CD25, also known as IL2RA, is the alpha chain of the interleukin-2 receptor, a heterotrimeric protein complex that also includes beta （IL2RB） and the common gamma chain （IL2RG）. It is a membranous glycoprotein primarily expressed on activated T lymphocytes and plays a crucial role in immune homeostasis by interacting with interleukin-2, a pleiotropic cytokine. CD25 is involved in the proliferation of T and B lymphocytes and is essential for the assembly of the high-affinity interleukin-2 receptor. In addition to its role in the immune system, CD25 is also expressed on certain non-immune cells and has been identified as a potential therapeutic target in cancers.