Repeated oral dosing with Listeria monocytogenes in mice as a model of central nervous system listeriosis in man

Human listeriosis is a food-borne disease of immunosuppressed or previously healthy adults. The repeated oral administration of a sublethal dose (5x10(9)colony-forming units) of Listeria monocytogenes for 7 or 10 consecutive days led to the development of severe central nervous system (CNS) lesions in 25% of experimental mice. Histopathological examination of the brain revealed rhombencephalitis and ventriculitis as two distinct inflammatory patterns, resembling those seen in human listeriosis. This model would seem to be potentially useful for research on pathogenesis, predisposing factors and therapy in CNS listeriosis in man. 1999 W.B. Saunders and Company Ltd.

Comparative efficacies of antibiotics in a rat model of meningoencephalitis due to Listeria monocytogenes

The antibacterial activities of amoxicillin-gentamicin, trovafloxacin, trimethoprim-sulfamethoxazole (TMP-SMX) and the combination of trovafloxacin with TMP-SMX were compared in a model of meningoencephalitis due to Listeria monocytogenes in infant rats. At 22 h after intracisternal infection, the cerebrospinal fluid was cultured to document meningitis, and the treatment was started. Treatment was instituted for 48 h, and efficacy was evaluated 24 h after administration of the last dose. All tested treatment regimens exhibited significant activities in brain, liver, and blood compared to infected rats receiving saline (P < 0.001). In the brain, amoxicillin plus gentamicin was more active than all of the other regimens, and trovafloxacin was more active than TMP-SMX (bacterial titers of 4.1 +/- 0.5 log10 CFU/ml for amoxicillin-gentamicin, 5.0 +/- 0.4 log10 CFU/ml for trovafloxacin, and 5.8 +/- 0.5 log10 CFU/ml for TMP-SMX; P < 0.05). In liver, amoxicillin-gentamicin and trovafloxacin were similarly active (2.8 +/- 0.8 and 2.7 +/- 0.8 log10 CFU/ml, respectively) but more active than TMP-SMX (4.4 +/- 0. 6 log10 CFU/ml; P < 0.05). The combination of trovafloxacin with TMP-SMX did not alter the antibacterial effect in the brain, but it did reduce the effect of trovafloxacin in the liver. Amoxicillin-gentamicin was the most active therapy in this study, but the activity of trovafloxacin suggests that further studies with this drug for the treatment of Listeria infections may be warranted.

Dissemination of Listeria monocytogenes by infected phagocytes

In vitro data suggest that blood-borne Listeria monocytogenes organisms enter the central nervous system (CNS) by direct invasion of endothelial cells or by cell-to-cell spread from infected phagocytes to endothelial cells. However, a role for infected phagocytes in neuroinvasion and dissemination of L. monocytogenes in vivo has not been confirmed experimentally. Experiments described here tested whether L. monocytogenes-infected peripheral blood leukocytes (PBL) circulated in bacteremic mice and could establish organ infection in vivo. A mean of 30.5% of bacteria cultured from whole blood were PBL associated, and microscopy showed that 22.2% of monocytes and 1.6% of neutrophils were infected. PBL-associated bacteria spread to endothelial cells in vitro, indicating their potential for virulence in vivo. To test this possibility, mice were injected intravenously with infected PBL and CFU of bacteria in liver, spleen, and brain were quantified and compared with values for mice injected with broth-grown bacteria and in vitro-infected macrophage cell lines. An inoculum of infected macrophage cell lines led to greater numbers of bacteria in the liver than the numbers produced by a similar inoculum of broth-grown bacteria. In contrast, brain infection was best established by infected PBL. Results of intraperitoneal injection of infected peritoneal cells compared with results of injection with infected J774A.1 cells suggested that unrestricted intracellular bacterial replication within J774A.1 cells contributed to excessive liver infection in those mice. These data show dissemination of intracellular L. monocytogenes and indicate that phagocyte-facilitated invasion has a role in CNS infection in vivo. Heterogeneity with regard to bactericidal activity as well as to other phagocyte characteristics is a critical feature of this mechanism.

The role of Kupffer cells and regulation of neutrophil migration into the liver by macrophage inflammatory protein-2 in primary listeriosis in mice

Depletion of mouse Kupffer cells and splenic macrophages following intravenous administration of liposome-entrapped clodronate severely reduced host resistance to primary infection with Listeria monocytogenes. Infection of clodronate-treated mice with a sublethal dose of L. monocytogenes resulted in death of the mice within 3 days. The macrophage depletion resulted in marked increases in bacterial growth in the liver and spleen, but not in other tissues. The proliferation of L. monocytogenes was observed in a large number of hepatocytes that underwent apoptosis. Infiltration of neutrophils in the liver and rapid formation of microabscesses were observed in the control mice after L. monocytogenes infection. However, there was less accumulation of neutrophils in the liver of Kupffer cell-depleted mice than in the control mice. Expression of macrophage inflammatory protein-2 (MIP-2) was enhanced in the livers of both the control and Kupffer cell-depleted mice after L. monocytogenes infection. MIP-2 was also induced in a murine hepatocyte cell line following L. monocytogenes infection. The administration of neutralizing anti-interleukin-8 receptor homolog antibody severely abrogated neutrophil infiltration into the Listeria-infected mouse liver. Anti-MIP-2 antibody moderately reduced neutrophil infiltration and microabscess formation in the liver. These findings indicate that Kupffer cells protect hepatocytes from L. monocytogenes infection and the resultant apoptosis. Moreover, MIP-2 and its related molecules produced by the infected hepatocytes regulate neutrophil infiltration and microabscess formation in primary listeriosis.

