Rat IL-2 (Interleukin-2) is a central T cell–derived cytokine that regulates lymphocyte proliferation, differentiation, and immune homeostasis in rats (Rattus norvegicus). 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 critical for immune tolerance. In healthy rats, basal IL-2 expression is low but increases during infection, vaccination, and inflammatory stimulation. Dysregulated IL-2 responses have been implicated in rat models of autoimmune disease (such as adjuvant-induced arthritis and experimental autoimmune encephalomyelitis), transplant rejection, diabetes, and tumor immunity. Rats serve as important translational models for immunology, neuroinflammation, and cardiovascular research. In biomedical studies, rat IL-2 is widely used as a biomarker of T cell activation and cell-mediated immunity and as a tool for investigating immune regulation and therapeutic immunomodulation.