Blockade of CD14 aggravates experimental shigellosis

Shigella infections lead to severe inflammation associated with destruction of colonic mucosa. We assessed the effect of in vivo blockade of CD14 on the outcome of experimental Shigella infection in rabbits. A total of 17 rabbits were divided into two groups: 8 received a single i.v. dose of anti-rabbit CD14 monoclonal antibody prior to infection with an invasive Shigella flexneri strain; the remainder served as controls. The anti-CD14-treated rabbits exhibited more severe tissue destruction and a 50-fold increase in bacterial invasion of the intestinal mucosa when compared to controls. Similar numbers of polymorphonuclear leukocytes were recruited to the intestinal mucosa in both groups despite the massive bacterial invasion seen in the CD14-blocked group. No statistically significant differences were seen in levels of IL-1β nor in the ratio of IL-1RA/IL-1β for either group. In contrast, higher quantities of TNF-α were observed in the CD14-blocked group. To conclude, anti-CD14 treatment had a detrimental effect on the capacity of Shigella-infected animals to clear the infection.

Aedes mosquito saliva modulates Rift Valley fever virus pathogenicity

Background

Rift Valley fever (RVF) is a severe mosquito-borne disease affecting humans and domestic ruminants. Mosquito saliva contains compounds that counteract the hemostatic, inflammatory, and immune responses of the host. Modulation of these defensive responses may facilitate virus infection. Indeed, Aedes mosquito saliva played a crucial role in the vector's capacity to effectively transfer arboviruses such as the Cache Valley and West Nile viruses. The role of mosquito saliva in the transmission of Rift Valley fever virus (RVFV) has not been investigated.

Objective

Using a murine model, we explored the potential for mosquitoes to impact the course of RVF disease by determining whether differences in pathogenesis occurred in the presence or absence of mosquito saliva and salivary gland extract.

Methods

C57BL/6NRJ male mice were infected with the ZH548 strain of RVFV via intraperitoneal or intradermal route, or via bites from RVFV-exposed mosquitoes. The virus titers in mosquitoes and mouse organs were determined by plaque assays.

Findings

After intraperitoneal injection, RVFV infection primarily resulted in liver damage. In contrast, RVFV infection via intradermal injection caused both liver and neurological symptoms and this route best mimicked the natural infection by mosquitoes. Co-injections of RVFV with salivary gland extract or saliva via intradermal route increased the mortality rates of mice, as well as the virus titers measured in several organs and in the blood. Furthermore, the blood cell counts of infected mice were altered compared to those of uninfected mice.

Interpretation

Different routes of infection determine the pattern in which the virus spreads and the organs it targets. Aedes saliva significantly increases the pathogenicity of RVFV.

Rift Valley fever is an endemic and epidemic zoonosis in Africa and the Arabic Peninsula. In humans, in the most severe cases the viral infection causes fulminant hepatitis associated with haemorrhagic fever, permanent blindness or severe encephalitis. Despite the importance of vector transmission in the spread of arboviruses, few studies on the physiopathology of viral infection have considered the role of the arthropod in the efficiency of viral infection. Moreover, the route of virus inoculation and the presence of the vector's saliva can potentially affect virus pathogenicity. Our results show that saliva from Aedes mosquitoes increases Rift Valley fever pathogenicity. Importantly, our study also revealed that RVFV transmitted via mosquito bites spread differently than virus inoculated by other routes. These observations may have interesting repercussions given the role mosquitoes were shown to play in the transmission of RVFV in humans during the last outbreak of the disease in Saudi Arabia. Identification of salivary proteins able to increase RVFV virulence may pave the way to new approaches to prevent or cure the disease.

An encapsulated Yersinia pseudotuberculosis is a highly efficient vaccine against pneumonic plague

Background

Plague is still a public health problem in the world and is re-emerging, but no efficient vaccine is available. We previously reported that oral inoculation of a live attenuated Yersinia pseudotuberculosis, the recent ancestor of Yersinia pestis, provided protection against bubonic plague. However, the strain poorly protected against pneumonic plague, the most deadly and contagious form of the disease, and was not genetically defined.

