Quantitative analysis of contact sites between mast cells and sensory nerves in cutaneous psoriasis and lichen planus based on a histochemical double staining technique.

The aim of the present study was to test further our previous hypothesis that the inflammatory reaction in psoriasis is neurogenic. For this purpose, contact sites between mast cells and sensory nerves were morphometrically analysed in the basement membrane zone, papillary dermis and three dermal zones of lesional/non-lesional psoriatic and lichen planus skin as well as in healthy control skin. The analyses were made on sections stained with a histochemical double stain developed for this study. With the double stain, active mast cell tryptase was stained blue enzyme histochemically, and the sensory nerves black using specific monoclonal anti-neurofilament antibodies with immunogold. In psoriatic lesions, both mast cells and mast cell--nerve contacts were markedly more frequent in the basement membrane zone and in the papillary dermis when compared with the corresponding areas in the other groups. Mast cell numbers were increased in both lesional and symptom-free skin in lichen planus, but no increase was found in the mast cell--nerve contacts. Increased contacts between mast cells and sensory nerves indicate that the elements exist for neurogenic inflammation in psoriatic lesions. These increased contacts are not due to the extensive inflammatory reaction only, because they were not observed in lichen planus lesions.