Protective immunity and granuloma formation are mediated by two distinct tumor necrosis factor alpha- and gamma interferon-dependent T cell-phagocyte interactions in murine listeriosis: dissociation on the basis of phagocyte adhesion mechanisms

Human Listeriosis

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that can cause severe invasive infections upon ingestion with contaminated food. Clinically, listerial disease, or listeriosis, most often presents as bacteremia, meningitis or meningoencephalitis, and pregnancy-associated infections manifesting as miscarriage or neonatal sepsis. Invasive listeriosis is life-threatening and a main cause of foodborne illness leading to hospital admissions in Western countries. Sources of contamination can be identified through international surveillance systems for foodborne bacteria and strains' genetic data sharing. Large-scale whole genome studies have increased our knowledge on the diversity and evolution of L. monocytogenes, while recent pathophysiological investigations have improved our mechanistic understanding of listeriosis. In this article, we present an overview of human listeriosis with particular focus on relevant features of the causative bacterium, epidemiology, risk groups, pathogenesis, clinical manifestations, and treatment and prevention.

Eosinophils and mast cells in leishmaniasis

Leishmania spp. are parasitic protozoa endemic in tropical and subtropical regions and the causative agent of leishmaniasis, a collection of syndromes whose clinical manifestations vary according to host and pathogen factors. Leishmania spp. are inoculated into the mammalian host by the bite of an infected sand fly, whereupon they are taken up by phagocytosis, convert into the replicative amastigote stage within macrophages, reproduce, spread to new macrophages and cause disease manifestations. A curative response against leishmaniasis depends in the classical activation of macrophages and the IL-12-dependent onset of an adaptive type 1 response characterized by the production of IFN-γ. Emerging evidence suggests that neutrophils, dendritic cells and other immune cells can serve as either temporary or stable hosts for Leishmania spp. Furthermore, it is becoming apparent that the initial interactions of the parasite with resident or early recruited immune cells can shape both the macrophage response and the type of adaptive immune response being induced. In this review, we compile a growing number of studies demonstrating how the earliest interactions of Leishmania spp. with eosinophils and mast cells influence the macrophage response to infection and the development of the adaptive immune response, hence, determining the ultimate outcome of infection.

Septicaemia models using Streptococcus pneumoniae and Listeria monocytogenes: understanding the role of complement properdin

Streptococcus pneumoniae and Listeria monocytogenes, pathogens which can cause severe infectious disease in human, were used to infect properdin-deficient and wildtype mice. The aim was to deduce a role for properdin, positive regulator of the alternative pathway of complement activation, by comparing and contrasting the immune response of the two genotypes in vivo. We show that properdin-deficient and wildtype mice mounted antipneumococcal serotype-specific IgM antibodies, which were protective. Properdin-deficient mice, however, had increased survival in the model of streptococcal pneumonia and sepsis. Low activity of the classical pathway of complement and modulation of FcγR2b expression appear to be pathogenically involved. In listeriosis, however, properdin-deficient mice had reduced survival and a dendritic cell population that was impaired in maturation and activity. In vitro analyses of splenocytes and bone marrow-derived myeloid cells support the view that the opposing outcomes of properdin-deficient and wildtype mice in these two infection models is likely to be due to a skewing of macrophage activity to an M2 phenotype in the properdin-deficient mice. The phenotypes observed thus appear to reflect the extent to which M2- or M1-polarised macrophages are involved in the immune responses to S. pneumoniae and L. monocytogenes. We conclude that properdin controls the strength of immune responses by affecting humoral as well as cellular phenotypes during acute bacterial infection and ensuing inflammation.

Protective immunity to Listeria monocytogenes infection mediated by recombinant Listeria innocua harboring the VGC locus

In this study we propose a novel bacterial vaccine strategy where non-pathogenic bacteria are complemented with traits desirable for the induction of protective immunity. To illustrate the proof of principle of this novel vaccination strategy, we use the model organism of intracellular immunity Listeria. We introduced a, low copy number BAC-plasmid harbouring the virulence gene cluster (vgc) of L. monocytogenes (Lm) into the non-pathogenic L. innocua (L.inn) strain and examined for its ability to induce protective cellular immunity. The resulting strain (L.inn::vgc) was attenuated for virulence in vivo and showed a strongly reduced host detrimental inflammatory response compared to Lm. Like Lm, L.inn::vgc induced the production of Type I Interferon's and protection was mediated by Listeria-specific CD8⁺ T cells. Rational vaccine design whereby avirulent strains are equipped with the capabilities to induce protection but lack detrimental inflammatory effects offer great promise towards future studies using non-pathogenic bacteria as vectors for vaccination.

[Systemic granulomatosis of infectious origin]

PURPOSE

Granulomatous diseases are defined by specific histological features, following the local recruitment of macrophages and lymphocytes. Many infections can lead to the development of granuloma.

