Ferret TNFSF15 (Tumor Necrosis Factor Superfamily Member 15, also known as TL1A or VEGI—vascular endothelial growth inhibitor) is a cytokine belonging to the tumor necrosis factor (TNF) superfamily, which includes related ligands such as TNF-α, Fas ligand (FasL), CD40 ligand (CD40L), TRAIL, and RANKL that regulate immune signaling, apoptosis, and inflammatory responses. In ferrets (Mustela putorius furo), TNFSF15 is produced primarily by endothelial cells, macrophages, dendritic cells, and other immune cells in response to infection or inflammatory stimuli. TNFSF15 functions mainly by binding to its receptor death receptor 3 (DR3, TNFRSF25) expressed on T lymphocytes and other immune cells, activating intracellular signaling pathways such as NF-κB and MAPK that regulate T cell activation, cytokine production, and inflammatory responses. In ferrets, TNFSF15 is also associated with regulation of vascular endothelial cell proliferation and angiogenesis, consistent with its designation as VEGI. Because ferrets are widely used as animal models for respiratory viral infections, including influenza and coronaviruses, cytokines such as TNFSF15 are important for understanding T cell–mediated immune responses and inflammatory regulation during infection. Characterization of ferret TNFSF15 therefore supports research on immune signaling, cytokine regulation, and host–pathogen interactions relevant to both veterinary and human biomedical studies.