Ferret Interleukin-5 (IL-5) is a Th2-associated cytokine produced primarily by activated CD4⁺ T helper 2 (Th2) cells, mast cells, and group 2 innate lymphoid cells in ferrets (Mustela putorius furo), where it plays a central role in eosinophil differentiation, activation, recruitment, and survival. IL-5 belongs to the common beta chain (βc) cytokine family, which also includes IL-3 and granulocyte–macrophage colony-stimulating factor (GM-CSF); these cytokines share the βc receptor subunit and are involved in regulating hematopoiesis and myeloid cell function. IL-5 signals through a receptor complex composed of IL-5Rα and the shared βc chain, activating JAK/STAT and MAPK pathways that promote eosinophil maturation in the bone marrow and enhance their effector functions in peripheral tissues. In ferret health and research, IL-5 is relevant in models of allergic airway inflammation and respiratory viral infections, where Th2 polarization and eosinophilic responses may influence airway pathology, mucus production, and tissue remodeling. While IL-5 supports protective immunity against parasitic infections, excessive or prolonged IL-5 expression can contribute to eosinophilic inflammation and lung injury. Because ferrets are widely used as translational models for human respiratory disease and vaccine studies, characterization of ferret IL-5 supports investigations into Th1/Th2 immune balance, eosinophil biology, and development of targeted anti–IL-5 therapeutic strategies relevant to allergic and airway inflammatory disorders.