CD123, also known as Interleukin-3 receptor subunit alpha, belongs to the type I cytokine receptor family. In mouse, there are two classes of high-affinity IL3 receptors. One contains an IL3-specific beta subunit and the other contains the beta subunit also shared by high-affinity IL5 and GM-CSF receptors. CD123 stimulates the proliferation and differentiation of hemopoietic cells including the pluripotent hematopoietic stem cells as well as various lineage‑committed cells. CD123 is a heterodimer consisting of an alpha and a beta subunit. The alpha subunit alone binds IL‑3 with low affinity. The beta subunit does not bind IL‑3 by itself but is required for the high‑affinity binding of IL‑3 to the heterodimeric receptor complex.