TLR9 activation is a key event for the maintenance of a mycobacterial antigen-elicited pulmonary granulomatous response

Eosinophils and Bacteria, the Beginning of a Story

Eosinophils are granulocytes primarily associated with TH2 responses to parasites or immune hyper-reactive states, such as asthma, allergies, or eosinophilic esophagitis. However, it does not make sense from an evolutionary standpoint to maintain a cell type that is only specific for parasitic infections and that otherwise is somehow harmful to the host. In recent years, there has been a shift in the perception of these cells. Eosinophils have recently been recognized as regulators of immune homeostasis and suppressors of over-reactive pro-inflammatory responses by secreting specific molecules that dampen the immune response. Their role during parasitic infections has been well investigated, and their versatility during immune responses to helminths includes antigen presentation as well as modulation of T cell responses. Although it is known that eosinophils can present antigens during viral infections, there are still many mechanistic aspects of the involvement of eosinophils during viral infections that remain to be elucidated. However, are eosinophils able to respond to bacterial infections? Recent literature indicates that Helicobacter pylori triggers TH2 responses mediated by eosinophils; this promotes anti-inflammatory responses that might be involved in the long-term persistent infection caused by this pathogen. Apparently and on the contrary, in the respiratory tract, eosinophils promote TH17 pro-inflammatory responses during Bordetella bronchiseptica infection, and they are, in fact, critical for early clearance of bacteria from the respiratory tract. However, eosinophils are also intertwined with microbiota, and up to now, it is not clear if microbiota regulates eosinophils or vice versa, or how this connection influences immune responses. In this review, we highlight the current knowledge of eosinophils as regulators of pro and anti-inflammatory responses in the context of both infection and naïve conditions. We propose questions and future directions that might open novel research avenues in the future.

Maternal supplementation with Bifidobacterium breve M-16V prevents their offspring from allergic airway inflammation accelerated by the prenatal exposure to an air pollutant aerosol

Bifidobacterium breve M-16V is a probiotic bacterial strain with efficacy in infants achieved by suppressing T-helper type (Th) 2 immune responses and modulating the systemic Th1/Th2 balance. Exposure to air pollution during pregnancy increases asthma susceptibility in offspring. The aim of this study was to investigate the effects of the maternal intake of B. breve M-16V on susceptibility to asthma accelerated by prenatal exposure to air pollution. The intake of B. breve M-16V in residual oil fly ash (ROFA)-exposed pregnant mice resulted in fewer eosinophils in the bronchoalveolar lavage fluid of neonatal mice and reduced allergic lung inflammation. The expressions of Th2 cytokines including IL-5 and IL-13 were decreased in neonatal mice from ROFA-exposed mothers fed B. breve M-16V. The analysis of fecal microbiota from neonatal mice revealed that the intake of B. breve M-16V by mothers changed the composition of fecal microbiota in neonatal mice, which resulted in a decreased population of Firmicutes. Moreover, several bacterial strains of fecal microbiota from neonatal mice had a strong correlation with Th2 cytokines and histological score. These results suggest that the maternal intake of M-16V might have beneficial effects in neonates by preventing and/or alleviating allergic reactions accelerated by prenatal exposure to air pollution.

Persimmon-derived tannin has bacteriostatic and anti-inflammatory activity in a murine model of Mycobacterium avium complex (MAC) disease

Nontuberculous mycobacteria (NTM), including Mycobacterium avium complex (MAC), cause opportunistic chronic pulmonary infections. Notably, MAC susceptibility is regulated by various factors, including the host immune system. Persimmon (Ebenaceae Diospyros kaki Thunb.) tannin is a condensed tannin composed of a polymer of catechin groups. It is well known that condensed tannins have high antioxidant activity and bacteriostatic properties. However, it is hypothesized that condensed tannins might need to be digested and/or fermented into smaller molecules in vivo prior to being absorbed into the body to perform beneficial functions. In this study, we evaluated the effects of soluble persimmon-derived tannins on opportunistic MAC disease. Soluble tannins were hydrolyzed and evaluated by the oxygen radical absorbance capacity (ORAC) method. The ORAC value of soluble tannin hydrolysate was approximately five times greater than that of soluble tannin powder. In addition, soluble tannin hydrolysate exhibited high bacteriostatic activity against MAC in vitro. Furthermore, in an in vivo study, MAC infected mice fed a soluble tannin-containing diet showed significantly higher anti-bacterial activity against MAC and less pulmonary granuloma formation compared with those fed a control diet. Tumor necrosis factor α and inducible nitric oxide synthase levels were significantly lower in lungs of the soluble tannin diet group compared with the control diet group. Moreover, proinflammatory cytokines induced by MAC stimulation of bone marrow-derived macrophages were significantly decreased by addition of soluble tannin hydrolysate. These data suggest that soluble tannin from persimmons might attenuate the pathogenesis of pulmonary NTM infection.

Toll-like receptors in mycobacterial infection

Toll-like receptors are transmembrane glycoproteins predominantly expressed in tissues with immune function. They are considered one of the most important pattern recognition receptor families discovered at the end of 20th century and a key aspect of the innate immune system response to infectious disease. Here we present a review of the current knowledge of individual Toll-like receptors, 1 through 13, with a focus on their role in the immune system response to mycobacterial infection. We present literature to date about the Toll-like receptors structure, localization and expression, signaling pathways, and function. The Toll-like receptor family may have proven an important role in the immune system response to mycobacterial infections, including M. tuberculosis and non-tuberculous (NTM) organisms.

