Discription：Human IL-21 is encoded by IL-21 gene located on Chr.4. It is a pleiotropic cytokine produced by CD4+ T cells in response to antigenic stimulation and can regulating immune system cells, for instance cytotoxin T cells and natural killer cells. Additionally, it can induce target cells division or proliferation. IL-21 elicits its effect through binding to IL-21R, which also contains the gamma chain found in other cytokine receptors such as IL-2, IL-4, IL-7, IL-9 and IL-15. IL-21 shows having much relation with clinical illnesses, including cancer immunotherapy, viral infections and allergies. Mature human IL-21 protein shares 63％ and 61％ aa sequence identity with mouse and rat IL-21 protein, respectively. Recombinant IL-21 is a single non-glycosylated polypeptide chain containing 133 amino acids
