Description: The rabbit polyclonal antibody reacts with human IL-21; the antibody was raised against a synthetic peptide (tcpscdsyekkppke) corresponding to amino acids 121 to 135 of human IL-21 precursor (1). A novel cytokine was recently identified in human and mouse and designated IL-21 (1), which has significant homology to IL-2, IL-4, and IL-15. The receptor for IL-21 (IL-21R, also termed NILR for novel Interleukin receptor) is a new member of the class I cytokine receptor family (1,2). IL-21R forms a complex with the common cytokine receptor g chain, gc, and mediates IL-21 signaling (3,4). IL-21 and its receptor activate JAK-STAT signaling pathway. IL-21 is expressed in activated T cells, and HL-60 and THP-1 cell lines. IL-21 plays a role in the proliferation and maturation of NK, B and T cell populations.