Growth Factors & Cytokines

IL‐21 is a pleiotropic cytokine produced by CD4+ T cells in response to antigenic stimulation. Its action generally enhances antigen‐specific responses of immune cells. The biological effects of IL‐21 include: inducing the differentiation of T cell‐stimulated B cells into plasma cells and memory B cells; the stimulation of IgG production in conjunction with IL‐4; and the induction of apoptotic effects in naïve B cells and stimulated B cells in the absence of T cell signaling. Additionally, IL‐21 promotes the anti‐tumor activity of CD8+ T cells and NK cells. IL‐21 exerts its effect through binding to a specific type I cytokine receptor, IL‐21R, which also contains the γ chain (γc) found in other cytokine receptors, including IL‐2, IL‐4, IL‐7, IL‐9 and IL‐15. The IL‐21/IL‐21R interaction triggers a cascade of events, which includes activation of the tyrosine kinases JAK1 and JAK3, followed by activation of the transcription factors STAT1 and STAT3. Recombinant Rat IL‐21 is a 15.3 kDa protein containing 130 amino acid residues.