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.     

Interactions between endogenous gamma interferon and tumor necrosis factor in host resistance against primary and secondary Listeria monocytogenes infections.

Intravenous injection of rat anti-mouse gamma interferon (IFN-gamma) monoclonal antibody as well as rabbit anti-mouse tumor necrosis factor (TNF) antibody into mice which had received a sublethal infection with Listeria monocytogenes cells resulted in acceleration of listeriosis. Endogenous IFN-gamma seemed to be produced early in infection, because suppression of antilisterial resistance was significant when a single injection of anti-IFN-gamma monoclonal antibody was given on day 0 or day 1 of infection. Production of TNF but not of IFN-gamma in the bloodstream early in infection was inhibited by administration of anti-IFN-gamma monoclonal antibody. The suppressive effect of anti-IFN-gamma and anti-TNF antibodies on antilisterial resistance was not augmented by simultaneous administration of these antibodies. On the other hand, in the secondary infection, simultaneous administration of anti-IFN-gamma and anti-TNF antibodies, but not of either of these antibodies alone, into L. monocytogenes-immune mice resulted in high mortality and explosive multiplication of bacterial cells in the spleens and livers. These results suggest that endogenously produced IFN-gamma and TNF are both essential to the host defense against L. monocytogenes infection and that these cytokines might act by different modes between the primary infection and the secondary infection.     

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.     

An anti-CD3 monoclonal antibody protects mice against a lethal infection with Listeria monocytogenes through induction of endogenous cytokines.

Mice were protected against a lethal infection with Listeria monocytogenes when treated with low doses of an anti-CD3 monoclonal antibody (MAb). Injection of anti-CD3 MAb induced rapid production of endogenous tumor necrosis factor (TNF) in the spleens and endogenous gamma interferon (IFN-gamma) in the bloodstreams and spleens of mice. Administration of anti-Thy1.2 MAb or a combination of anti-CD4 MAb and anti-CD8 MAb resulted in suppression of anti-CD3 MAb-induced endogenous cytokine production and antilisterial resistance. Alternatively, in vivo depletion of anti-CD3 MAb-induced TNF and IFN-gamma by the simultaneous administration of antibodies against TNF and IFN-gamma suppressed anti-CD3 MAb-induced antilisterial resistance. Moreover, injection of anti-complement receptor type 3 (Mac-1, CD11b) resulted in inhibition of anti-CD3 MAb-induced antilisterial resistance. These results suggest that the preventive effect of anti-CD3 MAb might be due to activation of phagocytes by TNF and IFN-gamma induced by stimulating CD4+ T cells and CD8+ T cells with the MAb. Furthermore, treatment with anti-CD3 MAb did not inhibit establishment of acquired resistance against secondary infection with L. monocytogenes.     

Endogenous tumor necrosis factor (cachectin) is essential to host resistance against Listeria monocytogenes infection.

During a sublethal murine infection with Listeria monocytogenes cells, tumor necrosis factor (TNF) activity was detectable in neither sera nor spleen homogenates at any stage of the infection when a bioassay with L-929 cells (less than 4 U/ml) was used. However, injecting the mice with an immunoglobulin fraction obtained from a rabbit hyperimmunized with recombinant murine TNF-alpha resulted in acceleration of listeriosis. When 1 mg of anti-TNF antibody was injected per mouse, all the mice died from listeriosis, even though the infectious dose was sublethal for the untreated controls. The antigen-specific elimination of the bacterium from the spleens and livers of anti-TNF antibody-treated mice was delayed, depending on the dose of the antibody injected. Endogenous TNF seemed to be produced early in infection, because suppression of antilisterial resistance was significant when a single injection of anti-TNF antibody was given between day zero and day 2 of infection. The effect of endogenous TNF on antilisterial resistance was due to neither regulation of alpha interferon (IFN-alpha) and IFN-gamma production nor induction of IFN-beta subtype 1 (IFN-beta 1), because anti-TNF antibody treated-mice produced normal levels of IFN-alpha and IFN-gamma in the bloodstream during infection and administration of monoclonal anti-murine IFN-beta 1 antibody had no effect on the development of listeriosis. Alternatively, the listericidal activity of peritoneal macrophages of L. monocytogenes-infected mice could be abrogated by injection of anti-TNF antibody in vivo. These results suggest that the lower level of TNF is produced endogenously in mice that received L. monocytogenes infection and that it plays an essential role in the host defense against L. monocytogenes infection.     

