Virulence, immunopathology and transmissibility of selected strains of Mycobacterium tuberculosis in a murine model

Demonstrating the utility of the ex vivo murine mycobacterial growth inhibition assay (MGIA) for high-throughput screening of tuberculosis vaccine candidates against multiple Mycobacterium tuberculosis complex strains

Human tuberculosis (TB) is caused by various members of the Mycobacterium tuberculosis (Mtb) complex. Differences in host response to infection have been reported, illustrative of a need to evaluate efficacy of novel vaccine candidates against multiple strains in preclinical studies. We previously showed that the murine lung and spleen direct mycobacterial growth inhibition assay (MGIA) can be used to assess control of ex vivo mycobacterial growth by host cells. The number of mice required for the assay is significantly lower than in vivo studies, facilitating testing of multiple strains and/or the incorporation of other cellular analyses. Here, we provide proof-of-concept that the murine MGIA can be applied to evaluate vaccine-induced protection against multiple Mtb clinical isolates. Using an ancient and modern strain of the Mtb complex, we demonstrate that ex vivo bacillus Calmette-Guérin (BCG)-mediated mycobacterial growth inhibition recapitulates protection observed in the lung and spleen following in vivo infection of mice. Further, we provide the first report of cellular and transcriptional correlates of BCG-induced growth inhibition in the lung MGIA. The ex vivo MGIA represents a promising platform to gain early insight into vaccine performance against a collection of Mtb strains and improve preclinical evaluation of TB vaccine candidates.

Transmissibility of Mycobacterium pinnipedii in a murine model

The causative agent of tuberculosis in pinnipeds is Mycobacterium pinnipedii, a member of the Mycobacterium tuberculosis complex (MTC). The natural hosts are pinnipeds; however, other non-marine mammals, including humans, can also be infected. The transmissibility of a pathogen is related to its virulence. The transmissibility of a M. pinnipedii strain (i.e., 1856) was investigated in a murine model and compared with that of two Mycobacterium bovis strains (i.e., 534 and 04-303) with different reported virulence. Non-inoculated mice (sentinels) were co-housed with intratracheally inoculated mice. Detailed inspection of mice to search for visible tuberculosis lesions in the lungs and spleen was performed, and bacillus viability at 30, 60, and 90 days post-inoculation (dpi) was assayed. A transmissibility of 100% was recorded at 30 dpi in sentinel mice co-housed with the inoculated mice from the M. pinnipedii and M. bovis 04-303 groups, as evidenced by the recovery of viable M. pinnipedii and M. bovis from the lungs of sentinel mice. Mice inoculated with M. pinnipedii (1856) and M. bovis (534) survived until euthanized, whereas five of the M. bovis 04-303-inoculated mice died at 17 dpi. This study constitutes the first report of the transmissibility of a M. pinnipedii strain in mice and confirms the utility of this experimental model to study virulence features such as the transmission of poorly characterized MTC species.

The Use of Viral Vectors for Gene Therapy and Vaccination in Tuberculosis

Tuberculosis (TB), an infection caused by Mycobacterium tuberculosis (Mtb), is one of the primary causes of death globally. The treatment of TB is long and based on several drugs, producing problems in compliance and toxicity, increasing Mtb resistance to first-line antibiotics that result in multidrug-resistant TB and extensively drug-resistant TB. Thus, the need for new anti-TB treatments has increased. Here, we review some model strategies to study gene therapy based on the administration of a recombinant adenovirus that encodes diverse cytokines, such as IFNγ, IL12, GM/CSF, OPN, TNFα, and antimicrobial peptides to enhance the protective immune response against Mtb. These models include a model of progressive pulmonary TB, a model of chronic infection similar to latent TB, and a murine model of pulmonary Mtb transmission to close contacts. We also review new vaccines that deliver Mtb antigens via particle- or virus-based vectors and trigger protective immune responses. The results obtained in this type of research suggest that this is an alternative therapy that has the potential to treat active TB as an adjuvant to conventional antibiotics and a promising preventive treatment for latent TB reactivation and Mtb transmission. Moreover, Ad vector vaccines are adequate for preventing infectious diseases, including TB.

Bifurcation analysis of a tuberculosis progression model for drug target identification

Tuberculosis (TB) is a major cause of morbidity and mortality worldwide. The emergence and rapid spread of drug-resistant M. tuberculosis strains urge us to develop novel treatments. Experimental trials are constrained by laboratory capacity, insufficient funds, low number of laboratory animals and obsolete technology. Systems-level approaches to quantitatively study TB can overcome these limitations. Previously, we proposed a mathematical model describing the key regulatory mechanisms underlying the pathological progression of TB. Here, we systematically explore the effect of parameter variations on disease outcome. We find five bifurcation parameters that steer the clinical outcome of TB: number of bacteria phagocytosed per macrophage, macrophages death, macrophage killing by bacteria, macrophage recruitment, and phagocytosis of bacteria. The corresponding bifurcation diagrams show all-or-nothing dose-response curves with parameter regions mapping onto bacterial clearance, persistent infection, or history-dependent clearance or infection. Importantly, the pathogenic stage strongly affects the sensitivity of the host to these parameter variations. We identify parameter values corresponding to a latent-infection model of TB, where disease progression occurs significantly slower than in progressive TB. Two-dimensional bifurcation analyses uncovered synergistic parameter pairs that could act as efficient compound therapeutic approaches. Through bifurcation analysis, we reveal how modulation of specific regulatory mechanisms could steer the clinical outcome of TB.

Beneficial or detrimental activity of regulatory T cells, indoleamine 2,3-dioxygenase, and heme oxygenase-1 in the lungs is influenced by the level of virulence of Mycobacterium tuberculosis strain infection

Tuberculosis (TB) caused by the complex Mycobacterium tuberculosis (Mtb) is the main cause of death by a single bacterial agent. Last year, TB was the second leading infectious killer after SARS-CoV-2. Nevertheless, many biological and immunological aspects of TB are not completely elucidated, such as the complex process of immunoregulation mediated by regulatory T cells (Treg cells) and the enzymes indoleamine 2,3-dioxygenase (IDO) and heme oxygenase 1 (HO-1). In this study, the contribution of these immunoregulatory factors was compared in mice infected with Mtb strains with different levels of virulence. First Balb/c mice were infected by intratracheal route, with a high dose of mild virulence reference strain H37Rv or with a highly virulent clinical isolate (strain 5186). In the lungs of infected mice, the kinetics of Treg cells during the infection were determined by cytofluorometry and the expression of IDO and HO-1 by RT-PCR and immunohistochemistry. Then, the contribution of immune-regulation mediated by Treg cells, IDO and HO-1, was evaluated by treating infected animals with specific cytotoxic monoclonal antibodies for Treg cells depletion anti-CD25 (PC61 clone) or by blocking IDO and HO-1 activity using specific inhibitors (1-methyl-D,L-tryptophan or zinc protoporphyrin-IX, respectively). Mice infected with the mild virulent strain showed a progressive increment of Treg cells, showing this highest number at the beginning of the late phase of the infection (28 days), the same trend was observed in the expression of both enzymes being macrophages the cells that showed the highest immunostaining. Animals infected with the highly virulent strain showed lower survival (34 days) and higher amounts of Treg cells, as well as higher expression of IDO and HO-1 one week before. In comparison with non-treated animals, mice infected with strain H37Rv with depletion of Treg cells or treated with the enzymes blockers during late infection showed a significant decrease of bacilli loads, higher expression of IFN-g and lower IL-4 but with a similar extension of inflammatory lung consolidation determined by automated morphometry. In contrast, the depletion of Treg cells in infected mice with the highly virulent strain 5186 produced diffuse alveolar damage that was similar to severe acute viral pneumonia, lesser survival and increase of bacillary loads, while blocking of both IDO and HO-1 produced high bacillary loads and extensive pneumonia with necrosis. Thus, it seems that Treg cells, IDO and HO-1 activities are detrimental during late pulmonary TB induced by mild virulence Mtb, probably because these factors decrease immune protection mediated by the Th1 response. In contrast, Treg cells, IDO and HO-1 are beneficial when the infection is produced by a highly virulent strain, by regulation of excessive inflammation that produced alveolar damage, pulmonary necrosis, acute respiratory insufficiency, and rapid death.

