title: Transfer of monomeric endotoxin from MD-2 to CD14: characterization and functional consequences.
abstract: Potent Toll-like receptor 4 (TLR4)-dependent cell activation by endotoxin depends on sequential transfer of monomers of endotoxin from an aggregated form to CD14 via the lipopolysaccharide-binding protein and then to MD-2. We now show that monomeric endotoxin can be transferred in reverse from MD-2 to CD14 but not to lipopolysaccharide-binding protein. Reverse transfer requires an approximately 1000-fold molar excess of CD14 to endotoxin-MD-2. Transfer of endotoxin from MD-2 to extracellular soluble CD14 reduces activation of cells expressing TLR4 without MD-2. However, transfer of endotoxin from MD-2 to membrane CD14 (mCD14) makes cells expressing MD-2.TLR4 sensitive to activation by the endotoxin-MD-2 complex. An endotoxin-mutant (F126A) MD-2 complex that does not activate cells expressing TLR4 alone potently activates cells expressing mCD14, MD-2, and TLR4 by transferring endotoxin to mCD14, which then transfers endotoxin to endogenous wild-type MD-2.TLR4. These findings describe a novel pathway of endotoxin transfer that provides an additional layer of regulation of cell activation by endotoxin.
authors.affiliation: Department of Internal Medicine and the Inflammation Program, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City 52242, USA.
authors.forename: Athmane
authors.initials: A
authors.lastname: Teghanemt
authors.forename: Polonca
authors.initials: P
authors.lastname: Prohinar
authors.forename: Theresa L
authors.initials: TL
authors.lastname: Gioannini
authors.forename: Jerrold P
authors.initials: JP
authors.lastname: Weiss
mesh_terms: D000209:Acute-Phase Proteins / Q000378:metabolism; D019943:Amino Acid Substitution; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism* / Q000494:pharmacology; D051218:Lymphocyte Antigen 96 / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D020125:Mutation, Missense; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D000099231:Lipopolysaccharide-Binding Protein
chemical_list: D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D051218:Lymphocyte Antigen 96; D008562:Membrane Glycoproteins; D051197:Toll-Like Receptor 4; D000099231:Lipopolysaccharide-Binding Protein; C495377:LY96 protein, human; C495345:TLR4 protein, human