Interleukin 21 (IL21)

Interleukin 21 (IL-21), is a cytokine that has potent regulatory effects on cells of the immune system, including natural killer (NK) cells and cytotoxic T cells that can destroy virally infected or cancerous cells. This cytokine induces cell division/proliferation in its target cells. IL-21 elicits its effects on immune cells by interacting with a cell surface receptor known as the interleukin 21 receptor, IL-21R, that is expressed in bone marrow cells and various lymphocytes.

IL-21 is expressed in activated human CD4⁺ T cells but not in most other tissues. In addition, IL-21 expression is up-regulated in T_h2 and T_h17 subsets of T helper cells, as well as T follicular cells. Furthermore IL-21 is expressed in NK T cells regulating the function of these cells.