Effects of IL-13 on murine listeriosis

Acquired resistance against Listeria monocytogenes is a typical T helper (Th) 1 dominated immune response, whereas Th2 cytokines are thought to worsen listeriosis. We investigated effects of recombinant IL-13 (rIL-13) on the host response to L. monocytogenes in mice. Although IL-13 has been described as a Th2 cytokine with deactivating anti-inflammatory activities, it was found to enhance antilisterial resistance. In vitro, rIL-13 increased IL-12 p40 and p70 production by bone marrow macrophages infected with L. monocytogenes. In vivo, numbers of viable bacteria in spleens and livers were decreased after treatment of mice with rIL-13. In addition, granuloma formation was impaired and NK cell activity of spleen cells was enhanced. At the onset of infection, frequencies of IL-12-producing cells were increased and numbers of IL-4- and IFN-gamma-secreting cells were diminished in rIL-13-treated mice as compared to controls. In contrast, on day 6 after infection, IL-12, IL-4 and IFN-gamma levels in rIL-13-treated animals were equal to or even higher than those in controls. Although direct activation of host macrophages by IL-13 is possible, we consider it more likely that IL-13 acted indirectly through stimulation of IL-12 production and inhibition of IL-4 release early after infection. In contrast, our data argue against an apparent role of IFN-gamma in IL-13- induced antilisterial resistance.      

Adaptive immunity against Listeria monocytogenes in the absence of type I tumor necrosis factor receptor p55

Tumor necrosis factor (TNF) and the type I TNF receptor (TNFRI), p55, are critical for resistance against primary infections with the intracellular bacterial pathogen Listeria monocytogenes. Importantly, however, susceptibility to primary listeriosis in cytokine-deficient mice does not preclude the development or expression of effective adaptive immunity against virulent L. monocytogenes. We used TNFRI(-/-) mice to study adaptive antilisterial immunity in the absence of interactions between TNF and TNFRI. Our experiments indicate that TNFRI(-/-) mice survive and clear high-dose challenges with an attenuated strain of L. monocytogenes that is incapable of cell-to-cell spread. Furthermore, TNFRI(-/-) mice immunized with attenuated L. monocytogenes go on to develop potent adaptive immunity to subsequent high-dose challenges with virulent L. monocytogenes. Interestingly, CD8(+) T-cell depletion in vivo inhibits immunity to L. monocytogenes in the spleen but not in the liver of TNFRI(-/-) mice. The adaptive immune response in these animals is characterized by activation of listeriolysin O-specific CD8(+) T cells, which are capable of transferring antilisterial immunity to naive wild-type C57BL/6 host mice. These experiments demonstrate the development and expression of potent CD8(+) T-cell-mediated antilisterial immunity in the absence of TNFRI.     

Evidence that endogenous gamma interferon is produced early in Listeria monocytogenes infection.

It has been presumed that gamma interferon (IFN-gamma), which plays an essential role in antilisterial resistance, is produced late in Listeria monocytogenes infection. In the present study, however, IFN-gamma was detected in the bloodstreams and spleens of mice from days 1 to 4 of L. monocytogenes infection by both a double-sandwich enzyme-linked immunosorbent assay and an immunohistochemical technique, suggesting that endogenous IFN-gamma is produced early but not late in L. monocytogenes infection.     

Recombinant murine gamma interferon induces enhanced resistance to Listeria monocytogenes infection in neonatal mice.

Neonatal mice within 24 h of birth were highly susceptible to intraperitoneal infection with Listeria monocytogenes. The 50% lethal dose of bacterial cells was 6.3 X 10(1) CFU for neonates and 3.2 X 10(6) CFU for adult mice. A single injection of recombinant murine gamma interferon (rMuIFN-gamma) protected neonatal mice from simultaneous challenge with a lethal dose of L. monocytogenes cells. The rMuIFN-gamma effect was dose dependent: protection was consistently observed in mice treated with rMuIFN-gamma at doses of more than 4 X 10(2) U (0.1 microgram of protein) per mouse. Bacterial growth in the spleens and livers of rMuIFN-gamma-treated neonates was significantly suppressed in comparison with that in the nontreated controls. The infected neonatal mice showed acquired antilisterial resistance against secondary intravenous infection after 4 weeks of age, and this resistance was significantly augmented in mice that had been treated with rMuIFN-gamma.     

Antilisterial immunity includes specificity to listeriolysin O (LLO) and non-LLO-derived determinants.

