CCL25, also known as Thymus-Expressed Chemokine (TECK), is a small chemokine belonging to the CC subfamily, first isolated from mouse thymus in 1997. Its official full name is "C-C motif chemokine ligand 25". CCL25 is mainly expressed in the thymus and small-intestinal epithelium, and to a lesser extent by vascular endothelial cells and other parenchymal tissues. It selectively attracts dendritic cells, thymocytes, and activated macrophages via binding to its high-affinity G-protein-coupled receptor CCR9, while showing no chemotactic activity on peripheral blood lymphocytes or neutrophils. Through this CCR9-CCL25 axis it orchestrates T-cell development in the thymus and guides CCR9⁺ lymphocytes-especially IgA-producing plasma cells and intra-epithelial lymphocytes-to the small intestine, thus participating in mucosal immunity and gut homeostasis.