Bovine IL-2 (Interleukin-2) is a central T cell–derived cytokine that regulates lymphocyte proliferation, differentiation, and immune homeostasis in cattle (Bos taurus). 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 cattle, basal IL-2 expression is generally low but increases during infection, vaccination, and immune stimulation. Altered IL-2 responses have been associated with bovine viral diarrhea virus (BVDV), bovine leukemia virus (BLV), Mycobacterium bovis (bovine tuberculosis), mastitis, and bovine respiratory disease complex. Cattle serve as important natural models for human tuberculosis, retroviral infection, and mucosal immune responses, as well as for vaccine development and immunomodulatory therapies. In veterinary and translational research, bovine IL-2 is widely used as a biomarker of T cell activation and cell-mediated immunity and is studied in the context of host–pathogen interactions, vaccine efficacy, and immune regulation in livestock health.