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ludc webb

Harry Björkbacka

Researcher

ludc webb

Genome-Wide Expression Profiling and Mutagenesis Studies Reveal that Lipopolysaccharide Responsiveness Appears To Be Absolutely Dependent on TLR4 and MD-2 Expression and Is Dependent upon Intermolecular Ionic Interactions

Author

  • Jianmin Meng
  • Mei Gong
  • Harry Björkbacka
  • Douglas T. Golenbock

Summary, in English

Lipid A (a hexaacylated 1,4' bisphosphate) is a potent immune stimulant for TLR4/MD-2. Upon lipid A ligation, the TLR4/MD-2 complex dimerizes and initiates signal transduction. Historically, studies also suggested the existence of TLR4/MD-2-independent LPS signaling. In this article, we define the role of TLR4 and MD-2 in LPS signaling by using genome-wide expression profiling in TLR4- and MD-2-deficient macrophages after stimulation with peptidoglycan-free LPS and synthetic Escherichia coli lipid A. Of the 1396 genes significantly induced or repressed by any one of the treatments in the wild-type macrophages, none was present in the TLR4-or MD-2-deficient macrophages, confirming that the TLR4/MD-2 complex is the only receptor for endotoxin and that both are required for responses to LPS. Using a molecular genetics approach, we investigated the mechanism of TLR4/MD-2 activation by combining the known crystal structure of TLR4/MD-2 with computer modeling. According to our murine TLR4/MD-2-activation model, the two phosphates on lipid A were predicted to interact extensively with the two positively charged patches on mouse TLR4. When either positive patch was abolished by mutagenesis into Ala, the responses to LPS and lipid A were nearly abrogated. However, the MyD88-dependent and -independent pathways were impaired to the same extent, indicating that the adjuvant activity of monophosphorylated lipid A most likely arises from its decreased potential to induce an active receptor complex and not more downstream signaling events. Hence, we concluded that ionic interactions between lipid A and TLR4 are essential for optimal LPS receptor activation. The Journal of Immunology, 2011, 187: 3683-3693.

Department/s

  • Cardiovascular Research - Immunity and Atherosclerosis
  • EXODIAB: Excellence of Diabetes Research in Sweden

Publishing year

2011

Language

English

Pages

3683-3693

Publication/Series

Journal of Immunology

Volume

187

Issue

7

Document type

Journal article

Publisher

American Association of Immunologists

Topic

  • Immunology in the medical area

Status

Published

Research group

  • Cardiovascular Research - Immunity and Atherosclerosis

ISBN/ISSN/Other

  • ISSN: 1550-6606