Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) is a growth factor that supports the in-vitro colony formation of granulocytes-macrophages progenitor cells. It is a pleiotropic cytokine and is produced as a response to immune or inflammatory stimuli by activated cells of the hematopoietic system such as T cells, B cells, macrophages, mast cells, fibroblasts and alveolar epithelial cells. It plays an important role in regulating the proliferation, differentiation, survival and activation of hematopoietic cells such as granulocytes and monocytes, neutrophiles, basophiles and eosonophoiles, erythroid cells, megakaryocytes and T cells. Human and mouse GM-CSF have about 56% homology and are species specific. Human GM-CSF is not active