Non-specific resistance mechanisms to listeriosis: implications for experimental and naturally occurring infection

Nucleotide oligomerization domain-2 (NOD2)-induced uveitis: dependence on IFN-gamma

PURPOSE

Nucleotide oligomerization domain-2 (NOD2) plays an important role in innate immunity to sense muramyl dipeptide (MDP), a component of bacterial cell walls. Notably, NOD2 is linked to eye inflammation because mutations in NOD2 cause a granulomatous type of uveitis called Blau syndrome. A mouse model of NOD2-dependent ocular inflammation was employed to test the role of a cytokine strongly implicated in granuloma formation, IFN-gamma, in order to gain insight into downstream functional consequences of NOD2 activation within the eye triggering uveitis.

METHODS

Mice deficient in IFN-gamma, NOD2, or CD11b and their wild-type controls were treated with intravitreal injection of MDP in the presence or absence of IFN-gamma. IFN-gamma production in the eye was measured by ELISA. The intravascular inflammatory response within the iris was quantified by intravital microscopy.

RESULTS

NOD2 activation resulted in the production of IFN-gamma within the eye. Deficiency in IFN-gamma diminished the development of MDP-induced uveitis, indicating its crucial role in downstream inflammatory events triggered by NOD2. Moreover, exogenous IFN-gamma markedly exacerbated MDP-induced ocular inflammation in a NOD2-dependent mechanism. The potential of IFN-gamma to enhance inflammation required the adhesion molecule CD11b because CD11b-deficient mice failed to show the synergistic effects of IFN-gamma and MDP cotreatment on adhering and infiltrating cells.

CONCLUSIONS

IFN-gamma was identified as a downstream mediator of NOD2-driven inflammation and the capacity of IFN-gamma in vivo to enhance the inflammatory potential of NOD2 was demonstrated. Extrapolation of these findings in mice suggests that the dysregulation of IFN-gamma may occur in patients with Blau syndrome, thereby contributing to the granulomatous nature of the disease.

Bacterial host resistance models in the evaluation of immunotoxicity

To assess potential immunomodulatory effects of a drug, pollutant, or natural product, an analysis of an exposed host's ability to resist challenge with a viable bacteria is one of the best gauges. Many factors govern whether a host exposed to a test agent and then infected becomes ill or dies at rates greater than infected control counterparts. Beyond the status of the host's immunocompetence, a bacterium's route of entry into the host and its inherent virulence are important variables determining how (and rate at which) an infection resolves. A pre-determination of endpoint(s) to be defined is critical during planning of resistance assays. If a study is to determine overall changes in immunocompetence due to exposure (regardless of regimen or dosage of test agent), then assessing shifts in morbidity/mortality at a defined lethal dose [LD(x)] value for the chosen route of infection would suffice. However, if a study is to define extent of immunomodulation in a particular body organ/cavity--or specific alterations in particular aspects of the humoral or cell-mediated immune responses--then careful selection of the pathogen, dose of the inoculum, means of infection of target site, and extent of the post-infection period to be examined, need to be made prior to host exposure to the test toxicant. This review will provide the Reader with background information about bacterial infections and how endpoint selection could be approached when designing resistance assays. An overview of protocols involved in the assays (e.g., bacterial preparation, host infection, post-infection endpoint analyses) and information about three bacteria that are among the most commonly employed in resistance assays is provided as well.

Six-color segmentation of multicolor images in the infection studies ofListeria monocytogenes

Multiple immunofluorescent staining is a powerful strategy for visualizing the spatial and temporal relationship between antigens, cell populations, and tissue components in histological sections. To segment different cell populations from the multicolor image generated by immunostaining based on color addition theory, a systems approach is proposed for automatic segmentation of six colors. After image acquisition and processing, images are automatically segmented with the proposed approach and six-pseudo channels for individual or colocalized fluorescent dye are generated to distinguish different cell types. The principle of this approach is the classification of each pixel into one of six colors (red, green, blue, yellow, magenta, and cyan) by choosing the minimal angular deviation between the RGB vector of the given pixel and six classically defined edge vectors. In the present infection studies of Listeria monocytogenes, the new multicolor staining methods based on the color addition were applied and the proposed color segmentation was performed for multicolor analysis. Multicolor analysis was accomplished to study the migration and interaction of Listeria and different cell subpopulations such as CD4CD25 double positive T regulatory cells; we also visualized simultaneously the B cells, T cells, dendritic cells, macrophages, and Listeria in another experiment. After Listeria infection, ERTR9 macrophages and dendritic cells formed cluster with Listeria in the infection loci. The principle of color addition and the systems approach for segmentation may be widely applicable in infection and immunity studies requiring multicolor imaging and analysis. This approach can also be applied for image analysis in the multicolor in vivo imaging, multicolor FISH or karyotyping or other studies requiring multicolor analysis.

