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Infect. Immun. doi:10.1128/IAI.00486-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A potential role for TLR4 in mediating Escherichia coli maltose-binding protein activation of dendritic cells

Department of Virus Diseases, Department of Pathology, Walter Reed Army Institute of Research, Viral Diseases Department, Naval Medical Research Center, Silver Spring, MD 20910

^* To whom correspondence should be addressed. Email: stefan.fernandez{at}na.amedd.army.mil.

	Abstract

The Escherichia coli maltose binding protein (MBP) is used to increase the stability and solubility of proteins in bacterial protein expression systems and is increasingly being used to facilitate the production and delivery of subunit vaccines against various pathogenic bacteria and viruses. The MBP tag is presumed inert with minimum effects on the bioactivity of the tagged protein or its biodistribution. However, few studies have characterized the immunological attributes of MBP. Here, we analyze the phenotypic and functional outcome of MBP-treated dendritic cells (DCs) and show that MBP induced DC activation and production of pro-inflammatory cytokines (IL-1, IL-6, IL-8, TNF-, IL-12p70) within 24h, and strongly increased I phosphorylation in treated cells. Interestingly, phosphorylation of I was largely abrogated by the addition of anti-human Toll-like receptor (TLR) 4 antibodies indicating that MBP activates signaling for DC maturation via TLR4. Consistent with this hypothesis, MBP activated the TLR4-expressing cell line 293-hTLR4A but not control cultures to secrete IL-8. The observed data were independent of LPS contamination and support a role for TLR4 in mediating the effects of MBP. These results provide insight into a mechanism by which MBP might enhance immune responses to vaccine fusion proteins.