Roles of interleukin-17 in an experimental Legionella pneumophila pneumonia model

Coxiella burnetii actively blocks IL-17-induced oxidative stress in macrophages

Coxiella burnetii is a highly infectious pathogen that causes Q fever, a leading cause of culture-negative endocarditis. Coxiella first targets alveolar macrophages and forms a phagolysosome-like compartment called the Coxiella-Containing Vacuole (CCV). Successful host cell infection requires the Type 4B Secretion System (T4BSS), which translocates bacterial effector proteins across the CCV membrane into the host cytoplasm, where they manipulate numerous cell processes. Our prior transcriptional studies revealed that Coxiella T4BSS blocks IL-17 signaling in macrophages. Given that IL-17 is known to protect against pulmonary pathogens, we hypothesize that C. burnetii T4BSS downregulates intracellular IL-17 signaling to evade the host immune response and promote bacterial pathogenesis. Using a stable IL-17 promoter reporter cell line, we confirmed that Coxiella T4BSS blocks IL-17 transcription activation. Assessment of the phosphorylation state of NF-κB, MAPK, and JNK revealed that Coxiella downregulates IL-17 activation of these proteins. Using ACT1 knockdown and IL-17RA or TRAF6 knockout cells, we next determined that IL17RA-ACT1-TRAF6 pathway is essential for the IL-17 bactericidal effect in macrophages. In addition, macrophages stimulated with IL-17 generate higher levels of reactive oxygen species, which is likely connected to the bactericidal effect of IL-17. However, C. burnetii T4SS effector proteins block the IL-17-mediated oxidative stress, suggesting that Coxiella blocks IL-17 signaling to avoid direct killing by the macrophages.

N-acetyl-cysteine mediates protection against Mycobacterium avium through induction of human β-defensin-2 in a mouse lung infection model

Mycobacterium avium complex is a causative organism for refractory diseases. In this study, we examined the effects of N-acetyl-cysteine on M. avium infection in vitro and in vivo. N-acetyl-cysteine treatment suppressed the growth of M. avium in A549 cells in a concentration-dependent manner. This effect was related to the induction of the antibacterial peptide human β-defensin-2. In a mouse model, N-acetyl-cysteine treatment significantly reduced the number of bacteria in the lungs and induced murine β-defensin-3. In interleukin-17-deficient mice, the effects of N-acetyl-cysteine disappeared, indicating that these mechanisms may be mediated by interleukin-17. Moreover, an additional reduction in bacterial load was observed in mice administered N-acetyl-cysteine in combination with clarithromycin. Our findings demonstrate the potent antimycobacterial effects of N-acetyl-cysteine against M. avium by inducing antimicrobial peptide, suggesting that N-acetyl-cysteine may have applications as an alternative to classical treatment regimens.

IL-23 costimulates antigen-specific MAIT cell activation and enables vaccination against bacterial infection

Mucosal-associated invariant T (MAIT) cells are activated in a TCR-dependent manner by antigens derived from the riboflavin synthesis pathway, including 5-(2-oxopropylideneamino)-6-d-ribitylaminouracil (5-OP-RU), bound to MHC-related protein-1 (MR1). However, MAIT cell activation in vivo has not been studied in detail. Here, we have found and characterized additional molecular signals required for optimal activation and expansion of MAIT cells after pulmonary Legionella or Salmonella infection in mice. We show that either bone marrow-derived APCs or non-bone marrow-derived cells can activate MAIT cells in vivo, depending on the pathogen. Optimal MAIT cell activation in vivo requires signaling through the inducible T cell costimulator (ICOS), which is highly expressed on MAIT cells. Subsequent expansion and maintenance of MAIT-17/1-type responses are dependent on IL-23. Vaccination with IL-23 plus 5-OP-RU augments MAIT cell-mediated control of pulmonary Legionella infection. These findings reveal cellular and molecular targets for manipulating MAIT cell function under physiological conditions.

Friend or Foe: The Protective and Pathological Roles of Inducible Bronchus-Associated Lymphoid Tissue in Pulmonary Diseases

Inducible bronchus-associated lymphoid tissue (iBALT) is a tertiary lymphoid structure that resembles secondary lymphoid organs. iBALT is induced in the lung in response to Ag exposure. In some cases, such as infection with Mycobacterium tuberculosis, the formation of iBALT structure is indicative of an effective protective immune response. However, with persistent exposure to Ags during chronic inflammation, allergy, or autoimmune diseases, iBALT may be associated with exacerbation of inflammation. iBALT is characterized by well-organized T and B areas enmeshed with conventional dendritic cells, follicular dendritic cells, and stromal cells, usually located surrounding airways or blood vessels. Several of the molecular signals and cellular contributors that mediate formation of iBALT structures have been recently identified. This review will outline the recent findings associated with the formation and maintenance of iBALT and their contributions toward a protective or pathogenic function in pulmonary disease outcome.

