Role of mast cells and sensory nerves in skin inflammation.

Mast cells are powerful inflammatory cells which are in close functional and anatomical association with sensory nerves in the skin. During psychological stress the neuroendocrine system and peripheral sensory nerves are activated leading to release of mediators, such as neuropeptides, neurotrophins, corticotropin-releasing hormone and a-melanocyte-stimulating hormone, which are capable of activating mast cells. On the other hand, mast cell mediators released, e.g. histamine, tryptase and nerve growth factor, can in turn excite and stimulate surrounding neuropeptide-containing C-fibers possibly resulting in feedforward loop and potentiation of neurogenic inflammation. In these mechanisms, proinflammatory cytokines and chemokines are released from mast cells. In chronic skin diseases, psoriasis, atopic dermatitis and palmoplantar pustulosis, the contacts between tryptase-positive mast cells and sensory nerves are increased in number, which provides the morphological basis for increased mast cell - sensory nerve interaction in chronically inflamed skin. Hence, in this review the current understanding of the role of cutaneous mast cells and sensory nerves and their activation in psychic stress is discussed.