TLR9-dependent and independent pathways drive activation of the immune system by Propionibacterium acnes

Propionibacterium acnes is usually a relatively harmless commensal. However, under certain, poorly understood conditions it is implicated in the etiology of specific inflammatory diseases. In mice, P. acnes exhibits strong immunomodulatory activity leading to splenomegaly, intrahepatic granuloma formation, hypersensitivity to TLR ligands and endogenous cytokines, and enhanced resistance to infection. All these activities reach a maximum one week after P. acnes priming and require IFN-γ and TLR9. We report here the existence of a markedly delayed (1-2 weeks), but phenotypically similar TLR9-independent immunomodulatory response to P. acnes. This alternative immunomodulation is also IFN-γ dependent and requires functional MyD88. From our experiments, a role for MyD88 in the IFN-γ-mediated P. acnes effects seems unlikely and the participation of the known MyD88-dependent receptors, including TLR5, Unc93B-dependent TLRs, IL-1R and IL-18R in the development of the alternative response has been excluded. However, the crucial role of MyD88 can partly be attributed to TLR2 and TLR4 involvement. Either of these two TLRs, activated by bacteria and/or endogenously generated ligands, can fulfill the required function. Our findings hint at an innate immune sensitizing mechanism, which is potentially operative in both infectious and sterile inflammatory disorders.     

Adjuvant effect of killed Propionibacterium acnes on mouse peritoneal B-1 lymphocytes and their early phagocyte differentiation

B-1 lymphocytes are the predominant cells in mouse peritoneal cavity. They express macrophage and lymphocyte markers and are divided into B-1a, B-1b and B-1c subtypes. The role of B-1 cells is not completely clear, but they are responsible for natural IgM production and seem to play a regulatory role. An enriched B-1b cell population can be obtained from non-adherent peritoneal cell cultures, and we have previously demonstrated that these cells undergo differentiation to acquire a mononuclear phagocyte phenotype upon attachment to the substrate in vitro. Nevertheless, the B-1 cell response to antigens or adjuvants has been poorly investigated. Because killed Propionibacterium acnes exhibits immunomodulatory effects on both macrophages and B-2 lymphocytes, we analyzed whether a killed bacterial suspension or its soluble polysaccharide (PS) could modulate the absolute number of peritoneal B-1 cells in BALB/c mice, the activation status of these cells and their ability to differentiate into phagocytes in vitro. In vivo, P. acnes treatment elevated the absolute number of all B-1 subsets, whereas PS only increased B-1c. Moreover, the bacterium increased the number of B-1b cells that were positive for MHC II, TLR2, TLR4, TLR9, IL-4, IL-5 and IL-12, in addition to up-regulating TLR9, CD80 and CD86 expression. PS increased B-1b cell expression of TLR4, TLR9, CD40 and CD86, as well as IL-10 and IL-12 synthesis. Both of the treatments decreased the absolute number of B-1b cells in vitro, suggesting their early differentiation into B-1 cell-derived phagocytes (B-1CDP). We also observed a higher phagocytic activity from the phagocytes that were derived from B-1b cells after P. acnes and PS treatment. The adjuvant effect that P. acnes has on B-1 cells, mainly the B-1b subtype, reinforces the importance of B-1 cells in the innate and adaptive immune responses.     

Cutting edge: TLR9 and TLR2 signaling together account for MyD88-dependent control of parasitemia in Trypanosoma cruzi infection

Activation of innate immune cells by Trypanosoma cruzi-derived molecules such as GPI anchors and DNA induces proinflammatory cytokine production and host defense mechanisms. In this study, we demonstrate that DNA from T. cruzi stimulates cytokine production by APCs in a TLR9-dependent manner and synergizes with parasite-derived GPI anchor, a TLR2 agonist, in the induction of cytokines by macrophages. Compared with wild-type animals, T. cruzi-infected Tlr9(-/-) mice displayed elevated parasitemia and decreased survival. Strikingly, infected Tlr2(-/-)Tlr9(-/-) mice developed a parasitemia equivalent to animals lacking MyD88, an essential signaling molecule for most TLR, but did not show the acute mortality displayed by MyD88(-/-) animals. The enhanced susceptibility of Tlr9(-/-) and Tlr2(-/-)Tlr9(-/-) mice was associated with decreased in vivo IL-12/IFN-gamma responses. Our results reveal that TLR2 and TLR9 cooperate in the control of parasite replication and that TLR9 has a primary role in the MyD88-dependent induction of IL-12/IFN-gamma synthesis during infection with T. cruzi.     

