Role of Toll-Like Receptor 9 in
            <i>Legionella pneumophila</i>
            -Induced Interleukin-12 p40 Production in Bone Marrow-Derived Dendritic Cells and Macrophages from Permissive and Nonpermissive Mice

Newton, Cathy; Perkins, Izabella; Widen, Raymond; Friedman, Herman; Klein, Thomas

doi:10.1128/iai.01011-06

Cited by 40 publications

(34 citation statements)

References 46 publications

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“…Previous studies used knockout mice and BMD macrophages from these knockout mice to demonstrate that during intracellular infection, L. pneumophila stimulates TLRs, including both cell surface TLR2 (via the recognition of lipoprotein and LPS) and TLR5 (flagellin) and intracellular TLR9 (CpG oligodeoxynucleotide) (64)(65)(66)(67)(68)(69). In order to test, for the first time, the importance of these pathways in human macrophages, we started out by generating a stable knockdown of MyD88 with a 76% decrease in protein expression (Fig.…”

Section: Resultsmentioning

confidence: 99%

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

2017

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Previously, we reported that mutants of Legionella pneumophila lacking a type II secretion (T2S) system elicit higher levels of cytokines (e.g., interleukin-6 [IL-6]) following infection of U937 cells, a human macrophage-like cell line. We now show that this effect of T2S is also manifest upon infection of human THP-1 macrophages and peripheral blood monocytes but does not occur during infection of murine macrophages. Supporting the hypothesis that T2S acts to dampen the triggering of an innate immune response, we observed that the mitogen-activated protein kinase (MAPK) and nuclear transcription factor kappa B (NF-B) pathways are more highly stimulated upon infection with the T2S mutant than upon infection with the wild type. By using short hairpin RNA to deplete proteins involved in specific pathogen-associated molecular pattern (PAMP) recognition pathways, we determined that the dampening effect of the T2S system was not dependent on nucleotide binding oligomerization domain (NOD)-like receptors (NLRs), retinoic acid-inducible protein I (RIG-I)-like receptors (RLRs), double-stranded RNA (dsRNA)-dependent protein kinase receptor (PKR), or TIR domain-containing adaptor inducing interferon beta (TRIF) signaling or an apoptosis-associated speck-like protein containing a CARD (ASC)-or caspase-4-dependent inflammasome. However, the dampening effect of T2S on IL-6 production was significantly reduced upon gene knockdown of myeloid differentiation primary response 88 (MyD88), TANK binding kinase 1 (TBK1), or Toll-like receptor 2 (TLR2). These data indicate that the L. pneumophila T2S system dampens the signaling of the TLR2 pathway in infected human macrophages. We also document the importance of PKR, TRIF, and TBK1 in cytokine secretion during L. pneumophila infection of macrophages.KEYWORDS Legionella pneumophila, TLR2, cytokine, innate immunity, macrophage, type II secretion L egionella pneumophila, a Gram-negative bacterium that is widespread in aquatic habitats, is the principal agent of Legionnaires' disease pneumonia (1-6). In the lungs, Legionella bacteria invade and grow in resident macrophages and then trigger severe inflammation (2). In macrophages, L. pneumophila evades the degradative lysosomal pathway and replicates to large numbers within a membrane-bound vacuole, the Legionella-containing vacuole (LCV) (7,8). Two protein secretion systems, Lsp type II secretion (T2S) and Dot/Icm type IV secretion (T4S), play major roles in the pathogenesis of L. pneumophila (9, 10). In T2S, protein substrates are first translocated across the inner membrane, and upon the action of the T2S pilus-like apparatus, they then exit the bacterial cell through a specific outer membrane pore (11). Using proteomics and enzymatic assays, we have shown that the T2S system of L. pneumo-

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Section: Resultsmentioning

confidence: 99%

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

2017

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“…These data address an important question in microbial recognition regarding redundancy among TLRs. L. pneumophila is recognized by several TLRs including TLR2, TLR4, TLR5, and TLR9 (17)(18)(19)(20)(22)(23)(24). Interestingly, Legionella LPS signals predominantly through TLR2, rather than TLR4, suggesting an important role for TLR2 in Legionella recognition (18).…”

Section: Discussionmentioning

confidence: 99%

“…TLRs recognize microbes at the plasma membrane or within organelles, such as phagosomes and endosomes, while NLRs mediate pathogen recognition in the cytosol. We, and others, have used in vitro and in vivo studies to demonstrate that L. pneumophila is recognized by several TLRs including TLR2, TLR4, TLR5, and TLR9 (17)(18)(19)(20)(21)(22)(23)(24). Using human genetic studies, we previously found that a common stop codon polymorphism in TLR5, a receptor for bacterial flagellin, abrogates signaling and is associated with altered susceptibility to Legionnaires' Disease (20).…”