Th17 Cells in Helicobacter pylori Infection: a Dichotomy of Help and Harm

Helicobacter pylori is a Gram-negative bacterium that infects the gastric epithelia of its human host. Everyone who is colonized with these pathogenic bacteria can develop gastric inflammation, termed gastritis. Additionally, a small proportion of colonized people develop more adverse outcomes, including gastric ulcer disease, gastric adenocarcinoma, or gastric mucosa-associated lymphoid tissue lymphoma. The development of these adverse outcomes is dependent on the establishment of a chronic inflammatory response. The development and control of this chronic inflammatory response are significantly impacted by CD4⁺ T helper cell activity. Noteworthy, T helper 17 (Th17) cells, a proinflammatory subset of CD4⁺ T cells, produce several proinflammatory cytokines that activate innate immune cell antimicrobial activity, drive a pathogenic immune response, regulate B cell responses, and participate in wound healing. Therefore, this review was written to take an intricate look at the involvement of Th17 cells and their affiliated cytokines (interleukin-17A [IL-17A], IL-17F, IL-21, IL-22, and IL-26) in regulating the immune response to H. pylori colonization and carcinogenesis.

A Recombinant Attenuated Yersinia pseudotuberculosis Vaccine Delivering a Y. pestis YopENt138-LcrV Fusion Elicits Broad Protection against Plague and Yersiniosis in Mice

In this study, a novel recombinant attenuated Yersinia pseudotuberculosis PB1+ strain (χ10069) engineered with ΔyopK ΔyopJ Δasd triple mutations was used to deliver a Y. pestis fusion protein, YopE amino acid 1 to 138-LcrV (YopENt138-LcrV), to Swiss Webster mice as a protective antigen against infections by yersiniae. χ10069 bacteria harboring the pYA5199 plasmid constitutively synthesized the YopENt138-LcrV fusion protein and secreted it via the type 3 secretion system (T3SS) at 37°C under calcium-deprived conditions. The attenuated strain χ10069(pYA5199) was manifested by the establishment of controlled infection in different tissues without developing conspicuous signs of disease in histopathological analysis of microtome sections. A single-dose oral immunization of χ10069(pYA5199) induced strong serum antibody titers (log10 mean value, 4.2), secretory IgA in bronchoalveolar lavage (BAL) fluid from immunized mice, and Yersinia-specific CD4+ and CD8+ T cells producing high levels of tumor necrosis factor alpha (TNF-α), gamma interferon (IFN-γ), and interleukin 2 (IL-2), as well as IL-17, in both lungs and spleens of immunized mice, conferring comprehensive Th1- and Th2-mediated immune responses and protection against bubonic and pneumonic plague challenges, with 80% and 90% survival, respectively. Mice immunized with χ10069(pYA5199) also exhibited complete protection against lethal oral infections by Yersinia enterocolitica WA and Y. pseudotuberculosis PB1+. These findings indicated that χ10069(pYA5199) as an oral vaccine induces protective immunity to prevent bubonic and pneumonic plague, as well as yersiniosis, in mice and would be a promising oral vaccine candidate for protection against plague and yersiniosis for human and veterinary applications.

Cytokine Milieu in Infectious Disease: A Sword or a Boon?

Cytokines have a myriad role in an infectious disease, whether being pathogenic, bacterial, or viral. All proinflammatory and anti-inflammatory cytokine biological function are dependent on its concentration, followed by combination with the other cytokines and the stage of the disease. Plasticity in switching off from one phenotype to the other of these regulatory mediators in congruence with the traditional concept of inhibitory and stimulatory effects on immune system is dealt with. This review highlights the dual functionality of some of these cytokines and cytokine-based immunotherapy.

Viewing Legionella pneumophila Pathogenesis through an Immunological Lens

Legionella pneumophila is the causative agent of the severe pneumonia Legionnaires' disease. L. pneumophila is ubiquitously found in freshwater environments, where it replicates within free-living protozoa. Aerosolization of contaminated water supplies allows the bacteria to be inhaled into the human lung, where L. pneumophila can be phagocytosed by alveolar macrophages and replicate intracellularly. The Dot/Icm type IV secretion system (T4SS) is one of the key virulence factors required for intracellular bacterial replication and subsequent disease. The Dot/Icm apparatus translocates more than 300 effector proteins into the host cell cytosol. These effectors interfere with a variety of cellular processes, thus enabling the bacterium to evade phagosome-lysosome fusion and establish an endoplasmic reticulum-derived Legionella-containing vacuole, which facilitates bacterial replication. In turn, the immune system has evolved numerous strategies to recognize intracellular bacteria such as L. pneumophila, leading to potent inflammatory responses that aid in eliminating infection. This review aims to provide an overview of L. pneumophila pathogenesis in the context of the host immune response.

