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.     

Prevention by gamma interferon of fatal infection with Listeria monocytogenes in mice treated with cyclosporin A.

The significance of interferons (IFNs) induced by Listeria monocytogenes in the antilisterial defense mechanism was studied in mice. Cyclosporin A (CsA) had no effect on IFN-alpha production that was induced in the bloodstream after intravenous infection of mice with L. monocytogenes, whereas IFN-gamma that was induced in the bloodstreams of control mice 6 h after stimulation with specific antigen in the late phase of infection was suppressed in CsA-treated mice, depending on the dose of the drug injected. The decrease in IFN-gamma production caused an increase in bacterial growth in the spleens and livers of CsA-treated mice. Furthermore, administration of a daily dose of CsA at 80 or 100 mg/kg of body weight resulted in fatal listeriosis, even though the dose was nonlethal for normal mice. The administration of recombinant murine IFN-gamma on day 0 of L. monocytogenes infection prevented CsA-treated mice from developing fatal listeriosis and restored their ability to produce IFN-gamma in the bloodstream, in response to specific antigen in the late phase of infection.     

Endogenous tumor necrosis factor, interleukin-6, and gamma interferon levels during Listeria monocytogenes infection in mice.

Mice were infected intravenously with a sublethal dose of Listeria monocytogenes cells and then levels of tumor necrosis factor (TNF), interleukin-6 (IL-6), and gamma interferon (IFN-gamma) in the bloodstreams, spleens, and livers were monitored. The maximum level of TNF was detected at 72 h in the spleens and livers, but TNF was never detected in the bloodstreams. IL-6 appeared in the bloodstreams and spleens and peaked at 48 h. The maximum level of IFN-gamma could be detected in all three specimens, and the highest titer was shown in the spleens. Endogenous TNF production was suppressed by in vivo administration of anti-CD4 monoclonal antibody (MAb) or anti-asialo GM1 antibody but not by anti-CD8 MAb, whereas none of these antibodies suppressed endogenous IL-6 production. Endogenous production of neither IL-6 nor IFN-gamma was inhibited in rabbit anti-recombinant mouse TNF-alpha antibody-treated mice. Similarly, production of TNF and IL-6 did not decrease in anti-mouse IFN-gamma MAb-treated animals, but TNF production was augmented in these animals. These results suggest that the these endogenous cytokines are produced by different mechanisms in L. monocytogenes infection.     

Induction of alpha/beta interferon and gamma interferon in mice infected with Listeria monocytogenes during pregnancy.

Alpha/beta interferon (IFN-alpha/beta) was induced in the bloodstream of mice 48 h after intravenous infection with Listeria monocytogenes, whereas IFN-gamma was induced in the bloodstream 6 h after stimulation with specific antigen on day 5 of infection in virgin mice. In contrast, no IFN-alpha/beta or IFN-gamma was produced in the bloodstream of pregnant mice after L. monocytogenes infection. However, unusual acid-labile IFN-alpha/beta instead of IFN-gamma was produced in some of the pregnant mice in response to specific antigen. The bacterial growth in the organs of pregnant mice in the early stage of infection was normal, but resulted in the delay of T-cell-dependent elimination of bacteria from the organs of pregnant animals in the late stage, and numerous bacteria were detected in both the placenta and the fetus. The significance of the IFN system induced by L. monocytogenes infection in pregnant mice is discussed.     

The human intracellular Mx-homologous protein is specifically induced by type I interferons

