Interleukin-2(IL-2)is a O-glycosylated four α-helix bundle cytokine that has potent stimulatory activity for antigenactivated T cells. It is expressed by CD4+ and CD8+ T cells, γδ T cells, B cells, dendritic cells, and eosinophils. Mature rat IL-2 shares 66% and 73% amino acid sequence identity with human and mouse IL-2,respectively. The receptor for IL-2 consists of three subunits that are present on the cell surface in varying preformed complexes. IL-2 is a powerful immunoregulatory lymphokine produced by T-cells in response to antigenic or mitogenic stimulation. IL-2/IL-2R signaling is required for T-cell proliferation and other fundamental functions that are essential for the immune response. IL-2 stimulates growth and differentiation of B-cells, NK cells, lymphokine-activated killer cells, monocytes, macrophages and oligodendrocytes.