Neuroimmunological Mechanism of Pruritus in Atopic Dermatitis Focused on the Role of Serotonin

Although pruritus is the critical symptom of atopic dermatitis that profoundly affect the patients' quality of life, controlling and management of prurirtus still remains as unmet needs mainly due to the distinctive multifactorial pathogenesis of pruritus in atopic dermatitis. Based on the distinct feature of atopic dermatitis that psychological state of patients substantially influence on the intensity of pruritus, various psychotropic drugs have been used in clinic to relieve pruritus of atopic dermatitis patients. Only several psychotropic drugs were reported to show real antipruritic effects in atopic dermatitis patients including naltrexone, doxepin, trimipramine, bupropion, tandospirone, paroxetine and fluvoxamine. However, the precise mechanisms of antipruritic effect of these psychotropic drugs are still unclear. In human skin, serotonin receptors and serotonin transporter protein are expressed on skin cells such as keratinocytes, melanocytes, dermal fibroblasts, mast cells, T cells, natural killer cells, langerhans cells, and sensory nerve endings. It is noteworthy that serotonergic drugs, as well as serotonin itself, showed immune-modulating effect. Fenfluramine, fluoxetine and 2, 5-dimethoxy-4-iodoamphetamine significantly decreased lymphocyte proliferation. It is still questionable whether these serotonergic drugs exert the immunosuppressive effects via serotonin receptor or serotonin transporter. All these clinical and experimental reports suggest the possibility that antipruritic effects of selective serotonin reuptake inhibitors in atopic dermatitis patients might be at least partly due to their suppressive effect on T cells. Further studies should be conducted to elucidate the precise mechanism of neuroimmunological interaction in pruritus of atopic dermatitis.