Pairing Bacteroides vulgatus LPS Structure with Its Immunomodulatory Effects on Human Cellular Models

The gut microbiota guide the development of the host immune system by setting a systemic threshold for immune activation. Lipopolysaccharides (LPSs) from gut bacteria are able to trigger systemic and local proinflammatory and immunomodulatory responses, and this capability strongly relies on their fine structures. Up to now, only a few LPS structures from gut commensals have been elucidated; therefore, the molecular motifs that may be important for LPS-mammalian cell interactions at the gut level are still obscure. Here, we report on the full structure of the LPS isolated from one of the prominent species of the genus Bacteroides, Bacteroides vulgatus. The LPS turned out to consist of a particular chemical structure based on hypoacylated and mono-phosphorylated lipid A and with a galactofuranose-containing core oligosaccharide and an O-antigen built up of mannose and rhamnose. The evaluation of the immunological properties of this LPS on human in vitro models revealed a very interesting capability to produce anti-inflammatory cytokines and to induce a synergistic action of MD-2/TLR4- and TLR2-mediated signaling pathways.

Dynamic density shaping of photokinetic E. coli

Many motile microorganisms react to environmental light cues with a variety of motility responses guiding cells towards better conditions for survival and growth. The use of spatial light modulators could help to elucidate the mechanisms of photo-movements while, at the same time, providing an efficient strategy to achieve spatial and temporal control of cell concentration. Here we demonstrate that millions of bacteria, genetically modified to swim smoothly with a light controllable speed, can be arranged into complex and reconfigurable density patterns using a digital light projector. We show that a homogeneous sea of freely swimming bacteria can be made to morph between complex shapes. We model non-local effects arising from memory in light response and show how these can be mitigated by a feedback control strategy resulting in the detailed reproduction of grayscale density images.

Many bacteria can move in response to environmental signals. This helps guide them towards better conditions for growth and survival. Escherichia coli is a bacterium that can swim quickly through liquid, using tiny propeller-like structures that rotate many times per second. These ‘propellers’ are powered by a cellular motor, called the flagellar motor, which similar to an electric motor, requires an energy source to drive movement.

Proteorhodopsin, a protein originally isolated from free-swimming micro-organisms in the ocean, is an alternative energy source that helps bacteria move. The protein is located close to the surface of the cell, where it acts like a solar panel and captures energy from light. In cells powered by proteorhodopsin, the intensity of light from their environment determines their swimming speed: brighter light means faster movement, and less light, slower movement. Proteorhodopsin is now also a useful tool in the laboratory. For example, genetically engineering bacteria to produce proteorhodopsin provides a way to control their movement remotely, using a light source.

Swimming bacteria, much like cars in city traffic, are known to accumulate in areas where their speed decreases. By controlling swimming speed with proteorhodopsin, researchers can manipulate the local density of bacteria simply by projecting different patterns of light.

To study the factors influencing this phenomenon, Frangipane et al. used genetically modified E. coli that could respond to light via proteorhodopsin to make layers of cells that could then have light patterns projected onto them. The results showed that the bacteria responded slowly to these stimuli, which was the main factor limiting the resolution of the final pattern they formed. A simple feedback mechanism, which compared the pattern formed by the cells to the desired image and updated the projected light accordingly, was enough to solve this problem. This way, the layers of E.coli could be turned into a near-perfect copy of the original image.

This work allows us to control the movement of large populations of bacteria more precisely than ever before. This could be extremely valuable for building the next generation of microscopic devices. For example, bacteria could be made to surround a larger object such as a machine part or a drug carrier, and then used as living propellers to transport it where it is needed.

The Helicobacter cinaedi antigen CAIP participates in atherosclerotic inflammation by promoting the differentiation of macrophages in foam cells

Recent studies have shown that certain specific microbial infections participate in atherosclerosis by inducing inflammation and immune reactions, but how the pathogens implicated in this pathology trigger the host responses remains unknown. In this study we show that Helicobacter cinaedi (Hc) is a human pathogen linked to atherosclerosis development since at least 27% of sera from atherosclerotic patients specifically recognize a protein of the Hc proteome, that we named Cinaedi Atherosclerosis Inflammatory Protein (CAIP) (n = 71). CAIP appears to be implicated in this pathology because atheromatous plaques isolated from atherosclerotic patients are enriched in CAIP-specific T cells (10%) which, in turn, we show to drive a Th1 inflammation, an immunopathological response typically associated to atherosclerosis. Recombinant CAIP promotes the differentiation and maintenance of the pro-inflammatory profile of human macrophages and triggers the formation of foam cells, which are a hallmark of atherosclerosis. This study identifies CAIP as a relevant factor in atherosclerosis inflammation linked to Hc infection and suggests that preventing and eradicating Hc infection could reduce the incidence of atherosclerosis.