The role of the activated macrophage in clearing Listeria monocytogenes infection

Macrophage activation often contributes to the strong immune response elicited upon infection. The ability of macrophages to become activated was discovered when sub-lethal primary infections of mice with the bacterium Listeria monocytogenes provided protection against secondary infections through non-humoral immunity. L. monocytogenes infect and propagate in macrophages by escaping the phagosome into the cytosol, where they avoid humoral immune mediators. Activated macrophages kill L. monocytogenes by blocking phagosomal escape. The timing of the antimicrobial activities within the phagosome is crucial to the outcome. In non-activated macrophages, bacterial factors generally prevail, and L. monocytogenes can escape from the vacuoles and grow within cytoplasm. Activated macrophages generate reactive oxygen or nitrogen intermediates early after bacterial uptake, which prevent the bacteria from escaping vacuoles into cytoplasm. The heterogeneity in the interactions between L. monocytogenes and the macrophage indicate a complex relationship between the host and the pathogen governed by chemistries that promote and inhibit escape from vacuoles. This review examines the mechanisms used by activated and non-activated macrophages to kill microbes, and how those mechanisms are employed against L. monocytogenes.

n-3 PUFA fail to affect in vivo, antigen-driven CD8+T-cell proliferation in the spleen of naïve mice

One of the most frequently reported immunomodulatory actions of n-3 PUFA is their ability to diminish in vitro lymphocyte proliferation. The purpose of this study was to determine if n-3 PUFA intake affects the kinetics or magnitude of the antigen-driven expansion of CD8(+)T-lymphocytes in vivo. In this study we utilized a well-characterized model of T-cell immunity (i.e. infection with the intracellular bacterium, Listeria monocytogenes). Weanling BALB/c mice were fed one of two experimental diets that differed solely in fat source. Our control diet contained lard (180 g/kg) and was devoid of long-chain n-3 PUFA. The experimental diet contained 150 g/kg menhaden fish oil and 30 g/kg corn oil, thus providing approximately 8 % of energy from long-chain n-3 PUFA. After 4 weeks, mice were infected intravenously with 10(6) colony-forming units of actA-deficient L. monocytogenes. Clonal expansion of antigen-specific CD8(+)T-cells in the spleen was measured at 5, 7, 9 and 14 d post-challenge using a class I MHC tetramer loaded with the immunodominant peptide from this pathogen (i.e. K(d):LLO91-99). We report that feeding mice a diet rich in n-3 fatty acids did not significantly impact either the kinetics or magnitude of in vivo, antigen-driven expansion of CD8(+)T-cells. Furthermore, contraction of this T-cell population was not affected by n-3 PUFA treatment. To our knowledge this is the first time MHC tetramers have been used to investigate the influence of n-3 PUFA on in vivo CD8(+)T-cell proliferation.

Innate immune responses in NF-kappaB-repressing factor-deficient mice

NF-kappaB-repressing factor (NRF) is a transcriptional silencer protein that specifically counteracts the basal activity of several NF-kappaB-dependent promoters by direct binding to specific neighboring DNA sequences. In cell culture experiments, the reduction of NRF mRNA leads to a derepression of beta interferon, interleukin-8, and inducible nitric oxide synthase transcription. The X chromosome-located single-copy NRF gene is ubiquitously expressed and encodes a protein of 690 amino acids. The N-terminal part contains a nuclear localization signal, the DNA-binding domain, and the NF-kappaB-repressing domain, while the C-terminal part is responsible for double-stranded RNA binding and nucleolar localization. To study the function of NRF in a systemic context, transgenic mice lacking the NRF gene were created. Against predictions from in vitro experiments, mice with a deletion of the NRF gene are viable and have a phenotype that is indistinguishable from wild-type mice, even after challenge with different pathogens. The data hint towards an unexpected functional redundancy of NRF.

