Mouse interleukin 2 (IL-2) is a T cell-derived cytokine known to promote growth and differentiation of T cells and to have pleiotropic effects on many other leukocytes. IL-2 is rapidly secreted upon activation by naive T helper cells and certain subsets of memory cells. Mature mouse IL-2 is a 15.5 kDa protein containing 133 amino acid residues after several posttranslational processing. It is primarily produced by activated T and B cells and macrophages in mice. It is also produced by other cell types such as fibroblasts and CD24+ cells when stimulated by TNF-α, IL-1, IL-2 and IFN-γ. Mouse IL-2 stimulates growth of macrophages, granulocytes, dendritic cells and other granulose cells. There are two kinds of IL-2, a membrane-bound form and a soluble form in a complex associated with the extracellular matrix. Both play biological functions based on research. In addition, recombinant IL-2 generated in E. coli is nonglycosylated but is biologically active.