The murine Mx-1 protein is one of the best biochemically and functionally characterized interferon (IFN)-induced proteins that is necessary, and sufficient, for providing resistance to murine cells against viral influenza infection. Recently an intracellular human protein homologous to the murine Mx-1 protein has been identified by means of a specific monoclonal antibody. The restricted induction of this intracellular protein in human mononuclear cells (MNC) by various cytokines was investigated. MNC from 26 of 28 healthy people and 35 of 36 cancer patients before IFN-alpha therapy had no detectable Mx-homologous protein. Incubation of human MNC with IFN-alpha and IFN-beta for 24 h at different concentrations led to a dose-dependent induction of the Mx-homologous protein. All IFN-alpha or IFN-beta preparations tested were equally effective in eliciting this intracellular protein. IFN-gamma induced only 1% of the Mx amount elicited by type-1 IFN compared on a weight basis. Neither interleukin (IL) 1 nor IL3, IL4, IL5, IL6, tumor necrosis factor-alpha/beta, granulocyte colony-stimulating factor (CSF) or granulocyte macrophage-CSF at any of the concentrations tested were capable of eliciting any detectable amount of the Mx homolog, while IL2 was a poor Mx-homologous protein inducer. In the presence of high-titered IFN-alpha antisera both IL2 and IFN-gamma were unable to stimulate this protein, proving that IFN-gamma and IL2 indirectly induce the Mx homolog via IFN-alpha. Therefore, the human Mx-homologous protein is a strictly by type I IFN-regulated protein in human peripheral blood lymphocytes.     

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

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

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

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

Decreased susceptibility of mice to infection with Listeria monocytogenes in the absence of interleukin-18

The induction of proinflammatory cytokines such as gamma interferon (IFN-gamma) and tumor necrosis factor alpha is crucial for the early control of bacterial infections. Since interleukin-18 (IL-18) acts as a potent inducer of IFN-gamma, it might play an important role in the induction of a protective immune response in listeriosis. We used a murine model of systemic Listeria monocytogenes infection to study the immune response to these intracellular bacteria in the absence of IL-18. For this purpose, IL-18-deficient mice and mice treated with anti-IL-18 neutralizing antibody were infected with L. monocytogenes, and their innate and adaptive immune responses were compared to those of control mice. Unexpectedly, we found that mice deficient in IL-18 were partially resistant to primary infection with L. monocytogenes. At day 3 after infection, the numbers of listeriae in the livers and spleens of control mice were up to 500 times higher than those in IL-18-deficient or anti-IL-18 antibody-treated mice. In addition, the level of proinflammatory cytokines was markedly reduced in IL-18-deficient mice. Enhanced resistance to L. monocytogenes infection in IL-18-deficient mice was accompanied by increased numbers of leukocytes and reduced apoptosis in the spleen 48 to 72 h after infection. In contrast, control and IL-18-deficient mice showed no significant differences in their abilities to mount a protective L. monocytogenes-specific T-cell response.     

Tumour necrosis factor (TNF alpha) in leishmaniasis. I. TNF alpha mediates host protection against cutaneous leishmaniasis.

Genetically resistant CBA mice developed significantly larger lesions to Leishmania major infection when they were injected with rabbit anti-tumour necrosis factor (TNF)-specific antibodies compared to control mice injected with normal rabbit immunoglobulin. BALB/c mice recovered from a previous infection following prophylactic sublethal irradiation also developed exacerbated lesions when treated with the anti-TNF antibody. Injection of TNF into the lesion of infected CBA mice significantly reduced the lesion development. Furthermore, TNF activates macrophages to kill Leishmania in vitro. These data demonstrate that TNF plays an important role in mediating host-protection against cutaneous leishmaniasis.     

IL-12 is dispensable for innate and adaptive immunity against low doses of Listeria monocytogenes

We have studied IL-12p35-deficient (IL-12p35(-/-)) mice to evaluate the role of IL-12 in resistance against Listeria monocytogenes. In the absence of bioactive IL-12p75, mutant mice acquired higher bacterial organ burden than wild-type mice and died during the first week following infection with normally sublethal doses of Listeria. Moreover, blood IFN-gamma levels were strikingly reduced in mutant mice at day 2 post-infection. These results suggest that in IL-12p35-deficient mice impaired production of IFN-gamma which is crucial for activation of listericidal effector functions of macrophages leads to defective innate immunity against Listeria. In contrast to mice deficient for IFN-gamma or IFN-gamma receptor which are unable to resist very low infection doses of Listeria, IL-12p35(-/-) mice resisted up to 1000 c.f.u. and were able to eliminate Listeria. Spleen cells from mutant mice re-stimulated with heat-killed Listeria produced considerable amounts of IFN-gamma, suggesting that at low dose infection sufficient IFN-gamma is produced independently of IL-12. Subsequent challenge of these immunized mice with high doses of L. monocytogenes resulted in sterile elimination demonstrating efficient memory responses. These results demonstrate for the first time that at low doses of Listeria IL-12 is neither critical for innate immunity nor for the development of protective T cell-dependent acquired immunity.     

