Dolphin Interleukin-4 (IL-4) is a Th2-associated cytokine produced primarily by activated CD4⁺ T helper cells and other type 2 immune populations in dolphins, particularly the bottlenose dolphin (Tursiops truncatus), 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 dolphin health, IL-4 may be particularly relevant in responses to parasitic infections, chronic dermatitis, respiratory disease, and wound healing, where balanced type 2 immune responses support tissue repair while limiting excessive inflammation. Dysregulated IL-4 signaling could contribute to chronic inflammatory or fibrotic conditions, especially in the context of environmental stressors such as pollutant exposure or harmful algal blooms. As dolphins serve as sentinel species for marine ecosystem health, IL-4 represents an important biomarker of Th2 immune polarization and immune balance in both managed and free-ranging populations. Characterization of dolphin IL-4 supports research into host–pathogen interactions, immune adaptation to marine environments, and comparative Th1/Th2 immune regulation relevant to wildlife conservation and broader mammalian immunology.