Toll-Like Receptor 4-Dependent Early Elicited Tumor Necrosis Factor Alpha Expression Is Critical for Innate Host Defense againstBordetella bronchiseptica

Abstract

Toll-like receptor 4 (TLR4) mediates the response to lipopolysaccharide, and its activation induces the expression of a large number of inflammatory genes, many of which are also induced by other pathogenassociated molecular patterns. Interestingly, the subset of genes that are dependent on TLR4 for optimal expression during gram-negative bacterial infection has not been determined. We have previously shown that TLR4-deficient mice rapidly develop acute pneumonia after inoculation with Bordetella bronchiseptica, suggesting that TLR4 is required for expression of early elicited gene products in this model. Microarray analysis with macrophages derived from wild-type and TLR4-deficient mice was used to identify genes whose expression, within 1 h of bacterial exposure, is dependent on TLR4. The results of this investigation suggest that TLR4 is not required for the majority of the transcriptional response to B. bronchiseptica. However, early tumor necrosis factor alpha (TNF-␣) mRNA expression is primarily dependent on TLR4 and in vitro and in vivo protein levels substantiate this finding. TLR4-deficient mice and TNF-␣ ؊/؊ mice are similarly susceptible to infection with relatively low doses of B. bronchiseptica and in vivo neutralization studies indicate that it is the TLR4-dependent early elicited TNF-␣ response that is critical for preventing severe pneumonia and limiting bacterial growth. These results suggest that one critical role for TLR4 is the generation of a robust but transient TNF-␣ response that is critical to innate host defense during acute gram-negative respiratory infection.

Redundant Toll-like receptor signaling in the pulmonary host response toPseudomonas aeruginosa

“…These results are similar to those of Ramphal and colleagues (46) but differ somewhat from those of Faure et al (14), who reported inoculum-dependent impairments in bacterial clearance and survival after endobronchial instillation of the PA103 strain of P. aeruginosa. TLR4-deficient mice also have been shown to exhibit reduced resistance to pulmonary infection with other gram-negative bacteria, including Pasteurella pneumotropica (8), Haemophilus influenzae (65,66), Klebsiella pneumoniae (7,50), Bordetella bronchiseptica (38), and Acinetobacter baumanii (32), but not Legionella pneumophila (34), Francisella tularensis (9), or Escherichia coli (33). TLR2 had a subtler role than TLR4 in the host response to P. aeruginosa.…”

Renal Collecting Duct Epithelial Cells React to Pyelonephritis-Associated Escherichia coli by Activating Distinct TLR4-Dependent and -Independent Inflammatory Pathways

“…For in vivo TNF-␣ neutralization experiments, Lps n and Lps d mice were i.p. injected 1 h before bacterial inoculation with 1 ml of PBS containing 1 mg of purified anti-mouse TNF-␣ from the MP6-XT3 mAb or with 1 mg of the rat IgG1 isotype control (eBioscience) (31). All experiments were performed in accordance with the guidelines of the French Agricultural Office and in compliance with the legislation governing animal studies.…”

The Complex Mechanism of Antibody-Mediated Clearance of Bordetella from the Lungs Requires TLR4

“…We have previously shown that one such receptor, TLR4, is critical for controlling the respiratory pathogen B. bronchiseptica (22). TLR4 d mice inoculated with a standard dose (5 ϫ 10 5 CFU in 50 l of PBS given by intranasal route) of B. bronchiseptica succumbed to bordetellosis as early as day 3 postinoculation, whereas TLR4 s mice survive and eventually clear bacteria from the lower respiratory tract (16).…”