Effector cells of both nonhemopoietic and hemopoietic origin are required for interferon (IFN)-gamma- and tumor necrosis factor (TNF)-alpha-dependent host resistance to the intracellular pathogen, Toxoplasma gondii

Although interferon (IFN)-gamma-activated, mononuclear phagocytes are considered to be the major effectors of resistance to intracellular pathogens, it is unclear how they control the growth of microorganisms that reside in nonhemopoietic cells. Pathogens within such cells may be killed by metabolites secreted by activated macrophages or, alternatively, directly controlled by cytokine-induced microbicidal mechanisms triggered within infected nonphagocytic cells. To distinguish between these two basic mechanisms of cell-mediated immunity, reciprocal bone marrow chimeras were constructed between wild-type and IFN-gamma receptor-deficient mice and their survival assessed following infection with Toxoplasma gondii, a protozoan parasite that invades both hemopoietic and nonhemopoietic cell lineages. Resistance to acute and persistent infection was displayed only by animals in which IFN-gamma receptors were expressed in both cellular compartments. Parallel chimera experiments performed with tumor necrosis factor (TNF) receptor-deficient mice also indicated a codependence on hemopoietic and nonhemopoietic lineages for optimal control of the parasite. In contrast, in mice chimeric for inducible nitric oxide synthase (iNOS), an enzyme associated with IFN-gamma-induced macrophage microbicidal activity, expression by cells of hemopoietic origin was sufficient for host resistance. Together, these findings suggest that, in concert with bone marrow-derived effectors, nonhemopoietic cells can directly mediate, in the absence of endogenous iNOS, IFN-gamma- and TNF-alpha-dependent host resistance to intracellular infection.

[Brain stem infection caused by Listeria monocytogenes]

Rhombencephalitis due to Listeria monocytogenes is a serious form of brainstem inflammation. It is difficult to diagnose on the basis of clinical and laboratory findings alone. We describe a fatal case of Listeria monocytogenes rhombencephalitis in a previously healthy female teenager. Clinical and pathogenetic aspects of this condition are discussed.

[Listeria monocytogenes--the perfect parasite?]

The pathogen Listeria monocytogenes has an extraordinary intracellular life cycle, based on adaption to and exploitation of normal cellular mechanisms. Extracellular organisms induce their own phagocytosis, followed by destruction of the phagosomal membrane. Cytoplasmatic bacteria organize the intracellular protein actin into "comet tails", and thus gain motility. In contact with the plasma membrane, motile bacteria induce a pseudopodium, corresponding to an invagination of the plasma membrane of the neighbouring cell. Eventually, the pseudopodium is engulfed by the neighbouring cell, creating a double membrane vacuole. L. monocytogenes destroys the double membrane, and escapes into the cytoplasm. This article reviews the molecular biology of Listeria infection, and how research in this field has yielded increased insight into normal cellular processes. Finally, we propose that the neuroinvasive properties of L. monocytogenes is caused by actin-dependent transport within axons from the periphery to the central nervous system.

Restraint stress-induced immunosuppression by inhibiting leukocyte migration and Th1 cytokine expression during the intraperitoneal infection of Listeria monocytogenes

In this study, a murine model of Listeria monocytogenes infection was used to investigate effects of restraint stress (RST) on host defense. We observed that the L. monocytogenes infection as well as RST induced an elevation of endogenous corticosterone (CORT) levels and RST synergistically enhanced endogenous CORT levels during the listerial infection. RST suppressed the migration of leukocytes including macrophages, neutrophils, NK cells and lymphocytes into the peritoneal cavities after the intraperitoneal inoculation of L. monocytogenes. RST also suppressed the increase of the surface MHC class II antigen expression in both peritoneal macrophages and B cells during the listerial infection. Interestingly, gene expression of iNOS, MCP-1 (JE) and Th1-type cytokines including IFN-gamma and IL-12 was down-regulated but Th2-type cytokine (IL-4 and IL-6) gene expression in the PEC was rather up-regulated on day 7 after infection, indicating that Th2-type immune response is more resistant to the elevated endogenous CORT levels than Th1-type response. Treatment of mice with RU486, a glucocorticoid receptor antagonist, restored the immune responses suppressed by RST to their normal levels in the infected mice, suggesting that the RST-induced elevation of endogenous corticosterone levels is mainly responsible for the induction of the immunosuppressive events during L. monocytogenes infection.

Early IFN-gamma production and innate immunity during Listeria monocytogenes infection in the absence of NK cells

NK cells are believed to play a mandatory role during the early phases of Listeria monocytogenes infection by producing IFN-gamma, which is required for the activation of macrophage effector functions. Mice deficient in the common cytokine receptor gamma-chain (gamma(c)-/-), which completely lack NK cells, were used to examine whether NK cells were essential for resistance to Listeria infection in vivo. Surprisingly, infected gamma(c)-/- mice showed normal innate immunity and macrophage responses against sublethal Listeria infection 2 days postinfection. At this time point, gamma(c)-/- mice showed increased blood IFN-gamma levels compared with those in noninfected controls, demonstrating an NK-independent source of IFN-gamma, which explains early resistance. Listeria-infected gamma(c)-/- x recombinase-activating gene-2-/- double-deficient mice were unable to produce IFN-gamma and were highly susceptible to L. monocytogenes. Since T cells, but not B cells, are major IFN-gamma producers, and gamma(c)-/- T cells were found to be efficient IFN-gamma producers in vitro, we conclude from these results that T cells functionally replace NK cells for the early IFN-gamma production that is necessary for activating the innate immune system following infection with L. monocytogenes. This novel observation in listeriosis underscores how the adaptive immune response can maintain and influence innate immunity.

