The type I macrophage scavenger receptor binds togram-positive bacteria and recognizes lipoteichoic acid.

Macrophage scavenger receptors exhibit unusuallybroad binding specificity for polyanionic ligands and have been implicated inatherosclerosis and various host defense functions. Using a radiolabeled,secreted form of the type I bovine macrophage scavenger receptor in an in vitrobinding assay, we have found that this receptor binds to intact Gram-positivebacteria, including Streptococcus pyogenes, Streptococcus agalactiae,Staphylococcus aureus, Enterococcus hirae, and Listeria monocytogenes.Competition binding studies using purified lipoteichoic acid, an anionic polymerexpressed on the surface of most Gram-positive bacteria, show that lipoteichoicacids are scavenger receptor ligands and probably mediate binding of thereceptor to Gram-positive bacteria. Lipoteichoic acids, for which no host cellreceptors have previously been identified, are implicated in the pathogenesis ofseptic shock due to Gram-positive bacteria. Scavenger receptors may participatein host defense by clearing lipoteichoic acid and/or intact bacteria fromtissues and the circulation during Gram-positive sepsis. Since scavengerreceptors have been previously shown to bind to and facilitate bloodstreamclearance of Gram-negative bacterial endotoxin (lipopolysaccharide), thesereceptors may provide a general mechanism for macrophage recognition andinternalization of pathogens and their cell surface components.