CURRENT KNOWLEDGE AND KEY POINTS

Microorganisms responsible for granuloma include mainly mycobacteria, many viral and fungal species, as well as schistosoma in endemic areas. Nevertheless, almost all microorganisms can lead to granuloma, especially if their clearance needs macrophages pathway. New immunosuppressive drugs such as tumor necrosis factor antagonists are associated with a high risk of infectious granulomatous complications. All patients with granuloma must be carefully screened to find a potential underlying infection, since an immunosuppressive therapy could be otherwise considered. We here review the general diagnostic process with a specific glance to the main organs.

FUTURE PROSPECTS AND PROJECTS

Without clinical or epidemiological clue, diagnosis can be very tedious. New molecular tools now assist classical microbiological and histological techniques. Their specificity and sensitivity have recently been better characterized, and their use will probably increase in the near future for the diagnosis of infectious granuloma. They may also lead to discover new infectious aetiologies of granulomatous diseases formerly considered as idiopathic. We describe here the main microorganisms that can be responsible for granuloma, with a specific focus on the use of new diagnostic tools.

IDO-expressing regulatory dendritic cells in cancer and chronic infection

Immune evasion and T cell tolerance induction have been associated both with malignant disease and chronic infection. In recent years, increasing evidence has been accumulated that antigen-presenting cells such as dendritic cells (DC) play a major role in immune regulation. They are not only involved in the induction of immunity but also can inhibit immune responses. Interesting parallels for major molecular mechanisms involved in turning DC from stimulatory to regulatory cells have been uncovered between malignant disease and chronic infection. Apparently, not only inhibitory cytokines such as IL-10 seem to play a role, but also metabolic mechanisms dysregulating tryptophan metabolism, thereby, leading to inhibition of T cells and pathogens. We focus here on recent findings establishing the tryptophan catabolizing enzyme indoleamine-pyrrole 2,3 dioxygenase (IDO) as a central feature of DC with regulatory function both in cancer and chronic infection. Induction of enzymatically active IDO can be triggered by various soluble and membrane-bound factors, and in general, require interferon (IFN) signaling. In addition, based on the most recently established link between tumor necrosis factor alpha (TNFalpha), prostaglandin E2 and IDO, a new model of regulation of IDO in context of cancer and infection is proposed. In light of the increasing use of anti-TNFalpha drugs, these findings are also of great interest to the clinician scientist.

Influence of Yersinia pseudotuberculosis outer proteins (Yops) on interleukin-12, tumor necrosis factor alpha and nitric oxide production by peritoneal macrophages

An essential key to pathogenicity in Yersinia is the presence of a 70 kb plasmid (pYV) which encodes a type-III secretion system and several virulence outer proteins whose main function is to enable the bacteria to survive in the host. Thus, a specific immune response is needed in which cytokines are engaged. The aim of this study was to assess the influence of Yersinia outer proteins (Yops) released by Yersinia pseudotuberculosis on the production of the proinflammatory cytokines, interleukin-12 (IL-12), and tumor necrosis factor alpha (TNF-alpha), and nitric oxide (NO) by murine peritoneal macrophages. To this end, female Swiss mice were infected intravenously with wild-type Y. pseudotuberculosis or with mutant strains unable to secrete specific Yops (YopE, YopH, YopJ, YopM, and YpkA). On the 7th, 14th, 21st, and 28th days after infection, the animals were sacrificed and the cytokines and NO were assayed in the peritoneal macrophages culture supernatants. A fall in NO production was observed during the course of infection with all the strains tested, though during the infection with the strains that did not secrete YopE and YopH, the suppression occurred later. There was, in general, an unchanged or sometimes increased production of TNF-alpha between the 7th and the 21st day after infection, compared to the control group, followed by an abrupt decrease on the last day of infection. The IL-12 production was also suppressed during the infection, with most of the strains tested, except with those that did not secrete YopJ and YopE. The results suggest that Yops may suppress IL-12, TNF-alpha, and NO production and that the most important proteins involved in this suppression are YopE and YopH.

Infections in patients with inherited defects in phagocytic function

Patients with defects in phagocytic function are predisposed to intracellular microorganisms and typically have early dissemination of the infection. Recognition of the underlying disorder and aggressive antimicrobial therapy has been beneficial for the patients. Improved understanding of the pathophysiology has also affected patient management by allowing specific, targeted immunomodulatory intervention. The disorders described in this review are not common but have had a significant impact on our understanding of the role of phagocytic cells in host defense. Conversely, understanding the role of the neutrophil and macrophage in infection has benefited not just the patients described in this review but also other patients with similar disease processes.

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.

