Immunobiological activities of Helicobacter pylori porins

Sodium sulfite-driven Helicobacter pylori eradication: Unraveling oxygen dynamics through multi-omics investigation

Due to the emergence and spread of multidrug resistance in Helicobacter pylori (H. pylori), its eradication has become difficult. Sodium sulfite (SS), a widely used food additive for ensuring food safety and storage, has been recognized as an effective nonbactericidal agent for H. pylori eradication. However, the mechanism by which H. pylori adapts and eventually succumbs under low- or no-oxygen conditions remains unknown. In this study, we aimed to evaluate the anti-H. pylori effect of SS and investigated the multiomics mechanism by which SS kills H. pylori. The results demonstrated that SS effectively eradicated H. pylori both in vitro and in vivo. H. pylori responds to the oxygen changes regulated by SS, downregulates the HcpE gene, which is responsible for redox homeostasis in bacteria, decreases the activities of enzymes related to oxidative stress, and disrupts the outer membrane structure, increasing susceptibility to oxidative stress. Furthermore, SS downregulates the content of cytochrome C in the microaerobic respiratory chain, leading to a sharp decrease in ATP synthesis. Consequently, the accumulation of triglycerides (TGs) in bacteria due to oxidative stress supports anaerobic respiration, meeting their energy requirements. The multifaceted death of H. pylori caused by SS does not result in drug resistance. Thus, screening of the redox homeostasis of HcpE as a new target for H. pylori infection treatment could lead to the development of a novel approach for H. pylori eradication therapy.

Modulation of host cellular responses by gram-negative bacterial porins

The outer membrane of a gram-negative bacteria encapsulates the plasma membrane thereby protecting it from the harsh external environment. This membrane acts as a sieving barrier due to the presence of special membrane-spanning proteins called "porins." These porins are β-barrel channel proteins that allow the passive transport of hydrophilic molecules and are impermeable to large and charged molecules. Many porins form trimers in the outer membrane. They are abundantly present on the bacterial surface and therefore play various significant roles in the host-bacteria interactions. These include the roles of porins in the adhesion and virulence mechanisms necessary for the pathogenesis, along with providing resistance to the bacteria against the antimicrobial substances. They also act as the receptors for phage and complement proteins and are involved in modulating the host cellular responses. In addition, the potential use of porins as adjuvants, vaccine candidates, therapeutic targets, and biomarkers is now being exploited. In this review, we focus briefly on the structure of the porins along with their important functions and roles in the host-bacteria interactions.

Genetic Alterations in Gastric Cancer Associated with Helicobacter pylori Infection

Gastric cancer is a world health problem and depicts the fourth leading mortality cause from malignancy in Mexico. Causation of gastric cancer is not only due to the combined effects of environmental factors and genetic variants. Recent molecular studies have transgressed a number of genes involved in gastric carcinogenesis. The aim of this review is to understand the recent basics of gene expression in the development of the process of gastric carcinogenesis. Genetic variants, polymorphisms, desoxyribonucleic acid methylation, and genes involved in mediating inflammation have been associated with the development of gastric carcinogenesis. Recently, these genes (interleukin 10, Il-17, mucin 1, β-catenin, CDX1, SMAD4, SERPINE1, hypoxia-inducible factor 1 subunit alpha, GSK3β, CDH17, matrix metalloproteinase 7, RUNX3, RASSF1A, TFF1, HAI-2, and COX-2) have been studied in association with oncogenic activation or inactivation of tumor suppressor genes. All these mechanisms have been investigated to elucidate the process of gastric carcinogenesis, as well as their potential use as biomarkers and/or molecular targets to treatment of disease.

Offense and defense: microbial membrane vesicles play both ways

Microbes have evolved over millennia to become adapted and specialized to the environments that they occupy. These environments may include water or soil, extreme environments such as hydrothermal vents, and can even include a host organism. To become adapted to these locations, microbes have evolved specific tools to mediate interactions with the environment. One such tool that prokaryotes have evolved includes the production of membrane vesicles (MVs). MVs are 10-300 nm spherical blebs derived from the outermost membrane and have known functions in protein secretion, immune activation and suppression, stress response, attachment, internalization and virulence. In this review, we consider the highly conserved role of membrane vesicles derived from Gram-negative, Gram-positive and archaeal species as a mechanism to facilitate intermicrobial and microbe-host interaction. We examine both the offensive and defensive capabilities of MVs in regard to the interaction of MVs with both host and microbial cells in their environment.

Klebsiella pneumoniae secretes outer membrane vesicles that induce the innate immune response

Outer membrane vesicles (OMVs) derived from pathogenic Gram-negative bacteria are an important vehicle for delivery of effector molecules to host cells, but the production of OMVs from Klebsiella pneumoniae, an opportunistic pathogen of both nosocomial and community-acquired infections, and their role in bacterial pathogenesis have not yet been determined. In the present study, we examined the production of OMVs from K. pneumoniae and determined the induction of the innate immune response against K. pneumoniae OMVs. Klebsiella pneumoniae ATCC 13883 produced and secreted OMVs during in vitro culture. Proteomic analysis revealed that 159 different proteins were associated with K. pneumoniae OMVs. Klebsiella pneumoniae OMVs did not inhibit cell growth or induce cell death. However, these vesicles induced expression of proinflammatory cytokine genes such as interleukin (IL)-1β and IL-8 in epithelial cells. An intratracheal challenge of K. pneumoniae OMVs in neutropenic mice resulted in severe lung pathology similar to K. pneumoniae infection. In conclusion, K. pneumoniae produces OMVs like other pathogenic Gram-negative bacteria and K. pneumoniae OMVs are a molecular complex that induces the innate immune response.

Virulence and immunomodulatory roles of bacterial outer membrane vesicles

Outer membrane (OM) vesicles are ubiquitously produced by Gram-negative bacteria during all stages of bacterial growth. OM vesicles are naturally secreted by both pathogenic and nonpathogenic bacteria. Strong experimental evidence exists to categorize OM vesicle production as a type of Gram-negative bacterial virulence factor. A growing body of data demonstrates an association of active virulence factors and toxins with vesicles, suggesting that they play a role in pathogenesis. One of the most popular and best-studied pathogenic functions for membrane vesicles is to serve as natural vehicles for the intercellular transport of virulence factors and other materials directly into host cells. The production of OM vesicles has been identified as an independent bacterial stress response pathway that is activated when bacteria encounter environmental stress, such as what might be experienced during the colonization of host tissues. Their detection in infected human tissues reinforces this theory. Various other virulence factors are also associated with OM vesicles, including adhesins and degradative enzymes. As a result, OM vesicles are heavily laden with pathogen-associated molecular patterns (PAMPs), virulence factors, and other OM components that can impact the course of infection by having toxigenic effects or by the activation of the innate immune response. However, infected hosts can also benefit from OM vesicle production by stimulating their ability to mount an effective defense. Vesicles display antigens and can elicit potent inflammatory and immune responses. In sum, OM vesicles are likely to play a significant role in the virulence of Gram-negative bacterial pathogens.

