Ferret CCL21 (C-C motif chemokine ligand 21, also known as secondary lymphoid-tissue chemokine, SLC, or 6Ckine) is a homeostatic chemokine that plays a key role in lymphocyte trafficking and organization of adaptive immune responses in ferrets (Mustela putorius furo). CCL21 primarily signals through the CCR7 receptor, directing chemotaxis of naïve T cells, central memory T cells, and mature dendritic cells to secondary lymphoid tissues such as lymph nodes and spleen. In ferrets, CCL21 is produced mainly by stromal cells and high endothelial venules within lymphoid tissues, where it helps guide immune cells into T-cell zones and facilitates interactions between antigen-presenting dendritic cells and lymphocytes necessary for initiation of adaptive immunity. In ferret health and research, CCL21-mediated CCR7 signaling is particularly relevant in respiratory viral infection models, including influenza virus and SARS-CoV-2, where efficient trafficking of dendritic cells and T cells to lymph nodes is essential for generating antiviral immune responses. Proper regulation of CCL21 contributes to immune surveillance and effective development of adaptive immunity, while altered chemokine signaling may influence inflammatory responses or impaired immune activation. Because ferrets are widely used as translational models for human respiratory infections and vaccine research, characterization of ferret CCL21 supports studies of lymphoid tissue organization, immune cell migration, and adaptive immune responses relevant to human infectious disease and immunology.