Dendritic cells: bridging innate and adaptive immunity in atopic dermatitis.

Much knowledge has been gained about the multifaceted functions of dendritic cells (DCs). The central role of various DC subtypes as bridges between innate and adaptive immunity has become more and more evident. However, a high number of differences exist in the expression of pattern-recognition receptors, the first sensors of the innate immune system, in particular Toll-like receptors (TLRs) by distinct DC subtypes (including myeloid and plasmacytoid DCs), their maturation stage, and tissue distribution, as well as state of health or disease. Furthermore, a plethora of variations in human and murine model systems have to be considered. This review sheds some light on this complex and rapidly growing field. It summarizes the most recent findings and deals with the role of TLR-expressing DCs as promoters of chronic inflammatory immune responses in patients with atopic dermatitis, as well as tolerogenic pathways. Therefore TLR-bearing DCs represent promising targets, which might help to improve tolerance induction during immunotherapeutic approaches in the future.