Cell-Intrinsic NF-κB Activation Is Critical for the Development of Natural Regulatory T Cells in Mice

Background: Naturally occurring CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells develop in the thymus and represent a mature T cell subpopulation critically involved in maintaining peripheral tolerance. The differentiation of Treg cells in the thymus requires T cell receptor (TCR)/CD28 stimulation along with cytokine-promoted Foxp3 induction. TCR-mediated nuclear factor kappa B (NF-kappa B) activation seems to be involved in differentiation of Treg cells because deletion of components of the NF-kappa B signaling pathway, as well as of NF-kB transcription factors, leads to markedly decreased Treg cell numbers in thymus and periphery. Methodology/ Principal Findings: To investigate if Treg cell-intrinsic NF-kappa B activation is required for thymic development and peripheral homeostasis of Treg cells we used transgenic (Tg) mice with thymocyte-specific expression of a stable I kappa B alpha mutant to inhibit NF-kappa B activation solely within the T cell lineage. Here we show that Treg cell-intrinsic NF-kappa B activation is important for the generation of cytokine-responsive Foxp3(-) thymic Treg precursors and their further differentiation into mature Treg cells. Treg cell development could neither be completely rescued by the addition of exogenous Interleukin 2 (IL-2) nor by the presence of wild-type derived cells in adoptive transfer experiments. However, peripheral NF-kappa B activation appears to be required for IL-2 production by conventional T cells, thereby participating in Treg cell homeostasis. Moreover, pharmacological NF-kappa B inhibition via the I kappa B kinase beta (IKK beta) inhibitor AS602868 led to markedly diminished thymic and peripheral Treg cell frequencies. Conclusion/Significance: Our results indicate that Treg cell-intrinsic NF-kappa B activation is essential for thymic Treg cell differentiation, and further suggest pharmacological NF-kappa B inhibition as a potential therapeutic approach for manipulating this process.