The Lipid A from Rhodopseudomonas palustris Strain BisA53 LPS Possesses a Unique Structure and Low Immunostimulant Properties

The search for novel lipid A analogues from any biological source that can act as antagonists, displaying inhibitory activity towards the production of pro-inflammatory cytokines, or as immunomodulators in mammals, is a very topical issue. To this aim, the structure and immunological properties of the lipopolysaccharide lipid A from the purple nonsulfur bacterium Rhodopseudomonas palustris strain BisA53 have been determined. This lipid A displays a unique structural feature, with a non-phosphorylated skeleton made up of the tetrasaccharide Manp-α-(1→4)-GlcpN3N-β-1→6-GlcpN3N-α-(1→1)-α-GalpA, and four primary amide-linked 14:0(3-OH) and, as secondary O-acyl substituents, a 16:0 and the very long-chain fatty acid 26:0(25-OAc), appended on the GlcpN3N units. This lipid A architecture is definitely rare, so far identified only in the genus Bradyrhizobium. Immunological tests on both murine bone-marrow-derived and human monocyte-derived macrophages revealed an extremely low immunostimulant capability of this LPS lipid A.

Thermophiles as potential source of novel endotoxin antagonists: the full structure and bioactivity of the lipo-oligosaccharide from Thermomonas hydrothermalis

Thermomonas hydrothermalis is a Gram-negative thermophilic bacterium that is able to live at 50 °C. This ability is attributed to chemical modifications, involving those to bacterial cell-wall components, such as proteins and (glyco)lipids. As the main component of the outer membrane of Gram-negative bacteria, lipopolysaccharides (LPSs) are exposed to the environment, thus they can undergo structural chemical changes to allow thermophilic bacteria to live at their optimal growth temperature. Furthermore, as one of the major target of the eukaryotic innate immune system, LPS elicits host immune response in a structure-dependent mode; thus the uncommon chemical features of thermophilic bacterial LPSs might exert a different biological action on the innate immune system-an antagonistic effect, as shown in studies of LPS structure-activity relationship in the ongoing research into antagonist LPS candidates. Here, we report the complete structural and biological activity analysis of the lipo-oligosaccharide isolated from Thermomonas hydrothermalis, achieved by a multidisciplinary approach (chemical analysis, NMR, MALDI MS and cellular immunology). We demonstrate a tricky and interesting structure combined with a very interesting effect on human innate immunity.

Effective interactions between colloidal particles suspended in a bath of swimming cells

The dynamics of passive colloidal tracers in a bath of self-propelled particles is receiving a lot of attention in the context of nonequilibrium statistical mechanics. Here we demonstrate that active baths are also capable of mediating effective interactions between suspended bodies. In particular we observe that a bath of swimming bacteria gives rise to a short range attraction similar to depletion forces in equilibrium colloidal suspensions. Using numerical simulations and experiments we show how the features of this interaction arise from the combination of nonequilibrium dynamics (peculiar of bacterial baths) and excluded volume effects.

Pseudomonas aeruginosa exploits lipid A and muropeptides modification as a strategy to lower innate immunity during cystic fibrosis lung infection

Pseudomonas aeruginosa can establish life-long airways chronic infection in patients with cystic fibrosis (CF) with pathogenic variants distinguished from initially acquired strain. Here, we analysed chemical and biological activity of P. aeruginosa Pathogen-Associated Molecular Patterns (PAMPs) in clonal strains, including mucoid and non-mucoid phenotypes, isolated during a period of up to 7.5 years from a CF patient. Chemical structure by MS spectrometry defined lipopolysaccharide (LPS) lipid A and peptidoglycan (PGN) muropeptides with specific structural modifications temporally associated with CF lung infection. Gene sequence analysis revealed novel mutation in pagL, which supported lipid A changes. Both LPS and PGN had different potencies when activating host innate immunity via binding TLR4 and Nod1. Significantly higher NF-kB activation, IL-8 expression and production were detected in HEK293hTLR4/MD2-CD14 and HEK293hNod1 after stimulation with LPS and PGN respectively, purified from early P. aeruginosa strain as compared to late strains. Similar results were obtained in macrophages-like cells THP-1, epithelial cells of CF origin IB3-1 and their isogenic cells C38, corrected by insertion of cystic fibrosis transmembrane conductance regulator (CFTR). In murine model, altered LPS structure of P. aeruginosa late strains induces lower leukocyte recruitment in bronchoalveolar lavage and MIP-2, KC and IL-1beta cytokine levels in lung homogenates when compared with early strain. Histopathological analysis of lung tissue sections confirmed differences between LPS from early and late P. aeruginosa. Finally, in this study for the first time we unveil how P. aeruginosa has evolved the capacity to evade immune system detection, thus promoting survival and establishing favourable conditions for chronic persistence. Our findings provide relevant information with respect to chronic infections in CF.

