Ferret Interleukin-15 (IL-15) is a cytokine that plays an important role in regulating innate and adaptive immune responses in ferrets (Mustela putorius furo). IL-15 is produced by a variety of cell types, including monocytes, macrophages, dendritic cells, and epithelial cells, in response to infection or inflammatory stimuli. Ferret IL-15 signals through a receptor complex composed of IL-15Rα together with the shared IL-2/15Rβ (CD122) and common γ chain (γc), activating intracellular signaling pathways such as JAK–STAT that promote lymphocyte proliferation, survival, and activation. In ferrets, IL-15 is particularly important for the development, maintenance, and activation of natural killer (NK) cells and memory CD8⁺ T cells, supporting cytotoxic immune responses against infected cells. It also contributes to regulation of mucosal immunity in respiratory tissues. In cell culture, recombinant ferret IL-15 is commonly used to stimulate proliferation and survival of NK cells and cytotoxic T lymphocytes, maintain memory CD8⁺ T cell populations, and enhance cytotoxic activity during in vitro immune assays. Ferret IL-15 is widely studied in infectious disease and translational research because ferrets serve as an important animal model for human respiratory viruses; for example, ferret models of influenza and SARS-CoV-2 infection are used to investigate immune responses, including IL-15–mediated activation of cytotoxic lymphocytes, to better understand antiviral immunity and evaluate vaccine and therapeutic strategies relevant to human disease.