Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) is a cytokine which is made by activated T cells, macrophages, vascular endothelial cells and fibroblasts. It has potent stimulatory effects on the growth and differentiation of bone marrow progenitor cells that generate granulocytes monocytes/macrophages, and megakaryocytes. In peripheral tissues, GM-CSF can act on mature leukocytes to promote inflammatory responses. Recombinant rat GM-CSF (Cat. No. 555111) is supplied as a frozen liquid comprised of 0.22 µm sterile-filtered aqueous buffered solution, containing bovine serum albumin and glycerol, with no preservatives. Recombinant rat GM-CSF is ≥ 95% pure as determined by SDS-PAGE analysis, and an absorbance assay based on the Beers-Lambert Law. The endotoxin level is ≤ 0.1 ng per µg of GM-CSF, as measured in a chromogenic LAL assay.