Dietary (n-3) Polyunsaturated Fatty Acids Do Not Affect the In Vivo Development and Function of Listeria-Specific CD4+ and CD8+ Effector and Memory/Effector T Cells in Mice

We previously reported that in a mouse model, a diet high in (n-3) PUFA diminishes host survival following an infection from Listeria monocytogenes, a gram-positive bacterial pathogen. In this study we investigated the impact of (n-3) PUFA on the adaptive immune response to L. monocytogenes. BALB/c mice were fed experimental diets either devoid of or rich in (n-3) PUFA from fish oil for 4 wk and then infected with 10(6) actA-deficient L. monocytogenes. At 7 and 35 d postchallenge, effector and memory/effector T cells in the spleen were enumerated by flow cytometry. Surprisingly, the number of Listeria-specific CD4(+) and CD8(+) effector and memory/effector T cells in the spleen was not affected by (n-3) PUFA. Also, the effector cells derived from mice fed either diet were equally capable of conferring protective immunity upon adoptive transfer to naive recipients. Despite our previous data, which demonstrated that (n-3) PUFA profoundly impaired host resistance to L. monocytogenes, pathogen-specific T cell responses were not substantially affected by dietary (n-3) PUFA.

Omega-3 polyunsaturated fatty acid impairment of early host resistance against Listeria monocytogenes infection is independent of neutrophil infiltration and function

The primary objective of this study was to determine whether the n-3 PUFA-mediated changes in host response to a Listeria monocytogenes infection (e.g., cytokine production and bacterial clearance) were dependent upon neutrophils. Balb/c mice were fed one of two semi-purified diets that contained either 0 or 41 g of n-3 PUFA/kg. After 4 week, mice were injected with a neutrophil-depleting (RB6-8C5) or isotype-control antibody 24 h prior to infection. Bacterial clearance from the liver and spleen at 3 days post-challenge was measured and the concentration of five pro-inflammatory cytokines in sera 24 h post-infection were determined using a novel protein multiplexing kit. We found that neutrophil depletion impaired bacterial clearance independent of the effect of n-3 PUFA. Interestingly, we observed a rather complex interaction between neutrophil-depletion and n-3 PUFA intake on in vivo pro-inflammatory cytokine production. For example, neutrophil depletion elevated circulating IL-6 and MCP-1 (2- to 5-fold; p<0.05) in n-3 PUFA-fed mice, but less so or not at all in mice fed the control diet. In summary, our data suggest that n-3 PUFA-mediated reduction of host resistance to L. monocytogenes is independent of neutrophil activity.

Murine pulmonary infection with Listeria monocytogenes: differential susceptibility of BALB/c, C57BL/6 and DBA/2 mice

Murine listeriosis is a paradigm to understand host pathogen interactions. Airway infections with Listeria monocytogenes, although representing a serious problem in early onset neonatal listeriosis, has not been investigated in detail in animal models so far. Here, the susceptibility of BALB/c, DBA/2 and C57BL/6 mice towards an intratracheal (i.t.) infection with virulent L. monocytogenes EGDe and the attenuated variant L. monocytogenes EGD hlyW491A(pERL3-CMVGFP) is reported. The course of infection was characterized by determination of bacterial numbers in the organs and assessment of the health condition of the mice. The distribution and cellular localization of Listeria in the airways was assessed by immunocytochemistry and confocal and electron microscopy. The differential susceptibility of inbred mouse strains to airway infections with L. monocytogenes could be assigned to the major virulence factor listeriolysin O. Resistant C57BL/6 mice were not affected by the two listerial strains. In contrast, BALB/c and DBA/2 mice showed differential susceptibility towards L. monocytogenes EGDe and attenuated bacteria, with all the mice being killed by the wild-type bacteria but rarely by the variant that secretes a listeriolysin of only 10% activity of that of the wild-type toxin. Thus, listeriolysin is a decisive factor for differential susceptibility against Listeria. After i.t. application, bacteria were predominantly localized in the peribronchiolar space and invaded alveolar macrophages but rarely lung epithelial cells. Dissemination from the lung into the deep organs started almost immediately after application, although a pulmonary bacterial reservoir remained during the first 4 days.