Methodology and Principal Findings

The sequenced Y. pseudotuberculosis IP32953 has been irreversibly attenuated by deletion of genes encoding three essential virulence factors. An encapsulated Y. pseudotuberculosis was generated by cloning the Y. pestis F1-encoding caf operon and expressing it in the attenuated strain. The new V674pF1 strain produced the F1 capsule in vitro and in vivo. Oral inoculation of V674pF1 allowed the colonization of the gut without lesions to Peyer's patches and the spleen. Vaccination induced both humoral and cellular components of immunity, at the systemic (IgG and Th1 cells) and the mucosal levels (IgA and Th17 cells). A single oral dose conferred 100% protection against a lethal pneumonic plague challenge (33×LD₅₀ of the fully virulent Y. pestis CO92 strain) and 94% against a high challenge dose (3,300×LD₅₀). Both F1 and other Yersinia antigens were recognized and V674pF1 efficiently protected against a F1-negative Y. pestis.

Conclusions and Significance

The encapsulated Y. pseudotuberculosis V674pF1 is an efficient live oral vaccine against pneumonic plague, and could be developed for mass vaccination in tropical endemic areas to control pneumonic plague transmission and mortality.

Plague, among the most deadly infections of mankind's history, is present in Africa, Asia and America, and is currently re-emerging, recently causing cases in areas from where it had disappeared for decades. Pneumonic plague, its most deadly and contagious form, is responsible for human-to-human spreading of the infection. Vaccination would be an effective means to control the disease, but no efficient vaccine is currently available. Because live vaccines are potent inducers of protective immunity, our strategy was to use a Yersinia pseudotuberculosis, closely related to Y. pestis but genetically more stable, to make it suitable for use as live oral vaccine. We have developed a genetically defined Y. pseudotuberculosis strain strongly attenuated by deletion of virulence factors genes, which was also induced to produce the Y. pestis F1 pseudocapsule. A single oral dose was harmless and provided high- level protection against pneumonic plague. Such a candidate vaccine offers promising perspectives to control pneumonic plague mortality and transmission.

Isolation and characterization of new Leptospira genotypes from patients in Mayotte (Indian Ocean)

BACKGROUND

Leptospirosis has been implicated as a severe and fatal form of disease in Mayotte, a French-administrated territory located in the Comoros archipelago (southwestern Indian Ocean). To date, Leptospira isolates have never been isolated in this endemic region.

METHODS AND FINDINGS

Leptospires were isolated from blood samples from 22 patients with febrile illness during a 17-month period after a PCR-based screening test was positive. Strains were typed using hyper-immune antisera raised against the major Leptospira serogroups: 20 of 22 clinical isolates were assigned to serogroup Mini; the other two strains belonged to serogroups Grippotyphosa and Pyrogenes, respectively. These isolates were further characterized using partial sequencing of 16S rRNA and ligB gene, Multi Locus VNTR Analysis (MLVA), and pulsed field gel electrophoresis (PFGE). Of the 22 isolates, 14 were L. borgpetersenii strains, 7 L. kirschneri strains, and 1, belonging to serogoup Pyrogenes, was L. interrogans. Results of the genotyping methods were consistent. MLVA defined five genotypes, whereas PFGE allowed the recognition of additional subgroups within the genotypes. PFGE fingerprint patterns of clinical strains did not match any of the patterns in the reference strains belonging to the same serogroup, suggesting that the strains were novel serovars.

CONCLUSIONS

Preliminary PCR screening of blood specimen allowed a high isolation frequency of leptospires among patients with febrile illness. Typing of leptospiral isolates showed that causative agents of leptospirosis in Mayotte have unique molecular features.

