Lipoteichoic acid (LTA) is a cell surface glycoconjugate of gram-positive bacteria and is reported to activate the innate immune system. We previously reported that purified LTA obtained from Enterococcus hirae has no immunostimulating activity, but a subfraction (Eh-AF) in an LTA fraction possesses activity. In this study, we established a mouse monoclonal antibody neutralizing the activity of Eh-AF and investigated its inhibitory effects. Monoclonal antibody (MAbEh1) was established by the immunization of BALB/c mice with Eh-AF, followed by hybridoma screening based on its inhibitory effect for the production of interleukin-6 (IL-6) induced by Eh-AF. MAbEh1 neutralized the production of IL-6 by LTA fraction from not only E. hirae but also Staphylococcus aureus, while it failed to block that of lipopolysaccharide, suggesting that the antibody recognized a common active structure(s) in LTA fractions. Synthetic glycolipids in these LTAs did not induce cytokine production, at least in our system. Interestingly, the antibody was found to inhibit the activity of immunostimulating synthetic lipopeptides, Pam 3 CSK 4 and FSL-1. These results suggest that MAbEh1 neutralizes the activity of lipoprotein-like compounds which is responsible for the activity of the LTA fraction of E. hirae and S. aureus.Lipoteichoic acid (LTA) is a macroamphiphile distributing on the cell surfaces of gram-positive bacteria and is reported to exhibit immunostimulatory and inflammatory activities. LTA has been shown to have an antitumor effect (34, 36) and to induce inflammatory cytokines, such as tumor necrosis factor (TNF), interleukin-1 (IL-1), and 31,33). Recent research showed that such immunostimulatory activities of bacterial compounds were mediated by Toll-like receptor (TLR), a type I transmembrane receptor for innate immune activation (32). To date, more than 10 members of the TLR family have been discovered and most of their ligands were identified: TLR4 in combination with the adapter molecule MD-2 for lipopolysaccharide (LPS)/lipid A, an outer membrane component of gram-negative bacteria (21, 24); TLR9 for unmethylated CpG DNA (15); TLR3 and TLR7/8 for double-and single-stranded RNA (1, 14); TLR5 for bacterial flagellin (13); and TLR2 subfamily (TLR1, Ϫ2, and Ϫ6) for bacterial lipoprotein/lipopeptide (29, 30). LTA was also reported to be a ligand of TLR2 (22).The structures of LTAs have been well studied and proposed as a glycoconjugates generally composed of a glycolipid anchor part, such as ␤-kojibiosyldiacylglycerol for Enterococcus hirae and Streptococcus pyogenes and ␤-gentiobiosyldiacylglycerol for Staphylococcus aureus, and a 1,3-linked poly(glycerophosphate) substituted by sugars and D-alanine at position 2 of the glycerol (4). Previously, we attempted to determine a structure of the LTA responsible for these activities. Fukase et al. prepared chemically synthetic glycoconjugates having fundamental structures of LTA from E. hirae and S. pyogenes and their glycolipid anchor parts (5, 6). However, these synthetic compounds ...

No abstract