Enhanced resistance to Salmonella enterica serovar Typhimurium infection in mice after coumarin treatment

Coumarin and its derivatives are naturally occurring substances with multiple biological activities. Here we demonstrate that prophylactic peroral administration of coumarin or 7-hydroxycoumarin (7-OHC) enhances resistance to subsequent lethal Salmonella enterica Serovar Typhimurium infection in mice. 7-OHC decreased bacterial load in liver and spleen, and enhanced phagocytosis and bacterial killing by macrophages when applied in vitro and in vivo. 7-OHC treatment induced significant NO release in peritoneal macrophage cultures. The observed protective effect correlated with the induction of Th1-associated cytokines, such as IL-12, IFN-gamma, and TNF-alpha. These data demonstrate a clear immunomodulatory potential of coumarins which might have important therapeutic implications to enhance resistance to infection.     

IL-18-binding protein protects against lipopolysaccharide- induced lethality and prevents the development of Fas/Fas ligand-mediated models of liver disease in mice.

IL-18-binding protein (IL-18BP) is a natural IL-18 inhibitor. Human IL-18BP isoform a was produced as fusion construct with human IgG1 Fc and assessed for binding and neutralizing IL-18. IL-18BP-Fc binds human, mouse, and rat IL-18 with high affinity (K(D) 0.3-5 nM) in a BIAcore-based assay. In vitro, IL-18BP-Fc blocks IL-18 (100 ng/ml)-induced IFN-gamma production by KG1 cells (EC(50) = 0.3 microg/ml). In mice challenged with an LD(90) of LPS (15 mg/kg), IL-18BP-Fc (5 mg/kg) administered 10 min before LPS blocks IFN-gamma production and protects against lethality. IL-18BP-Fc administered 10 min before LPS blocks IFN-gamma production induced by LPS (5 mg/kg) with ED(50) of 0.005 mg/kg. Furthermore, IL-18BP-Fc (5 mg/kg) abrogates LPS (5 mg/kg)-induced IFN-gamma production even when administered 6 days before LPS but shows no effect when administered 9 or 12 days before LPS. Given 10 min before LPS challenge to mice primed 12 days in advance with heat-killed Propionibacterium acnes, IL-18BP-Fc prevents LPS-induced liver damage and IFN-gamma and Fas ligand expression. Given at the moment of priming with P. acnes, IL-18BP-Fc decreases P. acnes-induced granuloma formation, macrophage-inflammatory protein-1alpha and macrophage-inflammatory protein-2 production and prevents sensitization to LPS. IL-18BP-Fc also prevents Con A-induced liver damage and IFN-gamma and Fas ligand expression as well as liver damage induced by Pseudomonas aeruginosa exotoxin A or by anti-Fas agonistic Ab. In conclusion, IL-18BP can be engineered and produced in recombinant form to generate an IL-18 inhibitor, IL-18BP-Fc, endowed with remarkable in vitro and in vivo properties of binding and neutralizing IL-18.     

MyD88-dependent activation of B220-CD11b+LY-6C+ dendritic cells during Brucella melitensis infection

IFN-gamma is a key cytokine controlling Brucella infection. One of its major function is the stimulation of Brucella-killing effector mechanisms, such as inducible NO synthase (iNOS)/NOS2 activity, in phagocytic cells. In this study, an attempt to identify the main cellular components of the immune response induced by Brucella melitensis in vivo is made. IFN-gamma and iNOS protein were analyzed intracellularly using flow cytometry in chronically infected mice. Although TCRbeta(+)CD4(+) cells were the predominant source of IFN-gamma in the spleen, we also identified CD11b(+)LY-6C(+)LY-6G(-)MHC-II(+) cells as the main iNOS-producing cells in the spleen and the peritoneal cavity. These cells appear similar to inflammatory dendritic cells recently described in the mouse model of Listeria monocytogenes infection and human psoriasis: the TNF/iNOS-producing dendritic cells. Using genetically deficient mice, we demonstrated that the induction of iNOS and IFN-gamma-producing cells due to Brucella infection required TLR4 and TLR9 stimulation coupled to Myd88-dependent signaling pathways. The unique role of MyD88 was confirmed by the lack of impact of Toll-IL-1R domain-containing adaptor inducing IFN-beta deficiency. The reduction of IFN-gamma(+) and iNOS(+) cell frequency observed in MyD88-, TLR4-, and TLR9-deficient mice correlated with a proportional lack of Brucella growth control. Taken together, our results provide new insight into how immune responses fight Brucella infection.     

