Endogenous interleukin-4, but not interleukin-10, is involved in suppression of host resistance against Listeria monocytogenes infection in interferon-depleted mice

Vitamin A Promotes the Fusion of Autophagolysosomes and Prevents Excessive Inflammasome Activation in Dextran Sulfate Sodium-Induced Colitis

Vitamin A ensures intestinal homeostasis, impacting acquired immunity and epithelial barrier function; however, its role in innate immunity is mostly unknown. Here, we studied the impact of vitamin A in different dextran sulfate sodium (DSS)-induced colitis animal models. Interestingly, more severe DSS-induced colitis was observed in vitamin A-deficient (VAD) mice than in vitamin A-sufficient (VAS) mice; the same was observed in VAD severe combined immunodeficient mice lacking T/B cells. Remarkably, IL-1β production, LC3B-II expression, and inflammasome activity in the lamina propria were significantly elevated in VAD mice. Electron microscopy revealed numerous swollen mitochondria with severely disrupted cristae. In vitro, non-canonical inflammasome signaling-induced pyroptosis, LC3B-II and p62 expression, and mitochondrial superoxide levels were increased in murine macrophages (RAW 264.7) pretreated with retinoic acid receptor antagonist (Ro41-5253). These findings suggest that vitamin A plays a crucial role in the efficient fusion of autophagosomes with lysosomes in colitis.

Interleukin-10 (IL-10) Produced by Mutant Toxic Shock Syndrome Toxin 1 Vaccine-Induced Memory T Cells Downregulates IL-17 Production and Abrogates the Protective Effect against Staphylococcus aureus Infection

Development of long-term memory is crucial for vaccine-induced adaptive immunity against infectious diseases such as Staphylococcus aureus infection. Toxic shock syndrome toxin 1 (TSST-1), one of the superantigens produced by S. aureus, is a possible vaccine candidate against infectious diseases caused by this pathogen. We previously reported that vaccination with less toxic mutant TSST-1 (mTSST-1) induced T helper 17 (Th17) cells and elicited interleukin-17A (IL-17A)-mediated protection against S. aureus infection 1 week after vaccination. In the present study, we investigated the host immune response induced by mTSST-1 vaccination in the memory phase, 12 weeks after the final vaccination. The protective effect and IL-17A production after vaccination with mTSST-1 were eliminated because of IL-10 production. In the presence of IL-10-neutralizing monoclonal antibody (mAb), IL-17A production was restored in culture supernatants of CD4⁺ T cells and macrophages sorted from the spleens of vaccinated mice. Vaccinated mice treated with anti-IL-10 mAb were protected against systemic S. aureus infection in the memory phase. From these results, it was suggested that IL-10 produced in the memory phase suppresses the IL-17A-dependent vaccine effect through downregulation of IL-17A production.

Infection with enteric pathogens Salmonella typhimurium and Citrobacter rodentium modulate TGF-beta/Smad signaling pathways in the intestine

Salmonella and Citrobacter are gram negative, members of Enterobacteriaceae family that are important causative agents of diarrhea and intestinal inflammation. TGF-β1 is a pleiotropic multifunctional cytokine that has been implicated in modulating the severity of microbial infections. How these pathogens alter the TGF-β1 signaling pathways in the intestine is largely unknown. Streptomycin-pretreated C57BL/6J mouse model colonized with S. typhimurium for 8 hours (acute) and 4 days (chronic) infection and FVB/N mice infected with C. rodentium for 6 days were utilized. Results demonstrated an increase in TGF-β1 receptor I expression (p<0.05) in S. typhimurium infected mouse ileum at both acute and chronic post-infection vs control. This was associated with activation of Smad pathways as evidenced by increased phosphorylated (p)-Smad2 and p-Smad3 levels in the nucleus. The inhibitory Smad7 mRNA levels showed a significant up regulation during acute phase of Salmonella infection but no change at 4d post-infection. In contrast to Salmonella, infection with Citrobacter caused drastic downregulation of TGF receptor I and II concomitant with a decrease in levels of Smad 2, 3, 4 and 7 expression in the mouse colon. We speculate that increased TGF-β1 signaling in response to Salmonella may be a host compensatory response to promote mucosal healing; while C. rodentium decreases TGF-β1 signaling pathways to promote inflammation and contribute to disease pathogenesis. These findings increase our understanding of how enteric pathogens subvert specific aspects of the host-cellular pathways to cause disease.

[Host responses to bacterial infections]

Pathogenic bacteria and host defense system have been evolved by their offense and defense. In vivo research is crucial for elucidation of interactions between them. I have investigated their offence and defense by various standpoints using mouse models of Listeria monocytogenes and Staphylococcus aureus infections. Herein, the results of my research including the roles of endogenous cytokines in host defense, the attenuation of host defense mechanism in obesity and diabetes, the development of vaccines against S. aureus infection by staphylococcal enterotoxin (SE) family molecules, and the emesis-inducing mechanism of SEA are described.

Listeria monocytogenesInduces the Expression of Retinoic Acid-Inducible Gene-I

Retinoic acid-inducible gene-I (RIG-I) is considered to play a role in innate immunity against virus infections. We showed by immunohistochemical study that RIG-I expression is upregulated in vivo in hepatic Kupffer cells and in splenic reticular cells of mice infected with Listeria monocytogenes. Both heat-killed L. monocytogenes and live L. monocytogenes induced the expression of RIG-I in cultured RAW264.7 murine macrophage-like cells in vitro. RIG-I may also be involved in innate immunity against Listeria infection.

Autolysin amidase of Listeria monocytogenes promotes efficient colonization of mouse hepatocytes and enhances host immune response

Listeria monocytogenes is an intracellularly growing pathogen which is able to infect and to spread from cells to cells. It produces several virulence factors required for invasion and intracellular niche colonization. Endogenous peptidoglycan hydrolases which are important for survival of bacteria have been shown to be involved in pathogenesis. An autolysin amidase (Ami)-deficient mutant of L. monocytogenes (Δami) is attenuated in virulence as evidenced by a reduction in mortality of infected mice. We showed that Ami is not essential for bacterial growth and protein secretion. Histopathological analysis suggests that Ami promotes bacterial colonization of hepatocytes. By using cultured eukaryotic cells, we present evidence that a critical function of Ami in pathogenesis is to promote an efficient listerial adherence and internalization into mouse hepatocytes. Simultaneously, the peptidoglycan hydrolase activity of Ami linked to the release of immunologically active cell wall components enhances production of tumor necrosis factor (TNF)-α and interleukin 6. In the early phase of infection, interferon-γ and TNF-α production of Δami-infected mice is significantly less than that of wild-type controls, suggesting a contribution of Ami to enhance the host innate immune response to listerial infection.