Full structural characterization of Shigella flexneri M90T serotype 5 wild-type R-LPS and its delta galU mutant: glycine residue location in the inner core of the lipopolysaccharide

Shigella flexneri is a gram-negative bacterium responsible for serious enteric infections that occur mainly in the terminal ileum and colon. High interest in Shigella, as a human pathogen, is driven by its antibiotic resistance and the necessity to develop a vaccine against its infections. Vaccines of the last generation use carbohydrate moieties of the lipopolysaccharide as probable candidates. For this reason, the primary structure of the core oligosaccharide from the R-LPS produced by S. flexneri M90T serotype 5 using chemical analysis, nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MALDI), is herein reported. This is the first time that the core oligosaccharide primary structure by S. flexneri M90T is established in an unambiguous multidisciplinary approach. Chemical and spectroscopical investigation of the de-acetylated LPS showed that the inner core structure is characterized by a L,D-Hep-(1 -->7)-L,D-Hep-(1 -->3)-L,D-Hep-(1 -->5)-[Kdo-(2 -->4)]-Kdo sequence that is the common structural theme identified in Enterobacteriaceae. In particular, in S. flexneri M90T serotype 5 LPS, a glucosamine residue is additionally sitting at O-7 of the last heptose whereas the outer core is characterized by glucose and galactose residues. Also, in order to exactly define the position of glycine that is an integral constituent of the core region of the LPS, we created a S. flexneri M90T delta galU mutant and studied its LOS. In this way it was possible to establish that glycine is sitting at O-6 of the second heptose in the inner core.

IpgB1 and IpgB2, two homologous effectors secreted via the Mxi-Spa type III secretion apparatus, cooperate to mediate polarized cell invasion and inflammatory potential of Shigella flexenri

Type III secretion systems (T3SS) are present in many pathogenic gram-negative bacteria and mediate the translocation of bacterial effector proteins into host cells. Here, we report the phenotypic characterization of S. flexneri ipgB1 and ipgB2 mutants, in which the genes encoding the IpgB1 and IpgB2 effectors have been inactivated, either independently or simultaneously. Like IpgB1, we found that IpgB2 is secreted by the T3SS and its secretion requires the Spa15 chaperone. Upon infection of semi-confluent HeLa cells, the ipgB2 mutant exhibited the same invasive capacity as the wild-type strain and the ipgB1 mutant was 50% less invasive. Upon infection of polarised Caco2-cells, the ipgB2 mutant did not show a significant defect in invasion and the ipgB1 mutant was slightly more invasive than the wild-type strain. Entry of the ipgB1 ipgB2 mutant in polarized cells was reduced by 70% compared to the wild-type strain. Upon infection of the cornea in Guinea pigs, the ipgB2 mutant exhibited a wild-type phenotype, the ipgB1 mutant was hypervirulent and elicited a more pronounced proinflammatory response, while the ipgB1 ipgB2 mutant was highly attenuated. The attenuated phenotype of the ipgB1 ipgB2 mutant was confirmed using a murine pulmonary model of infection and histopathology and immunochemistry studies.

Muramylpeptide shedding modulates cell sensing of Shigella flexneri

Bacterial infections trigger the activation of innate immunity through the interaction of pathogen-associated molecular patterns (PAMPs) with pattern recognition molecules (PRMs). The nucleotide-binding oligomerization domain (Nod) proteins are intracellular PRMs that recognize muramylpeptides contained in peptidoglycan (PGN) of bacteria. It is still unclear how Nod1 physically interacts with PGN, a structure internal to the Gram-negative bacterial envelope. To contribute to the understanding of this process, we demonstrate that, like Escherichia coli, Bordetella pertussis and Neisseria gonorrheae, the Gram-negative pathogen Shigella spontaneously releases PGN fragments and that this process can be increased by inactivating either ampG or mppA, genes involved in PGN recycling. Both Shigella mutants, but especially the strain carrying the mppA deletion, trigger Nod1-mediated NF-kappaB activation to a greater extent than the wild-type strain. Likewise, muramylpeptides spontaneously shed by Shigella are able per se to trigger a Nod1-mediated response consistent with the relative amount. Finally, we found that qualitative changes in muramylpeptide shedding can alter in vivo host responses to Shigella infection. Our findings support the idea that muramylpeptides released by pathogens during infection could modulate the immune response through Nod proteins and thereby influence the outcome of disease.

CTACK /CCL27 expression in psoriatic skin and its modification after administration of etanercept

BACKGROUND

Tumour necrosis factor-alpha upregulates the expression of a cutaneous T cell-attracting chemokine (CTACK/CCL27), that promotes migration of cutaneous lymphocyte-associated antigen-positive lymphocytes into the skin. The role of CTACK/CCL27 in pathogenesis of psoriasis has recently been documented but no data are available at the present time on its modification in psoriatic cutaneous tissue after administration of etanercept.

