Human IL-2 R alpha, also known as Tac antigen and as CD25, is a 272 amino acid (aa) precursor type I membrane protein with a 21 aa signal peptide, a 219 aa extracellular region, a 19 aa transmembrane region, and a 13 aa cytoplasmic domain. By itself, IL 2 R alpha binds IL-2 with low affinity. However, when IL-2 R alpha is associated with IL-2 R beta and the common gamma chain, a high affinity heterotrimeric receptor complex that transduces IL-2 signals is formed.
Image: IL-2 Rα staining of frozen tissue sections of human lymph node. Tissue sections were stained using anti-mouse ABC-HRP, NovaRed (red) substrate and Haematoxylin (blue) counterstain.