The type II interleukin-1 receptor (IL-1R11) of the bony fish gilthead seabream Sparus aurata is strongly induced after infection and tightly regulated at transcriptional and post-transcriptional levels

Interleukin-1 beta (IL-1 beta) is the prototypic pro-inflammatory cytokine. A] I the biological effects of IL-I beta are mediated through interaction with type 1 IL-1 receptor (IL-IRI), whereas another receptor, called type 2 IL-IR (IL-1RII), lacks an intracellular signalling domain and acts as a decoy receptor that down-regulates responses to IL-1 beta. Although both receptors are present in bony fish, their expression and biological role in the regulation of IL-1 beta activity in non-mammalian vertebrates remain to be established. In this study, a homologue of mammalian IL-1RII was isolated and characterized in the gilthead seabream (Sparus aurata). The seabream IL-1RII harboured two Ig-like domains in its extracellular region and a short cytoplasmic tail lacking a signalling domain. The seabream IL-1RII cDNA showed an unexpectedly long 3'UTR compared with that from other species and contained three ATTTA instability motifs, which seem to be responsible for its relatively short half-life (less than 2h). The expression of seabream IL-1RII was dramatically up-regulated after infection with Vibrio anguillarum in all the immune tissues examined and was even more strongly induced than the IL-1 beta gene in the head kidney, spleen and liver. Strikingly, the mRNA levels of IL-1RII were 15-fold higher than those of IL-1 beta in the liver, suggesting a role for this organ in the neutralization of IL-1 beta leaking into the systemic circulation from the sites of inflammation. In vitro, bacterial DNA and flagellin increased the mRNA levels of IL-1RII in macrophages, while only flagellin was able to weakly induce its expression in acidophilic granulocytes. Finally, the seabream IL-1RII was localized in the plasma membrane when expressed in HEK293 cells and was able to bind IL-1 beta. (c) 2006 Elsevier Ltd. All rights reserved.