Monoassociation with probiotic Lactobacillus delbrueckii UFV-H2b20 stimulates the immune system and protects germfree mice against Listeria monocytogenes infection

In the present study, we investigated the protective effects of Lactobacillus delbrueckii UFV-H2b20 on the resistance to Listeria monocytogenes infection in gnotobiotic mice. Germfree mice or monoassociated mice were infected with L. monocytogenes, and the microbiological and immunological responses were evaluated after 1, 3, and 5 days of infection. Monoassociation with L. delbrueckii was capable of protecting mice against death caused by L. monocytogenes and induced a faster clearance of the bacteria in the liver, spleen, and peritoneal cavity at days 1, 3, and 5 post-infection. Also, monoassociated mice displayed less liver injury than germfree mice. The production of TNF-α in the serum, peritoneal cavity, and gut was augmented in monoassociated mice. Likewise, the levels of IFN-γ found on supernatants of spleen cells cultures were higher after the monoassociation. In addition, increased production of nitric oxide in peritoneal cell cultures supernatants and in serum was observed in mice that received L. delbrueckii. The monoassociation with L. delbrueckii induced higher production of IL-10 in the mucosal immune system. We conclude that monoassociation with L. delbrueckii UFV-H2b20 protects mice from death caused by L. monocytogenes infection by favoring effector responses while preventing their immunopathological consequences.

Role of interleukin-17A in cell-mediated protection against Staphylococcus aureus infection in mice immunized with the fibrinogen-binding domain of clumping factor A

Clumping factor A (ClfA) is a fibrinogen-binding cell wall-attached protein and an important virulence factor of Staphylococcus aureus. Previous studies reported that an immunization with the fibrinogen-binding domain of ClfA (ClfA(40-559)) protected animals against S. aureus infection. It was reported that some cytokines are involved in the pathogenesis of staphylococcal diseases and in host defense against S. aureus infection. However, the role of cytokines in the protective effect of ClfA(40-559) as a vaccine has not been elucidated. In this study, we demonstrated that the spleen cells of ClfA(40-559)-immunized mice produced a large amount of interleukin-17A (IL-17A). The protective effect of immunization was exerted in wild-type mice but not in IL-17A-deficient mice. IL-17A mRNA expression was increased in the spleens and kidneys of immunized mice after infection. CXCL2 and CCL2 mRNA expression was increased in the spleens and kidneys, respectively. Consistent with upregulation of the mRNA expression, neutrophils infiltrated into the spleens extensively and macrophage infiltration was observed in the kidneys of immunized mice. These results suggest that immunization with ClfA(40-559) induces the IL-17A-producing cells and that IL-17-mediated cellular immunity is involved in the protective effect induced by immunization with ClfA(40-559) against S. aureus infection.

Single pre-exposure to a high dose of zymosan enhances lung defense mechanisms and accelerates the pulmonary clearance of a bacterial pathogen in rats

The present study examines the effects of pre-exposure to zymosan (a 1 --> 3-beta-glucan from baker yeast) on lung defense against bacterial infection. Rats received a single dose of zymosan A (0.6, 1.2, or 2.5 mg/kg body weight [bw]) or vehicle control (saline) via intratracheal instillation 3 days prior to intratracheal inoculation with 5 x 10(5) Listeria monocytogenes. Left lungs were homogenized and cultured to assess bacterial clearance, and bronchoalveolar lavage was performed on the right lungs to monitor lung inflammation and injury. Prior to bacterial infection, zymosan exposure resulted in elevated inflammation and oxidant production in the lungs. Zymosan treatment followed by infection led to an accelerated pulmonary clearance of bacteria when compared to the saline control group in a dose-dependent fashion. In addition, lower levels of injury and inflammation were associated with the enhanced bacteria clearance observed in zymosan-infected rats. Our findings suggest that zymosan exposure may enhance the lung immune response by activating alveolar macrophages prior to infection, and stimulating T cells involved in the adaptive immune response early after infection, thus resulting in a heightened pulmonary immune response.

Upregulation of vascular endothelial growth factor by heat-killed Listeria monocytogenes in macrophages

We investigated the effect of heat-killed Listeria monocytogenes (HKLM) on the expression of vascular endothelial growth factor (VEGF) in RAW264.7 macrophage-like cells. The expression of VEGF was induced in RAW264.7 cells treated with HKLM. Pretreatment of cells with cycloheximide, a protein synthesis inhibitor, inhibited the induction of VEGF mRNA by HKLM. Induction of VEGF by HKLM was partially inhibited by treatment of cells with SB203580, a p38 mitogen-activated protein kinase (MAPK) inhibitor, or a neutralizing antibody against tumor necrosis factor-alpha (TNF-alpha). In addition, HKLM induced phosphorylation of p38 MAPK. These results suggest that p38 MAPK and TNF-alpha are involved in the VEGF expression induced by HKLM in RAW264.7 cells. We confirmed that increased VEGF expression is immunohistochemically detected in splenic macrophages of mice infected with L. monocytogenes (L. monocytogenes). VEGF is thought to be involved in inflammatory reactions induced by L. monocytogenes infection.

Salmon cartilage proteoglycan modulates cytokine responses to Escherichia coli in mouse macrophages

Proteoglycans (PGs) are complex glycohydrates, which are composed of core proteins and glycosaminoglycans and widely distributed in connective tissues and on the cell surface of mammalian tissues. We investigated the effect of PG extracted from salmon cartilage on cytokine responses to stimulation with heat-killed Escherichia coli (HKEC) in a mouse macrophage cell line, RAW264.7. PG exhibited the suppression of tumor necrosis factor-alpha production compared with chondroitin 4 sulfate (C4S) and chondroitin 6 sulfate (C6S). PG also revealed the up-regulation of interleukin-10 production. HKEC-induced Toll-like receptor 4 (TLR4) and inducible nitric oxide synthase expression was dose-dependently suppressed by treatment with PG, C4S or C6S, and the PG showed the strongest suppressive effect among 3 compounds. Only PG dramatically up-regulated the expression of signal transducer and activator of transcription 3 (STAT3), and the phosphorylation of STAT3 in mouse macrophages. Our results suggested that the novel interaction might exist between the extracellular matrix and immune system.