An ex-vivo human intestinal model to study Entamoeba histolytica pathogenesis

Amoebiasis (a human intestinal infection affecting 50 million people every year) is caused by the protozoan parasite Entamoeba histolytica. To study the molecular mechanisms underlying human colon invasion by E. histolytica, we have set up an ex vivo human colon model to study the early steps in amoebiasis. Using scanning electron microscopy and histological analyses, we have established that E. histolytica caused the removal of the protective mucus coat during the first two hours of incubation, detached the enterocytes, and then penetrated into the lamina propria by following the crypts of Lieberkühn. Significant cell lysis (determined by the release of lactodehydrogenase) and inflammation (marked by the secretion of pro-inflammatory molecules such as interleukin 1 beta, interferon gamma, interleukin 6, interleukin 8 and tumour necrosis factor) were detected after four hours of incubation. Entamoeba dispar (a closely related non-pathogenic amoeba that also colonizes the human colon) was unable to invade colonic mucosa, lyse cells or induce an inflammatory response. We also examined the behaviour of trophozoites in which genes coding for known virulent factors (such as amoebapores, the Gal/GalNAc lectin and the cysteine protease 5 (CP-A5), which have major roles in cell death, adhesion (to target cells or mucus) and mucus degradation, respectively) were silenced, together with the corresponding tissue responses. Our data revealed that the signalling via the heavy chain Hgl2 or via the light chain Lgl1 of the Gal/GalNAc lectin is not essential to penetrate the human colonic mucosa. In addition, our study demonstrates that E. histolytica silenced for CP-A5 does not penetrate the colonic lamina propria and does not induce the host's pro-inflammatory cytokine secretion.

Entamoeba histolytica is the causative agent of amoebiasis, a human disease. Like other enteric infections, the lack of animal models enhances the difficulty of studying the development of amoebiasis. To date, no experimental model has been developed that reproduces the invasive intestinal amoebic lesions seen in human colon. We present the first study that examines, using human colon explants, the early steps of the human colonic barrier invasion by E. histolytica. With this ex vivo integrative model we have investigated both parasite behaviour and the human tissue response. Remarkably, in this model E. histolytica was able to cross and destroy the intestinal barrier evoking a tissue inflammatory response, while E. dispar, a non-pathogenic species, was unable to penetrate nor induce tissue responses. Furthermore, we have explored the role of three virulence factors during the invasive process, using gene-silenced E. histolytica trophozoites, particularly the kinetics of invasion, tissue destruction and induction of an early inflammatory responses. This is, to our knowledge, the first time that their role is highlighted in a complex human system. Our study provides new insights in the molecular mechanisms involved in the early steps of human colon invasion by E. histolytica.

Methylcitrate synthase from Aspergillus fumigatus is essential for manifestation of invasive aspergillosis

Invasive aspergillosis is a life-threatening disease mainly caused by the fungus Aspergillus fumigatus. In immunocompromised individuals conidia are not efficiently inactivated, which can end in invasive fungal growth. However, the metabolic requirements of the fungus are hardly known. Earlier investigations revealed an accumulation of toxic propionyl-CoA in a methylcitrate synthase mutant, when grown on propionyl-CoA-generating carbon sources. During invasive growth propionyl-CoA could derive from proteins, which are released from infected host tissues. We therefore assumed that a methylcitrate synthase mutant might display an attenuated virulence. Here we show that the addition of propionate to cell culture medium enhanced the ability of alveolar macrophages to kill methylcitrate synthase mutant but not wild-type conidia. When tested in a murine infection model, the methylcitrate synthase mutant displayed attenuated virulence and, furthermore, was cleared from tissues when mice survived the first phase of acute infection. The amplification of cDNA from infected mouse lungs confirmed the transcription of the methylcitrate synthase gene during invasion, which leads to the suggestion that amino acids indeed serve as growth-supporting nutrients during invasive growth of A. fumigatus. Thus, blocking of methylcitrate synthase activity abrogates fungal growth and provides a suitable target for new antifungals.

The regulation of zinc homeostasis by the ZafA transcriptional activator is essential for Aspergillus fumigatus virulence