Role of CD4 T cell help and costimulation in CD8 T cell responses during Listeria monocytogenes infection

CD4 T cells are known to assist the CD8 T cell response by activating APC via CD40-CD40 ligand (L) interactions. However, recent data have shown that bacterial products can directly activate APC through Toll-like receptors, resulting in up-regulation of costimulatory molecules necessary for the efficient priming of naive T cells. It remains unclear what role CD4 T cell help and various costimulation pathways play in the development of CD8 T cell responses during bacterial infection. In this study, we examined these questions using an intracellular bacterium, Listeria monocytogenes, as a model of infection. In CD4 T cell-depleted, CD4(-/-), and MHC class II(-/-) mice, L. monocytogenes infection induced CD8 T cell activation and primed epitope-specific CD8 T cells to levels commensurate with those in normal C57BL/6 mice. Furthermore, these epitope-specific CD8 T cells established long-term memory in CD4(-/-) mice that was capable of mounting a protective recall response. In vitro analysis showed that L. monocytogenes directly stimulated the activation and maturation of murine dendritic cells. The CD8 T cell response to L. monocytogenes was normal in CD40L(-/-) mice but defective in CD28(-/-) and CD137L(-/-) mice. These data show that in situations where infectious agents or immunogens can directly activate APC, CD8 T cell responses are less dependent on CD4 T cell help via the CD40-CD40L pathway but involve costimulation through CD137-CD137L and B7-CD28 interactions.

“Emergency” granulopoiesis in G-CSF–deficient mice in response to Candida albicans infection

Granulocyte colony-stimulating factor (G-CSF) is a glycoprotein believed to play an important role in regulating granulopoiesis both at steady state and during an “emergency” situation. Generation of G-CSF and G-CSF receptor–deficient mice by gene targeting has demonstrated unequivocally the importance of G-CSF in the regulation of baseline granulopoiesis. This study attempted to define the physiologic role of G-CSF during an emergency situation by challenging a cohort of wild-type and G-CSF–deficient mice with Candida albicans. Interestingly, after infection, G-CSF–deficient mice developed an absolute neutrophilia that was observed both in blood and bone marrow. In addition, 3 days after Candida infection increased numbers of granulocyte-macrophage (GM) and macrophage (M) progenitors were observed in the bone marrow of G-CSF–deficient mice. Of the cytokines surveyed, interleukin (IL)-6 levels in serum were elevated; interestingly, levels of IL-6 were higher and more sustained in G-CSF–deficient mice infected with C albicans than similarly infected wild-type mice. Despite the higher levels of serum IL-6, this cytokine is dispensable for the observed neutrophilia because candida-infected IL-6–deficient mice, or mice simultaneously deficient in G-CSF and IL-6, developed neutrophilia. Similarly, mice lacking both G-CSF and GM-CSF developed absolute neutrophilia and had elevated numbers of GM and M progenitors in the bone marrow; thus, G-CSF and GM-CSF are dispensable for promoting the emergency response to candidal infection.

“Emergency” granulopoiesis in G-CSF–deficient mice in response to Candida albicans infection

Granulocyte colony-stimulating factor (G-CSF) is a glycoprotein believed to play an important role in regulating granulopoiesis both at steady state and during an “emergency” situation. Generation of G-CSF and G-CSF receptor–deficient mice by gene targeting has demonstrated unequivocally the importance of G-CSF in the regulation of baseline granulopoiesis. This study attempted to define the physiologic role of G-CSF during an emergency situation by challenging a cohort of wild-type and G-CSF–deficient mice with Candida albicans. Interestingly, after infection, G-CSF–deficient mice developed an absolute neutrophilia that was observed both in blood and bone marrow. In addition, 3 days after Candida infection increased numbers of granulocyte-macrophage (GM) and macrophage (M) progenitors were observed in the bone marrow of G-CSF–deficient mice. Of the cytokines surveyed, interleukin (IL)-6 levels in serum were elevated; interestingly, levels of IL-6 were higher and more sustained in G-CSF–deficient mice infected with C albicans than similarly infected wild-type mice. Despite the higher levels of serum IL-6, this cytokine is dispensable for the observed neutrophilia because candida-infected IL-6–deficient mice, or mice simultaneously deficient in G-CSF and IL-6, developed neutrophilia. Similarly, mice lacking both G-CSF and GM-CSF developed absolute neutrophilia and had elevated numbers of GM and M progenitors in the bone marrow; thus, G-CSF and GM-CSF are dispensable for promoting the emergency response to candidal infection.