Clinical isolates of Mycobacterium tuberculosis with different genotypes exhibit distinct host macrophage responses in vitro

Introduction. Mycobacterium tuberculosis (M.tb), the causative agent of tuberculosis, can survive as an intracellular parasite after entering macrophages via phagocytosis. M.tb strains are genotypically distinct and engage in diverse pathogen-host interactions, with different host immune responses triggered by different M.tb strains. Importantly, differences in intracellular accumulation and triggering of host macrophage responses during early infection stages are key determinants that shape the final outcomes of host innate immune responses to different M.tb strains.Hypothesis/Gap Statement. Clinical M.tb strains with different genotypes elicit different host innate immune responses in vitro.Aim. This work aimed to compare host innate immune responses elicited by genotypically diverse, clinically derived M.tb strains in vitro.Methodology. RAW264.7 cells were infected with three lineage 2 and lineage 4 clinically derived M.tb strains and strain H37Rv. Strains were evaluated for differences in intracellular growth, induction of macrophage apoptosis, and induction of expression of proinflammatory cytokines and associated pattern recognition receptors.Results. Highly variable cytokine profiles were observed subsequent to RAW264.7 cell infection with the different strains. The Beijing genotype strain, a modern Beijing strain belonging to lineage 2, induced milder host proinflammatory responses and less apoptosis and exhibited greater intracellular growth as compared to the other strains. Moreover, mRNA expression levels of iNOS in Beijing and MANU2 genotype strains exceeded corresponding levels obtained for the T1 genotype strain. Meanwhile, mRNA expression levels of toll-like receptor (TLR)-encoding genes TLR2 and TLR7 in macrophages infected with the Beijing genotype strain were higher than corresponding levels observed in MANU2 genotype strain-infected macrophages.Conclusion. The higher intracellular survival rate and lower level of host cell apoptosis associated with macrophage infection with the Beijing genotype strain indicated greater virulence of this strain relative to that of the other strains. Furthermore, in vitro immune responses induced by the Beijing genotype strain were unique in that this strain induced a weaker inflammatory response than was induced by T1 or MANU2 genotype strains. Nevertheless, additional evidence is needed to confirm that Beijing genotype strains possess greater virulence than strains with other genotypes.

The Cholinergic System Contributes to the Immunopathological Progression of Experimental Pulmonary Tuberculosis

The cholinergic system is present in both bacteria and mammals and regulates inflammation during bacterial respiratory infections through neuronal and non-neuronal production of acetylcholine (ACh) and its receptors. However, the presence of this system during the immunopathogenesis of pulmonary tuberculosis (TB) in vivo and in its causative agent Mycobacterium tuberculosis (Mtb) has not been studied. Therefore, we used an experimental model of progressive pulmonary TB in BALB/c mice to quantify pulmonary ACh using high-performance liquid chromatography during the course of the disease. In addition, we performed immunohistochemistry in lung tissue to determine the cellular expression of cholinergic system components, and then administered nicotinic receptor (nAChR) antagonists to validate their effect on lung bacterial burden, inflammation, and pro-inflammatory cytokines. Finally, we subjected Mtb cultures to colorimetric analysis to reveal the production of ACh and the effect of ACh and nAChR antagonists on Mtb growth. Our results show high concentrations of ACh and expression of its synthesizing enzyme choline acetyltransferase (ChAT) during early infection in lung epithelial cells and macrophages. During late progressive TB, lung ACh upregulation was even higher and coincided with ChAT and α7 nAChR subunit expression in immune cells. Moreover, the administration of nAChR antagonists increased pro-inflammatory cytokines, reduced bacillary loads and synergized with antibiotic therapy in multidrug resistant TB. Finally, in vitro studies revealed that the bacteria is capable of producing nanomolar concentrations of ACh in liquid culture. In addition, the administration of ACh and nicotinic antagonists to Mtb cultures induced or inhibited bacterial proliferation, respectively. These results suggest that Mtb possesses a cholinergic system and upregulates the lung non-neuronal cholinergic system, particularly during late progressive TB. The upregulation of the cholinergic system during infection could aid both bacterial growth and immunomodulation within the lung to favor disease progression. Furthermore, the therapeutic efficacy of modulating this system suggests that it could be a target for treating the disease.

Evidence for the Effect of Vaccination on Host-Pathogen Interactions in a Murine Model of Pulmonary Tuberculosis by Mycobacterium tuberculosis

The global control of Tuberculosis remains elusive, and Bacillus Calmette-Guérin (BCG) -the most widely used vaccine in history-has proven insufficient for reversing this epidemic. Several authors have suggested that the mass presence of vaccinated hosts might have affected the Mycobacterium tuberculosis (MTB) population structure, and this could in turn be reflected in a prevalence of strains with higher ability to circumvent BCG-induced immunity, such as the recent Beijing genotype. The effect of vaccination on vaccine-escape variants has been well-documented in several bacterial pathogens; however the effect of the interaction between MTB strains and vaccinated hosts has never been previously described. In this study we show for the first time the interaction between MTB Beijing-genotype strains and BCG-vaccinated hosts. Using a well-controlled murine model of progressive pulmonary tuberculosis, we vaccinated BALB/c mice with two different sub-strains of BCG (BCG-Phipps and BCG-Vietnam). Following vaccination, the mice were infected with either one of three selected MTB strains. Strains were selected based on lineage, and included two Beijing-family clinical isolates (strains 46 and 48) and a well-characterized laboratory strain (H37Rv). Two months after infection, mice were euthanized and the bacteria extracted from their lungs. We characterized the genomic composite of the bacteria before and after exposure to vaccinated hosts, and also characterized the local response to the bacteria by sequencing the lung transcriptome in animals during the infection. Results from this study show that the interaction within the lungs of the vaccinated hosts results in the selection of higher-virulence bacteria, specifically for the Beijing genotype strains 46 and 48. After exposure to the BCG-induced immune response, strains 46 and 48 acquire genomic mutations associated with several virulence factors. As a result, the bacteria collected from these vaccinated hosts have an increased ability for immune evasion, as shown in both the host transcriptome and the histopathology studies, and replicates far more efficiently compared to bacteria collected from unvaccinated hosts or to the original-stock strain. Further research is warranted to ascertain the pathways associated with the genomic alterations. However, our results highlight novel host-pathogen interactions induced by exposure of MTB to BCG vaccinated hosts.

Lineage-specific differences in lipid metabolism and its impact on clinical strains of Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tb) is the causative agent of TB and its incidences has been on the rise since 1993. Lipid metabolism is an imperative metabolic process, which grants M. tb the ability to utilize host-derived lipids as a secondary source of nutrition during infection. In addition to degrading host lipids, M. tb is proficient at using lipids, such as cholesterol, to facilitate its entry into macrophages. Mycolic acids, constituents of the mycobacterial cell wall, offer protection and aid in persistence of the bacterium. These are effectively synthesized using a complex fatty acid synthase system. Many pathogenesis studies have reported differences in lipid-metabolism of clinical strains of M. tb that belongs to diverse lineages of the Mycobacterium tuberculosis complex (MTBC). East-Asian and Euro-American lineages possess "unique" cell wall-associated lipids compared to the less transmissible Ethiopian lineage, which may offer these lineages a competitive advantage. Therefore, it is crucial to comprehend the complexities among the MTBC lineages with lipid metabolism and their impact on virulence, transmissibility and pathogenesis. Thus, this review provides an insight into lipid metabolism in various lineages of the MTBC and their impact on virulence and persistence during infection, as this may provide critical insight into developing novel therapeutics to combat TB.

