Swine IL-2 (Interleukin-2) is a central T cell–derived cytokine that regulates lymphocyte proliferation, differentiation, and immune homeostasis in pigs (Sus scrofa). IL-2 is produced primarily by activated CD4⁺ and CD8⁺ T lymphocytes 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 the development and maintenance of regulatory T cells (Tregs), which are essential for immune balance. In healthy swine, basal IL-2 expression is generally low but increases during infection, vaccination, and immune stimulation. Altered IL-2 responses have been associated with porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus, African swine fever virus (ASFV), enteric infections, and immune-mediated inflammatory conditions. Pigs serve as important translational models for human immunology, transplantation research, and vaccine development due to similarities in immune system structure and function. In veterinary and biomedical research, swine IL-2 is widely used as a biomarker of T cell activation and cell-mediated immunity and as a tool for evaluating vaccine efficacy, host–pathogen interactions, and immunomodulatory therapies.