Interleukin-2 (IL-2) is a pleiotropic cytokine that plays a pivotal role in immune responses. Initially discovered as a T-cell growth factor, IL-2 also promotes CD8+ T cell and NK cell cytolytic activity and modulates T cell differentiation. It is essential for the development and maintenance of T regulatory (Treg) cells and activation-induced cell death, mediating tolerance and limiting inappropriate immune reactions. IL-2 signaling involves multiple transcription factors and signaling pathways, including JAK kinases and STAT proteins. The cytokine has complex actions on various immune cells, influencing T helper cell differentiation, Treg cell function, and effector memory CD8+ T cell development. IL-2 is used clinically in immunotherapy for certain cancers, but its toxicity limits its broader application. Inhibition of IL-2 signaling through JAK inhibitors is being explored as a therapeutic approach. Understanding the molecular mechanisms and cellular actions of IL-2 is crucial for developing more effective and specific therapeutic strategies.Interleukin-2 (IL-2) is a pleiotropic cytokine that plays a pivotal role in immune responses. Initially discovered as a T-cell growth factor, IL-2 also promotes CD8+ T cell and NK cell cytolytic activity and modulates T cell differentiation. It is essential for the development and maintenance of T regulatory (Treg) cells and activation-induced cell death, mediating tolerance and limiting inappropriate immune reactions. IL-2 signaling involves multiple transcription factors and signaling pathways, including JAK kinases and STAT proteins. The cytokine has complex actions on various immune cells, influencing T helper cell differentiation, Treg cell function, and effector memory CD8+ T cell development. IL-2 is used clinically in immunotherapy for certain cancers, but its toxicity limits its broader application. Inhibition of IL-2 signaling through JAK inhibitors is being explored as a therapeutic approach. Understanding the molecular mechanisms and cellular actions of IL-2 is crucial for developing more effective and specific therapeutic strategies.