Detailed in vivo analysis of the role of Helicobacter pylori Fur in colonization and disease

Helicobacter pylori persistently colonizes the harsh and dynamic environment of the stomach in over one-half of the world's population and has been identified as a causal agent in a spectrum of pathologies that range from gastritis to invasive adenocarcinoma. The ferric uptake regulator (Fur) is one of the few regulatory proteins that has been identified in H. pylori. Fur regulates genes important for acid acclimation and oxidative stress and has been shown to be important for colonization of H. pylori in both murine and Mongolian gerbil models of infection. To more thoroughly define the role of Fur in vivo, we conducted an extensive temporal analysis of the location of, competitive ability of, and resultant pathology induced by a Deltafur strain in the Mongolian gerbil model of infection and compared the results to results for its wild-type parent. We found that at the earliest time points postinfection, significantly more Deltafur bacteria than wild-type bacteria were recovered. However, this trend was reversed by day 3, when there was significantly increased recovery of the wild-type strain. The increased recovery of the Deltafur strain at 1 day postinfection reflected increased recovery from both the corpus and the antrum of the stomach. When the wild-type strain was allowed to colonize first, the Deltafur strain was unable to compete for colonization at any time postinfection. However, when the Deltafur strain was allowed to colonize first, the wild type efficiently outcompeted the Deltafur strain only at early times postinfection. Finally, we demonstrated that there was a delay in the development and severity of inflammation and pathology of the Deltafur strain in the gastric mucosa even after comparable levels of colonization occurred. Together, these data indicate that H. pylori Fur is most important at early stages of infection and illustrate the importance of the ability of H. pylori to adapt to its constantly fluctuating environment when it is establishing infection, inflammation, and disease.

Stable surface expression of a gene for Helicobacter pylori toxic porin protein with pBAD expression system

Helicobacter pylori (H. pylori) infection causes peptic and duodenal diseases in humans. Among a 32-protein family of outer membrane proteins, a porin-like protein, HopE, has been a subject of note, mainly for its conservative nature among H. pylori, and for its potential as a vaccine candidate. To achieve stable surface expression of this host cell-toxic protein, hopE gene was introduced into pBAD expression system. After induction with arabinose, all 15 randomly-chosen E. coli LMG 194 colonies from 3 successive passages could express HopE protein, while only 1 from 5 E. coli colonies that contained lac operon-regulated plasmid encoding hopE gene could express HopE. Indirect immunofluorescence confirmed the expression of HopE on E. coli cell surface.

Posttranscriptional regulation of flagellin synthesis in Helicobacter pylori by the RpoN chaperone HP0958

The Helicobacter pylori protein HP0958 is essential for flagellum biogenesis. It has been shown that HP0958 stabilizes the sigma(54) factor RpoN. The aim of this study was to further investigate the role of HP0958 in flagellum production in H. pylori. Global transcript analysis identified a number of flagellar genes that were differentially expressed in an HP0958 mutant strain. Among these, the transcription of the major flagellin gene flaA was upregulated twofold, suggesting that HP0958 was a negative regulator of the flaA gene. However, the production of the FlaA protein was significantly reduced in the HP0958 mutant, and this was not due to the decreased stability of the FlaA protein. RNA stability analysis and binding assays indicated that HP0958 binds and destabilizes flaA mRNA. The HP0958 mutant was successfully complemented, confirming that the mutant phenotype described was due to the lack of HP0958. We conclude that HP0958 is a posttranscriptional regulator that modulates the amount of the flaA message available for translation in H. pylori.

Recurrent headache as the main symptom of acquired cerebral toxoplasmosis in nonhuman immunodeficiency virus-infected subjects with no lymphadenopathy: the parasite may be responsible for the neurogenic inflammation postulated as a cause of different types of headaches

Headache and/or migraine, a common problem in pediatrics and internal medicine, affect about 5% to 10% children and adolescents, and nearly 30% of middle-aged women. Headache is also one of the most common clinical manifestations of acquired Toxoplasma gondii infection of the central nervous system (CNS) in immunosuppressed subjects. We present 11 apparently nonhuman immunodeficiency virus-infected children aged 7 to 17 years (8 girls, 3 boys) and 1 adult woman with recurrent severe headaches in whom latent chronic CNS T. gondii infection not manifested by enlarged peripheral lymph nodes typical for toxoplasmosis, was found. In 7 patients, the mean serum IgG Toxoplasma antibodies concentration was 189 +/- 85 (SD) IU/mL (range 89 to 300 IU/mL), and in 5 other subjects, the indirect fluorescent antibody test titer ranged from 1:40 to 1:5120 IU/mL (n= <1:10 IU/mL). Some of the patients suffered also from atopic dermatitis (AD) and were exposed to cat and/or other pet allergens, associated with an increased IL-4 and decreased IFN-gamma production. These cytokine irregularities caused limited control of cerebral toxoplasmosis probably because IL-4 down-regulated both the production of IFN-gamma and its activity, and stimulated production of a low NO-producing population of monocytes, which allowed cysts rupture, increased parasite multiplication and finally reactivation of T. gondii infection. The immune studies performed in 4 subjects showed a decreased percentage of T lymphocytes, increased total number of lymphocytes B and serum IgM concentration, and impaired phagocytosis. In addition, few of them had also urinary tract diseases known to produce IL-6 that can mediate immunosuppressive functions, involving induction of the anti-inflammatory cytokine IL-10. These disturbances probably resulted from the host protective immune reactions associated with the chronic latent CNS T. gondii infection/inflammation. This is consistent with significantly lower enzyme indoleamine 2,3-dioxygenase (IDO) activity reported in atopic than in nonatopic individuals, and an important role that IDO and tryptophan degradation pathways plays in both, the host resistance to T. gondii infection and its reactivation. Analysis of literature information on the subjects with different types of headaches caused by foods, medications, and other substances, may suggest that their clinical symptoms and changes in laboratory data result at least in part from interference of these factors with dietary tryptophan biotransformation pathways. Several of these agents caused headache attacks through enhancing NO production via the conversion of arginine to citrulline and NO by the inducible nitric oxide synthase enzyme, which results in the high-output pathway of NO synthesis. This increased production of NO is, however, quickly down-regulated by NO itself because this biomolecule can directly inactivate NOS, may inhibit Ia expression on IFN-gamma-activated macrophages, which would limit antigen-presenting capability, and block T-cell proliferation, thus decreasing the antitoxoplasmatic activity. Moreover, NO inhibits IDO activity, thereby suppressing kynurenine formation, and at least one member of the kynurenine pathway, 3-hydroxyanthranilic acid, has been shown to inhibit NOS enzyme activity, the expression of NOS mRNA, and activation of the inflammatory transcription factor, nuclear factor-kB. In addition, the anti-inflammatory cytokines IL-4 and IL-10, TGF-beta, and a cytokine known as macrophage deactivating factor, have been shown to directly modulate NO production, sometimes expressing synergistic activity. On the other hand, IL-4 and TGF-beta can suppress IDO activity in some cells, for example human monocytes and fibroblasts, which is consistent with metabolic pathways controlled by IDO being a significant contributor to the proinflammatory system. Also, it seems that idiopathic intracranial hypertension, pseudotumor cerebri, and aseptic meningitis, induced by various factors, may result from their interference with IDO and inducible nitric oxide synthase activities, endogenous NO level, and cytokine irregularities which finally affect former T. gondii status 2mo in the brain. All these biochemical disturbances caused by the CNS T. gondii infection/inflammation may also be responsible for the relationship found between neurologic symptoms, such as headache, vertigo, and syncope observed in apparently immunocompetent children and adolescents, and physical and psychiatric symptoms in adulthood. We therefore believe that tests for T. gondii should be performed obligatorily in apparently immunocompetent patients with different types of headaches, even if they have no enlarged peripheral lymph nodes. This may help to avoid overlooking this treatable cause of the CNS disease, markedly reduce costs of hospitalization, diagnosis and treatment, and eventually prevent developing serious neurologic and psychiatric disorders.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