Overlapping Roles for Interleukin-36 Cytokines in Protective Host Defense against Murine Legionella pneumophila Pneumonia

Legionella pneumophila causes life-threatening pneumonia culminating in acute lung injury. Innate and adaptive cytokines play an important role in host defense against L. pneumophila infection. Interleukin-36 (IL-36) cytokines are recently described members of the larger IL-1 cytokine family known to exert potent inflammatory effects. In this study, we elucidated the role for IL-36 cytokines in experimental pneumonia caused by L. pneumophila Intratracheal (i.t.) administration of L. pneumophila induced the upregulation of both IL-36α and IL-36γ mRNA and protein production in the lung. Compared to the findings for L. pneumophila-infected wild-type (WT) mice, the i.t. administration of L. pneumophila to IL-36 receptor-deficient (IL-36R^-/-) mice resulted in increased mortality, a delay in lung bacterial clearance, increased L. pneumophila dissemination to extrapulmonary organs, and impaired glucose homeostasis. Impaired lung bacterial clearance in IL-36R^-/- mice was associated with a significantly reduced accumulation of inflammatory cells and the decreased production of proinflammatory cytokines and chemokines. Ex vivo, reduced expression of costimulatory molecules and impaired M1 polarization were observed in alveolar macrophages isolated from infected IL-36R^-/- mice compared to macrophages from WT mice. While L. pneumophila-induced mortality in IL-36α- or IL-36γ-deficient mice was not different from that in WT animals, antibody-mediated neutralization of IL-36γ in IL-36α^-/- mice resulted in mortality similar to that observed in IL-36R^-/- mice, indicating redundant and overlapping roles for these cytokines in experimental murine L. pneumophila pneumonia.

Coxiella burnetii Blocks Intracellular Interleukin-17 Signaling in Macrophages

Coxiella burnetii is an obligate intracellular bacterium and the etiological agent of Q fever. Successful host cell infection requires the Coxiella type IVB secretion system (T4BSS), which translocates bacterial effector proteins across the vacuole membrane into the host cytoplasm, where they manipulate a variety of cell processes. To identify host cell targets of Coxiella T4BSS effector proteins, we determined the transcriptome of murine alveolar macrophages infected with a Coxiella T4BSS effector mutant. We identified a set of inflammatory genes that are significantly upregulated in T4BSS mutant-infected cells compared to mock-infected cells or cells infected with wild-type (WT) bacteria, suggesting that Coxiella T4BSS effector proteins downregulate the expression of these genes. In addition, the interleukin-17 (IL-17) signaling pathway was identified as one of the top pathways affected by the bacteria. While previous studies demonstrated that IL-17 plays a protective role against several pathogens, the role of IL-17 during Coxiella infection is unknown. We found that IL-17 kills intracellular Coxiella in a dose-dependent manner, with the T4BSS mutant exhibiting significantly more sensitivity to IL-17 than WT bacteria. In addition, quantitative PCR confirmed the increased expression of IL-17 downstream signaling genes in T4BSS mutant-infected cells compared to WT- or mock-infected cells, including the proinflammatory cytokine genes Il1a, Il1b, and Tnfa, the chemokine genes Cxcl2 and Ccl5, and the antimicrobial protein gene Lcn2 We further confirmed that the Coxiella T4BSS downregulates macrophage CXCL2/macrophage inflammatory protein 2 and CCL5/RANTES protein levels following IL-17 stimulation. Together, these data suggest that Coxiella downregulates IL-17 signaling in a T4BSS-dependent manner in order to escape the macrophage immune response.

Potential Role of Gr-1+ CD8+ T Lymphocytes as a Source of Interferon-γ and M1/M2 Polarization during the Acute Phase of Murine Legionella pneumophila Pneumonia

In this study, we analyzed interferon (IFN)-γ-producing cells and M1/M2 macrophage polarization in Legionella pneumophila pneumonia following anti-Gr-1 antibody treatment. Anti-Gr-1 treatment induced an M1-to-M2 shift of macrophage subtypes in the lungs and weakly in the peripheral blood, which was associated with increased mortality in legionella-infected mice. CD8+ T lymphocytes and natural killer cells were the dominant sources of IFN-γ in the acute phase, and anti-Gr-1 treatment reduced the number of IFN-γ-producing CD8+ T lymphocytes. In the CD3-gated population, most Gr-1-positive cells were CD8+ T lymphocytes in the lungs and lymph nodes (LNs) of infected mice. Additionally, the number of IFN-γ-producing Gr-1+ CD8+ T lymphocytes in the lungs and LNs increased 2 and 4 days after L. pneumophila infection, with anti-Gr-1 treatment attenuating these populations. Antibody staining revealed that Gr-1+ CD8+ T lymphocytes were Ly6C-positive cells rather than Ly6G, a phenotype regarded as memory type cells. Furthermore, the adoptive transfer of Gr-1+ CD8+ T lymphocytes induced increases in IFN-γ, M1 shifting and reduced bacterial number in the Legionella pneumonia model. These data identified Ly6C+ CD8+ T lymphocytes as a source of IFN-γ in innate immunity and partially associated with reduced IFN-γ production, M2 polarization, and high mortality in anti-Gr-1 antibody-treated mice with L. pneumophila pneumonia.

