Ovine IL-2 (Interleukin-2) is a central T cell–derived cytokine that regulates lymphocyte proliferation, differentiation, and immune homeostasis in sheep (Ovis aries). 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/CD122, and the common γ chain/CD132) 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), which are essential for maintaining immune balance. In healthy sheep, basal IL-2 expression is generally low but increases during infection, vaccination, and immune stimulation. Altered IL-2 responses have been associated with ovine lentivirus (maedi-visna), parasitic infections such as Haemonchus contortus, bacterial respiratory disease, and chronic inflammatory conditions. Sheep serve as important large-animal models for respiratory disease, vaccine development, and mucosal immunology. In veterinary and translational research, ovine IL-2 is widely used as a biomarker of T cell activation and cell-mediated immunity and supports studies of host–pathogen interactions, immunoregulation, and vaccine efficacy in small ruminant health.