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

[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.

Involvement of CD4⁺ Foxp3⁺ regulatory T cells in persistence of Leishmania donovani in the liver of alymphoplastic aly/aly mice

Visceral leishmaniasis (VL) is a chronic and fatal disease in humans and dogs caused by the intracellular protozoan parasites, Leishmania donovani and L. infantum (L. chagasi). Relapse of disease is frequent in immunocompromised patients, in which the number of VL cases has been increasing recently. The present study is aimed to improve the understanding of mechanisms of L. donovani persistence in immunocompromised conditions using alymphoplastic aly/aly mice. Hepatic parasite burden, granuloma formation and induction of regulatory T cells were determined for up to 7 months after the intravenous inoculation with L. donovani promastigotes. While control aly/+ mice showed a peak of hepatic parasite growth at 4 weeks post infection (WPI) and resolved the infection by 8 WPI, aly/aly mice showed a similar peak in hepatic parasite burden but maintained persistent in the chronic phase of infection, which was associated with delayed and impaired granuloma maturation. Although hepatic CD4⁺Foxp3⁺ but not CD8⁺Foxp3⁺ T cells were first detected at 4 WPI in both strains of mice, the number of CD4⁺Foxp3⁺ T cells was significantly increased in aly/aly mice from 8 WPI. Immunohistochemical analysis demonstrated the presence of Foxp3⁺ T cells in L. donovani–induced hepatic granulomas and perivascular neo-lymphoid aggregates. Quantitative real-time PCR analysis of mature granulomas collected by laser microdissection revealed the correlation of Foxp3 and IL-10 mRNA level. Furthermore, treatment of infected aly/aly mice with anti-CD25 or anti-FR4 mAb resulted in significant reductions in both hepatic Foxp3⁺ cells and parasite burden. Thus, we provide the first evidence that CD4⁺Foxp3⁺ Tregs mediate L. donovani persistence in the liver during VL in immunodeficient murine model, a result that will help to establish new strategies of immunotherapy against this intracellular protozoan pathogen.

The protozoan parasite Leishmania donovani is the causative agent of visceral leishmaniasis (VL) with a variety of outcomes ranging from asymptomatic to fatal infection. In the last decade, an increasing number of VL cases in immunocompromised conditions have been reported. Loss of the control of parasite persistence causes relapse of the disease in these patients. To clarify why parasite persistence and disease are caused in an immunocompromised condition, we examined L. donovani infection in alymphoplastic aly/aly mice that completely lack lymph nodes and have disturbed spleen architecture. Although parasites grew in the liver of aly/+ mice for the first 4 weeks post infection (WPI) and parasites were eliminated by 8 WPI, we found that parasites persisted in the liver of aly/aly mice with the ineffective of granuloma formation to kill the parasites. These aly/aly mice showed significant increases in CD4⁺Foxp3⁺ regulatory T cells in the liver. Consequently, we treated infected mice with anti-CD25 or anti-FR4 mAb to inhibit the function of Tregs, and found significant reductions in both hepatic Foxp3⁺ cells and parasite burden. These results clearly demonstrated for the first time that the expansion of CD4⁺Foxp3⁺ Tregs is involved in hepatic L. donovani persistence in immunodeficient murine model.

The TNF receptor and Ig superfamily members form an integrated signaling circuit controlling dendritic cell homeostasis

Dendritic cells (DC) constitute the most potent antigen presenting cells of the immune system, playing a key role bridging innate and adaptive immune responses. Specialized DC subsets differ depending on their origin, tissue location and the influence of trophic factors, the latter remain to be fully understood. Myeloid-associated lymphotoxin-beta receptor (LTbetaR) signaling is required for the local proliferation of lymphoid tissue DC. This review focuses on the LTbetaR signaling cascade as a crucial positive trophic signal in the homeostasis of DC subsets. The noncanonical coreceptor pathway comprised of the immunoglobulin (Ig) superfamily member, B and T lymphocyte attenuator (BTLA) and TNFR superfamily member, herpesvirus entry mediator (HVEM) counter regulates the trophic signaling by LTbetaR. Together both pathways form an integrated signaling circuit achieving homeostasis of DC subsets.

Reduction of human T-cell leukemia virus type-1 infection in mice lacking nuclear factor-kappaB-inducing kinase

Human T-cell lymphotropic virus type 1 (HTLV-1) causes adult T-cell leukemia and inflammatory disorders. Aberrant activation of nuclear factor-kappaB (NF-kappaB) has been linked to HTLV-1 pathogenesis and to various kinds of cancers, including adult T-cell leukemia. NF-kappaB-inducing kinase (NIK) is critical for non-canonical activation of NF-kappaB and for the development of lymphoid organs. HTLV-1 activates NF-kappaB by the non-canonical pathway, but examination of the role of NIK in proliferation of HTLV-1-infected cells in vivo has been hindered by lack of a suitable animal model. Alymphoplasia (aly/aly) mice bear a mutation of NIK, resulting in defects in the development of lymphoid organs and severe deficiencies in both humoral and cell-mediated immunity. In the present study we therefore used a mouse model of HTLV-1 infection with aly/aly mice. The number of HTLV-1-infected cells in the reservoir organs in aly/aly mice was significantly smaller than in the control group 1 month after infection. In addition, aly/aly mice did not maintain provirus for 1 year and antibodies against HTLV-1 were undetectable. These results demonstrate that the absence of functional NIK impairs primary HTLV-1 proliferation and abolishes the maintenance of provirus. Interestingly, clonal proliferation of HTLV-1-infected mouse cells was not detected in aly/aly mice, which is consistent with the lack of HTLV-1 persistence. These observations imply that the clonal proliferation of HTLV-1-infected cells in secondary lymphoid organs might be important for HTLV-1 persistence.