Recognition of conserved antigens by Th17 cells provides broad protection against pulmonary Haemophilus influenzae infection

Nontypeable Haemophilus influenzae (NTHi) is a major cause of community acquired pneumonia and exacerbation of chronic obstructive pulmonary disease. A current effort in NTHi vaccine development has focused on generating humoral responses and has been greatly impeded by antigenic variation among the numerous circulating NTHi strains. In this study, we showed that pulmonary immunization of mice with killed NTHi generated broad protection against lung infection by different strains. While passive transfer of immune antibodies protected only against the homologous strain, transfer of immune T cells conferred protection against both homologous and heterologous strains. Further characterization revealed a strong Th17 response that was cross-reactive with different NTHi strains. Responding Th17 cells recognized both cytosolic and membrane-associated antigens, while immune antibodies preferentially responded to surface antigens and were highly strain specific. We further identified several conserved proteins recognized by lung Th17 cells during NTHi infection. Two proteins yielding the strongest responses were tested as vaccine candidates by immunization of mice with purified proteins plus an adjuvant. Immunization induced antigen-specific Th17 cells that recognized different strains and, upon adoptive transfer, conferred protection. Furthermore, immunized mice were protected against challenge with not only NTHi strains but also a fully virulent, encapsulated strain. Together, these results show that the immune mechanism of cross-protection against pneumonia involves Th17 cells, which respond to a broad spectrum of antigens, including those that are highly conserved among NTHi strains. These mechanistic insights suggest that inclusion of Th17 antigens in subunit vaccines offers the advantage of inducing broad protection and complements the current antibody-based approaches.

Bacterial pathogenesis and interleukin-17: interconnecting mechanisms of immune regulation, host genetics, and microbial virulence that influence severity of infection

Interleukin-17 (IL-17) is a pro-inflammatory cytokine involved in the control of many different disorders, including autoimmune, oncogenic, and diverse infectious diseases. In the context of infectious diseases, IL-17 protects the host against various classes of microorganisms but, intriguingly, can also exacerbate the severity of some infections. The regulation of IL-17 expression stems, in part, from the activity of Interleukin-23 (IL-23), which drives the maturation of different classes of IL-17-producing cells that can alter the course of infection. In this review, we analyze IL-17/IL-23 signalling in bacterial infection, and examine the interconnecting mechanisms that link immune regulation, host genetics, and microbial virulence in the context of bacterial pathogenesis. We consider the roles of IL-17 in both acute and chronic bacterial infections, with a focus on mouse models of human bacterial disease that involve infection of mucosal surfaces in the lungs, urogenital, and gastrointestinal tracts. Polymorphisms in IL-17-encoding genes in humans, which have been associated with heightened host susceptibility to some bacterial pathogens, are discussed. Finally, we examine the implications of IL-17 biology in infectious diseases for the development of novel therapeutic strategies targeted at preventing bacterial infection.

Metformin Mediates Protection against Legionella Pneumonia through Activation of AMPK and Mitochondrial Reactive Oxygen Species

In Legionella pneumophila infection, macrophages play a critical role in the host defense response. Metformin, an oral drug for type 2 diabetes, is attracting attention as a new supportive therapy against a variety of diseases, such as cancer and infectious diseases. The novel mechanisms for metformin actions include modulation of the effector functions of macrophages and other host immune cells. In this study, we have examined the effects of metformin on L. pneumophila infection in vitro and in vivo. Metformin treatment suppressed growth of L. pneumophila in a time- and concentration-dependent fashion in bone marrow-derived macrophages, RAW cells (mouse), and U937 cells (human). Metformin induced phosphorylation of AMP-activated protein kinase (AMPK) in L. pneumophila-infected bone marrow-derived macrophages, and the AMPK inhibitor Compound C negated metformin-mediated growth suppression. Also, metformin induced mitochondrial reactive oxygen species but not phagosomal NADPH oxidase-derived reactive oxygen species. Metformin-mediated growth suppression was mitigated in the presence of the reactive oxygen species scavenger glutathione. In a murine L. pneumophila pneumonia model, metformin treatment improved survival of mice, which was associated with a significant reduction in bacterial number in the lung. Similar to in vitro observations, induction of AMPK phosphorylation and mitochondrial ROS was demonstrated in the infected lungs of mice treated with metformin. Finally, glutathione treatment abolished metformin effects on lung bacterial clearance. Collectively, these data suggest that metformin promotes mitochondrial ROS production and AMPK signaling and enhances the bactericidal activity of macrophages, which may contribute to improved survival in L. pneumophila pneumonia.

Yin and yang of interleukin-17 in host immunity to infection

The interleukin-17 (IL-17) family cytokines, such as IL-17A and IL-17F, play important protective roles in host immune response to a variety of infections such as bacterial, fungal, parasitic, and viral. The IL-17R signaling and downstream pathways mediate induction of proinflammatory molecules which participate in control of these pathogens. However, the production of IL-17 can also mediate pathology and inflammation associated with infections. In this review, we will discuss the yin-and-yang roles of IL-17 in host immunity to pathogens.

