Delineation of the function of a major gamma delta T cell subset during infection

Gammadelta T cells play important but poorly defined roles in pathogen-induced immune responses and in preventing chronic inflammation and pathology. A major obstacle to defining their function is establishing the degree of functional redundancy and heterogeneity among gammadelta T cells. Using mice deficient in Vgamma1+ T cells which are a major component of the gammadelta T cell response to microbial infection, a specific immunoregulatory role for Vgamma1+ T cells in macrophage and gammadelta T cell homeostasis during infection has been established. By contrast, Vgamma1+ T cells play no significant role in pathogen containment or eradication and cannot protect mice from immune-mediated pathology. Pathogen-elicited Vgamma1+ T cells also display different functional characteristics at different stages of the host response to infection that involves unique and different populations of Vgamma1+ T cells. These findings, therefore, identify distinct and nonoverlapping roles for gammadelta T cell subsets in infection and establish the complexity and adaptability of a single population of gammadelta T cells in the host response to infection that is not predetermined, but is, instead, shaped by environmental factors.

Systemic NKG2D down-regulation impairs NK and CD8 T cell responses in vivo

The immunoreceptor NKG2D stimulates activation of cytotoxic lymphocytes upon engagement with MHC class I-related NKG2D ligands of which at least some are expressed inducibly upon exposure to carcinogens, cell stress, or viruses. In this study, we investigated consequences of a persistent NKG2D ligand expression in vivo by using transgenic mice expressing MHC class I chain-related protein A (MICA) under control of the H2-K(b) promoter. Although MICA functions as a potent activating ligand of mouse NKG2D, H2-K(b)-MICA mice appear healthy without aberrations in lymphocyte subsets. However, NKG2D-mediated cytotoxicity of H2-K(b)-MICA NK cells is severely impaired in vitro and in vivo. This deficiency concurs with a pronounced down-regulation of surface NKG2D that is also seen on activated CD8 T cells. As a consequence, H2-K(b)-MICA mice fail to reject MICA-expressing tumors and to mount normal CD8 T cell responses upon Listeria infection emphasizing the importance of NKG2D in immunity against tumors and intracellular infectious agents.

Hepatocytes express abundant surface class I MHC and efficiently use transporter associated with antigen processing, tapasin, and low molecular weight polypeptide proteasome subunit components of antigen processing and presentation pathway

Hepatic expression levels of class I MHC Ags are generally regarded as very low. Because the status of these Ags and their ability to present peptides are important for the understanding of pathogen clearance and tolerogenic properties of the liver, we set out to identify the factors contributing to the reported phenotype. Unexpectedly, we found that the surface densities of K(b) and D(b) on C57BL/6 mouse hepatocytes are nearly as high as on splenocytes, as are the lysate concentrations of mRNA encoding H chain and beta(2)-microglobulin (beta(2)m). In contrast, the components of the peptide-loading pathway are reduced in hepatocytes. Despite the difference in the stoichiometric ratios of H chain/beta(2)m/peptide-loading machineries, both cell types express predominantly thermostable class I and are critically dependent on TAP and tapasin for display of surface Ags. Minor differences in the expression patterns in tapasin(-/-) background suggest cell specificity in class I assembly. Under immunostimulatory conditions, such as exposure to IFN-gamma or Listeria monocytogenes, hepatocytes respond with a vigorous mRNA synthesis of the components of the Ag presentation pathway (up to 10-fold enhancement) but up-regulate H chain and beta(2)m to a lesser degree (<2-fold). This type of response should promote rapid influx of newly generated peptides into the endoplasmic reticulum and preferential presentation of foreign/induced Ag by hepatic class I.

IL-12-assisted immunization against Listeria monocytogenes using replication-restricted VSV-based vectors

Co-administration of IL-12 with vaccine immunogens has proven to be an effective strategy for eliciting potent Th1-biased immunity. Unfortunately, the use of IL-12 as a vaccine component has been limited because it is unstable at ambient temperatures, expensive to produce, and toxic when administered at excessive dosages. Using reverse genetics, we created a recombinant replication-restricted vesicular stomatitis virus that expresses large quantities of an IL-12 fusion protein (VSVDeltaG-IL12F), but can only establish a single round of infection because the genome does not encode the viral glycoprotein (G protein) that is required for viral entry into host cells. Here, we report that immunization of mice with a poorly immunogenic listerial antigen preparation (LMAg) in combination with VSVDeltaG-IL12F elicits potent T cell- and B cell-mediated responses that confer protective listerial immunity.

Listeria monocytogenes-infected bone marrow myeloid cells promote bacterial invasion of the central nervous system

Listeria monocytogenes is a facultative intracellular pathogen that is able to invade the central nervous system causing meningoencephalitis and brain abscesses. The mechanisms allowing bacteria to cross the blood-brain barrier are poorly understood. In this work, we used an experimental model of acute listeriosis in the mouse inducing a reproducible invasion of the central nervous system. At the early phase of infection, we find that bacteria invade and rapidly grow in bone marrow cells identified as bone marrow myelomonocytic cells expressing the phenotype CD31pos:Ly-6Cpos:CD11b(pos):LY-6Glow. We demonstrate that central nervous system invasion is facilitated by injecting L. monocytogenes-infected bone marrow cells in comparison with free bacteria or infected spleen cells. In mice transplanted with bone marrow cells from transgenic donor mice expressing the green fluorescent protein (GFP), we show that infected myeloid GFP+ cells adhere to activated brain endothelial cells, accumulate in brain vessels and participate to the pathogenesis of meningoencephalitis and brain abscesses. Our results demonstrate that bone marrow, the main haematopoietic tissue, is a previously unrecognized reservoir of L. monocytogenes-infected myeloid cells, which can play a crucial role in the pathophysiology of meningoencephalitis by releasing infected cells into the circulation that ultimately invade the central nervous system.

Gene expression profiling of mouse host response to Listeria monocytogenes infection

The purpose of this study was to evaluate gene expression profiles in the liver and blood for prediction of infection severity from Listeria monocytogenes (LM). Mice were injected with medium broth (control) or a nonlethal or lethal dose of LM and sacrificed 6 h later. Gene expression changes were determined using Affymetrix MGU74Av2 GeneChips and confirmed by real-time polymerase chain reaction analysis. We identified discernable genes whose gene expression profiles can be used in pattern recognition to predict and classify samples in differently treated groups, with >or=90% accuracy in liver samples and 80% accuracy in blood at prediction; however, different genes were predictive in each tissue. Our results suggest that gene expression profiling in response to LM in mice may be able to distinguish samples in groups with varying severity of infection and provide information in finding molecular mechanisms and early biomarkers for subsequent conventional clinical endpoints.

