Eotaxin/CCL11 is a potent eosinophil chemoattractant that was originally purified from bronchoalveolar lavage fluid of guinea pigs sensitized by aerosol challenge with ovalbumin. Human CCL11 cDNA encodes a 97 amino acid residue precursor protein from which the aminoterminal 23 amino acid residues are cleaved to generate the 74 amino acid residue mature human CCL11. At the protein sequence level, mature human CCL11 is approximately 60% identical to mature mouse and guinea pig CCL11. Human CCL11 is chemotactic for eosinophils, but not mononuclear cells or neutrophils. The CC chemokine receptor 3 (CCR3) has now been identified to be a specific human CCL11 receptor. CCR3 has also been shown to serve as a cofactor for a restricted subset of primary HIV viruses and binding of CCL11 to CCR3 inhibited infection by the HIV isolates.