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confidence: 99%

Altered Inflammatory Responses in TLR5-Deficient Mice Infected with Legionella pneumophila

Hawn

Berrington

Smith

et al. 2007

The Journal of Immunology

107

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Legionella pneumophila (Lp), an important cause of morbidity and mortality from pneumonia, infects alveolar macrophages (AMs) and is recognized by several TLRs as well as Birc1e (NAIP5) and IL-1 converting enzyme-protease activating factor. We examined the role of TLR5 during the murine response to aerosolized Lp infection. At 4 h after infection, Tlr5−/− mice had lower numbers of polymorphonuclear neutrophils (PMNs) in their broncho-alveolar lavage fluid in comparison to wild-type (WT) mice. At 24 and 72 h, the PMN recruitment was similar. WT mice infected with a flagellin-deficient strain (LpFlaA−) also showed an impaired early PMN response at 4 h compared with those infected with the WT strain. There was no consistent difference in bacterial counts at any of the time points when comparing the Tlr5−/− and WT mice. However, at 6 days after infection, the Tlr5−/− mice had increased leukocytic infiltrates in the alveolar and peribronchial interstitial spaces that were consistent with organizing pneumonia. We also examined the role of TLR5 during macrophage infection. In contrast to bone marrow-derived macrophages, AMs secreted TNF-α after stimulation with purified flagellin. In addition, WT, but not Tlr5−/−, AMs produced TNF-α after stimulation with Lp. Live LpFlaA− did not induce TNF-α secretion in AM. These results suggested that AMs recognize Lp flagellin and that a majority of the Lp-induced TNF-α response is TLR5-mediated. Thus, TLR5 mediates recognition of Lp in AMs and performs a distinct role during the in vivo pulmonary immune response through regulation of early PMN recruitment and subsequent later development of pneumonia.

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“…Several studies have reported that TLRs contribute to the host response against L. pneumophila during in vitro and in vivo infection (Girard et al, 2003;Kikuchi et al, 2004;Akamine et al, 2005;Hawn et al, 2006Hawn et al, , 2007Fuse et al, 2007;Newton et al, 2007). However, there have been no studies to elucidate immunostimulatory properties of isolated individual proteins from L. pneumophila in terms of engagement of TLRs and linking to elicit the antigen-specific adaptive immune responses.…”

Section: Introductionmentioning

confidence: 99%

Legionella lipoprotein activates toll-like receptor 2 and induces cytokine production and expression of costimulatory molecules in peritoneal macrophages

Shim

Kim

et al. 2009

Exp Mol Med

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Legionella bacterium, an intracellular pathogen of mononuclear phagocytes, causes acute fatal pneumonia, especially in patients with impaired cellular immune responses. Until recently, however, the toll-like receptor (TLR) engagement of bacterial proteins derived from Legionella is uncertain. We previously showed that a 19-kDa highly conserved peptidoglycan-associated lipoprotein (PAL) of Legionella pneumophila induced the PAL-specific B cell and T cell responses in mice. In this study, we observed that the rPAL antigen of L. pneumophila, as an effector molecule, activated murine macrophages via TLR2 and produced proinflammatory cytokines such as IL-6 and TNF-α. In both BALB/c and TLR4-deficient C3H/HeJ mice, pretreatment of macrophages with anti-TLR2 mAb showed severely impaired cytokine production in response to the rPAL. In addition, in vitro the rPAL treatment increased the cell surface expression of CD40, CD80, CD86 and MHC I/II molecules. We further showed that the synthetic CpG-oligodeoxynucleotides (CpG ODN) coadministered with the rPAL enhanced IL-12 and IL-6 production and expression of CD40, CD80 and MHC II compared to the rPAL treatment alone. In conclusions, these results indicate that Legionella PAL might activate macrophages via a TLR2-dependent mechanism which thus induce cytokine production and expression of costimulatory and MHC molecules.

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Role of Toll-Like Receptor 9 in Legionella pneumophila -Induced Interleukin-12 p40 Production in Bone Marrow-Derived Dendritic Cells and Macrophages from Permissive and Nonpermissive Mice

Cited by 40 publications

References 46 publications

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

Altered Inflammatory Responses in TLR5-Deficient Mice Infected with Legionella pneumophila

Legionella lipoprotein activates toll-like receptor 2 and induces cytokine production and expression of costimulatory molecules in peritoneal macrophages

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