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Nir Paran,
Yasemin Suezer,
Shlomo Lustig,
Tomer Israely,
Astrid Schwantes,
Sharon Melamed,
Lior Katz,
Thomas Preuss,
Kay-Martin Hanschmann,
Ulrich Kalinke,
Noam Erez,
Reuven Levin,
Baruch Velan,
Johannes Löwer, Avigdor Shafferman,
Gerd Sutter
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ABSTRACT: Protective antigen (PA), a key component of anthrax toxin, mediates the entry of lethal factor (LF) or edema factor (EF) through a membranal pore into target cells. We have previously reported the isolation and chimerization of cAb29, an anti-PA monoclonal antibody that effectively neutralizes anthrax toxin in an unknown mechanism. The aim of this study was to elucidate the neutralizing mechanism of this antibody in vitro and to test its ability to confer post-exposure protection against anthrax in vivo. By systematic evaluation of the steps taking place during the PA-based intoxication process, we found that cAb29 did not interfere with the initial steps of intoxication, namely its ability to bind to the anthrax receptor, the consecutive proteolytic cleavage to PA(63), oligomerization, prepore formation, or LF binding. However, the binding of cAb29 to the prepore prevented its pH-triggered transition to the transmembranal pore, thus preventing the last step of intoxication, i.e. the translocation of LF/EF into the cell. Epitope mapping, using a phage display peptide library, revealed that cAb29 binds the 2α(1) loop in domain 2 of PA, a loop that undergoes major conformational changes during pore formation. In vivo, we found that 100% of anthrax-infected rabbits survived when treated with cAb29 12 h after exposure. In conclusion, these experiments demonstrate that cAb29 exerts its potent neutralizing activity in a unique manner by blocking the prepore-to-pore conversion process.
Journal of Biological Chemistry 08/2012; 287(39):32665-73. · 4.77 Impact Factor
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ABSTRACT: This study examines the efficacy, bacterial load, and humoral response of extensively delayed ciprofloxacin or doxycycline treatments following airway exposure of mice to Francisella tularensis subsp. holarctica (strain LVS) or to the highly virulent F. tularensis subsp. tularensis (strain SchuS4). A delay in onset of both antibiotic treatments allowed the rescue of all LVS-infected animals. However, for animals infected with SchuS4, only ciprofloxacin was efficacious and prolongation of treatment rescued all animals.
Antimicrobial Agents and Chemotherapy 07/2012; 56(10):5406-8. · 4.84 Impact Factor
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ABSTRACT: In an event of a smallpox outbreak in humans, the window for efficacious treatment by vaccination with vaccinia viruses (VACV) is believed to be limited to the first few days post-exposure (p.e.). We recently demonstrated in a mouse model for human smallpox, that active immunization 2-3 days p.e. with either VACV-Lister or modified VACV Ankara (MVA) vaccines, can rescue animals from lethal challenge of ectromelia virus (ECTV), the causative agent of mousepox. The present study was carried out in order to determine whether a single dose of the anti-viral cidofovir (CDV), administered at different times and doses p.e. either alone or in conjunction with active vaccination, can rescue ECTV infected mice.
Animals were infected intranasally with ECTV, treated on different days with various single CDV doses and monitored for morbidity, mortality and humoral response. In addition, in order to determine the influence of CDV on the immune response following vaccination, both the "clinical take", IFN-gamma and IgG Ab levels in the serum were evaluated as well as the ability of the mice to withstand a lethal challenge of ECTV. Finally the efficacy of a combined treatment regime of CDV and vaccination p.e. was determined.
A single p.e. CDV treatment is sufficient for protection depending on the initiation time and dose (2.5 - 100 mg/kg) of treatment. Solid protection was achieved by a low dose (5 mg/kg) CDV treatment even if given at day 6 p.e., approximately 4 days before death of the control infected untreated mice (mean time to death (MTTD) 10.2). At the same time point complete protection was achieved by single treatment with higher doses of CDV (25 or 100 mg/kg). Irrespective of treatment dose, all surviving animals developed a protective immune response even when the CDV treatment was initiated one day p.e.. After seven days post treatment with the highest dose (100 mg/kg), virus was still detected in some organs (e.g. lung and liver) yet all animals survived, suggesting that efficacious single CDV treatment requires a potent immune system. The combination of CDV and vaccination provided no additional protection over CDV alone. Yet, combining CDV and vaccination maintained vaccination efficacy.
