[Barriers and Potential Improvements in the Diagnosis and Treatment of Asylum Seekers with Tuberculosis in Germany: A Qualitative Study]. / Hemmnisse und Verbesserungspotenziale bei der Diagnose und der Therapie asylsuchender Tuberkulosepatienten in Deutschland: Ergebnisse einer qualitativen Untersuchung.

Since 2014, the number of new cases of tuberculosis (TB) has risen in Germany by about 20%. This coincides with a large number of people applying for asylum in Germany. Some of them are from countries in which TB is much more prevalent than in Germany. The objectives of this contribution are to identify and explain barriers in the diagnosis and treatment of asylum seekers with TB and potential improvements in those fields. Data are derived from 14 problem-centred interviews that were carried out with doctors and staff from public health offices, representing the views of experts in the field of health care. On the one hand, the results suggest that structural factors are responsible for some of the barriers mentioned by the experts. For example, the restricted access to health care for asylum seekers leads to a delayed diagnosis since they visit the doctor too late (if at all). Accordingly, a nationwide implementation of an electronic health card for asylum seekers was proposed. On the other hand, individual and cultural factors play important roles as well. To those belong language barriers: they not only complicate history taking and diagnosis, but also educating patients about their disease and therapy. Moreover, the lack of knowledge concerning the German health care system increases the risk of treatment interruptions. To alleviate those problems, experts propose to carry out train-the-trainer-programmes and to install "guides" who pilot asylum seekers with TB through the German health care system.

Suppressor of Cytokine Signaling 3 in Macrophages Prevents Exacerbated Interleukin-6-Dependent Arginase-1 Activity and Early Permissiveness to Experimental Tuberculosis.

Suppressor of cytokine signaling 3 (SOCS3) is a feedback inhibitor of interleukin (IL)-6 signaling in macrophages. In the absence of this molecule, macrophages become extremely prone to an IL-6-dependent expression of arginase-1 (Arg1) and nitric oxide synthase (NOS)2, the prototype markers for alternative or classical macrophage activation, respectively. Because both enzymes are antipodean macrophage effector molecules in Mycobacterium tuberculosis (Mtb) infection, we assessed the relevance of SOCS3 for macrophage activation during experimental tuberculosis using macrophage-specific SOCS3-deficient (LysMcreSOCS3loxP/loxP) mice. Aerosol infection of LysMcreSOCS3loxP/loxP mice resulted in remarkably higher bacterial loads in infected lungs and exacerbated pulmonary inflammation. This increased susceptibility to Mtb infection was accompanied by enhanced levels of both classical and alternative macrophage activation. However, high Arg1 expression preceded the increased induction of NOS2 and at early time points of infection mycobacteria were mostly found in cells positive for Arg1. This sequential activation of Arg1 and NOS2 expression in LysMcreSOCS3loxP/loxP mice appears to favor the initial replication of Mtb particularly in Arg1-positive cells. Neutralization of IL-6 in Mtb-infected LysMcreSOCS3loxP/loxP mice reduced arginase activity and restored control of mycobacterial replication in LysMcreSOCS3loxP/loxP mice. Our data reveal an unexpected role of SOCS3 during experimental TB: macrophage SOCS3 restrains early expression of Arg1 and helps limit Mtb replication in resident lung macrophages, thereby limiting the growth of mycobacteria. Together, SOCS3 keeps IL-6-dependent divergent macrophage responses such as Nos2 and Arg1 expression under control and safeguard protective macrophage effector mechanisms.

A Mutation in IL4RA Is Associated with the Degree of Pathology in Human TB Patients.

