Background：CD122 is a 70-75 kD type I transmembrane glycoprotein and member of the Ig superfamily. It is IL-2 receptor b chain also known as IL-2Rb, which is also shared by the IL-15 receptor. CD122 is constitutively expressed by NK cells and at lower levels by a subset of T cells. Its expression is upregulated upon activation. The IL-2Rb chain can combine with either the common gamma subunit （gammac, CD132） alone or with the gammac subunit and the IL-2Ra subunit （CD25） to generate intermediate or high affinity IL-2 receptor complexes, respectively. CD122 expression levels can be upregulated by activation.
