A Low Interleukin-2 Receptor Signaling Threshold Supports the Development and Homeostasis of T Regulatory Cells

Interleukin-2 receptor (IL-2R) signaling is essential for T regulatory (Treg) cell development and homeostasis. Here, we show that expression of IL-2R beta chains that lack tyrosine residues important for the association of the adaptor Shc and the transcription factor STAT5 in IL-2R beta-deficient mice resulted in production of a normal proportion of natural Treg cells that suppressed severe autoimmunity related with deficiency in IL-2 or IL-2R. These mutant IL-2R beta chains supported suboptimal and transient STAT5 activation that upregulate the transcription factor Foxp3 to normal amounts in natural, but not induced, Treg cells. Nevertheless, gene expression profiling revealed many targets in peripheral natural Treg cells that were IL-2 dependent and a substantial overlap between the Treg cell IL-2-dependent gene program and the Treg cell transcriptional signature. Collectively, these findings demonstrate that a critical, and perhaps minor, subset of IL-2-dependent targets is indexed to a low IL-2R signaling threshold and that a substantial proportion of the Treg cell gene program is regulated by IL-2.