Interleukin 6 receptor (IL-6R) alpha is a type I transmembrane glycoprotein that forms a complex with type I transmembrane signal transducer protein gp130 (CD130) and mediates the biological activities of IL-6. IL-6 binds to the membrane-bound non-signaling IL-6R alpha (mIL-6R), and the complex binds to two molecules of gp130 and leads to "˜classical' IL-6-signal transduction, which includes activation of JAK/STAT, ERK, and PI3K signal transduction pathways (Scheller et al.). In contrast, a soluble form of IL-6R alpha (sIL-6R), which comprises the extracellular portion of the receptor, binds to the secreted IL-6 to form a complex that promotes bioavailability of IL-6. The complex of IL-6 and sIL-6R can bind to gp130 on cells that do not express the IL-6R and are unresponsive to IL-6. This process is known as trans-signaling (Hunter & Jones; Rose-John S). sIL-6R regulates both local and systemic IL-6-mediated events. Elevated levels of sIL-6R have been documented in several disease conditions such as rheumatoid arthritis, myeloma, and Crohn's disease (Jones et al.; Mihara et al.).