Time-dependent modulation of serotonin and its receptors 1A and 2A expression in allergic contact dermatitis.

Background  Serotonin implication in allergic contact dermatitis was earlier suggested. Objective  To study the expression of serotonin (5-HT) and its receptors 1A and 2A during the kinetics of allergic contact dermatitis (ACD). Method  Biopsies from 10 female nickel-allergic patients were obtained at 0, 6, 24, 48 and 72 h after nickel application using a patch testing procedure and then analysed by immunohistochemistry. Results  Higher 5-HT epidermal immunoreactivity was seen at 0 and 6 h compared with 24, 48 and 72 h. The number of 5-HT labelled platelets was higher at 48 and 72 h compared with 0, 6 and 24 h. There was a decrease in the number of 5-HT1AR positive cells at 24, 48 and 72 h compared with 0 h. Furthermore, epidermal 5-HT1AR immunoreactivity was stronger at 48 and 72 h compared with 0 h. Total (dermis plus epidermis) number of 5-HT2AR positive cells was gradually increased in a time-dependent manner at 6, 24, 48 and 72 h compared with 0 h. Conclusions  Our results suggest the implication of 5-HT, 5-HT1AR and 5-HT2AR in the development of human ACD and the possibility to target those receptors at an early stage of this inflammatory condition.