OBJECTIVES

To evaluate modifications of CTACK/CCL27 expression in skin of patients with psoriasis after administration of etanercept and their relation with disease activity.

METHODS

Twenty-two patients with moderate to severe psoriasis underwent clinical, histological and immunohistochemical evaluations of disease activity at baseline and at 12 and 24 weeks after starting treatment with etanercept.

RESULTS

All selected patients experienced an improvement of Psoriasis Area and Severity Index (PASI) score (P < 0.001) and Dermatology Life Quality Index score (P < 0.001) during the treatment. Skin histological abnormalities showed statistically significant modifications during treatment (P < 0.001). Immunohistochemical expression of CTACK/CCL27 decreased significantly (P < 0.001) and its relation with final PASI score was statistically significant (P < 0.05); the pattern of distribution of CTACK/CCL27 immunoreactivity significantly moved from diffuse and predominantly suprabasal to basal (P < 0.001) and the restoration of basal distribution of CTACK/CCL27 was also significantly related to clinical improvement of cutaneous disease (P < 0.001).

CONCLUSIONS

Etanercept induces a clinical and histological improvement of psoriatic disease, promoting a reduction in CTACK/CCL27 cutaneous immunostaining and favouring the restoration of physiological CTACK/CCL27 epidermal expression. Moreover, CTACK/CCL27 reduction in cutaneous expression during administration of etanercept could be considered a favourable prognostic marker.

Diagnosing Sjögren-Larsson syndrome in a 7-year-old Moroccan boy

Sjögren-Larsson syndrome (SLS) is an autosomal recessively inherited neurocutaneous disorder characterized by the triad of congenital ichthyosis, mental deficiency, and spastic diplegia or tetraplegia. Less common features are retinal changes, short stature, kyphoscoliosis, preterm birth, photophobia, reduction of visual acuity, seizures, and delayed speech. SLS is characterized by a genetic block in the oxidation of fatty alcohol to fatty acid because of deficient activity of fatty aldehyde dehydrogenase (FALDH), a component of the fatty alcohol: NAD oxidoreductase enzyme complex. As in other rare multisystem diseases, the diagnosis of SLS is often delayed. The definitive test for SLS is considered the measurement of FALDH or fatty alcohol: NAD oxidoreductase in cultured skin fibroblasts. Nevertheless, if specific FALDH activity test or DNA FALDH gene mutation tests are not available (as in our country), a reliable diagnosis of SLS is also possible when it is based on the matching of peculiar clinical, histologic and ultrastructural, laboratoristic, and imaging features. The simultaneous presence of cutaneous histologic features including hyperkeratosis, orthokeratosis, thickening of granular layer, abnormal lamellar inclusions in the cytoplasm of granular and horny cells (demonstrated by light and electron microscopy) in a child with ichthyosis, and typical neurologic abnormalities is highly suggestive of SLS. We describe the case of a young Moroccan boy presenting with ichthyosis, mental retardation, spastic diplegia, and peculiar skin histologic findings.

Mucosal Lymphoid Infiltrate Dominates Colonic Pathological Changes in Murine Experimental Shigellosis

BACKGROUND

Shigella species are invasive human pathogens that cause acute rectocolitis by triggering a dysregulated inflammatory reaction in the colonic and rectal mucosa. Because mice are naturally resistant to shigellosis, there is no mouse model that mimics human disease. We explore the susceptibility of intestinal flora-depleted mice to shigellosis after intragastric infection with Shigella strains.

METHODS

Mice given 5 g/L streptomycin as a beverage were infected intragastrically with 1 x 108 cfu of either invasive or noninvasive Shigella strains.

RESULTS

We found that invasive Shigella strains persist up to 30 days in feces, whereas the persistence of noninvasive Shigella strains was reduced. Colonization primarily involves the colon and the cecum and, to a lesser extent, the ileum. The hallmark of inflammation in the intestinal tissue is a dramatic expansion of the lymphoid follicles, in which a high apoptotic index is recorded.

CONCLUSIONS

We provide a murine model in which shigellae are able to reach their natural tissue target: the colon. Moreover, the absence of polymorphonuclear leukocyte recruitment and of epithelial cell lesions reveal some aspects of shigellosis that are usually hidden by the prevalence of this cell population. This novel model may contribute to the identification of new targets for vaccines and therapies.

