IL4 and Alzheimer disease: Neuropeptides can stimulate keratinocytes to produce pro-inflammatory cytokines (such as IL-1α, IL-6, and IL-8), enhance the migration, antigen expression, and sensitization of Langerhans cells, induce mast cell degranulation and release of histamine and other mediators, and trigger peripheral blood mononuclear leukocytes to release IFN-γ, IL-4, TNF-α, and IL-10, thus eventually initiating inflammatory skin diseases (such as AD, psoriasis, and rosacea) [31,32].