The I76-539 antibody reacts with interleukin-21 (IL-21), an ~ 15 kDa member of the type-I-cytokine family of proteins. IL-21 is expressed primarily by CD4+ T cells and has a broad range of immunoregulatory functions on B cells, CD8+ T cells, NK cells and dendritic cells. The effects of IL-21 include promotion of antibody production, NK cell differentiation, proliferation and differentiation of cells of monocyte and granulocyte lineages, costimulation of T cells and augmentation of antitumor activity of CD8+ T cells. It has been speculated that IL-21, through its varies positive and negative regulatory effects on cell-mediated and humoral immunity, may play a role in autoimmuninty, allergy, asthma and tumor regression. Human IL-21 sandwich ELISA curve: The curve was generated by a sandwich ELISA using the purified J148-1134 as capture antibody(Cat. No. 558503), doubling dilutions of recombinant human IL-21 protein and biotin I76-539 as detection antibody. Streptavidin-HRP (Cat. No. 554066) plus TMB substrate (Cat. No. 555214)were used to develop the ELISA.