Analysis of virulence plasmid gene expression defines three classes of effectors in the type III secretion system of Shigella flexneri

Proteins directly involved in entry and dissemination of Shigella flexneri into epithelial cells are encoded by a virulence plasmid of 200 kb. A 30-kb region (designated the entry region) of this plasmid encodes components of a type III secretion (TTS) apparatus, substrates of this apparatus and their dedicated chaperones. During growth of bacteria in broth, expression of these genes is induced at 37 degrees C and the TTS apparatus is assembled in the bacterial envelope but is not active. Secretion is activated upon contact of bacteria with host cells and is deregulated in an ipaB mutant. The plasmid encodes four transcriptional regulators, VirF, VirB, MxiE and Orf81. VirF controls transcription of virB, whose product is required for transcription of entry region genes. MxiE, with the chaperone IpgC acting as a co-activator, controls expression of several effectors that are induced under conditions of secretion. Genes under the control of Orf81 are not known. The aim of this study was to define further the repertoires of virulence plasmid genes that are under the control of (i) the growth temperature, (ii) each of the known virulence plasmid-encoded transcriptional regulators (VirF, VirB, MxiE and Orf81) and (iii) the activity of the TTS apparatus. Using a macroarray analysis, the expression profiles of 71 plasmid genes were compared in the wild-type strain grown at 37 and 30 degrees C and in virF, virB, mxiE, ipaB, ipaB mxiE and orf81 mutants grown at 37 degrees C. Many genes were found to be under the control of VirB and indirectly of VirF. No alteration of expression of any gene was detected in the orf81 mutant. Expression of 13 genes was increased in the secretion-deregulated ipaB mutant in an MxiE-dependent manner. On the basis of their expression profile, substrates of the TTS apparatus can be classified into three categories: (i) those that are controlled by VirB, (ii) those that are controlled by MxiE and (iii) those that are controlled by both VirB and MxiE. The differential regulation of expression of TTS effectors in response to the TTS apparatus activity suggests that different effectors might be required at different times following contact of bacteria with host cells.

Epidemiology of onychomycosis and paronychia in the area of ANCONA (ITALY) over a period of 5 years

We retrospectively evaluated the epidemiology of onychomycosis and/or paronychia in 172 patients attending the Clinic of Dermatology and Venereology over a 5 year period. Although yeast isolates, belonging to the Candida species, represented the most frequent etiologic agents of these infections, an increasing prevalence of fungal infections due to emerging fungal pathogens (EFP) was noted throughout this time period. In particular, EFP as causative agents of these infections increased from 0 to 28.4% from 1998 to 2002.

Intravenous infection of virulent shigellae causes fulminant hepatitis in mice

Shigella spp. are pathogenic bacteria responsible for bacillary dysentery in humans. The major lesions in colonic mucosa are intense inflammation with apoptosis of macrophages and release of pro-inflammatory cytokines. The study of shigellosis is hindered by the natural resistance of rodents to oral infection with Shigella. Therefore, animal models exploit other routes of infection. Here, we describe a novel murine model in which animals receive shigellae via the caudal vein. Mice infected with 5 x 10(6) (LD(50)) virulent shigellae died at 48 h post infection, whereas animals receiving non-invasive mutants survived. The liver is the main target of infection, where shigellae induce microgranuloma formation. In mice infected with invasive bacteria, high frequency of apoptotic cells is observed within hepatic microgranulomas along with significant levels of mRNA for pro-inflammatory cytokines such as IL-1beta, IL-18, IL-12 and IFN-gamma. Moreover, in the blood of these animals high levels of IL-6 and transaminases are detected. Our results demonstrate the intravenous model is suitable for pathogenicity studies and useful to explore the immune response after Shigella infection.

Expression of vascular endothelial growth factor, apoptosis inhibitors (survivin and p16) and CCL27 in alopecia areata before and after diphencyprone treatment: an immunohistochemical study

BACKGROUND

Alopecia areata (AA) is a relatively common inflammatory form of nonscarring hair loss of unknown pathogenesis, but possibly of autoimmune origin. Topical immunotherapy, using a potent contact allergen such as diphencyprone (DPC), is currently considered the most effective mode of treatment. However, the way in which DPC operates on hair follicles in AA still remains to be elucidated. Vascular endothelial growth factor (VEGF), essential for angiogenesis and vascular permeability, may be responsible for maintaining proper vasculature around hair follicles, and several studies provide evidence that apoptosis is a central element in the regulation of hair follicle and vascular regression. The cutaneous lymphocyte-associated antigen (CLA) and the skin-associated chemokine CCL27 highlight an important role for epithelial cells in controlling homeostatic lymphocyte trafficking.

OBJECTIVES

To determine the expression pattern of VEGF, factor (F)VIII, survivin, p16, CD4, CD8, CLA and CCL27 in alopecic skin before and after treatment with DPC. Methods Immunohistochemical staining methods were applied to skin biopsy specimens obtained from alopecic areas of 14 patients before and after DPC treatment and from five healthy subjects. Sections were incubated with monoclonal antibodies against VEGF, FVIII, survivin, p16, CCL27, CLA, CD4 and CD8, and their immunohistochemical expression was evaluated by light microscopy.