Effect of feline immunodeficiency virus on cytokine response to Listeria monocytogenes in vivo

Feline immunodeficiency virus (FIV) is a lentivirus that induces an acquired immunodeficiency in domestic cats. The objective of this study was to compare the immune response of chronically FIV-infected cats and specific pathogen free (SPF) cats to Listeria monocytogenes, a facultative intracellular bacterium. Regional lymph nodes were removed at various times after subcutaneous inoculation with L. monocytogenes and evaluated. Lymph nodes of chronically FIV-infected cats enlarged more slowly and to a lesser degree than SPF cats. This was due to delayed and blunted lymphoid follicle formation and markedly diminished histiocyte influx. The cellular response correlated with a marked upregulation in IL10 transcription and delayed increase in TNF-alpha upregulation in FIV-infected cats. Transcriptional upregulation of IFN-gamma, IL4, and the p40 chain of IL12 was similar in lymph nodes of FIV-infected and SPF cats. Clinically, FIV-infected cats had a more severe response at the site of L. monocytogenes injection and showed signs of systemic bacterial dissemination while SPF cats remained clinically normal. FIV-infected cats generated a delayed hypersensitivity response similar to SPF cats but also had a significantly greater antibody response. Taken together, these data suggest excessive IL10 production may be responsible for the deficiency observed in the innate immune response of chronically FIV-infected cats challenged with L. monocytogenes.

Failure to induce organ-specific autoimmunity by breaking of tolerance: importance of the microenvironment

Peripheral tolerance is considered to be a safeguard against autoimmunity. Using a TCR-transgenic mouse system displaying peripheral tolerance against a liver-specific MHC class I Kb antigen, we investigated whether the breaking of tolerance would result in autoimmunity. Reversal of tolerance was achieved by simultaneous challenge with cells expressing the Kb autoantigen and IL-2. Tolerance could not be broken with IL-2 alone or when Kb- and IL-2-expressing cells were applied to different sites of the mice. However, despite the presence of activated autoreactive T cells that were able to reject Kb-positive grafts no autoaggression against the Kb-positive liver was observed. These results indicate that breaking of tolerance per se is not sufficient to cause liver-specific autoimmunity. However, when in addition to breaking tolerance the mice were infected with a liver-specific pathogen, autoaggression occurred. Thus, in this system at least two independent steps seem to be required for organ-specific autoimmunity: reversal of peripheral tolerance resulting in functional activation of autoreactive T cells and conditioning of the liver microenvironment which enables the activated T cells to cause tissue damage.

Bone marrow cellular composition in Listeria monocytogenes infected mice detected using ER-MP12 and ER-MP20 antibodies: a flow cytometric alternative to differential counting

Detailed assessment of bone marrow cellular composition is essential in the evaluation of various experimental in vivo systems, such as expression of transgenes, null mutations and stimulation of host defence in infection. Traditional morphological analysis of mouse bone marrow is laborious, requires specific cytological expertise, and is somewhat subjective. As an alternative, we have examined whether double labelling of bone marrow with the anti-precursor monoclonal antibodies ER-MP12 and ER-MP20 could be used for differential analysis by flow cytometry, as these antibodies define six relatively homogeneous cell populations in mouse bone marrow. Following a sublethal infection of mice with Listeria monocytogenes, we monitored changes in cellular composition of the bone marrow at various time points in three ways: differential morphological count; single-color flow cytometric analysis using markers for the myeloid, erythroid and lymphoid lineages; and double labelling with ER-MP12 and ER-MP20. As expected, the bone marrow composition changed dramatically during infection, leading to an increase of myeloid cells which peaked after 1 week of infection. Data determined by ER-MP12/20 flow cytometric analysis appeared to be in close agreement with both morphology and lineage marker analysis. In addition, ER-MP12/20 analysis provided more detailed information with regards to the presence of early myeloid precursors compared to lineage marker analysis. These data show that flow cytometric analysis of bone marrow using ER-MP12 and ER-MP20 monoclonal antibodies provides a relatively simple, rapid and objective assay when evaluating cellular composition in the bone marrow of the mouse.

Disruption of the cellular inflammatory response to Listeria monocytogenes infection in mice with disruptions in targeted genes

The results of this study to dissect the nature of the acquired immune response to infection with Listeria monocytogenes in mice with targetted gene disruptions show that successful resolution of disease requires the essential presence of alphabeta T cells and the capacity to elaborate gamma interferon. In the absence of either of these entities, mice experience increasingly severe hepatitis and tissue necrosis and die within a few days. The data from this study support the hypothesis that the protective process is the efficient replacement of neutrophils in lesions by longer-lived mononuclear phagocytes; alphabeta-T-cell-knockout mice died from progressive infection before neutrophil replacement could occur, whereas in gammadelta-T-cell-knockout mice this replacement process in the liver has previously been shown to be much slower. In the present study we attribute this delay to reduced production of the macrophage-attracting chemokine MCP-1 in the gammadelta-T-cell-knockout animals. These data further support the hypothesis that gammadelta T cells are important in controlling the inflammatory process rather than being essential to the expression of protection.

Comprehensive study of the intestinal stage of listeriosis in a rat ligated ileal loop system

The intestinal stage of listeriosis was studied in a rat ligated ileal loop system. Listeria monocytogenes translocated to deep organs with similar efficiencies after inoculation of loops with or without Peyer's patches. Bacterial seeding of deep organs was demonstrated as early as 15 min after inoculation. It was dose dependent and nonspecific, as the delta inlAB, the delta hly, and the delta actA L. monocytogenes mutants and the nonpathogenic species, Listeria innocua, translocated similarly to wild-type L. monocytogenes strains. The levels of uptake of listeriae by Peyer's patches and villous intestine were similar and low, 50 to 250 CFU per cm2 of tissue. No listeria cells crossing the epithelial sheet of Peyer's patches and villous intestine were observed by transmission electron microscopy. The lack of significant interaction of listeriae and the follicle-associated epithelium of Peyer's patches was confirmed by scanning electron microscopy. The follicular tissue of Peyer's patches was a preferential site of Listeria replication. With all doses tested, the rate of bacterial growth was 10 to 20 times higher in Peyer's patches than in villous intestine. At early stages of Peyer's patch infection, listeriae were observed inside mononuclear cells of the dome area. Listeriae then disseminated throughout the follicular tissue except for the germinal center. The virulence determinants hly and, to a lesser extent, actA, but not inlAB, were required for the completion of this process. This study suggests that Peyer's patches are preferential sites for replication rather than for entry of L. monocytogenes, due to the presence of highly permissive mononuclear cells whose nature remains to be defined.

