{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n CCL17—also known as thymus‐ and activation‐regulated chemokine (TARC)—has emerged as a key mediator in immune regulation by linking innate activation with adaptive T‐cell responses. Multiple studies demonstrate that CCL17 is produced predominantly by antigen‐presenting cells such as dendritic cells and macrophages upon stimulation by epithelial‐derived cytokines (e.g., TSLP, IL‐33) or engagement of endocytic receptors. For instance, TSLP released from epithelial cells activates dendritic cells to secrete CCL17 together with related chemokines, thereby favoring the initiation of Th2‐driven allergic inflammation (see."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " In allergic airway disorders such as asthma—and even in chronic obstructive pulmonary disease—there is a marked elevation of CCL17 expression in the bronchial mucosa that correlates with airway obstruction and promotes the selective recruitment of CCR4‐expressing Th2 cells (see."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": " Furthermore, IL‐33–induced alternatively activated macrophages and eosinophils can produce CCL17 to amplify local inflammation (see"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": ", while in the tumor microenvironment elevated CCL17 contributes to the recruitment of regulatory T cells that may facilitate immune evasion (see."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": " In cutaneous T‐cell lymphoma, high levels of CCL17 in skin lesions support the accumulation of skin‐homing T cells expressing CCR4 (see."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": " Collectively, these findings identify CCL17 as a central chemokine that orchestrates Th2 polarization and the recruitment of both effector and regulatory T cells across allergic and neoplastic contexts, highlighting its potential as a therapeutic target in disorders marked by dysregulated immune cell trafficking (1,2,3,4,5,6,8,9,10).\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Vassili Soumelis, Pedro A Reche, Holger Kanzler, et al. 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