Serotonin in human allergic contact dermatitis. An immunohistochemical and high-performance liquid chromatographic study.

Allergic contact dermatitis (ACD) is a common clinical condition leading to considerable morbidity. We have recently demonstrated that ketanserin, a serotonin antagonist, significantly inhibits nickel sulphate-induced ACD. Furthermore, serotonin-immunoreactive (IR) cells have previously been demonstrated in normal human cutaneous melanocytes. To further elucidate the role of serotonin in cutaneous contact hypersensitivity, we compared ACD involved skin and uninvolved skin from nickel-allergic patients, and normal skin from healthy volunteers, for the presence of serotonin-like immunoreactive cells using immunohistochemistry. In addition, serotonin concentrations in ACD involved and uninvolved skin were compared by high-performance liquid chromatography (HPLC). In the skin of normal healthy volunteers, the serotonin-IR cells were situated in the basal layer of the epidermis. In uninvolved skin the cells were also situated in the basal layer, but they were more numerous and the immunofluorescence intensity was greater. In involved skin, the IR cells were fewer and they were found higher up in the epidermis. Also, the configuration of these cells was different: they showed enlarged and elongated dendrites as well as dendritic spines. The serotonin antiserum-labelled cells in ACD involved skin were also NKI-beteb positive (the latter is known as a reliable marker of melanocytes). The concentration of serotonin in involved skin was significantly higher than that in uninvolved skin in ACD patients (P < 0.05). Taken together, our previous and present results indicate that serotonin plays an important role in ACD. The basal epidermal serotonin-IR cells are more dendritic in ACD, and are found more superficial in the epidermis, where they might release their content of serotonin, thereby influencing the inflammatory process.