The role of macrophage migration inhibitory factor in lethal Listeria monocytogenes infection in mice

Macrophage migration inhibitory factor (MIF) has been characterized as a proinflammatory cytokine. Previous studies have indicated that MIF may play a beneficial role or a detrimental role in microbial infections, depending on pathogens. In this study, we investigated the role of MIF in Listeria monocytogenes infection. The MIF titers increased 6h after lethal L. monocytogenes infection but not in the sublethal infection. The elimination of bacteria from the spleens and livers was not affected by anti-MIF antibody (Ab) injection in the sublethal infection, whereas anti-MIF Ab treatment rescued mice from the lethal infection, suggesting that MIF plays a deteriorating role in lethal L. monocytogenes infection. Anti-MIF Ab treatment significantly augmented interleukin (IL)-10 production in the spleens and livers 24h after infection, suggesting that MIF might down-regulate IL-10 production. Although the administration of anti-IL-10 monoclonal Ab showed no significant effect on the bacterial growth in the organs, the bacterial infection was deteriorated by the combined administration of Abs against MIF and IL-10. On the other hand, anti-MIF Ab treatment also increased in the serum cortisol titer 6h after infection compared with the control immunoglobulin G-injected group. Depletion of endogenous IL-10 decreased serum cortisol titers. These results suggested that IL-10 and cortisol might be involved in the deteriorating effect of MIF on lethal L. monocytogenes infection.

Urocortin 2 suppresses host resistance to Listeria monocytogenes infection via up-regulation of interleukin-10

Previous studies have showed that corticotropin-releasing factor (CRF) modulates immune response during inflammation. We investigated the effect of CRF family peptides on host resistance to Listeria monocytogenes infection in mice. When mice were administered ip with CRF, urocortin (Ucn), or Ucn2 30 min prior a sublethal infection with L. monocytogenes, the numbers of bacteria in the organs of Ucn2-treated mice were dramatically increased, and most of these mice succumbed. However, host resistance to the infection was retained in CRF- or Ucn-treated mice. The suppressive effect of Ucn2 was dependent on CRF receptor type 2 because an antagonist to the receptor canceled the effect of Ucn2. IL-10 production was significantly increased, and interferon-gamma and TNFalpha production was decreased in the spleens of Ucn2-treated mice, compared with those in Ucn2-untreated control mice. The effect of Ucn2 was canceled by treatment with anti-IL-10 monoclonal antibody and in IL-10-deficient mice. The expression and activation of signal transducers and activators of transcription (STAT) 3 were up-regulated, and the expression and activation of STAT1 were down-regulated in the spleens from Ucn2-treated mice, compared with vehicle-treated mice. Moreover, suppression of TNFalpha production and augmentation of IL-10 production and expression and activation of STAT3 by Ucn2 treatment were observed in heat-killed L. monocytogenes-stimulated macrophages. These results suggested that Ucn2 suppresses host resistance to L. monocytogenes infection via up-regulation of IL-10 production.

A defective Th1 response of the spleen in the initial phase may explain why splenectomy helps prevent a Listeria infection

Listeria monocytogenes (Listeria) are known to grow and proliferate in the liver while a splenectomy induces host resistance against a Listeria infection despite the fact that a splenectomy inhibits the Th1 response. Therefore, the mechanism by which a splenectomy helps to prevent the growth of Listeria still remains to be elucidated. After an i.v. challenge of Listeria (1 x 10(6) CFU) in C57BL/6 mice, Listeria rapidly increased in the spleen but not in the liver until 48 h. However, after this initial phase, Listeria remarkably grew in the liver. In contrast, when the mice received a splenectomy beforehand, no remarkable growth of Listeria in the liver was observed after Listeria challenge despite the fact that serum IFN-gamma and IL-12 levels at 24 h after Listeria challenge were significantly lower than those in the sham mice. However, the liver leucocytes from mice by 6 h after infection produced a substantial amount of IFN-gamma while spleen MNC did not, whereas spleen leucocytes at 24 h after Listeria challenge did. Consistently, the IFN-gamma and IL-12 levels in the tissue homogenates of the spleen were significantly lower than in those of the liver until 6 h after infection. This defective spleen Th1 response in the early phase of Listeria infection was corrected by an IL-18 i.p. injection just after the Listeria challenge. Our findings suggest that Listeria exploit the defective Th1 environment of the spleen in the initial phase and afterwards overcome the host defense mechanism of the liver.

Changes in the immune functions and susceptibility to Listeria monocytogenes infection in mice fed dietary lipids

The direct examination of the effects that fish oil diets (composed of long-chain n-3 polyunsaturated fatty acids) exert on immune system function indicates a reduction of host natural resistance to infectious diseases mainly because of a suppression of immune function generated by the fatty acids contained in this diet. Here, we evaluated the concentration of IL-12, IL-4, prostaglandin E2 and leukotriene B4 in the serum from BALB/c mice receiving four different diets. Each group was fed a diet that differed only in the source of fat: a low-fat diet (2.5% by weight), an olive oil diet (20% by weight), a fish oil diet (20% by weight) or a hydrogenated coconut oil diet (20% by weight). Mice were fed for 4 weeks and then infected with the intracellular pathogen Listeria monocytogenes. An initial reduction in the Th1-type response as a result of a decrease in IL-12p70 secretion, an inefficient action of IL-4 (Th2-type response) and no modification of pro-inflammatory lipid-mediator production could be, at least in part, the key events responsible for the inadequate elimination of L. monocytogenes from the spleens of mice fed a fish oil diet. Furthermore, our results suggest that the type of dietary lipids may affect the circulating concentration of IL-12p70 and IL-4, leading to a modulation in the protective cellular immune response to L. monocytogenes infection.

A mutant of staphylococcal enterotoxin C devoid of bacterial superantigenic activity elicits a Th2 immune response for protection against Staphylococcus aureus infection

Staphylococcal enterotoxin C (SEC), a bacterial superantigenic exotoxin, is commonly produced by invasive Staphylococcus aureus isolates, especially methicillin-resistant strains and isolates from animal diseases. We constructed and expressed a nontoxic mutant SEC (mSEC) and investigated whether immunization with mSEC, which is devoid of superantigenic activity, can protect against S. aureus infection. Mice were immunized with mSEC and challenged with viable S. aureus. The bacterial counts in the organs of mSEC-immunized mice were significantly lower and the survival rate was higher than the corresponding values for the control group. Immunization with mSEC strongly induced the production of T-helper 2 type antibodies, immunoglobulin G1, and immunoglobulin G2b. The production of interleukin-10 (IL-10) and IL-4 was significantly greater in immunized mice challenged with S. aureus than in the control mice, whereas the production of gamma interferon (IFN-gamma) was significantly decreased in the immunized mice. The cytokine response in a spleen cell culture that was stimulated with heat-killed S. aureus or SEC showed that immunization with mSEC inhibited IFN-gamma production and up-regulated IL-10 production in vitro. Furthermore, IFN-gamma and tumor necrosis factor alpha production in vitro was significantly inhibited by sera from mSEC-immunized mice but not by sera from control mice. These results suggest that immunization with mSEC devoid of superantigenic properties provides protection against S. aureus infection and that the protection might be mediated by SEC-specific neutralizing antibodies.