Immunomodulation by non-absorbable antibiotics given by the intragastric route

To test the role of bacterial fractions released from intestinal flora during immunomodulation by antimicrobial agents, BALB/c mice were treated with the non-absorbable antibiotics polymyxin B or teicoplanin by the intragastric route. The composition of faecal microbiota and the capacity of spleen cells to proliferate in response to B-cell and T-cell mitogens were assessed at several times during the treatment. Both antibiotics lowered the count of some bacteria of the intestinal flora and induced significant modifications in spleen cell ability to proliferate in response to mitogens. Thus, the active fractions released from intestinal bacteria during antibiotic treatments may be able to induce immunomodulating effects.

Molecular basis of bacterial outer membrane permeability revisited

Gram-negative bacteria characteristically are surrounded by an additional membrane layer, the outer membrane. Although outer membrane components often play important roles in the interaction of symbiotic or pathogenic bacteria with their host organisms, the major role of this membrane must usually be to serve as a permeability barrier to prevent the entry of noxious compounds and at the same time to allow the influx of nutrient molecules. This review summarizes the development in the field since our previous review (H. Nikaido and M. Vaara, Microbiol. Rev. 49:1-32, 1985) was published. With the discovery of protein channels, structural knowledge enables us to understand in molecular detail how porins, specific channels, TonB-linked receptors, and other proteins function. We are now beginning to see how the export of large proteins occurs across the outer membrane. With our knowledge of the lipopolysaccharide-phospholipid asymmetric bilayer of the outer membrane, we are finally beginning to understand how this bilayer can retard the entry of lipophilic compounds, owing to our increasing knowledge about the chemistry of lipopolysaccharide from diverse organisms and the way in which lipopolysaccharide structure is modified by environmental conditions.

Bacterial components induce cytokine and intercellular adhesion molecules-1 and activate transcription factors in dermal fibroblasts

This study investigated the effect of various structural components of Gram-positive (lipotheichoic acid and protein A) and Gram-negative (porins and lipopolysaccharide) bacteria on human dermal fibroblasts. Fibroblasts are important effector cells which have a potential role in augmenting the inflammatory response in various diseases. In this study we present a profile of TNF-alpha, IL-6 and IL-8, the expression of intercellular adhesion molecules (ICAM-1) and the activation of transcriptional nuclear factor NF-kB and AP-1 in human dermal fibroblasts stimulated by bacterial surface components. Compared to the controls, increased ICAM-1, IL-6 and IL-8 gene expression after stimulation of LPS and porins at 2 and 4 h was more evident than that obtained following stimulation of LTA and PA. Gene expression was also associated with the production of cytokine proteins in culture supernatants. TNF-alpha gene expression remained undetectable. Moreover, LPS and porin treatments determined IkBalpha phosphorylation and degradation in human dermal fibroblasts and the subsequent activation of nuclear factors NF-kB and AP-1. These data suggest the importance of such stimuli in the first step of the inflammatory process, as well as the important role played by fibroblasts in skin inflammatory disease.

Stem cell factor expressed in human gastric mucosa in relation to mast cell increase in Helicobacter pylori-infected gastritis

We previously reported mast cell increases in H. pylori gastritis. To determine the mechanism, we investigated the kinetics of mast cells and mast cell growth factor (stem cell factor, SCF) in H. pylori-positive and -negative gastric mucosa. Biopsy specimens from 12 H. pylori-negative and 28 positive subjects were examined. Sections were stained for mast cells, proliferating cell nuclear antigen (PCNA), and SCF. Densities of mast cells, PCNA-positive mast cells, and SCF-positive cells were significantly greater in H. pylori-positive than -negative subjects. SCF was expressed in mast cells and fibroblasts. The density of SCF-positive fibroblasts increased in H. pylori-positive gastritis and decreased after cure of infection. SCF mRNA was detected in H. pylori-positive gastric mucosa. Fibroblasts isolated from the normal gastric mucosa expressed SCF mRNA after incubation with H. pylori water extract. SCF may be one of the factors for mast cell increase. Fibroblasts may participate in mast cell increase and inflammation in H. pylori infection.

Diethyl phthalate, a chemotactic factor secreted by Helicobacter pylori

The structure of a small-molecule, non-peptide chemotactic factor has been determined from activity purified to apparent homogeneity from Helicobacter pylori supernatants. H. pylori was grown in brucella broth media until one liter of solution had 0.9 absorbance units. The culture was centrifuged, and the bacteria re-suspended in physiological saline and incubated at 37 degrees C for 4 h. A monocyte migration bioassay revealed the presence of a single active chemotactic factor in the supernatant from this incubation. The chemotactic factor was concentrated by solid phase chromatography and purified by reverse phase high pressure liquid chromatography. The factor was shown to be indistinguishable from diethyl phthalate (DEP) on the basis of multiple criteria including nuclear magnetic resonance spectroscopy, electron impact mass spectroscopy, UV visible absorption spectrometry, GC and high pressure liquid chromatography retention times, and chemotactic activity toward monocytes. Control experiments with incubated culture media without detectable bacteria did not yield detectable DEP, suggesting it is bacterially derived. It is not known if the bacteria produce diethyl phthalate de novo or if it is a metabolic product of a precursor molecule present in culture media. DEP produced by H. pylori in addition to DEP present in man-made products may contribute to the high levels of DEP metabolites observed in human urine. DEP represents a new class of chemotactic factor.

pathogenesis of Helicobacter pylori-induced gastric inflammation

Helicobacter pylori causes persistent inflammation in the human stomach, yet only a minority of persons harbouring this organism develop peptic ulcer disease or gastric malignancy. An important question is why such variation exists among colonized individuals. Recent evidence has demonstrated that H. pylori isolates possess substantial phenotypic and genotypic diversity, which may engender differential host inflammatory responses that influence clinical outcome. For example, H. pylori strains that possess the cag pathogenicity island induce more severe gastritis and augment the risk for developing peptic ulcer disease and distal gastric cancer. An alternative, but not exclusive, hypothesis is that enhanced inflammation and injury is a consequence of an inappropriate host immune response to the chronic presence of H. pylori within the gastric niche. Investigations that precisely delineate the mechanisms responsible for induction of gastritis will ultimately help to define which H. pylori-colonized persons bear the highest risk for subsequent development of clinical disease, and thus, enable physicians to focus eradication therapy.