RESULTS

The intensity of VEGF staining in alopecic human hair follicles was significantly lower than in healthy scalp tissue. FVIII immunostaining showed a significantly reduced development of the microvasculature in AA in comparison with healthy scalp tissue. After DPC therapy, cells of alopecic hair follicles showed a significant increase of VEGF immunopositivity, and the number of capillary vessels expressing FVIII was markedly increased in comparison with untreated scalp tissue. The increase in microvessels was associated with strong survivin expression in endothelial cells after treatment. All alopecic specimens showed expression of p16 in the hair follicle outer root sheath (ORS), with a significant increase after therapy. After treatment we observed a significantly decreased number of CD4+ cells and an increase of CD8+ cells (CD4/CD8 ratio 0.85) in alopecic skin compared with untreated scalp tissue (CD4/CD8 ratio 3.45). Most of the T lymphocytes found in inflammatory skin lesions expressed CLA antigen and after therapy we observed a significantly higher CLA positivity in hair follicles (50% or more) in comparison with untreated alopecic scalp tissue. Alopecic patients showed a CCL27 immunopositivity significantly lower than in normal scalp tissue. After DPC therapy the labelling intensity for CCL27 showed a significant increase both in the ORS and in the inner root sheath; similarly, in the basal interfollicular keratinocytes we observed a moderate increase in CCL27 expression.

CONCLUSIONS

Topical immunotherapy exerts an important role in angiogenesis, upregulating VEGF in human hair follicle keratinocytes and upregulating survivin to preserve endothelial cell viability. Moreover, it considerably alters the peribulbar CD4/CD8 ratio, restoring a condition close to normal scalp skin. Our study could contribute to explaining some aspects of AA pathogenesis that are still unknown and aid understanding of how DPC could act in this complex disease.

Analysis of virulence and inflammatory potential of Shigella flexneri purine biosynthesis mutants

Several Shigella flexneri mutants with defects in aromatic amino acid and/or purine biosynthesis have been evaluated as vaccines in humans or in animal models. To be suitable as a vaccine, a mutant has to show virulence attenuation, minimal reactogenicity, and a good immunogenic potential in animal models. With this aim, we have constructed five S. flexneri 5 (wild-type strain M90T) mutants with inactivation of one or two of the loci purEK, purHD, and guaBA, governing early or late steps of purine biosynthesis. The mutants have been analyzed in vitro in cell cultures and in vivo in the Sereny test and in the murine pulmonary model of shigellosis. M90T guaBA, M90T guaBA purEK, M90T guaBA purHD, and M90T purHD purEK gave a negative result in the Sereny test. In contrast, in the murine pulmonary model all of the strains had the same 50% lethal dose as the wild type, except M90T guaBA purHD, which did not result in death of the animals. Nevertheless, bacterial counts in infected lungs, immunohistochemistry, and reverse transcription-PCR analysis of mRNAs for tumor necrosis factor alpha (TNF-alpha), gamma interferon (IFN-gamma), interleukin-1beta (IL-1beta), IL-6, IL-12, and inducible nitric oxide synthase (iNOS) revealed significant differences among the strains. At 72 h postinfection, M90T guaBA purHD still induced proinflammatory cytokines and factors such as IL-1beta, IL-6, TNF-alpha, and iNOS, along with cytokines such as IL-12 and IFN-gamma. Moreover, in the absence of evident lesions in murine tissues, this mutant highly stimulated major histocompatibility complex class II expression, showing a significant ability to activate the innate immunity of the host.

Selection of Shigella flexneri candidate virulence genes specifically induced in bacteria resident in host cell cytoplasm

We describe an in vivo expression technology (IVET)-like approach, which uses antibiotic resistance for selection, to identify Shigella flexneri genes specifically activated in bacteria resident in host cell cytoplasm. This procedure required construction of a promoter-trap vector containing a synthetic operon between the promoterless chloramphenicol acetyl transferase (cat) and lacZ genes and construction of a library of plasmids carrying transcriptional fusions between S. flexneri genomic fragments and the cat-lacZ operon. Clones exhibiting low levels (<10 micro g ml-1) of chloramphenicol (Cm) resistance on laboratory media were analysed for their ability to induce a cytophatic effect--plaque--on a cell monolayer, in the presence of Cm. These clones were assumed to carry a plasmid in which the cloned fragment acted as a promoter/gene which is poorly expressed under laboratory conditions. Therefore, only strains harbouring fusion-plasmids in which the cloned promoter was specifically activated within host cytoplasm could survive within the cell monolayer in the presence of Cm and give a positive result in the plaque assay. Pai (plaque assay induced) clones, selected following this procedure, were analysed for intracellular (i) beta-galactosidase activity, (ii) proliferation in the presence of Cm, and (iii) Cm resistance. Sequence analysis of Pai plasmids revealed genes encoding proteins of three functional classes: external layer recycling, adaptation to microaerophilic environment and gene regulation. Sequences encoding unknown functions were also trapped and selected by this new IVET-based protocol.

