Feline 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 signaling molecules such as TNF-α, Fas ligand (FasL), CD40 ligand (CD40L), TRAIL, and RANKL that regulate immune responses, apoptosis, and inflammatory signaling. In cats (Felis catus), TNFSF15 is primarily produced by endothelial cells, macrophages, dendritic cells, and other immune cells in response to inflammatory stimuli or infection. TNFSF15 functions mainly by binding to its receptor death receptor 3 (DR3, TNFRSF25) expressed on T lymphocytes and other immune cells, activating intracellular pathways such as NF-κB and MAPK that regulate T cell activation, cytokine production, and inflammatory responses. In feline immune physiology, TNFSF15 is thought to contribute to regulation of immune-mediated inflammation and vascular responses, while also influencing T cell–mediated immunity. Similar to other mammals, TNFSF15 may play roles in chronic inflammatory diseases, immune regulation, and host responses to infection. Because TNF superfamily cytokines are important regulators of inflammation and immune signaling, feline TNFSF15 is of interest in veterinary immunology and inflammatory disease research, contributing to the understanding of cytokine-mediated immune regulation in cats.