Interleukin-21 receptor (IL21R) is also known as CD antigen CD360, Novel interleukin receptor (NILR), is a receptor for interleukin-21 and belongs to the type I cytokine receptor family or type 4 subfamily. IL21R contains two fibronectin type-III domains. IL21R is selectively expressed in lymphoid tissues and most highly expressed in thymus and spleen. IL21R transduces the growth promoting signal of IL21, and is important for the proliferation and differentiation of T cells, B cells, and natural killer (NK) cells.