|Detection of CD25/IL-2 R alpha in Lymphocytes in Canine PBMCs by Flow Cytometry. Lymphocytes in canine peripheral blood mononuclear cells were stained with Mouse Anti-Canine CD4 APC‑conjugated Monoclonal Antibody (Catalog # FAB2410A) and either (A) Sheep Anti-Canine CD25/IL-2 R alpha PE‑conjugated Antigen Affinity-purified Polyclonal Antibody (Catalog # FAB6227P) or (B) Normal Sheep IgG Phycoerythrin Control (Catalog # IC016P). View our protocol for Staining Membrane-associated Proteins.|
IL-2 receptor alpha (IL-2 R alpha ), also known as CD25, is a 55-57 kDa type I transmembrane glycoprotein that belongs to the family of cytokine receptors that utilize the common gamma chain subunit ( gamma c). IL‑2 R alpha is primarily expressed on activated T cells, mast cells and on regulatory T cells plus regulatory B cells (1-3). The canine IL-2 R alpha cDNA encodes a 268 amino acid (aa) precursor that includes a 21 aa signal peptide, a 216 aa extracellular domain (ECD) with two Sushi domains, a 21 aa transmembrane segment, and a 10 aa cytoplasmic domain (4). Within the ECD, canine IL-2 R alpha shares 49%-60% aa sequence identity with human, mouse, and rat IL-2 R alpha. IL-2 R beta (CD122) and gamma c (IL‑2 R gamma /CD132) dimerize to form a constitutively expressed intermediate affinity IL-2 receptor (1, 5, 6). By itself, IL-2 R alpha binds IL-2 with low affinity. It associates with IL-2 R beta and gamma c to generate a ternary high affinity IL-2 receptor complex (7). 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 (8). In human, increased serum levels of soluble IL‑2 R alpha are found in some cancers and autoimmune disorders (9, 10). 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 (11, 12). 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 (11-13).