Redundant and cooperative interactions between TLR5 and NLRC4 in protective lung mucosal immunity against Pseudomonas aeruginosa.
Flagellin is the major structural component of flagella expressed by Pseudomonas aeruginosa (PA) and other bacteria. This protein has been shown to activate the Toll-like receptor TLR5 and the Nod-like receptor Nlrc4/Ipaf, culminating in the expression of innate cytokines and antimicrobial molecules. In this study, we tested the hypothesis that TLR5 and Nlrc4 in combination are required for maximal protective lung innate mucosal immunity against PA. To test this hypothesis, we compared innate immune responses in wild-type (WT) C57B6 mice challenged with PA intratracheally to those observed in mice genetically deficient in TLR5 (TLR5(-/-)) or Nlrc4 (Nlrc4(-/-)) alone or in combination (TLR5/Nlrc4(-/-)). As compared to WT, TLR5(-/-) and Nlrc4(-/-) mice, we observed a significant increase in mortality in TLR5/Nlrc4(-/-) mice, which was associated with a >5,000-fold increase in lung PA colony-forming units and systemic bacterial dissemination. The increased mortality observed in double-deficient mice was not attributable to differences in lung leukocyte influx or lung injury responses. Levels of biologically active IL-1β and IL-18 were reduced in the bronchoalveolar lavage fluid from PA-infected Nlrc4(-/-) and TLR5/Nlrc4(-/-) but not TLR5(-/-) mice, indicating the requirement for Nlrc4-dependent caspase-1 activation. Similarly, decreased production of biologically active IL-1β and activation of caspase-1 was observed in PA-stimulated pulmonary macrophages isolated from Nlrc4(-/-) and TLR5/Nlrc4(-/-) but not TLR5(-/-) mice, whereas the expression of iNOS and the production of NO were significantly reduced in cells from double-mutant but not single-mutant mice. Collectively, our findings indicate that TLR5 and Nlrc4 have both unique and redundant roles in lung antibacterial mucosal immunity, and the absence of both pathogen recognition receptors results in an increase in susceptibility to invasive lung infection.
Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Michigan Medical Center, Ann Arbor, Mich., USA.
Leslie
L
Tolle
Fu-shin
FS
Yu
Melissa A
MA
Kovach
Megan N
MN
Ballinger
Michael W
MW
Newstead
Xianying
X
Zeng
Gabriel
G
Nunez
Theodore J
TJ
Standiford
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D058491:Bacterial Load / Q000235:genetics; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020170:Caspase 1 / Q000378:metabolism; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000235:genetics; D018928:Immunity, Mucosal; D020382:Interleukin-18 / Q000235:genetics / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D008168:Lung / Q000276:immunology* / Q000382:microbiology; D016676:Macrophages, Alveolar / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D011552:Pseudomonas Infections / Q000276:immunology*; D011550:Pseudomonas aeruginosa / Q000276:immunology*; D051198:Toll-Like Receptor 5 / Q000235:genetics / Q000378:metabolism*
D051017:Apoptosis Regulatory Proteins; D002135:Calcium-Binding Proteins; D020382:Interleukin-18; D053583:Interleukin-1beta; C512299:Ipaf protein, mouse; D051198:Toll-Like Receptor 5; D052247:Nitric Oxide Synthase Type II; D020170:Caspase 1