Enhancing effect of IFN-gamma on helper T cell activity and IL 2 production

A single injection of young murine immune interferon (IFN-gamma) in young (3 mo) or old (14 to 24 mo) mice 3 days before carrier-priming significantly enhances helper T cell activity of their spleen cells. Maximal enhancement is attained when IFN-gamma is injected once immediately before priming or for 4 consecutive days from the time of priming. Helper activity for anti-TNP antibody response was titrated in vitro by adding graded numbers of spleen cells from HRBC-primed mice of a given age to cultures containing a constant number of spleen cells from 3-mo-old normal mice and TNP-HRBC. When T cell-enriched spleen cells from HRBC-primed young or old mice, uninjected or injected with IFN-gamma, were separated by nylon wool filtration into passed (Thi) and adherent (Th2) cells, the helper activity of both T cell subpopulations was found to be enhanced by IFN-gamma injection. Helper activity of purified Th1 and Th2 cells was also increased by their in vitro preincubation with IFN-gamma. Furthermore, interleukin 2 (IL 2) production by mitogen-activated spleen cells from young and old mice is enhanced by addition of IFN-gamma to cultures. These data altogether indicate that IFN-gamma plays an important role in immunoregulation of helper T cell activity.     

IFN-alphabeta-mediated inflammatory responses and antiviral defense in liver is TLR9-independent but MyD88-dependent during murine cytomegalovirus infection

Chemokine responses critical for inflammation and promotion of effective innate control of murine CMV (MCMV) in liver have been shown to be dependent on immunoregulatory functions elicited by IFN-alphabeta. However, it remains to be determined whether upstream factors that promote viral sensing resulting in the rapid secretion of IFN-alphabeta in liver differ from those described in other tissues. Because plasmacytoid dendritic cells (pDCs) are known producers of high levels of systemic IFN-alpha in response to MCMV, this study examines the in vivo contribution of pDCs to IFN-alpha production in the liver, and whether production of the cytokine and ensuing inflammatory events are dependent on TLR9, MyD88, or both. We demonstrate that whereas MyD88 deficiency markedly impaired secretion of IFN-alpha, production of the cytokine was largely independent of TLR9 signaling, in the liver. MyD88 and TLR9 were needed for IFN-alpha production in the spleen. Moreover, hepatic but not splenic pDCs produced significant amounts of intracellular IFN-alpha in the absence of TLR9 function during infection. Furthermore, production of CCL2, CCL3, and IFN-gamma, as well as the accumulation of macrophages and NK cells, was not affected in the absence of functional TLR9 in the liver. In contrast, these responses were dramatically reduced in MyD88(-/-) mice. Additionally, MyD88(-/-) but not TLR9(-/-) mice exhibited increased sensitivity to virus infection in liver. Collectively, our results define contrasting compartmental functions for TLR9 and MyD88, and suggest that the infected tissue site uniquely contributes to the process of virus sensing and regulation of localized antiviral responses.     

Novel function of IFN-gamma: negative regulation of dendritic cell migration and T cell priming