Altered Intestinal Immune System but Normal Antibacterial Resistance in the Absence of P-Selectin and ICAM-1

ICAM-1 and P-selectin are adhesion molecules that regulate leukocyte migration, extravasation to inflammatory sites, and other immune cell interactions. T cell-mediated resistance against acute infection with Listeria monocytogenes and chronic infection with Mycobacterium bovis Calmette-Guérin bacillus was investigated in mutant mice lacking P-selectin and/or ICAM-1. Mice deficient in P-selectin (Psel−/−), ICAM-1 (ICAM−/−), or the combination of both (Psel−/− × ICAM−/−) showed normal bacterial clearance, comparable delayed-type hypersensitivity reactions, and equivalent memory T cell responses. Additionally, the distribution of αβ vs γδ T lymphocyte populations was examined. Normal lymphocyte distributions were noted in thymus, spleen, and blood, whereas mutant mice showed marked alterations in the intestinal intraepithelial (i-IEL) and lamina propria lymphocytes. Differences in i-IEL populations were reflected functionally by differential lytic activities and cytokine productions of i-IEL populations from mutant mice. Despite these changes within the mucosal immune system of mutant mice, their resistance against oral infection with L. monocytogenes was apparently unimpaired. These findings demonstrate that P-selectin and ICAM-1 are critically involved in the shaping of lymphocyte populations of the gut but have only a minor influence on systemic and regional host defense against intracellular bacteria.

Cytokines in the induction and expression of T-cell-mediated granuloma formation and protection in the murine model of listeriosis

Lymphocyte-mediated inflammation is a hallmark of autoimmune diseases, such as multiple sclerosis. Crohn's disease, rheumatoid arthritis and sarcoidosis. However, this type of inflammation probably developed under evolutionary pressure from pathogenic microorganisms, such as mycobacteria and other intracellular infective agents. One such pathogen, the gram-positive bacterium Listeria monocytogenes (L. monocytogenes), induces a cascade of tissue alterations that ultimately results in the eradication of the bacteria associated with a granulomatous response. Consequently, murine listeriosis has been established as a model to analyze not only T-cell-dependent antibacterial protection but also T-cell-mediated mononuclear inflammation in parenchymal organs. Extensive studies of the molecular basis of the latter phenomenon led to the conclusion that the most decisive step from non-specific microabscess formation to granulomatous inflammation is the activation of non-specifically invading CD4+ T cells, which results in high local concentrations of TNF-alpha and IFN-gamma in the presence of IL-2. This in turn induces CD11b-independent mechanisms of intraparenchymal monocyte accumulation. Because any attempt to neutralize the effects of TNF-alpha and IFN-gamma to modulate T-cell-mediated inflammation will also dramatically decrease host resistance, other anti-inflammatory strategies based on the modulation of TNF-alpha and IFN-gamma-induced mechanisms of monocyte accumulation must be developed. Recalling the classical work by Dienes & Schoenheit on the induction of bacterial allergies (1), the cytokine phenotype of granuloma formation also has implications as regards the most potent adjuvant environment for the development of a T-cell response. The murine listeriosis model is the basis for all conclusions in this article on the role of cytokines in the induction and expression of T-cell-mediated inflammation and, as we will show, promises to yield still more insights into the rational design of vaccines.

Listeria monocytogenes infection in mice treated with pentoxifylline

The course of L. monocytogenes infection was followed in mice treated with pentoxifylline (POF), a known inhibitor of endogenous tumor necrosis factor (TNF) formation. Administration of POF caused a delay in L. monocytogenes elimination which was probably related to a reduction the listericidal activity of macrophages and to an attenuation of delayed type hypersensitivity (DTH) to Listeria antigens. In spite of this, some POF-treated mice were protected from lethal effects of virulent L. monocytogenes bacteria.

Cytokine gene expression in immune mice reinfected with Mycoplasma pneumoniae: the role of T cell subsets in aggravating the inflammatory response

Cytokine gene expression was examined by qualitative and semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) in the lungs of Mycoplasma pneumoniae infected immune C57BL/6 mice depleted of either CD4+, CD8+ or both CD4+ and CD8+ T cells. Immediately after M. pneumoniae reinfection of control immune mice, mRNAs for TNF-alpha, IFN-gamma, IL-1 beta, IL-6, IL-2 and IL-2 receptor were promptly detected in the lungs. In animals depleted of CD4+ T cells, mRNA expression for IL-2, IL-2 receptor and IFN-gamma were completely abrogated and mRNA expression for TNF-alpha, IL-1 beta and IL-6 were reduced by 10- to 100-fold. In mice depleted of CD8+ T cells, mRNA expression for IL-2 and the IL-2 receptor was also undetectable, while mRNA for TNF-alpha, IL-1 beta and IL-6 were only marginally decreased. Histological evaluation of the infected lungs performed in parallel revealed dense mononuclear infiltrations around small bronchi and small blood vessels in control reinfected mice. In contrast, in CD4+ T cell-depleted mice, these focal accumulation of lung tissue infiltrating cells were found to be greatly reduced. The data indicate that the inflammatory response in lung tissue thought to be mainly responsible for Mycoplasma pneumoniae disease is associated with an increased level and a prolonged expression of proinflammatory cytokines due to CD4+ lung infiltrating T cells.

