Interleukin 2 was initially identified as a T cell growth factor that is produced by T cells following activation by mitogens or antigens. Since then, it has been shown that in addition to its T cell growth factor activity, IL-2 can also stimulate the growth and differentiation of B cells, natural killer (NK) cells, lymphocyte activated killer (LAK) cells, monocytes/macrophages and oligodendrocytes. At the amino acid sequence level, there is approximately 72% similarity between mature porcine and human IL-2.
The biological activity of IL-2 is mediated by the binding of IL-2 to cell surface receptor complexes. The functional high-affinity receptor of IL-2 is composed of three distinct polypeptide chains, the IL-2 receptor alpha, beta and gamma subunits. The intermediate-affinity IL-2 receptor complex, which lacks the alpha subunit, but contains both the beta and gamma subunits, is also capable of transducing the IL-2 signal. In T cells, the beta and gamma subunits are shared with the IL-15 receptor complex. The gamma chain of the IL-2 receptor complex has also been shown to be a subunit of the receptor complexes of IL-4, IL-7, and IL-9.