The role of CD1d in the immune response against Listeria infection

To address the role of CD1d in mucosal immune regulation in bacterial infection, we infected CD1d KO mice with Listeria monocytogenes (Lm). A higher systemic bacterial burden associated with inflammatory lymphocytic infiltrations within the intestine was found in CD1d KO compared with wild type (WT) mice. Lm induced strong IFN-gamma mRNA expression in the liver of WT and the intestine of CD1d KO mice, thus demonstrating the dual, opposing immune activities of IFN-gamma in Lm infection that is dependent on CD1d and/or NKT cells. Analysis of hepatic T cell population demonstrated a reduction of NK1.1(+)TCRbeta+ cells in both mice, followed by recovery only in WT mice. Last, the proportion of alpha4beta1 integrin on lung lymphocytes from CD1d KO was dramatically increased compared with WT mice. Thus, the absence of CD1d resulted in increased susceptibility towards Listeria infection, induced changes in NKT cells, and increased trafficking of alpha4beta1 molecule to inflamed lung.

The Listeria monocytogenes lemA gene product is not required for intracellular infection or to activate fMIGWII-specific T cells

Clearance of the intracellular bacterial pathogen Listeria monocytogenes requires antigen-specific CD8(+) T cells. Recently it was shown that activation of class Ib major histocompatibility complex (MHC)-restricted CD8(+) T cells alone is sufficient for immune protection against listeriae. A major component of the class Ib MHC-restricted T-cell response is T cells that recognize formylated peptide antigens presented by M3 molecules. Although three N-formylated peptides derived from L. monocytogenes are known to bind to M3 molecules, fMIGWII is the immunodominant epitope presented by M3 during infection of mice. The source of fMIGWII peptide is the L. monocytogenes lemA gene, which encodes a 30-kDa protein of unknown function. In this report, we describe the generation of two L. monocytogenes lemA deletion mutants. We show that lemA is not required for growth of listeriae in tissue culture cells or for virulence during infection of mice. Surprisingly, we found that fMIGWII-specific T cells were still primed following infection with lemA mutant listeriae, suggesting that L. monocytogenes contains at least one additional antigen that is cross-reactive with the fMIGWII epitope. This cross-reactive antigen appears to be a small protease-resistant molecule that is secreted by L. monocytogenes.

A/J mice are susceptible and C57BL/6 mice are resistant to Listeria monocytogenes infection by intragastric inoculation

Previous studies demonstrated that the innate resistance of mice to Listeria monocytogenes infection by intravenous or intraperitoneal inoculation is regulated principally by the Hc locus on mouse chromosome 2. The A/J and C57BL/6 mouse strains were identified as prototype L. monocytogenes-susceptible and -resistant strains, respectively. In the present study, we compared the relative susceptibilities of A/J and C57BL/6 mice to intragastric (i.g.) inoculation with L. monocytogenes. The results of our study indicate that A/J mice are significantly more susceptible than C57BL/6 mice to an i.g. challenge with L. monocytogenes. This was reflected in the estimated 50% lethal doses for the two strains (10(6) and 10(8) CFU for A/J and C57BL/6 mice, respectively) and a more rapid and severe dissemination of the infection to the spleen and liver in A/J mice than in C57BL/6 mice. Histopathological examination of tissues from the infected mice confirmed the greater severity of disease in A/J mice. Clearance of a primary infection enhanced the resistance of both A/J and C57BL/6 mice to reinfection with L. monocytogenes via the gastrointestinal tract. However, the relative difference in susceptibility between the two strains was evident even after immunization. The A/J mouse holds promise as a model for investigating the pathogenesis of gastrointestinal listeriosis because of its ability to develop systemic infection following challenge with numbers of organisms similar to those recovered from some L. monocytogenes-contaminated food products.