Tumour necrosis factor, but not interferon-gamma, is essential for acquired resistance to Listeria monocytogenes during a secondary infection in mice

Mice with a secondary Listeria monocytogenes infection eliminate the bacteria much faster and more efficiently from their organs than mice with a primary infection. During the course of a secondary infection, serum concentrations of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF) are higher than during a primary infection. The aim of the present study was to determine whether these cytokines are involved in the acquired resistance to L. monocytogenes during a secondary infection in mice. In order to neutralize cytokines, alginate-encapsulated cells, which form anti-cytokine monoclonal antibodies, were injected into the nuchal region of mice during a Listeria infection. Mice recovered from a sublethal primary Listeria infection, which acquired cell-mediated immunity, received a subcutaneous injection of anti-IFN-gamma-forming cells, or anti-TNF-forming cells, and 4 days later received an intravenous injection with 10 50% lethal dose (LD50) L. monocytogenes. The number of bacteria recovered from the liver and spleen of immune mice treated with anti-IFN-gamma-forming cells was slightly larger (approximately 1 log10) than that found for immune mice treated with anti-beta-galactosidase-forming cells, called immune control mice. The organs of immune mice treated with anti-TNF-forming cells yielded significantly more (approximately 4 log10) bacteria than those of immune control mice, more than those of immune mice treated with anti-IFN-gamma-forming cells, and comparable numbers to those of non-immune mice. Taken together, these results demonstrate that TNF is essential in acquired resistance to L. monocytogenes during a secondary infection in mice, while IFN-gamma plays a minor role.

Interaction of interleukin-6, tumour necrosis factor and interleukin-1 during Listeria infection

Injected recombinant interleukin-6 (IL-6), tumour necrosis factor (TNF) and IL-1 all protect mice against experimental infection with Listeria monocytogenes. We have therefore investigated the interaction of these cytokines during infection. Treatment with recombinant (r)IL-6 enhanced TNF production by spleen cells during the first 2 days of infection. Anti-TNF antibody could totally abolish the protective effect of rIL-6, while the optimal protective function of TNF could not be achieved when IL-6 was neutralized by anti-IL-6 antibody. IL-1 induced a high level of IL-6 in the serum a short time after its administration, and neutralization of IL-6 totally abolished the protective function of rIL-1. The results thus provide further evidence for the complexity of cytokine interaction.

Sequential involvement of NK cells and CD8+ T cells in granuloma formation of Rhodococcus aurantiacus-infected mice

We investigated the effect of in vivo administration of antibodies against T-cell subsets and natural killer (NK) cells on endogenous gamma interferon (IFN-gamma) production and granuloma formation in Rhodococcus aurantiacus-infected mice. High titers of endogenous IFN-gamma were detected in the extracts of the livers and spleens during 24 hr of the infection, reaching the peak at 8 hr, and the IFN-gamma production was reduced by in vivo administration of anti-NK 1.1 monoclonal antibody (MAb) or antibody against asialo GM1+ cells. Endogenous IFN-gamma declined until 2 days of the infection, then reappeared from 1 week and peaked at 3 weeks. Endogenous IFN-gamma at 1 and 3 weeks was reduced by in vivo administration of anti-CD8 MAb, but not by anti-CD4 MAb or anti-NK 1.1 MAb. Granulomatous lesions in the livers and spleens began to appear from 1 week of the infection and developed in 3 weeks. In vivo administration of rat anti-IFN-gamma MAb reduced the development of granulomas. In addition, granuloma formation was reduced by depletion of NK cells prior to the infection or depletion of CD8+ T cells at 1 week of the infection. Based on these findings, it is presumed that the biphasic production of IFN-gamma is attributable to NK cells in the early phase of the infection and CD8+ T cells in the phase of granuloma formation, and that granuloma formation is regulated by NK cells and CD8+ T cells through the secretion of endogenous IFN-gamma.

Accumulation of gamma/delta T cells in human dysgerminoma and seminoma: roles in autologous tumor killing and granuloma formation