A chromosomal region surrounding the ompD porin gene marks a genetic difference between Salmonella typhi and the majority of Salmonella serovars

In this work it is shown that the majority of Salmonella serovars most frequently associated with the systemic infection of vertebrate hosts produce a major outer-membrane porin, OmpD. However, OmpD is absent from the outer-membrane protein profiles of Salmonella typhi strain Ty2 and 26 clinical isolates of S. typhi examined by SDS-PAGE. To determine whether the ompD gene is present in S. typhi, primers internal to the ompD coding sequence were used to amplify the gene by PCR. With the exception of S. typhi strains, the ompD gene was amplified from the genomes of all Salmonella serovars tested. Consistently, a specific ompD probe did not hybridize with DNA isolated from the S. typhi strains. Taken together, these results demonstrate that S. typhi does not produce OmpD due to the absence of the ompD gene. Furthermore, it was investigated whether the deletion of ompD extended to smvA. This gene is adjacent to ompD in the Salmonella typhimurium chromosome and encodes a protein involved in the resistance to methyl viologen, a superoxide-generating agent. Although PCR failed to amplify the smvA gene from the S. typhi strain Ty2 genome, it was possible to amplify it from the chromosome of the clinical strains. On the other hand, hybridization analyses showed that the smvA gene is present in all the S. typhi strains tested. In contrast to the other Salmonella serovars, S. typhi strain Ty2 and the clinical isolates showed sensitivity to methyl viologen, suggesting that smvA gene is inactive in S. typhi. In conclusion, the ompD-smvA region is variable in structure among Salmonella serovars. It is hypothesized that the absence of ompD may suggest a role in host specificity.

Characterization of proteins in the outer membrane preparation of a murine pathogen, Helicobacter bilis

Helicobacter bilis is a bacterial pathogen associated with multifocal hepatitis and inflammatory bowel disease in certain strains of mice. This bacterium colonizes the liver, bile, and lower intestine in mice and has also been isolated from a wide spectrum of laboratory animals. In this study, proteins present in the outer membrane preparation (OMP) of four H. bilis strains isolated from a mouse, a dog, a rat, and a gerbil were characterized and compared with that of Helicobacter pylori, a human gastric pathogen. All four H. bilis strains had similar OMP protein profiles that were distinct from those of H. pylori. Immunoblotting demonstrated that OMP proteins from H. bilis and H. pylori have little cross-reactivity, except for their flagellins. Nine major immunogenic polypeptides were present in the H. bilis OMPs. By using two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, five heat-modifiable proteins with molecular masses of 82, 66, 52, 47 and 37 kDa were identified. The N-terminal sequences of the 46- and 47-kDa OMP proteins had no homology with protein sequences available in public databases. These results indicate that H. bilis has a conserved, unique OMP protein profile that is distinct from those of H. pylori.

Apoptotic signaling pathway activated by Helicobacter pylori infection and increase of apoptosis-inducing activity under serum-starved conditions

The enhanced gastric epithelial cell apoptosis observed during infection with Helicobacter pylori has been suggested to be of significance in the etiology of gastritis, peptic ulcers, and neoplasia. To investigate the cell death signaling induced by H. pylori infection, human gastric epithelial cells were incubated with H. pylori for up to 72 h. H. pylori infection induced the activation of caspase -8, -9, and -3 and the expression of the proapoptotic Bcl-2 family proteins Bad and Bid. The peak of the activity of the caspases occurred at 24 h. At this time, the inhibition of caspase-8 or -9 almost completely suppressed H. pylori-induced apoptosis. Inhibition of caspase-8 suppressed the expression of Bad and Bid and the subsequent activation of caspase-9 and -3. These observations indicate that H. pylori induces apoptosis through a pathway involving the sequential induction of apical caspase-8 activity, the proapoptotic proteins Bad and Bid, caspase-9 activity, and effector caspase-3 activity. Activation of the pathway was independent of CagA or vacuolating toxin. A membrane fraction of H. pylori was sufficient to activate this pathway, and treatment with proteinase K eliminated the activity. Apoptotic activity of the membrane fraction was significantly increased by incubating the bacteria under serum-starved conditions for 24 h. These observations suggest that environmental conditions in the human stomach could induce H. pylori-mediated pathogenesis, leading to a variety of clinical outcomes.

An association between sudden infant death syndrome (SIDS) and Helicobacter pylori infection

BACKGROUND

Helicobacter pylori has recently been detected in the stomach and trachea of cases of sudden infant death syndrome (SIDS) and proposed as a cause of SIDS.

AIMS

To establish the incidence of H pylori in the stomach, trachea, and lung of cases of SIDS and controls.

METHODS

Stomach, trachea, and lung tissues from 32 cases of SIDS and eight control cases were examined retrospectively. Diagnosis of SIDS was based on established criteria. Controls were defined by death within 1 year of age and an identifiable cause of death. Tissues were examined histologically for the presence of bacteria. Extracted DNA from these tissues was tested for H pylori ureC and cagA sequences by nested polymerase chain reaction and amplicons detected by enzyme linked immunosorbent assay (ELISA). The cut off for each ELISA for each of the tissue types was taken as the mean optical density plus two times the standard deviation of a range of negative controls.

RESULTS

Ages of SIDS cases ranged from 2 to 28 weeks. Ages of controls ranged from 3 to 44 weeks. For the ureC gene, 25 SIDS cases were positive in one or more tissues compared with one of the controls. For the cagA gene, 25 SIDS cases were positive in one or more tissues compared with one of the controls.

CONCLUSIONS

There is a highly significant association between H pylori ureC and cagA genes in the stomach, trachea, and lung of cases of SIDS when compared with controls.

