IL-21 (interleukin-21) belongs to the IL-2 cytokine family. It is secreted by CD4+ T, natural killer (NK) and Th17 cells. IL-21 associates with IL-21 receptor and participates in B-cell proliferation, differentiation as well as apoptosis. It also promotes the cytotoxic activity of CD8+ T cells and natural killer cells.IL-21 plays a crucial role in the differentiation of follicular helper T cells. It also exhibits antitumor activity. It is also involved in the activation of JAK-ST at (Janus kinase - signal transducer and activator of transcription), PI3K (phosphatidylinositol 3-kinase) and MAPK (mitogen activated protein kinase) pathways.', 'IL-21 and its receptor have important roles in T and B cell proliferation and natural killer cell maturation. Human and mouse IL-21 share 57% amino acid identity.