TLR9 gene region polymorphisms and susceptibility to tuberculosis in Vietnam

Humans exposed to Mycobacterium tuberculosis (Mtb) show variation in susceptibility to infection and differences in tuberculosis (TB) disease outcome. Toll-like receptor 9 (TLR9) is a pattern recognition receptor that mediates recognition of Mtb and modulates Mtb-specific T-cell responses. Using a case-population design, we evaluated whether single nucleotide polymorphisms (SNPs) in the TLR9 gene region are associated with susceptibility to pulmonary or meningeal TB as well as neurologic presentation and mortality in the meningeal TB group. In a discovery cohort (n = 352 cases, 382 controls), three SNPs were associated with TB (all forms, p < 0.05) while three additional SNPs neared significance (0.05 < p < 0.1). When these six SNPs were evaluated in a validation cohort (n = 339 cases, 367 controls), one was significant (rs352142) while another neared significance (rs352143). When the cohorts were combined, rs352142 was most strongly associated with meningeal tuberculosis (dominant model; p = 0.0002, OR 2.36, CI 1.43-3.87) while rs352143 was associated with pulmonary tuberculosis (recessive model; p = 0.006, OR 5.3, CI 1.26-31.13). None of the SNPs were associated with mortality. This is the first demonstration of an association between a TLR9 gene region SNP and tuberculous meningitis. In addition, this extends previous findings that support associations of TLR9 SNPs with pulmonary tuberculosis.

Innate immune sensing of nucleic acids from mycobacteria

Endosomal and cytosolic receptors engage recognition of mycobacterial-derived nucleic acids (MyNAs). In contrast, virulent mycobacteria may utilize nucleic acid recognition pathways to escape the host immune system. This short review will summarize the mechanisms by which MyNAs are sensed and how they influence host protective responses.

Combined immunization using DNA-Sm14 and DNA-Hsp65 increases CD8+ memory T cells, reduces chronic pathology and decreases egg viability during Schistosoma mansoni infection

BACKGROUND

Schistosomiasis is one of the most important neglected diseases found in developing countries and affects 249 million people worldwide. The development of an efficient vaccination strategy is essential for the control of this disease. Previous work showed partial protection induced by DNA-Sm14 against Schistosoma mansoni infection, whereas DNA-Hsp65 showed immunostimulatory properties against infectious diseases, autoimmune diseases, cancer and antifibrotic properties in an egg-induced granuloma model.

METHODS

C57BL/6 mice received 4 doses of DNA-Sm14 (100 μg/dose) and DNA-Hsp65 (100 μg/dose), simultaneously administrated, or DNA-Sm14 alone, once a week, during four weeks. Three groups were included: 1- Control (no immunization); 2- DNA-Sm14; 3- DNA-Sm14/DNA-Hsp65. Two weeks following last immunization, animals were challenged subcutaneously with 30 cercariae. Fifteen, 48 and 69 days after infection splenocytes were collected to evaluate the number of CD8+ memory T cells (CD44(high)CD62(low)) using flow cytometry. Forty-eight days after challenge adult worms were collected by portal veins perfusion and intestines were collected to analyze the intestinal egg viability. Histological, immunohistochemical and soluble quantification of collagen and α-SMA accumulation were performed on the liver.

RESULTS

In the current work, we tested a new vaccination strategy using DNA-Sm14 with DNA-Hsp65 to potentiate the protection against schistosomiasis. Combined vaccination increased the number of CD8+ memory T cells and decreased egg viability on the intestinal wall of infected mice. In addition, simultaneous vaccination with DNA-Sm14/DNA-Hsp65 reduced collagen and α-SMA accumulation during the chronic phase of granuloma formation.

CONCLUSION

Simultaneous vaccination with DNA-Sm14/DNA-Hsp65 showed an immunostimulatory potential and antifibrotic property that is associated with the reduction of tissue damage on Schistosoma mansoni experimental infection.

In vivo and in vitro expression pattern of Toll-like receptors in Mycobacterium avium subspecies paratuberculosis infection

Johne's disease (JD) caused by Mycobacterium avium subspecies paratuberculosis (MAP) is a chronic infectious disease of ruminants. Activation of the Toll-like receptors (TLR) in response to microbial stimuli, including MAP, initiates responses in immune cells of the blood and within peripheral tissues. TLR2, 4 and 9 are believed to play a critical role in the initiation of immune responses against mycobacteria. In this study we report on the in vivo expression pattern of these receptors in sheep and cattle experimentally exposed to MAP. Experiments using the mouse macrophage cell line, RAW 264.7, and on isolated bovine monocytes were also carried out to assess the expression pattern of TLR2 and 4 in response to MAP and the non-pathogenic mycobacterial strain, M. smegmatis. Results from the in vivo study showed that there was a significant upregulation of TLR2 (P<0.05) at early time-points post-inoculation in the peripheral blood cells of sheep exposed to MAP S strain that went on to develop severe (multibacillary) disease. However, in the cattle during the initial months post-exposure to MAP C strain, TLR2 was significantly downregulated (P<0.05). TLR4 was significantly upregulated (P<0.05) at later stages (12 months post-inoculation) in MAP-exposed sheep with multibacillary disease; however significant differences in TLR4 expression were not observed in cattle. Expression of TLR9 was unchanged in MAP-exposed sheep and cattle. In vitro studies on mouse macrophages supported the findings of in vivo TLR2 gene expression increases seen in the sheep, in that the TLR2 receptor expression in response to MAP-infection was significantly increased in comparison to cells infected with a non-virulent mycobacterium, M. smegmatis. A likely role for TLR2 in the pathogenesis of Johne's disease is proposed.

The linkage of innate and adaptive immune response during granulomatous development

Granulomas represent a spectrum of inflammatory sequestration responses that may be initiated by a variety of agents, including non-infectious environmental factors and infectious microbial pathogens. Although this reaction is designed to be protective, the associated tissue injury is often responsible for a profound degree of pathology. While many of the mechanisms that sustain the development of the granuloma are enigmatic, it is accepted that the maintenance of this inflammatory process is dependent upon dynamic interactions between an inciting agent, inflammatory mediators, various immune and inflammatory cells, and structural cells of the involved tissue. The best studied of the host-dependent processes during granuloma development is the innate and adaptive immune response. The innate immune response by antigen-presenting cells [APCs; dendritic cells (DCs) and macrophages] is initiated quickly to protect from overwhelming pathogens, but with time, can also activate the adaptive immune response. APCs, essential regulators of the innate immune response, can respond to microbial ligands through Toll-like receptors (TLRs), which function in the recognition of microbial components and play an important role to link the innate and adaptive immune responses. CD4(+) T helper (Th) cells are essential regulators of adaptive immune responses and inflammatory diseases. Recently, the Notch system has been shown to be an important bridge between APCs and T cell communication circuits. In the present review, we discuss recent findings that explore the mechanisms in the linkage of innate and adaptive immunity, including granulomatous formation though TLRs and Notch activation.