Differential chemokine response of murine macrophages stimulated with cytokines and infected with Listeria monocytogenes

During inflammatory processes the infected macrophage is a rich source of chemokines which induce infiltration of leukocytes to the site of infection. We investigated the regulation of chemokine production by murine macrophages in response to infection with the intracellular bacterial pathogen, Listeria monocytogenes. As a source of quiescent macrophages, murine bone marrow-derived macrophages (BMM) cultured under serum-free conditions were used. With RT-PCR, we detected induction of RNA message for the chemokines macrophage inflammatory protein (MIP)-2, KC, MIP-1alpha, MIP-1beta, IFN-gamma-inducible protein- 10 and RANTES in L. monocytogenes-infected macrophages. Accordingly, ELISA-detectable MIP-1alpha, MIP-2 and KC protein was induced by infection with L. monocytogenes. In contrast, L. monocytogenes infection of BMM alone failed to induce considerable expression of monocyte chemoattractant protein (MCP)-1 at the mRNA or protein level, but co-treatment with IFN-gamma was necessary. Release of infection- triggered MIP-2, MIP-1alpha and KC was negatively regulated by IFN- gamma. Similarly, IL-4 stimulated MCP-1 release by infected macrophages but reduced production of MIP-1alpha, MIP-2 and KC. IL-10 turned out to be a general deactivator in terms of macrophage chemokine production. IL-13 had no effect on MIP-1alpha, MIP-2 and KC production by infected BMM, but slightly reduced MCP-1 release. By using IFN-gamma and IL-4 gene deletion mutant mice, in vivo regulation of these chemokines by IL- 4 and IFN-gamma in listeriosis was studied. In summary, our results show that chemokines are produced by macrophages infected with L. monocytogenes, and that chemokine release is differentially regulated by the macrophage modulators IFN-gamma, IL-4, IL-10 and IL-13.      

Gamma interferon induces monocyte killing of Listeria monocytogenes by an oxygen-dependent pathway; alpha- or beta-interferons by oxygen-independent pathways

Human peripheral blood monocytes purified by counterflow centrifugal elutriation were treated with recombinant interferons-gamma (IFN-gamma), alpha (IFN-alpha), or beta (IFN-beta)--and tested for their capacity to kill Listeria monocytogenes. All three IFNs increased the monocyte bactericidal activity in a dose-dependent fashion. Exogeneous catalase, an inhibitor of monocyte-generated hydrogen peroxide, did not affect bactericidal activity. However, exogenous superoxide dismutase inhibited killing by IFN-gamma-activated monocytes, but not by IFN-alpha- or IFN-beta-activated monocytes. By contrast, exogenous soybean trypsin inhibitor inhibited killing by IFN-alpha or IFN-beta-activated monocytes, but not by IFN-gamma-activated monocytes. Combinations of IFN-gamma and IFN-alpha resulted in no increase in bactericidal activity. Finally, treatment with IFN-gamma resulted in different receptiveness of the cell to subsequent oxidative burst-stimulating signals than did treatment with either IFN-alpha or IFN-beta. These results suggest that monocytes treated with IFN-gamma kill L. monocytogenes by an oxygen-dependent mechanism, but treatment with IFN-alpha or IFN-beta elicits principally oxygen-independent mechanisms.     

Early gamma interferon production by natural killer cells is important in defense against murine listeriosis.

