Interleukin-7 receptor alpha chain (IL7R) binds interleukin-7 (IL7), forming a stable 1:1 IL7:IL7R complex, with a dissociation constant (Kd) of approximately 200 pM (Goodwin et al. 1990, Park et al. 1990). The full-length Interleukin-7 receptor alpha is a 439-residue single-pass transmembrane glycoprotein consisting of three domains: a 219-residue extracellular domain (ECD), a 25-residue transmembrane domain and a 195-residue cytoplasmic domain. The ECD belongs to the cytokine receptor homology class 1 (CRH1) family, consisting of two fibronectin type III (FNIII) domains with three potential disulfide bonds in the N-terminal FNIII domain and a WSXWS primary sequence motif in the C-terminal domain (Bazan 1990). Recruitment of kinases to the cytoplasmic tail of IL7R is required for signal transduction because the intracellular portion of IL7R does not contain intrinsic tyrosine kinase activity. IL7 interacts directly with the extracellular region of IL7R and this leads to the recruitment of the Cytokine receptor common subunit gamma (IL2RG, Gc) and formation of a receptor complex. IL7 binds glycosylated IL7R 300-fold more tightly than unglycosylated. It is thought that IL7 interacts with both IL7R and IL2RG in the final complex (McElroy et al. 2007).