Pseudomonas aeruginosa LPS or flagellin are sufficient to activate TLR-dependent signaling in murine alveolar macrophages and airway epithelial cells.
BACKGROUND
The human lung is exposed to a large number of airborne pathogens as a result of the daily inhalation of 10,000 liters of air. Innate immunity is thus essential to defend the lungs against these pathogens. This defense is mediated in part through the recognition of specific microbial ligands by Toll-like receptors (TLR) of which there are at least 10 in humans. Pseudomonas aeruginosa is the main pathogen that infects the lungs of cystic fibrosis patients. Based on whole animal experiments, using TLR knockout mice, the control of this bacterium is believed to occur by the recognition of LPS and flagellin by TLRs 2,4 and 5, respectively.


RESULTS
In the present study, we investigated in vitro the role of these same TLR and ligands, in alveolar macrophage (AM) and epithelial cell (EC) activation. Cellular responses to P. aeruginosa was evaluated by measuring KC, TNF-alpha, IL-6 and G-CSF secretion, four different markers of the innate immune response. AM and EC from WT and TLR2, 4, 5 and MyD88 knockout mice for were stimulated with the wild-type P. aeruginosa or with a mutant devoid of flagellin production.


CONCLUSIONS
The results clearly demonstrate that only two ligand/receptor pairs are necessary for the induction of KC, TNF-alpha, and IL-6 synthesis by P. aeruginosa-activated cells, i.e. TLR2,4/LPS and TLR5/flagellin. Either ligand/receptor pair is sufficient to sense the bacterium and to trigger cell activation, and when both are missing lung EC and AM are unable to produce such a response as were cells from MyD88(-/-) mice.
Raoust
Eloïse
E
Unité de Défense Innée et Inflammation, Institut Pasteur, Paris, France.
Balloy
Viviane
V
Garcia-Verdugo
Ignacio
I
Touqui
Lhousseine
L
Ramphal
Reuben
R
Chignard
Michel
M
D000818:Animals; D054360:Chemokine CXCL1 / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology*; D005260:Female; D005408:Flagellin / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D015850:Interleukin-6 / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000378:metabolism*; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D051198:Toll-Like Receptor 5 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*
D054360:Chemokine CXCL1; C475895:Cxcl1 protein, mouse; D015850:Interleukin-6; D008070:Lipopolysaccharides; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051198:Toll-Like Receptor 5; D014409:Tumor Necrosis Factor-alpha; D005408:Flagellin