The interleukin 2 receptor alpha chain (also known as CD25) is a protein that is encoded by the human IL2RA gene. The interleukin 2 receptor alpha chain (IL2RA) and beta chain (IL2RB) together with the common gamma chain (IL2RG) constitute the high affinity IL2 receptor. The homodimeric alpha chain (IL2RA) results in a low affinity receptor, while the homodimeric beta (IL2RB) chain produces an intermediate affinity receptor. Normally, integral membrane proteins, soluble IL2RA have been isolated and identified as being produced by extracellular proteolysis. Alternative spliced IL2RA mRNA has been isolated, but the significance of each mRNA is currently unknown. IL2RA is a type I transmembrane protein present on activated T cells, activated B cells, some thymocytes, myeloid precursors, and oligodendrocytes. Although IL2RA has been used as a marker to identify CD4+ FoxP3+ regulatory T cells in mice, it has been found that most resting memory T cells constitutively express IL2RA in humans. IL2RA is expressed in most B cell tumors, some acute non-lymphocytic leukemias, neuroblastomas, mastocytosis, and tumor infiltrating lymphocytes. It functions as a receptor for HTLV-1 and therefore is expressed in tumor cells of adult T-cell lymphoma/leukemia. Its soluble form (sIL-2R) may be elevated in these diseases and occasionally used to track disease progression. Daclizumab (trade name Zinbryta) is a therapeutic humanized monoclonal antibody used to treat adults with relapsing multiple sclerosis (MS). Daclizumab works by binding to CD25.
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