protein_function: Receptor for interleukin-2.
CD25 is the alpha chain of the IL-2 receptor. It is a type I transmembrane protein present on activated T cells, activated B cells, some thymocytes, myeloid precursors, and oligodendrocytes that associates with CD122 to form a heterodimer that can act as a high-affinity receptor for IL-2. CD25 has been used as a marker to identify CD4+FoxP3+ regulatory T cells in mice. By in situ hybridization, the IL2R gene was mapped to 10p15-p14. Its soluble form, called sIL-2R may be elevated in these diseases and is occasionally used to track disease progression.