Altogether, our data substantiate the feasibility of single post-exposure antiviral treatment to face orthopoxvirus infection.
Virology Journal 06/2012; 9:119. · 2.34 Impact Factor
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ABSTRACT: The virulence of Bacillus anthracis, the causative agent of anthrax, stems from its antiphagocytic capsule, encoded by pXO2, and the tripartite toxins encoded by pXO1. The accepted paradigm states that anthrax is both an invasive and toxinogenic disease and that the toxins play major roles in pathogenicity. We tested this assumption by a systematic study of mutants with combined deletions of the pag, lef, and cya genes, encoding protective antigen (PA), lethal factor (LF), and edema factor (EF), respectively. The resulting seven mutants (single, double, and triple) were evaluated following subcutaneous (s.c.) and intranasal (i.n.) inoculation in rabbits and guinea pigs. In the rabbit model, virulence is completely dependent on the presence of PA. Any mutant bearing a pag deletion behaved like a pXO1-cured mutant, exhibiting complete loss of virulence with attenuation indices of over 2,500,000 or 1,250 in the s.c. or i.n. route of infection, respectively. In marked contrast, in guinea pigs, deletion of pag or even of all three toxin components resulted in relatively moderate attenuation, whereas the pXO1-cured bacteria showed complete attenuation. The results indicate that a pXO1-encoded factor(s), other than the toxins, has a major contribution to the virulence mechanism of B. anthracis in the guinea pig model. These unexpected toxin-dependent and toxin-independent manifestations of pathogenicity in different animal models emphasize the importance and need for a comprehensive evaluation of B. anthracis virulence in general and in particular for the design of relevant next-generation anthrax vaccines.
Infection and immunity 05/2012; 80(8):2623-31. · 4.21 Impact Factor
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ABSTRACT: Deciphering the cellular immunome of a bacterial pathogen is challenging due to the enormous number of putative peptidic determinants. State-of-the-art prediction methods developed in recent years enable to significantly reduce the number of peptides to be screened, yet the number of remaining candidates for experimental evaluation is still in the range of ten-thousands, even for a limited coverage of MHC alleles. We have recently established a resource-efficient approach for down selection of candidates and enrichment of true positives, based on selection of predicted MHC binders located in high density "hotspots" of putative epitopes. This cluster-based approach was applied to an unbiased, whole genome search of Francisella tularensis CTL epitopes and was shown to yield a 17-25 fold higher level of responders as compared to randomly selected predicted epitopes tested in Kb/Db C57BL/6 mice. In the present study, we further evaluate the cluster-based approach (down to a lower density range) and compare this approach to the classical affinity-based approach by testing putative CTL epitopes with predicted IC(50) values of <10 nM. We demonstrate that while the percent of responders achieved by both approaches is similar, the profile of responders is different, and the predicted binding affinity of most responders in the cluster-based approach is relatively low (geometric mean of 170 nM), rendering the two approaches complimentary. The cluster-based approach is further validated in BALB/c F. tularensis immunized mice belonging to another allelic restriction (Kd/Dd) group. To date, the cluster-based approach yielded over 200 novel F. tularensis peptides eliciting a cellular response, all were verified as MHC class I binders, thereby substantially increasing the F. tularensis dataset of known CTL epitopes. The generality and power of the high density cluster-based approach suggest that it can be a valuable tool for identification of novel CTLs in proteomes of other bacterial pathogens.
