FoxP3: a life beyond regulatory T cells.

This review analyzes the current dogma that FoxP3 functions exclusively in the regulatory T cells (Treg) and that FoxP3(+) Treg is indispensable for survival of immune competent mice. We outline evidence that FoxP3 is expressed well beyond Treg and that the FoxP3 mutation in thymic stromal cells causes defective thymopoiesis, which in turn leads to increased homeostatic proliferation. We argue that the lethal autoimmune disease in mice with germline mutation of FoxP3 is due to both lack of Treg and enhanced homeostatic proliferation.