A spot enzyme-linked immunosorbent assay was used to show that subcutaneous inoculation of a sublethal number of Listeria monocytogenes resulted in the early appearance of gamma interferon (IFN-gamma)-producing cells in the draining lymph nodes. In contrast, inoculation of UV-killed L. monocytogenes failed to cause the appearance of IFN-gamma-producing cells. The appearance of IFN-gamma-secreting cells in response to the living organisms peaked at 24 h of infection and then declined. The draining lymph node cells responsible for secreting IFN-gamma belonged to a cell population that was positive for the NK1.1, asialo-GM1, and Thy-1 markers but negative for the CD4 and CD8 T cell subset markers. Early elimination of natural killer (NK) cells by treatment with anti-NK cell antibodies resulted in severe exacerbation of infection, as did early neutralization of endogenous IFN-gamma by treatment with a rat anti-murine IFN-gamma monoclonal antibody. In contrast, depletion of CD4+ and CD8+ T cells failed to exacerbate infection. The results serve to show that the early production of IFN-gamma by NK cells, rather than by T cells, is an essential event in resistance to listeriosis.     

Factor XI-deficient mice display reduced inflammation, coagulopathy, and bacterial growth during listeriosis

In mice infected sublethally with Listeria monocytogenes, fibrin is deposited at low levels within hepatic tissue, where it functions protectively by limiting bacterial growth and suppressing hemorrhagic pathology. Here we demonstrate that mice infected with lethal doses of L. monocytogenes produce higher levels of fibrin and display evidence of systemic coagulopathy (i.e., thrombocytopenia, fibrinogen depletion, and elevated levels of thrombin-antithrombin complexes). When the hepatic bacterial burden exceeds 1×10(6) CFU, levels of hepatic fibrin correlate with the bacterial burden, which also correlates with levels of hepatic mRNA encoding the hemostatic enzyme factor XI (FXI). Gene-targeted FXI-deficient mice show significantly improved survival upon challenge with high doses of L. monocytogenes and also display reduced levels of hepatic fibrin, decreased evidence of coagulopathy, and diminished cytokine production (interleukin-6 [IL-6] and IL-10). While fibrin limits the bacterial burden during sublethal listeriosis in wild-type mice, FXI-deficient mice display a significantly improved capacity to restrain the bacterial burden during lethal listeriosis despite their reduced fibrin levels. They also show less evidence of hepatic necrosis. In conjunction with suboptimal antibiotic therapy, FXI-specific monoclonal antibody 14E11 improves survival when administered therapeutically to wild-type mice challenged with high doses of L. monocytogenes. Together, these findings demonstrate the utility of murine listeriosis as a model for dissecting qualitative differences between protective and pathological host responses and reveal novel roles for FXI in exacerbating inflammation and pathogen burden during a lethal bacterial infection.     

Regulation of gamma interferon production by natural killer cells in scid mice: roles of tumor necrosis factor and bacterial stimuli.

CB-17 scid mice exhibit a T-cell-independent but gamma interferon (IFN-gamma)-dependent immunity to Listeria monocytogenes. In this study, we analyzed the specific cellular interactions involved in this process. scid mouse-derived natural killer (NK) cells cultured with heat-killed (HK) L. monocytogenes and macrophages secreted IFN-gamma. No IFN-gamma was produced in cultures containing HK L. monocytogenes but lacking macrophages. However, medium derived from macrophages incubated with HK L. monocytogenes or other microorganisms stimulated IFN-gamma production by isolated NK cells. Treatment of macrophage-conditioned supernatants with neutralizing monoclonal anti-tumor necrosis factor (TNF) significantly reduced their capacity to stimulate NK cells to produce IFN-gamma. Yet, purified recombinant TNF-alpha by itself was unable to stimulate NK cells. Thus, TNF was necessary but not sufficient to induce maximal IFN-gamma production by NK cells. Sonicated L. monocytogenes stimulated production of IFN-gamma by NK cells that was resistant to anti-TNF. Stimulation was markedly enhanced by the addition of recombinant TNF-alpha. These studies demonstrated that activation of scid NK cells for secretion of IFN-gamma requires two signals: TNF-alpha and a second product which may be of bacterial origin and may require processing by mononuclear phagocytes. We suggest that the T-cell-independent production of IFN-gamma by NK cells provides the host with a rapid mechanism to temporarily heighten nonspecific resistance to infection until such time as T-cell-dependent sterilizing immune responses can be generated.     

Oromucosal interferon therapy: marked antiviral and antitumor activity.

