Regulatory T cells prevent catastrophic autoimmunity throughout the lifespan of mice

Mice lacking the transcription factor Foxp3 (Foxp3−) lack regulatory T (Treg) cells and develop fatal autoimmune pathology. In Foxp3− mice, many activated effector T cells express self-reactive T cell receptors that are expressed in Treg cells in wild-type mice. Thus, in wild-type mice, most self-reactive thymocytes escaping negative selection are diverted into the Treg lineage, and whether Treg cells are critical in self-tolerance in wild-type mice remains unknown. Here, acute in vivo ablation of Treg cells demonstrated a vital function for Treg cells in neonatal and adult mice. We suggest that self-reactive T cells are continuously suppressed by Treg cells and that when suppression is relieved, self-reactive T cells become activated and facilitate accelerated maturation of dendritic cells.