Legionnaires' Disease Bacterium (Legionella pneumophila) Multiplies Intracellularly in Human Monocytes

Horwitz, Marcus A.; Silverstein, Samuel C.

doi:10.1172/jci109874

Cited by 626 publications

(546 citation statements)

References 50 publications

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“…pneumophila harvested in the same way and then flash-frozen and maintained at -80"C until use; under these conditions the bacteria maintained their viability (1). In all other experiments, freshly harvested L. pneumophila were used.…”

Section: Ph Of the L Pneumophila Phagosomementioning

confidence: 99%

Legionella pneumophila inhibits acidification of its phagosome in human monocytes.

Horwitz¹,

Maxfield²

1984

The Journal of Cell Biology

357

229

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We used quantitative fluorescence microscopy to measure the pH of phagosomes in human monocytes that contain virulent Legionella pneumophila, a bacterial pathogen that multiplies intracellularly in these phagocytes. The mean pH of phagosomes that contain live L. pneumophila was 6.1 in 14 experiments. In the same experiments, the mean pH of phagosomes containing dead L. pneumophila averaged 0.8 pH units lower than the mean pH of phagosomes containing live L. pneumophila, a difference that was highly significant (P < 0.01 in all 14 experiments). In contrast, the mean pH of phagosomes initially containing live E. coil, which were then killed by monocytes, was the same as for phagosomes initially containing dead E. coli. The mean pH of L. pneumophila phagosomes in activated monocytes, which inhibit L. pneumophila intracellular multiplication, was the same as in nonactivated monocytes.To simultaneously measure the pH of different phagosomes within the same monocyte, we digitized and analyzed fluorescence images of monocytes that contained both live L. pneumophila and sheep erythrocytes. Within the same monocyte, live L. pneumophila phagosomes had a pH of ~6.1 and sheep erythrocyte phagosomes had a pH of ~5.0 or below.This study demonstrates that L. pneumophila is capable of modifying the pH of its phagocytic vacuole. This capability may be critical to the intracellular survival and multiplication of this and other intracellular pathogens.Legionella pneumophila, the agent of Legionnaires' disease, multiplies intracellularly in human mononuclear phagocytes within a membrane-bound cytoplasmic phagosome (1, 2).Live L. pneumophila inhibits fusion of the phagosome with monocyte lysosomes and induces the formation of a novel ribosome-lined phagosome. In contrast, formalin-killed L. pneumophila does not inhibit fusion or induce the formation of the specialized phagosome, and the dead bacteria are degraded within the phagolysosome (3, 4).The intraphagosomal pH has been measured or estimated in several bacteria and other particles that are phagocytized by mammalian phagocytes and later reside in phagolysosomes (5-11). These phagolysosomes become acidified. Since live and formalin-killed L. pneumophila have different intracellular destinies, we were interested in comparing the pH of phagosomes containing these two types of bacteria and exploring the possibility that alteration of intraphagosomal pH may play a role in L. pneumophila intracellular survival.In this paper, we used quantitative fluorescence microscopy to measure the pH of monocyte phagosomes that contain L.

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Section: Ph Of the L Pneumophila Phagosomementioning

confidence: 99%

Legionella pneumophila inhibits acidification of its phagosome in human monocytes.

Horwitz¹,

Maxfield²

1984

The Journal of Cell Biology

357

229

View full text Add to dashboard Cite

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“…After inhalation of L. pneumophila by immunocompromised humans, bacteria survive and replicate within alveolar macrophages (Horwitz and Silverstein 1980). Within the host cell, the bacteria establish a specialized Legionella-containing vacuole (LCV) in which L. pneumophila starts to replicate (Horwitz 1983;Horwitz and Maxfield 1984;Sturgill-Koszycki and Swanson 2000).…”

Section: Introductionmentioning

confidence: 99%

FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

et al. 2012

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“…Legionella pneumophila, the causative agent of Legionnaires' disease, is an intracellular pathogen that multiplies in nature inside amoebae and in human macrophages during disease (24,47). The icm/dot type IV secretion system is the major virulence system known in L. pneumophila; this system consists of 26 Icm/Dot proteins that probably constitute the secretion complex itself, as well as accessory proteins, such as chaperones (for a review, see reference 49).…”

mentioning

confidence: 99%

The Response Regulator CpxR Directly Regulates Expression of SeveralLegionella pneumophila icm/dotComponents as Well as New Translocated Substrates

2008

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Legionella pneumophila has been shown to utilize the icm/dot type IV secretion system for pathogenesis. This system was shown to be composed of icm/dot complex components and accessory proteins, as well as a large number of translocated substrates. Bioinformatic analysis of the regulatory regions of all the genes revealed that several icm/dot genes, as well as two genes encoding icm/dot translocated substrates, contain the conserved CpxR regulatory element, a regulator that has been shown previously to control the expression of the icmR gene. An experimental analysis, which included a comparison of gene expression in a L. pneumophila wild-type strain and gene expression in a cpxR deletion mutant, construction of mutants with mutations in the CpxR conserved regulatory elements, controlled expression studies, and mobility shift assays, demonstrated the direct relationship between the CpxR regulator and the expression of the genes. Furthermore, genomic analysis identified nine additional genes that contain a putative CpxR regulatory element; five of these genes (two legA genes and three ceg genes) were suggested previously to be putative icm/dot translocated substrates. The three ceg genes identified, which were shown previously to contain a putative PmrA regulatory element, were found here to be regulated by both CpxR and PmrA. The other six genes (two legA genes and four new genes products were found to be regulated by CpxR. Moreover, using the CyaA translocation assay, these nine gene products were found to be translocated into host cells in an Icm/Dot-dependent manner. Our results establish that the CpxR regulator is a fundamental regulator of the icm/dot type IV secretion system in L. pneumophila.

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Legionnaires' Disease Bacterium (Legionella pneumophila) Multiplies Intracellularly in Human Monocytes

Cited by 626 publications

References 50 publications

Legionella pneumophila inhibits acidification of its phagosome in human monocytes.

Legionella pneumophila inhibits acidification of its phagosome in human monocytes.

FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

The Response Regulator CpxR Directly Regulates Expression of SeveralLegionella pneumophila icm/dotComponents as Well as New Translocated Substrates

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