Expression of serotonin receptors in allergic contact eczematous human skin

The expression of the serotonin (5-HT) receptors 5-HT1AR, 5-HT2AR and 5-HT3R was investigated in allergic contact eczematous human skin by an indirect fluorescence method. 5-HT1AR expression was found in basal epidermal NK1-beteb-positive cells, which were more elongated and showed longer dendritic processes in contact eczematous skin than in control skin. Immunoreactivity for 5-HT1AR was also found in the upper part of the epidermis, with no difference between eczematous and control skin. 5-HT1AR expression was also found in 33.3+/-6.5% and 63.7+/-11.3% of papillary dermal mononuclear cells in inflamed skin and control skin, respectively ( P<0.001), as well as in vessel walls. Some of these mononuclear cells were tryptase-positive, and found in both eczematous and control skin. 5-HT2AR-positive cells were found in the upper part of the epidermis in eczematous skin, but were more evenly distributed in the epidermis of control skin. In addition, inflammatory dermal mononuclear cells and vessel walls showed immunoreactivity for this receptor. 5-HT3R expression was found in the basal epidermal layer of eczematous and control skin. These findings indicate a plasticity in the effects of serotonin, especially regarding 5-HT1AR, in allergic contact eczematous skin.