IFN-gamma is considered to be a Th1 cytokine with immunomodulatory effects on a variety of immune cells. In this study, we determined whether dendritic cell (DC) function was aberrant in IFN-gamma knockout (GKO) mice. The results demonstrated that IFN-gamma deficiency did not interfere with bone marrow-derived DC development and maturation in vitro. However, functional analysis showed that bone marrow-derived DC from GKO mice had altered cytokine secretion, allostimulatory and Ag presentation capacity, chemokine receptor expression, and in vitro chemotaxis. LPS induced the recruitment of DC from different organs into the spleen; epicutaneously sensitized DC with hapten (FITC) accumulated in the draining lymph nodes and CD11c(+) DC levels in the draining lymph nodes from autoantigen (interphotoreceptor retinoid-binding protein) immunized mice were enhanced in GKO mice as compared with wild-type mice. After treatment of GKO mice with i.p. IFN-gamma injection restored IFN-gamma levels in vivo, DC migration decreased in response to LPS or FITC. IFN-gamma altered the adaptive immune responses in vivo, since T cell priming and IL-2 production were increased in interphotoreceptor retinoid-binding protein-immunized GKO mice. Furthermore, in IFN-gamma-treated GKO mice, experimental autoimmune uveitis score enhancement and T cell activation were eliminated. Taken together, IFN-gamma appears to play a negative regulatory role on in vivo DC function, resulting in suppression of Ag-specific T cell priming.     

Enhanced resistance to Gram-positive bacterium and increased susceptibility to bacterial endotoxin in mice sensitized with Propionibacterium acnes: involvement of Toll-like receptor

Mice sensitized with Propionibacterium acnes showed an enhanced resistance against infection with Listeria monocytogenes in contrast to the increased susceptibility to LPS-induced endotoxin shock. The enhanced protection to L. monocytogenes was mediated by activated innate immunity but not by generation of Listeria-specific acquired immunity. After infection with L. monocytogenes, the elimination of bacteria was observed earlier in accordance with a higher level of endogenous cytokine production in P. acnes-sensitized mice than in control mice. Peritoneal cells from P. acnes-sensitized mice produced a larger amount of IL-12p70 and nitric oxide after stimulation with heat-killed L. monocytogenes or peptidoglycan purified from Staphylococcus aureus. RT-PCR analysis showed that the expression of TLR2 but not TLR1, TLR4 nor TLR6 was induced by injection of P. acnes in peritoneal cells. These results indicated that P. acnes-sensitization could induce the activation of innate immunity against L. monocytogenes through increased recognition of bacterial components by TLR2.     

TLR2 synergizes with both TLR4 and TLR9 for induction of the MyD88-dependent splenic cytokine and chemokine response to Streptococcus pneumoniae

We previously demonstrated that induction of splenic cytokine and chemokine secretion in response to Streptococcus pneumoniae (Pn) is MyD88-, but not critically TLR2-dependent, suggesting a role for additional TLRs. In this study, we investigated the role of TLR2, TLR4, and/or TLR9 in mediating this response. We show that a single deficiency in TLR2, TLR4, or TLR9 has only modest, selective effects on cytokine and chemokine secretion, whereas substantial defects were observed in TLR2(-/-)xTLR9(-/-) and TLR2(-/-)xTLR4(-/-) mice, though not as severe as in MyD88(-/-) mice. Chloroquine, which inhibits the function of intracellular TLRs, including TLR9, completely abrogated detectable cytokine and chemokine release in spleen cells from TLR2(-/-)xTLR4(-/-) mice, similar to what is observed for mice deficient in MyD88. These data demonstrate significant synergy between TLR2 and both TLR4 and TLR9 for induction of the MyD88-dependent splenic cytokine and chemokine response to Pn.     

NK dendritic cells are innate immune responders to Listeria monocytogenes infection

NK dendritic cells (NKDC) are recently described immunologic cells that possess both lytic and Ag-presenting function and produce prolific quantities of IFN-gamma. The role of NKDC in innate immunity to bacterial infection is unknown. Because IFN-gamma is important in the immune response to Listeria monocytogenes (LM), we hypothesized that NKDC play a critical role during LM infection in mice. We found that LM increased the frequency and activation state of NKDC in vivo. Using in vivo intracellular cytokine analysis, we demonstrated that NKDC are a major source of early IFN-gamma during infection with LM. Adoptive transfer of wild-type NKDC into IFN-gamma-deficient recipients that were subsequently infected with LM decreased bacterial burden in the liver and spleen and prolonged survival. In contrast, NK cells were depleted early during LM infection, produced less IFN-gamma, and conferred less protection upon adoptive transfer into IFN-gamma-deficient mice. In vitro, LM induction of IFN-gamma secretion by NKDC depended on TLR9, in addition to IL-18 and IL-12. Our study establishes NKDC as innate immune responders to bacterial infection by virtue of their ability to secrete IFN-gamma.     

