Interleukin-2 (IL2), also known as a T-cell growth factor, TCGF, and Aldesleukin, is a secreted protein that belongs to the IL-2 family. IL2 has potent stimulatory activity for antigen-activated T cells, and is expressed by T cells, B cells, dendritic cells, and eosinophils [1-3]. Mature human IL-2 shares 56% aa sequence identity with mouse IL-2. Human and mouse IL-2 exhibit cross-species activity [4]. The receptor for IL-2 consists of three subunits that are present on the cell surface in varying preformed complexes [5-7]. The 55 kDa IL-2 R alpha is specific for IL-2 and binds with low affinity. The 75 kDa IL-2R beta, which is also a component of the IL-15 receptor, binds IL-2 with intermediate affinity. The 64 kDa common gamma chain gamma c/IL-2 R gamma, which is shared with the receptors for IL-4, -7, -9, -15, and -21, does not independently interact with IL-2. Upon ligand binding, signal transduction is performed by both IL-2 R beta and gamma c. IL-2 is best known for its autocrine and paracrine activity on T cells. It drives resting T cells to proliferate and induces IL-2 and IL-2 R alpha synthesis [1,2]. It contributes to T cell homeostasis by promoting the Fas-induced death of naive CD4+ T cells but not activated CD4+ memory lymphocytes [8]. IL-2 plays a central role in the expansion and maintenance of regulatory T cells, although it inhibits the development of Th17 polarized cells [9-11]. Thus, IL-2 may be a key cytokine in the natural suppression of autoimmunity [12,13].
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[12]. Afzali, B. et al. (2007) Clin. Exp. Immunol. 148:32.
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