Essential roles for granulocyte-macrophage colony-stimulating factor (GM-CSF) and G-CSF in the sustained hematopoietic response of Listeria monocytogenes-infected mice

The in vivo roles of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte (G)-CSF were studied in factor-deficient gene-targeted knockout mice infected with the facultative intracellular bacterium Listeria monocytogenes. Previous results showed that G-CSF-/- mice had an underlying selective deficiency in granulopoiesis, but GM-CSF-/- mice had little disturbance in resting hematopoiesis. Nevertheless, in this study it is revealed that 3 days after intraperitoneal infection with 2 x 10(5) Listeria, GM-CSF-/- mice harbored 50-fold more organisms in their spleen and liver than similarly infected wild-type mice. This was accompanied by a severe depletion of bone marrow hematopoietic cells and a deficient inflammatory response in their peritoneal cavity. Thus, GM-CSF is essential for emergency, but not resting, hematopoiesis. In contrast, G-CSF-/- mice were markedly susceptible to low doses (2 x 10(4)) of Listeria intraperitoneally. After infection, the acute (1 day) granulocyte infiltration to the peritoneal cavity was normal compared with wild type, but the more prolonged monocyte response was deficient, reflecting a continued decrease in bone marrow cellularity and hematopoiesis over 3 days, which was not observed in infected wild-type mice. It is thus apparent that G-CSF deficiency affects monocytopoiesis as well as granulopoiesis during infection.

Mice lacking the murine interleukin-8 receptor homologue demonstrate paradoxical responses to acute and chronic experimental infection with Listeria monocytogenes

In this study we demonstrate that mice which lack the murine interleukin-8 receptor homologue exhibit enhanced resistance during the early stage of infection (1-4 days after i.v. challenge with Listeria monocytogenes). This result is surprising in that interleukin-8 and other CXC chemokines are key players in the accumulation of inflammatory neutrophils, which is thought to be critical for resistance to listeriosis. Paradoxically, some of the interleukin-8 receptor knockout mice that survived acute infection with L. monocytogenes demonstrated evidence of chronic infection with L. monocytogenes.

Evidence that the same gamma delta T cells respond during infection-induced and autoimmune inflammation

Inflammatory responses are induced in both testes of a mouse following injection of Listeria monocytogenes into one testis. Although the uninjected testis contains no detectable bacteria, it undergoes an autoimmune attack. Normally, the testis lacks lymphocytes, but in the infected and autoimmune state, both gamma delta and alpha beta T cells are found as infiltrates. Here, we have examined the repertoire of the infiltrating gamma delta T cells, using two different methods, and found a high frequency of V gamma 6/V delta 1 gamma delta T cells in both infected and autoimmune testes. All of these expressed the invariant V gamma 6/V delta 1 TCR previously reported. However, secondary gamma and delta transcripts present within V gamma 6/V delta 1 hybridomas indicated nonclonality. Interestingly, some of these secondary transcripts were derived from gamma gene rearrangements not previously found in this gamma delta T cell subset, implying a difference in its origin. The increase in V gamma 6/V delta 1 cells observed here in both infected and autoimmune testes, together with our previous finding of a preferential response by the same subset in Listeria-infected liver, indicates that their response is triggered by the inflammation rather than by the infectious agent or because they are already resident in the tissue. We and others have previously reported that the presence of gamma delta T cells during certain inflammatory conditions correlates with less host tissue damage. This result, together with the evidence presented here, further implies that a response by the V gamma 6/V delta 1 subset in some way exerts a controlling influence on the host inflammatory response.

Defects in macrophage recruitment and host defense in mice lacking the CCR2 chemokine receptor

Chemokines are a structurally related family of cytokines that are important for leukocyte trafficking. The C-C chemokine monocyte chemoattractant protein-1 (MCP-1) is a potent monocyte activator in vitro and has been associated with monocytic infiltration in several inflammatory diseases. One C-C chemokine receptor, CCR2, has been identified that mediates in vitro responses to MCP-1 and its close structural homologues. CCR2 has also recently been demonstrated to be a fusion cofactor for several HIV isolates. To investigate the normal physiological function of CCR2, we generated mice with a targeted disruption of the ccr2 gene. Mice deficient for CCR2 developed normally and had no hematopoietic abnormalities. However, ccr2(-/-) mice failed to recruit macrophages in an experimental peritoneal inflammation model. In addition, these mice were unable to clear infection by the intracellular bacteria, Listeria monocytogenes. These results suggest that CCR2 has a nonredundant role as a major mediator of macrophage recruitment and host defense against bacterial pathogens and that MCP-1 and other CCR2 ligands are effectors of those functions.

Penetration of Listeria monocytogenes in mice infected by the oral route

In this study, it is suggested that the Peyer's patches are the most important point of entry of Listeria monocytogenes in the host after subclinical infection by the oral route. Microbiological, histopathological and ultrastructural evidence of infection was obtained in mice inoculated with a sublethal dose of 10(9) cfu. No mortality was observed. L. monocytogenes was isolated from the mesenteric lymph nodes from 6 hours post infection (hpi) through day 7 p.i. and from the liver and spleen from 24 h p.i. until days 5 and 7 p.i. respectively. Lesions were mainly restricted to the dome area of Peyer's patches and consisted of a purulent to pyogranulomatous inflammatory reaction. Scarce and minor lesions were also observed in the mesenteric lymph nodes and liver. L. monocytogenes was detected by immunohistochemistry in the Peyer's patches from 12 h p. i. to day 6 p.i. Ultrastructural study of Peyer's patches showed that the majority of Listeria cells were free within the cytoplasm of neutrophils and macrophages, not surrounded by a phagosomal membrane, and some of them were dividing.

