Schematic model of the IL-6/gp130 receptor system. The specific cytokine-binding subunits and gp130 belong to a cytokine receptor superfamily characterized by four positionally conserved cysteine residues and a WSXWS motif. Functional receptor complexes are induced by the different gp130 cytokines: IL-6 and IL-11 induce gp130 homodimerization; CNTF, LIF, CT-1, and OSM induce LIFRα/gp130 heterodimers; and OSM may also induce OSMRα/gp130 heterodimers. Following ligand binding, gp130 is responsible for signal transduction through the JAK/STAT pathways.