Toll-like receptor 4 (TLR4) does not confer a resistance advantage on mice against low-dose aerosol infection with virulent type A Francisella tularensis

ABSTRACT Francisella tularensis is a gram-negative intracellular bacterium and the causative agent of the zoonotic disease tularemia. F. tularensis is a category A select agent and thus a potential agent of bioterrorism. Whereas an F. tularensis live, attenuated vaccine strain (LVS) is the basis of an investigational vaccine, this vaccine is not licensed for human use because of efficacy and safety concerns. In the present study, we immunized mice with isolated native outer membrane proteins (OMPs), ethanol-inactivated LVS (iLVS), or purified LVS lipopolysaccharide (LPS) and assessed the ability of each vaccine preparation to protect mice against pulmonary challenge with the virulent type A F. tularensis strain SchuS4. Antibody isotyping indicated that both Th1 and Th2 antibody responses were generated in mice after immunization with OMPs or iLVS, whereas LPS immunization resulted in only immunoglobulin A production. In survival studies, OMP immunization provided the greatest level of protection (50% survival at 20 days after infection with SchuS4), and there were associated 3-log reductions in the spleen and liver bacterial burdens (compared to nonvaccinated mice). Cytokine quantitation for the sera of SchuS4-challenged mice indicated that OMP and iLVS immunizations induced high levels of tumor necrosis factor alpha and interleukin-2 (IL-2) production, whereas only OMP immunization induced high levels of IL-10 production. By comparison, high levels of proinflammatory cytokines, including RANTES, granulocyte colony-stimulating factor, IL-6, IL-1α, IL-12p40, and KC, in nonvaccinated mice indicated that these cytokines may facilitate disease progression. Taken together, the results of this study demonstrate the potential utility of an OMP subunit (acellular) vaccine for protecting mammals against type A F. tularensis.

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Virulent Type A Francisella tularensis actively suppresses cytokine responses in human monocytes

Frontiers in Cellular and Infection Microbiology ◽

10.3389/fcimb.2014.00045 ◽

2014 ◽

Vol 4 ◽

Cited By ~ 11

Author(s):

Devyn D. Gillette ◽

Heather M. Curry ◽

Thomas Cremer ◽

David Ravneberg ◽

Kavin Fatehchand ◽

...

Keyword(s):

Francisella Tularensis ◽

Type A ◽

Human Monocytes ◽

Cytokine Responses ◽

Virulent Type

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Distinct Roles of Pattern Recognition Receptors CD14 and Toll-Like Receptor 4 in Acute Lung Injury

Infection and Immunity ◽

10.1128/iai.73.3.1754-1763.2005 ◽

2005 ◽

Vol 73 (3) ◽

pp. 1754-1763 ◽

Cited By ~ 78

Author(s):

Samithamby Jeyaseelan ◽

Hong Wei Chu ◽

Scott K. Young ◽

Mason W. Freeman ◽

G. Scott Worthen

Keyword(s):

Acute Lung Injury ◽

Lung Injury ◽

Low Dose ◽

Lung Damage ◽

Lung Pathology ◽

Toll Like Receptor ◽

Toll Like Receptor 4 ◽

Neutrophil Influx ◽

Microvascular Leakage ◽

Lps Binding

ABSTRACT Acute lung injury (ALI) induced by lipopolysaccharide (LPS) is a major cause of mortality among humans. ALI is characterized by microvascular protein leakage, neutrophil influx, and expression of proinflammatory mediators, followed by severe lung damage. LPS binding to its receptors is the crucial step in the causation of these multistep events. LPS binding and signaling involves CD14 and Toll-like receptor 4 (TLR4). However, the relative contributions of CD14 and TLR4 in the induction of ALI and their therapeutic potentials are not clear in vivo. Therefore, the aim of the present study was to compare the roles of CD14 and TLR4 in LPS-induced ALI to determine which of these molecules is the more critical target for attenuating ALI in a mouse model. Our results show that CD14 and TLR4 are necessary for low-dose (300-μg/ml) LPS-induced microvascular leakage, NF-κB activation, neutrophil influx, cytokine and chemokine (KC, macrophage inflammatory protein 2, tumor necrosis factor alpha, interleukin-6) expression, and subsequent lung damage. On the other hand, when a 10-fold-higher dose of LPS (3 mg/ml) was used, these responses were only partially dependent on CD14 and they were totally dependent on TLR4. The CD14-independent LPS response was dependent on CD11b. A TLR4 blocking antibody abolished microvascular leakage, neutrophil accumulation, cytokine responses, and lung pathology with a low dose of LPS but only attenuated the responses with a high dose of LPS. These data are the first to demonstrate that LPS-induced CD14-depdendent and -independent (CD11b-dependent) signaling pathways in the lung are entirely dependent on TLR4 and that blocking TLR4 might be beneficial in lung diseases caused by LPS from gram-negative pathogens.

