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Infection and Immunity, January 2006, p. 594-601, Vol. 74, No. 1
0019-9567/06/$08.00+0     doi:10.1128/IAI.74.1.594-601.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Identification and Characterization of a Novel Bacterial Virulence Factor That Shares Homology with Mammalian Toll/Interleukin-1 Receptor Family Proteins

Ruchi M. Newman, Prabhakar Salunkhe, Adam Godzik, and John C. Reed^*

Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, California 92037

Received 29 June 2005/ Returned for modification 29 August 2005/ Accepted 18 October 2005

Many important bacterial virulence factors act as mimics of mammalian proteins to subvert normal host cell processes. To identify bacterial protein mimics of components of the innate immune signaling pathway, we searched the bacterial genome database for proteins with homology to the Toll/interleukin-1 receptor (TIR) domain of the mammalian Toll-like receptors (TLRs) and their adaptor proteins. A previously uncharacterized gene, which we have named tlpA (for TIR-like protein A), was identified in the Salmonella enterica serovar Enteritidis genome that is predicted to encode a protein resembling mammalian TIR domains, We show that overexpression of TlpA in mammalian cells suppresses the ability of mammalian TIR-containing proteins TLR4, IL-1 receptor, and MyD88 to induce the transactivation and DNA-binding activities of NF-B, a downstream target of the TIR signaling pathway. In addition, TlpA mimics the previously characterized Salmonella virulence factor SipB in its ability to induce activation of caspase-1 in a mammalian cell transfection model. Disruption of the chromosomal tlpA gene rendered a virulent serovar Enteritidis strain defective in intracellular survival and IL-1ß secretion in a cell culture infection model using human THP1 macrophages. Bacteria with disrupted tlpA also displayed reduced lethality in mice, further confirming an important role for this factor in pathogenesis. Taken together, our findings demonstrate that the bacterial TIR-like protein TlpA is a novel prokaryotic modulator of NF-B activity and IL-1ß secretion that contributes to serovar Enteritidis virulence.

Editor: F. C. Fang

Present address: Harvard Medical School/NEPRC, 1 Pine Hill Dr., Southborough, MA 01772.

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