Prolonged persistence of Listeria monocytogenes after intragastric infection in corticosteroid-treated mice

In an attempt to obtain a model more closely resembling natural listeriosis, we studied the course of infection in mice inoculated by the intragastric route with Listeria monocytogenes. Corticosteroid-treated, and untreated mice both developed subclinical infection without mortality, but faecal shedding and persistence of bacteria in the liver and spleen of corticosteroid-treated mice were significantly more protracted than in untreated mice. Untreated mice cleared the bacteria from their livers and spleens by day 5 postinfection (PI), whereas treated mice did not clear the organisms until 8-9 days PI. In untreated mice faecal shedding lasted 5 days PI, whereas in treated mice the organisms were recovered at significantly higher levels until day 9 PI. The only intestinal lesions observed were mild pyogranulomatous changes in the dome area of some Peyer's patches in treated mice.

Lymphocyte apoptosis during early phase of Listeria infection in mice

During the acute phase of growth of Listeria monocytogenes in spleen and lymph nodes, the infective foci consist of macrophages and neutrophils accompanied by extensive death of lymphocytes. Many of the lymphocytes die by apoptosis. The lesions are found by 48 hours after infection and can regress with time. Depending on the dose, the infected foci can be restricted to the thymus-dependent areas or can occupy the entire lymphoid tissue. The Listeria in the lesions are primarily found inside macrophages, but a few are extracellular amid cellular debris. Lymphocyte death appears to be an obligatory step in primary Listeria infection, the extent of which is controlled by the early restriction of Listeria growth by the innate cellular system.

CD8alphaalpha T cells in lesions of Listeria monocytogenes-infected beta2m-deficient mice

The beta2-microglobulin (beta2m)-deficient mutant mice lack alphabeta TCR CD8alphabeta T cells. We found markedly impaired granuloma formation in Listeria monocytogenes-infected beta2m-/- mice. Abundant CD8alphaalpha T cells were identified in loosely structured infiltrative liver lesions. Microfluorescence analysis disclosed that these CD8alphaalpha T cells expressed mostly the gammadelta TCR. CD8alphaalpha T cells were also found in the spleen of Listeria-infected beta2m-/- mice. These data provide first evidence for CD8alphaalpha T cells in listerial lesions of beta2m-/- mice.

Impaired macrophage listericidal and cytokine activities are responsible for the rapid death of Listeria monocytogenes-infected IFN-gamma receptor-deficient mice

IFN-gamma receptor-deficient (IFN-gammaR -/-) mice were used to study the innate immune responses during infection with Listeria monocytogenes. Mutant mice were unable to limit bacterial growth and died of sepsis even with an infection dose of 70 Listeria. At day 2, they showed an exacerbated listeriosis and mice succumbed to infection before the onset of an effective specific immunity, demonstrating a defective innate immunity. Recruitment and extravasation of phagocytic cells to infected organs was present and dominated by neutrophils. However, during the early course of infection, mutant mice responded by an elevated inflammatory type 1 cytokine response, as determined by IL-12, IFN-gamma, TNF-alpha, and IL-1alpha-specific RNA expression. Induction of inducible nitric oxide synthase was present and also increased in mutant mice. Interestingly, IFN-gammaR -/- neutrophils expressed substantial TNF-alpha- and IL-1alpha-specific RNA, suggesting a substantial contribution in the overall inflammatory cytokine response. In contrast, IFN-gammaR -/- macrophages showed reduced MHC class II surface expression levels and impaired TNF-alpha and IL-1alpha but normal IL-6 production after restimulation with heat-killed L. monocytogenes. Moreover, IFN-gammaR -/- macrophages showed defective listericidal activities. In contrast to normal macrophages, Listeria escaped rapidly from the phagosome in IFN-gammaR -/- macrophages to the cytoplasm, where they productively survived. In conclusion, these data suggest that IFN-gammaR signaling activates yet unknown functions in macrophages, preventing Listeria-induced escape from the phagosome and consequent killing of the invader. Together with the impaired cytokine responses, these macrophage defects seem to be responsible for the dramatic susceptibility during innate immunity, whereas predominant neutrophil responses mediate limited protective role in mutant mice.

Listeria monocytogenes infection of cultured endothelial cells stimulates neutrophil adhesion and adhesion molecule expression

Microbial infection of the endothelium with the resultant up-regulation of adhesion molecule expression and stimulated leukocyte adhesion to endothelial cells can promote an inflammatory response. Previous work demonstrated that Listeria monocytogenes can replicate within cultured endothelial cells; thus, we tested whether L. monocytogenes infection of HUVEC stimulated an inflammatory phenotype on these cells. Infection with 10(4) CFU of bacteria increased neutrophil adhesion to HUVEC 40-fold and up-regulated E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 expression. Approximately 80% of neutrophil adhesion to infected HUVEC was blocked by anti-E-selectin mAb, 35% was blocked by anti-CD18 mAb, and anti-vascular cell adhesion molecule-1 mAb was without effect. Microscopy of infected HUVEC monolayers showed that neutrophils bound to infected and uninfected cells and that infected and uninfected HUVEC expressed E-selectin. Interestingly, uninfected HUVEC that bound neutrophils or expressed E-selectin typically were adjacent to infected cells. However, infected monolayers did not produce soluble factors that stimulated E-selectin expression on uninfected cells. Nuclear translocation of the p65 subunit of the transcription factor NF-kappaB accompanied the HUVEC response, and hemolysin secretion appeared critical for stimulating HUVEC. These studies show that L. monocytogenes infection stimulates up-regulation of adhesion molecule expression on endothelial cells, resulting in neutrophil adhesion to them. This response includes induction of an inflammatory phenotype on uninfected cells and may be triggered by listeriolysin O-mediated activation of host response mechanisms. Additionally, cell-to-cell spread of L. monocytogenes throughout the monolayer, without stimulating secondarily infected endothelial cells for neutrophil adhesion, is a possible means of immune avoidance.