Recombinant Mip-PilE-FlaA dominant epitopes vaccine candidate against Legionella pneumophila

Legionella pneumophila is the main causative agent of Legionnaires' disease, which is a severe multi-system disease with pneumonia as the primary manifestation. We designed a recombinant Mip-PilE-FlaA dominant epitopes vaccine against Legionella pneumophila to prevent the disease and evaluated its immunogenicity and protective immunity. The protein structures of Mip, PilE and FlaA were analyzed using a computer, and the gene sequences of the dominant epitopes of the three proteins were selected to construct and optimize the vaccine. The optimized mip, pilE, flaA and recombinant mip-pilE-flaA gene sequences were cloned, expressed and purified. The purified proteins were used as dominant epitopes vaccines to immunize BALB/c mice and determine the protective immunity and immunogenicity of these purified proteins. The identification confirmed that the recombinant mip-pilE-flaA was successfully cloned and expressed. ELISA revealed that the Mip-PilE-FlaA group produced the highest IgG response, and this protein may considerably improve the production of some cytokines in BALB/c mice. Histopathology analyses of lungs from mice immunized with Mip-PilE-FlaA revealed a certain protective effect. Our work demonstrated that the recombinant dominant epitopes of Mip-PilE-FlaA exhibited strong immunogenicity and immune protection, and this protein may be an efficient epitopes vaccine candidate against Legionella pneumophila.

Innate immunity against Legionella pneumophila during pulmonary infections in mice

Legionella pneumophila is an etiological agent of the severe pneumonia known as Legionnaires' disease (LD). This gram-negative bacterium is thought to replicate naturally in various freshwater amoebae, but also replicates in human alveolar macrophages. Inside host cells, legionella induce the production of non-endosomal replicative phagosomes by injecting effector proteins into the cytosol. Innate immune responses are first line defenses against legionella during early phases of infection, and distinguish between legionella and host cells using germline-encoded pattern recognition receptors such as Toll-like receptors , NOD-like receptors, and RIG-I-like receptors, which sense pathogen-associated molecular patterns that are absent in host cells. During pulmonary legionella infections, various inflammatory cells such as macrophages, neutrophils, natural killer (NK) cells, large mononuclear cells, B cells, and CD4+ and CD8+ T cells are recruited into infected lungs, and predominantly occupy interstitial areas to control legionella. During pulmonary legionella infections, the interplay between distinct cytokines and chemokines also modulates innate host responses to clear legionella from the lungs. Recognition by NK cell receptors triggers effector functions including secretion of cytokines and chemokines, and leads to lysis of target cells. Crosstalk between NK cells and dendritic cells, monocytes, and macrophages provides a major first-line defense against legionella infection, whereas activation of T and B cells resolves the infection and mounts legionella-specific memory in the host.

IFN-γ induction by neutrophil-derived IL-17A homodimer augments pulmonary antibacterial defense

The role of interleukin-17A (IL-17A) in host defense against Legionella pneumophila remains elusive. To address this issue, we used Il17a(-/-), Il17f(-/-), and Il17a/Il17f(-/-) mice on a C57Bl/6 (non-permissive) background and IL-17 neutralizing Abs in mice on an A/J (permissive) background. Higher bacterial (L. pneumophila) counts in the lung and blood along with reduced neutrophil recruitment were detected in Il17a(-/-), but not Il17f(-/-), mice. We found that neutrophils produce IL-17A homodimer (IL-17A) during L. pneumophila infection, and hematopoietic cell-derived IL-17A is known to be important for bacterial clearance. Thus, intratracheal administration of wild-type neutrophils or recombinant IL-17A restored bacterial clearance and neutrophil recruitment in Il17a(-/-) mice. Furthermore, neutrophil-depleted Rag2(-/-) and Rag2/Il-2rγ(-/-) mice exhibited increased bacterial burden, reduced neutrophil influx and IL-17A production in the lung. Recombinant IFN-γ administration in Il17a(-/-) mice augmented bacterial elimination, whereas IL-17A administration in Ifnγ(-/-) mice did not augment bacterial clearance. IFN-γ is produced by T cells, but not neutrophils or macrophages, suggesting that neutrophil-derived IL-17A induces IFN-γ in a paracrine fashion. Human pneumonic lungs and human neutrophils challenged with L. pneumophila exhibited increased numbers of IL-17A producing cells. These findings display a novel function of neutrophil-derived IL-17A in antibacterial defense via the induction of IFN-γ in a paracrine manner.

