Figure 1.

Cytokine contributions to regulatory T-cell (Treg) maturation in the thymus. Tregs develop from CD4 single-positive (SP) thymocyte precursors. Signaling through a high-affinity, self-reactive T-cell receptor (TCR) combined with CD28 costimulation is thought to trigger up-regulation of CD25. This potentiates the ability of Treg precursors to respond to interleukin (IL)-2, which prevents apoptosis, induces Foxp3 expression, and establishes Treg transcriptional identity and suppressive capacity. Boxes with dotted lines denote developmental stages where other cytokines may act. Dotted arrows denote a possible parallel pathway of Treg development. TGF-β, Transforming growth factor β.