Cell wall-deficient forms (L-forms) of Listeria monocytogenes in experimentally infected rats

Experimental infections were induced with different bacterial forms of Listeria monocytogenes: parental (S-forms), protoplastic (L-forms) and combined inoculum of both forms by i.p. injection of rats. The parental bacterial forms (S-forms) were isolated up to 7 days after challenge from the peritoneal cavity and the liver, while the L-forms were isolated up to 60 days from the peritoneal cavity. Continuous adhesion of L-forms on the peritoneal macrophage surface was found by scanning-electron microscopy. Erythrocyte and leucocyte count as well as some clinical chemistry parameters were measured during infections. They showed different dynamics in the three experimental groups. Histomorphological changes in the liver (microabscesses and mononuclear cellular granulomas) of infected animals were observed. They were less intensive and appeared later in rats infected with L-forms. The experiments demonstrated that infections caused by parental bacterial forms and by combined inoculum took an acute course, while the infection caused by L-forms could be distinguished as a prolonged and persistent one.

[Listeriosis in the third trimester of pregnancy]

A case of fatal intrauterine listeriosis in the third trimester of pregnancy is described. The patient presented with preterm labour and was delivered by emergency caesarean section on suspicion of foetal distress. The child was stillborn. The diagnosis was based on specific histopathological findings in the foetus and the placenta.

Musical auditory hallucinosis from Listeria rhombencephalitis

BACKGROUND

Complex auditory hallucinations have rarely been reported in cases of brainstem stroke or tumor.

METHOD

Case study.

RESULTS

A patient with acute Listeria rhombencephalitis complained of formed musical auditory hallucinations on the side of recent sensorineural deafness. MRI revealed an abscess in the middle cerebellar peduncule with extensive surrounding edema.

CONCLUSIONS

Disruption of brainstem auditory pathways may cause complex auditory hallucinations. Potential pathogenetic mechanisms are discussed and a diagnostic approach is proposed.

Abscess formation in Listeria monocytogenes-infected gamma delta T cell deficient mouse mutants involves alpha beta T cells

Although mutant mice lacking gamma delta T cells resolve Listeria monocytogenes infection, extensive abscesses are formed. Manifestation of these inflammatory lesions is prevented by in vivo depletion with monoclonal antibodies of CD4, CD8 or both T cell subsets. We conclude that these inflammatory tissue reactions develop when alpha beta T cells of either CD4 or CD8 phenotype are released from control by gamma delta T cells.

Primary Listeria monocytogenes infection in gestating mice

The facultative intracellular Gram-positive bacterium Listeria monocytogenes is a food-borne pathogen of frequently underestimated importance. Pregnant women represent the high-risk group for L. monocytogenes infection. Abortion, stillbirth or neonatal infection can be the serious outcome of such an infection. Recovery from listeriosis, resistance mechanisms of the host and the effect of L. monocytogenes on fetal development still remain to be fully understood. The results of our experiments showed an increased susceptibility of gestating BALB/c mice to primary L. monocytogenes infection. The duration of listeriosis in gestating animals was almost twice longer than in the control group. Furthermore, it was clearly shown that the detrimental effect of L. monocytogenes on fetal development was more pronounced if the infection was acquired earlier during gestation.

A method to recover, enumerate and identify lymphomyeloid cells present in an inflammatory dermal site: a study in laboratory mice

We describe a new method to recover and study cells present in the dermis of mouse ear at homeostasis or after intradermal injection of disturbing agents (lipopolysaccharide or Listeria monocytogenes). The ears either left untreated or inoculated were handled and processed as culture explants of the dorsal and ventral leaflets, their dermal sides being spread on a buffered medium. Within this medium emigrate/sediment, with different kinetics: neutrophils, mononuclear phagocytes, dendritic leucocytes, T lymphocytes expressing either gamma delta or alpha beta TCRs, and other minor subsets, the identification of which deserves more relevant reagents: they are likely to be NK, mast cells, eosinophils and their local progenitors. All the major subsets were identified through a combination of immunocytochemical and flow cytometry labeling. Two examples illustrating the advantages and limitations of this new method are given: either 1 microgram of LPS or 10(4) Listeria monocytogenes were injected within the ear 48, 24, 12, 6, 3 h before ear explant culture. This ear explant culture has been further compared to the ear sheet treatment with collagenase/disease for three cell populations, the epidermal dendritic leucocytes, the gamma delta epidermal T cells as well as the alpha beta T cells recirculating within the steady state dermis. This method provides the first evidence of the existence of recirculating T CD4 lymphocytes in the mouse dermis.

Neutrophils are involved in the non-specific resistance to listeriosis induced by mycobacterial infections

A major role has been recently ascribed to the neutrophil in the resistance to infection by Listeria monocytogenes (L. monocytogenes). Here we evaluated whether such neutrophils played a role in the non-specific resistance to listeriosis that develops in hosts infected by mycobacteria. We found that the depletion of neutrophils completely abrogated the resistance conferred by the activated macrophages induced during the mycobacterial infection. The lack of killing by activated Kupffer cells and the visualization of bacteria proliferating inside peritoneal macrophages in neutrophil-depleted mice allowed us to postulate a role for the cooperation between neutrophils and macrophages in the killing of L. monocytogenes. We also found listerial proliferation in hepatocytes of neutrophil-depleted, mycobacteria-infected mice showing that the neutrophils may be involved in the control of listeria infection of parenchymal cells.