Construction and Characterization of the Mycobacterium tuberculosis sigE fadD26 Unmarked Double Mutant as a Vaccine Candidate

Despite the great increase in the understanding of the biology and pathogenesis of Mycobacterium tuberculosis achieved by the scientific community in recent decades, tuberculosis (TB) still represents one of the major threats to global human health. The only available vaccine (Mycobacterium bovis BCG) protects children from disseminated forms of TB but does not effectively protect adults from the respiratory form of the disease, making the development of new and more-efficacious vaccines against the pulmonary forms of TB a major goal for the improvement of global health. Among the different strategies being developed to reach this goal is the construction of attenuated strains more efficacious and safer than BCG. We recently showed that a sigE mutant of M. tuberculosis was more attenuated and more efficacious than BCG in a mouse model of infection. In this paper, we describe the construction and characterization of an M. tuberculosis sigE fadD26 unmarked double mutant fulfilling the criteria of the Geneva Consensus for entering human clinical trials. The data presented suggest that this mutant is even more attenuated and slightly more efficacious than the previous sigE mutant in different mouse models of infection and is equivalent to BCG in a guinea pig model of infection.

EsxA mainly contributes to the miR-155 overexpression in human monocyte-derived macrophages and potentially affect the immune mechanism of macrophages through miRNA dysregulation

BACKGROUND/PURPOSE

Mycobacterium tuberculosis is a successful intracellular pathogen that uses multiple proteins to survive within macrophages, one of the most remarkable is the virulence factor EsxA. In this study, we evaluate the participation of EsxA in the miRNAs expression profile of human monocyte-derived macrophages (hMDM), to mapping out the contribution of this virulence factor in the miRNA profile and how these changes can influence and alter immune-related processes and pathways.

METHODS

The cytotoxic effect of rEsxA on hMDM was evaluated by the neutral red assay. The evaluation of miRNA expression profile in infected and rEsxA-stimulated hMDM was done using TaqMan Low Density Assays, and in silico analyses was carried on to construct Protein-Protein Interaction network of miRNAs targets.

RESULTS

miR-155 was the only miRNA upregulated consistently in hMDM infected with M. tuberculosis H37Rv or stimulated with rEsxA. In hMDM stimulated with rEsxA, we found 25 miRNA's dysregulated (8 up-regulated and 17 down-regulated). The most significant were the miR-155 and miR-622 that has been observed in the analysis carried out with two different endogenous controls (U6 snRNA and RNU44) for the normalization of expression analysis. This result suggests that rEsxA induces the deregulation of miRNAs that potentially target genes in key pathways for the infection control, like the MAPK signaling pathway, cytokines, and chemokine signaling pathways, and several connected pathways involved in mycobacterial uptake, vesicular traffic, and endosome maturation.

CONCLUSION

Higher expression levels of miR-155 suggest potential roles of these miRNA in EsxA-dependent immune subversion.

Variability in the virulence of specific Mycobacterium tuberculosis clinical isolates alters the capacity of human dendritic cells to signal for T cells

BACKGROUND

Once in the pulmonary alveoli, Mycobacterium tuberculosis (Mtb) enters into contact with alveolar macrophages and dendritic cells (DCs). DCs represent the link between the innate and adaptive immune system owing to their capacity to be both a sentinel and an orchestrator of the antigen-specific immune responses against Mtb. The effect that the virulence of Mtb has on the interaction between the bacilli and human DCs has not been fully explored.

OBJECTIVE

To evaluate the effect of Mtb virulence on human monocyte-derived DCs.

METHODS

We exposed human monocyte-derived DCs to Mtb clinical strains (isolated from an epidemiological Mtb diversity study in Mexico) bearing different degrees of virulence and evaluated the capacity of DCs to internalise the bacilli, control intracellular growth, engage cell death pathways, express markers for activation and antigen presentation, and expand to stimulate autologous CD4⁺ T cells proliferation.

FINDINGS

In the case of the hypervirulent Mtb strain (Phenotype 1, strain 9005186, lineage 3), we report that DCs internalise and neutralise intracellular growth of the bacilli, undergo low rates of apoptosis, and contribute poorly to T-cell expansion, as compared to the H37Rv reference strain. In the case of the hypovirulent Mtb strain (Phenotype 4, strain 9985449, lineage 4), although DCs internalise and preclude proliferation of the bacilli, the DCs also display a high level of apoptosis, massive levels of apoptosis that prevent them from maintaining autologous CD4⁺ T cells in a co-culture system, as compared to H37Rv.

MAIN CONCLUSIONS

Our findings suggest that variability in virulence among Mtb clinical strains affects the capacity of DCs to respond to pathogenic challenge and mount an immune response against it, highlighting important parallels to studies previously done in mouse models.

Raw starch microparticles as BCG adjuvant: Their efficacy depends on the virulence of the infection strains

The persistence of tuberculosis (TB) as one of the top 10 causes of death worldwide, the growing incidence of multidrug-resistant tuberculosis and the controversial efficacy of the Bacille Calmette-Guérin (BCG) vaccine drives the development of new generation multistage vaccines against this disease that can boost BCG-primed immunity. The use of polymeric microparticles for this purpose increases due to their advantages, especially their good safety levels and intrinsic immunostimulant properties. We recently explored and demonstrated the reinforcing and adjuvant potential of starch microparticles (SMPs) that administered intranasally to BCG-primed BALB/c mice, alone or in combination with a recombinant antigen, increased survival rates and induced a reduction of bacterial load in the lungs of mice infected with tuberculosis. Here, we tested the effect of SMPs added to the BCG vaccine as adjuvant to the whole-cell vaccine and investigated their contribution to the improvement of the protective efficacy of subcutaneous vaccination in mice challenged with virulent strains of Mycobacterium tuberculosis. As expected, our results were dependent on the infection strains, showing that virulence is a crucial factor that affects the adjuvant activity of SMPs. Our results also confirm the adjuvant activity of this carbohydrate and its usefulness in diverse vaccination strategies not only for mucosal but also for parenteral administration.

Linking Individual Natural History to Population Outcomes in Tuberculosis

Background

Substantial individual heterogeneity exists in the clinical manifestations and duration of active tuberculosis. We sought to link the individual-level characteristics of tuberculosis disease to observed population-level outcomes.

Methods

We developed an individual-based, stochastic model of tuberculosis disease in a hypothetical cohort of patients with smear-positive tuberculosis. We conceptualized the disease process as consisting of 2 states—progression and recovery—including transitions between the 2. We then used a Bayesian process to calibrate the model to clinical data from the prechemotherapy era, thus identifying the rates of progression and recovery (and probabilities of transition) consistent with observed population-level clinical outcomes.

Results

Observed outcomes are consistent with slow rates of disease progression (median doubling time: 84 days, 95% uncertainty range 62–104) and a low, but nonzero, probability of transition from disease progression to recovery (median 16% per year, 95% uncertainty range 11%–21%). Other individual-level dynamics were less influential in determining observed outcomes.

Conclusions

This simplified model identifies individual-level dynamics—including a long doubling time and low probability of immune recovery—that recapitulate population-level clinical outcomes of untreated tuberculosis patients. This framework may facilitate better understanding of the population-level impact of interventions acting at the individual host level.

