Legionella pneumophila Type II Secretion Dampens the Cytokine Response of Infected Macrophages and Epithelia
01 May 2011-Infection and Immunity (American Society for Microbiology)-Vol. 79, Iss: 5, pp 1984-1997
TL;DR: The impact of T2S on lung infection is a combination of at least three factors: the promotion of growth in macrophages, the facilitation ofrowth in epithelia, and the dampening of the chemokine and cytokine output from infected host cells.
Abstract: The type II secretion (T2S) system of Legionella pneumophila is required for the ability of the bacterium to grow within the lungs of A/J mice. By utilizing mutants lacking T2S (lsp), we now document that T2S promotes the intracellular infection of both multiple types of macrophages and lung epithelia. Following infection of macrophages, lsp mutants (but not a complemented mutant) elicited significantly higher levels of interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), IL-10, IL-8, IL-1β, and MCP-1 within tissue culture supernatants. A similar result was obtained with infected lung epithelial cell lines and the lungs of infected A/J mice. Infection with a mutant specifically lacking the T2S-dependent ProA protease (but not a complemented proA mutant) resulted in partial elevation of cytokine levels. These data demonstrate that the T2S system of L. pneumophila dampens the cytokine/chemokine output of infected host cells. Upon quantitative reverse transcription (RT)-PCR analysis of infected host cells, an lspF mutant, but not the proA mutant, produced significantly higher levels of cytokine transcripts, implying that some T2S-dependent effectors dampen signal transduction and transcription but that others, such as ProA, act at a posttranscriptional step in cytokine expression. In summary, the impact of T2S on lung infection is a combination of at least three factors: the promotion of growth in macrophages, the facilitation of growth in epithelia, and the dampening of the chemokine and cytokine output from infected host cells. To our knowledge, these data are the first to identify a link between a T2S system and the modulation of immune factors following intracellular infection.
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TL;DR: The reach of T2S is perhaps best illustrated by those bacteria that clearly use it for both environmental survival and virulence; e.g., L. pneumophila employs T1S for infection of amoebae, growth within lung cells, dampening of cytokines, and tissue destruction.
Abstract: Type II secretion (T2S) is one means by which Gram-negative pathogens secrete proteins into the extracellular milieu and/or host organisms. Based upon recent genome sequencing, it is clear that T2S is largely restricted to the Proteobacteria, occurring in many, but not all, genera in the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria classes. Prominent human and/or animal pathogens that express a T2S system(s) include Acinetobacter baumannii, Burkholderia pseudomallei, Chlamydia trachomatis, Escherichia coli, Klebsiella pneumoniae, Legionella pneumophila, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Vibrio cholerae, and Yersinia enterocolitica T2S-expressing plant pathogens include Dickeya dadantii, Erwinia amylovora, Pectobacterium carotovorum, Ralstonia solanacearum, Xanthomonas campestris, Xanthomonas oryzae, and Xylella fastidiosa T2S also occurs in nonpathogenic bacteria, facilitating symbioses, among other things. The output of a T2S system can range from only one to dozens of secreted proteins, encompassing a diverse array of toxins, degradative enzymes, and other effectors, including novel proteins. Pathogenic processes mediated by T2S include the death of host cells, degradation of tissue, suppression of innate immunity, adherence to host surfaces, biofilm formation, invasion into and growth within host cells, nutrient assimilation, and alterations in host ion flux. The reach of T2S is perhaps best illustrated by those bacteria that clearly use it for both environmental survival and virulence; e.g., L. pneumophila employs T2S for infection of amoebae, growth within lung cells, dampening of cytokines, and tissue destruction. This minireview provides an update on the types of bacteria that have T2S, the kinds of proteins that are secreted via T2S, and how T2S substrates promote infection.
140 citations
Cites background from "Legionella pneumophila Type II Secr..."
...Besides facilitating bacterial growth in macrophages, T2S is necessary for optimal replication within epithelial cells, which likely are a secondary host cell during lung infection (59)....
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...pneumophila intracellular infection of macrophages (26, 59)....
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...system dampens the cytokine output of infected macrophages and epithelial cells (59)....