The contribution of interleukin- (IL-) 4 receptor-alpha- (Rα-) dependent events in the pathogenesis of tuberculosis (TB) is controversial. We have recently shown IL-13 overexpression in mice to cause recrudescent Mtb replication and centrally necrotizing granulomas strongly resembling pathology of human TB. A deletion of IL-4Rα completely abrogates TB tissue pathology in these mice. To validate our results in human TB patients, we here determined the association of distinct variants of the IL4, IL13, IL4RA, IL13RA1, and IL13RA2 genes with cavity formation in a large Ghanaian cohort of HIV-negative individuals with newly diagnosed pulmonary TB. In fact, the structural variant of the IL4RA I50V, previously shown to result in enhanced signal transduction, was significantly associated with greater cavity size, and a variant of IL13RA2 was associated with disease in females. To evaluate whether the human-like TB pathology in IL-13-overexpressing mice is specifically mediated through the IL-4Rα subunit, we analyzed IL-13 transgenic mice with a genetic ablation of the IL-4Rα. In these mice, the IL-13-mediated increased susceptibility, human-like pathology of collagen deposition around centrally necrotizing granulomas, and alternative macrophage activation were abolished. Together, our genetic association study in human TB patients further supports the assumption that IL-13/IL-4Rα-dependent mechanisms are involved in mediating tissue pathology of human TB.

Cathepsin G in Experimental Tuberculosis: Relevance for Antibacterial Protection and Potential for Immunotherapy.

Neutrophil serine proteases, such as cathepsin G (CG) and neutrophil elastase (NE), have been implicated in the protective response against infections, including experimental mycobacterial infections. The goal of this study was to explore the role of CG in immunocompetent mice challenged aerogenically with Mycobacterium tuberculosis. We used genetically CG- or CG/NE-deficient mice to define the importance of these neutrophil serine proteases for antibacterial protection, granulomatous response, and survival. In addition, we explored the effect of intratracheally delivered liposomally encapsulated CG/NE as a therapeutic approach early during M. tuberculosis infection. Our data show that the presence of CG or CG/NE prolongs survival in M. tuberculosis-infected mice. However, CG is not directly involved in antibacterial defenses, and exogenous intratracheal administration of CG combined with NE does not reduce bacterial loads in the lungs of M. tuberculosis-infected mice.

Control of Mycobacterial Infections in Mice Expressing Human Tumor Necrosis Factor (TNF) but Not Mouse TNF.

Tumor necrosis factor (TNF) is an important cytokine for host defense against pathogens but is also associated with the development of human immunopathologies. TNF blockade effectively ameliorates many chronic inflammatory conditions but compromises host immunity to tuberculosis. The search for novel, more specific human TNF blockers requires the development of a reliable animal model. We used a novel mouse model with complete replacement of the mouse TNF gene by its human ortholog (human TNF [huTNF] knock-in [KI] mice) to determine resistance to Mycobacterium bovis BCG and M. tuberculosis infections and to investigate whether TNF inhibitors in clinical use reduce host immunity. Our results show that macrophages from huTNF KI mice responded to BCG and lipopolysaccharide similarly to wild-type macrophages by NF-κB activation and cytokine production. While TNF-deficient mice rapidly succumbed to mycobacterial infection, huTNF KI mice survived, controlling the bacterial burden and activating bactericidal mechanisms. Administration of TNF-neutralizing biologics disrupted the control of mycobacterial infection in huTNF KI mice, leading to an increased bacterial burden and hyperinflammation. Thus, our findings demonstrate that human TNF can functionally replace murine TNF in vivo, providing mycobacterial resistance that could be compromised by TNF neutralization. This new animal model will be helpful for the testing of specific biologics neutralizing human TNF.

The IL-13/IL-4Rα axis is involved in tuberculosis-associated pathology.

