Dolphin IL-2 (Interleukin-2) is a key T cell–derived cytokine that regulates lymphocyte proliferation, differentiation, and immune homeostasis in dolphins (e.g., Tursiops truncatus). IL-2 is produced primarily by activated CD4⁺ and CD8⁺ T lymphocytes following antigen recognition and costimulatory signaling, and it functions through the IL-2 receptor complex (IL-2Rα/CD25, IL-2Rβ, and the common γ chain) to promote clonal expansion of antigen-specific T cells, enhance cytotoxic T lymphocyte and natural killer (NK) cell activity, and support development and maintenance of regulatory T cells (Tregs). In healthy dolphins, basal IL-2 expression is expected to be low but increases during infection, inflammatory stimulation, or environmental stress exposure. Altered IL-2 responses may occur during viral or bacterial infections, chronic inflammatory conditions, or immune challenges observed in both managed and free-ranging populations. Dolphins serve as valuable comparative models for studying marine mammal immunology, environmental immunotoxicology, and host responses to emerging infectious diseases. In marine mammal and translational research, dolphin IL-2 is used as a biomarker of T cell activation and cell-mediated immunity, providing insight into adaptive immune function and immune system health in marine species.