The antiapoptotic protein Bcl-xL is dispensable for the development of effector and memory T lymphocytes

The antiapoptotic protein Bcl-x(L) is induced in activated T lymphocytes upon costimulation through CD28, 4-1BB, and OX40. Bcl-x(L) is also highly enriched in memory T lymphocytes. Based on this body of evidence, it was thought that Bcl-x(L) plays an essential role in the generation of effector and memory T lymphocytes. We report that mice with a conditional deletion of Bcl-x in T lymphocytes develop a normal CD8(+) T cell response to Listeria monocytogenes infection. Furthermore, Bcl-x conditional knockout mice exhibit normal T-dependent humoral immune responses. These results indicate that Bcl-x is dispensable for the generation of effector and memory T lymphocytes and suggest that costimulation of T lymphocytes promotes their survival through a Bcl-x(L) independent mechanism.

CD70+ antigen-presenting cells control the proliferation and differentiation of T cells in the intestinal mucosa

One unresolved issue in gut immunity is how mucosal T lymphocytes are activated and which antigen-presenting cell (APC) is critical for the regulation of this process. We have identified a unique population of APCs that is exclusively localized in the lamina propria. These APCs constitutively expressed the costimulatory molecule CD70 and had antigen-presenting functions. After oral infection of mice with Listeria monocytogenes, proliferation and differentiation of antigen-specific T cells occurred in the gut mucosa in situ and blockade of CD70 costimulation abrogated the mucosal T cell proliferation and effector functions. Thus, a potent CD70-dependent stimulation via specialized tissue-specific APCs is required for the proliferation and differentiation of gut mucosal T cells after oral infection.

[Brain abscesses due to Listeria monocytogenes]

INTRODUCTION

Listeria monocytogenes is a gram-positive bacillus which causes sporadic infections in immunocompromised humans, with a special propensity for the central nervous system, in the form of acute, subacute or chronic meningitis, rhombencephalitis or abscesses in the brain or spinal cord. The final diagnosis is established by germ culture in blood or in cerebrospinal fluid (CSF). Preferred treatment is ampicillin in association with aminoglycosides.

CASE REPORT

We report the case of a 70-year-old male patient with a history of arterial hypertension and chronic lymphatic leukaemia with no specific treatment, who suffered meningoencephalitis and brain abscesses caused by L. monocytogenes. Symptoms were a 48-hour history of headache and a febrile condition. The CSF showed lymphocytic pleocytosis with hypoglycorrhachia. Magnetic resonance scans of the brain revealed areas of cerebritis and multiple brain abscesses in the right frontal lobe. Specific treatment was established with ampicillin for 13 weeks, associated with gentamicin and vancomycin during the first few weeks, until x-rays showed the lesions to be resolved.

CONCLUSIONS

L. monocytogenes infections must be investigated in all patients with cellular immunosuppression who present febrile symptoms. The central nervous system may be the only area of the body infected. Moreover, this site will need studying in patients who present neurological focus data or an alteration in the state of consciousness and bacteraemia due to L. monocytogenes. Establishing suitable treatment as early as possible can improve the prognosis.

Shortening the infectious period does not alter expansion of CD8 T cells but diminishes their capacity to differentiate into memory cells

Following a primary immune response, a portion of effector T cells gives rise to long-lived memory cells. Although primary expansion and differentiation of effector CD8 T cells is dictated by a brief exposure to Ag, it is unclear whether full memory differentiation is also programmed within the same short window. By carefully modulating the kinetics of Listeria monocytogenes infection, we analyzed the requirements for the programming of effector and memory T cell development in vivo. We find that although limiting the infectious period to the first 24-48 h does not impact the size of the primary CD8 response, the ensuing memory population is significantly diminished. This effect is particularly pronounced in the development of tissue-homing memory cells and is inversely proportional to the initial infectious dose. In contrast to CD8 responses, the differentiation of primary CD4 responses was highly dependent on the continued presence of the infection. Shortening the duration of the infection greatly reduced the development of CD4 effector responses in the spleen and prevented their trafficking to peripheral sites of infection. We propose that the stimulus received by CD8 T cells during the early stages of infection largely contribute to the differentiation of CD8 effector cells, whereas continued or distinct signals received at later stages influence their ability to differentiate into memory cells.

[The incidence of bacterial CNS infections in roe deer (Capreolus capreolus), red deer (Cervus elaphus) and chamois (Rupicapra rupicapra) in Bavaria]

Brain samples of 849 wild ruminants (654 roe deer, 189 red deer and 6 chamois) from Bavaria were examined for the occurrence of encephalopathies caused by bacteria, using cultural, serological and genetic methods. In addition, 87 brain samples were investigated histologically for clarification of the pathogenetic relevance of specific microorganisms. Using conventional bacteriological methods, 464 different bacteria were isolated. 229 of them could be differentiated to the genus level and 235 to the species level. Totally, 35 different bacteria species were isolated, most frequently Micrococcus spp., Bacillus spp. and E. coli. Listeria spp. were detected in 43 brain samples (37 from roe deer, 5 from red deer and 1 from chamois). Sixteen strains were identified as L. innocua, 14 as L. monocytogenes, 9 as L. seeligeri and 4 as L. grayi. Serological investigations of L. monocytogenes showed that 9 strains belong to serotype 1/2a and five to 4b. Analysis of the geographical distribution of the Listeria findings indicate a statistically significant (p<0.011) regional aggregation in Unterfranken (prevalence for roe deer: 12.2%, versus 4.5% in Oberbayern-Schwaben, 6.1% in Niederbayern-Oberpfalz and 0% in Oberfranken-Mittelfranken). The histological investigation (HE staining) of 87 tissue samples contaminated with encephalitis relevant bacteria showed inflammation of different severity (mild meningitis and choroiditis (n = 26) to moderate (meningo)encephalitis (n = 13)) in 41 cases.

Antigen Presentation: Lysoyme, Autoimmune Diabetes, and Listeria What Do They Have in Common?

