title: Endotoxin{middle dot}albumin complexes transfer endotoxin monomers to MD-2 resulting in activation of TLR4.
abstract: Response to Gram-negative bacteria (GNB) is partially mediated by the recognition of GNB-derived endotoxin by host cells. Potent host response to endotoxin depends on the sequential interaction of endotoxin with lipopolysaccharide binding protein (LBP), CD14, MD-2 and TLR4. While CD14 facilitates the efficient transfer of endotoxin monomers to MD-2 and MD-2·TLR4, activation of MD-2·TLR4 can occur in the absence of CD14 through an unknown mechanism. Here, we show that incubation of purified endotoxin (E) aggregates (E(agg), M               (                  r               ) ≥ 20 million) in PBS with ≥ 0.1% albumin in the absence of divalent cations Ca(2+) and Mg(2+), yields E·albumin complexes (M               (                  r               ) ∼70,000). E·albumin transfers E monomers to sMD-2 or sMD-2·TLR4 ectodomain (TLR4(ecd)) with a 'K               (d)' of ∼4 nM and induces MD-2·TLR4-dependent, CD14-independent cell activation with a potency only 10-fold less than that of monomeric E·CD14 complexes. Our findings demonstrate, for the first time, a mechanistic basis for delivery of endotoxin monomers to MD-2 and for activation of TLR4 that is independent of CD14.
authors: Immunology Program, University of Iowa Graduate College, Iowa City, Iowa, USA.
authors: Gregory A
authors: GA
authors: Esparza
authors: Athmane
authors: A
authors: Teghanemt
authors: DeSheng
authors: D
authors: Zhang
authors: Theresa L
authors: TL
authors: Gioannini
authors: Jerrold P
authors: JP
authors: Weiss
mesh_terms: D000418:Albumins / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004731:Endotoxins / Q000378:metabolism*; D016908:Gram-Positive Bacterial Infections / Q000276:immunology*; D054884:Host-Pathogen Interactions; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism; D051218:Lymphocyte Antigen 96 / Q000378:metabolism*; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000378:metabolism; D058105:Polymerization; D015202:Protein Engineering; D021381:Protein Transport; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
chemical_list: D000418:Albumins; D004731:Endotoxins; D018950:Lipopolysaccharide Receptors; D051218:Lymphocyte Antigen 96; D046912:Multiprotein Complexes; D051197:Toll-Like Receptor 4