Hiroshi Sashinami

Lon, a Stress-Induced ATP-Dependent Protease, Is Critically Important for Systemic Salmonella enterica Serovar Typhimurium Infection of Mice

ABSTRACT Studies on the pathogenesis of Salmonella enterica serovar Typhimurium infections in mice have revealed the presence of two prominent virulence characteristics—the invasion of the nonphagocytic cells to penetrate the intestinal epithelium and the proliferation within host phagocytic cells to cause a systemic spread and the colonization of host organs. We have recently demonstrated that the ATP-dependent Lon protease of S. enterica serovar Typhimurium negatively regulates the efficiency of invasion of epithelial cells and the expression of invasion genes (A. Takaya et al., J. Bacteriol. 184:224-232, 2002). This study was performed to reveal the contribution of the Lon protease to the virulence of S. enterica serovar Typhimurium in mice. Determination of 50% lethal doses for the lon disruption mutant and wild-type strain revealed that the mutant was highly attenuated when administered either orally or intraperitoneally to BALB/c mice. The mutant was also found to be able to reach extraintestinal sites but unable to proliferate efficiently within the spleen and cause lethal systemic disease of mice. Macrophage survival assays revealed that the lon disruption mutant could not survive or proliferate within murine macrophages. In addition, the mutant showed extremely increased susceptibility to hydrogen peroxide, which contributes to the bactericidal capacity of phagocytes. The mutant also showed increased sensitivity to acidic conditions. Taken together, the impaired ability of the lon disruption mutant to survive and grow in macrophages could be due to the enhanced susceptibility to the oxygen-dependent killing mechanism associated with respiratory burst and the low phagosomal pH. These results suggest that the Lon protease is essentially involved in the systemic infection of mice with S. enterica serovar Typhimurium, which can be fatal. Of further interest is the finding that the lon disruption mutant persists in the BALB/c mice for long periods without causing an overwhelming systemic infection.

Vaccination with Nontoxic Mutant Toxic Shock Syndrome Toxin 1 Protects against Staphylococcus aureus Infection

To investigate whether vaccination with nontoxic mutant toxic shock syndrome toxin 1 (mTSST-1) can protect against Staphylococcus aureus infection, mice were vaccinated with mTSST-1 and challenged with viable S. aureus. Survival in the mTSST-1-vaccinated group was higher, and bacterial counts in organs were significantly lower than those of control mice. Passive transfer of mTSST-1-specific antibodies also provided protection against S. aureus-induced septic death. Interferon (IFN)-gamma production in the serum samples and spleens from vaccinated mice was significantly decreased compared with that in controls, whereas interleukin-10 titers were significantly higher in vaccinated mice. IFN-gamma and tumor necrosis factor-alpha production in vitro were significantly inhibited by serum samples from mTSST-1-immunized mice but not from control mice. These results suggest that vaccination with mTSST-1 devoid of superantigenic properties provides protection against S. aureus infection and that the protection might be mediated by TSST-1-neutralizing antibodies as well as by the down-regulation of IFN-gamma production.

Disruption of the Genes for ClpXP Protease in Salmonella enterica Serovar Typhimurium Results in Persistent Infection in Mice, and Development of Persistence Requires Endogenous Gamma Interferon and Tumor Necrosis Factor Alpha

ABSTRACT The enteric pathogen Salmonella enterica serovar Typhimurium, similar to other facultative intracellular pathogens, has been shown to respond to the hostile conditions inside macrophages of the host organism by producing a set of stress proteins that are also induced by various environmental stresses. The stress-induced ClpXP protease is a member of the ATP-dependent proteases, which are known to be responsible for more than 90% of all proteolysis inEscherichia coli. To investigate the contribution of the ClpXP protease to the virulence of serovar Typhimurium we initially cloned the clpP and clpX operon from the pathogenic strain serovar Typhimurium χ3306 and then created insertional mutations in the clpP and/or clpXgene. The ΔclpP and ΔclpX mutants were used to inoculate BALB/c mice by either the intraperitoneal or the oral route and found to be limited in their ability to colonize organs of the lymphatic system and to cause systemic disease in the host. A variety of experiments were performed to determine the possible reasons for the loss of virulence. An oxygen-dependent killing assay using hydrogen peroxide and paraquat (a superoxide anion generator) and a serum killing assay using murine serum demonstrated that all of the serovar Typhimurium ΔclpP and ΔclpX mutants were as resistant to these killing mechanisms as the wild-type strain. On the other hand, the macrophage survival assay revealed that all these mutants were more sensitive to the intracellular environment than the wild-type strain and were unable to grow or survive within peritoneal macrophages of BALB/c mice. In addition, it was revealed that the serovar Typhimurium ClpXP-depleted mutant was not completely cleared but found to persist at low levels within spleens and livers of mice. Interferon gamma-deficient mice and tumor necrosis factor alpha-deficient mice failed to survive the attenuated serovar Typhimurium infections, suggesting that both endogenous cytokines are essential for regulation of persistent infection with serovar Typhimurium.