We have previously shown that Aspergillus fumigatus is able to grow in zinc-limiting media and that this ability is regulated at transcriptional level by both the availability of zinc and pH. When A. fumigatus grows as a pathogen, it must necessarily obtain zinc from the zinc-limiting environment provided by host tissue. Accordingly, the regulation of zinc homeostasis by some zinc-responsive transcriptional regulator in A. fumigatus must be essential for fungal growth within tissues of an immunocompromised host and, in turn, for pathogenicity. Here we provide evidence of the role of the zafA gene in regulating zinc homeostasis and its relevance in the virulence of A. fumigatus. Thus, we observed that (i) zafA can functionally replace the ZAP1 gene from Saccharomyces cerevisiae that encodes the zinc-responsive transcriptional activator Zap1 protein; (ii) the expression of zafA itself is induced in zinc-limiting media and repressed by zinc; (iii) deletion of zafA impairs the germination and growth capacity of A. fumigatus in zinc-limiting media; and (iv) the deletion of zafA abrogates A. fumigatus virulence in a murine model of invasive aspergillosis. In light of these observations, we concluded that ZafA is a zinc-responsive transcriptional activator that represents an essential attribute for A. fumigatus pathogenicity. Consequently, ZafA may constitute a new target for the development of chemotherapeutic agents against Aspergillus, because no zafA orthologues have been found in mammals.

The OmpA-like protein Loa22 is essential for leptospiral virulence

Pathogenic mechanisms of Leptospira interrogans, the causal agent of leptospirosis, remain largely unknown. This is mainly due to the lack of tools for genetic manipulations of pathogenic species. In this study, we characterized a mutant obtained by insertion of the transposon Himar1 into a gene encoding a putative lipoprotein, Loa22, which has a predicted OmpA domain based on sequence identity. The resulting mutant did not express Loa22 and was attenuated in virulence in the guinea pig and hamster models of leptospirosis, whereas the genetically complemented strain was restored in Loa22 expression and virulence. Our results show that Loa22 was expressed during host infection and exposed on the cell surface. Loa22 is therefore necessary for virulence of L. interrogans in the animal model and represents, to our knowledge, the first genetically defined virulence factor in Leptospira species.

Evaluation of the placental environment with a new in vitro model of histocultures of early and term placentae: determination of cytokine and chemokine expression profiles

We aimed to set up and validate a new in vitro model of placental histocultures, for the evaluation of cytokine and chemokine profiles of the placental environment, over a long culture period. Micro-explant cultures from 6 early and 6 term placentae were set up on collagen sponge gel supports at a liquid/air interface. At various times during culture, we analyzed tissue morphology and cell death by microscopy and quantified beta-hCG production and mRNA levels for beta-hCG and insulin-like 4 (INSL4). Levels of IL-6, LIF, TNF alpha, IL-10, IFN-gamma, IL-16 and RANTES in the medium were measured by ELISA on days 1, 4 and 7 of culture. SDF-1 mRNA expression was determined by real-time PCR at the same time points. Histocultures from early and term placentae remained viable until day 10. High levels of IL-6 and LIF production, low levels of TNF alpha, IL-10 and IFN-gamma production and significant SDF-1 expression were observed. These data indicate that placental histoculture is a suitable and reliable in vitro model for studying the placental environment.

Spontaneous vitiligo in an animal model for human melanoma: role of tumor-specific CD8+ T cells

Tumor antigen-reactive T cells can be detected in a large proportion of melanoma patients, but their efficacy on tumor control in vivo remains unclear. On the other hand, vitiligo, a skin disorder characterized by patchy depigmented macules, may occur spontaneously or after antitumor therapies. Moreover, vitiligo is significantly associated with positive clinical response, but the mechanism is not understood. Therefore, the establishment of a relevant animal model in which melanoma and vitiligo spontaneously develop stepwise may be useful for better understanding of the parameters involved in the destruction of both benign and malignant melanocytes. In a previous work, we established a mouse model for melanoma in which MT/ret transgenic mice express the ret oncogene fused to the metallothionein promoter. Here we report that melanoma leads to spontaneous vitiligo. We further investigate, for the first time in this model, the natural antitumor T-cell response and evaluate the role of cellular immunity in the development of the disease. Interestingly, the occurrence of spontaneous tumor nodules in MT/ret mice with melanoma-associated vitiligo is significantly delayed when compared in melanoma mice without vitiligo. Moreover, a significant proportion of mice with melanoma-associated vitiligo resisted a challenge with syngeneic melanoma cells in contrast to animals without vitiligo. Our results confirm that vitiligo is associated with clinical benefit and further demonstrate the crucial role of CD8+ T cells for tumor control in melanoma-associated vitiligo.