Injury primes the innate immune system for enhanced Toll-like receptor reactivity

Severe injury causes a dramatic host response that disrupts immune homeostasis and predisposes the injured host to opportunistic infections. Because Toll-like receptors (TLRs) recognize conserved microbial Ags and endogenous danger signals that may be triggered by injury, we wanted to determine how injury influences TLR responses. Using an in vivo injury model, we demonstrate that injury significantly increased TLR2- and TLR4-induced IL-1beta, IL-6, and TNF-alpha production by spleen cells. This influence of injury on TLR reactivity was observed as early as 1 day after injury and persisted for at least 7 days. The outcome of similar studies performed using TLR4-mutant C57BL/10ScN/Cr mice revealed that TLR2 responses remained primed, thus suggesting that injury-induced priming can occur independently of endogenous TLR4 signaling. Increased TLR4 reactivity was also observed in vivo, because LPS-challenged injured mice demonstrated significantly higher cytokine expression levels in the lung, liver, spleen, and plasma. Macrophages and dendritic cells were the major source of these cytokines as judged by intracellular cytokine staining. Moreover, ex vivo studies using enriched macrophage and dendritic cell populations confirmed that T cells did not contribute to the enhanced TLR2 and TLR4 responses. The results of flow cytometry studies using TLR2- and TLR4-MD-2-specific Abs indicated that injury did not markedly alter cell surface TLR2 or TLR4-MD-2 expression. Taken together, these findings establish that injury primes the innate immune system for enhanced TLR2- and TLR4-mediated responses and provides evidence to suggest that augmented TLR reactivity might contribute to the development of heightened systemic inflammation following severe injury.     

Activation of toll-like receptor 2 in acne triggers inflammatory cytokine responses

One of the factors that contributes to the pathogenesis of acne is Propionibacterium acnes; yet, the molecular mechanism by which P. acnes induces inflammation is not known. Recent studies have demonstrated that microbial agents trigger cytokine responses via Toll-like receptors (TLRs). We investigated whether TLR2 mediates P. acnes-induced cytokine production in acne. Transfection of TLR2 into a nonresponsive cell line was sufficient for NF-kappa B activation in response to P. acnes. In addition, peritoneal macrophages from wild-type, TLR6 knockout, and TLR1 knockout mice, but not TLR2 knockout mice, produced IL-6 in response to P. acnes. P. acnes also induced activation of IL-12 p40 promoter activity via TLR2. Furthermore, P. acnes induced IL-12 and IL-8 protein production by primary human monocytes and this cytokine production was inhibited by anti-TLR2 blocking Ab. Finally, in acne lesions, TLR2 was expressed on the cell surface of macrophages surrounding pilosebaceous follicles. These data suggest that P. acnes triggers inflammatory cytokine responses in acne by activation of TLR2. As such, TLR2 may provide a novel target for treatment of this common skin disease.     

MyD88-dependent and -independent murine cytomegalovirus sensing for IFN-alpha release and initiation of immune responses in vivo

Antiviral immunity requires early and late mechanisms in which IFN-alpha and IL-12 play major roles. However, the initial events leading to their production remain largely unclear. Given the crucial role of TLR in innate recognition, we investigated their role in antiviral immunity in vivo. Upon murine CMV (MCMV) infection, both MyD88-/- and TLR9-/- mice were more susceptible and presented increased viral loads compared with C57BL/6, TLR2-/-, TLR3-/-, or TLR4-/- mice. However, in terms of resistance to infection, IFN-alpha production and in many other parameters of early inflammatory responses, the MyD88-/- mice showed a more defective response than TLR9-/- mice. In the absence of the TLR9/MyD88 signaling pathway, cytokine production was dramatically impaired with a complete abolition of bioactive IL-12p70 serum release contrasting with a high flexibility for IFN-alpha release, which is initially (36 h) plasmacytoid dendritic cell- and MyD88-dependent, and subsequently (44 h) PDC-, MyD88-independent and, most likely, TLR-independent. NK cells from MCMV-infected MyD88-/- and TLR9-/- mice displayed a severely impaired IFN-gamma production, yet retained enhanced cytotoxic activity. In addition, dendritic cell activation and critical inflammatory cell trafficking toward the liver were still effective. In the long term, except for isotype switching to MCMV-specific IgG1, the establishment of Ab responses was not significantly altered. Thus, our results demonstrate a critical requirement of TLR9 in the process of MCMV sensing to assure rapid antiviral responses, coordinated with other TLR-dependent and -independent events that are sufficient to establish adaptive immunity.     

