Human GM-CSF (Granulocyte/Macrophage-Colony Stimulating Factor) is a differentially glycosylated growth factor. It is secreted by activated T cells and macrophages or by endothelial cells and fibroblasts in response to TNF alpha, IL-1, IL-2 and IFN gamma. Along with its secreted form, GM-CSF can also be found associated with the extracellular matrix or bound to the cell membrane. GM-CSF stimulates proliferation, activation and differentiation of macrophages, granulocytes, and their progenitors.