Immunization with a Nontoxic Mutant of Staphylococcal Enterotoxin A, SEAD227A, Protects against Enterotoxin-Induced Emesis in House Musk Shrews

BACKGROUND Staphylococcal enterotoxins (SEs) are the most common cause of foodborne diseases and toxic shock throughout the world. However, no vaccine that prevents emesis induced by SEs has been described. METHODS A nontoxic mutant of SEA, SEAD227A, was constructed by site-directed mutagenesis and was purified by means of the Escherichia coli expression system. House musk shrews, a small emetic animal model, were immunized with SEAD227A and then challenged with wild-type SEA. SEA-induced emesis was recorded for 3 h. Antibody production was analyzed by gel double-immunodiffusion assay. Neutralizing activities of the antibodies with respect to superantigenic and emetic activities were analyzed in vitro and in vivo. RESULTS SEAD227A was devoid of both superantigenic and emetic activities but still retained its immunological activity. Immunization with SEAD227A strongly induced specific antibody production and provided significant protection against SEA-induced emesis. Antibodies from immunized shrews markedly inhibited the SEA-induced proliferation of spleen cells and also significantly ablated SEA-induced vomiting in the animals. CONCLUSIONS These results suggest that vaccination with SEAD227A, which is devoid of toxic properties, provides protection against SEA-induced emesis. This nontoxic mutant and its specific antibodies might be useful in the prevention and treatment of staphylococcal food poisoning.

Effective Induction of Acquired Resistance to Listeria monocytogenes by Immunizing Mice with In Vivo-Infected Dendritic Cells

ABSTRACT 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-γ) 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-γ-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-γ, 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.

Mouse peptidoglycan recognition protein PGLYRP-1 plays a role in the host innate immune response against Listeria monocytogenes infection.

ABSTRACT The role of mouse peptidoglycan recognition protein PGLYRP-1 in innate immunity against Listeria monocytogenes infection was studied. The recombinant mouse PGLYRP-1 and a polyclonal antibody specific to PGLYRP-1 were prepared. The mouse PGLYRP-1 showed antibacterial activities against L. monocytogenes and other Gram-positive bacteria. PGLYRP-1 mRNA expression was induced in the spleens and livers of mice infected with L. monocytogenes. The viable bacterial number increased, and the production of cytokines such as gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) was reduced in mice when mice had been injected with anti-PGLYRP-1 antibody before infection. The levels of IFN-γ and TNF-α titers in the organs were higher and the viable bacterial number was reduced in mice injected with recombinant mouse PGLYRP-1 (rmPGLYRP-1) before infection. PGLYRP-1 could directly induce these cytokines in spleen cell cultures. The elimination of intracellular bacteria was upregulated in NMuLi hepatocyte cells overexpressing PGLYRP-1. The enhancement of the elimination of L. monocytogenes from the organs was observed in IFN-γ−/− mice by rmPGLYRP-1 administration but not in TNF-α−/− mice. These results suggest that PGLYRP-1 plays a role in innate immunity against L. monocytogenes infection by inducing TNF-α.

Salmon cartilage proteoglycan suppresses mouse experimental colitis through induction of Foxp3+ regulatory T cells

Proteoglycans (PGs) are complex glycohydrates which are widely distributed in extracellular matrix (ECM). PGs are involved in the construction of ECM, cell proliferation and differentiation. ECM components are involved in transduction of proinflammatory responses, but it is still unknown whether PGs are involved in inflammatory response. In this study, we investigated the effect of PG extracted from salmon cartilage on the progression of experimental colitis-induced in severe combined immunodeficiency mice by cell transfer from interleukin-10 (IL-10)-/- mice. IL-10-/- cell-transferred mice showed weight loss, colon shortening and histological appearance of mild colitis. Daily oral administration of PG attenuated the clinical progression of colitis in a dose-dependent manner. Colitis-induced mice showed the elevated expression of IFN-γ, IL-12, TNF-α, IL-21, IL-23p19, IL-6, IL-17A and retinoic acid-related orphan receptor γt (RORγt) in lamina propria mononuclear cells (LPMCs) and oral administration of PG suppressed the expression of these factors. Conversely, expression of Foxp3 that induces CD4+CD25+ regulatory T cells in LPMCs was enhanced by PG administration. These findings suggested that salmon PG attenuated the progression of colitis due to suppression of inflammatory response by enhancement of regulatory T cell induction.

A Mutant of Staphylococcal Enterotoxin C Devoid of Bacterial Superantigenic Activity Elicits a Th2 Immune Response for Protection against Staphylococcus aureus Infection

ABSTRACT 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-γ) 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-γ production and up-regulated IL-10 production in vitro. Furthermore, IFN-γ 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.

Salmon proteoglycan suppresses progression of mouse experimental autoimmune encephalomyelitis via regulation of Th17 and Foxp3(+) regulatory T cells.

AIMS Proteoglycans (PGs) are complex glycohydrates, which are composed of core proteins and glycosaminoglycans and widely distributed in connective tissues. We investigated the effect of PG extracted from salmon cartilage in progression of mouse experimental autoimmune encephalomyelitis (EAE). MAIN METHODS EAE was induced by immunization with myelin-oligodendrocyte glycoprotein (MOG). Mice were given orally once daily with salmon cartilage PG and severity of EAE was monitored. Expression of Th17- and regulatory T cell-related factors was determined by ELISA and/or quantitative real time PCR. Expression of Foxp3(+) in CD4(+)CD25(+) cells was analyzed by flow cytometry. KEY FINDINGS Daily oral administration of PG attenuated clinical and histological severity of EAE in a dose-dependent manner. It suppressed interferon-β (IFN-β) production and CCL2 expression in spinal cord that is the inflamed site of EAE. Administration of PG suppressed IFN-γ and interleukin-17 (IL-17) production from lymphocytes from draining lymph nodes in response to MOG re-stimulation ex vivo. Moreover, administration of PG suppressed the expression of IL-6, IL-21, IL-23 receptor and retinoic acid-related orphan receptor γt and enhanced the expression of Foxp3 in both draining lymph nodes and spinal cords. SIGNIFICANCE Salmon cartilage PG attenuates the severity of EAE by suppressing the differentiation of Th17 linage and enhancement of Treg expansion. Our results indicated that PG has potential to be a novel prophylactic agent for autoimmune diseases.

Listeria monocytogenes Induces 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.