Neisseria gonorrhoeae porin modifies the oxidative burst of human professional phagocytes

A hallmark of infection with the gram-negative bacterium Neisseria gonorrhoeae is the local infiltration and subsequent activation of polymorphonuclear neutrophils. Several gonococcal outer membrane proteins are involved in the interaction with and the activation of these phagocytes, including gonococcal porin, the most abundant protein in the outer membrane. Previous work suggests that this porin plays a role in various cellular processes, including inhibiting neutrophils activation and phagosome maturation in professional phagocytes. Here we investigated the ability of porin to modify the oxidative metabolism of human peripheral blood neutrophils and monocytes in response to particulate stimuli (including live gonococci) and soluble agents. The activation of the oxidative metabolism was determined by chemiluminescence amplified with either luminol or lucigenin. We found that treatment of the phagocytes with porin inhibits the release of reactive oxygen species measured as luminol-enhanced chemiluminescence in response to zymosan, latex particles, and gonococci. The engulfment of these particles was not, however, affected by porin treatment. Similar effects of porin on the chemiluminescence response were observed in cytochalasin B-treated neutrophils exposed to the soluble chemotactic peptide N-formylmethionyl-leucyl-phenylalanine. This indicates that porin selectively inhibits granule fusion with those cellular membranes that are in direct contact with porin, namely, the phagosomal and plasma membranes. This porin-induced downregulation of oxidative metabolism may be a potent mechanism by which gonococci modulate oxygen-dependent reactions by activated phagocytes at inflammation sites.

Role of porin of Shigella dysenteriae type 1 in modulation of lipopolysaccharide mediated nitric oxide and interleukin-1 release by murine peritoneal macrophages

The ability of Shigella dysenteriae type 1 porin to induce the release of nitric oxide (NO) and interleukin-1 (IL-1) from peritoneal macrophages of mouse and to regulate lipopolysaccharide (LPS) and gamma interferon (IFN-gamma) mediated release of the two proinflammatory mediators was investigated. Porin released nitrite when added to macrophage cultures. A maximum of 3.2-fold nitrite release by macrophages was observed with 100 ng ml(-1) of porin. The nitrite release of LPS was enhanced significantly by lower concentrations of porin, whereas the effect of IFN-gamma was enhanced by porin at higher concentrations. Polysaccharide (PS) moiety of LPS stimulated the nitrite release of elicited macrophages by 1.6-fold compared to untreated control. It also enhanced the stimulatory effect of 1 and 10 ng ml(-1) of porin by 1.3-fold. Lipid A (LPA) moiety of LPS did not release nitrite, nor did it increase the porin mediated nitrite production. Porin treated 24 h old macrophage culture supernatants were applied for ConA activated thymocyte proliferation as a measure for determination of IL-1 release. Sixty percent depletion of thymocyte proliferation was observed when the porin treated macrophage supernatants were absorbed with anti-IL-1 antibody. A maximum of 5.5-fold increase of thymocyte proliferation over control was found with 1 and 10 ng ml(-1) of porin. One or 10 ng ml(-1) of porin and LPS augmented the thymocyte growth, 1.5-fold beyond that obtained by porin and 1.8-/1. 7-fold more than that obtained by LPS, alone. Similarly, porin and IFN-gamma co-stimulated the cell growth also. PS enhanced the thymocyte proliferation by 5-fold. It also enhanced the thymocyte growth by co-stimulating 1.4-fold the effect observed by 1 or 10 ng ml(-1) of porin alone. LPA could not participate in the cell proliferating activity nor did it enhance the stimulatory effect of porin. Therefore, both nitrite release and thymocyte proliferation by LPS could be substituted by PS only. The tight association of the two bacterial outer membrane components, porin and LPS, could be a necessary co-signal for boosting the release of the two proinflammatory mediators, namely NO and IL-1, which may be associated with the inflammatory response of the colon during Shigella invasion.

Expression of interleukin-1beta, tumor necrosis factor alpha, and interleukin-6 in human peripheral blood leukocytes exposed to human granulocytic ehrlichiosis agent or recombinant major surface protein P44

Human granulocytic ehrlichiosis (HGE) is an emerging febrile systemic disease caused by the HGE agent, an obligatory intracellular bacterium of granulocytes. The pathogenicity- and immunity-related mechanisms of HGE are unknown. In this study, several cytokines generated in human peripheral blood leukocytes (PBLs) incubated with the HGE agent or a recombinant 44-kDa major surface protein (rP44) of the HGE agent were examined by reverse transcription-PCR and a capture enzyme-linked immunosorbent assay. The HGE agent induced expression of interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), and IL-6 mRNAs and proteins in PBLs in a dose-dependent manner to levels as high as those resulting from Escherichia coli lipopolysaccharide stimulation. The kinetics of induction of these three cytokines in PBLs by rP44 and by the HGE agent were similar. Proteinase K treatment of the HGE agent or rP44 eliminated the ability to induce these three cytokines. Induction of these cytokine mRNAs was not dependent on superoxide generation. These results suggest that P44 proteins have a major role in inducing the production of proinflammatory cytokines by PBLs. Expression of IL-8, IL-10, gamma interferon, transforming growth factor beta, and IL-2 mRNAs in response to the HGE agent was not remarkable. Among PBLs, neutrophils and lymphocytes expressed IL-1beta mRNA but not TNF-alpha or IL-6 mRNA in response to the HGE agent, whereas monocytes expressed all three of these cytokine mRNAs. These observations suggest that induction of proinflammatory-cytokine gene expression by the major outer membrane protein of the HGE agent in monocytes, which are not the primary host cells of the HGE agent, contributes to HGE pathogenesis and immunomodulation.

A role for the bacterial outer membrane in the pathogenesis of Helicobacter pylori infection

Helicobacter pylori infection in humans is associated with diverse of clinical outcomes which are partly attributed to bacterial strain differences. Secreted bacterial products are thought to be involved in the pathogenesis caused by this non-invasive bacterium. Electron microscopy of gastric biopsies from infected individuals revealed blebbing of the H. pylori outer membrane, similar to the process of outer membrane vesicle shedding which occurs when the bacterium is grown in broth. Porins, a class of proinflammatory proteins, were observed in the outer membrane vesicles. The VacA cytotoxin, which is produced by 50-60% of H. pylori strains and associated with increased pathogenesis of infection, was also found to be vesicle-associated and biologically active. This supports the hypothesis that these vesicles represent a vehicle for the delivery of damaging bacterial products to the gastric mucosa.

Porin from Pseudomonas aeruginosa induces apoptosis in an epithelial cell line derived from rat seminal vesicles

Micromolar concentrations of porin, purified from the outer membranes of Pseudomonas aeruginosa, induced in vitro the classic morphological and biochemical signs of apoptosis in an epithelial cell line (SVC1) derived from the rat seminal vesicle secretory epithelium. The programmed cell death (PCD) was p53 independent and associated with significant decrease of bcl-2 expression, a marked increase of c-myc transcriptional activity, and an absence of the mRNA coding for tissue transglutaminase. The Ca(2+) influx, caused by the porin treatment of SVC1 cells, appears to play an important role in the triggering of apoptosis in our biological model. The possibility that the porin property of inducing PCD plays a role in the infertility of individuals chronically infected by gram-negative bacteria is discussed.