Analysis of Immune Response Markers in Jorge Lobo's Disease Lesions Suggests the Occurrence of Mixed T Helper Responses with the Dominance of Regulatory T Cell Activity

Jorge Lobo's disease (JLD) is a chronic infection that affects the skin and subcutaneous tissues. Its etiologic agent is the fungus Lacazia loboi. Lesions are classified as localized, multifocal, or disseminated, depending on their location. Early diagnosis and the surgical removal of lesions are the best therapeutic options currently available for JLD. The few studies that evaluate the immunological response of JLD patients show a predominance of Th2 response, as well as a high frequency of TGF-β and IL-10 positive cells in the lesions; however, the overall immunological status of the lesions in terms of their T cell phenotype has yet to be determined. Therefore, the objective of this study was to evaluate the pattern of Th1, Th2, Th17 and regulatory T cell (Treg) markers mRNA in JLD patients by means of real-time PCR. Biopsies of JLD lesions (N = 102) were classified according to their clinical and histopathological features and then analyzed using real-time PCR in order to determine the expression levels of TGF-β1, FoxP3, CTLA4, IKZF2, IL-10, T-bet, IFN-γ, GATA3, IL-4, IL-5, IL-13, IL-33, RORC, IL-17A, IL-17F, and IL-22 and to compare these levels to those of healthy control skin (N = 12). The results showed an increased expression of FoxP3, CTLA4, TGF-β1, IL-10, T-bet, IL-17F, and IL-17A in lesions, while GATA3 and IL-4 levels were found to be lower in diseased skin than in the control group. When the clinical forms were compared, TGF-β1 was found to be highly expressed in patients with a single localized lesion while IL-5 and IL-17A levels were higher in patients with multiple/disseminated lesions. These results demonstrate the occurrence of mixed T helper responses and suggest the dominance of regulatory T cell activity, which could inhibit Th-dependent protective responses to intracellular fungi such as L. loboi. Therefore, Tregs may play a key role in JLD pathogenesis.

Localization of CD8 T cell epitope within cardiac myosin heavy chain-α334-352 that induces autoimmune myocarditis in A/J mice

BACKGROUND

Cardiac myosin heavy chain-α (Myhc), an intracellular protein expressed in the cardiomyocytes, has been identified as a major autoantigen in cardiac autoimmunity. In our studies with Myhc334-352-induced experimental autoimmune myocarditis in A/J mice (H-2a), we discovered that Myhc334-352, supposedly a CD4 T cell epitope, also induced antigen-specific CD8 T cells that transfer disease to naive animals.

METHODS AND RESULTS

In our efforts to identify the CD8 T cell determinants, we localized Myhc338-348 within the full length-Myhc334-352, leading to four key findings. (1) By acting as a dual epitope, Myhc338-348 induces both CD4 and CD8 T cell responses. (2) In a major histocompatibility complex (MHC) class I-stabilization assay, Myhc338-348 was found to bind H-2Dd-but not H-2Kk or H-2Ld-alleles. (3) The CD8 T cell response induced by Myhc338-348 was antigen-specific, as evaluated by MHC class I/H-2Dd dextramer staining. The antigen-sensitized T cells predominantly produced interferon-γ, the critical cytokine of effector cytotoxic T lymphocytes. (4) Myhc338-348 was found to induce myocarditis in immunized animals as determined by histology and magnetic resonance microscopy imaging.

CONCLUSIONS

Our data provide new insights as to how different immune cells can recognize the same antigen and inflict damage through different mechanisms.

Fusion of Legionella pneumophila outer membrane vesicles with eukaryotic membrane systems is a mechanism to deliver pathogen factors to host cell membranes

The formation and release of outer membrane vesicles (OMVs) is a phenomenon observed in many bacteria, including Legionella pneumophila. During infection, this human pathogen primarily invades alveolar macrophages and replicates within a unique membrane-bound compartment termed Legionella-containing vacuole. In the current study, we analysed the membrane architecture of L. pneumophila OMVs by small-angle X-ray scattering and biophysically characterized OMV membranes. We investigated the interaction of L. pneumophila OMVs with model membranes by Förster resonance energy transfer and Fourier transform infrared spectroscopy. These experiments demonstrated the incorporation of OMV membrane material into liposomes composed of different eukaryotic phospholipids, revealing an endogenous property of OMVs to fuse with eukaryotic membranes. Cellular co-incubation experiments showed a dose- and time-dependent binding of fluorophore-labelled OMVs to macrophages. Trypan blue quenching experiments disclosed a rapid internalization of OMVs into macrophages at 37 and 4 °C. Purified OMVs induced tumour necrosis factor-α production in human macrophages at concentrations starting at 300 ng ml(-1). Experiments on HEK293-TLR2 and TLR4/MD-2 cell lines demonstrated a dominance of TLR2-dependent signalling pathways. In summary, we demonstrate binding, internalization and biological activity of L. pneumophila OMVs on human macrophages. Our data support OMV membrane fusion as a mechanism for the remote delivery of virulence factors to host cells.

Immune responses to non-tumor antigens in the central nervous system

The central nervous system (CNS), once viewed as an immune-privileged site protected by the blood-brain barrier (BBB), is now known to be a dynamic immunological environment through which immune cells migrate to prevent and respond to events such as localized infection. During these responses, endogenous glial cells, including astrocytes and microglia, become highly reactive and may secrete inflammatory mediators that regulate BBB permeability and recruit additional circulating immune cells. Here, we discuss the various roles played by astrocytes, microglia, and infiltrating immune cells during host immunity to non-tumor antigens in the CNS, focusing first on bacterial and viral infections, and then turning to responses directed against self-antigens in the setting of CNS autoimmunity.

