Interleukin-6 (IL-6) mediates its biological effects through the type I IL-6 receptor system that consists of two chains IL-6RÎ and gp130. The IL-6RÎ chain is the binding component specific to IL-6 while the gp130 only transmits signals of IL-6 when bound to IL-6RÎ. IL-6R has a role in various signaling cascades. The gp130 also can transmit signals from leukemia inhibitory factor (LIf) oncostatin M (OSM) ciliary neurotrophic factor (CNTf) interleukin-11 (IL-11) and cardiotrophin-1 (CT-1) in conjunction with other receptor subunits. The low-affinity binding site for IL-6 is composed of IL-6RÎ alone. IL-6RÎ is expressed in a wide range of cells including T cells fibroblasts and macrophages. Soluble IL-6RÎ which consists of only the extracellular domain of the IL-6RÎ chain acts as an agonist of IL-6 activity at low concentrations. Recombinant human sIL-6RÎ is a 37.6kDa protein consisting of the extracellular domain of the IL-6RÎ chain (339 amino acid residues).