Stemcell, 200-1007, Human IL-21 ELISpot Kit

Human interleukin-21 (IL-21) ELISpot Kit is designed for the quantitative detection and enumeration of cells secreting human IL-21 in a suspension of peripheral blood mononuclear cells (PBMCs). ELISpot is commonly used for evaluating specific immune responses, such as determining the frequency of activated T cell subsets in response to antigenic stimulation. IL-21 is a signature cytokine secreted by activated T helper 17 (Th17) cells, which mediates immune responses against extracellular pathogens particularly at mucosal and epithelial barriers, and it plays a role in autoimmunity. ELISpot is highly sensitive and can detect secreted analytes at a single cell level. This assay is used in research of infectious diseases, cancers, allergies, and autoimmune diseases.

The assay is based on a modified version of the sandwich ELISA method, in which cells are added to ELISpot plates pre-coated with capture antibodies specific for the cytokine. The cytokine is then captured throughout the culture period and is detected by the addition of a biotinylated detection antibody, followed by streptavidin-alkaline phosphatase (SA-ALP), which binds to the biotinylated antibody. Addition of the chromogenic enzyme substrate 5-bromo-4-chloro-3-indolyl-1-phosphate (BCIP)/nitroblue tetrazolium (NBT), results in the formation of colored spots. The number, size, and intensity of these spots are directly proportional to the frequency of cytokine-secreting cells in the sample and the amount of analyte secreted.