Feline IL-2 (Interleukin-2) is a central T cell–derived cytokine that regulates lymphocyte proliferation, differentiation, and immune homeostasis in cats (Felis catus). 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 cats, basal IL-2 expression is typically low but increases rapidly during infection, vaccination, or immune stimulation. Altered IL-2 production has been associated with feline immunodeficiency virus (FIV) infection, feline leukemia virus (FeLV) infection, feline infectious peritonitis (FIP), chronic inflammatory conditions, and immune-mediated diseases. Cats serve as important natural and translational animal models for human diseases including HIV/AIDS (FIV model), lymphoma and other cancers, asthma, and certain neuroinflammatory and infectious diseases. In veterinary and comparative medicine research, feline IL-2 is studied as a biomarker of T cell activation and adaptive immune competence and has been investigated as an immunotherapeutic agent in oncology and chronic viral infection settings.