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Infect. Immun. doi:10.1128/IAI.00856-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Mechanisms of Dexamethasone-mediated inhibition of Toll-like receptor signaling induced by Neisseria meningitidis and Streptococcus pneumoniae

Trine H. Mogensen^*, Randi S. Berg, Søren R. Paludan, and Lars stergaard

Department of Infectious Diseases, Skejby Hospital, Aarhus, Denmark; Institute of Medical Microbiology and Immunology, University of Aarhus, Denmark

^* To whom correspondence should be addressed. Email: trine.mogensen{at}dadlnet.dk.

	Abstract

Excessive inflammation contributes to the pathogenesis of bacterial meningitis, which remains a serious disease despite treatment with antibiotics. Therefore, anti-inflammatory drugs have important therapeutic potential, and clinical trials have revealed that early treatment with dexamethasone significantly reduces mortality and morbidity from bacterial meningitis. Here we investigate the molecular mechanisms behind the inhibitory effect of dexamethasone upon the inflammatory response evoked by Neisseria meningitidis and Streptococcus pneumoniae, two of the major causes of bacterial meningitis. The inflammatory cytokine response was dependent on Toll-like receptor signaling and was strongly inhibited by dexamethasone. Activation of the NF-B pathway was targeted at several levels, including inhibition of IB phosphorylation and NF-B DNA binding activity as well as upregulation of IB synthesis. Our data also revealed that timing of steroid treatment relative to infection was important for achieving strong inhibition, particularly in response to S. pneumoniae. Altogether, we here describe important targets of dexamethasone in the inflammatory response evoked by N. meningitidis and S. pneumoniae, which may contribute to understanding of the clinical effect and the importance of timing with respect to corticosteroid treatment during bacterial meningitis.