Advances in the understanding of Mycobacterium tuberculosis transmission in HIV-endemic settings

Tuberculosis claims more human lives than any other infectious disease. This alarming epidemic has fuelled the development of novel antimicrobials and diagnostics. However, public health interventions that interrupt transmission have been slow to emerge, particularly in HIV-endemic settings. Transmission of tuberculosis is complex, involving various environmental, bacteriological, and host factors, among which concomitant HIV infection is important. Preventing person-to-person spread is central to halting the epidemic and, consequently, tuberculosis transmission is now being studied with renewed interest. In this Series paper, we review recent advances in the understanding of tuberculosis transmission, from the view of source-case infectiousness, inherent susceptibility of exposed individuals, appending tools for predicting risk of disease progression, the biophysical nature of the contagion, and the environments in which transmission occurs and is sustained in populations. We focus specifically on how HIV infection affects these features with a view to describing novel transmission blocking strategies in HIV-endemic settings.

Effective delivery of the anti-mycobacterial peptide NZX in mesoporous silica nanoparticles

BACKGROUND

Intracellular delivery of antimicrobial agents by nanoparticles, such as mesoporous silica particles (MSPs), offers an interesting strategy to treat intracellular infections. In tuberculosis (TB), Mycobacterium tuberculosis avoids components of the immune system by residing primarily inside alveolar macrophages, which are the desired target for TB therapy.

METHODS AND FINDINGS

We have previously identified a peptide, called NZX, capable of inhibiting both clinical and multi-drug resistant strains of M. tuberculosis at therapeutic concentrations. In this study we analysed the potential of MSPs containing NZX for the treatment of tuberculosis. The MSPs released functional NZX gradually into simulated lung fluid and the peptide filled MSPs were easily taken up by primary macrophages. In an intracellular infection model, the peptide containing particles showed increased mycobacterial killing compared to free peptide. The therapeutic potential of peptide containing MSPs was investigated in a murine infection model, showing that MSPs preserved the effect to eliminate M. tuberculosis in vivo.

CONCLUSIONS

In this study we found that loading the antimicrobial peptide NZX into MSPs increased the inhibition of intracellular mycobacteria in primary macrophages and preserved the ability to eliminate M. tuberculosis in vivo in a murine model. Our studies provide evidence for the feasibility of using MSPs for treatment of tuberculosis.

Virulence of Mycobacterium tuberculosis Clinical Isolates Is Associated With Sputum Pre-treatment Bacterial Load, Lineage, Survival in Macrophages, and Cytokine Response

It is uncertain whether differences in Mycobacterium tuberculosis (Mtb) virulence defined in vitro influence clinical tuberculosis pathogenesis, transmission, and mortality. We primarily used a macrophage lysis model to characterize the virulence of Mtb isolates collected from 153 Vietnamese adults with pulmonary tuberculosis. The virulence phenotypes were then investigated for their relationship with sputum bacterial load, bacterial lineages, bacterial growth, and cytokine responses in macrophages. Over 6 days of infection, 34 isolates (22.2%) showed low virulence (< 5% macrophages lysed), 46 isolates (30.1%) showed high virulence (≥90% lysis of macrophages), and 73 isolates (47.7%) were of intermediate virulence (5–90% macrophages lysed). Highly virulent isolates were associated with an increased bacterial load in patients' sputum before anti-tuberculosis therapy (P = 0.02). Isolate-dependent virulence phenotype was consistent in both THP-1 and human monocyte-derived macrophages. High virulence isolates survived better and replicated in macrophages one hundred fold faster than those with low virulence. Macrophages infected with high virulence isolates produced lower concentrations of TNF-α and IL-6 (P = 0.002 and 0.0005, respectively), but higher concentration of IL-1β (P = 5.1 × 10⁻⁵) compared to those infected with low virulence isolates. High virulence was strongly associated with East Asian/Beijing lineage [P = 0.002, Odd ratio (OR) = 4.32, 95% confident intervals (CI) 1.68–11.13]. The association between virulence phenotypes, bacterial growth, and proinflammatory cytokines in macrophages suggest the suppression of certain proinflammatory cytokines (TNF-α and IL-6) but not IL-1β allows better intracellular survival of highly virulent Mtb. This could result in rapid macrophage lysis and higher bacterial load in sputum of patients infected with high virulence isolates, which may contribute to the pathogenesis and success of the Beijing lineage.

A novel derivative of the fungal antimicrobial peptide plectasin is active against Mycobacterium tuberculosis

Tuberculosis has been reaffirmed as the infectious disease causing most deaths in the world. Co-infection with HIV and the increase in multi-drug resistant Mycobacterium tuberculosis strains complicate treatment and increases mortality rates, making the development of new drugs an urgent priority. In this study we have identified a promising candidate by screening antimicrobial peptides for their capacity to inhibit mycobacterial growth. This non-toxic peptide, NZX, is capable of inhibiting both clinical strains of M. tuberculosis and an MDR strain at therapeutic concentrations. The therapeutic potential of NZX is further supported in vivo where NZX significantly lowered the bacterial load with only five days of treatment, comparable to rifampicin treatment over the same period. NZX possesses intracellular inhibitory capacity and co-localizes with intracellular bacteria in infected murine lungs. In conclusion, the data presented strongly supports the therapeutic potential of NZX in future anti-TB treatment.

Mycobacterium tuberculosis cording in alveolar macrophages of patients with pulmonary tuberculosis is likely associated with increased mycobacterial virulence

Mycobacterium tuberculosis (Mtb) is an infectious agent that causes tuberculosis (TB) in humans. A study of the volume of Mtb population and the detection of Mtb virulence in the lungs of patients with pulmonary TB are of great importance for understanding the infectious process and the outcome of the disease. We analyzed the functional state of Mtb and their number in alveolar macrophages obtained from the resected lungs of patients with TB in ex vivo culture and determined that the number of Mtb, referred mainly to the Beijing genotype family (A0 and B0/W148 clusters), were significantly different in cells between different patients. Only single Mtb were found in alveolar macrophages of some patients, while Mtb were actively replicated in colonies in alveolar macrophages of other patients, including cord morphology of Mtb growth (the indicator of Mtb virulence). Our data demonstrated association between the formation of Mtb cording in alveolar macrophages of patients and increased virulence of Mtb from the lungs of these patients in guinea pig TB model. The find of cording formation by replicating Mtb in human alveolar macrophages may be used for preliminary quick estimation of increased Mtb virulence in individual patients with pulmonary TB.

Immune response elicited by two rBCG strains devoid of genes involved in c-di-GMP metabolism affect protection versus challenge with M. tuberculosis strains of different virulence

Pellicles, a type of biofilm, have gathered a renewed interest in the field of tuberculosis as a structure that mimics some characteristics occurring during M. tuberculosis infection, such as antibiotic recalcitrance and chronicity of infection, and as a source of antigens for humoral response in infected guinea pigs. In other bacteria, it has been well documented that the second messenger c-di-GMP modulates the transition from planktonic cells to biofilm formation. In this work, we used the live vaccine Mycobacterium bovis BCG to determine whether deletion of genes involved in c-di-GMP metabolism would affect interaction with macrophages, capacity to induce immune response in a murine cell line and mice, and how the protein profile was modified when grown as surface pellicles. We found that deletion of the BCG1419c (Delta c-di-GMP phosphodiesterase, ΔPDE) gene, or deletion of the BCG1416c (Delta c-di-GMP diguanylate cyclase, ΔDGC) gene, altered production of TNF-α, IL-6, and IL-1β, in murine macrophages, and resulted in attenuation in intra-macrophage replication. Moreover, in addition to the improved immunogenicity of the BCGΔBCG1419c mutant already reported, deletion of the BCG1416c gene leads to increased T CD4⁺ and T CD8⁺ activation. This correlated with protection versus lethality in mice infected with the highly virulent M. tuberculosis 5186 afforded by vaccination with all the tested BCG strains, and controlled the growth of the mildly virulent M. tuberculosis H37Rv in lungs by vaccination with BCGΔBCG1419c during chronic late infection from 4 to 6 months after challenge. Furthermore, when grown as surface pellicles, a condition used to manufacture BCG vaccine, in comparison to BCG wild type, both rBCGs changed expression of antigenic proteins such as DnaK, HbhA, PstS2, 35KDa antigen, GroEL2, as well as AcpM, a protein involved in synthesis of mycolic acids, molecules relevant to modulate inflammatory responses.