TLR9-dependent IL-23/IL-17 is required for the generation of Stachybotrys chartarum-induced hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is an inflammatory lung disease that develops after repeated exposure to inhaled particulate Ag. Stachybotrys chartarum is a dimorphic fungus that has been implicated in a number of respiratory illnesses, including HP. In this study, we have developed a murine model of S. chartarum-induced HP that reproduces pathology observed in human HP, and we have hypothesized that TLR9-mediated IL-23 and IL-17 responses are required for the generation of granulomatous inflammation induced by inhaled S. chartarum. Mice that undergo i.p. sensitization and intratracheal challenge with 10(6) S. chartarum spores developed granulomatous inflammation with multinucleate giant cells, accompanied by increased accumulation of T cells. S. chartarum sensitization and challenge resulted in robust pulmonary expression of IL-17 and IL-23. S. chartarum-mediated granulomatous inflammation required intact IL-23 or IL-17 responses and required TLR9, because TLR9(-/-) mice displayed reduced IL-17 and IL-23 expression in whole lung associated with decreased accumulation of IL-17 expressing CD4(+) and γδ T cells. Compared with S. chartarum-sensitized dendritic cells (DC) isolated from WT mice, DCs isolated from TLR9(-/-) mice had a reduced ability to produce IL-23 in responses to S. chartarum. Moreover, shRNA knockdown of IL-23 in DCs abolished IL-17 production from splenocytes in response to Ag challenge. Finally, the intratracheal reconstitution of IL-23 in TLR9(-/-) mice recapitulated the immunopathology observed in WT mice. In conclusion, our studies suggest that TLR9 is critical for the development of Th17-mediated granulomatous inflammation in the lung in response to S. chartarum.

Characteristics of suppressor macrophages induced by mycobacterial and protozoal infections in relation to alternatively activated M2 macrophages

In the advanced stages of mycobacterial infections, host immune systems tend to change from a Th1-type to Th2-type immune response, resulting in the abrogation of Th1 cell- and macrophage-mediated antimicrobial host protective immunity. Notably, this type of immune conversion is occasionally associated with the generation of certain types of suppressor macrophage populations. During the course of Mycobacterium tuberculosis (MTB) and Mycobacterium avium-intracellulare complex (MAC) infections, the generation of macrophages which possess strong suppressor activity against host T- and B-cell functions is frequently encountered. This paper describes the immunological properties of M1- and M2-type macrophages generated in tumor-bearing animals and those generated in hosts with certain microbial infections. In addition, this paper highlights the immunological and molecular biological characteristics of suppressor macrophages generated in hosts with mycobacterial infections, especially MAC infection.

Stachybotrys chartarum-induced hypersensitivity pneumonitis is TLR9 dependent

Hypersensitivity pneumonitis (HP), an inflammatory lung disease, develops after repeated exposure to inhaled particulate antigen and is characterized by a vigorous T helper type 1-mediated immune response, resulting in the release of IL-12 and interferon (IFN)-γ. These T helper type 1 cytokines may participate in the pathogenesis of HP. Stachybotrys chartarum (SC) is a dimorphic fungus implicated in a number of respiratory illnesses, including HP. Here, we have developed a murine model of SC-induced HP that reproduces pathology observed in human HP and hypothesized that toll receptor-like 9 (TLR9)-mediated dendritic cell responses are required for the generation of granulomatous inflammation induced by inhaled SC. Mice sensitized and challenged with 10(6) SC spores develop granulomatous inflammation with multinucleate giant cells, accompanied by increased accumulation of neutrophils and CD4(+) and CD8(+) T cells. SC sensitization and challenge resulted in robust pulmonary expression of tumor necrosis factor-α, IL-12, and IFN-γ. SC-mediated granulomatous inflammation required IFN-γ and was TLR9 dependent, because TLR9(-/-) mice displayed reduced peribronchial inflammation, decreased accumulation and/or activation of polymorphonuclear (PMN) and CD4(+) and CD8(+) T cells, and reduced lung expression of type 1 cytokines and chemokines. T-cell production of IFN-γ was IL-12 dependent. Our studies suggest that TLR9 is critical for dendritic cell-mediated development of a type 1 granulomatous inflammation in the lung in response to SC.

Arc of a vicious circle: pathways activated by Mycobacterium tuberculosis that target the HIV-1 long terminal repeat

In this review, we examine how a subset of signal transduction cascades initiated by Mycobacterium tuberculosis (Mtb) infection modulates transcription mediated by the human immunodeficiency virus type 1 long terminal repeat (HIV-1 LTR). We describe two distinct phases of signaling that target transcription factors known to bind the HIV-1 LTR, and thus drive viral transcription and replication, in cells of the Mtb-infected host. First, Mtb-derived molecules, including cell wall components and DNA, interact with a number of host pattern recognition receptors. Second, cytokines and chemokines secreted in response to Mtb infection initiate signal transduction cascades through their cognate receptors. Given the variation in cell wall components among distinct clinical Mtb strains, the initial pattern recognition receptor interaction leading to direct LTR activation and differential cytokine and chemokine production is likely to be an important aspect of Mtb strain-specific regulation of HIV-1 transcription and replication. Improved understanding of these molecular mechanisms in the context of bacterial and host genetics should provide key insights into the accelerated viral replication and disease progression characteristic of HIV/TB coinfection.