Chronic intestinal nematode infection induces Stat6-independent interleukin-5 production and causes eosinophilic inflammatory responses in mice

The role of Stat6 (signal transducers and activators of transcription) in the recruitment and activation of eosinophils has been studied in detail in asthma and other allergic diseases. In this study, we demonstrated that eosinophil responses occur in a Stat6-independent manner in mice infected with the intestinal nematode, Nippostrongylus brasiliensis. Stat6-deficient (Stat6(-/-)) mice cannot expel N. brasiliensis and establish chronic infections. Prominent blood and intestinal eosinophilia were induced after day 14 postinfection (p.i.) and maintained at this level in Stat6(-/-) mice, whereas in wild-type mice eosinophil responses reached a peak on day 10 p.i. and declined thereafter. The introduction of a secondary infection of N. brasiliensis into wild-type mice induced rapid and exaggerated eosinophilia, whereas secondary infection in Stat6(-/-) mice resulted in almost the same eosinophil responses as those of the primary infection, suggesting a lack of memory responses. Blood eosinophilia was also induced in Stat6(-/-) mice implanted with N. brasiliensis in the small intestine, suggesting that intestinal exposure to parasitic antigen is sufficient to induce eosinophil responses. Furthermore, this prominent eosinophil response of Stat6(-/-) mice after day 14 was closely associated with an increase of interleukin (IL)-5 production in serum and intestine. Neither IL-4 nor eotaxin were significantly induced in Stat6(-/-) mice after infection with N. brasiliensis. We also found that mRNA for IL-5, GATA-3 and eosinophil peroxidase (EPO) are induced in the intestine of Stat6(-/-) mice on day 14 p.i. Taken together, these results provide evidence for Stat6-independent IL-5 production and subsequent eosinophil responses after chronic infection with N. brasiliensis.

Tumor necrosis factor-α is required for gastritis induced by Helicobacter felis infection in mice

Helicobacter pylori colonizes the gastric mucosa of human and causes chronic gastritis. The previous studies have demonstrated that gamma interferon (IFN-gamma) but not tumor necrosis factor-alpha (TNF-alpha) plays a critical role in pathogenesis of gastritis induced by H. pylori infection. In this study we investigated the induction of gastritis induced by H. felis infection in TNF-alpha-deficient mice, comparing with IFN-gamma-deficient mice. The scores of gastritis and epithelial changes of TNF-alpha-deficient mice and IFN-gamma-deficient mice were significantly lower than that of C57BL/6 mice. Moreover, the degrees of gastritis and epithelial changes of TNF-alpha-deficient mice were rather low compared with that of IFN-gamma-deficient mice. In spleen cell cultures stimulated with heat-killed H. felis, IFN-gamma production by TNF-alpha-deficient mice and TNF-alpha production by IFN-gamma-deficient mice were significantly reduced compared with those in C57BL/6 mice. These results suggested that TNF-alpha is involved in pathogenesis of gastritis induced by H. felis infection as IFN-gamma and that an interaction between TNF-alpha and IFN-gamma might be required in pathogenesis of gastritis induced by Helicobacter infection.

Induction of immune responses by attenuated isogenic mutant strains of Listeria monocytogenes

We have generated isogenic Listeria monocytogenes mutant strains to study the induction of protective immunity in mice. These strains harbored either a specific deletion within the actin nucleator (actA) and/or have multiple deletions within the actA and phospholipase B (plcB) genes. In comparison to the wild type parental L. monocytogenes EGDe strains, the mutant strains were extremely low in virulence and were rapidly eliminated by the host during the first days of infection. Nevertheless, a single immunization with both mutant strains (EGDe DeltaactA2 and DeltaactADeltaplcB) efficiently induced and maintained effector memory (CD8(+)) T cells and has provided animals with a state of long-lasting protective immunity against wild type L. monocytogenes. These mutant strains can be used as live vaccines against the corresponding virulent pathogen and as carriers for introducing heterologous protective antigens into animals and humans.

Effective induction of acquired resistance to Listeria monocytogenes by immunizing mice with in vivo-infected dendritic cells

Splenic dendritic cells (DCs) obtained from mice at 48 h after Listeria monocytogenes infection exhibited up-regulation of CD80 and produced higher titers of gamma interferon (IFN-gamma) and interleukin-12 (IL-12) than did DCs obtained from uninfected mice. Mice immunized with DCs obtained from mice that had been infected with L. monocytogenes 48 h before acquired host resistance to lethal infection with L. monocytogenes at 4 and 8 weeks. Immunization with DCs from heat-killed L. monocytogenes failed to induce resistance. Acquired antilisterial resistance is specific, since the immunized mice could not be protected from Salmonella enterica serovar Typhimurium infection. Infected DCs stimulated proliferation of naive CD4(+) and CD8(+) cells in vitro, suggesting that in vivo-infected DCs activate CD8(+) T cells, which are critical in acquired antilisterial resistance, as well as CD4(+) T cells. When wild-type mice were immunized with DCs from IFN-gamma-deficient mice, they were protected against a lethal L. monocytogenes challenge. In contrast, when mice were immunized with DCs from anti-IL-12 p40 monoclonal antibody-injected mice, they failed to gain acquired antilisterial resistance. These results suggest that DC-derived IL-12, but not IFN-gamma, may play a critical role in induction of acquired antilisterial resistance. Our present results suggest that splenic DCs obtained from mice infected with L. monocytogenes in vivo may be an effective immunogen with which to induce antigen-specific immunity.

Comparison of host resistance to primary and secondary Listeria monocytogenes infections in mice by intranasal and intravenous routes

There have been no studies on the susceptibility and host immune responses to an intranasal infection with Listeria monocytogenes. In this study, we compared the susceptibilities and cytokine responses between intranasal and intravenous infections with L. monocytogenes in mice. Moreover, we compared efficiency of acquisition of host resistance to L. monocytogenes infection between intranasally and intravenously immunized mice because an intranasal immunization of vaccines is reportedly available for induction of adaptive immunity against various infectious pathogens. The susceptibility to an intranasal infection with L. monocytogenes was markedly lower than that to the intravenous infection. The bacterial growth in the lungs, spleens, and livers was substantially similar between intranasally and intravenously infected mice. Titers of endogenous gamma interferon (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in the spleens, livers, and lungs were parallel to bacterial numbers in each organ of mice during intranasal infection and intravenous infection. IFN-gamma-deficient mice and TNF-alpha-deficient mice were highly susceptible to intranasal infection as well as intravenous infection. Susceptibilities to intranasal and intravenous L. monocytogenes infection were the same in these cytokine-deficient mice. These results suggest that both IFN-gamma and TNF-alpha play critical roles in host resistance to intranasal L. monocytogenes infection as well as the intravenous infection. Acquisition of host resistance to intravenous and intranasal L. monocytogenes infection was induced in intranasally immunized mice as well as intravenously immunized mice, suggesting that intranasal immunization is effective for prevention of a systemic infection with L. monocytogenes.