Ability of the Listeria monocytogenes strain Scott A to cause systemic infection in mice infected by the intragastric route

Listeriosis is an important food-borne disease that causes high rates of morbidity and mortality. For reasons that are not clear, most large outbreaks of human listeriosis involve Listeria monocytogenes serotype 4b. Relatively little is known about the pathogenesis of listeriosis following gastrointestinal exposure to food-borne disease isolates of L. monocytogenes. In the present study, we investigated the pathogenesis of systemic infection by the food-borne isolate Scott A in an intragastric (i.g.) mouse challenge model. We found that the severity of infection with L. monocytogenes Scott A was increased in mice made neutropenic by administration of monoclonal antibody RB6-8C5. This observation was similar to a previous report on a study with the laboratory strain L. monocytogenes EGD. Prior administration of sodium bicarbonate did not enhance the virulence of L. monocytogenes strain Scott A for i.g. inoculated mice. Following i.g. inoculation of mice, two serotype 4b strains of L. monocytogenes (Scott A and 101M) achieved a greater bacterial burden in the spleen and liver and elicited more severe histopathological damage to those organs than did a serotype 1/2a strain (EGD) and a serotype 1/2b stain (CM). Of the four strains tested, only strain CM exhibited poor survival in synthetic gastric fluid in vitro. The other three strains exhibited similar patterns of survival at pHs of greater than 5 and relatively rapid (<30 min) loss of viability at pHs of less than 5.0. Growth of L. monocytogenes Scott A at temperatures of 12.5 to 37 degrees C did not affect its ability to cause systemic infection in i.g. inoculated mice. These observations suggest that the serotype 4b L. monocytogenes strains Scott A and 101M possess one or more virulence determinants that make them better able to cause systemic infection following inoculation via the g.i. tract than do the serotype 1/2 strains EGD and CM.

Relevance of dietary lipids as modulators of immune functions in cells infected with Listeria monocytogenes

Nutritional status may have significant importance for the immune system, and particularly, unsaturated fatty acids may serve as modulators of immune functions. Clinical and epidemiological studies have demonstrated that fatty acids are involved in the reduction of the inflammatory processes that occur in diseases characterized by an overactivation of the immune system. At the same time, an increase in susceptibility to infection has also been reported. The importance of immune system modulation by dietary lipids in the presence of an intracellular bacterial pathogen, such as Listeria monocytogenes, was evaluated in the present study. BALB/c mice were divided into four groups which were each fed a low-fat (2.5% by weight) diet, an olive oil (OO; 20% by weight) diet, a fish oil (FO; 20% by weight) diet, or a hydrogenated coconut oil (HCO; 20% by weight) diet for 4 weeks. In each group, lymphocye proliferation was measured, and a reduction in the stimulation index was observed in the FO and HCO groups. Cytotoxicity exerted by L. monocytogenes was increased in the groups fed diets containing OO and FO after 6 h of incubation with the bacterium. An important increase in the production of reactive oxygen species was found in the groups fed the HCO diet after 12 h of incubation with L. monocytogenes. Finally, invasion and adhesion factors were not modified substantially by the action of dietary lipids, although these factors were reduced in cells from mice fed an FO diet. These results underline the importance of several dietary lipids as biological modulators of immune functions and their crucial role in the alteration of host natural resistance.

Passive immunization with convalescent serum, or oral immunization with formalin-killed organisms, does not protect mice against gastrointestinal challenge with Listeria monocytogenes

Listeria monocytogenes is an important foodborne pathogen in both humans and animals. In addition, murine listeriosis is a widely used model for studying the molecular pathogenesis of an intracellular pathogen, and the regulation of protective cellular immunity. Little attention has been paid to protective immunity against L. monocytogenes in the gastrointestinal tract, where a secretory immune response might prevent attachment of the bacteria to the intestinal epithelium. In this study we found that neither opsonization of L. monocytogenes with immune serum, nor repeated oral administration of killed L. monocytogenes, protected mice against gastrointestinal challenge with L. monocytogenes.

