IL-2 was discovered through its function as a T cell growth factor and plays a pivotal role in immune responses against pathogenic infection. Recognition and binding of the foreign antigens by the TCRs stimulate both the secretion of IL-2 and the expression of IL-2R on the T cell surface. Subsequently, the IL-2/IL-2R interaction activates the intracellular Ras/Raf/MAPK, JAK/STAT, and PI3K/AKT signal pathways, and ultimately stimulates the growth, differentiation, and survival of T cells. IL-2 acts on additional cell types, such as B cells, NK cells, monocytes and macrophages. It is primarily produced by activated CD4+ T cells, but has also been reportedly made by CD8+ T cells, NK cells, dendritic cells, and macrophages.
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