The JES6-5H4 monoclonal antibody specifically binds to mouse interleukin-2 (IL-2), a multifunctional cytokine that plays pivotal roles in immunity and tolerance. It is produced by activated T cells and affects the activation, growth, proliferation and/or differentiation of various cell types including T and B lymphocytes and their precursors, LAK cells, NK cells, and monocytes/macrophages. IL-2 mediates its biological activities by binding to IL-2 receptor complexes. The intermediate affinity IL-2R is comprised of IL-2Rβ (CD122) and common gamma chain (γc; CD132) subunits, whereas the high-affinity IL-2R is comprised of IL-2Rα (CD25), IL-2Rβ, and γc subunits. The JES6-5H4 monoclonal antibody binds to IL-2 and neutralizes its biological activity.