Effect of 6-hydroxydopamine on host resistance against Listeria monocytogenes infection

Recent studies have shown that immunocompetent cells bear receptors of neuropeptides and neurotransmitters and that these ligands play roles in the immune response. In this study, the role of the sympathetic nervous system in host resistance against Listeria monocytogenes infection was investigated in mice pretreated with 6-hydroxydopamine (6-OHDA), which destroys sympathetic nerve termini. The norepinephrine contents of the plasma and spleens were significantly lower in 6-OHDA-treated mice than in vehicle-treated mice. The 50% lethal dose of L. monocytogenes was about 20 times higher for 6-OHDA-treated mice than for vehicle-treated mice. Chemical sympathectomy by 6-OHDA upregulated interleukin-12 (IL-12) and tumor necrosis factor-alpha (TNF-alpha) production in enriched dendritic cell cultures and gamma interferon (IFN-gamma) and TNF-alpha production in spleen cell cultures, whereas chemical sympathectomy had no apparent effect on phagocytic activities, listericidal activities, and nitric oxide production in peritoneal exudate cells and splenic macrophages. Augmentation of host resistance against L. monocytogenes infection by 6-OHDA was abrogated in IFN-gamma(-/-) or TNF-alpha(-/-) mice, suggesting that upregulation of IFN-gamma, IL-12, and TNF-alpha production may be involved in 6-OHDA-mediated augmentation of antilisterial resistance. Furthermore, adoptive transfer of spleen cells immune to L. monocytogenes from 6-OHDA-treated mice resulted in untreated naive recipients that had a high level of resistance against L. monocytogenes infection. These results suggest that the sympathetic nervous system may modulate host resistance against L. monocytogenes infection through regulation of production of IFN-gamma, IL-12, and TNF-alpha, which are critical in antilisterial resistance.

Immunostimulatory DNA from Paracoccidioides brasiliensis acts as T-helper 1 promoter in susceptible mice

Th1 immune responses afford protection against some pathogens like the fungus P. brasiliensis (P.b.), etiological agent of Paracoccidioidomycosis (PCM). It is well known that nonmethylated CpG sequences from bacterial DNA have immunomodulatory properties and can be used as a Th1-promoting adjuvant. By analyzing the available gene sequences of P.b. we observed a high number of unmethylated CpG dinucleotides. In a murine model of the PCM infection, the isogenic mouse strain known to be susceptible presents a predominant Th2 pattern. In order to access the possibility of the genomic DNA to act as a Th1-promoting adjuvant, in vitro assays were made and indicated a significant increase in phagocytosis when the macrophages were stimulated with DNA from P.b. and in vivo assays of a decreased production of antibodies antigp43, the main antigen of the PCM system. The analysis of the antibody isotypes and the cytokine production suggested a Th1 modulation in the susceptible animals. Thus, when mice were infected with fungus plus synthetic oligodeoxynucleotide (ODN), made from the available sequence of gp43, a decrease in the fungus dissemination was observed. Results herein described suggest that genomic DNA from P.b. could have a immunostimulatory function as a Th-1-promoting adjuvant in susceptible mice.

Interference between host resistance to Listeria monocytogenes infection and ovalbumin-induced allergic responses in mice

Listeria monocytogenes promotes the induction of the T-helper 1 (Th1) cell response, while ovalbumin (OVA) induces a Th2 cell response and allergic reactions, such as airway hyperreactivity and immunoglobulin E (IgE) production. When mice were immunized with OVA on day 7 after L. monocytogenes infection, eosinophilia in bronchoalveolar lavage and the production of total IgE, OVA-specific IgE, interleukin-4 (IL-4), and IL-5 in the circulation were markedly suppressed. Cytokine responses, including IL-4, IL-5, IL-10, IL-13, and gamma interferon, to OVA were decreased in the spleen cell cultures obtained from OVA-immunized mice that had been infected with L. monocytogenes. Conversely, when OVA-immunized mice were infected with L. monocytogenes, conversion from the nonlethal infection to the lethal infection occurred. Host resistance to L. monocytogenes infection in OVA-immunized mice was enhanced by the administration of anti-IL-10 monoclonal antibody. The present study indicates that striking interference is observed between Th1-inducing L. monocytogenes infection and Th2-driven OVA-induced airway hyperreactivity.

Effect of a matrix metalloproteinase inhibitor on host resistance against Listeria monocytogenes infection

Hydroxy acid-based matrix metalloproteinase (MMP) inhibitors have been shown to inhibit tumor infiltration and growth, endotoxin shock, and acute graft-versus-host disease. Blockade of the release of soluble tumor necrosis factor-alpha (TNF-alpha) and CD95 ligand (CD95L; FasL) from cell-associated forms is reportedly involved in the mechanism of the drug effect. We investigated the effect of a MMP inhibitor, KB-R7785, on host resistance against Listeria monocytogenes infection, in which TNF-alpha is essentially required for the defense, in mice. The administration of KB-R7785 exacerbated listeriosis, while the drug prevented lethal shock induced by lipopolysaccharide and D-galactosamine. KB-R7785 inhibited soluble TNF-alpha production in spleen cell cultures stimulated by heat-killed L. monocytogenes and the drug treatment reduced serum TNF-alpha levels in infected mice, whereas the compound was ineffective on the modulation of interferon-gamma and interleukin-10 production. The effect of KB-R7785 was considered to be dependent on TNF-alpha because the drug failed to affect L. monocytogenes infection in anti-TNF-alpha monoclonal antibody-treated mice and TNF-alpha knockout mice. Anti-CD95L monoclonal antibody was also ineffective on the infection. These results suggest that induction of infectious diseases, to which TNF-alpha is critical in host resistance, should be considered in MMP inhibitor-treated hosts.

