IL-2 (interleukin 2) is a cytokine that is produced primarily by stimulated Th cells and its crucial role is induction of T cell proliferation. However, IL-2 also stimulates growth and differentiation of B cells, NK cells, monocytes and other cell types, such as LAK cells or oligodendrocytes and is one of the key molecules of the immune system. IL-2 signaling pathways lead to induction of Bcl-2 protein.