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TL;DR: Analysis of the Legionella pneumophila strain 130b chromosome detected a subtype II-B CRISPR-Cas locus that contains cas9, cas1, cas2, cas4, and an array with 60 repeats and 58 unique spacers that indicates that cas2 has a role in the transmission of Legionnaires' disease.
Abstract: Recent studies have shown that the clustered regularly interspaced palindromic repeats (CRISPR) array and its asso- ciated (cas) genes can play a key role in bacterial immunity against phage and plasmids. Upon analysis of the Legionella pneumo- philastrain 130b chromosome, we detected a subtype II-B CRISPR-Cas locus that contains cas9,cas1,cas2,cas4, and an array with 60 repeats and 58 unique spacers. Reverse transcription (RT)-PCR analysis demonstrated that the entire CRISPR-Cas locus is expressed during 130b extracellular growth in both rich and minimal media as well as during intracellular infection of macro- phages and aquatic amoebae. Quantitative reverse transcription-PCR (RT-PCR) further showed that the levels of castranscripts, especially those ofcas1andcas2, are elevated during intracellular growth relative to exponential-phase growth in broth. Mutants lacking components of the CRISPR-Cas locus were made and found to grow normally in broth and on agar media. cas9,cas1, cas4, and CRISPR array mutants also grew normally in macrophages and amoebae. However, cas2mutants, although they grew typically in macrophages, were significantly impaired for infection of both Hartmannella andAcanthamoeba species. A comple- mentedcas2mutant infected the amoebae at wild-type levels, confirming that cas2is required for intracellular infection of these host cells. IMPORTANCE Given that infection of amoebae is critical for L. pneumophila persistence in water systems, our data indicate that cas2has a role in the transmission of Legionnaires' disease. Because our experiments were done in the absence of added phage, plasmid, or nucleic acid, the event that is facilitated by Cas2 is uniquely distinct from current dogma concerning CRISPR-Cas function.
93 citations
Cites background or methods from "Legionella pneumophila Type II Secr..."
...5 105 cells, and after 3 days in RPMI with 10% FBS and 10% L-cell supernatant, monolayers were infected with bacteria as before (98)....
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...2) and bone marrow-derived (BMD) macrophages obtained from mice (98)....
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TL;DR: Studies from the past 5 years that have reported the induction of IL-10 by different classes of pathogenic microorganisms, including protozoa, nematodes, fungi, viruses and bacteria are summarized and the impact of this induction on the persistence and/or clearance of microorganisms in the host is discussed.
Abstract: Since its initial description as a Th2-cytokine antagonistic to interferon-alpha and granulocyte-macrophage colony-stimulating factor, many studies have shown various anti-inflammatory actions of interleukin-10 (IL-10), and its role in infection as a key regulator of innate immunity. Studies have shown that IL-10 induced in response to microorganisms and their products plays a central role in shaping pathogenesis. IL-10 appears to function as both sword and shield in the response to varied groups of microorganisms in its capacity to mediate protective immunity against some organisms but increase susceptibility to other infections. The nature of IL-10 as a pleiotropic modulator of host responses to microorganisms is explained, in part, by its potent and varied effects on different immune effector cells which influence antimicrobial activity. A new understanding of how microorganisms trigger IL-10 responses is emerging, along with recent discoveries of how IL-10 produced during disease might be harnessed for better protective or therapeutic strategies. In this review, we summarize studies from the past 5 years that have reported the induction of IL-10 by different classes of pathogenic microorganisms, including protozoa, nematodes, fungi, viruses and bacteria and discuss the impact of this induction on the persistence and/or clearance of microorganisms in the host.
81 citations
Cites background from "Legionella pneumophila Type II Secr..."
...…2008; Lazarus et al., 2008; Rocha-Ramirez et al., 2008; Souza et al., 2008; Bogaert et al., 2009; Fang et al., 2009; Strle et al., 2009; Sinsimer et al., 2010; Vargas-Inchaustegui et al., 2010; Groseth et al., 2011; McCoy-Simandle et al., 2011; Ota et al., 2011; Stabel & Robbe-Austerman, 2011)....