A delicate dance: host response to mycobacteria

Mycobacterium tuberculosis is an enormously successful human pathogen that can infect its host for decades without causing clinical disease, only to reactivate when host immunity is compromised. A normal immune response thus contains bacterial spread without inducing sterilizing immunity, therefore benefitting both host and pathogen. Recent work has begun to outline the complexity of this host-pathogen interaction and to reveal how the homeostatic balance between the two is achieved. This review focuses on two significant aspects of this delicate dance: the host's initial innate response and the mature granuloma that later contains the pathogen. Here, we review the fine balance of inflammatory events triggered or controlled by both the host and bacteria and implications for the survival of each.

The suppressive tumor microenvironment: a challenge in cancer immunotherapy

In this review, we introduce the changing public perception of vaccines and immunotherapy in cancer treatments. We discuss the roles that different immunosuppressive cells play in the tumor microenvironment. Tumor associated macrophages (TAMs) and M1 and M2 macrophage phenotypes are discussed in depth. Additionally, the role that myeloid derived suppressor cells (MDSC) and T regulatory cells (Tregs) play in the tumor microenvironment is addressed. Highlighted are examples of therapies used against each suppressive cell type, which vary from the hypothetical to the ineffective; the inefficient to the successful. A variety of treatments have been tried to combat this fundamental problem, indeed the cause that allows cancerous mutated cells to survive, multiply and overtake the body. Efficient methods to disable each particular suppressive type of cell have been introduced; this review summarizes the discussion with a table to guide future development. We see gene therapy as the most innovative and flexible method to lead the charge to specifically modifying the tumor microenvironment.

Dysregulated cytokine expression by CD4+ T cells from post-septic mice modulates both Th1 and Th2-mediated granulomatous lung inflammation

Previous epidemiological studies in humans and experimental studies in animals indicate that survivors of severe sepsis exhibit deficiencies in the activation and effector function of immune cells. In particular, CD4+ T lymphocytes can exhibit reduced proliferative capacity and improper cytokine responses following sepsis. To further investigate the cell-intrinsic defects of CD4+ T cells following sepsis, splenic CD4+ T cells from sham surgery and post-septic mice were transferred into lymphopenic mice. These recipient mice were then subjected to both TH1-(purified protein derivative) and TH2-(Schistosoma mansoni egg antigen) driven models of granulomatous lung inflammation. Post-septic CD4+ T cells mediated smaller TH1 and larger TH2 lung granulomas as compared to mice receiving CD4+ T cells from sham surgery donors. However, cytokine production by lymph node cells in antigen restimulation assays indicated increased pan-specific cytokine expression by post-septic CD4+ T cell recipient mice in both TH1 and TH2 granuloma models. These include increased production of T_H2 cytokines in TH1 inflammation, and increased production of T_H1 cytokines in TH2 inflammation. These results suggest that cell-intrinsic defects in CD4+ T cell effector function can have deleterious effects on inflammatory processes post-sepsis, due to a defect in the proper regulation of TH-specific cytokine expression.

Therapeutic DNA vaccine reduces schistosoma mansoni-induced tissue damage through cytokine balance and decreased migration of myofibroblasts

Helminths are known to elicit a wide range of immunomodulation characterized by dominant Th2-type immune responses. Our group previously showed that a DNA vaccine encoding the mycobacterial 65-kDa heat shock protein (DNA-hsp65) showed immunomodulatory properties. We also showed, using a helminth-tuberculosis (TB) co-infection model, that the DNA-hsp65 vaccine protected mice against TB. We next investigated the mechanistic role of the vaccine during helminth-TB co-infection. Clinically, helminth infection causes type 2 granulomas in the lung. Mice were immunized with DNA-hsp65 while they were submitted to the type 2 granuloma induction protocol by Schistosoma mansoni eggs infusion. In this work we investigated the effects of DNA-hsp65 on the pathology and immune response during the development of type 2 granuloma induced by S. mansoni eggs. Histologic analyses of lung parenchyma showed that the DNA-hsp65 vaccine protected mice against exacerbated fibrosis induced by Schistosoma eggs, and decreased the size of the granulomas. These changes were correlated with a reduction in the number of T cells specific for the egg antigens in the lung and also with modulation of Th2 cytokine expression. Taken together, our results showed that the adjuvant properties of the DNA-hsp65 vaccine regulated the immune response in this Th2 model, and resulted in a preserved lung parenchyma.

Macrophages and control of granulomatous inflammation in tuberculosis

The granuloma that forms in response to Mycobacterium tuberculosis must be carefully balanced in terms of immune responses to provide sufficient immune cell activation to inhibit the growth of the bacilli, yet modulate the inflammation to prevent pathology. There are likely many scenarios by which this balance can be reached, given the complexity of the immune responses induced by M. tuberculosis. In this review, we focus on the key role of the macrophage in balancing inflammation in the granuloma.

Toll-like receptor 9 is required for full host resistance to Mycobacterium avium infection but plays no role in induction of Th1 responses

To investigate the role of Toll-like receptor 9 (TLR9) in innate immunity to Mycobacterium avium, TLR9, TLR2, and MyD88 knockout (KO) mice were infected with this bacterium. Bacterial burdens were higher in the spleens, livers, and lungs of infected TLR9 KO mice than in those of C57BL/6 mice, indicating that TLR9 is required for efficient control of M. avium infection. However, TLR9 KO or TLR2 KO spleen cells displayed normal M. avium-induced tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ) responses. This finding was confirmed by determining the number of splenic CD4(+) T cells producing IFN-γ by flow cytometry. Furthermore, TLR2 and MyD88, but not TLR9, played a major role in interleukin-12 and TNF-α production by M. avium-infected macrophages and dendritic cells (DCs). We also found that major histocompatibility complex class II molecule expression on DCs is regulated by TLR2 and MyD88 signaling but not by TLR9. Finally, lack of TLR9, TLR2, or MyD88 reduced the numbers of macrophages, epithelioid cells, and lymphocytes in M. avium-induced granulomas but only MyD88 deficiency affected the number of liver granulomas. In summary, our data demonstrated that the involvement of TLR9 in the control of M. avium infection is not related to the induction of Th1 responses.

