Interleukin 2 (IL-2) is a pleiotropic cytokine produced primarily by mitogen- or antigen-activated T lymphocytes (1, 2). Human IL-2 (also known as T-cell growth factor) is produced by T-cells in response to antigenic or mitogenic stimulation. IL-2 is a potent lymphoid cell growth factor which exerts its biological activity primarily on T cells promoting proliferation and maturation.

IL-2 has been found to stimulate growth and differentiation of B cells, NK cells, LAK cells, monocytes, and oligodendocytes. IL-2 is involved in treatment of cancers such as melanoma and renal cell cancer. It plays a key role in promoting the clonal expansion of antigen-specific T cells. In addition, IL-2 has also been shown to mediate multiple immune responses on a variety of cell types.

The sequence of human IL-2 cDNA predicts a 153 amino acid (aa) residue precursor glycoprotein containing a 20 aa residue signal peptide that is cleaved to form the mature protein (3). At the amino acid sequence level, mouse IL-2 is approximately 60% identical to human IL-2 (1, 2, 4, 5). Whereas human IL-2 is active on mouse cells, mouse IL-2 is species-specific and is inactive on human cells. The gene for IL-2 has been mapped to human chromosome 4q (6).

The biological effects of IL-2 are mediated by specific cell surface receptor complexes. The functional high-affinity receptor for IL-2 is composed of three distinct polypeptide chains (7, 8).

IL-2 stimulates the proliferation of thymocytes; stimulates the proliferation and differentiation of activated B cells; promotes the growth, differentiation and cytocidal activity of monocytes; induces the growth of natural killer cells and stimulates cytokine production by these cells as well as the cytolytic activity of these cells; enhances the production of lymphocyte-activated killer (LAK) cells; and induces the proliferation and differentiation of oligodendrocytes (1, 2).