[Neuro-immuno-cutaneous system (NICS)].

The concept of neuro-immuno-cutaneous system (NICS) means narrow interrelations between nervous system, immunity and skin. Indeed, there are numerous cellular contacts between nerve fibers, cutaneous cells and immune cells; cutaneous cells can synthesize neuromediators and they express receptors to these molecules; neuromediators are able to modulate functions of cutaneous and/or immune cells. Using confocal or electron microscopy, connexions between nerve fibers and cutaneous cells have been observed. In the skin, nerve fibers may secrete neuromediators: substance P, vaso-active intestinal peptide (VIP), somatostatin, calcitonin-gene related peptide (CGRP), gastrin-releasing peptide (GRP), neuropeptide Y, peptide histidine-isoleucine (PHI), neurotensin, neurokinins A et B, bradykinin, acetylcholine, catecholamines, endorphins and enkephalins. Neurohormones such as prolactin, melano-stimulating hormone (MSH) or adreno-corticotrophic hormone (ACTH) are also expressed in the skin. Neuromediators and neurohormones are also secreted by cutaneous cells and these cells express receptors. Functions of epidermal or dermal cells are modulated by these substances. Immune cells transiently present in the skin (macrophages, lymphocytes...) are modulated by neuromediators through receptors. In the course of skin diseases, especially inflammatory diseases, the NICS is destabilized. Psoriasis and atopic dermatitis are good examples. This phenomenon might be due to inflammation but is also responsible for induction and maintenance of the inflammation.