Porins and lipopolysaccharide (LPS) from Salmonella typhimurium induce leucocyte transmigration through human endothelial cells in vitro

Bacteria or bacterial products may constitute important inducers of surface molecule expression on endothelial cells and leucocytes. This study was undertaken to determine the effects of the Salmonella typhimurium porins, LPS-S and LPS-R on the transendothelial migration of leucocytes through human umbilical vein endothelial cells (HUVEC). Treatment of the HUVEC with either porins or LPS-S or LPS-R increased the transmigration of different leucocyte populations, in particular that of neutrophils. The maximal increase occurred using LPS-S treatment, whereas porin stimulation fell between LPS-S and LPS-R. The transmigration increase was dose-dependent and reached its maximum at about 100-1000 ng/ml of stimulus. Optimal endothelial activation occurred after 2-4 h and 4-6 h using LPS and porin, respectively. Stimulation of leucocytes with either porins or LPS slightly increased their transmigration through non-activated endothelial cells. Transmigration increased remarkably during the simultaneous stimulation of endothelial cells by IL-1ss together with either porins or LPS. To assess participation of E-selectin, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and leucocyte adhesion complex (CD11/18) in porin- or LPS-mediated leucocyte migration, blocking MoAbs were used. Each blocking MoAb partially and selectively decreased leucocyte transmigration. The obtained results contribute to clarify some aspects of the inflammatory process at sites of infection.

Changes in the evolution of the antigenic profiles and morphology during coccoid conversion of Helicobacter pylori

OBJECTIVES

The significance of the coccoid forms of H. pylori is still controversial and the questions of whether these forms are viable and infective or degenerative are still open. We induced conversion from rod to coccoid forms and studied morphological changes and antigenic evolutions during this conversion and, thereby, elucidated the viability of coccoid forms.

METHODS

The H. pylori strain (C001) used for Western blotting was isolated from the patient with gastric cancer. The antigenic evolution during coccoid conversion of H. pylori was studied by Western blotting, using different sera from thirty patients known to be culture positive. These sera were used to reveal the total antigens of the strain cultured for 2 days (100% rod) and 15 days (> 99% coccoid). After SDS-PAGE, with 10% separating gel of total antigens (rod and coccoid), transblotting (Trans-Blot electrophoretic cell, Bio-Rad) was taken onto a nitrocellulose membrane (Bio-Rad). Then, the blots, with human sera diluted at 1/100, were developed with color reaction by goat serum anti-human IgG with alkaline phosphatase and BCIP.

RESULTS

The antigenic profiles were not changed in 46.7% (14/30 cases) and were changed in 53.3% (16/30 cases) during coccoid conversion. Antigenic fractions changed during coccoid conversion were protein band at 120 kDa and band at 35 kDa, and were not detected in coccus forms. The rest of the profiles were identical between rod and coccoid forms. The protein which disappeared include CagA (120 kDa) and porin, or adhesin (35 kDa). The morphological changes during coccoid conversion were U shaped at day 7, doughnut shaped at day 9 and full coccoid at day 15.

CONCLUSIONS

The results showed that coccoid forms of H. pylori retain cellular structures similar to rod form, and some of the antigens (CagA and porin) disappeared during coccoid conversion. Therefore, coccoid form might be viable and represent one of the stages of H. pylori biological cycle.

Interleukin-6 (IL-6) and IL-8 are induced in human oral epithelial cells in response to exposure to periodontopathic Eikenella corrodens

Periodontitis is the inflammatory response in periodontal tissues elicited by bacterial colonization in periodontal pockets. In this response, pocket epithelial cells are the first cells to come into contact with bacteria. To elucidate this mechanism, we determined the adherence of the periodontopathic bacterium Eikenella corrodens 1073, which has a GalNAc-sensitive lectin-like adhesin (EcLS), to a human oral epithelial carcinoma cell line (KB) and the induction of proinflammatory cytokine production in the cells following exposure to this bacterium in vitro. In the adherence assay, EcLS played a role as the adhesin of this bacterium in adherence to KB cells. In a reverse transcriptase PCR, significant interleukin-8 (IL-8) and IL-6 mRNA levels were induced in response to exposure to this bacterium. In an enzyme-linked immunosorbent assay after an 8-h bacterial exposure, the IL-8 and IL-6 protein levels were 13.5- and 8.3-fold higher than those in the nonexposed controls, respectively. These protein responses were time dependent. Interestingly, when E. corrodens was separated from KB cells by cell culture inserts, a slight stimulation of the IL-6 and IL-8 mRNA and secreted protein levels was seen. These results imply that the direct contact of E. corrodens 1073 with oral epithelial cells is not necessarily required for the stimulation of IL-6 and IL-8 secretion. We suggest that E. corrodens induces the epithelial cells to secrete proinflammatory cytokines which serve as an early signaling system to host immune and inflammatory cells in underlying connective tissues.

Bacterial factors and immune pathogenesis in Helicobacter pylori infection

Virulent Helicobacter pylori strains which have been clinically associated with severe outcome induce increased gastric mucosal immune responses. Although several bacterial pathogenic factors have been shown to have a considerable role in H pylori infection, variability in host immune responses may also contribute to mucosal damage in H pylori associated gastritis.

Molecular basis of host-pathogen interaction in septic shock

Specific mechanisms of recognition of microbial products have been developed by host cells. Among these mechanisms, recognition of lipopolysaccharide of Gram-negative bacteria by CD14, a glycoprotein expressed at the surface of myelomonocytic cells, plays a major role. There is increasing evidence that CD14 also serves as a receptor for other microbial products including peptidoglycan of Gram-positive bacteria. A common theme is that CD14 represents a key molecule in innate immunity. Recognition of microbial products by host cells leads to cell activation and production of a large array of mediators that are necessary for the development of controlled inflammatory processes. When the activation process is out of control, such as in septic shock, these mediators can be detrimental to the host.

Effect of Pasteurella haemolytica outer membrane proteins on bovine neutrophils

The major outer membrane proteins (OMPs) isolated from Pasteurella haemolytica induce alterations of the biological activity of bovine polymorphonuclear leukocytes (PMNs). A dose-dependent reduction of the capacity of adherence to nylon wool in vitro was observed. OMPs also acted as chemotaxins at concentrations between 5 and 20 microg/ml. Concentrations lower than 5 microg/ml did not give considerable results. Preincubation with 5 microg/ml of OMPs led to modifications in the values of the phagocytic index and of intracellular killing, which were found to be diminished with respect to controls.