Novel tumor necrosis factor-knockout mice that lack Peyer's patches

We generated a novel tumor necrosis factor (TNF) null mutation using Cre-loxP technology. Mice homozygous for this mutation differ from their "conventional" counterparts; in particular, they completely lack Peyer's patches (PP) but retain all lymph nodes. Our analysis of these novel TNF-knockout mice supports the previously disputed notion of the involvement of TNF-TNFR1 signaling in PP organogenesis. Availability of TNF-knockout strains both with and without PP enables more definitive studies concerning the roles of TNF and PP in various immune functions and disease conditions. Here, we report that systemic ablation of TNF, but not the presence of PP per se, is critical for protection against intestinal Listeria infection in mice.

Dysregulation of interleukin-10 and interleukin-12 are involved in the reduced host resistance to Listeria monocytogenes 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 and disorganized splenic and thymic structures with immunodeficiency. Our previous study demonstrated that resistance to Listeria monocytogenes infection and interferon-gamma (IFN-gamma) production are attenuated in the mutant mice. In this study, we investigated the mechanism of decrease in antilisterial resistance and IFN-gamma production in aly mice. Interleukin (IL)-12 production in response to heat-killed L. monocytogenes (HK-LM) was decreased but IL-10 production was increased in aly/aly macrophage cultures, compared with those in aly/+ macrophages. Nonadherent cells and macrophages obtained from the spleens of naive aly/+ mice and aly/aly mice were reconstituted and stimulated with HK-LM. IFN-gamma production was markedly decreased when macrophages derived from aly/aly mice were used. IFN-gamma production in aly/aly spleen cell cultures was recovered in the presence of anti-IL-10 monoclonal antibody (mAb) or recombinant IL-12. When aly/+ mice and aly/aly mice were injected with mAb against IL-10 or IL-12 p40, antilisterial resistance was inhibited by injection of anti-IL-12 p40 mAb, while anti-IL-10 mAb treatment augmented the resistance. Administration of anti-IFN-gamma mAb attenuated antilisterial resistance in aly/+ mice but not in aly/aly mice. The present results suggest that downregulation of IL-12 and upregulation of IL-10 in macrophages might be involved in the decrease in antilisterial resistance and IFN-gamma production in aly/aly mice in addition to the structural defect in lymphoid organs. Moreover, the results predict that an IL-12-dependent and IFN-gamma-independent mechanism may be also involved in the decrease in antilisterial resistance in aly/aly 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.

Impaired protective immunity and T helper 2 responses in alymphoplasia (aly) mutant mice infected with Trichinella spiralis

The alymphoplasia (aly) mutation of mice prevents the development of systemic lymph nodes and Peyer's patches. The mutant homozygotes (aly/aly) are partially deficient in both humoral and cell-mediated immune functions. In the present study, we show that adult worm expulsion was slightly delayed and that T helper 2 (Th2)-type responses were partially defective in aly/aly mice after infection with Trichinella spiralis. Male aly/aly and aly/+ mice (8-weeks old) were infected with 400 muscle larvae. There was no difference in worm recovery between the two groups on day 5. However, worm recovery in aly/aly mice was significantly higher than that in aly/+ mice on day 14. Mucosal mast cells increased in number and peaked 14 days after infection in aly/+ mice. aly/aly mice were deficient in their mucosal mast cell response through out the primary infection. To examine the existence of mast cell precursors, aly/aly mice were treated with recombinant interleukin-3 (rIL-3) before infection. The mast cell response was poorly induced in aly/aly mice treated with rIL-3. An immunoglobulin E (IgE) response was not detected in aly/aly mice during the course of infection. Serum IgG1 levels in aly/aly mice were significantly lower than that of aly/+. The serum IgG2a levels increased in both strains of mice. However, IgG2a production in aly/aly mice on day 14 was half as much as that in aly/+mice. Stimulation of splenic T cells in vitro with anti-CD3 monoclonal antibody (mAb) showed that spleen cells from aly/+ mice on day 5 produced more IL-4 than spleen cells from aly/aly mice. IL-4 production from aly/aly mice on day 14 was half that from aly/+ mice. Interferon-gamma (IFN-gamma) was produced in both aly/aly and aly/+ mice on day 14. Proliferation assay showed that T cells of aly/aly mice responded poorly when cultured with antigen-presenting cells. These results suggest that aly gene is needed for the induction of protective immunity and Th2 responses in mice infected with T. spiralis.

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.

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.