The precise biological function of a subset of T cells bearing gamma/delta T cell receptor (TCR) remains poorly understood. The present study demonstrated the presence of gamma/delta T cells in tumor-infiltrating lymphocytes (TIL) and peripheral blood lymphocytes (PBL) of human patients with dysgerminoma and seminoma when determined by flow cytometry and in situ immunohistochemical staining. TIL contained a high percentage of gamma/delta T cells, ranging from 17.3 to 35.1%. gamma/delta T cells often accumulated within the granulomatous inflammation of tumor tissues. The majority of gamma/delta T cells were V gamma 9/V delta 2+ cells. Freshly isolated PBL, TIL and purified gamma/delta T cells showed autologous tumor killing (ATK) activity, which could be inhibited by monoclonal antibodies (mAb) against V delta 2. Furthermore, two gamma/delta T cell clones established from TIL showed cytotoxicity against autologous and allogeneic dysgerminoma, while they had low or no lytic effects on other cell types including carcinomas of ovary and tumor cell lines such as K562, Daudi and Molt-4. Lysis of autologous tumor cells by the clone was inhibited completely by anti-V delta 2 mAb and partially by mAb against CD3, LFA-1 alpha and ICAM-1 molecules, while it was resistant to anti-CD8, anti-HLA-ABC and anti-HLA-DR mAb. Supernatants produced by gamma/delta T cell clones induced adhesion, aggregation and increased DNA synthesis of monocytes and some characteristics of activated macrophages or epithelioid cells. Tumor necrosis factor (TNF)-alpha, granulocyte-macrophage colony stimulating factor (GM-CSF) and interferon (IFN)-gamma were detected in the supernatants of gamma/delta T cell clone. These results suggest that gamma/delta T cells accumulating in dysgerminoma and seminoma exhibit ATK activity through V gamma 9/delta 2 TCR and these gamma/delta T cells also play a role in the formation of granulomatous inflammation, which is associated with human dysgerminoma and seminoma.

Bacterial evasion of host immune defense: Yersinia enterocolitica encodes a suppressor for tumor necrosis factor alpha expression

The ability of the enteropathogenic Yersinia enterocolitica to survive and proliferate in host tissue depends on a 70-kb plasmid known to encode a number of released Yersinia outer proteins that act as virulence factors by inducing cytotoxicity and inhibiting phagocytosis. This study demonstrates that one of the Yersinia outer proteins, the 41-kDa YopB, suppresses the production of tumor necrosis factor alpha (TNF-alpha), a macrophage-derived cytokine with central roles in the regulation of immune and inflammatory responses to infection. This conclusion is based on several lines of evidence. First, in macrophage cultures, suppression of TNF-alpha mRNA expression was induced by culture supernatant (CS+) of plasmid-bearing yersiniae, the effect which was blocked by anti-YopB antiserum. Second, suppression of TNF-alpha production, but not of interleukin-1 (IL-1) and IL-6, was induced by purified YopB. Third, in Yersinia-infected mice, no increase in TNF-alpha mRNA expression was observed in Peyer's patches, the primary site of bacterial invasion, compared with IL-1 (alpha and beta) mRNA. Finally, administration of anti-YopB antiserum to mice prior to infection with Y. enterocolitica increased TNF activity levels in Peyer's patches and coincided with a reduction in bacterial growth. The results thus provide direct evidence for a secreted eubacterial virulence factor that mediates selective suppression of TNF-alpha production. Although suppression of this single cytokine response is probably not sufficient to facilitate survival of the infecting organisms, the results suggest that suppression of TNF-alpha production by YopB significantly contributes to the evasion of Y. enterocolitica from antibacterial host defense.

Heterogeneity of Kupffer cells and splenic, alveolar, and peritoneal macrophages for the production of TNF, IL-1, and IL-6

Kupffer cells and alveolar, splenic, and peritoneal macrophages from normal rats were incubated for various periods of time in the presence of LPS, and the culture supernatants were analyzed for IL-6, IL-1, and TNF. There was very little difference in the amounts of the cytokines produced by the macrophages when stimulated with 0.01-10 micrograms/ml of LPS. The shapes of the time course curves for the production of the cytokines by the different types of macrophages were generally similar, although only Kupffer cells continued to produce IL-6 throughout the entire incubation period and splenic macrophages showed a lag period in the production of IL-1. Kupffer cells produced more IL-6 than that produced by the other populations of macrophages, and alveolar macrophages produced more IL-1 compared to that produced by splenic cells. Kupffer cells and peritoneal macrophages produced more IL-6 in 24 h than in 6 h of culture, and splenic macrophages produced more IL-1 in 24 compared to 6 h of culture. Alveolar macrophages produced more TNF than that produced by the other populations of cells but only when integrated over the entire incubation period. These results confirm and extend the observed functional heterogeneity of macrophages obtained from different tissues of the same animal. This study and future studies will lead to a better understanding of the role of cytokines in the inflammatory response.

The mRNA-phenotype of granuloma formation: CD4+ T cell-associated cytokine gene expression during primary murine listeriosis

In murine listeriosis, elimination of bacteria and immunity to reinfection critically depend on Thy1+ CD4- cells, while cell-mediated inflammatory phenomena such as DTH and granuloma formation are mostly mediated by CD4+ T cells. In an attempt to correlate T cell phenotype and function with a particular set of cytokines produced, we examined the cytokine gene expression profile associated with the presence or absence of Thy1+, CD4+ and/or CD8+ cells in the livers of mice during a primary infection with L. monocytogenes. The presence of CD4+ cells was found to be closely associated with mRNA expression for IL-2, IL-3 and IL-4, a 5-fold increase in expression of TNF-alpha and GM-CSF and a 25-fold increase in expression of IFN-gamma and TNF-beta mRNAs, and temporally coincided with the development of granulomatous lesions. In vivo neutralization of TNF-alpha and, to a lesser extent, IFN-gamma resulted in abrogation of granuloma formation. A similar correlation between the presence of CD8+ cells and mRNA expression for any one of the cytokines studied did not exist, pointing to a qualitatively different mechanism of CD8+ T cell mediated cure of listeriosis.