Proposed link between Helicobacter pylori and sudden infant death syndrome

Helicobacter pylori may be linked to sudden infant death syndrome (SIDS) through synthesis of inflammatory cytokines, particularly interleukin-1, which can produce fever, activation of the immune system, and increased deep sleep. A relatively minor respiratory or enteric infection, together with overwrapping and prone sleep position could then induce terminal hypoxemia. Alternatively, H. pylori produces large amounts of urease which, if aspirated in gastric juice, could reach the alveolae, react with plasma urea, and produce ammonia toxicity leading to respiratory arrest. Epidemiological similarities between H. pylori and SIDS are presented along with possible transmission mechanisms for H. pylori which support this hypothesis.

Role of adherence in interleukin-8 induction in Helicobacter pylori-associated gastritis

Active Helicobacter pylori-associated gastritis is characterized by a dense mucosal infiltration with granulocytes. Since H. pylori is noninvasive, secondary signals must induce the accumulation of granulocytes. Interleukin-8 (IL-8) has been shown to play a key role in this event. Using competitive reverse transcriptase-PCR on mRNA from gastric biopsies, we could show a clear correlation between the amount of IL-8 transcripts and the activity of H. pylori gastritis. Due to the inability of the bacterium to invade host cells, the epithelial layer is a potential candidate as an IL-8 source. To study the mechanism of IL-8 induction, established gastric carcinoma epithelial cell lines (AGS and Kato III) and well-defined H. pylori strains were used in a modified in vitro system. The experimental design enabled us to prevent direct contact of bacteria with epithelial cells by use of a filter membrane which did not block secreted bacterial products crossing the membrane. The data clearly showed that the direct contact of the bacterial cell with the epithelial cell is necessary for optimal IL-8 production because not only live bacteria, but also metabolically inactive bacteria, increased IL-8 secretion. Neither purified lipopolysaccharide nor water-soluble protein fractions of H. pylori NCTC 11637 and Tx30a nor the cytotoxin of H. pylori was able to increase IL-8 production significantly by the epithelial cells used. Furthermore, preparations of total membrane and outer membrane proteins of H. pylori were not able to stimulate IL-8 release in vitro. Accumulatively, these results imply that active metabolism is not necessary for stimulation as long as there is an intact membrane aiding the presentation of a stimulating membrane complex or aggregate on the surface of the bacteria. From these results, we conclude that whole bacteria and their direct contact with epithelial cells may be critical for IL-8 induction in vivo.

Mechanisms involved in Helicobacter pylori-induced interleukin-8 production by a gastric cancer cell line, MKN45

Accumulating evidence suggests an important role of interleukin-8 (IL-8) in Helicobacter pylori infection-associated chronic atrophic gastritis and peptic ulcer. We observed in this study that a gastric cancer-derived cell line, MKN45, produced a massive amount of IL-8 upon coculture with live H. pylori but not with killed H. pylori, H. pylori culture supernatants, or live H. pylori separated by a permeable membrane, indicating that IL-8 production requires a direct contact between the cells and live bacteria. Moreover, the tyrosine kinase inhibitor herbimycin but neither a protein kinase C inhibitor (staurosporine) nor a protein kinase A inhibitor (H89) inhibited IL-8 production by MKN45 cells cocultured with live bacteria, suggesting the involvement of a tyrosine kinase(s) in H. pylori-induced IL-8 production. In addition, coculture of H. pylori induced IL-8 mRNA expression in MKN45 cells and an increase in luciferase activity in cells which were transfected with a luciferase expression vector linked with a 5'-flanking region of the IL-8 gene (bp -133 to +44), indicating that the induction of IL-8 production occurred at the transcriptional level. This region contain three cis elements important for induction of IL-8 gene expression: AP-1 (-126 to -120 bp), NF-IL6 (-94 to -81 bp), and NF-kappaB (-80 to -70 bp) binding sites. Mutation of the NF-kappaB binding site abrogated completely the induction of luciferase activity, whereas that of the AP-1 site partially reduced the induction. However, mutation of the NF-IL6 binding site resulted in no decrease in the induction of luciferase activity. Moreover, specific NF-kappaB complexes were detected in the nuclear proteins extracted from MKN45 cells which were infected with H. pylori. Collectively, these results suggest that H. pylori induced the activation of NF-kappaB as well as AP-1, leading to IL-8 gene transcription.

Cure of Helicobacter pylori infection improves gastric acid secretion in patients with corpus gastritis

BACKGROUND

For more than 30 years it has been known that gastric acid secretion is inversely related to the extent and severity of corpal gastritis. We therefore evaluated the effect of cure of Helicobacter pylori infection on basal and pentagastrin-stimulated acid secretion.

METHODS

Basal acid output (BAO) and maximal acid output (MAO) were assessed in 11 H. pylori-infected dyspeptic patients (8 women and 3 men; mean age, 28 years) before and after successful anti-H. pylori therapy.

RESULTS

The gastritis index was significantly lower after therapy and was associated with an increase in both BAO and MAO after cure of the H. pylori infection (BAO from 0.3 mmol/h and MAO from 4.8 mmol/h to 19 mmol/ h). Basal and stimulated acid concentrations also increased (29.1 +/- 36.6 to 54 +/- 31 mmol/l and 72.5 +/- 46 to 120.1 +/- 30 mmol/l, respectively, for basal and stimulated acid concentrations; P < 0.05 for peak and MAO, P = 0.07 for BAO).

CONCLUSION

Gastric acid secretion increased into the normal range after successful treatment of H. pylori infection, suggesting that gastric function can recover to normal or almost normal after cure of H. pylori infection.

Porins of Pseudomonas aeruginosa induce release of tumor necrosis factor alpha and interleukin-6 by human leukocytes

The aim of this study was to examine the ability of Pseudomonas aeruginosa components to induce release of cytokines from human leukocytes. Human whole-blood cultures were incubated with several concentrations of purified P. aeruginosa products, including porins, exomucopolysaccharide, lipopolysaccharide, and toxin A. Supernatants were assayed for tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) activities. All of the P. aeruginosa components except toxin A were able to stimulate the release of both cytokines. On a weight basis, porins were as effective as lipopolysaccharide and significantly more effective than exomucopolysaccharide in inducing IL-6 release (P < 0.05). Moreover, porins were more potent than either exomucopolysaccharide or lipopolysaccharide in inducing TNF-alpha release (P < 0.05). Further experiments using isolated leukocytes suggested that monocytes were the cell population predominantly responsible for the production of both cytokines. These data indicate that P. aeruginosa porins are able to induce significant cytokine production. These components may be responsible for the chronically overactive inflammatory response associated with persistent lung infection in cystic fibrosis patients.