Human tuberculosis (TB) is a leading global health threat and still constitutes a major medical challenge. However, mechanisms governing tissue pathology during post-primary TB remain elusive, partly because genetically or immunologically tractable animal models are lacking. In human TB, the demonstration of a large relative increase in interleukin (IL)-4 and IL-13 expression, which correlates with lung damage, indicates that a subversive T helper (TH)2 component in the response to Mycobacterium tuberculosis (Mtb) may undermine protective immunity and contribute to reactivation and tissue pathology. Up to now, there has been no clear evidence regarding whether IL-4/IL-13-IL-4 receptor-α (Rα)-mediated mechanisms may in fact cause reactivation and pathology. Unfortunately, the virtual absence of centrally necrotizing granulomas in experimental murine TB is associated with a poor induction of a TH2 immune response. We therefore hypothesize that, in mice, an increased production of IL-13 may lead to a pathology similar to human post-primary TB. In our study, aerosol Mtb infection of IL-13-over-expressing mice in fact resulted in pulmonary centrally necrotizing granulomas with multinucleated giant cells, a hypoxic rim and a perinecrotic collagen capsule, with an adjacent zone of lipid-rich, acid-fast bacilli-containing foamy macrophages, thus strongly resembling the pathology in human post-primary TB. Granuloma necrosis (GN) in Mtb-infected IL-13-over-expressing mice was associated with the induction of arginase-1-expressing macrophages. Indirect blockade of the endogenous arginase inhibitor l-hydroxyarginine in Mtb-infected wild-type mice resulted in a strong arginase expression and precipitated a similar pathology of GN. Together, we here introduce an experimental TB model that displays many features of centrally necrotizing granulomas in human post-primary TB and demonstrate that IL-13/IL-4Rα-dependent mechanisms leading to arginase-1 expression are involved in TB-associated tissue pathology.

Wnt6 is expressed in granulomatous lesions of Mycobacterium tuberculosis-infected mice and is involved in macrophage differentiation and proliferation.

The Wnt signaling network, an ancient signaling system governing ontogeny and homeostatic processes, has recently been identified to exert immunoregulatory functions in a variety of inflammatory and infectious disease settings including tuberculosis. In this study, we show that Wnt6 is expressed in granulomatous lesions in the lung of Mycobacterium tuberculosis-infected mice. We identified foamy macrophage-like cells as the primary source of Wnt6 in the infected lung and uncovered a TLR-MyD88-NF-κB-dependent mode of induction in bone marrow-derived macrophages. Analysis of Wnt6-induced signal transduction revealed a pertussis toxin-sensitive, ERK-mediated, but ß-catenin-independent induction of c-Myc, a master regulator of cell proliferation. Increased Ki-67 mRNA expression levels and enhanced thymidine incorporation in Wnt6-treated macrophage cultures demonstrate a proliferation-promoting effect on murine macrophages. Further functional studies in M. tuberculosis-infected macrophages using Wnt6 conditioned medium and Wnt6-deficient macrophages uncovered a Wnt6-dependent induction of macrophage Arginase-1 and downregulation of TNF-α. This identifies Wnt6 as a novel factor driving macrophage polarization toward an M2-like phenotype. Taken together, these findings point to an unexpected role for Wnt6 in macrophage differentiation in the M. tuberculosis-infected lung.

Clade-specific virulence patterns of Mycobacterium tuberculosis complex strains in human primary macrophages and aerogenically infected mice.

UNLABELLED: In infection experiments with genetically distinct Mycobacterium tuberculosis complex (MTBC) strains, we identified clade-specific virulence patterns in human primary macrophages and in mice infected by the aerosol route, both reflecting relevant model systems. Exclusively human-adapted M. tuberculosis lineages, also termed clade I, comprising "modern" lineages, such as Beijing and Euro-American Haarlem strains, showed a significantly enhanced capability to grow compared to that of clade II strains, which include "ancient" lineages, such as, e.g., East African Indian or M. africanum strains. However, a simple correlation of inflammatory response profiles with strain virulence was not apparent. Overall, our data reveal three different pathogenic profiles: (i) strains of the Beijing lineage are characterized by low uptake, low cytokine induction, and a high replicative potential, (ii) strains of the Haarlem lineage by high uptake, high cytokine induction, and high growth rates, and (iii) EAI strains by low uptake, low cytokine induction, and a low replicative potential. Our findings have significant implications for our understanding of host-pathogen interaction and factors that modulate the outcomes of infections. Future studies addressing the underlying mechanisms and clinical implications need to take into account the diversity of both the pathogen and the host. IMPORTANCE: Clinical strains of the Mycobacterium tuberculosis complex (MTBC) are genetically more diverse than previously anticipated. Our analysis of mycobacterial growth characteristics in primary human macrophages and aerogenically infected mice shows that the MTBC genetic differences translate into pathogenic differences in the interaction with the host. Our study reveals for the first time that "TB is not TB," if put in plain terms. We are convinced that it is very unlikely that a single molecular mechanism may explain the observed effects. Our study refutes the hypothesis that there is a simple correlation between cytokine induction as a single functional parameter of host interaction and mycobacterial virulence. Instead, careful consideration of strain- and lineage-specific characteristics must guide our attempts to decipher what determines the pathological potential and thus the outcomes of infection with MTBC, one of the most important human pathogens.

