Canine CCL17 (C-C motif chemokine ligand 17), also known as thymus and activation-regulated chemokine (TARC), is a member of the CC chemokine family that plays a central role in regulating Th2-associated immune responses in dogs (Canis lupus familiaris). CCL17 is produced primarily by dendritic cells, macrophages, endothelial cells, and keratinocytes in response to inflammatory cytokines, particularly those linked to type 2 immunity. It functions predominantly through the CCR4 receptor to promote chemotaxis and activation of Th2 lymphocytes and regulatory T cells, contributing to allergic inflammation and immune modulation. In healthy dogs, basal circulating CCL17 levels are typically low; however, concentrations increase significantly in allergic conditions, most notably canine atopic dermatitis, where serum CCL17 has emerged as a clinically useful biomarker of disease severity and treatment response. Elevated CCL17 expression has also been observed in allergic airway disease and certain inflammatory conditions. In veterinary and translational research, canine CCL17 is widely studied as a marker of Th2 polarization and allergic inflammation, providing insight into disease pathogenesis and serving as a target for immunomodulatory therapies in canine and comparative dermatology research.