Interleukin-7 receptor subunit alpha (IL7R-α) also known as CD127 (Cluster of Differentiation 127) is a protein that in humans is encoded by the IL7R gene. IL7R-α is a type I cytokine receptor and is a subunit of the functional Interleukin-7 receptor and Thymic Stromal Lymphopoietin (TSLP) receptors that plays an important role in lymphocyte differentiation, proliferation, and survival. IL-7 R alpha is expressed on double negative (CD44-/CD8+) and CD4+ or CD8+ single positive T cells as well as on CD8+ memory T cells and their precursors. It is expressed early in B cell development, prior to the appearance of surface IgM. IL-7 induces the downregulation and shedding of cell surface IL‑7 R alpha.IL-7 R alpha additionally associates with TSLP R to form the functional receptor for thymic stromal lymphopoietin.