IL-22 is mainly produced by IFNγ-secreting cells but is dispensable for host protection against Mycobacterium tuberculosis infection.

Anti-inflammatory treatment of autoimmune diseases is associated with an increased risk of reactivation tuberculosis (TB). Besides interleukin (IL-17)A, IL-22 represents a classical T helper (TH)17 cytokine and shares similar pathological effects in inflammatory diseases such as psoriasis or arthritis. Whereas IL-17A supports protective immune responses during mycobacterial infections, the role of IL-22 after infection with Mycobacterium tuberculosis (Mtb) is yet poorly characterized. Therefore, we here characterize the cell types producing IL-22 and the protective function of this cytokine during experimental TB in mice. Like IL-17A, IL-22 is expressed early after infection with Mtb in an IL-23-dependent manner. Surprisingly, the majority of IL-22-producing cells are not positive for IL-17A but have rather functional characteristics of interferon-gamma-producing TH1 cells. Although we found minor differences in the number of naive and central memory T cells as well as in the frequency of TH1 and polyfunctional T cells in mice deficient for IL-22, the absence of IL-22 does not affect the outcome of Mtb infection. Our study revealed that although produced by TH1 cells, IL-22 is dispensable for protective immune responses during TB. Therefore, targeting of IL-22 in inflammatory disease may represent a therapeutic approach that does not incur the danger of reactivation TB.

Mincle is not essential for controlling Mycobacterium tuberculosis infection.

Individually and combined, Toll-like receptors (TLR)-2, -4, -9, nucleotide oligomerization domain (NOD) 2 and NALP3 contribute to the Mycobacterium tuberculosis (Mtb)-induced innate immune response only to a limited extent, particularly in terms of inducing antibacterial protection and granuloma formation in vivo. A singular essential sensory component of this initial response has not been discovered yet. Trehalose-6,6'-dimycolate (TDM), a well known mycobacterial cell wall glycolipid, is believed to be involved in these early inflammatory processes after Mtb infection. Only recently the macrophage inducible C-type lectin (Mincle) was demonstrated as an essential receptor for TDM. However, not much is known about the sensing capacity of Mincle during infection with live mycobacteria. To determine the significance of Mincle during tuberculosis (TB), we analyzed the outcome of Mtb infection in Mincle-deficient mice. Whereas in the absence of Mincle macrophages did not respond to TDM, Mincle-deficient mice were capable of mounting an efficient granulomatous and protective immune response after low and high dose infections with Mtb. Mutant mice generated a normal T helper (TH) 1 and TH17 immune response followed by the induction of efficient macrophage effector mechanisms and control of mycobacterial growth identical to wildtype mice. From our results we conclude that absence of the innate receptor Mincle can be fully compensated for in vivo in terms of sensing Mtb and mounting a protective inflammatory immune response.

Lipid-labeling facilitates a novel magnetic isolation procedure to characterize pathogen-containing phagosomes.

