Transforming growth factor-beta: an important role in CD4+CD25+ regulatory T cells and immune tolerance.

The transforming growth factor-beta (TGF-beta) protein family is highly evolutionarily conserved and they have been implicated in many biological processes. Also, TGF-beta can exert pivotal functions in the immune system. It is widely accepted that regulatory T cells (Treg cells) play an important role in the maintenance of the immune homeostasis, but the underlying molecular mechanisms through which they can gain and/or perform suppressive functions in an active way remains to be defined. Though the engagement of TGF-beta in the Treg cells has been discounted for a period of time, an emerging body of data has established a close link between Treg cells and TGF-beta, as TGF-beta has been demonstrated to induce the expression of Foxp3, which acts as a master regulator for the development and function of Treg cells. We will, herein, focus on the crucial role of TGF-beta signaling in Treg cell biology and summarize the current studies regarding TGF-beta in the generation and function of CD4+CD25+Treg cells both in vivo and in vitro.