Dendritic cells and the immunity/tolerance decision

The role of dentritic cells in initiating the immune response has been well established. Recent studies point to an important role for DCs in the induction of peripheral tolerance as well. It was proposed that the role of DC in the immunity/tolerance decision could be associated simply with DC maturation states. However, it has been observed that immature DC do not process endocytosed antigens well to form MHC + peptide complexes and therefore self-specific T cells would not be able to recognize their ligands on immature DCs. Then how might immature DCs induce tolerance to self-antigens? Below it is discussed a new mechanism which might control whether the DCs behavior will be tolerogenic or immunogenic. The hypothesis proposed that DCs should have two maturation programs operating in absence/presence of Danger signals leading to mature-tolerogenic and mature-immunogenic phenotypes, respectively. (C) 2004 Published by Elsevier Ltd.