Understanding latent tuberculosis: a moving target

Tuberculosis (TB) remains a threat to the health of people worldwide. Infection with Mycobacterium tuberculosis can result in active TB or, more commonly, latent infection. Latently infected persons, of which there are estimated to be approximately 2 billion in the world, represent an enormous reservoir of potential reactivation TB, which can spread to other people. The immunology of TB is complex and multifaceted. Identifying the immune mechanisms that lead to control of initial infection and prevent reactivation of latent infection is crucial to combating this disease.

TLR9 signaling is required for generation of the adaptive immune protection in Cryptococcus neoformans-infected lungs

To determine whether TLR9 signaling contributes to the development of the adaptive immune response to cryptococcal infection, wild-type (TLR9+/+) and TLR9 knockout (TLR9-/-) BALB/c mice were infected intratracheally with 10(4) C. neoformans 52D. We evaluated 1) organ microbial burdens, 2) pulmonary leukocyte recruitment, 3) pulmonary and systemic cytokine induction, and 4) macrophage activation profiles. TLR9 deletion did not affect pulmonary growth during the innate phase, but profoundly impaired pulmonary clearance during the adaptive phase of the immune response (a 1000-fold difference at week 6). The impaired clearance in TLR9-/- mice was associated with: 1) significantly reduced CD4(+), CD8+ T cell, and CD19+ B cell recruitment into the lungs; 2) defects in Th polarization indicated by altered cytokine responses in the lungs, lymphonodes, and spleen; and 3) diminished macrophage accumulation and altered activation profile, including robust up-regulation of Arg1 and FIZZ1 (indicators of alternative activation) and diminished induction of inducible nitric oxide synthase (an indicator of classical activation). Histological analysis revealed defects in granuloma formation and increased numbers of intracellular yeast residing within macrophages in the lungs of TLR9-/- mice. We conclude that TLR9 signaling plays an important role in the development of robust protective immunity, proper recruitment and function of effector cells (lymphocytes and macrophages), and, ultimately, effective cryptococcal clearance from the infected lungs.

More than just SCID--the phenotypic range of combined immunodeficiencies associated with mutations in the recombinase activating genes (RAG) 1 and 2

Combined immunodeficiencies with impaired numbers and function of T- and B-cells can be attributed to defects in the recombinase activating genes (RAG). The products of these genes, the RAG1 and 2 proteins, are key players in the V(D)J recombination process leading to the assembly of antigen receptor genes. Complete RAG deficiency (RAGD) with no V(D)J (<1% recombination activity of wild type) is associated with classical SCID and absence of T- and B-cells. In RAGD with residual V(D)J activity (>1% recombination activity of wild type), several clinical and immunological subtypes have been described: RAGD with skin inflammation and alphabeta T-cell expansion (classical Omenn syndrome), RAGD with skin inflammation and without T-cell expansion (incomplete Omenn syndrome), RAGD with gammadelta T-cell expansion and RAGD with granulomas. Engraftment of maternal T-cells can add to variation in phenotype. The potential role of epigenetic factors that influence the emergence of these phenotypes is discussed. Thorough assessment and interpretation of clinical and immunological findings will guide treatment modalities as intense as hematopoietic stem cell transplantation.

Pulmonary infection with an interferon-gamma-producing Cryptococcus neoformans strain results in classical macrophage activation and protection

Alternative macrophage activation is associated with exacerbated disease in murine models of pulmonary cryptococcosis. The present study evaluated the efficacy of interferon-gamma transgene expression by Cryptococcus neoformans strain H99gamma in abrogating alternative macrophage activation in infected mice. Macrophage recruitment into the lungs of mice after infection with C. neoformans strain H99gamma was comparable with that observed in mice challenged with wild-type C. neoformans. However, pulmonary infection in mice with C. neoformans strain H99gamma was associated with reduced pulmonary fungal burden, increased pulmonary Th1-type and interleukin-17 cytokine production, and classical macrophage activation as evidenced by increased inducible nitric oxide synthase expression, histological evidence of enhanced macrophage fungicidal activity, and resolution of inflammation. In contrast, progressive pulmonary infection, enhanced Th2-type cytokine production, and the induction of alternatively activated macrophages expressing arginase-1, found in inflammatory zone 1, Ym1, and macrophage mannose receptor were observed in the lungs of mice infected with wild-type C. neoformans. These alternatively activated macrophages were also shown to harbor highly encapsulated, replicating cryptococci. Our results demonstrate that pulmonary infection with C. neoformans strain H99gamma results in the induction of classically activated macrophages and promotes fungal clearance. These studies indicate that phenotype, as opposed to quantity, of infiltrating macrophages correlates with protection against pulmonary C. neoformans infection.

Biomarker changes associated with Tuberculin Skin Test (TST) conversion: a two-year longitudinal follow-up study in exposed household contacts

Background

A high prevalence (50–80%) of Tuberculin Skin Test Positivity (TST+ ≥10 mm indurations) has been reported in TB endemic countries. This pool forms a huge reservoir for new incident TB cases. However, immune biomarkers associated with TST conversion are largely unknown. The objective of this study was to identify immune biomarkers associated with TST conversion after acute Mycobacterium tuberculosis (MTB) exposure.

