Dendritic cells and (CD4+)CD25+ T regulatory cells: crosstalk between two professionals in immunity versus tolerance.

Dendritic cells (DCs) are professional antigen presenting cells (APCs). (CD4+)CD25+ T regulatory cells (T regs) are recognized as professional regulatory cells. DCs not only initiate T cell immunity by uptake, processing and presentation of specific antigens, but also induce immune tolerance by deletion of T cells and/or induction of regulatory T cells. (CD4+)CD25+ T regs maintain immune tolerance by suppressing the function of CD4+ and CD8+ T cells, B cells, macrophages, DCs and NK cells. It would be inconceivable that the delicate balance between immunity and tolerance could be kept impeccable without the crosstalk between DCs and (CD4+)CD25+ T regs. This review focuses on the recent development in our understanding of DCs and (CD4+)CD25+ T regs in immune tolerance, with transforming growth factor-beta (TGF-beta) serving as a potential link between these two professionals.