We discuss three areas of antigen presentation and macrophage biology being investigated in the laboratory. Using hen egg-white lysozyme as a protein antigen, all the segments of the molecules selected by the class II histocompatibility molecule I-A(k) were identified and characterized. The display of each family of peptides was explained biochemically and quantitated. Conformational isomers of a peptide-major histocompatibility complex (MHC) complex were identified. The relationship between the amounts of peptide-MHC displayed by the antigen-presenting cells and two biologic responses, central thymic selection and T-cell responses after immunization in adjuvant, were examined. The class II MHC molecule of the nonobese diabetic I-Ag7 is being examined for its properties of peptide selection. The objective is to identify the diabetogenic peptides, as well as the repertoire of protein antigens from beta-cells that trigger autoantibodies. The I-Ag7 molecule selects peptides that show very distinctive sequence motifs: one or more acidic residues at the carboxy terminus that interact at the P9 pocket of the binding groove. Finally, the investigations in listeriosis examined the early events in immune induction. More important, we found that Listeria causes marked apoptosis of lymphocytes around infective foci resulting from the apoptogenic properties of the pore-forming molecule Listeriolysin O.

Suppression in lung defense responses after bacterial infection in rats pretreated with different welding fumes

Epidemiology suggests that inhalation of welding fumes increases the susceptibility to lung infection. The effects of chemically distinct welding fumes on lung defense responses after bacterial infection were compared. Fume was collected during gas metal arc (GMA) or flux-covered manual metal arc (MMA) welding using two consumable electrodes: stainless steel (SS) or mild steel (MS). The fumes were separated into water-soluble and -insoluble fractions. The GMA-SS and GMA-MS fumes were found to be relatively insoluble, whereas the MMA-SS was highly water soluble, with the soluble fraction comprised of 87% Cr and 11% Mn. On day 0, male Sprague-Dawley rats were intratracheally instilled with saline (vehicle control) or the different welding fumes (0.1 or 2 mg/rat). At day 3, the rats were intratracheally inoculated with 5 x 10(3) Listeria monocytogenes. On days 6, 8, and 10, left lungs were removed, homogenized, cultured overnight, and colony-forming units were counted to assess pulmonary bacterial clearance. Bronchoalveolar lavage (BAL) was performed on right lungs to recover phagocytes and BAL fluid to measure the production of nitric oxide (NO) and immunomodulatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-2, IL-6, and IL-10. In contrast to the GMA-SS, GMA-MS, and saline groups, pretreatment with the highly water soluble MMA-SS fume caused significant body weight loss, extensive lung damage, and a dramatic reduction in pulmonary clearance of L. monocytogenes after infection. NO concentrations in BAL fluid and lung immunostaining of inducible NO synthase were dramatically increased in rats pretreated with MMA-SS before and after infection. MMA-SS treatment caused a significant decrease in IL-2 and significant increases in TNF-alpha, IL-6, and IL-10 after infection. In conclusion, pretreatment with MMA-SS increased production of NO and proinflammatory cytokines (TNF-alpha and IL-6) after infection, which are likely responsible for the elevation in lung inflammation and injury. In addition, MMA-SS treatment reduced IL-2 (involved in T cell proliferation) and enhanced IL-10 (involved in inhibiting macrophage function) after bacterial infection, which might result in a possible suppression in immune response and an increase in susceptibility to infection.

Endogene Endophthalmitis, verursacht durch Listeria monocytogenes

PURPOSE

Listeria monocytogenes is a rare cause of endogenous endophthalmitis. Controversy exists concerning clinical progress and prognosis in this bacterial infection. However, only a few reports about the clinical features have been previously published in the literature.

CASE REPORT

The case of a 24-year-old woman is reported. She developed an endogenous endophthalmitis within 3 weeks. The patient received a pars-plana vitrectomy showing Listeria monocytogenes in the vitreous body. An intensive antibiotic therapy was initiated (local, subconjunctival, intravitreal and systemic). Visual acuity was increased from hand motion to 0.5 by the end of the clinical attendance and to 1.0 three months later. There were no hints concerning systemic manifestation of listeriosis or granuloma formation.

CONCLUSION

Frequently, endogenous endophthalmitis has a very poor prognosis. However, the presented case report describes a very prosperous progress of endogenous endophthalmitis caused by an infection with Listeria monocytogenes.

Characteristics of the gastritis induced by Listeria monocytogenes in mice: microbiology, histopathology, and mRNA expression of inflammatory mediators with time course of infection

Listeria monocytogenes induces the suppurative gastritis in some mice strains. In this study, characteristics of the gastritis caused by L. monocytogenes infection in mice were examined with time course of infection. Mice were administered intragastrically with 1.8 x 10(8) CFU of L. monocytogenes. Each three mice were sacrificed by cervical dislocation at 1, 3, 5, 7, 10, 14, 17, 21, and 28 days postinoculation (pi), respectively. Bacterial colonization in the stomachs reached the peak at 3 days pi, maintained over 4.3 log10 CFU/g tissue until 14 days pi, and was cleared by 28 days pi. However, in the spleens and livers, the bacteria could not be detected after 7 days pi. The gastric lesions were the most prominent at between 3 and 7 days pi. The lesions consisted of marked neutrophilic infiltration, edema, vacuolar degeneration and necrosis of muscle cells and were more severe in the nonglandular region and fundus than in the pylorus, and were in submucosa, lamina muscularis, and serosa than in mucosa. mRNA expression of several cytokines (INF-gamma, IL-1beta, IL-5, IL-6, IL-12, and TNF-alpha) and chemokines (KC, MCP-1) increased in the gastric tissue of infected mice at 1-7 days pi and slightly decreased at 14 days pi. These findings would be useful for studying the pathological mechanism of human febrile gastroenteritis due to L. monocytogenes infection.

Reduced Apoptosis and Ameliorated Listeriosis in TRAIL-Null Mice

Listeriosis is an infectious disease caused by the bacterium Listeria monocytogenes. Although it is well recognized that apoptosis plays a critical role in the pathogenesis of the disease, the molecular mechanisms of cell death in listeriosis remain to be established. We report in this study that mice deficient in TRAIL were partially resistant to primary listeriosis, and blocking TRAIL with a soluble death receptor 5 markedly ameliorated the disease. The numbers of Listeria in the liver and spleen of TRAIL+/+ mice were 10-100 times greater than those in TRAIL-/- mice following primary Listeria infection. This was accompanied by a significant increase in the survival rate of TRAIL-/- mice. Lymphoid and myeloid cell death was significantly inhibited in TRAIL-/- mice, which led to marked enlargement of the spleen. These results establish a critical role for TRAIL in apoptosis during listeriosis.