Breaking Transmission with Vaccines: The Case of Tuberculosis

Members of the Mycobacterium tuberculosis complex (MTBC) have evolved causing tuberculosis (TB) in different mammalian hosts. MTBC ecotypes have adapted to diverse animal species, with M. bovis being the most common cause of TB in livestock. Cattle-to-human transmission of M. bovis through ingestion of raw milk was common before introduction of the pasteurization process. TB in humans is mainly caused by M. tuberculosis. This bacterium is considered a genetically clonal pathogen that has coevolved with humans due to its ability to manipulate and subvert the immune response. TB is a major public health problem due to airborne person-to-person transmission of M. tuberculosis. The essential yet unanswered question on the natural history of TB is when M. tuberculosis decides to establish latent infection in the host (resambling the lysogenic cycle of lambda phage) or to cause pulmonary disease (comparable to the lytic cycle of lambda phage). In this latter case, M. tuberculosis kills the host with the aim of achieving transmission to new hosts. Combating the TB epidemic requires stopping transmission. M. bovis BCG, the present vaccine against TB, is derived from M. bovis and only protects against disseminated forms of TB. Thus, a priority in TB research is development of new effective vaccines to prevent pulmonary disease. Attenuated vaccines based on M. tuberculosis as MTBVAC are potential candidates that could contribute to break the TB transmission cycle.

Biology of clinical strains of Mycobacterium tuberculosis with varying levels of transmission

Transmission of Mycobacterium tuberculosis bacilli from one individual to another is the basis of the disease process. While considerable emphasis has been placed on the role of host mechanisms of resistance in establishing or preventing new infection, far less has been expended on understanding possible factors operative at the bacterial level. In this study we established a panel of clinical isolates of M. tuberculosis strains obtained from the Western Cape region of South Africa, each of which had been carefully tracked in terms of their degree of transmission in the community. Each of the panel were used to infect guinea pigs with 15-20 bacilli by aerosol exposure and the course of the infection then determined. Strains with different degrees of transmission could not be distinguished in terms of their capacity to grow in the main target organs of infected animals. However, rather surprisingly, while strains with no evidence of transmission [NOT] in general caused moderate to severe lung damage, this parameter in animals infected with highly transmitted [HT] strains was mostly mild. In terms of TH1 immunity these signals were strongest in these latter animals, as was IL-17 gene expression, whereas minimal signals for regulatory molecules including IL-10 and FoxP3 were seen across the entire panel. In terms of T cell numbers, responses of both CD4 and CD8 were both far faster and far higher in animals infected with the HT strains. At the gene expression level we observed a major three-fold difference [both up and down] between NOT and HT strains, but in terms of proteins of key interest only a few [including PD-L1 and HIF-3] showed major differences between the two groups. Overall, it was apparent that NOT strains were far more inflammatory that HT strains, and appeared to trigger a much larger number of genes, possibly explaining the observed damage to the lungs and progressive pathology. In contrast, the HT strains, while equally virulent, were more immunogenic and developed much stronger T cell responses, while keeping lung damage to a minimum. Hence, in terms of trying to explain the capacity of these strains to cause transmission, these results are clearly paradoxical.

Experimental animal models of central nervous system tuberculosis: A historical review

Animal models are and will remain valuable tools in medical research because their use enables a deeper understanding of disease development, thus generating important knowledge for developing disease control strategies. Central nervous system tuberculosis (CNS TB) is the most devastating disease in humans. Moreover, as the variability of signs and symptoms delay a timely diagnosis, patients usually arrive at the hospital suffering from late stage disease. Therefore, it is impossible to obtain fresh human tissue for research before an autopsy. Because of these reasons, studies on human CNS TB are limited to case series, pharmacological response reports, and post mortem histopathological studies. Here, we review the contribution of the different animal models to understand the immunopathology of the disease and the host-parasitic relationship, as well as in the development of new strategies of vaccination and to test new drugs for the treatment of CNS TB.

Type-2 diabetes alters the basal phenotype of human macrophages and diminishes their capacity to respond, internalise, and control Mycobacterium tuberculosis

BACKGROUND

Type 2 diabetes (T2D) is a risk factor for the development of tuberculosis (TB), although the associated mechanisms are not known.

OBJECTIVES

To study the association between T2D and the basal phenotype of macrophages, and their immune response to Mycobacterium tuberculosis (Mtb) infection.

METHODS

We evaluated the influence of T2D on the response of monocyte-derived macrophages (MDM) to Mtb in patients with T2D (n = 10) compared to healthy subjects (n = 9), before and after infection with Mtb clinical isolates bearing different degrees of virulence. The levels of cell surface markers for activation secreted cytokines and chemokines, bacterial association, and intracellular bacterial growth were evaluated.

FINDINGS

The expression levels of HLA-DR, CD80, and CD86 were low while those of of PD-L1 were high in uninfected MDMs derived from patients with diabetes; as a result of Mtb infection, changes were only observed in the expression levels of PD-L1. The levels of cytokines (e.g., IL-6, IL-1β, IL-10, and IL-12) and chemokines (e.g., MCP-1, MIG, and RANTES) are perturbed in MDMs derived from patients with diabetes, both before infection and in response to Mtb infection. In response to the more virulent Mtb strains, the levels of association and bacterial clearance were diminished in MDMs derived from patients with diabetes.

CONCLUSIONS

T2D affects the basal activation state of the macrophages and its capacity to respond and control Mtb infection.

Raw starch microparticles have immunostimulant activity in mice vaccinated with BCG and challenged with Mycobacterium tuberculosis

The main challenge for vaccine development or improvement is the lack of safe adjuvants or immunostimulants that induce protective immune responses and can be used for mucosal immunization, which is a highly desirable strategy for vaccination against infectious diseases acquired by oral or intranasal routes. One promising alternative is the use of biodegradable and biocompatible polymeric microparticles. Recently, we developed an immobilization and delivery system with starch microparticles (SMPs) and a starch-binding domain (SBD_tag) suitable for the mucosal administration of antigens and the induction of antigen-specific immune responses. Here, we explore the immunostimulant and reinforcing potential of the system using BALB/c mice with progressive pulmonary tuberculosis (PPT). The heat shock protein alpha-crystallin from Mycobacterium tuberculosis immobilized on SMPs (µAcr-SBD_tag) or SMPs alone were administered nasally as boosters to BCG-vaccinated mice without any extra adjuvant. The mice were challenged intratracheally with either moderately virulent or highly virulent M. tuberculosis strains. Our results showed that the administration of either the immobilized antigen or SMPs asa booster for the BCG vaccination induced a significant reduction of bacterial loads in the lungs of mice, even more than in mice that received the BCG vaccination alone. Since no difference was observed in pulmonary bacillary burdens between the two reinforced groups, the obtained effect was most likely primarily caused by the starch. As determined by histological study, the administration of boosters did not contribute to the progress of pneumonia, which diminishes the safety concerns related to the administration of SMPs intranasally. Taken together, our findings suggest that this system may be considered asa new carbohydrate-based adjuvant suitable for mucosal vaccines against tuberculosis and other infectious diseases, and more generally, they highlight the potential of particulate α-glucans as immune response modifiers.

lysX gene is differentially expressed among Mycobacterium tuberculosis strains with different levels of virulence

Antimicrobial peptides (AMPs) are mainly produced by epithelial cells and macrophages to eliminate infecting mycobacteria through direct antimicrobial activity and immunomodulation. Indeed, it has been described that this line of defense is essential to control infection. However, Mycobacterium tuberculosis (Mtb) has developed mechanisms to avoid AMPs activity, for instance lysX adds lysine residues to surface phospholipids changing their net charge, leading to the repelling of the AMPs. In the present study, we determined that lysX gene is differentially expressed among Mtb strains. To achieve this aim we used several well-characterized Mtb clinical isolates, lysX mutated strains and reference strains. Our results showed that in the presence of AMPs, lysX expression increased significantly. Strains with higher lysX expression showed increased levels of intracellular survival in vivo and in vitro and induced more severe lesion related with pneumonia. Results showed that ability of Mtb to replicate intracellularly was directly correlated to the level of lysX expression showing that the amount of lysX produced by the bacterial cell is an important variable for the modulation of Mtb virulence.

