CD25, also known as IL2RA, is the alpha chain of the high-affinity interleukin-2 receptor, which is a heterotrimeric complex that also includes beta (IL2RB) and the common gamma chain (IL2RG). This receptor interacts with interleukin-2, a cytokine crucial for immune homeostasis. CD25 is typically expressed on activated T lymphocytes and plays a significant role in their proliferation and function. It is also found on certain B cells, where its expression can be upregulated by specific Toll-like receptor ligands. In addition to its role in the immune system, CD25 has potential as a therapeutic target in cancer treatment due to its expression on various tumor cells.