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Prior Inoculation with Type B Strains of Francisella tularensis Provides Partial Protection against Virulent Type A Strains in Cottontail Rabbits

PLoS ONE ◽

10.1371/journal.pone.0140723 ◽

2015 ◽

Vol 10 (10) ◽

pp. e0140723 ◽

Cited By ~ 1

Author(s):

Vienna R. Brown ◽

Danielle R. Adney ◽

Francisco Olea-Popelka ◽

Richard A. Bowen

Keyword(s):

Francisella Tularensis ◽

Type A ◽

Type B ◽

Partial Protection ◽

Virulent Type

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Lack of In Vitro and In Vivo Recognition of Francisella tularensis Subspecies Lipopolysaccharide by Toll-Like Receptors

Infection and Immunity ◽

10.1128/iai.00934-06 ◽

2006 ◽

Vol 74 (12) ◽

pp. 6730-6738 ◽

Cited By ~ 107

Author(s):

Adeline M. Hajjar ◽

Megan D. Harvey ◽

Scott A. Shaffer ◽

David R. Goodlett ◽

Anders Sjöstedt ◽

...

Keyword(s):

Francisella Tularensis ◽

Lipid A ◽

Early Recognition ◽

Proinflammatory Response ◽

Toll Like Receptor 4 ◽

Gram Negative ◽

Francisella Novicida ◽

Virulent Type

ABSTRACT Francisella tularensis is an intracellular gram-negative bacterium that is highly infectious and potentially lethal. Several subspecies exist of varying pathogenicity. Infection by only a few organisms is sufficient to cause disease depending on the model system. Lipopolysaccharide (LPS) of gram-negative bacteria is generally recognized by Toll-like receptor 4 (TLR4)/MD-2 and induces a strong proinflammatory response. Examination of human clinical F. tularensis isolates revealed that human virulent type A and type B strains produced lipid A of similar structure to the nonhuman model pathogen of mice, Francisella novicida. F. novicida LPS or lipid A is neither stimulatory nor an antagonist for human and murine cells through TLR4 or TLR2. It does not appear to interact with TLR4 or MD-2, as it is not an antagonist to other stimulatory LPS. Consistent with these observations, aerosolization of F. novicida LPS or whole bacteria induced no inflammatory response in mice. These results suggest that poor innate recognition of F. tularensis allows the bacterium to evade early recognition by the host innate immune system to promote its pathogenesis for mammals.

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Live Attenuated Mutants of Francisella tularensis Protect Rabbits against Aerosol Challenge with a Virulent Type A Strain

Infection and Immunity ◽

10.1128/iai.01498-14 ◽

2014 ◽

Vol 82 (5) ◽

pp. 2098-2105 ◽

Cited By ~ 19

Author(s):

Douglas S. Reed ◽

Le'Kneitah P. Smith ◽

Kelly Stefano Cole ◽

Araceli E. Santiago ◽

Barbara J. Mann ◽

...

Keyword(s):

Weight Loss ◽

Francisella Tularensis ◽

Type A ◽

Content Type ◽

Time To Death ◽

Virulent Type ◽

No Weight Loss ◽

The 1960S ◽

Schu S4 ◽

Derivatives Of

ABSTRACTFrancisella tularensis, a Gram-negative bacterium, is the causative agent of tularemia. No licensed vaccine is currently available for protection against tularemia, although an attenuated strain, dubbed the live vaccine strain (LVS), is given to at-risk laboratory personnel as an investigational new drug (IND). In an effort to develop a vaccine that offers better protection, recombinant attenuated derivatives of a virulent type A strain, SCHU S4, were evaluated in New Zealand White (NZW) rabbits. Rabbits vaccinated via scarification with the three attenuated derivatives (SCHU S4 ΔguaBA, ΔaroD, and ΔfipBstrains) or with LVS developed a mild fever, but no weight loss was detected. Twenty-one days after vaccination, all vaccinated rabbits were seropositive for IgG toF. tularensislipopolysaccharide (LPS). Thirty days after vaccination, all rabbits were challenged with aerosolized SCHU S4 at doses ranging from 50 to 500 50% lethal doses (LD50). All rabbits developed fevers and weight loss after challenge, but the severity was greater for mock-vaccinated rabbits. The ΔguaBAand ΔaroDSCHU S4 derivatives provided partial protection against death (27 to 36%) and a prolonged time to death compared to results for the mock-vaccinated group. In contrast, LVS and the ΔfipBstrain both prolonged the time to death, but there were no survivors from the challenge. This is the first demonstration of vaccine efficacy against aerosol challenge with virulent type AF. tularensisin a species other than a rodent since the original work with LVS in the 1960s. The ΔguaBAand ΔaroDSCHU S4 derivatives warrant further evaluation and consideration as potential vaccines for tularemia and for identification of immunological correlates of protection.

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