Antagonistic activity of Lactobacillus casei strain shirota against gastrointestinal Listeria monocytogenes infection in rats

In the present study, the effect of ingested viable Lactobacillus casei Shirota strain YIT9029 on oral infection with the enteric pathogen Listeria monocytogenes in Wistar rats was investigated. Rats were orally infected with 10(9) viable L. monocytogenes. Starting 3 days before the infection, rats received a daily dosage of 10(9) viable L. casei. It was shown that supplementation of L. casei significantly reduced the numbers of L. monocytogenes in stomach, caecum, faeces, spleen and liver, 2 days after L. monocytogenes infection. The number of L. monocytogenes in the mesenteric lymph nodes was not affected by the ingestion of L. casei. In comparison with control animals, the levels of the liver-specific alanine aminotransferase were lower in L. casei-fed rats. Histological analysis of spleen and liver revealed no differences between the experimental and control animals. In a parallel study with orally L. monocytogenes infected rats, it was shown that L. casei was able to increase cellular immunity significantly as determined with the delayed-type hypersensitivity response against heat-killed L. monocytogenes. In conclusion, in the present study it was shown that orally administered L. casei is able to enhance host resistance against oral L. monocytogenes infection. In the gastrointestinal tract, as well as in the spleen and liver, L. monocytogenes numbers were reduced. Furthermore, it is concluded that the enhancement of this anti-Listeria activity might be, at least partly, due to increased cell-mediated immunity.

Evaluation of Caesalpinia ferrea extract on bone marrow hematopoiesis in the murine models of listeriosis and Ehrlich ascites tumor

The capacity of hematopoietic tissues to produce and mobilize phagocytes to the site of infection and tumor growth is of central importance to mediate the early immunological response. In this perspective, studies from our laboratory have defined Listeria monocytogenes infection and the Ehrlich ascites tumor (EAT) as useful models to investigate the effects of natural compounds on the growth and differentiation of granulocyte-macrophage progenitor cells (CFU-GM). As expected, a significant reduction in the number of bone marrow CFU-GM was observed in the initial stages of infection with a sublethal dose of Listeria. Similarly, the bone marrow CFU-GM decreased sharply 4 days after the EAT transplantation. Treatment of infected and tumor-bearing mice with 500 and 1,000 mg/kg of Caesalpinia ferrea aqueous extract, given 3 times orally, significantly stimulated myelopoiesis, whereas no effects were observed with the 250 mg/kg dose. Similar results were obtained in normal mice. The administration of the two higher doses of the extract also protected 15-20% of mice from a lethal dose of Listeria and significantly prolonged survival of EAT-bearing mice. In summary, these results demonstrate that C. ferrea extract acts as a positive regulator of myelopoiesis, and suggest that the therapeutic effect of C. ferrea may be partially mediated by this action.

Detection, characterisation and purification of a murine liver factor capable of desensitising towards the lethal activity of tumour necrosis factor

Tumour necrosis factor (TNF) is a major mediator in septic shock and several inflammatory diseases such as hepatitis. Galactosamine (GalN) sensitises experimental animals for TNF and the combination TNF/GalN leads to a lethal inflammatory hepatitis. We describe that a single injection of lipopolysaccharide (LPS), interleukin-1 (IL-1) or TNF can desensitise against the lethality induced by TNF/GalN, but also against changes in metabolic parameters such as hypothermia and transaminase release, in a dose responsive way. We also describe the desensitising capacity of a component present in Mouse Liver Extract (MLE). The MLE desensitises mice against the effects of TNF/GalN in a dose responsive way. The activity of the MLE is heat labile and does not involve LPS, TNF, IL-1 or TNF soluble receptors. We describe partial and complete purification of the factor. Partially pure material protects mice against all changes induced by TNF/GalN. The protection is dose dependent and heat labile and also possible in endotoxin-hyporesponsive C3H/HeJ mice. The pure material protects against lethality, hypothermia and AST release and it appears as a heat labile protein of relative molecular weight of 70 kDa probably with a break down product of 35 kDa.