Suppurative gastritis in BALB/c mice infected with Listeria monocytogenes via the intragastric route

Suppurative gastritis was demonstrated in BALB/c mice 3 days after intragastric inoculation with 10(9) organisms of Listeria monocytogenes strain ATCC19113 (serotype 3). Also tested were four other strains of mice (C3H, C57BL/6, FVB and ICR) and three other strains of L. monocytogenes (HPB 3 [serotype 4b], HPB 410 [serotype 1/2a] and HPB 503 [serotype 1/2b]). After inoculation with ATCC19113 the numbers of bacteria found in the stomach wall were greater in C57BL/6 and ICR mice than in C3H and FVB mice; moreover, the gastritis produced in BALB/c and C57BL/6 mice was more severe than that produced in the other mouse strains. The gastritis produced in BALB/c mice with L. monocytogenes HPB 3, HPB 410 and HPB 503 was much more severe than that produced by ATCC19113. The inflammatory response occurred in the lamina muscularis and mucosa of the fundus. Massive necrosis of the gastric epithelium was observed, and there was oedema in a large part of the mucosal layer of the fundus. In addition, the submucosal layer was apparently expanded due to oedema, and in the cardia, the mucosal layer had become thin and flattened. Immunohistochemically, a polyclonal antibody against Listeria spp. produced labelling in areas of the gastric mucosa in which there was an inflammatory response and gastric epithelial necrosis.

Subpopulations of mouse blood monocytes differ in maturation stage and inflammatory response

Blood monocytes are well-characterized precursors for macrophages and dendritic cells. Subsets of human monocytes with differential representation in various disease states are well known. In contrast, mouse monocyte subsets have been characterized minimally. In this study we identify three subpopulations of mouse monocytes that can be distinguished by differential expression of Ly-6C, CD43, CD11c, MBR, and CD62L. The subsets share the characteristics of extensive phagocytosis, similar expression of M-CSF receptor (CD115), and development into macrophages upon M-CSF stimulation. By eliminating blood monocytes with dichloromethylene-bisphosphonate-loaded liposomes and monitoring their repopulation, we showed a developmental relationship between the subsets. Monocytes were maximally depleted 18 h after liposome application and subsequently reappeared in the circulation. These cells were exclusively of the Ly-6C(high) subset, resembling bone marrow monocytes. Serial flow cytometric analyses of newly released Ly-6C(high) monocytes showed that Ly-6C expression on these cells was down-regulated while in circulation. Under inflammatory conditions elicited either by acute infection with Listeria monocytogenes or chronic infection with Leishmania major, there was a significant increase in immature Ly-6C(high) monocytes, resembling the inflammatory left shift of granulocytes. In addition, acute peritoneal inflammation recruited preferentially Ly-6C(med-high) monocytes. Taken together, these data identify distinct subpopulations of mouse blood monocytes that differ in maturation stage and capacity to become recruited to inflammatory sites.

The Ly-6Chigh monocyte subpopulation transports Listeria monocytogenes into the brain during systemic infection of mice

Mononuclear phagocytes can be used by intracellular pathogens to disseminate throughout the host. In the bloodstream these cells are generically referred to as monocytes. However, blood monocytes are a heterogeneous population, and the exact identity of the leukocyte(s) relevant for microbial spreading is not known. Experiments reported in this study used Listeria monocytogenes-infected mice to establish the phenotype of parasitized blood leukocytes and to test their role in systemic dissemination of intracellular bacteria. More than 90% of the blood leukocytes that were associated with bacteria were CD11b(+) mononuclear cells. Analysis of newly described monocyte subsets showed that most infected cells belonged to the Ly-6C(high) monocyte subset and that Ly-6C(high) and Ly-6C(neg-low) monocytes harbored similar numbers of bacteria per cell. Interestingly, systemic infection with wild-type or DeltaactA mutants of L. monocytogenes, both of which escape from phagosomes and replicate intracellularly, caused expansion of the Ly-6C(high) subset. In contrast, this was not evident after infection with Deltahly mutants, which neither escape phagosomes nor replicate intracellularly. Importantly, when CD11b(+) leukocytes were isolated from the brains of lethally infected mice, 88% of these cells were identified as Ly-6C(high) monocytes. Kinetic analysis showed a significant influx of Ly-6C(high) monocytes into the brain 2 days after systemic infection. This coincided with both bacterial invasion and up-regulation of brain macrophage chemoattractant protein-1 gene expression. These data indicate that the Ly-6C(high) monocyte subset transports L. monocytogenes into the brain and establish their role as Trojan horses in vivo.

Prolonged antigen presentation, APC-, and CD8+ T cell turnover during mycobacterial infection: comparison with Listeria monocytogenes

We expressed the CTL epitope of OVA (OVA(257-264)) in an acute (Listeria monocytogenes (LM)-OVA) and a chronic intracellular pathogen (Mycobacterium bovis (BCG)-OVA), to evaluate the kinetics of Ag presentation. LM-OVA proliferated rapidly in vivo, resulting in profound LM-OVA expansion within the first 24 h of infection, culminating in the generation of a potent CD8+ T cell response, which peaked on day 7 but underwent a rapid attrition subsequently. In contrast, BCG-OVA exhibited reduced growth in vivo, resulting in a delayed CD8+ T cell response that increased progressively with time. Relative to LM-OVA, BCG-OVA induced persistently increased numbers of apoptotic (annexin V+) CD8+ T cells. Ag presentation in vivo was evaluated by transferring Thy1.2+ carboxyfluorescein-labeled OT1 transgenic CD8+ T cells into infected Thy1.1+ congeneic recipient mice. LM-OVA induced rapid Ag presentation that was profound in magnitude, with most of the transferred cells getting activated within 4 days and resulting in a massive accumulation of activated donor CD8+ T cells. In contrast, Ag presentation induced by BCG-OVA was delayed, weaker in magnitude, which peaked around the second week of infection and declined to a low level subsequently. Increasing the dose of BCG-OVA while enhancing the magnitude of Ag presentation did not change the kinetics. Furthermore, a higher dose of BCG-OVA also accelerated the attrition of OVA(257-264)-specific CD8+ T cells. Relative to LM-OVA, the dendritic cells in BCG-OVA-infected mice were apoptotic for prolonged periods, suggesting that the rapid death of APCs may limit the magnitude of Ag presentation during chronic stages of mycobacterial infection.

Oral inoculation of A/J mice for detection of invasiveness differences between Listeria monocytogenes epidemic and environmental strains

Four-week-old Harlan A/J mice were orally infected with six epidemic and six environmental strains of Listeria monocytogenes. Epidemic strains were significantly more invasive as a group than were environmental strains (P < 0.05), and the intestines of some mice infected with epidemic strains had extensive hemorrhage. Mice inoculated with epidemic strains were significantly more likely to become systemically infected than mice inoculated with environmental strains (P < 0.01).

