Chicken CCL17 (C-C motif chemokine ligand 17), also referred to as thymus and activation-regulated chemokine (TARC)-like in avian species, is a member of the CC chemokine family involved in regulating T cell trafficking and type 2–associated immune responses in chickens (Gallus gallus). CCL17 is expressed primarily by dendritic cells, macrophages, and certain epithelial and endothelial cells in response to inflammatory and immune stimuli. It functions through a CCR4-like receptor to promote chemotaxis and activation of Th2-type lymphocytes and regulatory T cells, contributing to adaptive immune polarization and modulation of inflammatory responses. In healthy chickens, basal expression of CCL17 is generally low, but levels may increase during parasitic infections (e.g., coccidiosis), allergic-type inflammation, viral infections such as Marek’s disease virus (MDV) or infectious bursal disease virus (IBDV), and following vaccination. In poultry immunology research, chicken CCL17 serves as a biomarker of T cell recruitment and Th2-associated immune activity, providing insight into host–pathogen interactions, vaccine responses, and immune regulation in commercial and experimental poultry systems.