Role of neurokinin-1 receptor in the initiation and maintenance of skin chronic inflammatory diseases.

To fulfill its immunologic functions, the skin is richly populated with dendritic cells (DCs), the most potent professional Ag-processing and Ag-presenting cells of the immune system. The immune-stimulatory and tolerogenic functions of skin DCs are regulated by the immune and neuroendocrine systems. Pro-inflammatory neuropeptides like substance P and calcitonin gene-related peptide secreted by cutaneous Aδ and C nerve fibers are the main initiators of neuro-inflammatory responses in the skin. Conversely, anti-inflammatory neuropeptides like the products of cleavage of proopiomelanocortin (α-melanocyte-stimulating hormone and adrenocorticotropic hormone) negatively regulate immune responses in the skin. Likewise, the control of immune responses against stimuli applied to the skin depends on the balance between the release and neutralization of pro-inflammatory and anti-inflammatory neuropeptides, a matter that has been somehow overlooked by the immunology field until recently.