CD25 is a 55 kD type I transmembrane glycoprotein also known as the low affinity IL-2 receptor α chain or Tac. It is expressed on progenitor lymphocytes, activated T and B cells, and activated monocytes/macrophages. CD25 is also expressed on a subset of non-stimulated CD4+ T cells termed T regulatory cells. CD25 associates with the IL-2 receptor β (CD122) and common γ chains (CD132) to form the high affinity IL-2R complex.
