title: Phagocytosis and intracellular killing of MD-2 opsonized gram-negative bacteria depend on TLR4 signaling.
abstract: Both Toll-like receptor 4 (TLR4)- and MD-2-deficient mice succumb to otherwise nonfatal gram-negative bacteria inocula, demonstrating the pivotal role played by these proteins in antibacterial defense in mammals. MD-2 is a soluble endogenous ligand for TLR4 and a receptor for lipopolysaccharide (LPS). LPS-bound MD-2 transmits an activating signal onto TLR4. In this report, we show that both recombinant and endogenous soluble MD-2 bind tightly to the surface of live gram-negative bacteria. As a consequence, MD-2 enhances cellular activation, bacterial internalization, and intracellular killing, all in a TLR4-dependent manner. The enhanced internalization of MD-2-coated bacteria was not observed in macrophages expressing Lps(d), a signaling-incompetent mutant form of TLR4, suggesting that the enhanced phagocytosis observed is dependent on signal transduction. The data confirm the notion that soluble MD-2 is a genuine opsonin that enhances proinflammatory opsonophagocytosis by bridging live gram-negative bacteria to the LPS transducing complex. The presented results extend our understanding of the role of the TLR4/MD-2 signaling axis in bacterial recognition by phagocytes.
authors.affiliation: Division of Infectious Diseases and Immunology, University of Massachusetts Medical School, Worcester 01605, USA.
authors.forename: Vishal
authors.initials: V
authors.lastname: Jain
authors.forename: Annett
authors.initials: A
authors.lastname: Halle
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Halmen
authors.forename: Egil
authors.initials: E
authors.lastname: Lien
authors.forename: Marie
authors.initials: M
authors.lastname: Charrel-Dennis
authors.forename: Sanjay
authors.initials: S
authors.lastname: Ram
authors.forename: Douglas T
authors.initials: DT
authors.lastname: Golenbock
authors.forename: Alberto
authors.initials: A
authors.lastname: Visintin
mesh_terms: D000818:Animals; D006090:Gram-Negative Bacteria / Q000276:immunology*; D051218:Lymphocyte Antigen 96 / Q000276:immunology*; D051379:Mice; D009895:Opsonin Proteins / Q000378:metabolism; D010587:Phagocytosis; D015398:Signal Transduction / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000502:physiology*
chemical_list: C411728:Ly96 protein, mouse; D051218:Lymphocyte Antigen 96; D009895:Opsonin Proteins; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4