Bordetella bronchiseptica persists in the nasal cavities of mice and triggers early delivery of dendritic cells in the lymph nodes draining the lower and upper respiratory tract

Early after the intranasal instillation of Bordetella bronchiseptica into mice, not only are mature dendritic leukocytes recovered from lung parenchyma and bronchoalveolar lavage fluid but their numbers are also increased in the mediastinal lymph nodes and the nasal mucosa-associated lymphoid tissue. Later during the infectious process, the bacteria persist mainly in the nasal cavity.

Analysis of intra-hepatic peptide-specific cell recruitment in mice immunised with Plasmodium falciparum antigens

The liver stage of Plasmodium spp. now appears as a relevant target of immune effectors triggered by the so-called "anti-sporozoite" vaccine. Since the monitoring of immune responses at the systemic level may not faithfully reflect the local protective mechanisms, the aim of the present work was to set up a model to study the local intra-hepatic cellular responses and to compare these with the peripheral immune responses. This was achieved by intra-portal delivery of epitopic peptides, i.e. peptides containing B and T cell epitopes, which were coated onto the surface of polystyrene microbeads. The peptide-coated beads presumably mimic the hepatic schizont, and when distinct peptides are administered separately, this method of delivery allows us to decipher the immune responses resulting in mice immunised with recombinant proteins spanning several such epitopes. Using the P. falciparum liver stage antigen-3 (LSA3) molecule, which can induce protection against a sporozoite challenge, our results show that 25-microm microbeads could easily access the liver parenchyma by intra-portal injection and were distributed evenly in the liver. Also, LSA3-derived synthetic peptides coated onto microbeads initiated specific cell recruitment within 6 h. Depending on the LSA3 peptide used, the infiltrates induced differed in size, with the strongest cell recruitment obtained using nonrepeat II peptide (NR2)-coated microbeads with a mean leukocyte number of 79 per granuloma. Immunohistological studies of liver sections revealed that, irrespective of the delivered peptide, cells infiltrating the liver towards microbeads were mainly CD3(+) T lymphocytes, both CD4(+) (70 to 80%) and CD8(+) (20 to 30%) subtypes, macrophages and dendritic cells. Cells infiltrating the granuloma had features of activated cells, with evidence of VLA-4 cell-surface expression, and production of IFN-gamma and IL-4. Analysis of the peripheral B and T-cell responses in the same animals revealed that, whereas the local responses were directed mainly towards NR2 and repeat peptides (RE), the peripheral T-cell response to these peptides was weak and infrequent, although antibody production was high.

Transgenic B lymphocytes expressing a human cold agglutinin escape tolerance following experimental infection of mice by Mycoplasma pulmonis

Several microbial infections, including Mycoplasma pneumoniae respiratory infection, are capable, in man, of transiently inducing the expression of anti-red blood cell autoantibody called cold agglutinins (CA). To analyze the mechanisms by which immune tolerance is broken following a mycoplasma infection, we used transgenic mice expressing a pathogenic human CA, designated CA-GAS, specific for sialylated carbohydrates. In these mice peripheral deletion of autoreactive B lymphocytes and receptor editing, prevent the development of autoimmune hemolytic anemia. Experimental infections of transgenic mice with Mycoplasma pulmonis resulted in a high anti-mycoplasma antibody response (despite a severe B cell depletion at the onset of infection), and an important induction of serum CA concentrations, reaching in some mice pathological titers. Whereas in naïve mice, only a small percentage of CA-expressing cells could be detected, in infected mice, a majority of circulating B lymphocytes were large B220(-) cells, which expressed the transgenic immunoglobulin. Immunization of the transgenic mice with keyhole limpet hemocyanin and Freund's adjuvant, to nonspecifically stimulate the expression of the passenger transgenes, only moderately increased the CA titers. These results indicate that M. pulmonis infection is capable of breaking immune tolerance in the CA-transgenic mice, in part through specific activation of CA-expressing B lymphocytes. This experimental infection mimics the induction of CA in humans and provide an animal model for studying the genesis of the autoimmune hemolytic anemia.

