The cytokine protein Interleukin-2 is an important factor for the maintenance of CD4+ regulatory T cells. It plays a critical role in the differentiation of CD4+ T cells into a variety of subsets as well as promotes CD8+ T-cell and NK cell cytotoxicity. The IL-2 (Human) Colorimetric Detection Kit is designed for detecting and quantifying human interleukin-2 in cell culture medium. Only a few simple steps on a microtiter plate are required for the assay. First, the capture antibody is coated on a 96-well plate. Next, samples containing IL-2 are incubated on the coated plate followed by detecting the captured IL-2 with the detection antibody. Finally, the plate is treated with streptavidin-HRP followed by addition of a colorimetric HRP substrate to produce color, which can then be measured using a UV/Vis spectrophotometer microplate reader.