CD14 has been shown to enhance Toll-like receptor 2 (TLR2)-mediated signaling in response to peptidoglycan. Anti-CD14 monoclonal antibody MEM-18, whose epitope was located at the amino acid residues 57-64, blocked the binding of sCD14 to the recombinant soluble form of the extracellular TLR2 domain (sTLR2). The deletion mutant sCD14(Delta57-64) lacking the amino acid residues 57-64 failed to bind to sTLR2. Cotransfection of wild type mCD14 but not mCD14(Delta57-64) with TLR2 enhanced NF-kappaB activation in response to peptidoglycan. These results indicate that the CD14 region spanning amino acids 57-64 is critical for interacting with TLR2 and enhancing TLR2-mediated peptidoglycan signaling. (C) 2005 Elsevier Inc. All rights reserved.