Effect of IFN-gamma and endogenous TNF on the histopathological changes in the liver of Listeria monocytogenes-infected mice

During primary infection of mice with Listeria monocytogenes, the bacteria proliferate extensively in the liver resulting in the development of inflammatory lesions in this organ. In the present study, the effect of interferon-gamma (IFN-gamma) on the development of these lesions, and the involvement of endogenous tumour necrosis factor-alpha (TNF-alpha) in the IFN-gamma-induced effects were evaluated. During an infection of naive mice with L. monocytogenes, two types of inflammatory lesions in the liver could be distinguished: large necrotic lesions consisting of granulocytes and/or exudate macrophages and small lesions containing mainly mature macrophages, i.e. BM8-expressing cells. Necrotic lesions were characterized by the presence of CD11b-expressing cells and consisted mainly of granulocytes during days 1 and 2 of infection and thereafter of exudate macrophages. The lesions consisting of mature macrophages and lymphocytes were not associated with necrosis and were called granulomatous lesions. Some of the granulomatous lesions contained many cells that expressed Ia antigen, i.e. activated cells. Treatment of mice with recombinant (r)IFN-gamma before injection of L. monocytogenes resulted in a decrease in the number of necrotic lesions and an increase in the number of granulomatous lesions in the liver, which was accompanied by a reduced bacterial proliferation in the liver. The effect of rIFN-gamma on the development of the various types of inflammatory lesions in the liver during infection with L. monocytogenes was abrogated by anti-TNF-alpha antibody and this antibody abrogated the rIFN-gamma-induced reduction of bacterial proliferation in the liver as well. Together, the results demonstrate that endogenous TNF-alpha plays a key role in the effects of rIFN-gamma on the inflammatory response in the liver during an infection with L. monocytogenes.

Cytokines and the host defense against Listeria monocytogenes and Salmonella typhimurium

The host defense against intracellular pathogens depends largely on activation of phagocytes and is regulated by a complex network of cytokines. Modulation of this cytokine network might lead to new or additional therapies in the treatment of infections with intracellular pathogens. Therefore, insight in the role of various cytokines in the host defense against these pathogens is required. The present contribution summarizes the results of various studies on the role of different cytokines in the host defense against the intracellular bacteria Listeria monocytogenes and Salmonella typhimurium.

The role of cytokines in experimental listeriosis

Listeria monocytogenes is a Gram-positive, intracytoplasmatically replicating pathogen that elicits host reactions which are very similar in man and rodents. Using murine listeriosis as a highly reproducible and convenient experimental model for studying the immune response to infections with facultative intracellular bacteria, Mackaness developed the concept of T cell-mediated macrophage activation as the pivotal mechanism in host defense against this type of infectious agents. Continued research in listeriosis itself, however, provided paradoxical findings that challenged the original dogma. In particular, the finding that T cell-mediated inflammatory events, like DTH and granuloma formation, can be dissociated from protective effector mechanisms has provided a new impetus and experimental access to characterizing the molecular mediators responsible for these diverging phenomena. This review first summarizes the cellular basis for the dichotomy of immunological phenomena outlined above and will then relate recent findings on cytokine expression in infected tissues to these dual categories of the host response to infection. The authors will focus on data obtained from in vivo experiments and draw on evidence from in vitro systems only when appropriate in vivo verification is still lacking. The data presented will cover the developments made in the field of cytokine research since our previous review in 1981 (Rev. Infect. Dis. 3: 1221-1250). Detectable numbers of listeria-specific T cells become apparent on day 4 to 5 of a primary infection. Whereas the localized and sustained release of TNF and IFN-gamma mediated by CD4+ cells seems to be the focusing event triggering mononuclear cell accumulation, the coincidental eradication of bacteria critically depends on CD8+ and/or CD4-CD8-Thy1+ cells. Their effector functions, however, remain obscure, since cytokines cannot be identified that will substitute for their presence. None of the cytokines studied thus far has been demonstrated to effectively cure an established infection. In addition, the increased production of cytokines characteristic of an anamnestic response (IL-2, IL-3, IL-4, IFN-gamma and TNF) can be dramatically reduced by depleting CD4+ T cells without any effect on the animal's ability to eradicate high lethal doses of bacteria and Listeria-specific CD8+ T cells can mediate protection even in the presence of neutralizing antibodies to IFN-gamma. In conclusion, the murine model of Listeria infection provides an interesting experimental approach for the development of immunotherapeutic strategies aimed at reducing T cell-mediated immunopathology without interfering with innate resistance and T cell-mediated cure and prevention of disease.