Interleukin-10 has different effects on proliferation of Listeria monocytogenes in livers and spleens of mice

The aim of this study was to investigate the effect of interleukin-10 (IL-10) on the course of Listeria monocytogenes infection in naive and immune mice. Treatment with IL-10 during the course of a primary infection significantly decreased the number of bacteria in the spleen and did not affect the number in the liver. During a secondary infection in immune mice treated with IL-10, the number of bacteria was significantly lower in the spleen but significantly higher in the liver in comparison to mock-treated immune mice. IL-10 treatment during a primary Listeria infection decreased the concentration of gamma interferon (IFN-gamma) in plasma and the toxoplasmastatic activity of macrophages, whereas it increased the percentage of mildly CD3-positive T cells in the spleen. During a secondary infection, the concentration of IFN-gamma in plasma was decreased on day 1 but remained unaffected during later days of infection. From these results, we conclude that IL-10 has different effects on the proliferation of L. monocytogenes in the spleen and liver during primary and secondary Listeria infections.

Roles of endogenous cytokines in liver apoptosis of mice in lethal Listeria monocytogenes infection

Various bacterial pathogens have been identified as mediators of apoptosis. Apoptosis reportedly shows both detrimental and beneficial effects on biological functions. We studied the role of liver apoptosis in lethal Listeria monocytogenes infection and the regulation of apoptosis by endogenous cytokines during infection. Apoptosis was observed in the spleen but not in the liver of infected mice, whereas the induction of liver necrosis was evident by rising levels of serum aminotransferases in these animals. Apoptosis was detected in the liver of L. monocytogenes-infected mice which had been treated with monoclonal antibody (mAb) against tumor necrosis factor-alpha (TNF-alpha) or interleukin-6 (IL-6), or in TNF-alpha(-/-) mice, but not in gamma- interferon (IFN-gamma)(-/-) mice or mice which had been treated with mAb against IL-4 or IL-10. Augmentation of liver apoptosis in mice treated with mAb against TNF-alpha or IL-6 or in TNF-alpha(-/-) mice correlated with the increase in bacterial numbers in the organ, while no augmentation of apoptosis was observed in the liver of IFN-gamma(-/-) mice irrespective of the marked increase in bacterial numbers in the organs, indicating that augmentation of liver apoptosis may not be merely due to the increase in bacterial growth in the organs. These results suggest that TNF-alpha and IL-6 may play an important role in protecting the liver from apoptosis in lethal L. monocytogenes infection.

Host resistance to Listeria monocytogenes infection is enhanced but resistance to Staphylococcus aureus infection is reduced in acute graft-versus-host disease in mice

Acute graft-versus-host disease (GVHD) is characterized by the production of high levels of T helper 1 (Th1)-type cytokines. Bone marrow transplantation from allogeneic C57BL/6 cells to CBF(1) mice produced acute GVHD. Host resistance to Th1-driven Listeria monocytogenes was enhanced, whereas host resistance to Th2-driven Staphylococcus aureus was reduced during acute GVHD. These results suggest that opposite host responses are observed between Th1-driven and Th2-driven bacterial infections in acute GVHD.

Interleukin-4 and interleukin-10 are involved in host resistance to Staphylococcus aureus infection through regulation of gamma interferon

Our previous study showed that gamma interferon (IFN-gamma), a T-helper 1 (Th1)-type cytokine, plays a detrimental role in Staphylococcus aureus infection in mice. In this study, the role of Th2-type cytokines such as interleukin-4 (IL-4) and IL-10 in S. aureus infection was investigated. IL-10 mRNA was induced in parallel with IFN-gamma in the spleens and kidneys of mice during S. aureus infection, whereas IL-4 mRNA was induced in the spleens but not in the kidneys of these animals. Spleen cells obtained from S. aureus-infected mice produced lower titers of IFN-gamma and higher titers of IL-4 and IL-10 in response to heat-killed S. aureus than did those from uninfected mice. Administration of anti-IL-4 monoclonal antibody (MAb) or anti-IL-10 MAb inhibited the elimination of S. aureus cells from the kidneys of mice. IFN-gamma mRNA expression was enhanced in the spleens of anti-IL-4 MAb- or anti-IL-10 MAb-treated mice and also in the kidneys of anti-IL-4 MAb-treated animals. Next, we evaluated the role of IFN-gamma in S. aureus infection in IFN-gamma(-/-) mice. An increase in survival rates, a decrease in bacterial numbers in the kidneys, and an amelioration of histologic abnormalities in these organs were observed in IFN-gamma(-/-) mice compared with those in IFN-gamma(+/+) mice. Administration of MAb against IL-4 or IL-10 failed to affect bacterial growth in the spleens and kidneys of IFN-gamma(-/-) mice irrespective of the expression of Th2 response. These results suggest that S. aureus infection induced a Th2 response and that IL-4 and IL-10 might play a protective role through the regulation of IFN-gamma in S. aureus infection.

Role of IL-10 in a Neonatal Mouse Listeriosis Model

This study was undertaken to test the hypothesis that altered IL-10 production plays a role in the increased susceptibility of neonates to listeriosis. Plasma IL-10 levels were measured in neonatal and adult mice at various times after infection with Listeria monocytogenes. Relative to adults, neonatal mice had markedly increased IL-10 levels early in the course of infection with Listeria using a 90% lethal dose. Higher neonatal IL-10 responses were also observed after injecting adults and pups with equal doses of killed organisms. Splenic macrophages from neonates produced higher IL-10 levels than those of adults after in vitro stimulation with killed bacteria, confirming in vivo observations. Moreover, IL-10 blockade had differential effects in neonates and adults infected with live Listeria. In adult mice, anti-IL-10 Abs decreased bacterial burden early in the course of infection, but were no longer effective at 6 days or later after challenge. In the pups, however, the same treatment had beneficial effects both early and late during infection and resulted in increased survival. Collectively, our data suggest that an overproduction of IL-10 by macrophages may at least partially explain the increased susceptibility of neonates to listeriosis, and provide further evidence that cytokine production is different in adults and neonates.

Endogenous cytokines during a lethal infection with Listeria monocytogenes in mice

It has been demonstrated that endogenous cytokines including gamma interferon (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) play protective roles but that IL-4 and IL-10 play detrimental roles in nonlethal Listeria monocytogenes infection in mice. In this paper, we studied the roles of endogenous cytokines in a lethal infection with L. monocytogenes in mice. TNF-alpha and IL-6 titres in the bloodstreams, spleens and livers paralleled bacterial numbers in the organs, and both these cytokines and the bacterial numbers peaked just before the mice died. The high titres of TNF-alpha notably detected in the circulation in lethal infection were different from those in nonlethal infection. The maximum production of IFN-gamma was observed before the peaks of TNF-alpha and IL-6, and IFN-gamma almost disappeared from the bloodstreams and organs just before the mice died. No notable difference of IFN-gamma titres between lethal infection and nonlethal infection in the specimens obtained from mice was observed. IL-10 was also detected in the bloodstreams earlier than the peaks of TNF-alpha and IL-6 during lethal infection, while IL-4 was never detected in the sera. The administration of monoclonal antibodies (mAbs) against TNF-alpha, IFN-gamma, IL-6, IL-4 or IL-10 failed to rescue mice from lethal L. monocytogenes infection, whereas anti-TNF-alpha mAb and anti-IFN-gamma mAb prevented mice from lethality by high-dose endotoxin shock. These results suggest that lethality in L. monocytogenes infection might not be determined solely by these cytokines.