Correlates of tuberculosis risk: predictive biomarkers for progression to active tuberculosis

New approaches to control the spread of tuberculosis (TB) are needed, including tools to predict development of active TB from latent TB infection (LTBI). Recent studies have described potential correlates of risk, in order to inform the development of prognostic tests for TB disease progression. These efforts have included unbiased approaches employing “omics” technologies, as well as more directed, hypothesis-driven approaches assessing a small set or even individual selected markers as candidate correlates of TB risk. Unbiased high-throughput screening of blood RNAseq profiles identified signatures of active TB risk in individuals with LTBI, ≥1 year before diagnosis. A recent infant vaccination study identified enhanced expression of T-cell activation markers as a correlate of risk prior to developing TB; conversely, high levels of Ag85A antibodies and high frequencies of interferon (IFN)-γ specific T-cells were associated with reduced risk of disease. Others have described CD27⁻IFN-γ⁺CD4⁺ T-cells as possibly predictive markers of TB disease. T-cell responses to TB latency antigens, including heparin-binding haemagglutinin and DosR-regulon-encoded antigens have also been correlated with protection.

Further studies are needed to determine whether correlates of risk can be used to prevent active TB through targeted prophylactic treatment, or to allow targeted enrolment into efficacy trials of new TB vaccines and therapeutic drugs.

Promising biomarkers may allow accurate prediction of progression from infection to active TB diseasehttp://ow.ly/OzCL304ezfk

Prophylactic potential of defensins and L-isoleucine in tuberculosis household contacts: an experimental model

AIM

Patients with pulmonary tuberculosis (TB) are the most important source for TB infection, being the risk of infection determined by the source case infectiousness and the contact closeness. Currently, the administration of isoniazid is used to prevent the infection to some extent in household contacts. At experimental level, defensins are efficient molecules for the treatment of TB and other infectious diseases.

MATERIALS & METHODS

In this work, we used a model of Mycobacterium tuberculosis transmission by long cohabitation of infected and noninfected mice, and treated the latter group with antimicrobial peptides in order to determine the potential capacity of defensins to prevent the infection.

RESULTS

Our results showed that the intratracheal administration of human neutrophil peptide-1, human β-defensin-2 alone or in combination and the use of L-isoleucine significantly prevents bacterial transmission, diminishing pulmonary lesions and bacterial loads.

CONCLUSION

Data suggest the potential use of L-isoleucine as prophylactic for TB household contacts.

Expression kinetics of metalloproteinases and their tissue inhibitors in experimental murine pulmonary tuberculosis

AIM

Explore the temporal expression of metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) during experimental tuberculosis induced by virulent Mycobacterium tuberculosis strain H37Rv.

METHODS

BALB/c mice were infected via endotracheal instillation with H37Rv. Groups of mice were euthanized at different time points during infection. RNA was isolated from the lungs, and the expression of MMP-3, 8, 9, 10, 12, 13 and TIMP-1-4 was determined by quantitative PCR. Immunohistochemical detection of MMP-3, MMP-9, and MMP-10 was done to determine the cell source.

RESULTS

The infection with H37Rv-induced inflammation resulted in maximal up-regulation of MMP-3, 8, 9, 10, 12 and 13 at day 21 postinfection. Additionally, MMP-13 showed another expression peak during late disease at day 60. Airway epithelium and macrophages were the most common MMP-3 and MMP-9 immunopositive cells, while for MMP-10, macrophages and endothelial cells were the most common, particularly at days 14 and 21 in well-formed granulomas. During late disease, vacuolated macrophages in pneumonic areas and bronchial epithelium showed mild MMP immunostaining.

CONCLUSIONS

MMP-3, 8, 9, 10, 12, and 13 are maximally expressed at the peak of granuloma formation in the mouse tuberculosis model, with no compensation in levels or timing of TIMP expression. This data opens the possibility of participation of these molecules in the granuloma process.

Specific interaction between Mycobacterium tuberculosis lipoprotein-derived peptides and target cells inhibits mycobacterial entry in vitro

Tuberculosis (TB) continues being one of the diseases having the greatest mortality rates around the world, 8.7 million cases having been reported in 2011. An efficient vaccine against TB having a great impact on public health is an urgent need. Usually, selecting antigens for vaccines has been based on proteins having immunogenic properties for patients suffering TB and having had promising results in mice and non-human primates. Our approach has been based on a functional approach involving the pathogen-host interaction in the search for antigens to be included in designing an efficient, minimal, subunit-based anti-TB vaccine. This means that Mycobacterium tuberculosis has mainly been involved in studies and that lipoproteins represent an important kind of protein on the cell envelope which can also contribute towards this pathogen's virulence. This study has assessed the expression of four lipoproteins from M. tuberculosis H37Rv, that is, Rv1411c (LprG), Rv1911c (LppC), Rv2270 (LppN) and Rv3763 (LpqH), and the possible biological activity of peptides derived from these. Five peptides were found for these proteins which had high specific binding to both alveolar A549 epithelial cells and U937 monocyte-derived macrophages which were able to significantly inhibit mycobacterial entry to these cells in vitro.

Recent developments in tuberculosis vaccines

Substantial efforts have been made over the past decade to develop vaccines against tuberculosis. We review recent developments in tuberculosis vaccines in the global portfolio, including those designed for use in a prophylactic setting, either alone or as boosts to Bacille Calmette-Guérin, and therapeutic vaccines designed to improve chemotherapy. While there is no doubt that progress is still being made, there are limitations to our animal model screening processes, which are further amplified by the lack of understanding of the immunological responses involved and the precise type of long-lived immunity that new vaccines need to induce. The challenge ahead is to optimize the planning for advanced clinical trials in poor endemic settings, which could be greatly facilitated by identifying correlates of protection.

Long-term dominance of Mycobacterium tuberculosis Uganda family in peri-urban Kampala-Uganda is not associated with cavitary disease

Background

Previous studies have shown that Mycobacterium tuberculosis (MTB) Uganda family, a sub-lineage of the MTB Lineage 4, is the main cause of tuberculosis (TB) in Uganda. Using a well characterized patient population, this study sought to determine whether there are clinical and patient characteristics associated with the success of the MTB Uganda family in Kampala.

Methods

A total of 1,746 MTB clinical isolates collected from1992-2009 in a household contact study were genotyped. Genotyping was performed using Single Nucleotide Polymorphic (SNP) markers specific for the MTB Uganda family, other Lineage 4 strains, and Lineage 3, respectively. Out of 1,746 isolates, 1,213 were from patients with detailed clinical data. These data were used to seek associations between MTB lineage/sub-lineage and patient phenotypes.