PLoS ONE 01/2012; 7(5):e36440. · 4.09 Impact Factor
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Yaron Vagima,
Yinon Levy,
David Gur,
Avital Tidhar,
Moshe Aftalion,
Hagar Abramovich,
Eran Zahavy,
Ayelet Zauberman,
Yehuda Flashner, Avigdor Shafferman,
Emanuelle Mamroud
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ABSTRACT: Bacterial infection of the lungs triggers a swift innate immune response that involves the production of cytokines and chemokines that promote recruitment of immune cells from the bone marrow (BM) into the infected tissue and limit the ability of the pathogen to replicate. Recent in vivo studies of pneumonic plague in animal models indicate that the pulmonary pro-inflammatory response to airway infection with Yersinia pestis is substantially delayed in comparison to other pathogens. Consequently, uncontrolled proliferation of the pathogen in the lungs is observed, followed by dissemination to internal organs and death. While the lack of an adequate early immune response in the lung is well described, the response of BM-derived cells is poorly understood. In this study, we show that intranasal (i.n.) infection of mice with a fully virulent Y. pestis strain is sensed early by the BM compartment, resulting in a reduction in CXCR4 levels on BM neutrophils and their subsequent release into the blood 12 hours (h) post infection. In addition, increased levels of BM-derived hematopoietic stem and progenitor cells (HSPC) were detected in the blood early after infection. Mobilization of both immature and mature cells was accompanied by the reduction of BM SDF-1 (CXCL-12) levels and the reciprocal elevation of SDF-1 in the blood 24 h post infection. RT-PCR analysis of RNA collected from total BM cells revealed an early induction of myeloid-associated genes, suggesting a prompt commitment to myeloid lineage differentiation. These findings indicate that lung infection by Y. pestis is sensed by BM cells early after infection, although bacterial colonization of the BM occurs at late disease stages, and point on a potential cross-talk between the lung and the BM at early stages of pneumonic plague.
Frontiers in cellular and infection microbiology. 01/2012; 2:143.
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ABSTRACT: We demonstrate that disruption of the htrA (high temperature requirement A) gene in either the virulent Bacillus anthracis Vollum (pXO1(+) , pXO2(+) ), or in the ΔVollum (pXO1(-), pXO2(-), nontoxinogenic and noncapsular) strains, affect significantly the ability of the resulting mutants to withstand heat, oxidative, ethanol and osmotic stress. The ΔhtrA mutants manifest altered secretion of several proteins, as well as complete silencing of the abundant extracellular starvation-associated neutral protease A (NprA). VollumΔhtrA bacteria exhibit delayed proliferation in a macrophage infection assay, and despite their ability to synthesize the major B. anthracis toxins LT (lethal toxin) and ET (oedema toxin) as well as the capsule, show a decrease of over six orders of magnitude in virulence (lethal dose 50% = 3 × 10(8) spores, in the guinea pig model of anthrax), as compared with the parental wild-type strain. This unprecedented extent of loss of virulence in B. anthracis, as a consequence of deletion of a single gene, as well as all other phenotypic defects associated with htrA mutation, are restored in their corresponding trans-complemented strains. It is suggested that the loss of virulence is due to increased susceptibility of the ΔhtrA bacteria to stress insults encountered in the host. On a practical note, it is demonstrated that the attenuated Vollum ΔhtrA is highly efficacious in protecting guinea pigs against a lethal anthrax challenge.
Molecular Microbiology 08/2011; 81(6):1542-59. · 5.01 Impact Factor
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ABSTRACT: Plague, which is initiated by Yersinia pestis infection, is a fatal disease that progresses rapidly and leads to high mortality rates if not treated. Antibiotics are an effective plague therapy, but antibiotic-resistant Y. pestis strains have been reported and therefore alternative countermeasures are needed. In the present study, we assessed the potential of an F1 plus LcrV-based vaccine to provide protection shortly pre- or post-exposure to a lethal Y. pestis infection. Mice vaccinated up to one day before or even several hours after subcutaneous challenge were effectively protected. Mice immunized one or three days pre-challenge were protected even though their anti-F1 and anti-LcrV titers were below detection levels at the day of challenge. Moreover, using B-cell deficient μMT mice, we found that rapidly induced protective immunity requires the integrity of the humoral immune system. Analysis of the individual contributions of vaccine components to protection revealed that rF1 is responsible for the observed rapid antibody-mediated immunity. Applying anti-F1 passive therapy in the mouse model of bubonic plague demonstrated that anti-F1 F(ab')(2) can delay mortality, but it cannot provide long-lasting protection, as do intact anti-F1 molecules. Fc-dependent immune components, such as the complement system and (to a lesser extent) neutrophils, were found to contribute to mouse survival. Interestingly, T cells but not B cells were found to be essential for the recovery of infected animals following passive anti-F1 mediated therapy. These data extend our understanding of the immune mechanisms required for the development of a rapid and effective post-exposure therapy against plague.