Effector role of blood monocytes in experimental visceral leishmaniasis

In BALB/c mice, liver granulomas provoked by visceral infection with intracellular Leishmania donovani are rapidly populated by influxing blood monocytes. To determine the host defense effector role of these mononuclear phagocytes, we treated three populations of infected animals with 5C6, an anti-type 3 complement receptor monoclonal antibody (MAb), which inhibits monocyte recruitment into inflamed tissues. In naive BALB/c mice, injections of 5C6 impaired the initial acquisition of antileishmanial resistance and arrested the development of mature liver granulomas. In sensitized mice with established immunity, both resistance to rechallenge and accelerated granuloma formation were similarly inhibited by MAb administration. Finally, in naive mice, 5C6 MAb also abolished the antileishmanial activity induced by treatment with the macrophage-activating lymphokine gamma interferon. Together, these results suggest a key effector role for the influxing blood monocyte in both initial and established antileishmanial defense and granuloma assembly and in the infected liver as the mononuclear phagocyte target for the antimicrobial effects of gamma interferon.

Association between virulence of Yersinia pestis and suppression of gamma interferon and tumor necrosis factor alpha

It is established that Yersinia pestis, the causative agent of bubonic plague, and enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica share a ca. 70-kb low-calcium response or Lcr plasmid (Lcr+). The latter is known to encode regulatory functions that restrict growth at 37 degrees C in Ca(2+)-deficient medium and virulence factors that are expressed only in vitro within this environment (e.g., certain Yops and V antigen). In this study, gamma interferon (IFN-gamma) was never detected in mice infected with 10 minimum lethal doses (MLD) of Lcr+ cells of Y. pestis, and significant levels of tumor necrosis factor alpha (TNF-alpha) arose only prior to death. Prompt and marked synthesis of these cytokines was observed upon infection with avirulent Lcr- mutants. Treatment of mice with exogenous IFN-gamma plus TNF-alpha inhibited multiplication of Lcr+ yersiniae in vivo, thereby providing protection against challenge with 10 MLD. Administration of both cytokines was required for absolute survival, suggesting a synergistic rather than cumulative interaction. This protective effect entailed cytokine priming as judged by subsequent detection of substantial levels of endogenous IFN-gamma and TNF-alpha. Monospecific anti-V-antigen, known to provide passive immunity against 10 MLD of Lcr+ Y. pestis, permitted significant synthesis of endogenous IFN-gamma and TNF-alpha. These findings demonstrate that Lcr+ yersiniae suppress synthesis of cytokines and suggest that this effect is mediated by one or more Lcr plasmid-encoded virulence factors.

Endogenous tumor necrosis factor alpha is required for enhanced antimicrobial activity against Toxoplasma gondii and Listeria monocytogenes in recombinant gamma interferon-treated mice

In vitro studies have shown that macrophages stimulated with recombinant gamma interferon (rIFN-gamma) produce tumor necrosis factor alpha (TNF-alpha), which in an autocrine fashion activates these cells. The aim of the present study was to determine whether endogenously formed TNF-alpha also is required for rIFN-gamma-induced macrophage activation and enhanced antimicrobial activity in vivo. After an intraperitoneal injection of rIFN-gamma into CBA/J mice, their peritoneal macrophages released enhanced amounts of NO2- and inhibited the intracellular proliferation of Toxoplasma gondii. Injection of neutralizing antibodies against TNF-alpha simultaneously with the rIFN-gamma completely inhibited both the release of NO2- by macrophages and their toxoplasmastatic activity. Similar results were observed after intraperitoneal injection of a competitive inhibitor of L-arginine, NG-monomethyl-L-arginine, together with rIFN-gamma, demonstrating that in vivo L-arginine-derived reactive nitrogen intermediates are essential for the induction of toxoplasmastatic activity. Intravenous injection of rIFN-gamma inhibited the growth of Listeria monocytogenes in the livers and spleens of mice; this effect was abrogated by antibodies against TNF-alpha. Intravenous injection of a large dose of rTNF-alpha resulted in a decrease in the number of bacteria in the liver and spleen, but an injection of rIFN-gamma and rTNF-alpha did not result in enhanced inhibition of the proliferation of L. monocytogenes. Together, the results of the present study are the first to demonstrate that endogenous TNF-alpha is required in vivo for the expression of macrophage activation with respect to the release of reactive nitrogen intermediates and toxoplasmastatic activity and for enhanced listericidal activity in the livers and spleens of mice stimulated with rIFN-gamma.