Comparison of innate immune agonists for induction of tracheal antimicrobial peptide gene expression in tracheal epithelial cells of cattle

Bovine respiratory disease is a complex of bacterial and viral infections of economic and welfare importance to the beef industry. Although tracheal antimicrobial peptide (TAP) has microbicidal activity against bacterial pathogens causing bovine respiratory disease, risk factors for bovine respiratory disease including BVDV and stress (glucocorticoids) have been shown to inhibit the induced expression of this gene. Lipopolysaccharide is known to stimulate TAP gene expression, but the maximum effect is only observed after 16 h of stimulation. The present study investigated other agonists of TAP gene expression in primary cultures of bovine tracheal epithelial cells. PCR analysis of unstimulated tracheal epithelial cells, tracheal tissue and lung tissue each showed mRNA expression for Toll-like receptors (TLRs) 1–10. Quantitative RT-PCR analysis showed that Pam3CSK4 (an agonist of TLR1/2) and interleukin (IL)-17A significantly induced TAP gene expression in tracheal epithelial cells after only 4–8 h of stimulation. Flagellin (a TLR5 agonist), lipopolysaccharide and interferon-α also had stimulatory effects, but little or no response was found with class B CpG ODN 2007 (TLR9 agonist) or lipoteichoic acid (TLR2 agonist). The use of combined agonists had little or no enhancing effect above that of single agonists. Thus, Pam3CSK4, IL-17A and lipopolysaccharide rapidly and significantly induce TAP gene expression, suggesting that these stimulatory pathways may be of value for enhancing innate immunity in feedlot cattle at times of susceptibility to disease.

Acute high-level exposure to WTC particles alters expression of genes associated with oxidative stress and immune function in the lung

First responders (FR) present at Ground Zero in the first 72 h after the World Trade Center (WTC) collapsed have progressively exhibited significant respiratory injuries. The few toxicology studies performed to date evaluated effects from just fine (< 2.5 µm) WTC dusts; none examined health effects/toxicities from atmospheres bearing larger particle sizes, despite the fact the majority (> 96%) of dusts were > 10 µm and most FR likely entrained dusts by mouth breathing. Using a system that generated/delivered supercoarse (10-53 µm) WTC dusts to F344 rats (in a manner that mimicked FR exposures), this study sought to examine potential toxicities in the lungs. In this exploratory study, rats were exposed for 2 h to 100 mg WTC dust/m(3) (while under isoflurane [ISO] anesthesia) or an air/ISO mixture; this dose conservatively modeled likely exposures by mouth-breathing FR facing ≈750-1000 mg WTC dust/m(3). Lungs were harvested 2 h post-exposure and total RNA extracted for subsequent global gene expression analysis. Among the >  1000 genes affected by WTC dust (under ISO) or ISO alone, 166 were unique to the dust exposure. In many instances, genes maximally-induced by the WTC dust exposure (relative to in naïve rats) were unchanged/inhibited by ISO only; similarly, several genes maximally inhibited in WTC dust rats were largely induced/unchanged in rats that received ISO only. These outcomes reflect likely contrasting effects of ISO and the WTC dust on lung gene expression. Overall, the data show that lungs of rats exposed to WTC dust (under ISO) - after accounting for any impact from ISO alone - displayed increased expression of genes related to lung inflammation, oxidative stress, and cell cycle control, while several involved in anti-oxidant function were inhibited. These changes suggested acute inflammogenic effects and oxidative stress in the lungs of WTC dust-exposed rats. This study, thus, concludes that a single very high exposure to WTC dusts could potentially have adversely affected the respiratory system - in terms of early inflammatory and oxidative stress processes. As these changes were not compared with other types of dusts, the uniqueness of these WTC-mediated effects remains to be confirmed. It also still remains to be determined if these effects might have any relevance to chronic lung pathologies that became evident among FR who encountered the highest dust levels on September 11, 2001 and the 2 days thereafter. Ongoing studies using longer-range post-exposure analyses (up to 1-year or more) will help to determine if effects seen here on genes were acute, reversible, or persistent, and associated with corresponding histopathologic/biochemical changes in situ.

Effects of Ureaplasma parvum lipoprotein multiple-banded antigen on pregnancy outcome in mice

