Mast cells, nerves and neuropeptides in atopic dermatitis and nummular eczema.

The association between mast cells and sensory nerves and the distribution of the neuropeptides substance P (SP), vasoactive intestinal polypeptide (VIP) and calcitonin gene-related peptide (CGRP) were studied immunohistochemically in lesional and nonlesional skin of 26 atopic dermatitis (AD) and 23 nonatopic nummular eczema (NE) patients. Mast cell-nerve contacts were counted morphometrically and confirmed by confocal laser scanning microscopy. Neuropeptide positivity was assessed semiquantitatively. Dermal contacts between mast cells and nerves were increased in number in both lesional and nonlesional samples of AD and NE when compared to those in normal controls, although only the values in lesional AD reached statistical significance ( P<0.05). Nerve-mast cell contacts in the basement membrane zone were seen practically only in lesional NE. SP and CGRP fibres were prominently increased in lesional samples when compared to their nonlesional controls both in AD and NE in the epidermis and in the papillary dermis. In both AD and NE, only small differences were found regarding VIP positivity in lesional and nonlesional biopsies. The epidermis was devoid of VIP positivity. In conclusion, SP and CGRP but not VIP fibres were more frequent in lesional than in nonlesional papillary dermis of both AD and NE. Since mast cells are also increased in number in lesions of AD and NE, they are able to maintain neurogenic inflammation through activation by SP and CGRP. The increased SP/CGRP nerves in the epidermis of AD and NE lesions may stimulate keratinocytes to release cytokines which affect various cell types enhancing inflammation.