IL-7 R-alpha (IL-7 receptor alpha; also CD127) is a 60-70kD member of the type I cytokine receptor family of molecules. It is expressed on resting naïve and memory CD8+ T cells, DN thymocytes, pre-B cells, Th1 CD4+ T cells, dendritic cells and monocytes. IL-7 R-alpha heterodimerizes with both the gc chain to create the IL-7 receptor, and the TSLPR subunit to generate the TSLP receptor. IL-7 R-alpha participates in T cell differentiation, naïve T cell survival, and CD4+ thymocyte proliferation. Mature rat IL-7 R-alpha is a 437aa type I transmembrane glycoprotein. It contains a 219aa extracellular region (aa21-239) that possesses one type III fibronectin domain (aa129-222), and a 193aa cytoplasmic tail that shows a key phosphorylation site at Tyr447.