|Detection of IL‑6 R alpha in Mouse Splenocytes by Flow Cytometry. Mouse splenocytes were stained with Goat Anti-Mouse IL‑6 R alpha Alexa Fluor® 488‑conjugated Antigen Affinity-purified Polyclonal Antibody (Catalog # FAB8108G, filled histogram) or isotype control antibody (Catalog # IC108G, open histogram). View our protocol for Staining Membrane-associated Proteins.|
Interleukin 6 (IL-6) is a multifunctional cytokine that exerts its activities by binding to a high-affinity receptor complex consisting of two membrane glycoproteins: an 80 kDa ligand binding subunit (IL-6 R alpha /CD126) and a 130 kDa nonligand-binding signal-transducing subunit (gp130/CD130) (1‑4). The mouse IL-6 R alpha cDNA encodes a precursor type I transmembrane protein of 460 amino acids (aa) that contains a 19 aa signal sequence, a 345 aa extracellular ligand binding domain, a 21 aa transmembrane region, and a 75 aa cytoplasmic segment (2). The extracellular segment contains an Ig-like and a fibronectin-type III domain, plus a membrane proximal WSXWS motif. In their extracellular regions, mouse IL-6 R alpha shares 89%, 51% and 50% aa identity with rat, human and porcine IL-6 R alpha, respectively. Unlike gp130 that is expressed ubiquitously, the cellular distribution of IL-6 R alpha is predominantly limited to hepatocytes and leukocyte subpopulations such as monocytes, neutrophils, T and B cells. Soluble IL-6 R alpha has been found in various body fluids (5). Two soluble receptor isoforms that arise either from proteolytic cleavage of the membrane-bound IL-6 R alpha, or by alternative mRNA splicing (reported only in human) have been described (6, 7). Soluble IL-6 R alpha binds IL-6 with an affinity similar to that of the membrane-bound IL-6 R alpha. More importantly, the soluble IL-6 R alpha /IL-6 complex is capable of interacting with the membrane-bound gp130 to activate cells that lack an integral membrane IL-6 R alpha. It has been documented that elevated soluble IL-6 R is associated with numerous diseases including arthritic lesions, multiple myeloma and Crohn’s disease (6, 7).