Enzymatic deacylation of the lipid A moiety of Salmonella typhimurium lipopolysaccharides by human neutrophils.

Lipid A, the toxic moiety of Gram-negative bacterial lipopolysaccharides (endotoxins), is a glucosamine disaccharide to which fatty acid and phosphate residues are covalently attached. Recent studies of Salmonella lipid A indicate that 3-hydroxytetradecanoic acid (3-OH-14:0) residues are directly linked to the glucosamine backbone and the nonhydroxylated fatty acids (principally dodecanoic and tetradecanoic acids) are esterified to the hydroxyl groups of some of the 3-OH-14:0 molecules. We report here that the granule fraction of human neutrophils contains one or more enzymes that partially deacylate Salmonella typhimurium lipid A by removing the nonhydroxylated fatty acids, leaving almost all of the 3-OH-14:0 residues linked to glucosamine. The available evidence suggests that similar reactions also occur in living neutrophils that ingest lipopolysaccharides by antibody-dependent phagocytosis.