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Infection and Immunity, January 2009, p. 557-564, Vol. 77, No. 1
0019-9567/09/$08.00+0 doi:10.1128/IAI.00903-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Toll-Like Receptor Prestimulation Increases Phagocytosis of Escherichia coli DH5
and Escherichia coli K1 Strains by Murine Microglial Cells 
,
Sandra Ribes,1*
Sandra Ebert,1
Dirk Czesnik,2
Tommy Regen,3
Andre Zeug,2,4
Stephanie Bukowski,1
Alexander Mildner,6
Helmut Eiffert,5
Uwe-Karsten Hanisch,3
Sven Hammerschmidt,7 and
Roland Nau1,8
Department of Neurology,1 Department of Neurophysiology and Cellular Biophysics,2 Institute of Neuropathology,3 DFG Research Center Molecular Physiology of the Brain (FZT 103),4 Department of Medical Microbiology, University of Göttingen, D-37075 Göttingen, Germany,5 Department of Neuropathology, University of Freiburg, D-79106 Freiburg, Germany,6 Max von Pettenkofer Institute, Ludwig-Maximilians University of München, D-80336 München, Germany,7 Department of Geriatrics, Evangelisches Krankenhaus Göttingen-Weende, D-37075 Göttingen, Germany8
Received 22 July 2008/ Returned for modification 23 August 2008/ Accepted 28 October 2008
Meningitis and meningoencephalitis caused by Escherichia coli are associated with high rates of mortality. When an infection occurs, Toll-like receptors (TLRs) expressed by microglial cells can recognize pathogen-associated molecular patterns and activate multiple steps in the inflammatory response that coordinate the brain's local defense, such as phagocytosis of invading pathogens. An upregulation of the phagocytic ability of reactive microglia could improve the host defense in immunocompromised patients against pathogens such as E. coli. Here, murine microglial cultures were stimulated with the TLR agonists Pam3CSK4 (TLR1/TLR2), lipopolysaccharide (TLR4), and CpG oligodeoxynucleotide (TLR9) for 24 h. Upon stimulation, levels of tumor necrosis factor alpha and the neutrophil chemoattractant CXCL1 were increased, indicating microglial activation. Phagocytic activity was studied after adding either E. coli DH5
or E. coli K1 strains. After 60 and 90 min of bacterial exposure, the number of ingested bacteria was significantly higher in cells prestimulated with TLR agonists than in unstimulated controls (P < 0.01). Addition of cytochalasin D, an inhibitor of actin polymerization, blocked >90% of phagocytosis. We also analyzed the ability of microglia to kill the ingested E. coli strains. Intracellularly surviving bacteria were quantified at different time points (90, 150, 240, and 360 min) after 90 min of phagocytosis. The number of bacteria killed intracellularly after 6 h was higher in cells primed with the different TLR agonists than in unstimulated microglia. Our data suggest that microglial stimulation by the TLR system can increase bacterial phagocytosis and killing. This approach could improve central nervous system resistance to infections in immunocompromised patients.
* Corresponding author. Mailing address: Department of Neurology, University of Göttingen, Robert Koch Str. 40, D-37075 Göttingen, Germany. Phone: 49 551 396689. Fax: 49 551 399337. E-mail: sribes{at}med.uni-goettingen.de
Published ahead of print on 3 November 2008.
Supplemental material for this article may be found at http://iai.asm.org/.
Infection and Immunity, January 2009, p. 557-564, Vol. 77, No. 1
0019-9567/09/$08.00+0 doi:10.1128/IAI.00903-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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