Diversity of TCRs on natural Foxp3⁺ T cells in mice lacking Aire expression

Medullary thymic epithelial cells expressing the Aire gene play a critical role in the induction of tolerance to tissue-specific Ags (TSAs). It was postulated that recognition of Aire-controlled TSAs by immature thymocytes results in the selection of natural CD4⁺Foxp3⁺ regulatory T cells (Tregs) and enriches this repertoire in self-reactive receptors, contributing to its vast diversity. In this study, we compared the TCRs on individual Tregs in Aire⁺ and Aire^- mice expressing a miniature TCR repertoire (TCR^mini) along with GFP driven by the Foxp3 promoter (Foxp3^GFP). The Treg TCR repertoires in Aire⁺ and Aire^- TCR^miniFoxp3^GFP mice were similar and more diverse than their repertoires on CD4⁺ Foxp3^- thymocytes. Further, TCRs found on potentially self-reactive T cells, with an activated phenotype (CD4⁺Foxp3^-CD62L^low) in Aire^- TCR^miniFoxp3^GFP mice, appear distinct from TCRs found on Tregs in Aire⁺ TCR^miniFoxp3 ^GFP mice. Lastly, we found no evidence that TSAs presented by medullary thymic epithelial cells in Aire⁺TCR^mini mice are often recognized as agonists by Treg-derived TCR hybridomas or CD4 ⁺CD25⁺ thymocytes, containing both natural Tregs and precursors. Thus, positive selection and self-reactivity of the global Treg repertoire are not controlled by Aire-dependent TSAs.