Exploration of host-pathogen interactions using Listeria monocytogenes and Drosophila melanogaster

The facultative intracellular bacterial pathogen Listeria monocytogenes is capable of replicating within a broad range of host cell types and host species. We report here the establishment of the fruit fly Drosophila melanogaster as a new model host for the exploration of L. monocytogenes pathogenesis and host response to infection. Listeria monocytogenes was capable of establishing lethal infections in adult fruit flies and larvae with extensive bacterial replication occurring before host death. Bacteria were found in the cytosol of insect phagocytic cells, and were capable of directing host cell actin polymerization. Bacterial gene products necessary for intracellular replication and cell-to-cell spread within mammalian cells were similarly found to be required within insect cells, and although previous work has suggested that L. monocytogenes virulence gene expression requires temperatures above 30 degrees C, bacteria within insect cells were found to express virulence determinants at 25 degrees C. Mutant strains of Drosophila that were compromised for innate immune responses demonstrated increased susceptibility to L. monocytogenes infection. These data indicate L. monocytogenes infection of fruit flies shares numerous features of mammalian infection, and thus that Drosophila has the potential to serve as a genetically tractable host system that will facilitate the analysis of host cellular responses to L. monocytogenes infection.

Increased Dendritic Cell Numbers Impair Protective Immunity to Intracellular Bacteria Despite Augmenting Antigen-Specific CD8+T Lymphocyte Responses

Dendritic cells (DCs) reside in tissues, where they function as sentinels, providing an essential link between innate and adaptive immunity. Increasing the numbers of DCs in vivo augments T cell responses, and can cause dramatic CTL-dependent tumor regression. To determine whether greater DC numbers promoted T cell-mediated protection in the context of host defense against intracellular bacteria, we treated mice with Flt3 ligand (Flt3-L) to increase DCs in vivo and challenged them with Listeria monocytogenes. Unexpectedly, after primary challenge with Listeria, the overall control of Listeria infection was impaired in Flt3-L-treated mice, which had greater bacterial burden and mortality than controls. Similar results were obtained when DC numbers were increased by treatment with polyethylene glycol-conjugated GM-CSF rather than Flt3-L and in mice infected with Mycobacterium tuberculosis. Impaired protection was not due to dysfunctional T cell responses, as Flt3-L-treated mice had a greater frequency and absolute number of Ag-specific CD8+ T cells, which produced IFN-gamma, exhibited cytolytic activity, and transferred protection. The increased Listeria burden in Flt3-L-treated mice was preferentially associated with DCs, which were unable to kill Listeria and more resistant to CTL lysis compared with macrophages in vitro. Although we cannot exclude the possibility that other potential effects, in addition to increased numbers of DCs, are shared by Flt3-L and polyethylene glycol-conjugated GM-CSF and contributed to the increase in susceptibility observed in treated mice, these results support the notion that DC numbers must be properly controlled within physiological limits to optimize host defense to intracellular bacterial pathogens.

Activation of antigen-specific CD8 T cells results in minimal killing of bystander bacteria

Memory CD8 T cells play a critical role in protective immunity against intracellular pathogens. In addition to their ability to specifically recognize and lyse infected targets, activated CD8 T cells secrete cytokines that induce phagocytic cells to engulf and kill bacterial pathogens. In this study, we asked whether activation of Ag-specific CD8 T cells results in nonspecific killing of bystander bacteria during a mixed infection. Mice with epitope-specific memory CD8 T cells were coinfected with two isogenic strains of recombinant Listeria monocytogenes that differ in the cognate epitope. Recall responses by epitope-specific CD8 T cells rapidly inhibited the growth of epitope-bearing bacteria, impeding the course of infection within 6 h after challenge. This rapid inhibition was highly specific and did not affect the growth of coinfecting bacteria without the epitope. CTL recall did not enhance activation of innate immune cells, as evidenced by the absence of inducible NO synthase production in infectious foci. Our observations demonstrate the remarkable specificity of the bactericidal mechanisms of CTL and reveal the possibility for escape mutants to prevail in the hostile environment of a specific immune response. This implication has a bearing on subunit vaccine design strategies and understanding failure of immunization against bacterial infection.

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.

Splenic norepinephrine and serum corticosterone level fluctuations associated with bacteria-induced stress

Corticosterone (CORT) and norepinephrine (NE), two effector molecules of the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-lymphoid (SL) axes, respectively, differentially influence murine host resistance to Listeria monocytogenes (LM). Serum CORT and splenic NE levels early (< or =24 h) after infection correlated positively with host resistance, as long as the LM burden did not exceed approximately 10(6) cfu LM per spleen. As previously reported, mice with right-circling preference (R-mice) have significantly greater host resistance to LM than those with left-circling preference (L-mice) and early after infection, R-mice had significantly higher serum CORT levels than L-mice. However, rapid pathogenesis with a high bacterial burden induced high activation of the HPA and SL axes, which prevented observable differences in the defense against LM, especially later in infection. With the high bacterial inoculum (10(5) LM), the splenic NE levels significantly increased, but no differences among R- and L-mice were discernible. We suggest that endogenous asymmetry of neuroimmune circuits contributes to differential host resistance, but the level of stress (bacterial inoculum) is critical. With regard to the neuroendocrine factors assessed, CORT, but not NE, levels significantly correlated with the enhanced defenses of R-mice in comparison to L-mice. The differential host resistance based on brain laterality seems to be more a function of the HPA axis and possibly other CNS effects on peripheral immunity than neurotransmitter release by the sympathetic innervation of the spleen.

Selective Depletion of Nonspecific T Cells During the Early Stage of Immune Responses to Infection

Transient T cell depletion occurs before the development of an effective immune response to infection. In this study we show that most T cells, regardless of specificity, are induced to express early activation markers soon after infection with Listeria monocytogenes or lymphocytic choriomeningitis virus. Ag-specific T cells are further activated to display late activation markers and undergo extensive proliferation. As Ag-specific T cells begin to expand, nonspecific T cells are depleted en masse and exhibit no sign of further activation or proliferation before their depletion. This selective depletion of nonspecific T cells is due to in situ death via apoptosis, as visualized by confocal microscopy. Thus, early activation and subsequent depletion of nonspecific T cells are integral parts of the immune response to proinflammatory infections. These results have important implications for our understanding of early events in the development of a robust T cell response.