Parameters underlying successful protection with live attenuated mutants in experimental shigellosis

Because the use of live attenuated mutants of Shigella spp. represents a promising approach to protection against bacillary dysentery (M. E. Etherridge, A. T. M. Shamsul Hoque, and D. A. Sack, Lab. Anim. Sci. 46:61-66, 1996), it becomes essential to rationalize this approach in animal models in order to optimize attenuation of virulence in the vaccine candidates, as well as their route and mode of administration, and to define the correlates of protection. In this study, we have compared three strains of Shigella flexneri 5--the wild-type M90T, an aroC mutant, and a double purE aroC mutant--for their pathogenicity, immunogenicity, and protective capacity. Protection against keratoconjunctivitis, induced by wild-type M90T, was used as the protection read out in guinea pigs that were inoculated either intranasally or intragastrically. Following intranasal immunization, the aroC mutant elicited weak nasal tissue destruction compared to M90T and achieved protection correlated with high levels of local anti-lipopolysaccharide immunoglobulin A (IgA), whereas the purE aroC double mutant, which also elicited weak tissue destruction, was not protective and elicited a low IgA response. Conversely, following intragastric immunization, only the M90T purE aroC double mutant elicited protection compared to both the aroC mutant and the wild-type strain. This mutant caused mild inflammatory destruction, particularly at the level of Peyer's patches, but it persisted much longer within the tissues. This could represent an essential parameter of the protective response that, in this case, did not clearly correlate with high anti-lipopolysaccharide IgA titers.

Role of cytomegalovirus replication in alopecia areata pathogenesis

BACKGROUND

Cytomegalovirus (CMV) infection has been correlated with various autoimmune disorders. Using molecular biology techniques, DNA sequences of CMV have been reported in paraffin sections of alopecia areata (AA) lesions. Reactivation of the CMV infection has been postulated as one of the pathogenic mechanisms in AA. Other studies, using different techniques however have demonstrated no correlation between CMV and AA.

OBJECTIVES

This study was to clarify the role of CMV infection and to demonstrate the absence of replication of other autoimmune diseases-related herpes virus (EBV) in the pathogenesis of AA.

METHODS

After extraction of mRNA from tissue samples of a patient with active patchy AA, reverse transcriptase-polymerase chain reaction was carried out using primers specific for some viral members of the beta-herpes viridae family (CMV, EBV, HSV).

RESULTS

No replication of the CMV or other beta-herpes viridae has been detected in any of the samples collected.

CONCLUSIONS

The results strongly support the hypothesis that CMV is not the triggering factor in AA, neither as a re-activator of the immune response nor as a trigger of the autoimmunity. No other herpes virus is implicated in the pathogenesis of this disease.

Intracellular multiplication and virulence of Shigella flexneri auxotrophic mutants

We have constructed and analyzed a group of Shigella flexneri 5 auxotrophic mutants. The wild-type strain M90T was mutagenized in genes encoding enzymes involved in the synthesis of (i) aromatic amino acids, (ii) nucleotides, and (iii) diaminopimelic acid. In this way, strains with single (aroB, aroC, aroD, purE, thyA, and dapB) and double (purE aroB, purE aroC, purE aroD, purE thyA) mutations were obtained. Although the Aro mutants had the same nutritional requirements when grown in laboratory media, they showed different degrees of virulence in vitro and in vivo. The aroB mutant was not significantly attenuated, whereas both the aroC and aroD strains were severely attenuated. p-Aminobenzoic acid (PABA) appeared to be the main requirement for the Aro mutants' growth in tissue culture. Concerning nucleotides, thymine reduced the pathogenicity, whereas adenine did not. However, when combined with another virulence-affecting mutation, adenine auxotrophy appeared to potentiate that mutation's effects. Consequently, the association of either the purE and aroC or the purE and aroD mutations had a great effect on virulence as measured by the Sereny test, whereas the purE aroB double mutation appeared to have only a small effect. All mutants except the dapB strain seemed to move within a Caco-2 cell monolayer after 3 h of infection. Nevertheless, the auxotrophs showing a high intracellular generation time were negative in the plaque assay. Knowledge of each mutation's role in attenuating Shigella strains will provide useful tools in designing vaccine candidates.

