IL-15 is a recently discovered factor that can be produced by a variety of cells such as activated monocytes-macrophages, epidermal cells, and fibroblasts. The molecular structure of IL-15 is much similar to that of IL-2, so that the β-chain and the γ-chain of the IL-2 receptor can be utilized to bind to target cells to exert a biological activity similar to IL-2. IL-15 can induce B cell proliferation and differentiation, and is the only cytokine that can partially replace IL-2 to induce initial antibody production; IL-15 can stimulate T cell and NK cell proliferation, induce LAK cell activity, and can also interact with IL-12. Synergistically stimulate NK cells to produce IFN-γ.