Methodology/Principal Findings

A 24 month longitudinal study was carried out in a recently MTB exposed cohort of household contacts (HC = 93; 75% TST+). Control group consisted of unexposed community controls (EC = 59; 46%TST+). Cytokine secretion was assessed in whole blood cultures in response to either mycobacterial culture filtrate (CF) antigens or mitogens (PHA or LPS) using Elisa methodology. Compared to the EC group, the HC group at recruitment (Kruskal-Wallis Test) showed significantly suppressed IFN γ (p = 0.0001), raised IL-10 (p = 0.0005) and raised TNF α (p = 0.001) in response to CF irrespective of their TST status. Seventeen TST-HC, showed TST conversion when retested at 6 months. Post TST conversion (paired t tests) significant increases were observed for CF induced IFN γ (p = 0.038), IL-10 (p = 0.001) and IL-6 (p = 0.006). Cytokine responses were also compared in the exposed HC group with either recent infection [(TST converters (N = 17)] or previous infection [TST+ HC (N = 54)] at 0, 6, 12 and 24 months using ANOVA on repeated measures. Significant differences between the exposed HC groups were noted only at 6 months. CF induced IFN γ was higher in previously infected HC group (p = 0.038) while IL-10 was higher in recently infected HC group (p = 0.041). Mitogen induced cytokine secretion showed similar differences for different group.

Conclusions/Significance

Our results suggest that TST conversion is associated with early increases in IFN γ and IL-10 responses and precedes latency by several months post exposure.

Toll-like receptor 9 activation is a key mechanism for the maintenance of chronic lung inflammation

RATIONALE

Accumulating evidence supports the hypothesis that the continuous host response to a persistent challenge can polarize the cytokine environment toward a Th2 cytokine phenotype, but the mechanisms responsible for this skewing are not clear.

OBJECTIVES

We investigated the role of Toll-like receptor 9 (TLR9) in a Th2-driven pulmonary granulomatous response initiated via the embolization of Schistosoma mansoni eggs to the lungs of mice.

METHODS

Mice were intravenously injected with S. mansoni eggs. Histological and flow cytometric analysis, cytokine measurement, adoptive transfer of bone marrow (BM)-derived dendritic cells (DCs), and in vitro T-cell treatments with antigen-presenting cells were examined.

MEASUREMENTS AND MAIN RESULTS

In comparison to wild-type mice, TLR9(-/-) mice showed increased pulmonary granuloma size, augmented collagen deposition, increased Th2 cytokine phenotype, and impaired accumulation of DCs. BM-derived DCs, but not macrophages, recovered from animals with developed Th2-type lung granulomas promoted the production of type 2 cytokines from CD4(+) T cells. BM-derived DCs from TLR9(-/-) mice induced impaired Th1 cytokine and enhanced Th2 cytokine production by T cells, compared with DCs from WT mice. Macrophages from TLR9(-/-) mice expressed a significantly higher alternatively activated (M2) phenotype characterized by increased "found in inflammatory zone-1" (FIZZ1) and arginase-1 expression. The adoptive transfer of BM-derived DCs from syngeneic WT mice into TLR9(-/-) mice restored the granuloma phenotype seen in WT mice.

CONCLUSIONS

These studies suggest that TLR9 plays an important mechanistic role in the maintenance of the pulmonary granulomatous response.

Early growth response-1 is involved in foam cell formation and is upregulated by the TLR9-MyD88-ERK1/2 pathway

Early growth response-1 (Egr-1), a zinc finger transcription factor, plays a key regulatory role in pathological cardiovascular processes including atherosclerosis. Here, we investigate whether Egr-1 expression and foam cell formation require toll-like receptor 9 (TLR9) and myeloid differentiation factor 88 (MyD88). CpG DNA and its related synthetic CpG oligodeoxynucleotides (CpG ODN) play an important role in immunity and inflammation. CpG ODN increased expression of Egr-1 and formation of foam cells in Raw264.7 cells or bone marrow-derived macrophages. Egr-1 siRNA decreased foam cell formation by CpG ODN compared to that of control siRNA. In addition, when TLR9 or MyD88 was knocked down, CpG ODN-induced Egr-1 expression was also attenuated. CpG ODN increased ERK1/2 phosphorylation. U0126, a MEK pathway inhibitor, suppressed activation of Egr-1 expression by CpG ODN. CpG ODN-induced expression of tissue factor (TF) and NGFI-A binding protein 2 (Nab2), and the expression of both genes is blocked by knockdown of TLR9 or MyD88 siRNA or MEK inhibition. These results suggest that CpG ODN activates the TLR9-MyD88-ERK1/2 pathway causing expression of Egr-1 and its target genes such as TF and Nab2, thus inducing foam cell formation.

Granulomatous disease in common variable immunodeficiency

Granulomatous disease occurs in 8-22% of patients with common variable immunodeficiency (CVID). We examined the clinical and immunologic information of all 37 of 455 (8.1%) CVID subjects with this complication. The median age at diagnosis of CVID was 26 (2-59). 14 had granulomas 1-18 years before diagnosis of CVID. In 6 detection of granulomas coincided with this diagnosis; for 17, granulomas were documented later. 54% had lung granulomas, 43% in lymph nodes and 32% in liver. 54% of the group had had autoimmune diseases, mostly immune thrombocytopenia and hemolytic anemia. 24% had had a splenectomy. Nineteen (51.3%) required steroid treatment for granulomas; other immune suppressants were used in some. Over 25 years 28.5% died (median age 37.5), but not significantly more when compared to our CVID patients without granulomas (19.8%). Those with lung granulomas had similar mortality to those with granulomas in other tissues.

Attenuation of toll-like receptor expression and function in latent tuberculosis by coexistent filarial infection with restoration following antifilarial chemotherapy

Mycobacterium tuberculosis (Mtb) and filarial coinfection is highly prevalent, and the presence of filarial infections may regulate the Toll-like receptor (TLR)-dependent immune response needed to control Mtb infection. By analyzing the baseline and mycobacterial antigen–stimulated expression of TLR1, 2, 4, and 9 (in individuals with latent tuberculosis [TB] with or without filarial infection), we were able to demonstrate that filarial infection, coincident with Mtb, significantly diminishes both baseline and Mtb antigen-specific TLR2 and TLR9 expression. In addition, pro-inflammatory cytokine responses to TLR2 and 9 ligands are significantly diminished in filaria/TB-coinfected individuals. Definitive treatment of lymphatic filariasis significantly restores the pro-inflammatory cytokine responses in individuals with latent TB. Coincident filarial infection exerted a profound inhibitory effect on protective mycobacteria-specific TLR-mediated immune responses in latent tuberculosis and suggests a novel mechanism by which concomitant filarial infections predispose to the development of active tuberculosis in humans.