Host resistance of CD18 knockout mice against systemic infection with Listeria monocytogenes

Mice with targeted mutations of CD18, the common beta2 subunit of CD11/CD18 integrins, have leukocytosis, impaired transendothelial neutrophil emigration, and reduced host defense to Streptococcus pneumoniae, a gram-positive extracellular bacterium. Previous studies using blocking monoclonal antibodies suggested roles for CD18 and CD11b in hepatic neutrophil recruitment and host innate response to Listeria monocytogenes, a gram-positive intracellular bacterium. We induced systemic listeriosis in CD18 knockout (CD18-ko) and wild-type (WT) mice by tail vein injection with Listeria. By 14 days postinjection (dpi), 8 of 10 WT mice died, compared with 2 of 10 CD18-ko mice (P < 0.01). Quantitative organ culture showed that numbers of Listeria organisms in livers and spleens were similar in both groups at 20 min postinfection. By 3, 5, and 7 dpi, however, numbers of Listeria organisms were significantly lower in livers and spleens of CD18-ko mice than in WT mice. Histopathology showed that following Listeria infection, CD18-ko mice had milder inflammatory and necrotizing lesions in both spleens and livers than did WT mice. Cytokine assays indicated that baseline interleukin-1beta and granulocyte colony-stimulating factor (G-CSF) levels were higher in CD18-ko mice than in WT mice and that CD18-ko splenocytes produced higher levels of interleukin-1beta and G-CSF than WT splenocytes under the same amount of Listeria stimulation. These findings show that CD18 is not an absolute requirement for antilisterial innate immunity or hepatic neutrophil recruitment. We propose that the absence of CD18 in the mice results in the priming of innate immunity, as evidenced by elevated cytokine expression, and neutrophilic leukocytosis, which augments antilisterial defense.

The uterine NK cell population requires IL-15 but these cells are not required for pregnancy nor the resolution of a Listeria monocytogenes infection

During pregnancy in mice, uterine natural killer (uNK) cells abundantly accumulate on the mesometrial side of the placenta. In this study, we show that the presence of both mature and immature uNK cells requires IL-15. Bone marrow transplantation of NK cell-negative mice due to null mutations in the recombination-activating gene (Rag) 2/common cytokine receptor gamma-chain (Rag2(-/-)gamma(c)(-/-)) genes indicated that uNK cells originate from the bone marrow and require IL-15 to develop. NK cells are thought to be central players in the immune response to intracellular pathogens such as Listeria monocytogenes, a bacterium that also has a predilection for replication in the placenta. However, IL-15(-/-), NK cell-deficient mice were relatively protected from this infection compared with wild-type mice, and during pregnancy the absence of NK cells did not compromise the immune response at this site. The loss of uNK cells results in decidual abnormalities, including thickening of the arterial walls with luminal narrowing and a hypocellular decidua basalis. These defects were rescued by bone marrow transplantation of the Rag2(-/-)gamma(c)(-/-) mice that restored the uNK cell population. The decidual abnormalities in the IL-15(-/-) mice however did not result in infertility as gestation times and litter sizes were comparable to those of wild-type mice. Fetal weights were mildly compromised, consistent with the arterial pathologies. These results show that uNK cells are not required for successful pregnancy and that NK cells are not essential for an adequate immune response to L. monocytogenes in either pregnant or nonpregnant mice.

[Listeria pathogenicity factors and their role in pathogenesis and laboratory diagnosis of listeriosis]

The mechanisms of relationships between Listeria and eukaryotic cells on the level of the main biomolecules are analyzed. These mechanisms determine the penetration and multiplication of Listeria and their importance for the pathogenesis of listeriosis. The theoretical and practical aspects of the regulation of the expression of pathogenicity factors in Listeria, connected with the activation of the regulatory protein PrfA and autoregulatory mechanisms, are considered. The elimination of the autorepressor from the cultivation medium results in the activation of the regulatory protein and the induction of the pathogenicity factors. The effective identification method for L. monocytogenes, permitting the differentiation of pathogenic and non-pathogenic Listeria, has been developed on the basis of the study of lecithinase expression in the presence of activated charcoal.

Neutrophilia in LFA-1-deficient mice confers resistance to listeriosis: possible contribution of granulocyte-colony-stimulating factor and IL-17

LFA-1 (CD11a/CD18) plays a crucial role in various inflammatory responses. In this study, we show that LFA-1(-/-) mice are far more resistant to Listeria monocytogenes infection than LFA-1(+/-) mice. Consistent with this, we found the following: 1) the numbers of granulocytes infiltrating the liver were markedly higher in LFA-1(-/-) mice than in LFA-1(+/-) mice, 2) increased antilisterial resistance in LFA-1(-/-) mice was abrogated by depletion of granulocytes, and 3) the numbers of granulocytes in peripheral blood, and the serum levels of both G-CSF and IL-17 were higher in LFA-1(-/-) mice than in LFA-1(+/-) mice. Neither spontaneous apoptosis nor survival of granulocytes from LFA-1(-/-) mice were affected by physiological concentrations of G-CSF. Our data suggest regulatory effects of LFA-1 on G-CSF and IL-17 secretion, and as a corollary on neutrophilia. Consequently, we conclude that increased resistance of LFA-1(-/-) mice to listeriosis is due to neutrophilia facilitating liver infiltration by granulocytes promptly after L. monocytogenes infection, although it is LFA-1 independent.

Tailoring host immune responses to Listeria by manipulation of virulence genes -- the interface between innate and acquired immunity

Although attenuated strains of microbial pathogens have triggered vaccine development from its origin, the role of virulence factors in determining host immunity has remained largely unexplored. Using the murine listeriosis model, we investigated whether the induction and expansion of protective and inflammatory T cell responses may be modified by selective manipulation of virulence genes. We intentionally deleted specific genes of Listeria monocytogenes, including those encoding the positive regulatory factor (prfA), hemolysin (hly), the actin nucleator (actA), and phospholipase B (plcB). The resulting strains showed decisive differences in their immunogenic properties. In particular, we identified a double-deletion mutant that retained Listeria's profound ability to induce protective CD8(+) T cells, but that is strongly attenuated and exhibits a significantly reduced ability to induce CD4(+) T cell-mediated inflammation. We conclude that this mutant, L. monocytogenes DeltaactADeltaplcB, is at present the most promising mutant for a bacterial vaccine vector and is able to safely induce potent CD8(+) T cell-mediated immunity.

