Regulation of epidermal Langerhans cells by calcitonin gene-related peptide

Skin is an immune organ which is heavily innervated. Recent findings of bidirectional interaction between nervous system and immune system in the skin suggest the dynamic regulation of skin condition by the nervous system and immune system. The human body is equipped with various protection mechanisms against environmental and psychological stimuli. The skin responds to the endogenous stress reaction as well as the external stimuli. It is often stated that some skin disorders, such as psoriasis and atopic dermatitis, are exacerbated by stress [1]. The linkage was confirmed in an animal model of contact hypersensitivity in our laboratory [2]. The results of the study indicated the importance of adrenal hormones and also of the existence of other factors contributing to the effect of stress. Keller's study also suggested participation of corticoid-independent mechanisms in suppression of lymphocyte by stress [3]. Central nervous system signals are transferred and the homeostasis of the body is maintained by the endocrine system and by the nervous system. Immune organs, including the thymus, spleen, and lymph nodes, are innervated. The skin is also a heavily innervated organ. Free nerve endings reach the epidermis. Various neuropeptides, such as calcitonin gene-related peptide (CGRP), substance P, and vasoactive intestinal peptide, are found in the skin [4]. This article reviews some findings on neurologic influences on antigen presentation within the epidermis. These studies suggest the functional regulation of antigen presenting cells by nerves.