Lymphatic filariasis afflicts over 120 million people worldwide, while Mycobacterium tuberculosis infects over 2 billion people worldwide. Almost 90% of infected people harbor latent tuberculosis infection with no clinical manifestations. Toll-like receptors (TLRs), pattern-recognition receptors that are present on host immune cells, constitute an important facet of host immune response initiation against a variety of pathogens. Because lymphatic filariasis and tuberculosis are co-endemic in many parts of the world and because TLR modulation is an important feature of both infections, we examined the effect of coexisting filarial infection on TLR-specific immune responses in latent tuberculosis by comparing cellular immune responses to Toll ligands in individuals with latent tuberculosis with or without concomitant lymphatic filariasis. We first examined modulation of TLRs at the gene expression level and determined that downregulation of TLR2 and 9 is associated with coexisting filarial infection. We then determined that Toll ligand-induced pro-inflammatory cytokine production—which is crucial in host defense against TB—is diminished in the presence of filarial coinfection. Treatment of filarial infection restores cytokine production in individuals with latent TB. Thus, we conclude that coexisting filarial infections might significantly compromise essential immune responses in tuberculosis and that treatment of filarial infections would potentially confer tremendous benefit in combating tuberculosis.

Specificity of the zebrafish host transcriptome response to acute and chronic mycobacterial infection and the role of innate and adaptive immune components

Pathogenic mycobacteria have the ability to survive within macrophages and persist inside granulomas. The complex host-pathogen interactions that determine the outcome of a mycobacterial infection process result in marked alterations of the host gene expression profile. Here we used the zebrafish model to investigate the specificity of the host response to infections with two mycobacterium strains that give distinct disease outcomes: an acute disease with early lethality or a chronic disease with granuloma formation, caused by Mycobacterium marinum strains Mma20 and E11, respectively. We performed a microarray study of different stages of disease progression in adult zebrafish and found that the acute and the chronic strains evoked partially overlapping host transcriptome signatures, despite that they induce profoundly different disease phenotypes. Both strains affected many signaling cascades, including WNT and TLR pathways. Interestingly, the strongest differences were observed at the initial stage of the disease. The immediate response to the acute strain was characterized by higher expression of genes encoding MHC class I proteins, matrix metalloproteinases, transcription factors, cytokines and other common immune response proteins. In contrast, small GTPase and histone gene groups showed higher expression in response to the chronic strain. We also found that nearly 1000 mycobacterium-responsive genes overlapped between the expression signatures of infected zebrafish adults and embryos at different stages of granuloma formation. Since adult zebrafish possess an adaptive immune system similar to mammals and zebrafish embryos rely solely on innate immunity, this overlap indicates a major contribution of the innate component of the immune system in the response to mycobacterial infection. Taken together, our comparison of the transcriptome responses involved in acute versus chronic infections and in the embryonic versus adult situation provides important new leads for investigating the mechanism of mycobacterial pathogenesis.

Clinical features, adenovirus types, and local production of inflammatory mediators in adenovirus infections

BACKGROUND

Adenovirus infection manifests in many ways, with respiratory and gastrointestinal symptoms predominating.

METHODS

We performed a retrospective chart review on children evaluated at our center who had a nasal wash culture positive for adenovirus. Archived nasal washes were retrieved. Polymerase chain reaction for 15 respiratory viruses was performed on these samples. Patients who were coinfected with another virus were excluded. Adenovirus typing was performed using polymerase chain reaction primers directed at the conserved hexon gene. Bead proteomics was used to measure concentrations of inflammatory mediators.

RESULTS

Seventy-eight patients were infected only with adenovirus. The clinical diagnosis was upper respiratory infection in 60%, pneumonia in 18%, febrile seizure in 8%, and bronchiolitis in 6%. Subgroup-C and B1 infections were most common. Seventy percent of patients with upper respiratory infection and all 5 patients with bronchiolitis had a subgroup-C infection; pneumonia was caused by subgroup-B1 and C viruses. Compared with asymptomatic control patients, adenovirus infected patients had higher nasal wash concentrations of interleukin (IL)-1alpha, IL-6, inducible protein-10, macrophage inflammatory protein-1alpha, tumor necrosis factor alpha, monokine induced by gamma interferon, and interferon-alpha (P < 0.05). In addition, we found that IL-8 and IL-1alpha (P < 0.05) were higher in the nasal washes obtained from hospitalized patients than in nonhospitalized patients.

CONCLUSIONS

Adenovirus infection causes an array of clinical disease and is associated with local production of several proinflammatory cytokines. The observation that nasal wash IL-8 and IL-1alpha concentrations were higher in patients requiring hospitalization suggests that these mediators contribute to disease severity.

Imprinted DC mediate the immune-educating effect of early-life microbial exposure

It has been long proposed that exposure to environmental factors early in life may have an educating effect on the development of immune regulatory functions. However, experimental studies on this issue are limited and the related molecular and cellular basis remains unclear. Here we report that neonatal exposure to killed bacteria (Chlamydia muridarum, originally called Chlamydia trachomatis mouse pneumonitis (MoPn)) changed the pattern of the hosts' immune responses to a model allergen (OVA) in adulthood. This was associated with altered phenotype and function of DC. We found that DC from adult mice treated neonatally with UV-killed MoPn exhibited distinct patterns of surface marker and TLR expression and cytokine production from control mice (DC from adult mice neonatally treated with vehicle, (Sham-DC)). More importantly, DC from adult mice treated neonatally with UV-killed MoPn induced significantly lower type-2 antigen-specific T-cell responses than Sham-DC shown in DC:T co-culture experiments in vitro and in adoptive transfer experiments in vivo. In addition, depletion of T cells in vivo largely abolished the phenotypic and functional alterations of DC caused by bacterial exposure, suggesting the involvement of T cell in this process. Our study demonstrates a central role of DC in linking the early-life exposure to microbial products and the balanced development of immune regulatory functions and the involvement of T cells in imprinting of the DC function.