OmpC is involved in invasion of epithelial cells by Shigella flexneri

Osmoregulation of the Shigella flexneri ompC gene and the role of OmpC in Shigella virulence have been investigated. OmpC was highly expressed when bacteria were grown in medium of either low or high osmolarity. This constitutive expression is in contrast with the regulation observed in Escherichia coli, in which the expression of OmpC is repressed at low osmolarity and induced at high osmolarity. In addition, the Shigella ompC gene was barely expressed by a delta ompB (delta ompR and delta envZ) mutant. We described in a previous report that such a mutant was severely impaired in virulence both in vitro and in vivo. Starting from this observation, and in order to assess which gene(s) regulated by ompR and envZ are involved in virulence, we constructed an S. flexneri delta ompC mutant. Three S. flexneri mutants, ompF'-lacZ, delta ompC, and delta ompB, were compared for virulence. The ompF'lacZ mutant behaved like the S. flexneri serotype 5 wild-type strain M90T in all in vitro and in vivo virulence tests. On the contrary, the delta ompB and delta ompC strains were considerably impaired in their virulence phenotypes. The ability of these two mutants to spread from cell to cell and to kill epithelial cells was severely affected. Consequently delta ompC, as previously described for delta ompB, was unable to elicit a positive Sereny test. The delta ompB mutant was restored to virulence by introducing a recombinant multicopy plasmid carrying the cloned E. coli ompC gene, indicating that a functional OmpC protein was necessary and sufficient to restore virulence to this mutant of S. flexneri.

OmpB (osmo-regulation) and icsA (cell-to-cell spread) mutants of Shigella flexneri: vaccine candidates and probes to study the pathogenesis of shigellosis

Genetic and molecular data now available on the pathogenic properties of Shigella flexneri allow rational design of live attenuated vaccine strains. The genes required at given steps of the infection process can be selectively mutated to impair the bacterium's capacity to interact with intestinal epithelial cells and/or survive within intestinal tissues in general. We have tested two mutations in S. flexneri serotype 5a (M90T) which, alone or in combination, have yielded promising results when evaluated as vaccine prototypes in orally infected macaque monkeys. The first mutation, icsA, blocks intracellular and cell-to-cell spread of the micro-organism. This mutant (SC560) appeared reasonably well tolerated and elicited protection against homologous challenge. The second mutation, ompB, disconnects the bacterium from one of its major environmental regulatory factors, osmolarity. This mutant (SC433) still caused slight dysenteric symptoms in vaccinees. It was also perfectly protective. When these two mutations were combined, the double mutant (SC445), was perfectly tolerated but failed to protect one out of five animals. These studies bring interesting prospects of the possibility of immunizing against shigellosis. In addition to providing new possibilities for vaccine design, construction and evaluation of these mutants allowed substantial progress in understanding the pathogenesis of shigellosis.

The two-component regulatory system ompR-envZ controls the virulence of Shigella flexneri

In Shigella flexneri, the ompB locus (containing the ompR and envZ genes) was found to modulate expression of the vir genes, which are responsible for invasion of epithelial cells. vir gene expression was markedly enhanced under conditions of high osmolarity (300 mosM), similar to that encountered in tissues both extra- and intracellularly. Two ompB mutants were constructed and tested for virulence and for osmotic regulation of vir genes. An envZ::Tn10 mutant remained invasive, although its virulence was significantly decreased as a result of its inability to survive intracellularly. By using a vir::lac operon fusion, this mutation was shown to decrease beta-galactosidase expression both in low- and high-osmolarity conditions but did not affect vir expression in response to changes in osmolarity. A delta ompB deletion mutant was also constructed via allelic exchange with an in vitro-mutagenized ompB locus of Escherichia coli. This mutation severely impaired virulence and abolished expression of the vir::lac fusion in both low- and high-osmolarity conditions. Therefore, a two-component regulatory system modulates virulence according to environmental conditions. In addition, the mutation affecting a spontaneous avirulent variant of S. flexneri serotype 5, M90T, has been mapped at the ompB locus and was complemented by the cloned E. coli ompB locus. Introduction of the vir::lac fusion into this mutant did not result in the expression of beta-galactosidase (Lac-).

Identification of icsA, a plasmid locus of Shigella flexneri that governs bacterial intra- and intercellular spread through interaction with F-actin

The capacity of Shigella to spread within the cytosol of infected epithelial cells and to infect adjacent cells is critical for the development of infection foci, which lead to mucosal abscesses. Shigella is a nonmotile microorganism that appears to utilize host cell microfilaments to generate intra- as well as intercellular movements, since this movement was inhibited by cytochalasin D and involvement of F-actin was demonstrated by direct labeling of infected cells with the specific dye N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phallacidin. Such movements led to the formation of extracellular protrusions, which may explain cell to cell spread. icsA, a locus necessary for intra- and intercellular spread, was identified on the Shigella flexneri virulence plasmid pWR100. This locus was cloned and shown to express a 120-kDa outer membrane protein, which plays an important role in the interactions established between host cell microfilaments and the bacterial surface, thus leading to intracellular movement.