Ureaplasma spp. are members of the family Mycoplasmataceae and have been considered to be associated with chorioamnionitis and preterm delivery. However, it is unclear whether Ureaplasma spp. have virulence factors related to these manifestations. The purpose of the present study was to determine whether the immunogenic protein multiple-banded antigen (MBA) from Ureaplasma parvum is a virulence factor for preterm delivery. We partially purified MBA from a type strain and clinical isolates of U. parvum, and also synthesized a diacylated lipopeptide derived from U. parvum, UPM-1. Using luciferase assays, both MBA-rich fraction MRF and UPM-1 activated the NF-κB pathway via TLR2. UPM-1 upregulated IL-1β, IL-6, IL-12p35, TNF-α, MIP2, LIX, and iNOS in mouse peritoneal macrophage. MRF or UPM-1 was injected into uteri on day 15 of gestation on pregnant C3H/HeN mice. The intrauterine MRF injection group had a significantly higher incidence of intrauterine fetal death (IUFD; 38.5%) than the control group (14.0%). Interestingly, intrauterine injection of UPM-1 caused preterm deliveries at high concentration (80.0%). In contrast, a low concentration of UPM-1 induced a significantly higher rate of fetal deaths (55.2%) than the control group (14.0%). The placentas of the UPM-1 injection group showed neutrophil infiltration and increased iNOS protein expression. Our data indicate that MBA from the clinical isolate of U. parvum is a potential virulence factor for IUFD and preterm delivery in mice and that the N-terminal diacylated lipopeptide is essential for the initiation of inflammation.

Mouse models of Legionnaires' disease

Legionella pneumophila is an accidental respiratory pathogen of humans that provokes a robust inflammatory response upon infection. While most people exposed to L. pneumophila will clear the infection, certain groups with underlying susceptibility will develop Legionnaires' disease. Mice, like most humans, are inherently resistant to L. pneumophila and infection of most inbred strains reflects the response of immune competent people to L. pneumophila exposure. Hence, the use of mouse models of L. pneumophila infection has taught us a great deal about the innate and adaptive factors that lead to successful clearance of the pathogen and avoidance of Legionnaires' disease. At the same time, L. pneumophila has provided new insight into innate immunity in general and is now a model pathogen with which to study acute lung inflammation and inflammasome activation. This chapter will explore the history and use of the mouse model of L. pneumophila infection and examine what we know about the innate and adaptive factors that contribute to the control of L. pneumophila in the mouse lung.

Mechanisms regulating regional localization of inflammation during CNS autoimmunity

Multiple sclerosis (MS) is a disease of the central nervous system (CNS) characterized by inflammatory, demyelinating lesions localized in the brain and spinal cord. Experimental autoimmune encephalomyelitis (EAE) is an animal model of MS that is induced by activating myelin-specific T cells and exhibits immune cell infiltrates in the CNS similar to those seen in MS. Both MS and EAE exhibit disease heterogeneity, reflecting variations in clinical course and localization of lesions within the CNS. Collectively, the differences seen in MS and EAE suggest that the brain and spinal cord function as unique microenvironments that respond differently to infiltrating immune cells. This review addresses the roles of the cytokines interferon-γ and interleukin-17 in determining the localization of inflammation to the brain or spinal cord in EAE.

A method for quantifying pulmonary Legionella pneumophila infection in mouse lungs by flow cytometry

Background

Pulmonary load of Legionella pneumophila in mice is normally determined by counting serial dilutions of bacterial colony forming units (CFU) on agar plates. This process is often tedious and time consuming. We describe a novel, rapid and versatile flow cytometric method that detects bacteria phagocytosed by neutrophils.

Findings

Mice were infected with L. pneumophila via intratracheal or intranasal administration. At various times after bacteria inoculation, mouse lungs were harvested and analysed concurrently for bacterial load by colony counting and flow cytometry analysis. The number of L. pneumophila-containing neutrophils correlated strongly with CFU obtained by bacteriological culture.

Conclusions

This technique can be utilised to determine pulmonary bacterial load and may be used in conjunction with other flow cytometric based analyses of the resulting immune response.

Biofilm-infected intracerebroventricular shunts elicit inflammation within the central nervous system

Central nervous system catheter infections are a serious complication in the treatment of hydrocephalus. These infections are commonly caused by Staphylococcus epidermidis and Staphylococcus aureus, both known to form biofilms on the catheter surface. Our objective was to generate a novel murine model of central nervous system catheter-associated biofilm infection using a clinical S. aureus isolate and characterize the nature of the inflammatory response during biofilm growth. Silicone catheters were precoated with S. aureus to facilitate bacterial attachment, whereupon infected or sterile catheters were stereotactically inserted into the lateral ventricle of the brain in C57BL/6 mice and evaluated at regular intervals through day 21 postinsertion. Animals tolerated the procedure well, with no clinical signs of illness or bacterial growth seen in the control group. Bacterial titers associated with central nervous system catheters were significantly elevated compared to those from the surrounding parenchyma, consistent with biofilm formation and minimal planktonic spread of infection. Catheter-associated bacterial burdens progressively increased, with maximal colonization achieved at day 7 postinfection. Analysis of inflammatory infiltrates by fluorescence-activated cell sorting (FACS) revealed significant macrophage and neutrophil influx, which peaked at days 3 and 5 to 7, respectively. In contrast, there were no detectable immune infiltrates associated with tissues surrounding sterile catheters. Biofilm infection led to significant increases in chemokine (CXCL1 and CCL2) and proinflammatory cytokine (interleukin 17 [IL-17]) expression in tissues surrounding infected central nervous system catheters. Based on these results, we propose this approach is a valid animal model for further investigations of catheter-associated central nervous system shunt infections.