IFN-gamma primes RAW264 macrophages and human monocytes for enhanced oxidant production in response to CpG DNA via metabolic signaling: roles of TLR9 and myeloperoxidase trafficking

Macrophages and monocytes are activated by CpG DNA motifs to produce NO, which is enhanced dramatically by IFN-gamma. We hypothesize that synergistic cellular responses to IFN-gamma and CpG DNA are due to cross-talk between metabolic signaling pathways of leukocytes. Adherent RAW264.7 macrophages and human monocytes exhibited NAD(P)H autofluorescence oscillation periods of approximately 20 s. IFN-gamma increased the oscillatory amplitude, which was required for CpG DNA-mediated metabolic changes. These alterations in metabolic dynamics required the appropriate combinations of murine/human TLR9 and murine/human-specific CpG DNA. Other factors that also promoted an increase in metabolic oscillatory amplitude could substitute for IFN-gamma. Because recent studies have shown that the metabolic frequency is coupled to the hexose monophosphate shunt, and the amplitude is coupled to the peroxidase cycle, we tested the hypothesis that myeloperoxidase (MPO) participates in IFN-gamma priming for oxidant production. MPO inhibitors blocked cell responses to IFN-gamma and CpG DNA. In the absence of IFN-gamma exposure, the effects of CpG DNA could be duplicated by MPO addition to cell samples. Moreover, monocytes from MPO knockout mice were metabolically unresponsive to IFN-gamma and CpG DNA. NAD(P)H frequency doubling responses due to CpG DNA were blocked by an inhibitor of the hexose monophosphate shunt. Because NAD(P)H participates in electron trafficking to NO and superoxide anions, we tested oxidant production. Although CpG DNA alone had no effect, IFN-gamma plus CpG enhanced NO and reactive oxygen metabolite release compared with IFN-gamma treatment alone. We suggest that amplitude and frequency modulation of cellular metabolic oscillations contribute to intracellular signaling synergy.     

Protection of Staphylococcus aureus-infected septic mice by suppression of early acute inflammation and enhanced antimicrobial activity by ginsan

Ginsan, an acidic polysaccharide prepared from Panax ginseng, demonstrated multiple immunomodulatory effects in previous studies. This study was conducted to elucidate the antiseptic mechanism induced by ginsan in mice infected with Staphylococcus aureus. When mice were treated with ginsan before the bacterial challenge with S. aureus, they were highly protected from sepsis-induced death. The numbers of S. aureus recovered from ginsan-treated mice were considerably lower than those recovered from nontreated mice. The in vivo depletion of monocytes/macrophages caused more S. aureus to be recovered from the bacteria-infected mice. Nevertheless, mice treated with both etoposide and ginsan were able to maintain an antibacterial activity. In addition, the phagocytic activity of ginsan-treated macrophage against S. aureus was considerably enhanced. The synthesis of inflammatory cytokines, such as tumor necrosis factor-alpha interleukin (IL)-1beta, IL-6, IFN-gamma, IL-12, IL-18 and interferon gamma, was significantly downregulated at the early phase of sepsis in mice that were treated with ginsan before the bacterial challenge. Expression of Toll-like receptors (TLRs), including TLR2, TLR4, and TLR9, as well as the adaptor molecule MyD88, was considerably reduced in peritoneal macrophages that were treated with ginsan before a subsequent contact with S. aureus. These data indicated that ginsan protected mice from S. aureus-induced sepsis through the suppression of acute inflammatory responses at an early phase and the enhancement of antimicrobial activities at subsequent phases of infection.     

