Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
. 2005 Jun 14;102(24):8722-7.
doi: 10.1073/pnas.0501863102. Epub 2005 Jun 6.

Virulent Coxiella burnetii does not activate human dendritic cells: role of lipopolysaccharide as a shielding molecule

Jeffrey G Shannon  1 , Dale Howe, Robert A Heinzen
Affiliations
Comparative Study

Virulent Coxiella burnetii does not activate human dendritic cells: role of lipopolysaccharide as a shielding molecule

Jeffrey G Shannon et al. Proc Natl Acad Sci U S A. .

Abstract

Coxiella burnetii is an obligate intracellular bacterium and the etiological agent of the zoonotic disease Q fever. Acute human Q fever is characterized by flu-like symptoms that, in some cases, can result in a persistent infection that may reactivate months or years after initial exposure. Mechanisms by which this obligate parasite evades clearance by the host immune response during persistent infection are unknown. Here, we characterized the interaction of C. burnetii with dendritic cells (DC), critical components of both innate and adaptive immunity. Human DC were infected with two isogenic C. burnetii strains that differ in LPS length. Infection by the Nine Mile phase I (NMI) strain, which is fully virulent and produces full-length LPS, did not result in DC maturation. In contrast, infection by the avirulent Nine Mile phase II strain, producing a severely truncated LPS, resulted in toll-like receptor 4-independent DC maturation and approximately 10-fold more IL-12 and TNF production. NMI did not actively inhibit DC maturation as NMI-infected DC subsequently matured if treated with Escherichia coli LPS or Nine Mile phase II. Furthermore, removal of LPS from NMI dramatically increased its ability to stimulate DC. We propose a model whereby LPS of virulent C. burnetii masks toll-like receptor ligands from innate immune recognition by DC, thereby allowing replication without significant maturation or inflammatory cytokine production. This immune evasion strategy may allow C. burnetii to persist in an immunocompetent host.

PubMed Disclaimer

Figures

Fig. 1.
Fig. 1.
FACS analysis of DC maturation in response to infection by NMI or NMII C. burnetii. Human monocyte-derived DC were either mock-infected or infected with C. burnetii NMI or NMII for 48 h, then stained for the maturation markers CD86, CD83, CD80, HLA-DR(MHC-II), and CD40. Cell staining was measured by flow cytometry. Treatment with E. coli LPS served as a positive control for DC maturation. The blue histograms depict staining of mock-infected cells. The red histograms depict either infected or LPS-treated cells. The dotted black histogram depicts isotype control staining. The results shown are from one experiment and are representative of five independent experiments.
Fig. 2.
Fig. 2.
DC produce IL-12 and TNF in response to infection by NMII, but not NMI, C. burnetii. Human DC were either mock-infected or infected (MOI = 20) for 48 h with C. burnetii NMI or NMII. Cell culture supernatants were collected, and their IL-12p70 and TNF concentrations were determined by ELISA. The results shown are from one experiment and are representative of three independent experiments.
Fig. 3.
Fig. 3.
p38 MAPK is phosphorylated in DC in response to infection by NMII C. burnetii. Human DC were either mock-infected or infected (MOI = 20) with C. burnetii NMI or NMII for 48 h. (Upper) Proteins in cell extracts were separated by SDS/PAGE, blotted, and probed with anti-phospho-p38 MAPK antibody. (Lower) Blots were then stripped and reprobed for total p38 MAPK with anti-p38 MAPK antibody. Results shown are representative of three independent experiments.
Fig. 4.
Fig. 4.
C. burnetii NMI and NMII productively infect human DC. (A) Human DC infected for 48 h were stained by indirect immunofluorescence for C. burnetii (green) and CD63 (red). Micrographs depict spacious CD63-positive vacuoles harboring NMI or NMII bacteria. The fields shown here are representative of the majority of the sample. The percentage of infected, vacuole-containing cells approached 100%. (Bars: 5 μm.) (B) Human DC were infected with either NMI (MOI = 100) or NMII (MOI = 10) as described in Materials and Methods. The number of bacterial genomes at 0, 48, 96, 144, and 192 h postinfection was determined by quantitative PCR. The results shown are from one experiment performed in triplicate and are representative of three independent experiments.
Fig. 5.
Fig. 5.
NMI C. burnetii does not actively inhibit DC maturation. DC were either mock-infected or infected with NMI (MOI = 20) for 18 h, then both samples were left untreated (black histograms), treated with LPS (blue histograms), or infected with NMII (red histograms) (MOI = 20) for an additional 24 h. CD86 expression was measured by flow cytometry. (Left) Staining of cells that were mock-infected before LPS treatment or NMII infection. (Right) Staining of cells that were preinfected with NMI.
Fig. 6.
Fig. 6.
DC maturation in response to NMII C. burnetii is CD14-independent. Human DC were transferred to DC medium containing 5% human AB serum in place of FBS, then incubated with an anti-CD14 blocking antibody or a nonspecific isotype control antibody for 30 min. Cells were then infected with NMII (Left) (MOI = 20) or treated with E. coli LPS (Right) for 24 h. CD86 expression was measured by flow cytometry. The solid black histogram represents staining of cells treated with isotype control antibody. The dashed histogram represents staining of cells treated with CD14 blocking antibody. The shaded histogram is the staining isotype control.
Fig. 7.
Fig. 7.
TCA-extracted NMI C. burnetii induces DC maturation. Both NMI and NMII were TCA-extracted in an identical fashion. C. burnetii treated with K-36 buffer served as controls. Extracted bacteria were then added to human DC cultures for 48 h at an MOI of 20, and CD86 expression was measured by flow cytometry. The solid black histogram represents staining of mock-infected cells. The blue histogram represents staining of cells exposed to K-36-treated control bacteria. The red histogram represents staining of cells exposed to TCA-extracted bacteria. The shaded histogram is the isotype staining control. Results shown are representative of three independent experiments.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Maurin, M. & Raoult, D. (1999) Clin. Microbiol. Rev. 12, 518-553. - PMC - PubMed
    1. Moos, A. & Hackstadt, T. (1987) Infect. Immun. 55, 1144-1150. - PMC - PubMed
    1. Hoover, T. A., Culp, D. W., Vodkin, M. H., Williams, J. C. & Thompson, H. A. (2002) Infect. Immun. 70, 6726-6733. - PMC - PubMed
    1. Toman, R. & Skultety, L. (1996) Carbohydr. Res. 283, 175-185. - PubMed
    1. Vishwanath, S. & Hackstadt, T. (1988) Infect. Immun. 56, 40-44. - PMC - PubMed

Publication types

MeSH terms

LinkOut - more resources

-