Adjuvant effect of Pluchea quitoc extract on the resistance of tumor-bearing mice by modulation of the host hematopoietic response

Progressive tumor growth is regularly accompanied by changes in the cellular constituents of the immune system. Evidence suggests that soluble factors generated during tumor growth can affect the amount of granulocyte-macrophage progenitors. In vitro colony growth of progenitor cells may be an early indicator of the cellular changes associated with tumor growth. Pluchea quitoc has been previously found to modulate the hematopoietic response during bacterial infection. This study was designed to investigate the effects of P. quitoc on the growth and differentiation of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) in Ehrlich ascites tumor-bearing mice. In contrast to the myelosuppression developed in the tumor-bearing animals, treatment with P. quitoc ethanolic extract (250, 500 or 1000 mg/kg) for 3 consecutive days after tumor challenge reversibly stimulated myelopoiesis, restoring the number of CFU-GM to normal. This same dose-schedule also increased colony formation in normal mice as compared to controls. In addi tion, P. quitoc significantly enhanced survival of tumor-bearing mice. These results suggest an immunoregulatory role for P. quitoc in counteracting the tumor-induced myelopoietic suppression as well as usefulness as adjuvant treatment of cancer.

Ozone-induced modulation of cell-mediated immune responses in the lungs

Most pulmonary immunotoxicology studies of ambient pollutants have been broadly designed to discern if overall humoral or cell-mediated immunity (CMI) was altered; few have assessed effects on particular aspects of immune function. We hypothesized that effects from ozone (O3) exposure on pulmonary CMI are linked in part to changes in local immune cell capacities to form and/or to interact with immunoregulatory cytokines. Rats exposed to 0.1 or 0.3 ppm O3 4 h/day 5 days/week, for 1 or 3 weeks were assessed for resistance to, and pulmonary clearance of, a subsequent Listeria monocytogenes challenge. In situ cytokine release and immune cell profiles were also analyzed at different stages of the antilisterial response. Although O3 exposure modulated CMI, effects were not consistently concentration- or duration-dependent. Exposure did not effect cumulative mortality from infection, but induced concentration-related effects upon morbidity onset and persistence. All 1-week exposed rats had listeric burdens trending higher than controls; 0.3 ppm rats displayed continual burden increases rather than any onset of resolution. Rats exposed for 3 weeks had no O3-related changes in clearance. No exposure-related effect on neutrophil or pulmonary macrophage (PAM) numbers or percentages was noted. Bacterial burden analyses with respect to cell type showed that Listeria:PAM ratios in 0.3 ppm rats ultimately became greatest compared to all other rats. In situ IL-1alpha and TNFalpha levels were consistently higher in O3-exposed rats. All rats displayed increasing in situ IFNgamma levels as infection progressed, but no constant relationship was evident between IFNgamma and initial IL-1alpha/TNFalpha levels in O3-exposed hosts. It seems that short-term (i.e., 1 week) repeated O3 exposures imparted more effects upon CMI than a more prolonged (i.e., 3 week) regimen, with effects manifesting at the level of the PAM and in the cytokine network responsible for immunoactivation.

Dietary supplementation with conjugated linoleic acid does not alter the resistance of mice to Listeria monocytogenes infection

Conjugated linoleic acid (CLA) has been used experimentally as a dietary supplement to increase lean body weight and to modulate inflammation in a variety of animal species. In addition, human use of dietary CLA as a supplement to regulate body fat has received both scientific and public attention. No reports have been published regarding the effects of dietary CLA on antimicrobial resistance. In this study, we provide evidence that feeding CLA for up to 4 wk does not alter host defense against Listeria monocytogenes in mice. These findings suggest that the anti-inflammatory effects of CLA do not impair cellular immunity to this intracellular pathogen.

Stimulation of myelopoiesis in Listeria monocytogenes-infected mice by an aggregated polymer isolated from Aspergillus oryzae

In this work, we investigated the effects of the proteic aggregated polymer of magnesium ammonium phospholinoleate-palmitoleate anhydride (MAPA) isolated from Aspergillus oryzae on the growth and differentiation of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) in Listeriamonocytogenes-infected mice. A significant reduction in the CFU-GM number was observed in the initial phase of infection with a sublethal dose of Listeria. Treatment of mice with 0.5, 2.0 and 5.0 mg/kg MAPA for 7 days prior to infection significantly stimulated myelopoiesis in a dose-dependent manner. Moreover, treatment with 0.5 and 5.0 mg/kg MAPA resulted in 30% and 40% cures of mice lethally infected with Listeria, respectively. MAPA added directly to the culture dishes hardly affected colony formation by bone marrow cells, suggesting an indirect effect ofthis compound on myelopoiesis in vivo. In summary, the data show that MAPA can modulate the CFU-GM generation and antibacterial resistance in listeriosis. As the ability of hematopoietic tissues to produce phagocytes is of particular significance to mediate resistance to Listeria, the promotion of bone marrow CFU-GM by MAPA may contribute to a rapid restoration of phagocyte numbers in infected sites, thus mitigating the course of infection.