Subclinical infection of BALB/c mice with virulent Listeria monocytogenes leads to the generation of Listeria-specific T-cell populations required for the expression of protective immunity. The L. monocytogenes-produced hemolysin listeriolysin O (LLO) is a virulence factor which appears to be crucial for the induction of protective antilisterial immunity. Analysis of the specificity of antilisterial cytotoxic cells from Listeria-immune BALB/c donors has shown a dominant response to an epitope corresponding to amino acids 91 to 99 of LLO. Demonstration of antilisterial T cells with specificity to non-LLO-derived epitopes has been difficult to achieve because of the requirement of LLO in facilitating escape of the bacteria to the cytoplasm of the host cell and the apparent dominance of an anti-LLO response in antilisterial immunity. In this study we show that antilisterial immunity also includes specificity to non-LLO-derived determinants. We used as an immunogen an LLO- mutant of L. monocytogenes which expresses the hemolysin perfringolysin O (PFO). The LLO- PFO+ L. monocytogenes mutant possesses invasive properties similar to those of wild-type L. monocytogenes and escape from the phagocytic vacuole because of the activity of PFO. We found that J774 target cells infected with the LLO- PFO+ L. monocytogenes mutant were lysed by antilisterial cytotoxic T cells obtained from BALB/c mice immunized with wild-type L. monocytogenes. In addition, BALB/c mice immunized with the LLO- PFO+ L. monocytogenes mutant were immune to challenge with LLO+ wild-type L. monocytogenes, a finding indicative of protective antilisterial immunity specific to Listeria-derived epitopes other than LLO. Spleen cells from BALB/c mice immunized with the LLO- PFO+ L. monocytogenes mutant adoptively transferred antilisterial protection to a subsequent challenge with wild-type L. monocytogenes. This splenocyte population also contained cytotoxic cells which lysed target cells infected with either the LLO- PFO+ L. monocytogenes mutant or wild-type LLO+ L. monocytogenes but did not lyse target cells infected with an LLO-expressing Bacillus subtilis transformant. These results establish that during the immune response to L. monocytogenes, immune splenocytes with specificity for LLO and other, non-LLO-derived epitopes develop. These non-LLO epitopes serve as targets for antilisterial cytotoxic cells and for lymphocytes which adoptively transfer antilisterial immunity.     

Reduced antilisterial activity of TNF-deficient bone marrow-derived macrophages is due to impaired superoxide production.

Mice deficient for TNF ligand and receptor type 1 have demonstrated the importance of TNF in the host defense against Listeria monocytogenes. To investigate the particular deficiency of macrophages derived from TNF/lymphotoxin (LT)-alpha(-/-) mice in antilisterial growth control, bone marrow-derived macrophages (BMDM) were used for in vitro infection experiments. After the combined treatment with IFN-gamma and lipopolysaccharide (LPS), production of NO by wild-type (wt) and TNF/LT-alpha(-/-) BMDM was induced to comparable levels, but only wt BMDM controlled L. monocytogenes growth efficiently. Nevertheless, inhibition of NO production led to a remarkable loss of antilisterial activity. This suggests that presence of NO is necessary but not sufficient for L. monocytogenes killing and that elimination of L. monocytogenes requires additional effector molecules. The LPS-inducible superoxide production of TNF/LT-alpha(-/-) BMDM was impaired. Accordingly both scavenging of superoxide and peroxynitrite led to reduced L. monocytogenes killing by wt BMDM. In addition, peroxynitrite was able to kill L. monocytogenes in vitro. Together these findings suggest that the defective host defense of TNF/LT-alpha-deficient mice against L. monocytogenes partially stems from reduced superoxide production of macrophages due to the absence of TNF and imply a function for peroxynitrite, the reaction product of NO and superoxide, in the intracellular killing of L. monocytogenes.     

Suppression of host resistance against Listeria monocytogenes infection by 15-deoxyspergualin in mice

The effects of 15-deoxyspergualin (DSG), an immunosuppressive agent, on host resistance against Listeria monocytogenes were studied in mice. Administration of DSG in the early phase of infection resulted in fatal listeriosis by preventing acquired anti-listerial resistance, even though the infectious dose was sublethal for the untreated controls. In contrast, DSG treatment started after development of the acquired immunity was ineffective. Endogenous production of interferon-gamma (IFN-gamma) and tumour necrosis factor (TNF) in the bloodstreams induced by the infection was normal in DSG-treated mice. Nevertheless, augmentation of macrophage functions such as expression of major histocompatibility complex (MHC) class II antigens, phagocytic activity and listericidal activity induced by the infection was abrogated by DSG treatment. These results suggest that the inhibitory effect of DSG on anti-listerial resistance might be different from cyclosporine A (CsA).     

Host resistance to an intragastric infection with Listeria monocytogenes in mice depends on cellular immunity and intestinal bacterial flora.