CpG DNA-mediated induction of acute liver injury in D-galactosamine-sensitized mice: the mitochondrial apoptotic pathway-dependent death of hepatocytes

Unmethylated CpG motifs present in bacterial DNA (CpG DNA) induce innate inflammatory responses, including rapid induction of proinflammatory cytokines. Although innate inflammatory responses induced by CpG DNA and other pathogen-associated molecular patterns are essential for the eradication of infectious microorganisms, excessive activation of innate immunity is detrimental to the host. In this study, we demonstrate that CpG DNA, but not control non-CpG DNA, induces a fulminant liver failure with subsequent shock-mediated death by promoting massive apoptotic death of hepatocytes in D-galactosamine (D-GalN)-sensitized mice. Inhibition of mitochondrial membrane permeability transition pore opening or caspase 9 activity in vivo protects D-GalN-sensitized mice from the CpG DNA-mediated liver injury and death. CpG DNA enhanced production of proinflammatory cytokines in D-GalN-sensitized mice via a TLR9/MyD88-dependent pathway. In addition, CpG DNA failed to induce massive hepatocyte apoptosis and subsequent fulminant liver failure and death in D-GalN-sensitized mice that lack TLR9, MyD88, tumor necrosis factor (TNF)-alpha, or TNF receptor I but not interleukin-6 or -12p40. Taken together, our results provide direct evidence that CpG DNA induces a severe acute liver injury and shock-mediated death through the mitochondrial apoptotic pathway-dependent death of hepatocytes caused by an enhanced production of TNF-alpha through a TLR9/MyD88 signaling pathway in D-GalN-sensitized mice.     

Codominance of TLR2-dependent and TLR2-independent modulation of MHC class II in Mycobacterium tuberculosis infection in vivo

Mycobacterium tuberculosis is an exceptionally successful human pathogen. A major component of this success is the ability of the bacteria to infect immunocompetent individuals and to evade eradication by an adaptive immune response that includes production of the macrophage-activating cytokine, IFN-gamma. Although IFN-gamma is essential for arrest of progressive tuberculosis, it is insufficient for efficacious macrophage killing of the bacteria, which may be due to the ability of M. tuberculosis to inhibit selected macrophage responses to IFN-gamma. In vitro studies have determined that mycobacterial lipoproteins and other components of the M. tuberculosis cell envelope, acting as agonists for TLR2, inhibit IFN-gamma induction of MHC class II. In addition, M. tuberculosis peptidoglycan and IL-6 secreted by infected macrophages inhibit IFN-gamma induction of MHC class II in a TLR2-independent manner. To determine whether TLR2-dependent inhibition of macrophage responses to IFN-gamma is quantitatively dominant over the TLR2-independent mechanisms in vivo, we prepared mixed bone marrow chimeric mice in which the hemopoietic compartment was reconstituted with a mixture of TLR(+/+) and TLR2(-/-) cells. When the chimeric mice were infected with M. tuberculosis, the expression of MHC class II on TLR2(+/+) and TLR2(-/-) macrophages from the lungs of individual infected chimeric mice was indistinguishable. These results indicate that TLR2-dependent and -independent mechanisms of inhibition of responses to IFN-gamma are equivalent in vivo, and that M. tuberculosis uses multiple pathways to abrogate the action of an important effector of adaptive immunity. This work was supported by National Institutes of Health Grants AI 065357-AI 020010.     

Adjuvant effect of the Propionibacterium acnes and its purified soluble polysaccharide on the immunization with plasmidial DNA containing a Trypanosoma cruzi gene

In the present work we investigated the role of killed Propionibacterium acnes or a soluble polysaccharide extracted from bacterium cell wall in modulated experimental immunization with plasmidial DNA. We used a plasmid, p154/13, containing a gene-encoding catalytic domain of Trypanosoma cruzi (T. cruzi) trans-sialidase. As previously described, immunization of BALB/c mice with p154/13 elicited humoral, cell-mediated and protective immune responses against T. cruzi infection. In this study we describe that both P. acnes and its soluble polysaccharide fraction have the ability to modulate the immune response elicited by p154/13. Treatment with these adjuvants enhanced specific trans-sialidase Th1 immune response, as revealed by a lower IgG1/IgG2a ratio and stronger in vitro IFN-gamma synthesis by CD4+ T cells. The most important fact was that treatment with P. acnes or its soluble polysaccharide fraction in the presence of p154/13 significantly reduced the peak of parasitemia observed 7 to 8 days after T. cruzi challenge. These data suggest that P. acnes or its soluble polysaccharide fraction may improve the protective potential of a DNA vaccine against experimental T. cruzi infection.