Vaccine 07/2011; 29(40):6866-73. · 3.77 Impact Factor
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ABSTRACT: The lethal anthrax disease is caused by spores of the gram-positive Bacillus anthracis, a member of the cereus group of bacilli. Although the disease is very rare in the Western world, development of anthrax countermeasures gains increasing attention due to the potential use of B. anthracis spores as a bio-terror weapon. Protective antigen (PA), the non-toxic subunit of the bacterial secreted exotoxin, fulfills the role of recognizing a specific receptor and mediating the entry of the toxin into the host target cells. PA elicits a protective immune response and represents the basis for all current anthrax vaccines. Anti-PA neutralizing antibodies are useful correlates for protection and for vaccine efficacy evaluation. Post exposure anti-toxemic and anti-bacteremic prophylactic treatment of anthrax requires prolonged antibiotic administration. Shorter efficient postexposure treatments may require active or passive immunization, in addition to antibiotics. Although anthrax is acknowledged as a toxinogenic disease, additional factors, other than the bacterial toxin, may be involved in the virulence of B. anthracis and may be needed for the long-lasting protection conferred by PA immunization. The search for such novel factors is the focus of several high throughput genomic and proteomic studies that are already leading to identification of novel targets for therapeutics, for vaccine candidates, as well as biomarkers for detection and diagnosis.
Immunological Reviews 01/2011; 239(1):221-36. · 11.15 Impact Factor
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ABSTRACT: The cellular arm of the immune response plays a central role in the defense against intracellular pathogens, such as F. tularensis. To date, whole genome immunoinformatic analyses were limited either to relatively small genomes (e.g. viral) or to preselected subsets of proteins in complex pathogens. Here we present, for the first time, an unbiased bacterial global immunoinformatic screen of the 1740 proteins of F. tularensis subs. holarctica (LVS), aiming at identification of immunogenic peptides eliciting a CTL response. The very large number of predicted MHC class I binders (about 100,000, IC(50) of 1000 nM or less) required the design of a strategy for further down selection of CTL candidates. The approach developed focused on mapping clusters rich in overlapping predicted epitopes, and ranking these "hotspot" regions according to the density of putative binding epitopes. Limited by the experimental load, we selected to screen a library of 1240 putative MHC binders derived from 104 top-ranking highly dense clusters. Peptides were tested for their ability to stimulate IFNγ secretion from splenocytes isolated from LVS vaccinated C57BL/6 mice. The majority of the clusters contained one or more CTL responder peptides and altogether 127 novel epitopes were identified, of which 82 are non-redundant. Accordingly, the level of success in identification of positive CTL responders was 17-25 fold higher than that found for a randomly selected library of 500 predicted MHC binders (IC(50) of 500 nM or less). Most proteins (ca. 2/3) harboring the highly dense hotspots are membrane-associated. The approach for enrichment of true positive CTL epitopes described in this study, which allowed for over 50% increase in the dataset of known T-cell epitopes of F. tularensis, could be applied in immunoinformatic analyses of many other complex pathogen genomes.