Suckling and adult mice were infected intragastrically with different doses of viable Listeria monocytogenes. The 50% lethal dose for the intragastric infection was 10(3.7) CFU for suckling mice, while adult mice were highly resistant and the 50% lethal dose was more than 10(9.3) CFU. When adult mice were infected intragastrically with 5 x 10(8) CFU of L. monocytogenes, no mice died. However, 35% of adult mice died when they were treated with cyclosporin A 1 day before infection. Although mice did not die when treated with an L. monocytogenes-resistant broad-spectrum cephalosporin, sodium cefbuperazone, before and during infection, the number of L. monocytogenes bacteria increased in the feces. The sodium cefbuperazone treatment of mice resulted in superinfection, i.e., a marked decrease of Escherichia coli and an increase of Enterococcus spp. in the intestines. Furthermore, host resistance against the intragastric infection markedly decreased when the mice were treated with both drugs. The growth of L. monocytogenes was augmented in the spleens, mesenteric lymph nodes, Peyer's patches, and feces, and the mortality of the mice was 65%. These results suggest that both cellular immunity and the intestinal bacterial flora are required for host resistance against oral L. monocytogenes infection.     

Endogenous gamma interferon-independent host resistance against Listeria monocytogenes infection in CD4+ T cell- and asialo GM1+ cell-depleted mice.

The effects of in vivo administration of antibodies against T-cell subsets and asialo GM1 (ASGM1)-bearing cells on endogenous gamma interferon (IFN-gamma) production and host defense in Listeria monocytogenes-infected mice were investigated. Endogenous IFN-gamma titers in the bloodstreams and spleen extracts of mice on day 2 of infection were partially suppressed by administration of rabbit anti-ASGM1 antibody, but not by anti-CD4 monoclonal antibody (MAb) or anti-CD8 MAb. Of the different combinations of these three antibodies, the most suppressive effect on IFN-gamma production was observed after administration of anti-CD4 Mab and anti-ASGM1 antibody, although anti-CD8 MAb combined with anti-CD4 MAb partially inhibited IFN-gamma production. In contrast, antilisterial resistance was suppressed by the administration of anti-CD8 MAb but not by anti-CD4 MAb or anti-ASGM1 antibody. Antilisterial resistance in mice in which both CD4+ cells and ASGM1+ cells had been depleted was performed as efficiently as in normal mice in spite of the fact that endogenous IFN-gamma production was markedly suppressed. Furthermore, these mice also eliminated L. monocytogenes cells efficiently from the spleens even when they were pretreated with anti-mouse IFN-gamma MAb. These results indicate that CD4+ T cells, CD8+ T cells, and ASGM1+ cells are all responsible for endogenous IFN-gamma production and that antilisterial resistance and endogenous IFN-gamma production are not absolutely correlated.     

Characteristics of Mononuclear Phagocytes Mediating Antilisterial Resistance in Splenectomized Mice

The characteristics of mononuclear phagocytes mediating resistance to infection with Listeria monocytogenes during the early phase (up to 48 h) of the response were investigated in mice of the A strain that had undergone splenectomy. Although irradiation in the sham-operated host had no effect on its antilisterial response when administered immediately before infection, it markedly reduced the ability of the splenectomized host to resist listerial challenge. This effect of radiation was demonstrable in the high-dose range (600 r) and could not be reversed immediately by repopulation with 20 × 10⁶ syngeneic nucleated bone marrow cells. Administration of silica 24 h before infection profoundly enhanced the growth of L. monocytogenes in the liver of splenectomized mice. Shielding of the liver, but not the bone marrow, protected the splenectomized host against the effects of radiation, indicating that the cell population responsible for mediating the enhanced antilisterial resistance resides in the liver. The enhanced antilisterial resistance of splenectomized mice was specifically because of the absence of the spleen and not merely because of the removal of a favorable replicating environment for listeria organisms.     

A protective role of gamma delta T cells in primary infection with Listeria monocytogenes in autoimmune non-obese diabetic mice.

We investigated the host defense mechanism in primary infection with Listeria monocytogenes in non-obese diabetic (NOD) mice at pre-diabetic stage showing an impaired responsiveness of the alpha beta T cells to T-cell receptor (TCR) triggering. The NOD mice showed a deteriorated resistance at the late stage after an intraperitoneal infection with L. monocytogenes compared with BALB/c and C57BL/6 mice as assessed by bacterial growth in organs. Consistent with our previous findings, a prominent increase in number of gamma delta T cells was evident at the early stage after infection, while generation of Listeria-specific alpha beta T cells was impaired in these mice. In vivo administration of anti-TCR gamma delta monoclonal antibody (mAb) allowed L. monocytogenes to grow exaggeratedly in the NOD mice. These results imply that gamma delta T cells may be mainly involved in protection against primary infection with L. monocytogenes in NOD mice.     