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...It is sourced principally from monocytes/macrophages, dendritic cells, CD4(+) and T-reg lymphocytes during or shortly after antigen presentation (Ettinger et al., 1995; Bourreau et al., 2007; Bozza et al., 2007; De Witte et al., 2007; Ferreira et al., 2007; Goldmann et al., 2007; Kurokawa et al., 2007; McNally et al., 2007; Obonyo et al., 2007; Patrone & Stein, 2007; Setiawan et al., 2007; Xin et al., 2007; Yang et al., 2007; Couper et al., 2008a, b; Jongyota et al., 2008; Lazarus et al., 2008; Rocha-Ramirez et al., 2008; Souza et al., 2008; Bogaert et al., 2009; Fang et al., 2009; Strle et al., 2009; Sinsimer et al., 2010; Vargas-Inchaustegui et al., 2010; Groseth et al., 2011; McCoy-Simandle et al., 2011; Ota et al., 2011; Stabel & Robbe-Austerman, 2011)....
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TL;DR: The current knowledge of secretion systems in Acinetobacter species are summarized, and their unique aspects that contribute to the pathogenicity and persistence of these emerging pathogens are highlighted.
59 citations
TL;DR: T2S substrates NttA, NttB, and LegP were targeted for mutation and documented that the T2S system exports multiple effectors, including a novel one, which contribute in different ways to the broad host range of L. pneumophila.
Abstract: Type II protein secretion (T2S) by Legionella pneumophila is required for intracellular infection of host cells, including macrophages and the amoebae Acanthamoeba castellanii and Hartmannella vermiformis. Previous proteomic analysis revealed that T2S by L. pneumophila 130b mediates the export of >25 proteins, including several that appeared to be novel. Following confirmation that they are unlike known proteins, T2S substrates NttA, NttB, and LegP were targeted for mutation. nttA mutants were impaired for intracellular multiplication in A. castellanii but not H. vermiformis or macrophages, suggesting that novel exoproteins which are specific to Legionella are especially important for infection. Because the importance of NttA was host cell dependent, we examined a panel of T2S substrate mutants that had not been tested before in more than one amoeba. As a result, RNase SrnA, acyltransferase PlaC, and metalloprotease ProA all proved to be required for optimal intracellular multiplication in H. vermiformis but not A. castellanii. Further examination of an lspF mutant lacking the T2S apparatus documented that T2S is also critical for infection of the amoeba Naegleria lovaniensis. Mutants lacking SrnA, PlaC, or ProA, but not those deficient for NttA, were defective in N. lovaniensis. Based upon analysis of a double mutant lacking PlaC and ProA, the role of ProA in H. vermiformis was connected to its ability to activate PlaC, whereas in N. lovaniensis, ProA appeared to have multiple functions. Together, these data document that the T2S system exports multiple effectors, including a novel one, which contribute in different ways to the broad host range of L. pneumophila.
52 citations
Cites background or methods from "Legionella pneumophila Type II Secr..."
...These data indicated that ChiA, LipA, LipB, Map, PlaA, PlcA, and PlcB, like CelA, LapA, and LapB, are not required for infection of H. vermiformis or A. castellanii....
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...In order to isolate an lpw30971 (plaC) mutant, plasmid pGplaC (7) was digested with BamHI, and blunt ends were generated....
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...host cells, and elaborating tissue-destructive enzymes (7, 16, 28)....
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...pneumophila multiplies in alveolar macrophages although persistence likely also involves growth in lung epithelial cells and extracellular survival (6, 7)....
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...In testing the importance of plcA, we utilized a recently made double mutant that lacks both PlcA and PlcB, a putative T2S-dependent phospholipase C that is closely related to PlcA (7)....
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517 citations
Additional excerpts
...pneumophila, TLR2 recognizes lipopolysaccharide (LPS) and lipoprotein, TLR5 flagellin, TLR9 CpG sequences in DNA, NOD1 and NOD2 peptidoglycans, and Naip5 and Ipaf flagellin (1, 3, 7, 9, 13, 23, 30, 45, 48, 53, 54, 60, 65, 75, 81, 92, 102, 103, 117, 120)....
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