Figure 6. Possible interactions between interleukin 6 and its receptor complex, and regulation by soluble glycoprotein 130. Interleukin 6 Receptor can be present as both a transmembrane (IL-6R) and a soluble protein (sIL-6R). Glycoprotein (gp) 130 can be present linked to cell membranes and as a soluble fragment (sgp130). Interleukin (IL-) 6 can bind either IL-6R or sIL-6R, and both receptors are able to initiate the IL-6 signaling cascade by interacting as a homodimer with two copies of transmembrane gp130. However, sgp130 acts as an antagonist by binding sIL-6R/IL-6, inhibiting their interaction with transmembrane gp130, and blocking the IL-6 signaling pathway.