PLoS ONE 01/2011; 6(5):e20050. · 4.09 Impact Factor
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ABSTRACT: Two alternative promoter trap libraries, based on the green fluorescence protein (gfp) reporter and on the chloramphenicol acetyltransferase (cat) cassette, were constructed for isolation of potent Francisella tularensis promoters. Of the 26,000 F. tularensis strain LVS gfp library clones, only 3 exhibited visible fluorescence following UV illumination and all appeared to carry the bacterioferritin promoter (Pbfr). Out of a total of 2,000 chloramphenicol-resistant LVS clones isolated from the cat promoter library, we arbitrarily selected 40 for further analysis. Over 80% of these clones carry unique F. tularensis DNA sequences which appear to drive a wide range of protein expression, as determined by specific chloramphenicol acetyltransferase (CAT) Western dot blot and enzymatic assays. The DNA sequence information for the 33 unique and novel F. tularensis promoters reported here, along with the results of in silico and primer extension analyses, suggest that F. tularensis possesses classical Escherichia coli σ(70)-related promoter motifs. These motifs include the -10 (TATAAT) and -35 [TTGA(C/T)A] domains and an AT-rich region upstream from -35, reminiscent of but distinct from the E. coli upstream region that is termed the UP element. The most efficient promoter identified (Pbfr) appears to be about 10 times more potent than the F. tularensis groEL promoter and is probably among the strongest promoters in F. tularensis. The battery of promoters identified in this work will be useful, among other things, for genetic manipulation in the background of F. tularensis intended to gain better understanding of the mechanisms involved in pathogenesis and virulence, as well as for vaccine development studies.
Applied and environmental microbiology 12/2010; 77(5):1608-18. · 3.69 Impact Factor
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ABSTRACT: Plague, initiated by Yersinia pestis infection, is a fatal disease that progresses rapidly and leads to high mortality rates if not treated within a short period
of time after onset of symptoms. Antibiotics are effectively used for plague therapy yet antibiotic resistance Y. pestis strains have been reported and therefore alternative therapies are needed. In this study we demonstrate the ability of rabbit
polyclonal antibodies directed against Y. pestis F1 and LcrV antigens to confer protection in mouse models of bubonic and pneumonic plague.
KeywordsPlague-
Y. pestis
-Passive protection-Anti-F1-Anti-LcrV
07/2010: pages 269-274;
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ABSTRACT: In search for antigens which may form the basis for improved subunit or live attenuated B. anthracis vaccines, extensive genomic, proteomic and serologic analyses coupled with functional screens for surface exposed and/or
secreted proteins, were carried out. The screens resulted in selection of over 50 promising novel in-vivo expressed immunogens,
classified as S-Layer Homology (SLH) proteins, repeat proteins, hydrolytic enzymes and ABC transporters. DNA vaccination experiments
established that most of these novel antigens are indeed able to elicit a strong humoral response. Yet, unlike the major B. anthracis immunogen Protective Antigen (PA), none of the selected immunogens could provide protection against a subsequent virulent
B. anthracis strain challenge. When over-expressed in an attenuated non-toxinogenic and non-encapsulated B. anthracis platform strain, at least three of the novel antigens did confer partial protection against a lethal B. anthracis challenge.
Keywords
B. anthracis
-Bioinformatics-Functional genomics-Proteomics-
Vaccine
candidates
06/2010: pages 295-306;
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ABSTRACT: A bioinformatic
screen of Yersinia pestis genome identified 11 TPS components, carrying the POlypeptide TRansport-Associated (POTRA
) domain, found in other pathogens to be involved in immunogenicity
and pathogenicity. All rTpsBs (transporters
) cloned and expressed in Escherichia coli induced a humoral responses in immunized mice. Mice surviving intranasal
infection with fully virulent Y. pestis Kimberley53 strain generated sera cross reacting with some recombinants TpsBs. Moreover, at least 3 TpsB
polypeptides were directly detected in bacteria isolated following intranasal Y. pestis infection. All in vivo produced TpsBs appear to be truncated, missing about 75–85 amino acids. MALDI-TOF-MS analysis permitted
to identify the truncation at a region overlapping a domain of a closely related Bordetella pertussis TpsB (FhaC
), recently proposed to undergo a major conformational change that allows effector translocation.