Protein p60 participates in intestinal host invasion by Listeria monocytogenes

The role of p60 in intestinal invasion by Listeria monocytogenes was assessed after oral infection of mice with the p60 low-expressing mutant RIII, or with anti-p60 antibody coated wild-type EGD. Invasion by L. monocytogenes RIII bacteria has been unimpaired suggesting that a low density of p60 suffices for entry. Up to 24 h post infection (p.i.), intestinal penetration by L. monocytogenes EGD bacteria was markedly reduced by coating with anti-p60 antibodies. In histological sections, anti-p60 antibody-treated L. monocytogenes EGD, but not uncoated listeriae were still detectable 24 h p.i. at the apical surface of enterocytes in the intestine. We conclude that p60 contributes to host invasion through the natural port of listerial entry, the intestinal epithelium.

The effect of lead on the bone marrow stem cells of mice infected with Listeria monocytogenes

We investigated the effects of lead exposure on the growth and differentiation of bone marrow hematopoietic cells, the so called colony-forming cells, in normal and Listeria monocytogenes infected mice (resistant and susceptible strains). We also studied the effects of lead on the serum colony-stimulating activity (CSA), as well as on the survival of the mice after the infection. The doses of lead acetate were 13, 130 and 1300 ppm for 10, 30 and 70 d. At the end of this dosing, mice were infected with Listeria monocytogenes and killed 24, 48 or 72 h after inoculation of the bacteria. A dose-response suppressive effect of lead was observed in both strains in the 3 periods studied. However, in the resistant strain of mice the suppressive effects were overcome 48 h after the administration of the bacteria, whereas in the susceptible mice the suppressive effect of the infection was evident in all 3 time periods. The administration of lead caused no changes in serum hematopoietic growth factors, thus suggesting this metal acts by direct action on the myelopoietic cells. A significant decrease in host resistance, as measured by the mortality rate, was found when both strains of mice were challenged with sub-lethal doses of Listeria monocytogenes. Lethality was determined for a period of 10 d after dosing with 1300 ppm lead for 30 d.

Effects of ultraviolet-B exposure on the resistance to Listeria monocytogenes in the rat

A rat infection model using the bacterial pathogen Listeria monocytogenes was employed to analyze the immunosuppressive activity of UVB radiation. Rats were exposed to suberythemal doses of UVB radiation for 5 or 7 consecutive days, using Kromayer or FS40 lamps respectively. Subsequently, the rats were infected subcutaneously or intravenously with Listeria. Exposure to UVB resulted in an increased number of bacteria in the spleen 4 days after infection. Listeria-specific lymphocyte proliferation assays as well as delayed-type hypersensitivity reactions demonstrated that T cell-mediated immunity to Listeria was impaired by UVB as measured 4 and 8 days after infection. In addition, UVB exposure decreased phagocytotic activity of peripheral blood macrophages. This study demonstrated that suberythemal doses of UVB radiation caused a delay in the clearance of Listeria bacteria from the spleen of the rats and that this was probably caused by impaired nonspecific phagocytosis of Listeria by macrophages in addition to an impaired activity of Listeria-specific T cells.

Studies on the cell tropism of Listeria monocytogenes in ovine fetal brain cell cultures

The uptake of Listeria monocytogenes by cells in primary dissociated brain cell cultures prepared from ovine fetuses at approximately 50 to 60 days of gestation was studied using a sequential double immunofluorescence technique with antibodies against cell type-specific markers and the bacterial pathogen. Cell cultures were inoculated with bacteria at day 4, 8, and 15 in vitro. Listeria monocytogenes was predominately internalized by CD68-positive macrophages, followed by astrocytes, fibronectin-expressing cells, and neurons. An uptake of the bacterium by galactocerebroside (GC)-positive oligodendrocytes, which were first detected at day 15 in vitro, did not occur. Although a tropism for neurons was not observed, the susceptibility of neurons for infection with Listeria monocytogenes is in accordance with the supposed intraaxonal migration of the bacterium in the pathogenesis of focal brain stem encephalitis. The pattern of the infection rates of ovine brain cell types was similar to that shown in murine fetal brain cell cultures, indicating that there is no species-specific brain cell tropism of the bacterium.

Liver abscesses due to Listeria monocytogenes

Involvement of the liver in cases of Listeria monocytogenes is uncommon. We report a case of hepatitis due to L. monocytogenes, with a pathological finding of multiple abscesses. Blood cultures yielded L. monocytogenes. The patient died a few days after admission.

Listeria monocytogenes induces apoptosis of infected hepatocytes

Infection with blood-borne Listeria monocytogenes results in their early uptake by the liver. Foci of hepatocytes become heavily infected and develop into microabscesses. Infection results in apoptosis of the hepatocytes. This is particularly evident in the edge of the microabscess, where hepatocytes are not yet destroyed by the neutrophil. It is also apparent when neutrophils are depleted from the circulation. Infection of hepatocytes in culture induces their death by apoptosis with the release of neutrophil chemoattractants. Cytokines do not reduce the multiplication of Listeria in cultured hepatocytes. This study calls attention to an early program of inflammation induced in infected cells that are unresponsive to cytokines.