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.     

Assessment of interleukin-12, gamma interferon, and tumor necrosis factor alpha secretion in sera from mice fed with dietary lipids during different stages of Listeria monocytogenes infection

Recent experimental observations have determined that long-chain n-3 polyunsaturated fatty acids suppress immune functions and are involved in the reduction of infectious disease resistance. BALB/c mice were fed for 4 weeks with one of four diets containing either olive oil (OO), fish oil (FO), hydrogenated coconut oil, or a low fat level. Interleukin-12p70 (IL-12p70), gamma interferon (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha) production in the sera of mice fed these diets and challenged with Listeria monocytogenes were determined by enzyme-linked immunosorbent assay. In addition, bacterial counts from spleens of mice were carried out at 24, 72, or 96 h of infection. Here, we quantified an initial diminution of production of both IL-12p70 and IFN-gamma, which appear to play an important role in the reduction of host resistance to L. monocytogenes infection. In addition, an efficient elimination of L. monocytogenes was observed in spleens of mice fed a diet containing OO at 96 h of infection, despite reductions in IL-12p70 and TNF-alpha production, suggesting an improvement of immune resistance. Overall, our results indicate that the initial reduction of both IL-12 and IFN-gamma production before L. monocytogenes infection represents the most relevant event that corroborates the impairment of immune resistance by n-3 polyunsaturated fatty acids during the different stages of infection. However, we speculate that the modulation of other cytokines must be also involved in this response, because the alteration of cytokine production in mice fed an FO diet in a late phase of L. monocytogenes infection was similar to that in mice fed OO, whereas the ability to eliminate this bacterium from the spleen was improved in the latter group.     

Passive transfer of acquired resistance to Listeria monocytogenes infection is independent of mononuclear cell granuloma formation.

This study documents the formation of leukocyte foci in the livers of mice infused with either normal or immune T cells and then challenged intravenously with Listeria monocytogenes. The results show that the transfer of antilisterial resistance occurred before mononuclear cell granuloma formation and was associated instead with the appearance of foci of infiltrating lymphocytes and neutrophils. Numbers of these foci remained low in mice which received immune cells but increased progressively until death in mice which received normal cells. These findings do not support the previous hypothesis that a major component of acquired resistance against Listeria infection involves the rapid generation of mononuclear cell granuloma formation under the control of immune T cells.     

Acquired resistance against a secondary infection with Listeria monocytogenes in mice is not dependent on reactive nitrogen intermediates.

During an infection, inflammatory mediators can induce the production of nitric oxide, a reactive nitrogen intermediate (RNI) which plays a role in antimicrobial activity against a wide variety of pathogens. In vitro experiments have shown that release of RNI by macrophages is mediated by tumor necrosis factor alpha (TNF). Since TNF is essential for acquired resistance during a secondary Listeria monocytogenes infection in mice, the aim of the present study was to determine whether RNI are also involved in the course of such an infection. Mice which had recovered from a sublethal primary infection with 0.1 50% lethal dose of (LD50) L. monocytogenes were infected intravenously with 10LD50 of L. monocytogenes. During a primary infection, the number of bacteria in the liver and spleen, as well as the concentration of RNI in plasma, increased. During a secondary infection, the number of bacteria in the liver and spleen decreased whereas no significant increase in the concentration of RNI in plasma was observed. Neutralization of endogenously produced TNF and gamma interferon by subcutaneous injection of alginate-encapsulated monoclonal antibody-forming cells during a secondary infection resulted in an increase in the number of bacteria in the liver and spleen an increase in the concentration of RNI in plasma. When the production of RNI was inhibited by treatment of mice with competitive NO-synthase inhibitor N omega-nitro-L-arginine methyl ester hydrochloride (L-Name) and an iota-arginine-deficient diet during a secondary infection, the proliferation of L. monocytogenes in the liver and spleen was not affected whereas the concentration of RNI in plasma of these mice was significantly reduced. Our findings that inhibition of RNI formation during a secondary infection does not affect the proliferation of L. monocytogenes in the liver and spleen and that enhanced elimination of bacteria from these organs is not accompanied by an increase in the concentration of RNI in plasma led to the conclusion that resistance against a secondary infection with L. monocytogenes is not dependent on RNI.