CCL11 is a potent eosinophil chemoattractant that was originally purified from bronchoalveolar lavage fluid of guinea pigs sensitized by aerosol challenge with ovalbumin. Microsequencing of the purified protein revealed the guinea pig CCL11 to be a member of the beta (CC) chemokine family of inflammatory and immunoregulatory cytokines. cDNA clones for guinea pig, mouse and human CCL11 have been isolated. Mouse CCL11 cDNA encodes a 97 amino acid residue precursor protein from which the amino-terminal 23 amino acid residues are cleaved to generate the 74 amino acid residue mature mouse CCL11. At the protein sequence level, mature mouse CCL11 is approximately 60% identical to mature human and guinea pig CCL11. In addition, mouse CCL11 also shows high amino acid sequence identity to members of the MCP family. Mouse CCL11 is chemotactic for eosinophils, but not mononuclear cells or neutrophils. CCL11 mRNA is expressed in a variety of tissues. The expression of CCL11 mRNA is induced in cultured endothelial cells in response to IFN-gamma. In addition, CCL11 mRNA is also induced in response to the transplantation of IL-4-secreting tumor cells.