CCL17 and Alzheimer disease: Several mediators have been used as biomarkers for AD severity and activity.[11,12] Potential local and systemic biomarkers of AD include cytokines and chemokines, such as the levels of the Th2-related cytokine IL-13,[13,14] the Th2-related chemokine C-C motif ligand (CCL)17/thymus and activation-regulated chemokine (TARC),[15,16] CCL22/macrophage-derived chemokine,[17,18] and the Th22-related cytokine IL-22[17,19] in the blood and skin.