Multiple cerebral abscesses because of Listeria monocytogenes: three case reports and a literature review of supratentorial listerial brain abscess(es)

BACKGROUND

Central nervous system involvement often follows bacteremia because of Listeria monocytogenes. Meningitis is clinically the most common manifestation, while brain abscess occurs in about 1% of patients. Brain abscess is usually solitary but in recent years, probably in part because of the availability of computerized tomography and magnetic resonance imaging, several reports have described two or more separate supratentorial abscesses.

METHODS

We have described three patients with listerial brain abscesses and reviewed the North American and European literature of brain abscess(es) because of L. monocytogenes through December 2001. We have evaluated the role of underlying diseases and therapeutic immunosuppression on the development of solitary or greater than one brain abscess.

RESULTS

In contrast to meningitis, where immunosuppression does not predispose either to disease incidence or to higher mortality, patients with solitary and particularly those with more than one supratentorial abscess usually are immunosuppressed either by disease or by therapy. Corticosteroids in particular are significant predisposing factors, especially in those patients with two or more brain abscesses. Mortality resulting from listerial brain abscess, whether solitary or multiple, is nearly three times higher than nonlisterial brain abscess, probably in part because of both underlying diseases and immunosuppressive therapy.

CONCLUSIONS

Therapy with high-dose ampicillin in combination with gentamicin appear to be the drugs of choice, followed by trimethoprim/sufamethoxazole and vancomycin. In general, antimicrobial therapy appears to be satisfactory treatment without surgical intervention.

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.

[Listeria rhombencephalitis. Neuroradiological findings]

Rhombencephalitis due to listeria monocytogenes is an uncommon and serious form of brainstem infection. The disease has a characteristic biphasic course: a nonspecific prodrome of headache, nausea or vomiting, and fever lasting for a several days is followed by progressive asymmetrical cranial-nerve palsies. We report two cases of Listeria monocytogenes rhombencephalitis. The first case is a previously healthy 20 year-old-man who developed fever, headache, nausea and vomiting, followed by numbness in left trigeminal nerve. The second case is an immunosuppressed 77 year-old-man, who developed sudden left hemiparesis, followed by fever and severe brainstem dysfunction with ophthalmoplegia and dysphagia. In both cases, a brain magnetic resonance imaging (MRI) scan, showed increased intensity on T2-weighted lesions in the brainstem that enhanced after contrast on T1-weighted sequences. Both patients had a favorable outcome with full clinical recovery. We conclude that MRI aids in the early detection of parenchymal infections, therefore, MRI is crucial for early diagnosis and is very useful for follow-up examinations.

The changing epidemiology of bacterial meningitis and invasive non-meningitic bacterial disease in scotland during the period 1983-99

We reviewed population-based laboratory reports of invasive meningococcal, pneumococcal, Haemophilus influenzae, Group B Streptococcus (GBS) and Listeria monocytogenes isolates in order to examine the changing epidemiology of meningitis and invasive non-meningitic disease (INMD) caused by these 5 pathogens in the 2 periods before (1983-91) and after (1992-99) routine use of H. influenzae type B conjugate vaccine (Hib) in Scotland. Neissieria meningitidis was the most common cause of meningitis, accounting for 39.2% of cases of meningitis in 1983-91 and 47% of cases in 1992-99, followed by H. influenzae (31%), Streptococcus pneumoniae (22.4%), GBS (3.9%) and L. monocytogenes (3.5%) in 1983-91 and S. pneumoniae (36.3%), H. influenzae (7.8%), GBS (6.1%) and L. monocytogenes (2.8%) in 1992-99. The important epidemiological features of meningitis and INMD caused by these 5 pathogens between 1983-91 and 1992-99 include: 1. The incidence of bacterial meningitis due to S. pneumoniae and GBS was stable; 2. S. pneumoniae was the predominant cause of INMD in both periods; 3. The incidences of INMD caused by N. meningitidis, GBS and S. pneumoniae increased, by 27%, 55% and 56%, respectively; 4. Decreases in the incidences of bacterial meningitis (by 50%) and INMD (by 50%) due to L. monocytogenes were detected; and 5. There were dramatic reductions in the proportions of bacterial meningitis (by 92%) and INMD (by 56%) due to H. influenzae in vaccinated and non-vaccinated individuals. Continued surveillance is necessary to monitor the disease trend, population at risk, serotype distribution and antimicrobial susceptibility in order to implement appropriate public health interventions against invasive bacterial disease.

Residual oil fly ash increases the susceptibility to infection and severely damages the lungs after pulmonary challenge with a bacterial pathogen

Inhalation of residual oil fly ash (ROFA), a component of ambient particulate matter, has been shown to increase pulmonary morbidity and impair lung defense mechanisms in exposed workers. Our objective was to evaluate the effect of ROFA preexposure on lung defense and injury after pulmonary challenge with a bacterial pathogen. Male Sprague-Dawley rats were dosed intratracheally at day 0 with saline (control) or ROFA (0.2 or 1 mg/100 g body weight). Three days later, a low (5 x 10(3)) or high (5 x 10(5)) dose of Listeria monocytogenes was instilled intratracheally into the ROFA- and saline-treated rats. Bronchoalveolar lavage was performed on the right lungs at days 6, 8, and 10. The recovered cells were differentiated, and chemiluminescence (CL) and nitric oxide (NO) production, two indices of alveolar macrophage (AM) function, were measured. At the same time points, the left lung and spleen were removed, homogenized, and cultured, and colony-forming units were counted after an overnight incubation. Exposure to ROFA and the high dose of L. monocytogenes led to marked lung injury and inflammation as well as to an increase in mortality, compared with rats treated with saline and the high dose of L. monocytogenes. Preexposure to ROFA significantly enhanced injury and delayed the pulmonary clearance of L. monocytogenes at both bacterial doses when compared to the saline-treated control rats. ROFA had no effect on AM CL but caused a significant suppression of AM NO production, as compared to the saline control rats. We have demonstrated that acute exposure to ROFA slowed the pulmonary clearance of L. monocytogenes. The suppression in AM NO production by ROFA pretreatment likely plays an important role. These results suggest that pulmonary exposure to ROFA may alter AM function and lead to increased susceptibility to lung infection in exposed populations.

Genetically-modified-animal models for human infections: the Listeria paradigm

Several human pathogens exhibit a restricted host-tropism, relying on the species-specific interaction of microbial ligand(s) with host receptor(s). This specificity accounts for some of the difficulties in modeling human infections in animals. The discovery of L. monocytogenes host-specificity and elucidation of the underlying mechanism has led to the generation of transgenic mice expressing one of its human receptors, E-cadherin. This model is presented here as a paradigm of a genetically-modified-animal model for studying a human infectious disease.