High level monocyte chemoattractant protein-1 expression in transgenic mice increases their susceptibility to intracellular pathogens

We have constructed transgenic mice in which the mouse mammary tumor virus long terminal repeat controls the expression of murine monocyte chemoattractant protein-1 (MCP-1). Several independently derived lines of transgenic mice constitutively expressed MCP-1 protein in a variety of organs. Protein extracts from these organs had substantial in vitro monocyte chemoattractant activity that was neutralized by an anti-MCP-1 Ab, indicating that transgenic MCP-1 protein is biologically active. However, no transgenic mouse at any age displayed monocyte infiltrates in MCP-1-expressing organs. Two transgenic lines had circulating MCP-1 levels of 13 to 26 ng/ml, which is a concentration sufficient to induce maximal monocyte chemotaxis in vitro. These transgenic lines showed a 1 to 1.5 log greater sensitivity to infection with Listeria monocytogenes and Mycobacterium tuberculosis. A third transgenic line had lower serum levels of MCP-1 and was resistant to L. monocytogenes. The results suggest that this transgenic model is one of monocyte nonresponsiveness to locally produced MCP-1 due to either receptor desensitization or neutralization of a chemoattractant gradient by high systemic concentrations of MCP-1. Regardless of the mechanism, the data indicate that constitutively high levels of MCP-1 expression do not induce monocytic infiltrates, and that MCP-1 is involved in the host response to intracellular pathogens.

Listeria monocytogenes infection in pregnant mice: abnormalities in the function of non-adherent accessory light density dendritic cells

Pregnant A/J mice were found to be more susceptible to the lethal effect of Listeria monocytogenes bacteria than virgin females. However, during the first four days of post-infection there was no difference in the elimination of Listeria from the spleens of pregnant and virgin mice. This suggests that the increase in the susceptibility of pregnant mice to pathogenic activity of L. monocytogenes was related to the diminution in Listeria-specific cellular reactions. Indeed, we found that non-adherent light density dendritic cells (DCs) from pregnant mice showed a marked reduction in the ability to form clusters with L. monocytogenes immune T lymphocytes and it is known that cell cluster formation between antigen presenting cells (APC) and responding T cells is required for antigen recognition as well as for cell proliferation. DCs from pregnant mice also demonstrated the decrease and an instability in the expression of H-2 class II molecules which play a crucial role in the recognition of exogenous antigens. The abnormalities demonstrated in the function of the light density dendritic cells from the spleens of pregnant mice could compromise cellular reactions to L. monocytogenes bacteria possibly resulting in increased susceptibility of pregnant mice to experimental listeriosis.

Phenotypic characterization of the cells of the inflammatory response in ovine encephalitic listeriosis

The brainstem (pons cerebri and medulla oblongata) of 22 sheep aged between 6 months and 3 years which had developed clinical signs of central nervous system dysfunction were examined. Histopathological changes characterized by microabscesses, focal gliosis and perivascular cuffing compatible with natural infection with Listeria monocytogenes were present. The brains were examined by lectin histochemistry and immunohistochemistry with markers for T lymphocytes (CD4+ and CD8+ subsets), B lymphocytes, mononuclear phagocytes (including macrophages, ramified microglia, activated microglia and amoeboid microglia), astroglia and L. monocytogenes. These methods allowed semiquantitative analyses of the frequency of the different cell types in the brain lesions. The distribution of listerial antigen in the lesions was variable but always sparse. Mononuclear phagocytes and neutrophils appeared to be the most numerous inflammatory cells in the affected areas of the brainstem. T lymphocytes (CD8+ and CD4+ subsets) and B lymphocytes also played a part in the inflammatory process, in addition to activated astrocytes.

Bacterial infection of the testis leading to autoaggressive immunity triggers apparently opposed responses of alpha beta and gamma delta T cells

The mechanisms that lead to the breakdown of self-tolerance and testis-specific immune reactivity in the murine orchitis model are understood only in part. We investigated the histopathologic and immunologic consequences of a unilateral bacterial (Listeria monocytogenes) infection of the testis. Both infected and contralateral sides of this bilateral organ suffered severe inflammatory responses despite a conspicuous absence of bacteria in the contralateral tissue. Also, in both testicles, T cell populations increased, involving both alpha beta and gamma delta T cell subsets. Concomitant with the bilateral orchitis, testis-specific delayed type hypersensitivity and Ab responses developed. Ab depletion experiments indicated that in this orchitis model, as in others, alpha beta T cells are initiators of the autoaggressive reactivity. In contrast, Ab depletion of gamma delta T cells accelerated the inflammatory response in both testicles, suggesting a regulatory role for this type of T cells in both infection-induced and autoimmune orchitis.

iactA of Listeria ivanovii, although distantly related to Listeria monocytogenes actA, restores actin tail formation in an L. monocytogenes actA mutant

A gene homologous to the actA gene of Listeria monocytogenes was cloned from Listeria ivanovii (strain CLIP257) by chromosome walking starting from the ilo gene that encodes the pore-forming toxin ivanolysin. The nucleotide sequence revealed that this gene, named iactA, encodes a protein of 1,044 amino acids (IactA) comprising a central region with seven highly conserved tandem proline-rich repeats of 47 amino acids. Although IactA and ActA share an overall similar structure, these two proteins are only distantly related. Like ActA, IactA migrates aberrantly on sodium dodecyl sulfate gels. When expressed in an L. monocytogenes actA deletion mutant strain, iactA restored actin polymerization.

Bacteremia is required for invasion of the murine central nervous system by Listeria monocytogenes

The ability of the facultative intracellular pathogen Listeria monocytogenes to penetrate the central nervous system (CNS) was studied by following the kinetics of brain invasion and histological lesions during an acute intravenous (i.v.) infection in the mouse. CNS invasion occurred during the early phase of infection and produced severe meningoencephalitis characterized by multiple granulomatous foci predominantly located in the brainstem and associated with diffuse meningitis and an intense inflammatory reaction involving the choroid plexuses. Bacterial counts in the brain could reach 10(4.5)-10(5.8) by day 5 of infection with 1-2 x 10(6) bacteria i.v., depending upon the bacterial strain used. It was found that CNS invasion was highly dependent upon the level and the duration of bacteremia, thus indicating that persistent bacteremia is essential to induce meningoencephalitis to L. monocytogenes.