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 induction of differentiation of T cells-stimulated B-cells into plasma cells and memory B-cells, stimulation (in conjuction) with IL-4 of IgG production and induction of apoptotic effects in 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 ɣ chain (ɣc) 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 human IL-21 is a 15.4 kDa protein consisting of 132 amino acid residues.
Amino Acid Sequence
Assay #1: Measured by its ability to increase proliferation in mouse splenocytes induced by anti-hCD40 mAb. The expected ED50 is 15–20 ng/ml. Assay #2: Determined by its ability to stimulate the proliferation of human ANBL-6 cells. The expected ED50 is ≤ 1.0 ng/ml, corresponding to a specific activity of ≥ 1×106 units/mg
Endotoxin level is <0.1 ng/μg of protein (<1EU/μg).
Centrifuge the vial prior to opening. Reconstitute in water to a concentration of 0.1–1.0 mg/ml. Do not vortex. This solution can be stored at 2–8°C for up to 1 week. For extended storage, it is recommended to further dilute in a buffer containing a carrier protein (example 0.1% BSA) and store in working aliquots at –20°C to –80°C.