Differential binding of human interleukin‐1 (IL‐1) receptor antagonist to natural and recombinant soluble and cellular IL‐1 type I receptors

Publisher Website
Google Scholar
Abstract
A recently described factor, interleukin‐1 receptor antagonist binding factor (IL‐IraBF), in serum of normal individuals is immunologically related to the interleukin‐1 receptor type I (IL‐1RI). It is presumably a soluble form of the receptor that binds exclusively to interleukin‐1 receptor antagonist (IL‐1ra). Recombinant soluble human IL‐1RI expressed in COS cells (sIL‐1RI) consists of the extracellular part of the receptor and binds all three known IL‐1 species but preferentially to IL‐1ra. We further characterized the sizes and binding of IL‐1raBF and sIL‐1RI to IL‐1ra by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate, ligand binding interference analyses, N‐glycosidase treatment, concanavalin A affinity chromatography, and with the use of monoclonal antibodies (mAb) to human recombinant IL‐1ra. We also evaluated the binding of IL‐1ra to cellular IL‐1RI on MRC5 fibroblasts and the interference afforded by the soluble receptors. The results show that the protein backbones of IL‐1raBF and sIL‐1RI are of similar size (≈ 35–40 kDa) and that there are differences in the glycosylation of the two molecules. These carbohydrates were necessary for optimal binding of both molecules to IL‐1ra. Both factors blocked binding of IL‐1ra to cellular IL‐1RI, as did mAb to IL‐1ra, but the sites on IL‐1ra which bound to the mAb, and to IL‐1raBF and sIL‐1RI, differed. We conclude that there are important differences between the natural and recombinant forms of soluble IL‐1RI and that IL‐1ra binds differently to these molecules and to cellular IL‐1RI.