A systematic review and meta-analysis about the correlation between AD severity and biomarkers previously identified serum thymus and activation-regulated chemokine (TARC/CCL17), a member of the T-helper 2 (Th2) chemokine family (TARC), attractant of Th2 effector cells, as the most reliable AD severity biomarker for both children and adults (75, 76). Here, CCL17 is linked to Alzheimer disease.