Persistent infection of B lymphocytes by bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) is a major cause of respiratory disease in young cattle. Here we demonstrate BRSV persistence at low levels in tracheobronchial and mediastinal lymph nodes up to 71 days after the experimental infection of calves. Positive results were obtained on viral genomic RNA and messenger RNA coding for the nucleoprotein, glycoprotein (G), and fusion protein (F). G and F proteins were also detected in the pulmonary lymph nodes by immunohistochemistry. Double-staining experiments revealed that viral antigen was present in B-lymphocytes. Coculture experiments with the lymph node cells showed that the virus was still able to infect permissive target cells, even though no cytopathic effect was recorded. In vitro studies indicate that BRSV was still able to replicate in bovine B-lymphocyte cell lines 6 months after infection. These results may also be relevant to the understanding not only of the epidemiology and the peculiarities of the immune response of BRSV infections but also of human respiratory syncytial virus infections.

Blockade of CD14 aggravates experimental shigellosis

Shigella infections lead to severe inflammation associated with destruction of colonic mucosa. We assessed the effect of in vivo blockade of CD14 on the outcome of experimental Shigella infection in rabbits. A total of 17 rabbits were divided into two groups: 8 received a single i.v. dose of anti-rabbit CD14 monoclonal antibody prior to infection with an invasive Shigella flexneri strain; the remainder served as controls. The anti-CD14-treated rabbits exhibited more severe tissue destruction and a 50-fold increase in bacterial invasion of the intestinal mucosa when compared to controls. Similar numbers of polymorphonuclear leukocytes were recruited to the intestinal mucosa in both groups despite the massive bacterial invasion seen in the CD14-blocked group. No statistically significant differences were seen in levels of IL-1beta nor in the ratio of IL-1RA/IL-1beta for either group. In contrast, higher quantities of TNF-alpha were observed in the CD14-blocked group. To conclude, anti-CD14 treatment had a detrimental effect on the capacity of Shigella-infected animals to clear the infection.

High levels of viral replication during primary simian immunodeficiency virus SIVagm infection are rapidly and strongly controlled in African green monkeys

In contrast to pathogenic human immunodeficiency virus and simian immunodeficiency virus (SIV) infections, chronic SIVagm infections in African green monkeys (AGMs) are characterized by persistently low peripheral and tissue viral loads that correlate with the lack of disease observed in these animals. We report here data on the dynamics of acute SIVagm infection in AGMs that exhibit remarkable similarities with viral replication patterns observed in peripheral blood during the first 2 weeks of pathogenic SIVmac infections. Plasma viremia was evident at day 3 postinfection (p.i.) in AGMs, and rapid viral replication led by days 7 to 10 to peak viremias characterized by high levels of antigenemia (1.2 to 5 ng of p27/ml of plasma), peripheral DNA viral load (10(4) to 10(5) DNA copies/10(6) peripheral blood mononuclear cells [PBMC]), and plasma RNA viral load (2 x 10(6) to 2 x 10(8) RNA copies/ml). The lymph node (LN) RNA and DNA viral load patterns were similar to those in blood, with peaks observed between day 7 and day 14. These values in LNs (ranging from 3 x 10(5) to 3 x 10(6) RNA copies/10(6) LN cell [LNC] and 10(3) to 10(4) DNA copies/10(6) LNC) were at no time point higher than those observed in the blood. Both in LNs and in blood, rapid and significant decreases were observed in all infected animals after this peak of viral replication. Within 3 to 4 weeks p. i., antigenemia was no longer detectable and peripheral viral loads decreased to values similar to those characteristic of the chronic phase of infection (10(2) to 10(3) DNA copies/10(6) PBMC and 2 x 10(3) to 2 x 10(5) RNA copies/ml of plasma). In LNs, viral loads declined to 5 x 10(1) to 10(3) DNA copies and 10(4) to 3 x 10(5) RNA copies per 10(6) LNC at day 28 p.i. and continued to decrease until day 84 p.i. (<10 to 3 x 10(4) RNA copies/10(6) LNC). Despite extensive viremia during primary infection, neither follicular hyperplasia nor CD8(+) cell infiltration into LN germinal centers was detected. Altogether, these results indicate that the nonpathogenic outcome of SIVagm infection in its natural host is associated with a rapidly induced control of viral replication in response to SIVagm infection, rather than with a poorly replicating virus or a constitutive host genetic resistance to virus replication.