Keywords
Yersinia pestis
-Bioinformatics-Airway infection-Two partner secretion-POTRA
06/2010: pages 165-172;
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ABSTRACT: A comparative proteomic study of secretomes of virulent and avirulent Bacillus anthracis strains in various culturing conditions, including those encountered in the host (high CO2/bicarbonate), enabled identification of approximately 70 proteins representing collectively more than 99% of the secretome.
In-vivo expression of 50 proteins was established by 2-dimension Western-analysis using anti B. anthracis immune sera. Many of the abundant proteins harbor features characteristic of virulence determinants and exhibit different
patterns of expression. In minimal medium, virulent and avirulent B. anthracis strains manifest similar protein signatures and the metalloprotease NprA, (previously suggested to act in the context of
a starvation-induced mechanism), represents 90% of the total secretome. Under high CO2/bicarbonate, NprA is repressed (possibly by a mechanism which preserves toxin integrity), while other proteins, including
the bacterial toxins, are induced. One of the immunogens observed to be induced under high CO2-tension, was HtrA. We investigated the phenotype associated with disruption of HtrA by biochemical and proteomic approaches.
The HtrA- bacteria are severely affected in their ability to respond to stress and fail to secrete the most abundant extracellular
protease NprA. Most surprisingly, HtrA- cells do not possess the characteristic S-layer. This unique phenotype may have important implications for the role of HtrA
in manifestation of B. anthracis virulence. Furthermore, the data show that distinct CO2/bicarbonate responsive chromosome-and plasmid-encoded regulatory factors modulate the secretion of potential novel virulence
factors, most of which are associated with extracellular proteolytic activities.
Keywords
Bacillus anthracis
-Patterns of expression-Proteases-Proteomic/serological analysis-Virulence
06/2010: pages 11-22;
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ABSTRACT: Antibiotics are considered as an effective treatment against Francisella tularensis (FT), the causative agent of Tularemia. In this study we compared the efficacy of two types of antibiotics: the bacteriostatic
doxycycline and the bactericidic ciprofloxacin, for protection against intranasal FT-LVS in a mouse infection model. Antibiotic
treatments were initiated 24–72h post- bacterial infection, administered twice daily and for a period of 7 days (ciprofloxacin)
or 10 days (doxycycline), respectively.
All treated mice survived the infection, even when the treatment was initiated after the appearance of disease symptoms (72h).
Bacterial clearance from the lungs, liver and spleen was more efficient in the ciprofloxacin-treated mice while in doxycycline-treated
mice complete clearance was observed more than a week after cessation of antibiotic treatment. Nevertheless, no signs for
relapse were observed in doxycycline-treated mice, probably due to the development of an immune response against the invading
bacteria. Indeed, high antibody titers were observed in these mice, 10–50 fold higher than in the ciprofloxacin-treated mice.
Keywords
Francisella tularensis
-Antibiotic-Airways infection-LVS
06/2010: pages 207-212;
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ABSTRACT: The encounter between invading microorganisms and dendritic cells (DC) triggers a series of events which include uptake and
degradation of the microorganism, induction of a cell maturation process, as well as enhancement of DC migration to the draining
lymph nodes. Bacteria of the genera Yersinia and Francisella have developed different strategies to counteract these events as a measure to evade host defense.
We observed that interaction of the Yersinia enterocolitica with DC impairs their maturation into functional immune cells and triggers premature cell death. Y. pestis, has no effects on DC viability or maturation, yet impairs DC functions related to cytoskeleton rearrangement in a virulence
plasmid dependent way. DC pulsed with Y. pestis fails to migrate toward the chemokine CCL19. Moreover, while instillation of a virulence plasmid-cured Y. pestis strain into mice airways triggers effective transport of airway DC to the mediastinal lymph node (MdLN), instillation of
Y. pestis harboring the plasmid fails to do so.
Interaction of Francisella tularensis live vaccine strain (LVS) with DC leads to impairment of cell maturation but at the same time allows for intracellular bacterial
propagation and effective cell migration, thus paving the way to utilization of DC as vehicles for bacterial dissemination.