Results

Three MTB lineages were found to dominate the MTB population in Kampala during the last two decades. Overall, MTB Uganda accounted for 63% (1,092/1,746) of all cases, followed by other Lineage 4 strains accounting for 22% (394/1,746), and Lineage 3 for 11% (187/1,746) of cases, respectively. Seventy-three (4 %) strains remained unclassified. Our longitudinal data showed that MTB Uganda family occurred at the highest frequency during the whole study period, followed by other Lineage 4 strains and Lineage 3. To explore whether the long-term success of MTB Uganda family was due to increased virulence, we used cavitary disease as a proxy, as this form of TB is the most transmissible. Multivariate analysis revealed that even though cavitary disease was associated with known risk factors such as smoking (adjusted odds ratio (aOR) 4.8, 95% confidence interval (CI) 3.33-6.84) and low income (aOR 2.1, 95% CI 1.47-3.01), no association was found between MTB lineage and cavitary TB.

Conclusion

The MTB Uganda family has been dominating in Kampala for the last 18 years, but this long-term success is not due to increased virulence as defined by cavitary disease.

Virulence and immune response induced by Mycobacterium avium complex strains in a model of progressive pulmonary tuberculosis and subcutaneous infection in BALB/c mice

The genus Mycobacterium comprises more than 150 species, including important pathogens for humans which cause major public health problems. The vast majority of efforts to understand the genus have been addressed in studies with Mycobacterium tuberculosis. The biological differentiation between M. tuberculosis and nontuberculous mycobacteria (NTM) is important because there are distinctions in the sources of infection, treatments, and the course of disease. Likewise, the importance of studying NTM is not only due to its clinical significance but also due to the mechanisms by which some species are pathogenic while others are not. Mycobacterium avium complex (MAC) is the most important group of NTM opportunistic pathogens, since it is the second largest medical complex in the genus after the M. tuberculosis complex. Here, we evaluated the virulence and immune response of M. avium subsp. avium and Mycobacterium colombiense, using experimental models of progressive pulmonary tuberculosis and subcutaneous infection in BALB/c mice. Mice infected intratracheally with a high dose of MAC strains showed high expression of tumor necrosis factor alpha (TNF-α) and inducible nitric oxide synthase with rapid bacillus elimination and numerous granulomas, but without lung consolidation during late infection in coexistence with high expression of anti-inflammatory cytokines. In contrast, subcutaneous infection showed high production of the proinflammatory cytokines TNF-α and gamma interferon with relatively low production of anti-inflammatory cytokines such as interleukin-10 (IL-10) or IL-4, which efficiently eliminate the bacilli but maintain extensive inflammation and fibrosis. Thus, MAC infection evokes different immune and inflammatory responses depending on the MAC species and affected tissue.

Differential virulence and disease progression following Mycobacterium tuberculosis complex infection of the common marmoset (Callithrix jacchus)

Existing small-animal models of tuberculosis (TB) rarely develop cavitary disease, limiting their value for assessing the biology and dynamics of this highly important feature of human disease. To develop a smaller primate model with pathology similar to that seen in humans, we experimentally infected the common marmoset (Callithrix jacchus) with diverse strains of Mycobacterium tuberculosis of various pathogenic potentials. These included recent isolates of the modern Beijing lineage, the Euro-American X lineage, and M. africanum. All three strains produced fulminant disease in this animal with a spectrum of progression rates and clinical sequelae that could be monitored in real time using 2-deoxy-2-[(18)F]fluoro-d-glucose (FDG) positron emission tomography (PET)/computed tomography (CT). Lesion pathology at sacrifice revealed the entire spectrum of lesions observed in human TB patients. The three strains produced different rates of progression to disease, various extents of extrapulmonary dissemination, and various degrees of cavitation. The majority of live births in this species are twins, and comparison of results from siblings with different infecting strains allowed us to establish that the infection was highly reproducible and that the differential virulence of strains was not simply host variation. Quantitative assessment of disease burden by FDG-PET/CT provided an accurate reflection of the pathology findings at necropsy. These results suggest that the marmoset offers an attractive small-animal model of human disease that recapitulates both the complex pathology and spectrum of disease observed in humans infected with various M. tuberculosis strain clades.

Drug resistant clinical isolates of Mycobacterium tuberculosis from different genotypes exhibit differential host responses in THP-1 cells

Mycobacterium tuberculosis (MTB) persistently infects and survives within the host macrophages. Substantial genotypic variation exists among MTB strains which correlate with their interactions with the host. The present study was designed to establish a correlation, if any, between infection and induction of innate immune response by genetically diverse drug resistant MTB isolates from India. For this purpose, three clinical isolates from ancient and modern lineages, along with H37Ra and H37Rv were evaluated for intracellular growth, phagocytic index, induction of proinflammatory cytokines and apoptosis following infection in THP-1 cell line. A wide variation in the induction of cytokines was revealed subsequent to infection with different strains. EAI-5 strain from ancient lineage 1, induced higher proinflammatory responses, higher apoptosis and moderate intracellular growth compared to other strains, in contrast, for Beijing strain of modern lineage 2, all three parameters were lowest among the clinical isolates. Further, the responses induced by LAM-6 from modern lineage 4 were at a moderate level, similar to the laboratory strain H37Rv which also belongs to lineage 4. Thus, these profiles were specific to their respective lineages and/or genotypes and independent of their drug resistance status. Further, a positive correlation, among TNF-α, IL-1β, IL-6 and IL-12 induced in infected THP-1 cells was demonstrated. In addition, induction of all pro-inflammatory cytokines correlated well with the host cell apoptosis. A positive correlation was observed between phagocytic index in the category of ‘>10 bacilli/cell’ and induction of apoptosis, only for virulent strains, indicating that initial accumulation of MTB strains inside the host cell may be an important determining factor for different innate responses.

Immunotherapeutic effects of recombinant adenovirus encoding granulocyte-macrophage colony-stimulating factor in experimental pulmonary tuberculosis

BALB/c mice with pulmonary tuberculosis (TB) develop a T helper cell type 1 that temporarily controls bacterial growth. Bacterial proliferation increases, accompanied by decreasing expression of interferon (IFN)-γ, tumour necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS). Activation of dendritic cells (DCs) is delayed. Intratracheal administration of only one dose of recombinant adenoviruses encoding granulocyte-macrophage colony-stimulating factor (AdGM-CSF) 1 day before Mycobacterium tuberculosis (Mtb) infection produced a significant decrease of pulmonary bacterial loads, higher activated DCs and increased expression of TNF-α, IFN-γ and iNOS. When AdGM-CSF was given in female mice B6D2F1 (C57BL/6J X DBA/2J) infected with a low Mtb dose to induce chronic infection similar to latent infection and corticosterone was used to induce reactivation, a very low bacilli burden in lungs was detected, and the same effect was observed in healthy mice co-housed with mice infected with mild and highly virulent bacteria in a model of transmissibility. Thus, GM-CSF is a significant cytokine in the immune protection against Mtb and gene therapy with AdGM-CSF increased protective immunity when administered in a single dose 1 day before Mtb infection in a model of progressive disease, and when used to prevent reactivation of latent infection or transmission.

Two genetically-related multidrug-resistant Mycobacterium tuberculosis strains induce divergent outcomes of infection in two human macrophage models

Mycobacterium tuberculosis has a considerable degree of genetic variability resulting in different epidemiology and disease outcomes. We evaluated the pathogen-host cell interaction of two genetically closely-related multidrug-resistant M. tuberculosis strains of the Haarlem family, namely the strain M, responsible for an extensive multidrug-resistant tuberculosis outbreak, and its kin strain 410 which caused a single case in two decades. Intracellular growth and cytokine responses were evaluated in human monocyte-derived macrophages and dU937 macrophage-like cells. In monocyte-derived macrophages, strain M grew more slowly and induced lower levels of TNF-α and IL-10 than 410, contrasting with previous studies with other strains, where a direct correlation was observed between increased intracellular growth and epidemiological success. On the other hand, in dU937 cells, no difference in growth was observed between both strains, and strain M induced significantly higher TNF-α levels than strain 410. We found that both cell models differed critically in the expression of receptors for M. tuberculosis entry, which might explain the different infection outcomes. Our results in monocyte-derived macrophages suggest that strain M relies on a modest replication rate and cytokine induction, keeping a state of quiescence and remaining rather unnoticed by the host. Collectively, our results underscore the impact of M. tuberculosis intra-species variations on the outcome of host cell infection and show that results can differ depending on the in vitro infection model.

