CCL17 and Alzheimer disease: It is known that AD is characterized by a TH1/TH2 imbalance and increased level of IL-4, IL-5, IL-13, IL-25, IL-31 (itching mediator, also thymic stromal lymphopoietin [74]) and IL-33; CCL17, CCL18, CCL22 and CCL26 were also observed in AD skin lesions.