Regulation of regulatory T cells: role of dendritic cells and toll-like receptors.
Regulatory T cells (Treg) are characterized by high-level surface CD25 and intracellular FoxP3 expression. Treg are instrumental in the maintenance of peripheral immune tolerance and the control of adaptive immune responses. Naturally occuring Treg suppress T-cell responses by cell contact-dependent mechanisms, whereas induced regulatory cells, including Tr1 cells, secrete inhibitory cytokines such as transforming growth factor (TGF)-beta and interleukin-10. The interplay between Treg and antigen-responsive T cells is modulated by dendritic cells (DC). Whereas immature myeloid precursors of DC suppress T-cell activation per se and immature DC support Treg development, mature DC can override Treg-mediated suppression in vitro and in vivo. Mature DC activated through Toll-like receptor (TLR) pattern recognition receptors produce proinflammatory cytokines, including interleukin-6, which render responder T cells refractory to the suppressive effect of Treg. In addition, Treg also express certain TLR, and the activation and/or suppressor function of Treg is modulated directly by the respective ligands. In this review, we discuss current models of how signals delivered through innate immune receptors in response to pathogen-associated molecular patterns affect adaptive immune responses via modulation of Treg function.
Kabelitz
Dieter
D
Institute of Immunology, UK S-H Campus Kiel, Michaelisstr. 5, D-24105 Kiel, Germany. kabelitz@immunologie.uni-kiel.de
Wesch
Daniela
D
Oberg
Hans-Heinrich
HH
D000818:Animals; D003713:Dendritic Cells / Q000276:immunology*; D006801:Humans; D008024:Ligands; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D051193:Toll-Like Receptors / Q000502:physiology*
D008024:Ligands; D051193:Toll-Like Receptors