Dendritic cells: key cells for the induction of regulatory T cells?

Even though dendritic cells (DCs) are well known for their capacity to induce immune responses, recent results show that they are also involved in the induction of tolerance. These two contrary effects of otherwise homologous DCs on a developing immune response maybe explainedby different DC developmental stages, i.e., different subsets of DCs may exist and/or different spatial distribution of DCs in the body might influence their function. However, independently from the subtype(s), it is obvious that the ability of DCs to act in a tolerogenic fashion depends on the maturation status, since immature DCs are prone to induce regulatory T cells and hence promote tolerance, whereas mature DCs stimulate effector T cells, facilitating immunity. The means by which DCs convey tolerance are not entirely clear yet, but secretion of suppressive cytokines such as IL-10 and induction of regulatory lymphocytes are involved. In this review we focus on the interaction between DCs and T cells and highlight some mechanisms in the decision-making process of whether immunity or tolerance is induced.