CCL2, also called monocyte chemotactic protein- 1 (MCP- 1) or JE, is a member of the C- C or beta chemokine family that is best known as a chemotactic agent for mononuclear cells . Human CCL2 cDNA encodes a 99 amino acid (aa) precursor protein with a 23 aa signal peptide and a 76 aa mature protein . Removal of the first 5 aa of the mature protein, including the N-terminal pyrrolidone carboxylic acid- modified glutamine, occurs naturally by metalloproteinase cleavage and down- regulates activity but not receptor binding. CCL2 may form multiple bands from 8.7- 13.5 kDa on SDS- PAGE due to non- covalent dimerization and variable carbohydrate content. Mature human CCL2 shares 78- 79% aa identity with canine, porcine and equine CCL2, while mouse and rat express a form of CCL2 that is extended by 49 aa and shares only 56% aa identity within the common region. Human CCL2 can, however, induce a response in murine cells.