uk (C.J. Secombes). Developmental and Comparative Immunology (2008) 32, 673–681