Mouse IL-2 (Interleukin-2) is a central T cell–derived cytokine that regulates lymphocyte proliferation, differentiation, and immune homeostasis in mice (Mus musculus). IL-2 is produced primarily by activated CD4⁺ T helper cells and, to a lesser extent, by CD8⁺ T cells following antigen recognition and costimulatory signaling. 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 peripheral immune tolerance. In healthy mice, basal IL-2 expression is low but increases rapidly during infection, vaccination, or inflammatory stimulation. Genetic disruption of IL-2 or IL-2 receptor components in mice results in severe lymphoproliferative disease and autoimmunity, highlighting its critical role in immune regulation. Mouse IL-2 is extensively studied in models of autoimmune disease (e.g., experimental autoimmune encephalomyelitis and type 1 diabetes), cancer immunotherapy, transplant rejection, and chronic viral infection. In biomedical research, mouse IL-2 serves as a key biomarker of T cell activation and a foundational molecule for studying T cell biology and immune tolerance mechanisms.