Here we describe a novel approach for the isolation and biochemical characterization of pathogen-containing compartments from primary cells: We developed a lipid-based procedure to magnetically label the surface of bacteria and visualized the label by scanning and transmission electron microscopy (SEM, TEM). We performed infection experiments with magnetically labeled Mycobacterium avium, M. tuberculosis and Listeria monocytogenes and isolated magnetic bacteria-containing phagosomes using a strong magnetic field in a novel free-flow system. Magnetic labeling of M. tuberculosis did not affect the virulence characteristics of the bacteria during infection experiments addressing host cell activation, phagosome maturation delay and replication in macrophages in vitro. Biochemical analyses of the magnetic phagosome-containing fractions provided evidence of an enhanced presence of bacterial antigens and a differential distribution of proteins involved in the endocytic pathway over time as well as cytokine-dependent changes in the phagosomal protein composition. The newly developed method represents a useful approach to characterize and compare pathogen-containing compartments, in order to identify microbial and host cell targets for novel anti-infective strategies.

Increased frequencies of pulmonary regulatory T-cells in latent Mycobacterium tuberculosis infection.

Regulation of specific immune responses following exposure to Mycobacterium tuberculosis in humans and the role of regulatory T (Treg) cells in the immune control of latent infection with M. tuberculosis are incompletely understood. Latent infection was assayed by an interferon-γ release assay (IGRA) in healthcare workers regularly exposed to tuberculosis (TB) patients and in household TB contacts in Germany. Immunophenotypes of bronchoalveolar lavage (BAL) mononuclear cells and peripheral blood mononuclear cells (PBMCs) were analysed by fluorescence-activated cell sorting. All TB contacts with latent infection (n=15) had increased (p<0.0001) frequencies of CD4+ CD25+ CD127- Treg cells (median 2.12%, interquartile range (IQR) 1.63-3.01%) among BAL mononuclear cells compared with contacts (n=25) with negative IGRA results (median 0.68%, IQR 0.32-0.96%) No differences were seen when PBMC immunophenotypes of IGRA+ and IGRA- TB contacts were compared (IGRA+ median 9.6%, IQR 5.9-10.1%; IGRA- median 7.7%, IQR 4.6-11.3%; p=0.47). Five out of 25 contacts with negative blood IGRAs showed a positive IGRA from BAL cells, possibly indicating a limited local immune response. In Germany, latent infection with M. tuberculosis, as defined by a positive M. tuberculosis-specific IGRA response on cells from the peripheral blood, is characterised by an increased frequency of Treg cells in the BAL.

Therapeutic targeting of interleukin-6 trans-signaling does not affect the outcome of experimental tuberculosis.

Treatment of autoreactive inflammatory diseases such as rheumatoid arthritis with anti-inflammatory drugs is associated with an increased rate of reactivation tuberculosis (TB). Interleukin-6 (IL-6) plays a pivotal role in inflammation and protection against various infectious diseases. IL-6 signals by two mechanisms via the ubiquitous transmembrane protein gp130: 'classic' signaling using the membrane-bound IL-6 receptor (IL-6R), which is expressed mainly on hepatocytes and some leukocytes, and trans-signaling using soluble IL-6R (sIL-6R). Trans-signaling by the IL-6/sIL-6R complex is selectively inhibited by natural soluble gp130 (sgp130) and by sgp130 designer proteins. As specific blockade of IL-6 trans-signaling represents a promising approach for the therapy of inflammatory diseases, we evaluated the potential risk of interfering with this alternative pathway and analyzed the outcome of experimental TB after treatment with an IgG1-Fc fusion protein of soluble gp130 (sgp130Fc) and in sgp130Fc-overexpressing transgenic (sgp130Fc(tg)) mice. In contrast to treatment with anti-tumor necrosis factor (TNF) antibodies, administration of sgp130Fc did not interfere with protective immune responses after infection with Mycobacterium tuberculosis (Mtb). Moreover, Mtb-infected sgp130Fc(tg) mice were capable of controlling mycobacterial growth. Our finding that IL-6 trans-signaling plays no role for protective immune responses against Mtb supports the superior safety of therapeutic targeting of IL-6 trans-signaling compared to anti-TNF treatment.

The granuloma in tuberculosis: dynamics of a host-pathogen collusion.