Blockade of CD14 increases Shigella-mediated invasion and tissue destruction

Shigella is a diarrheal pathogen that causes disease through invasion of the large intestinal mucosa. The endotoxin of the invading bacterium may play a key role in the disease process by causing inflammation and tissue injury during infection. Earlier studies have shown that various animal species lacking functional CD14 were protected against endotoxin-mediated shock. Rabbits experimentally infected with Shigella were used to test the hypothesis that blockade of endotoxin-induced cell activation with anti-CD14 mAb would diminish inflammation and thus disease severity. Unexpectedly, we observed that the intestinal mucosa of anti-CD14-treated animals exhibited a 50-fold increase in bacterial invasion and more severe tissue injury compared with controls. Despite higher bacterial loads in treated animals, the numbers of polymorphonuclear leukocytes that were recruited to the infection site were similar to those in controls. Furthermore, the phagocytic cells of CD14-blocked animals produced IL-1 and TNF-alpha. Moreover, in vitro blockade of CD14 did not impede bactericidal activity. Thus, anti-CD14 treatment interfered with host defense mechanisms involved with removal/eradication of Shigella.

Antigenic variation of Borrelia turicatae Vsp surface lipoproteins occurs in vitro and generates novel serotypes

As a means of avoiding the host immune response, the tick-borne relapsing fever spirochete Borrelia turicatae undergoes antigenic variation in its abundant surface lipoproteins. In this study, B. turicatae strain Oz1, serotype B, was subcultured in vitro and cloned by limited dilutions after 50 passages. Four different serotypes (serotypes A, B, E, and F) differing by their expressed Vsp lipoproteins were isolated. Using pulsed-field gel electrophoresis, we showed that the variability in surface-exposed proteins is correlated with rearrangement between different linear plasmids, defining serotype-specific plasmid profiles. Moreover, we determined the nucleotide sequence of genes encoding the VspE and VspF lipoproteins, corresponding to the two novel serotypes E and F, respectively. Our results showed that antigenic variation in B. turicatae occurs spontaneously in vitro, in the absence of immune selection.

Abnormal organisation of the splenic marginal zone and the correlated leukocytosis in lymphotoxin-alpha and tumor necrosis factor alpha double deficient mice

In this study we further characterized the phenotype at the homeostasis of mice genetically deficient in Tumor Necrosis Factor-alpha and Lymphotoxin-alpha (LT-alpha TNF-alpha -/-). As initially observed in LT-alpha -/- mice, these mice are devoid of lymph nodes and Peyer's patches, while in their spleen the white and red pulp domains are no more detectable. In the blood the leukocytosis dominated by lymphocytosis is not solely due to the absence of lymph nodes. Indeed, this abnormality was shown to be correctable by the transfer of wild type bone marrow in the absence of lymph node. We now report that the metallophilic macrophages of the marginal zone are no more detectable with an antibody reactive to sialoadhesin, a macrophage restricted transmembrane molecule known to bind myeloid and lymphoid cells. The absence of sialoadhesin within the marginal zone, a critical domain for lymphocyte trafficking towards the white pulp suggests a possible cellular basis for the observed blood leukocytosis. In addition, in the peritoneal cavity of LT-alpha TNF-alpha-/- mice, the size of the resident leukocyte population is increased. By their amplitudes these leukocytosis are similar within the blood and the peritoneal compartments.

Virulence of alkaline protease-deficient mutants of Aspergillus fumigatus

The gene encoding the secreted alkaline protease, a suspected virulence factor of Aspergillus fumigatus, was inactivated by gene disruption. The disruption was performed by transformation of a pathogenic strain of the fungus with a linear DNA fragment carrying the gene from which the central part was replaced by the selectable Escherichia coli hygromycin B dominant resistance marker. Two transformants were shown to produce no alkaline protease. Restriction fragment analysis of the DNA of these two transformants was consistent for chromosomal integration of the disrupted gene by homologous recombination. Both isogenic alkaline protease-producing and non-producing A. fumigatus strains invaded lung tissues, causing comparable mortality in immunosuppressed mice. A significant residual proteolytic activity observed in alkaline protease non-producing strain cultures could play a role in the invasion of the tissues by the fungus.