Interleukin 3 is a pleiotropic factor produced primarily by activated T cells that can stimulate the proliferation. At the amino acid sequence level, mature human and murine IL-3 share only 29% sequence identity. Consistent with this lack of homology, IL-3 activity is highly species-specific and human IL-3 does not show activity on murine cells. Cytokines are actively involved in the host-defense system to coordinate the functional activity and the generation of effector cells. Some of these molecules function as inflammatory mediators and hematopoietic growth factors at the same time such as IL-3. IL-3 (or multi-CSF) is known as a pleiotropic cytokine with a broad spectrum of target cells and functions. IL-3 regulates the proliferation and differentiation of normal hematopoietic progenitor cells in the early stages of hematopoiesis. And IL-3 inhibits apoptosis and promotes the autonomous growth of blast cells.