Canine Interleukin-4 (IL-4) is a Th2-associated cytokine produced primarily by activated CD4⁺ T helper 2 (Th2) cells, mast cells, and basophils in dogs (Canis lupus familiaris), where it plays a central role in regulating humoral immunity, allergic inflammation, and alternative macrophage activation. IL-4 signals through receptor complexes containing IL-4Rα paired with the common gamma chain (γc) or IL-13Rα1, activating JAK/STAT6 pathways that promote B-cell proliferation, IgE production, antibody class switching, and suppression of Th1-associated cytokines such as IFN-γ. In canine health, IL-4 is particularly important in allergic and atopic conditions including atopic dermatitis, food hypersensitivity, allergic otitis, and eosinophilic airway disease, where Th2 polarization drives IgE-mediated responses, pruritus, and chronic skin or airway inflammation. IL-4 also influences immune balance during parasitic infections and may affect Th1/Th2 dynamics in chronic infectious diseases. While IL-4 supports protective humoral responses and tissue repair, excessive or persistent IL-4 signaling can contribute to chronic allergic inflammation and barrier dysfunction. As a biomarker of type 2 immune activation, canine IL-4 is widely studied in allergy research, vaccine response evaluation, and immune modulation strategies. In translational research, dogs serve as valuable spontaneous models for human atopic dermatitis and allergic airway disease, and characterization of canine IL-4 supports comparative investigations into Th2-mediated inflammation and development of targeted cytokine therapies relevant to both veterinary and human medicine.