Oromucosal administration of murine interferon-alpha/beta (IFN-alpha/beta) or individual recombinant species of murine IFN-alpha, IFN-beta, or IFN-gamma or recombinant human IFN-alpha1-8, which is active in the mouse, exerted a marked antiviral activity in mice challenged systemically with a lethal dose of encephalomyocarditis virus (EMCV), vesicular stomatitis virus (VSV), or varicella zoster virus (VZV). The effects observed were dose dependent and similar in magnitude to those observed following parenteral administration of the same dose of IFN. No antiviral activity was observed after oromucosal administration of murine IFN-alpha/beta in animals in which the IFN receptor had been inactivated by homologous recombination. In contrast to parenteral treatment, oromucosal IFN therapy was found to be ineffective when IFNs were administered before virus infection. Oromucosal administration of IFN-alpha also exerted a marked antitumor activity in mice injected i.v. with highly malignant Friend erythroleukemia cells or other transplantable tumors, such as L1210 leukemia, which has no known viral etiology, the EL4 tumor, or the highly metastatic B16 melanoma. These results show that high doses of IFN can be administered by the oromucosal route apparently without ill effect, raising the possibility that the oromucosal route will prove to be an effective means of administering high doses of IFN that are clinically effective but poorly tolerated.     

Early host-pathogen interactions in the liver and spleen during systemic murine listeriosis: an overview

Systemic listeriosis initiated by parenteral inoculation of mice with Listeria monocytogenes has been used extensively as a model infection for studying mammalian host defense against intracellular bacterial pathogens in general. Most effort has been expended on trying to understand the requirement for specific T cell-mediated immunity for combatting infection with this pathogen. By contrast, non-specific defenses have received much less attention. However, it is now obvious that these early innate defenses are critically important for the well-being of the host. If these early defenses fail to act, the murine host is rendered exquisitely susceptible to L. monocytogenes, and rapidly succumbs to overwhelming infection before T cell-mediated immunity can be generated and expressed. The most critical of these early defenses is mediated by neutrophils that rapidly accumulate in large numbers at foci of Listeria infection in the liver and spleen. These neutrophils act to curtail the growth of L. monocytogenes to levels that subsequently can be dealt with by specific defenses that are recruited into infectious foci later. In the absence of this neutrophil-mediated defense, an otherwise sublethal inoculum of L. monocytogenes rapidly grows to lethal numbers. An overview of this early aspect of murine listeriosis is presented below.     

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).     

Characterization of early gamma interferon (IFN-gamma) expression during murine listeriosis: identification of NK1.1+ CD11c+ cells as the primary IFN-gamma-expressing cells

Though it is well established that gamma interferon (IFN-gamma) is crucial to the early innate defense of murine listeriosis, its sources remain controversial. In this study, intracellular cytokine staining of IFN-gamma-expressing splenocytes early after Listeria monocytogenes infection revealed that NK1.1(+), CD11c(+), CD8(+) T, and CD4(+) T cells expressed IFN-gamma 24 h after infection. Contrary to the previous report, most IFN-gamma(+) dendritic cells (DC) were CD8alpha(-) DC. Unexpectedly, almost all CD11c(+) IFN-gamma-expressing cells also expressed NK1.1. These NK1.1(+) CD11c(+) cells represented primary IFN-gamma-expressing cells after infection. In situ studies showed these NK1.1(+) CD11c(+) cells were recruited to the borders of infectious foci and expressed IFN-gamma. A significant NK1.1(+) CD11c(+) population was found in uninfected spleen, lymph node, blood, and bone marrow cells. And its number increased significantly in spleen, lymph node, and bone marrow after L. monocytogenes infection. Using interleukin-12 (IL-12) p40(-/-) mice, IFN-gamma expression was found to be largely IL-12 p40 dependent, and the number of IFN-gamma-expressing cells was only about one-third of that of wild-type mice. Moreover, the IFN-gamma expression was absolutely dependent on live L. monocytogenes infection, as no IFN-gamma was detected after inoculation of heat-killed L. monocytogenes. Our findings not only provide an insight into IFN-gamma expression after in vivo infection but may also change the current perceptions of DC and natural killer cells.     

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.