Tumour necrosis factor and interferon-gamma are required in host resistance against virulent Rhodococcus equi infection in mice: cytokine production depends on the virulence levels of R. equi

Rhodococcus equi is a facultative intracellular bacterial pathogen that causes pneumonia in foals and immunosuppressed humans. There are at least three virulence levels of R. equi and these pathogenicities are associated, in mice, with the presence of virulence plasmids. This study focused on cytokine secretion, in mice, in the course of a primary infection with sublethal doses of R. equi strains of different virulence levels (virulent, intermediately virulent and avirulent). Tumour necrosis factor (TNF) and interferon-gamma (IFN-gamma), but not interleukin-4 (IL-4) and interleukin-10 (IL-10), were induced endogenously in mice in relation to the multiplication and clearance of virulent and intermediately virulent strains of R. equi. These cytokines were not detected in mice infected with avirulent R. equi. Deaths occurred among mice treated with monoclonal antibodies (mAbs) against either TNF or IFN-gamma prior to sublethal dose infection with virulent and intermediately virulent strains of R. equi, but not with avirulent R. equi. These results suggested that cytokine production depended largely on the virulence levels of R. equi: TNF and IFN-gamma were required early during infection with virulent R. equi to limit replication and clearance of bacteria within the organs, but they were not necessary for limiting infection with avirulent R. equi.

Host resistance against Listeria monocytogenes is reciprocal during the course of infection in alymphoplastic aly mutant mice

The aly is a unique spontaneous autosomal recessive mutation in mice that causes a systemic defect of lymph nodes and Peyer's patches. We investigated host resistance against Listeria monocytogenes infection in the mutant. The 50% lethal dose of L. monocytogenes in aly/aly mice was 10-fold higher than their heterozygotes, termed aly/+mice, or their wild-type C57BL/6 mice. The bacterial growth in the spleens and livers of aly/aly mice was more efficient early in infection, and their listericidal activity of peritoneal macrophages was higher than those of aly/+mice. In contrast, the complete elimination of bacteria from the spleens and livers of infected mice in the late stage of infection, in which a T-cell-dependent mechanism is required, was delayed in the aly/aly mice. Moreover, an acquired resistance against secondary infection with L. monocytogenes was markedly diminished in the aly/aly mice. The production of endogenous interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), which are critical in antilisterial resistance, was reduced in the aly/aly mice during the infection. The production of IFN-gamma, and interleukin-4 was also diminished in the spleen cell cultures of aly/aly mice when stimulated with heat-killed L. monocytogenes or the T-cell receptors were directly stimulated with anti-CD3-epsilon monoclonal antibody. These results suggest that acquired immunity against L. monocytogenes infection is attenuated in aly/aly mice, and that the insufficient production of IFN-gamma and TNF-alpha might be involved in the immunodeficiency.

Endogenous interleukin-4 does not suppress the resistance against a primary or a secondary Listeria monocytogenes infection in mice

Interleukin-4 (IL-4), a cytokine produced by T-helper 2 (Th2) cells, can inhibit the development of T-helper 1 (Th1) cells, which results in a decreased release of cytokines by the latter. As interferon-gamma (IFN-gamma), produced by Th1 cells, is involved in the resistance against a Listeria monocytogenes infection, the role of endogenously formed IL-4 during a Listeria infection in mice was investigated. Neutralization of endogenously formed cytokines by subcutaneously injected alginate-encapsulated monoclonal antibody (MoAb)-forming cells results in high antibody titres in the circulation over a long time period. The aim of the present study was to reevaluate the effect of neutralization of IL-4 during a primary Listeria infection and to investigate the role of IL-4 during a secondary infection in mice using encapsulated MoAb-forming cells. During the course of a primary infection in mice given anti-IL-4 antibody-forming cells (anti-IL-4-FC), the number of Listeria found in the liver and spleen was comparable to that found in control mice given anti-beta-galactosidase antibody-forming cells (anti-beta-gal-FC). Activation of macrophages measured by inhibition of Toxoplasma gondii proliferation and the release of reactive nitrogen intermediates (RNI) was not affected by anti-IL-4-FC treatment during infection. Furthermore, during a secondary L. monocytogenes infection the number of bacteria in the liver and spleen of anti-IL-4-treated immune mice was comparable to anti-beta-gal-FC-treated, control, immune mice. The concentration of IFN-gamma in plasma of anti-IL-4-treated immune mice was similar to that of control immune mice. Taken together, these findings demonstrate that neutralization of endogenously formed IL-4 does not affect resistance to a primary or a secondary L. monocytogenes infection in mice.

Protective role of nitric oxide in Staphylococcus aureus infection in mice

This study was carried out to determine the role of nitric oxide (NO) in Staphylococcus aureus infection in mice. NO production in spleen cell cultures was induced by heat-killed S. aureus. Expression of mRNA of the inducible isoform of NO synthase (iNOS) was induced in the spleens and kidneys of S. aureus-infected mice. When mice were treated with monoclonal antibodies (MAbs) against tumor necrosis factor alpha (TNF-alpha) or gamma interferon (IFN-gamma) before S. aureus infection, the induction of iNOS mRNA expression in the kidneys was inhibited. These MAbs also inhibited NO production in spleen cell cultures stimulated with heat-killed S. aureus. NO production in the spleen cell cultures and levels of urinary nitrate plus nitrite were suppressed by treatment with aminoguanidine (AG), a selective inhibitor of iNOS. The survival rates of AG-treated mice were significantly decreased by either lethal or sublethal S. aureus infections. However, an effect of AG administration on bacterial growth was not observed in the spleens and kidneys of mice during either type of infection. Production of TNF-alpha and IFN-gamma was not affected by AG treatment in vitro and in vivo. These results suggest that NO plays an important role in protection from lethality by the infection, but the protective role of NO in host resistance against S. aureus infection was not proved. Moreover, our results show that TNF-alpha and IFN-gamma regulate NO production while NO may not be involved in the regulation of the production of these cytokines during S. aureus infection.