Stimulatory action of Pluchea quitoc extract on the hematopoietic response during murine listeriosis

The importance of both granulocytes and macrophages in the response to Listeria monocytogenes infection make this infection a suitable choice to investigate the effects of Pluchea quitoc on hematopoiesis. A significant depletion of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) was observed at 48 and 72 h after intraperitoneal infection of mice with 1 x 10(4) L. monocytogenes. However, the treatment of infected animals with P. quitoc ethanolic extract (250, 500 or 1000 mg/kg) given orally for 3 consecutive days prior to infection produced a stimulatory effect on myelopoiesis, restoring the number of CFU-GM to normal. This same dose-schedule also increased colony formation in normal mice as compared to controls. In addition, P. quitoc significantly enhanced survival of infected mice. Thus, it is probable that the ability of P. quitoc to induce a higher reserve of granulocyte-macrophage precursors in the bone marrow is of major significance in determining early resistance to infection.

Interleukin-1 receptor signaling rather than that of tumor necrosis factor is critical in protecting the host from the severe consequences of a polymicrobe anaerobic infection

Infection of the dental pulp leads to an osteolytic lesion that results from a polymicrobial infection consisting largely of pathogenic anaerobes. Infection causes significant morbidity and mortality mediated by bacterial factors and in some cases by the up-regulation of inflammatory cytokines. The inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor (TNF), in particular, play a complex and central role in the responses to microbial pathogens. However, relatively little is known about the significance of these cytokines in protecting the host from focal polymicrobial anaerobic infections. To establish the relative importance of IL-1 and TNF in mediating the response to a mixed anaerobic infection, we inoculated the dental pulp of mice with six anaerobic pathogens containing functional deletions of receptors to IL-1 (IL-1R1(-/-)), TNF (TNFRp55(-/-)-p75(-/-)), or both (TNFRp55(-/-)-IL-1RI(-/-)). The results indicate that IL-1 receptor signaling and TNF receptor signaling both play similarly important roles in protecting the host from local tissue damage. However, IL-1 receptor signaling is considerably more important than TNF receptor signaling in preventing the spread of infection into surrounding fascial planes, since IL-1R1(-/-) but not TNFRp55(-/-)-p75(-/-) mice exhibited significantly higher morbidity and mortality. Moreover, all of the fatal infections occurred in male mice, suggesting the importance of gender differences in limiting the impact of these infections.

Effects of Chlorella vulgaris on bone marrow progenitor cells of mice infected with Listeria monocytogenes

In this study we investigated the effects of the treatment with Chlorella vulgaris extract (CVE) on the hematopoietic response of granulocyte-macrophage colony-forming unit (CFU-GM) of mice infected with a sublethal dose of Listeria monocytogenes (1 x 10(4) organisms/animal). CVE was given orally as 50 mg/kg/day for 5 days. In the CVE treated/infected groups L. monocytogenes was administered at the end of CVE treatment. The colony stimulating activity of the serum (CSA) was also studied in all groups. Although no effects on CFU-GM, as compared to controls, were observed in the groups receiving CVE alone, the extract produced an increase in CSA levels as compared to controls. On the other hand, the presence of the infection led to a significant reduction in the numbers of CFU-GM as observed at 48 and 72 h after the infection, in spite of the significant increase in serum CSA activity. CVE treatment of infected animals restored the numbers of CFU-GM to control levels. In the treated/ infected group the increased serum CSA was significantly higher than that observed in the only infected group. The CVE treatment (50 and 500 mg/kg) of mice infected with a dose of 3 x 10(5) bacteria/animal, which was lethal for all the non-treated controls, produced a dose-response protection which led to a 20 and 52% survival, respectively. These results demonstrated that CVE produces a significant increase in the resistance of the animals infected with L. monocytogenes, and that this protection is due, at least in part, to increased CFU-GM in the bone marrow of infected animals.