Listeria infection during pregnancy: a 10 year experience

BACKGROUND

Although Listeria monocytogenes is widely distributed in nature, it rarely causes clinical infection in previously healthy people. This microorganism, however, may cause severe invasive disease in pregnant women and newborns.

OBJECTIVES

To investigate--in our pregnant population--the impact, severity and outcome of listeriosis on both mother and fetus.

METHOD

The study was carried out at a level III, university two-hospital complex. In a retrospective chart review of 65,022 parturients during a 10 year period (1990-1999), we identified and evaluated 11 pregnant patients and their offspring with Listeria infection.

RESULTS

Chorioamnionitis with multiple placental abscesses were observed in all five placentae examined. Clinically, 4 of 11 parturients had a cesarean section for fetal distress (36.3%), as compared to the 14% mean CS rate in our general population. Two of 11 had a late abortion (18.1%), as compared with the 4% rate in our hospital. Four of 11 had premature labor (36%), which was about four times the rate in our population. Finally, although no intrauterine fetal death was recorded in our series, there was one neonatal death of a term infant (1/11, 9%), which is about 10 times higher than our corrected perinatal mortality rate.

CONCLUSIONS

If not promptly and adequately treated, listeriosis in pregnancy may present serious hazards to the fetus and newborn through direct infection of the placenta and chorioamnionitis.

Critical Roles of Myeloid Differentiation Factor 88-Dependent Proinflammatory Cytokine Release in Early Phase Clearance ofListeria monocytogenesin Mice

Listeria monocytogenes (LM), a facultative intracellular Gram-positive bacterium, often causes lethal infection of the host. In this study we investigated the molecular mechanism underlying LM eradication in the early phase of infection. Upon infection with LM, both IL-12 and IL-18 were produced, and then they synergistically induced IFN-gamma production, leading to normal LM clearance in the host. IFN-gamma knockout (KO) mice were highly susceptible to LM infection. IL-12/IL-18 double knockout mice were also highly susceptible. Their susceptibility was less than that of IFN-gamma KO mice, but more than that of single IL-12 or IL-18 KO mice. Mice deficient in myeloid differentiation factor 88 (MyD88), an essential adaptor molecule used by signal transduction pathways of all members of the Toll-like receptor (TLR) family, showed an inability to produce IL-12 and IFN-gamma following LM infection and were most susceptible to LM. Furthermore, MyD88-deficient, but not IFN-gamma-deficient, Kupffer cells could not produce TNF-alpha in response to LM in vitro, indicating the importance of MyD88-dependent TNF-alpha production for host defense. As TLR2 KO, but not TLR4 KO, mice showed partial impairment in their capacity to produce IL-12, IFN-gamma, and TNF-alpha, TLR2 activation partly contributed to the induction of IL-12-mediated IFN-gamma production. These results indicated a critical role for TLRs/MyD88-dependent IL-12/TNF-alpha production and for IL-12- and IL-18-mediated IFN-gamma production in early phase clearance of LM.

Effects of pregnancy-associated Listeria monocytogenes infection: necrotizing hepatitis due to impaired maternal immune response and significantly increased abortion rate

The impact of L. monocytogenes infection on maternal immune responses as well as on the outcome of pregnancy was studied in a murine model of pregnancy-associated listeriosis. Mice infected i.v. with L. monocytogenes at day 15 of pregnancy showed a significantly impaired bacterial elimination, which resulted in a severe necrotizing hemorrhagic hepatitis. The aggravated course of the infection could be attributed to a suppressed transcription and production of anti-listerial, pro-inflammatory cytokines and chemokines, namely interferon-gamma, tumor necrosis factor, interleukin-12p40, inducible nitric oxide synthase, murine monokine induced by interferon-gamma, and interferon-gamma-inducible protein-10. In addition, listeriosis significantly increased the abortion rate. Infection of the placenta and fetuses was characterized by placental and fetal necrosis with unrestricted bacterial multiplication. A weak transcription of anti-listerial cytokines in the placenta in the absence of a cellular immune response could not prevent the fatal outcome of pregnancy-associated listeriosis.

Protective immunosurveillance of the central nervous system by Listeria-specific CD4 and CD8 T cells in systemic listeriosis in the absence of intracerebral Listeria

The invasion of the CNS by pathogens poses a major risk for damage of the highly vulnerable brain. The aim of the present study was to analyze immunological mechanisms that may prevent spread of infections to the CNS. Intraperitoneal application of Listeria monocytogenes to mice induced infection of the spleen, whereas pathogens remained absent from the brain. Interestingly, Listeria-specific CD4 and CD8 T cells homed to the brain and persisted intracerebrally for at least 50 days after both primary and secondary infection. CD4 and CD8 T cells resided in the leptomeninges, in the choroid plexus, and, in low numbers, in the brain parenchyma. CD4 and CD8 T cells isolated from the brain early after infection (day 7) were characterized by an activated phenotype with spontaneous IFN-gamma production, whereas at a later stage of infection (day 28) restimulation with Listeria-specific peptides was required for the induction of IFN-gamma production by CD4 and CD8 T cells. In contrast to splenic T cells, T cells in the brain did not exhibit cytotoxic activity. Adoptively transferred T cells isolated from the brains of Listeria-infected mice reduced the bacterial load in cerebral listeriosis. The frequency of intracerebral Listeria-specific T cells was partially regulated by the time of exposure to Listeria and cross-regulated by CD4 and CD8 T cells. Collectively, these data reveal a novel T cell-mediated pathway of active immunosurveillance of the CNS during bacterial infections.

Metastatic Listeria monocytogenes infection of the peritoneum in mice with cyclosporine a-induced peritonitis

Inoculation of mice with Listeria monocytogenes intragastrically or by parenteral routes has not been reported to cause peritonitis. In this study, however, severe listerial peritonitis was induced in mice infected subcutaneously and treated intraperitoneally with cyclosporin A (Cs A) in an oil carrier. In both uninfected and listeria-infected mice, intraperitoneal administration of Cs A consistently produced overexpression of P-selectin in the peritoneal microvasculature and pyogranulomatous inflammation of the peritoneum, suggesting that Cs A causes endothelial damage. We suggest that in listeria-infected mice the non-specific irritant peritonitis induced by the intraperitoneal administration of Cs A results in transfer of listeria-infected phagocytes from the liver and spleen to the peritoneal microvasculature, producing metastatic infection.