Legionella pneumophila induces IFNbeta in lung epithelial cells via IPS-1 and IRF3, which also control bacterial replication.
Legionella pneumophila, a Gram-negative facultative intracellular bacterium, causes severe pneumonia (Legionnaires' disease). Type I interferons (IFNs) were so far associated with antiviral immunity, but recent studies also indicated a role of these cytokines in immune responses against (intracellular) bacteria. Here we show that wild-type L. pneumophila and flagellin-deficient Legionella, but not L. pneumophila lacking a functional type IV secretion system Dot/Icm, or heat-inactivated Legionella induced IFNbeta expression in human lung epithelial cells. We found that factor (IRF)-3 and NF-kappaB-p65 translocated into the nucleus and bound to the IFNbeta gene enhancer after L. pneumophila infection of lung epithelial cells. RNA interference demonstrated that in addition to IRF3, the caspase recruitment domain (CARD)-containing adapter molecule IPS-1 (interferon-beta promoter stimulator 1) is crucial for L. pneumophila-induced IFNbeta expression, whereas other CARD-possessing molecules, such as RIG-I (retinoic acid-inducible protein I), MDA5 (melanoma differentiation-associated gene 5), Nod27 (nucleotide-binding oligomerization domain protein 27), and ASC (apoptosis-associated speck-like protein containing a CARD) seemed not to be involved. Finally, bacterial multiplication assays in small interfering RNA-treated cells indicated that IPS-1, IRF3, and IFNbeta were essential for the control of intracellular replication of L. pneumophila in lung epithelial cells. In conclusion, we demonstrated a critical role of IPS-1, IRF3, and IFNbeta in Legionella infection of lung epithelium.
Opitz
Bastian
B
Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany. bastian.opitz@charite.de
Vinzing
Maya
M
van Laak
Vincent
V
Schmeck
Bernd
B
Heine
Guido
G
Günther
Stefan
S
Preissner
Robert
R
Slevogt
Hortense
H
N'Guessan
Philippe Dje
PD
Eitel
Julia
J
Goldmann
Torsten
T
Flieger
Antje
A
Suttorp
Norbert
N
Hippenstiel
Stefan
S
D021581:Active Transport, Cell Nucleus; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism*; D016899:Interferon-beta / Q000378:metabolism*; D016952:Legionella pneumophila / Q000378:metabolism / Q000502:physiology*; D008168:Lung / Q000166:cytology* / Q000378:metabolism / Q000382:microbiology*; D016328:NF-kappa B / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction
D048868:Adaptor Proteins, Signal Transducing; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; C505371:MAVS protein, human; D016328:NF-kappa B; D012313:RNA; D016899:Interferon-beta