Swine Interleukin-4 (IL-4) is a Th2-associated cytokine produced primarily by activated CD4⁺ T helper 2 (Th2) cells, mast cells, and basophils in pigs (Sus scrofa domesticus), where it plays a central role in regulating humoral immunity, alternative macrophage activation, and modulation of inflammatory responses. 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, antibody production, and suppression of Th1-associated cytokines such as IFN-γ. In swine health, IL-4 is particularly important in responses to gastrointestinal and respiratory parasitic infections, where Th2 polarization supports parasite clearance and mucosal repair. IL-4 also influences immune balance during viral infections such as porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza, where Th1/Th2 dynamics can affect viral persistence, vaccine responsiveness, and disease outcome. While IL-4-mediated responses are protective in supporting humoral immunity and limiting excessive inflammation, excessive or prolonged Th2 skewing may impair effective cell-mediated responses against intracellular pathogens. As a biomarker of type 2 immune activation, swine IL-4 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-4 supports comparative investigations into Th2-mediated immunity and cytokine-targeted therapeutic strategies.