Soluble interleukin-1 receptor, a potential negative regulator of orange-spotted grouper Epinephelus coioides interleukin-1 system

In this study, the cDNA sequence encoding interleukin-1 (Il-1) receptor-like protein of orange-spotted grouper Epinephelus coioides was obtained. The newly identified sequence was named soluble type I Il-1 receptor (sIl-1rI) owing to its structural composition, which had two Ig-like domains, lack of transmembrane region and the Toll/interleukin-1 receptor (TIR) domain, similar to the brown rat Rattus norvegicus soluble Il-1rI. In addition, sequence comparison and phylogenetic analysis indicated that E. coioides sequence had a closer relationship with Il-1rI than Il-1rII. Real-time PCR revealed that sil-1rI mRNA expression presented a process of decrease, restoration and increase in Cryptocaryon irritans-infected E. coioides. The negative correlation between Il-1 beta and sil-1rI mRNA in C. irritans-infected head-kidney implied the potential negative regulatory role of sil-1rI in E. coioides Il-1 system. The leucocytes incubated with lipopolysaccharide or polyriboinosinic polyribocytidylic acid exhibited different expression profiles of sil-1rI. Recombinant Il-1 beta (rIl-1 beta) protein was capable of inducing sil-1rI mRNA under the concentration of 100 ng ml(-1), suggesting that high dosage or excess Il-1 beta would stimulate the expression of sil-1rI to maintain the homoeostasis of E. coioides Il-1 system. For the first time, the role of teleost Il-1rI in parasite infection has been identified, and soluble Il-1r was found in fish. (C) 2013 The Fisheries Society of the British Isles