Bacterial porins stimulate bone resorption

Porins are abundant outer membrane proteins of gram-negative bacteria involved in transport of low-molecular-mass molecules. During the past decade, porins from a number of bacteria have also been shown to have proinflammatory activities including inducing the synthesis of proinflammatory mediators (cytokines, platelet-activating factor, and nitric oxide) in cultured cells and inducing inflammation in vivo. With this range of actions, it was possible that porins could also interact with bone cells to cause aberrant bone remodeling and that this could contribute to the bone destruction seen in gram-negative bone infections. By using purified preparations of Salmonella typhimurium and Pseudomonas aeruginosa porins, in the presence of polymyxin B, it was possible to induce concentration-dependent loss of calcium from cultured murine calvaria at porin concentrations in the range of 1 to 10 nM. The mechanism of action of the porins was determined by the inclusion of inhibitors of cyclooxygenase or inflammatory cytokines in the culture media. The bone-resorbing activity of both porins was not inhibited by the cyclooxygenase inhibitor indomethacin or by neutralizing the activity of tumor necrosis factor. Indeed, relatively high concentrations of these agents produced an unexpected increase in the bone resorption induced by the porins. In contrast, porin-induced bone resorption could be inhibited by relatively high concentrations of the natural inhibitor of interleukin-1 (IL-1 receptor antagonist). It appears that these porins stimulate bone resorption by a mechanism distinct from that of lipopolysaccharide, and the possibility therefore exists that porins play a role in bone destruction in gram-negative bacterial infections of bone.

Pathophysiology of Helicobacter pylori-induced gastritis and peptic ulcer disease

Helicobacter pylori causes persistent infection and inflammation in the human stomach, yet only a small fraction of persons harboring this organism develop peptic ulcer disease. An important question is why this variation in infection outcome exists. Recent studies have demonstrated that H pylori isolates possess substantial phenotypic and genotypic diversity that may engender differential host inflammatory responses that influence clinical outcome. Further investigation in this field may help to define which H pylori-infected persons bear the highest risk for subsequent development of peptic ulcer disease, and thus enable physicians to focus eradication therapy.

Cytokine-inducing components of periodontopathogenic bacteria

Pro-inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8 and tumour necrosis factor (TNF) are believed to be the major pathological mediators of inflammatory diseases ranging from arthritis to the periodontal diseases. The stimuli inducing proinflammatory cytokine induction in the former disease is unclear but in the periodontal diseases it is obvious that the stimulus is the accumulation of bacteria in the subgingival region. As these bacteria do not invade the lesional tissues in large numbers, it is believed that their soluble components or products interact with host tissues to induce cytokine gene transcription. The paradigm is that lipopolysaccharide is the key bacterial component inducing pro-inflammatory cytokine gene expression. However, over the past decade a growing number of reports on non-oral bacteria have established that many other bacterial components, as well as secretory products, have the capacity to induce cytokine synthesis. Some of these, such as the protein pneumolysin from Streptococcus pneumoniae, are incredibly potent (in this case inducing cytokine synthesis at femtomolar concentrations). This review surveys the range of bacterial components and products which have been shown to stimulate cytokine synthesis with particular emphasis on the hypothesis that these components play a role in the pathology of the periodontal diseases.

Changes in Helicobacter pylori ultrastructure and antigens during conversion from the bacillary to the coccoid form

In vitro, Helicobacter pylori converts from a bacillary to a full coccoid form via an intermediate U-shaped form. Organisms with a full coccoid form keep a double membrane system, a polar membrane, and invagination structures. Western blots (immunoblots) of sera from colonized patients show that some high-molecular-mass antigenic fractions are expressed only in coccoids. Conversely, fractions of 30 and 94 kDa were more intensively detected in the bacillary forms. These results suggest that (i) coccoid conversion is not a degenerative transformation and (ii) antigens specific to the coccoid forms are expressed in vivo.

Bacterial modulins: a novel class of virulence factors which cause host tissue pathology by inducing cytokine synthesis

Cytokines are a diverse group of proteins and glycoproteins which have potent and wide-ranging effects on eukaryotic cell function and are now recognized as important mediators of tissue pathology in infectious diseases. It is increasingly recognized that for many bacterial species, cytokine induction is a major virulence mechanism. Until recent years, the only bacterial component known to stimulate cytokine synthesis was lipopolysaccharide (LPS). It is only within the past decade that it has been clearly shown that many components associated with the bacterial cell wall, including proteins, glycoproteins, lipoproteins, carbohydrates, and lipids, have the capacity to stimulate mammalian cells to produce a diverse array of cytokines. It has been established that many of these cytokine-inducing molecules act by mechanisms distinct from that of LPS, and thus their activities are not due to LPS contamination. Bacteria produce a wide range of virulence factors which cause host tissue pathology, and these diverse factors have been grouped into four families: adhesins, aggressins, impedins, and invasins. We suggest that the array of bacterial cytokine-inducing molecules represents a new class of bacterial virulence factor, and, by analogy with the known virulence families, we suggest the term "modulin" to describe these molecules, because the action of cytokines is to modulate eukaryotic cell behavior. This review summarizes our current understanding of cytokine biology in relation to tissue homeostasis and disease and concisely reviews the current literature on the cytokine-inducing molecules produced by gram-negative and gram-positive bacteria, with an emphasis on the cellular mechanisms responsible for cytokine induction. We propose that modulins, by controlling the host immune and inflammatory responses, maintain the large commensal flora that all multicellular organisms support.

Immune and inflammatory responses to Helicobacter pylori infection

The gastroduodenal response to chronic Helicobacter pylori infection is characterized by the infiltration of plasma cells, lymphocytes, neutrophils and monocytes into the mucosa. Eradication studies have shown that this inflammatory response represents a specific reaction to the presence of H. pylori. As well as stimulating specific local T and B cell responses and a systemic antibody response, H. pylori infection also induces a local pro-inflammatory cytokine response. Interleukin-8 (IL-8), which is expressed and secreted by gastric epithelial cells, may be an important host mediator inducing neutrophil migration and activation. IL-8 mRNA and protein secretion in gastric epithelial cell lines can be up-regulated by the cytokines tumour necrosis factor-alpha and IL-1 and also by type I strains of H. pylori (expressing the vacuolating toxin and cytotoxin-associated protein, CagA). The gastric epithelium thus plays an active role in mucosal defence. Neutrophil activation and the production of reactive oxygen metabolites will be induced directly by bacterial factors and indirectly via host-derived cytokines, products of complement activation and bioactive lipids. Strain variation in the induction of both IL-8 from epithelial cells and the oxidative burst in neutrophils may be an important factor determining the extent of mucosal injury. There is now increasing evidence from both in vivo and in vitro studies that type I strains induce an enhanced inflammatory response and mucosal damage. An understanding of the bacterial mediators of mucosal inflammation is important in elucidating the role of chronic H. pylori infection in the pathogenesis of gastroduodenal disease.