A granuloma is defined as an inflammatory mononuclear cell infiltrate that, while capable of limiting growth of Mycobacterium tuberculosis, also provides a survival niche from which the bacteria may disseminate. The tuberculosis lesion is highly dynamic and shaped by both, immune response elements and the pathogen. In the granuloma, M. tuberculosis switches to a non-replicating but energy-generating life style whose detailed molecular characterization can identify novel targets for chemotherapy. To secure transmission to a new host, M. tuberculosis has evolved to drive T cell immunity to the point that necrotizing granulomas leak into bronchial cavities to facilitate expectoration of bacilli. From an evolutionary perspective it is therefore questionable whether vaccination and immunity enhancing strategies that merely mimic the natural immune response directed against M. tuberculosis infection can overcome pulmonary tuberculosis in the adult population. Juxtaposition of molecular pathology and immunology with microbial physiology and the use of novel imaging approaches afford an integrative view of the granuloma's contribution to the life cycle of M. tuberculosis. This review revisits the different input of innate and adaptive immunity in granuloma biogenesis, with a focus on the co-evolutionary forces that redirect immune responses also to the benefit of the pathogen, i.e., its survival, propagation, and transmission.

Inflammatory macrophages induce Nrf2 transcription factor-dependent proteasome activity in colonic NCM460 cells and thereby confer anti-apoptotic protection.

Adaptation of epithelial cells to persistent oxidative stress plays an important role in inflammation-associated carcinogenesis. This adaptation process involves activation of Nrf2 (nuclear factor-E2-related factor-2), which has been recently shown to contribute to carcinogenesis through the induction of proteasomal gene expression and proteasome activity. To verify this possible link between inflammation, oxidative stress, and Nrf2-dependent proteasome activation, we explored the impact of inflammatory (M1) macrophages on the human colon epithelial cell line NCM460. Transwell cocultures with macrophages differentiated from granulocyte monocyte-colony-stimulating factor-treated monocytes led to an increased activity of Nrf2 in NCM460 cells along with an elevated proteasome activity. This higher proteasome activity resulted from Nrf2-dependent induction of proteasomal gene expression, as shown for the 19 and 20 S subunit proteins S5a and α5, respectively. These effects of macrophage coculture were preceded by an increase of reactive oxygen species in cocultured NCM460 cells and could be blocked by catalase or by the reactive oxygen species scavenger Tiron, whereas transient treatment of NCM460 cells with H(2)O(2) similarly led to Nrf2-dependent proteasome activation. Through the Nrf2-dependent increase of proteasomal gene expression and proteasome activity, the sensitivity of NCM460 cells to tumor necrosis factor-related apoptosis-inducing ligand- or irinotecan-induced apoptosis declined. These findings indicate that inflammatory conditions such as the presence of M1 macrophages and the resulting oxidative stress are involved in the Nrf2-dependent gain of proteasome activity in epithelial cells, e.g. colonocytes, giving rise of greater resistance to apoptosis. This mechanism might contribute to inflammation-associated carcinogenesis, e.g. of the colon.

Variant G57E of mannose binding lectin associated with protection against tuberculosis caused by Mycobacterium africanum but not by M. tuberculosis.

Structural variants of the Mannose Binding Lectin (MBL) cause quantitative and qualitative functional deficiencies, which are associated with various patterns of susceptibility to infectious diseases and other disorders. We determined genetic MBL variants in 2010 Ghanaian patients with pulmonary tuberculosis (TB) and 2346 controls and characterized the mycobacterial isolates of the patients. Assuming a recessive mode of inheritance, we found a protective association between TB and the MBL2 G57E variant (odds ratio 0.60, confidence interval 0.4-0.9, P 0.008) and the corresponding LYQC haplotype (P(corrected) 0.007) which applied, however, only to TB caused by M. africanum but not to TB caused by M. tuberculosis. In vitro, M. africanum isolates bound recombinant human MBL more efficiently than did isolates of M. tuberculosis. We conclude that MBL binding may facilitate the uptake of M. africanum by macrophages, thereby promoting infection and that selection by TB may have favoured the spread of functional MBL deficiencies in regions endemic for M. africanum.

