Rat Monocyte Chemoattractant Protein (MCP-1) is a member of the C-C chemokine superfamily and a homolog of human MCP-1. MCP-1 is expressed by a variety of cell types including monocyte/macrophages, endothelial cells and mesangial cells.3 MCP-1 has chemoattractant activity for monocytes, lymphocytes and basophils but is not active for neutrophils. Recombinant rat MCP-1 is a highly glycosylated protein ranging in size from 27 - 30 kD as measured by SDS-PAGE analysis. Furthermore, there is evidence from experimental animal models that MCP-1 can suppress tumor formation by attracting monocytes to the tumor site. Recombinant rat MCP-1 (MN 555110) is supplied as a frozen liquid comprised of 0.22 μm sterile-filtered aqueous buffered solution containing glycerol and 1.0 mg/ml bovine serum albumin, with no preservatives. Recombinant rat MCP-1 is ≥ 95% pure as determined by SDS-PAGE, and an absorbance assay based on the Beers-Lambert law. The endotoxin level is ≤ 0.1 ng per µg of rat MCP-1, as measured in a chromogenic LAL assay.