TLR9 regulates the mycobacteria-elicited pulmonary granulomatous immune response in mice through DC-derived Notch ligand delta-like 4

TLR9 activation is important for the maintenance of mycobacteria-elicited pulmonary granulomatous responses, hallmarks of protective immune responses following mycobacterial infection. However, the mechanism or mechanisms underlying this effect of TLR9 are not clear. Here, we show that Tlr9-deficient mice challenged with a Mycobacterium antigen display an altered Th17 cytokine profile, decreased accumulation of granuloma-associated myeloid DCs, and profoundly impaired delta-like 4 (dll4) Notch ligand expression. Mechanistic analysis revealed that WT bone marrow-derived DCs but not macrophages promoted the differentiation of Th17 cells from bacillus Calmette-Guérin-challenged (BCG-challenged) lung CD4+ T cells. Both lung and bone marrow DCs isolated from Tlr9-deficient mice inoculated with Mycobacterium antigen expressed lower levels of dll4 Notch ligand than the same cells isolated from WT mice. Passively immunizing WT mice with neutralizing antibodies specific for dll4 during granuloma formation resulted in larger granulomas and lower levels of Th17-related cytokines. In addition, dll4 specifically regulated Th17 activation in vitro. Together, these results suggest dll4 plays an important role in promoting Th17 effector activity during a mycobacterial challenge. Furthermore, TLR9 seems to be required for optimal dll4 expression and the regulation of Mycobacterium antigen-elicited granuloma formation in mice.

Bone marrow-derived immune cells mediate sensitization to liver injury in a myeloid differentiation factor 88-dependent fashion

Toll-like receptors (TLRs) expressed on both immune cells and hepatocytes recognize microbial danger signals and regulate immune responses. Previous studies showed that TLR9 and TLR2 mediate Propionibacterium acnes-induced sensitization to lipopolysaccharide-triggered acute liver injury in mice. Ligand-specific activation of TLR2 and TLR9 are dependent on the common TLR adaptor, myeloid differentiation factor 88 (MyD88). Here, we dissected the role of MyD88 in parenchymal and bone marrow (BM)-derived cells in liver sensitization. Using chimeric mice with green fluorescent protein-expressing BM cells, we identified that P. acnes-induced liver inflammatory foci are of BM origin. Chimeras with MyD88-deficient BM showed no inflammatory foci after P. acnes or TLR2+TLR9 challenge, suggesting that recruitment of inflammatory cells to the liver required MyD88 expression in BM-derived cells. Further, selective MyD88 deficiency in parenchymal cells in mice with wild-type BM failed to prevent inflammatory cell infiltration. These results demonstrate that MyD88 in immune cells rather than in liver parenchymal cells plays an important role in inflammatory cell recruitment and liver injury.

Important role for Toll-like receptor 9 in host defense against meningococcal sepsis

Neisseria meningitidis is a leading cause of meningitis and sepsis. The pathogenesis of meningococcal disease is determined by both bacterial virulence factors and the host inflammatory response. Toll-like receptors (TLRs) are prominent activators of the inflammatory response, and TLR2, -4, and -9 have been reported to be involved in the host response to N. meningitidis. While TLR4 has been suggested to play an important role in early containment of infection, the roles of TLR2 and TLR9 in meningococcal disease are not well described. Using a model for meningococcal sepsis, we report that TLR9(-/-) mice displayed reduced survival and elevated levels of bacteremia compared to wild-type mice. In contrast, TLR2(-/-) mice controlled the infection in a manner comparable to that of wild-type mice. TLR9 deficiency was also associated with reduced bactericidal activity in vitro, which was accompanied by reduced production of nitric oxide by TLR9-deficient macrophages. Interestingly, TLR9(-/-) mice recruited more macrophages to the bloodstream than wild-type mice and produced elevated levels of cytokines at late time points during infection. At the cellular level, activation of signal transduction and induction of cytokine gene expression were independent of TLR2 or TLR9 in macrophages and conventional dendritic cells. In contrast, plasmacytoid dendritic cells relied entirely on TLR9 to induce these activities. Thus, our data demonstrate an important role for TLR9 in host defense against N. meningitidis.

What animal models teach humans about tuberculosis

Animal models have become standard tools for the study of a wide array of human infectious diseases. Although there are no true animal reservoirs for Mycobacterium tuberculosis, many different animal species are susceptible to infection with this organism and have served as valuable tools for the study of tuberculosis (TB). The most commonly used experimental animal models of TB are the mouse, rabbit, and guinea pig. Although substantial differences in TB susceptibility and disease manifestations exist between these species, they have contributed significantly to the understanding of TB immunopathogenesis, host genetic influence on infection, efficacy of antimicrobial therapy, and host/pathogen interactions that determine the outcome or severity of infection. Among the three species, mice are relatively resistant to TB infection, followed by rabbits and then guinea pigs, which are extremely vulnerable to infection. Mice are most often used in experiments on immune responses to TB infection and drug regimens against TB. Rabbits, unlike the other two animal models, develop cavitary TB and offer a means to study the factors leading to this form of the disease. Guinea pigs, due to their high susceptibility to infection, have been ideal for studies on airborne transmission and vaccine efficacy. In addition to these three species, TB research has occasionally involved nonhuman primates and cattle models. Current concepts in TB pathogenesis have also been derived from animal studies involving experimentally induced infections with related mycobacteria (e.g., Mycobacterium bovis) whose manifestations in select animal hosts mimic human TB.