Swine Interleukin-5 (IL-5) is a Th2-associated cytokine produced primarily by activated CD4⁺ T helper 2 (Th2) cells, mast cells, and type 2 innate lymphoid cells in pigs (Sus scrofa domesticus), 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 regulate 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 activity in peripheral tissues. In swine health, IL-5 is particularly important in immune responses to parasitic infections such as Ascaris suum and other helminths, where Th2 polarization and eosinophil activation contribute to parasite clearance and mucosal repair. IL-5 may also influence allergic-type inflammation and respiratory immune responses, affecting airway inflammation and tissue remodeling. While IL-5–mediated responses are protective in helminth defense, excessive or prolonged IL-5 signaling can drive persistent eosinophilic inflammation and tissue damage. As a biomarker of type 2 immune activation, swine IL-5 is relevant in vaccine development, host–parasite interaction studies, and immune resilience research. In translational research, pigs serve as valuable large-animal models due to physiological similarities to humans, and characterization of swine IL-5 supports comparative investigations into eosinophil biology and development of targeted anti–IL-5 therapeutic strategies for allergic and inflammatory diseases.