Protective role of gamma interferon in experimental pulmonary paracoccidioidomycosis

We have developed a murine model of pulmonary infection by Paracoccidioides brasiliensis in which resistance was associated with immunological activities governed by gamma interferon (IFN-gamma). To better characterize this model, we measured type 1 and type 2 cytokines in the lungs and investigated the effect of endogenous IFN-gamma depletion by monoclonal antibodies in the course of infection of susceptible (B10.A) and resistant (A/Sn) mice. At weeks 4 and 8 after infection, lungs from susceptible animals presented levels of IFN-gamma, interleukin-4 (IL-4), IL-5, and IL-10 higher than those in resistant mice. In both mouse strains, neutralization of endogenous IFN-gamma induced exacerbation of the pulmonary infection, earlier fungal dissemination to the liver and spleen, impairment of the specific cellular immune response resulting in significantly lower delayed-type hypersensitivity reactions, and increased levels of immunoglobulin G1 (IgG1)- and IgG2b-specific antibodies. Histopathological analysis demonstrated that depletion of IFN-gamma changes the focal granulomatous lesions found in the lungs of B10.A and A/Sn mice into coalescent granulomata which destroy the pulmonary architecture. These results suggest that irrespective of the mouse strain, IFN-gamma plays a protective role and that this cytokine is one major mediator of resistance against P. brasiliensis infection in mice.

Neuropeptides in the livers of mice during bacterial infections

Neuropeptides such as substance P (SP) and vasoactive intestinal peptide (VIP) are known to act as immunomodulators. We investigated the induction of SP and VIP in the livers of mice infected with Listeria monocytogenes or injected with Tsukamurella paurometabolum. VIP was detected in the livers of mice after L. monocytogenes infection by an immunohistochemical technique and preproVIP mRNA, which was detected by reverse transcription-polymerase chain reaction (PCR), was induced post infection. However, no SP was detected. In contrast, SP, but not VIP was detected within granulomas in the livers of T. paurometabolum-injected mice, suggesting VIP and SP might be selectively induced in the liver by different bacterial infections.

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.

Neutralization of interferon-gamma exacerbates pneumocystis-driven interstitial pneumonitis after bone marrow transplantation in mice

The role of IFNgamma in the development of infection-driven interstitial pneumonitis in a model of murine graft-versus-host disease was investigated. Mice were given either syngeneic or allogeneic bone marrow transplants along with lung Pneumocystis carinii infections and were treated with either control mAb or anti-IFNgamma mAb. At day 21 after transplant, lung weights were elevated nearly twofold in all groups. By day 41, mice in all groups had cleared the P. carinii but only the mice given allogeneic transplants and anti-IFNgamma had increased lung weights. Increased lung weights in the anti-IFNgamma-treated mice corresponded to alveolar infiltration of eosinophils, neutrophils, and multinucleated giant cells and exacerbated interstitial pneumonitis compared with mice treated with control antibody. Intracellular staining indicated that there were 3- to 10-fold more CD4+ cells producing IFNgamma than those producing IL-4 in the lung lavages of mice given either syngeneic or allogeneic transplant. Treatment of transplanted mice with anti-IFNgamma resulted in a significant decrease in IFN-gamma-producing CD4+ and CD8+ cells in the lung lavages but no change in the number of IL-4-producing CD4+ cells. These data indicate that IFNgamma is critical for controlling the development of P. carinii-driven interstitial pneumonia after either syngeneic or allogeneic bone marrow transplant in mice.

Requirement of the initial production of gamma interferon in the generation of protective immunity of mice against Listeria monocytogenes

Protective immunity of mice against Listeria monocytogenes, which is mediated mainly by gamma interferon (IFN-gamma)-producing T cells, was induced by immunization with viable bacteria but not with killed bacteria. By comparing mice immunized with either viable or killed L. monocytogenes, it was found that IFN-gamma was produced at the initial stage only after immunization with viable bacteria. This finding prompted us to investigate the effect of neutralizing the IFN-gamma on the final generation of protective T cells against L. monocytogenes. When endogenous IFN-gamma was neutralized by administration of anti-IFN-gamma monoclonal antibody for the initial 2 days in mice immunized with viable bacteria, the generation of protective T cells on day 6 was completely blocked, as revealed by T-cell adoptive transfer. The generation of listeria-specific IFN-gamma-producing T cells was also abolished. These results clearly demonstrated that endogenous IFN-gamma, which is produced at the initial stage of immunization, actually plays a critical role in the generation of protective T cells against L. monocytogenes in vivo. Moreover, this study suggested that the lack of IFN-gamma-inducing ability is responsible for the inability of killed L. monocytogenes to induce protective T cells in mice.

The protective role of endogenous cytokines in host resistance against an intragastric infection with Listeria monocytogenes in mice

It has been demonstrated that endogenous cytokines including gamma-interferon (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) play a protective role but that IL-4 plays a detrimental role in systemic Listeria monocytogenes infection in mice. The diverse roles of IL-10 have been reported in antilisterial resistance. In this paper, we studied the role of endogenous cytokines in host resistance against an intragastric infection with L. monocytogenes in mice. The expression of cytokine mRNAs including IFN-gamma, TNF-alpha, IL-4, IL-6, or IL-10, which were amplified by reverse transcription-PCR, was observed in intestinal intraepithelial lymphocytes irrespective of L. monocytogenes infection. Increased numbers of L. monocytogenes were detected in the ileal contents of infected mice which received monoclonal antibodies (mAbs) against IFN-gamma, TNF-alpha, IL-4, IL-6, or IL-10. By contrast, mAbs against IL-4 or IL-6 showed little effect on the growth of L. monocytogenes in the mesenteric lymph nodes (MLNs), spleen, and liver, but anti-IFN-gamma mAb and anti-TNF-alpha mAb suppressed the defense in these organs. Anti-IL-10 mAb enhanced bacterial elimination from the MLNs but not from the spleen or liver. These results suggest that the role of endogenous cytokines may differ between systemic and intestinal defenses.

Transforming growth factor beta is protective in host resistance against Listeria monocytogenes infection in mice

The role of transforming growth factor beta (TGF-beta) in host resistance against Listeria monocytogenes infection was studied with mice. The constitutive expression of TGF-beta 1 mRNA was observed in the spleens and livers of mice before and after infection. Injecting the mice with anti-TGF-beta 1 peptide serum resulted in diminished antilisterial resistance, whereas the administration of human platelet-derived TGF-beta 1 enhanced the resistance. Moreover, mice were protected against lethal infection when treated with TGF-beta 1. These results suggest the TGF-beta 1 might be involved in antilisterial resistance. On the other hand, injecting the mice with TGF-beta 1 resulted in a decrease in the titers of endogenous gamma interferon, tumor necrosis factor alpha, and interleukin-6, which are crucial in antilisterial resistance, in sera and in extracts of spleen and liver. Thus, a complicated mechanism might be involved in the role of TGF-beta 1 in host resistance against L. monocytogenes infection.