O034 Expression of the decoy type 2 interleukin-1 receptor in mouse and its putative role in inflammation

Abstract

Introduction The interleukin (IL)-1 system comprises two agonists, IL-1α and IL-1β (IL-1), a specific receptor antagonist (IL-1Ra) and two receptors, type 1 and type 2 IL-1 receptor (IL-1R1, IL-1R2). As opposed to IL-1R1, IL-1R2 is incapable of signaling because it lacks the intracellular TIR-domain, which is required for signal transduction. Thus, IL-1R2 acts as a decoy receptor for IL-1. This system, together with IL-1Ra, regulates IL-1 activity. In vitro data, mainly obtained in human cells, demonstrated that IL-1R2 is expressed by B cells, monocytes and neutrophils and can be proteolytically cleaved from the plasma membrane and shed as a soluble form to bind circulating IL-1β. However, although anti-inflammatory activity of IL-1R2 has been described in overexpression studies, the expression of endogenous IL-1R2 in the mouse and its contribution to the control of inflammatory responses has been poorly investigated. Methods The expression of IL-1R2 transcripts in mouse tissues and ex vivo -isolated or in vitro -differentiated immune cells was assessed by qRT-PCR. For further characterization of endogenously expressed IL-1R2 and its in vitro function, we used bone marrow-derived neutrophils (BMN) for qRT-PCR, extracellular fluorescence activated cell sorting (FACS) and immunoblot analyses. In addition, different mouse models of inflammation were investigated to confirm the expression of IL-1R2 in vivo . Results IL-1R2 mRNA levels are highly upregulated in lung tissue after LPS-administration. Furthermore, mRNA and protein data obtained using ex vivo Gr1 + Ly6G + -peripheral blood cells and in vitro differentiated Gr1 + Ly6G + -BMN indicated that, like in human, neutrophils are a major source of IL-1R2 in mouse. However, other mouse immune cells, including T and B lymphocytes, macrophages (both M1 and M2) and dendritic cells do not express detectable levels of the decoy receptor on their cell surface. The expression of IL-1R2 on BMN is regulated by the glucocorticoid hydrocortisone, which induces a strong upregulation of IL-1R2 mRNA and protein. In contrast, the expression of IL-1β but not that of IL-1Ra, is decreased by hydrocortisone, supporting its anti-inflammatory role. LPS treatment induces shedding of IL-1R2 from the membrane into the culture supernatant. We also demonstrate that IL-1R2 binds recombinant mouse IL-1β, but not IL-1Ra. Finally, in in vivo models of inflammation, including thioglycolate-induced acute peritonitis, acute lung injury and two models of arthritis, neutrophils infiltrating the site of inflammation express the decoy receptor IL-1R2. Conclusion These data indicate that the decoy receptor IL-1R2 is mainly expressed on neutrophils among immune cells in the mouse. It can trap IL-1β and is present during inflammatory situations. Taken together, these results suggest that IL-1R2 plays an important role in regulating IL-1 activity in vivo .