The main function of IL‐2 is to promote the development of T regulatory cells

Based primarily on vitro studies, interleukin (IL)‐2 has been considered a key growth and death factor for antigen‐activated T lymphocytes. IL‐2 is also essential to maintain self‐tolerance, as IL‐2‐ and IL‐2 receptor‐deficient mice exhibit lethal autoimmunity. The intrinsic death‐sensitizing activity of IL‐2 was thought to be a key mediator for apoptosis of peripheral autoreactive T cells. However, recent in vivo studies strongly favor a model whereby IL‐2 controls autoimmunity through the production of CD4+CD25+ T regulatory (Treg) cells. In this setting, IL‐2 is essential for expansion of Treg cells within the thymus and in peripheral neonatal‐immune tissue. Thus, from being considered the primary growth factor for antigen‐activated T lymphocytes, these new findings redefine the pivotal role for IL‐2 as the major inducer for the developmental production of suppressive Treg cells.

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