Indeed, airway infection of mice with LVS results in trafficking of bacteria-carrying DC from the respiratory tract to the
draining MdLN. Furthermore, impairment of DC migration in vivo by two independent mechanisms reduces bacterial colonization
of the lymph node and delays the onset of morbidity and the time to death of the infected mice.
Taken together, these observations attest to the major role of DC in mounting protection against pathogens, which has in turn
led to evolution of various bacterial strategies to counteract and even exploit DC functions.
Keywords
Francisella tularensis
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Yersinia pestis
-Dendritic cells-Migration-Immune-evasion
06/2010: pages 89-98;
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ABSTRACT: MglA (Macrophage Growth Locus A) is a pleiotropic transcription factor controlling the expression pattern of more than 100
genes in Francisella novicida, including all the ORFs located on the pathogenicity island. To further probe the role of MglA in the pathogenicity of the
related strain Francisella tularensis LVS, we generated a mutant LVS strain in which the mglA locus was disrupted by insertion of a non-polar selectable marker cassette.
In vitro and in vivo analysis of the phenotype associated with the mglA null mutation in comparison to the wild-type parental strain and to a complementation strain (ΔmglA:mglA), established that the mutated strain ΔmglA: (i) cannot multiply in vitro in macrophages, (ii) is severely attenuated in a murine model of infection, exhibiting over
10,000 and 10,000,000 fold decrease in virulence by intranasal (IN) administration, and intraperitoneal (IP) route of infection
respectively, (iii) unlike wild type LVS, the mutant strain cannot multiply in the lungs, liver and spleen of infected animals
following IP administration, (iv) the ΔmglA mutant do not disseminate to target organs (e.g. liver and spleen) following IN administration, (v) Infection by ΔmglA bacteria elicits a significant humoral response, and systemic IP administration of high doses of ΔmglA cells results in full protection of animals against a subsequent IP challenge with high doses of the virulent wild-type strain.
These results indicate that MglA plays a major role in F. tularensis LVS virulence as previously shown for F. novicida. Our studies suggest that inactivation of MglA may serve as a platform for the development of an improved attenuated vaccine
of virulent F. tularensis strains.
Keywords
Francisella
-Live vaccine strain-Pathogenicity island-Vaccine-MglA
06/2010: pages 219-227;
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ABSTRACT: Modulation of host cell death during infection is a prevalent virulence strategy developed by many bacterial pathogens. Yersinia pestis, the causative agent of the fatal plague disease was found to exert limited cytotoxicity towards target immune cells, mediated
by type III secretion system effector YopJ. In contrast, the highly cytotoxic closely related Y. enterocolitica O:8 causes a self limited gastrointestinal disease. This phenomenon led us to suggest that the reduced cytotoxic potency
of Y. pestis is related to its increased virulence potential. Generation of Y. pestis strain expressing YopP instead of YopJ, enhanced its cytotoxic potency towards macrophages in-vitro and mouse spleen target
cells in-vivo. The highly cytotoxic Y. pestis strain demonstrated a reduced ability to colonize internal organs of mice infected subcutaneously, and most strikingly was
avirulent in a mouse model of bubonic plague. These results indicate inverse relationship between cytotoxic potency and in-vivo
virulence. Still, the same YopP-expressing Y. pestis strain remained fully virulent to mice upon intravenous or intranasal infections, indicating retention of virulence potential.
In addition, it was found that subcutaneous administration of the highly cytotoxic Y. pestis strain activated extremely rapid, potent and systemic protective response against concomitant challenges with a virulent
strain via the subcutaneous, intravenous or airway routes. These findings may have important implications on the design of
future plague vaccine/therapies and contribute to our understanding of virulence strategies of Y. pestis in nature.
KeywordsPlague-
Y. pestis
-YopJ-YopP-Cytotoxicity-Protective immunity
06/2010: pages 45-55;
