Recombinant Canine CD25/IL-2R alpha Protein, CF

IL-2 receptor alpha (IL-2 R alpha), also known as CD25, is a 55 kDa type I membrane 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 and on regulatory T cells (Treg) (1-3).  The canine IL-2 R alpha cDNA encodes a 268 amino acid (aa) precursor that includes a 20 aa signal peptide, a 217 aa extracellular domain (ECD) with two Sushi domains, a 19 aa transmembrane segment, and an 12 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 (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, 9). Increased serum levels of soluble IL‑2 R alpha are found in some cancers and immune disorders (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).