|Detection of CD25/IL-2 R alpha in Rat Splenocytes by Flow Cytometry. Rat splenocytes were stained with APC-conjugated anti-rat CD4 antibody and either (A) Mouse Anti-Rat CD25/IL-2 R alpha PE‑conjugated Monoclonal Antibody (Catalog # FAB51561P) or (B) Mouse IgG1 Phycoerythrin Isotype Control (Catalog # IC002P). View our protocol for Staining Membrane-associated Proteins.|
IL-2 receptor alpha (IL-2 R alpha ), also known as CD25, is a 55 kDa type I transmembrane (TM) glycoprotein that functionally belongs to a family of cytokine receptors that utilize the common gamma chain subunit ( gamma c) (1-3). IL-2 R alpha is expressed on activated T cells, and on regulatory T cells (Treg), mast cells, fibroblasts, NK cells, endthelial cells and pre-B cells (4-6). The rat IL-2 R alpha cDNA encodes a 267 amino acid (aa) precursor that includes a 21 aa signal peptide, a 214 aa extracellular domain (ECD) with two Sushi domains, a 21 aa transmembrane segment, and an 11 aa cytoplasmic domain (7). Within the ECD, rat IL-2 R alpha shares 58% and 81% aa sequence identity with human and mouse IL-2 R alpha, respectively. It shares approximately 15% aa sequence identity with IL-4, -7, -9, -15, and -21 receptor subunits that also complex with gamma c. By itself, IL-2 R alpha binds IL-2 with low affinity. It then associates with IL-2 R beta and subsequently to gamma c to generate a ternary high affinity IL-2 receptor complex. Notably, it would appear that IL-2 R alpha also plays a role in the formation of supramolecular membrane complexes that also include MHC-II molecules and additional gamma c -related alpha -chains (8). A soluble form of IL-2 R alpha can be generated by proteolytic cleavage of the cell surface receptor, rendering the T cell unresponsive to IL-2 (9, 10). Increased serum levels of soluble IL-2 R alpha are found in some cancers and immune disorders (11). IL-2 R alpha is required for activation induced cell death (AICD) of naive T cells, a mechanism responsible for deleting autoreactive T cell clones (12, 13). IL-2 R alpha is also required for the development of CD4+CD25+ Treg which suppress autoreactive CD4+ T cells, thereby contributing to peripheral T cell homeostasis (12-15).