Expression of the ompATb operon accelerates ammonia secretion and adaptation of Mycobacterium tuberculosis to acidic environments.

Homeostasis of intracellular pH is a trait critical for survival of Mycobacterium tuberculosis in macrophages. However, mechanisms by which M. tuberculosis adapts to acidic environments are poorly understood. In this study, we analysed the physiological functions of OmpATb, a surface-accessible protein of M. tuberculosis. OmpATb did not complement the permeability defects of a Mycobacterium smegmatis porin mutant to glucose, serine and glycerol, in contrast to the porin MspA. Uptake rates of these solutes were unchanged in an ompATb operon mutant of M. tuberculosis indicating that OmpATb is not a general porin. Chemical analysis of low-pH culture filtrates showed that the proteins encoded by the ompATb operon are involved in generating a rapid ammonia burst, which neutralized medium pH and preceded exponential growth of M. tuberculosis. Addition of ammonia accelerated growth of the ompATb operon mutant demonstrating that ammonia secretion is indeed a mechanism by which M. tuberculosis neutralizes acidic environments. Infection experiments revealed that the ompATb operon was not required for full virulence in mice suggesting that M. tuberculosis has multiple mechanisms of resisting phagosomal acidification. Taken together, these results show that the ompATb operon is necessary for rapid ammonia secretion and adaptation of M. tuberculosis to acidic environments in vitro but not in mice.

Mycobacterium tuberculosis embB codon 306 mutations confer moderately increased resistance to ethambutol in vitro and in vivo.

Ethambutol (EMB) is a major component of the first-line therapy of tuberculosis. Mutations in codon 306 of embB (embB306) were suggested as a major resistance mechanism in clinical isolates. To directly analyze the impact of individual embB306 mutations on EMB resistance, we used allelic exchange experiments to generate embB306 mutants of M. tuberculosis H37Rv. The level of EMB resistance conferred by particular mutations was measured in vitro and in vivo after EMB therapy by daily gavage in a mouse model of aerogenic tuberculosis. The wild-type embB306 ATG codon was replaced by embB306 ATC, ATA, or GTG, respectively. All of the obtained embB306 mutants exhibited a 2- to 4-fold increase in EMB MIC compared to the wild-type H37Rv. In vivo, the one selected embB306 GTG mutant required a higher dose of ethambutol to restrict its growth in the lung compared to wild-type H37Rv. These experiments demonstrate that embB306 point mutations enhance the EMB MIC in vitro to a moderate, but significant extent, and reduce the efficacy of EMB treatment in the animal model. We propose that conventional EMB susceptibility testing, in combination with embB306 genotyping, may guide dose adjustment to avoid clinical treatment failure in these low-level resistant strains.

Wnt signaling in macrophages: augmenting and inhibiting mycobacteria-induced inflammatory responses.

Wnt proteins are secreted, palmitoylated glycoproteins with multiple functions in cell proliferation and migration as well as tissue organization. They are best known for their role in embryonic development and tissue homeostasis. In the last years, Wnt signaling was also shown to be involved in the regulation of inflammatory processes: Wnt5a is induced in human macrophages in response to mycobacteria and conserved bacterial structures and contributes to the regulation of pro-inflammatory cytokines via its receptor Frizzled (Fzd) 5. Wnt5a is also induced in other infectious and inflammatory diseases such as tuberculosis, sepsis, psoriasis, rheumatoid arthritis and atherosclerosis. In contrast, Wnt3a, a ligand of Fzd1, is constitutively expressed by bronchial epithelial cells and mediates anti-inflammatory effects on mycobacteria-infected macrophages via the Wnt/beta-Catenin signaling pathway. This pathway suppresses the activity of GSK3beta, a well known regulator of NF-kappaB-dependent gene transcription. Here we review recent data on immunomodulatory activities of Wnt proteins. Additional experiments using exogenous Wnt homologs further support the notion that TLR/NF-kappaB and Wnt signaling are functionally interconnected.