Prime-boost BCG vaccination with DNA vaccines based in β-defensin-2 and mycobacterial antigens ESAT6 or Ag85B improve protection in a tuberculosis experimental model

The World Health Organization (WHO) has estimated that there are about 8 million new cases annually of active Tuberculosis (TB). Despite its irregular effectiveness (0-89%), the Bacillus Calmette-Guérin) BCG is the only vaccine available worldwide for prevention of TB; thus, the design is important of novel and more efficient vaccination strategies. Considering that β-defensin-2 is an antimicrobial peptide that induces dendritic cell maturation through the TLR-4 receptor and that both ESAT-6 and Ag85B are immunodominant mycobacterial antigens and efficient activators of the protective immune response, we constructed two DNA vaccines by the fusion of the gene encoding β-defensin-2 and antigens ESAT6 (pDE) and 85B (pDA). After confirming efficient local antigen expression that induced high and stable Interferon gamma (IFN-γ) production in intramuscular (i.m.) vaccinated Balb/c mice, groups of mice were vaccinated with DNA vaccines in a prime-boost regimen with BCG and with BCG alone, and 2 months later were challenged with the mild virulence reference strain H37Rv and the highly virulent clinical isolate LAM 5186. The level of protection was evaluated by survival, lung bacilli burdens, and extension of tissue damage (pneumonia). Vaccination with both DNA vaccines showed similar protection to that of BCG. After the challenge with the highly virulent Mycobacterium tuberculosis strain, animals that were prime-boosted with BCG and then boosted with both DNA vaccines showed significant higher survival and less tissue damage than mice vaccinated only with BCG. These results suggest that improvement of BCG vaccination, such as the prime-boost DNA vaccine, represents a more efficient vaccination scheme against TB.

Spontaneous latency in a rabbit model of pulmonary tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is an exquisitely adapted human pathogen capable of surviving for decades in the lungs of immune-competent individuals in the absence of disease. The World Health Organization estimates that 2 billion people have latent TB infection (LTBI), defined by a positive immunological response to Mtb antigens, with no clinical signs of disease. A better understanding of host and pathogen determinants of LTBI and subsequent reactivation would benefit TB control efforts. Animal models of LTBI have been hampered generally by an inability to achieve complete bacillary clearance. Herein, we have characterized a rabbit model of LTBI in which, similar to most humans, complete clearance of pulmonary Mtb infection and pathological characteristics occurs spontaneously. The evidence that Mtb-CDC1551-infected rabbits achieve LTBI, rather than sterilization, is based on the ability of the bacilli to be reactivated after immune suppression. These rabbits showed early activation of T cells and macrophages and an early peak in the TNFα level, which decreased in association with clearance of bacilli from the lungs. In the absence of sustained tumor necrosis factor-α production, no necrosis was seen in the evolving lung granulomas. In addition, bacillary control was associated with down-regulation of several metalloprotease genes and an absence of lung fibrosis. This model will be used to characterize molecular markers of protective immunity and reactivation.

Use of mouse models to study the variability in virulence associated with specific genotypic lineages of Mycobacterium tuberculosis

The host response against Mycobacterium tuberculosis show a wide spectrum of clinical manifestations in those patients who fail to control the infection. The course of the infection and its epidemiological consequences depend upon a complex interplay of host, environmental and bacterial factors. Experimental animal models have helped to define the influence of bacterial genetic diversity on virulence and on the immune response that is induced. For this purpose, experimental animals such as mice, guinea pigs and rabbits have been infected with selected clinical isolates obtained from outbreaks or from clinical epidemiology settings. Here we review the contribution of mouse models to defining the variability in virulence and immune response in relation to mycobacterial genetic diversity. Low dose aerosol infection in C57Bl mice or high dose intratracheal infection in BALB/c mice have demonstrated wide variability in virulence and immune responses induced by different bacterial genotypes, and each genotype has different phenotypes, with high and low virulence variants. In general, these studies have shown that high prevalent strains from big clusters are more virulent than low prevalent sporadic clinical isolates, and highly virulent strains induce non-protective immune responses with some correlation with clinical-epidemiological data. In the future selected strains from these types of studies should be analyzed with molecular technologies. These kinds of study will contribute to the identification of mycobacterial genes associated with virulence and immunogenicity.

New insight into the molecular characterization of isoniazid and rifampicin resistant Mycobacterium tuberculosis strains from Saudi Arabia

Data on the genetic variation of isolates of Mycobacterium tuberculosis and spectrum of mutations determining resistance to principal anti-tuberculosis drugs isoniazid (INH) and rifampicin (RIF) have not yet been studied in Saudi Arabia. One hundred and fifty-one clinical isolates of M. tuberculosis from different regions in the country showing resistance to RIF and INH were subjected to drug susceptibility testing, characterization of mutations conferring drug resistance and genotyping. Phenotypically 17 (11.3%) isolates were resistance to RIF, 75 (49.6%) were resistant to INH and 59 (39.1%) were resistant to both RIF and INH, respectively. Sixteen (10.6%), 74 (49%) and 56 (37.1%) were determined as resistant to RIF, INH and to both by line probe assay. High frequency of rpoB 531 mutations (67.1%) in RIF resistant strains and katG 315 mutations (65.2%) in INH resistant strains were found. Mutations responsible for INH resistance, katG 315 (P value<0.001, odds ratio: 1.81, 95% CI [1.51, 2.18]) and inhA-15 (P value - 0.004, odds ratio: 1.48, 95% CI [1.22, 1.8]) were predominant among the newly diagnosed cases. Beijing strains were significantly associated with multi drug resistance and mutations in combination of rpoB531 and katG315 (P value - <0.001, odds ratio: 6.83, 95% CI [2.65, 17.58]). In addition multi drug resistance was significantly associated with treatment history (P value<0.001, odds ratio: 3.16, 95% CI [2.14, 4.67]). Furthermore, a higher rate (39.3%) of clustering among the multidrug resistant strains particularly with Beijing family (52.9%) was observed. Saudi Arabia harbors highly diverse drug resistant M. tuberculosis population with an ongoing transmission which needs to be immediately managed.

Increased Foxp3 expression in guinea pigs infected with W-Beijing strains of M. tuberculosis

There is increasing evidence that clinical isolates of Mycobacterium tuberculosis that belong to the W-Beijing genotype of newly emerging strains are often of very high virulence when tested in small animal models, including the mouse and guinea pig. In this report we provide further evidence to support this contention, and show that two W-Beijing strains are of very high virulence when introduced by low dose aerosol into outbred guinea pigs. In addition to severe lung pathology, each of these infections was associated with large influxes of activated CD4 and CD8 T cells into the lungs. Large influxes of macrophages were also observed, but the fraction of these showing evidence of activation by Class-II expression was relatively low. A progressive increase in neutrophils was also seen, with highest levels accumulating in the lungs of the W-Beijing infected animals. In the case of these two infections mRNA levels for TH1 cytokines was elevated early, but these then declined, and were replaced by increasing levels of message encoding for Foxp3, IL-10, and TGFβ. These observations support the hypothesis that W-Beijing strains are potent inducers of regulatory T cells, and that this event may enhance survival and transmission of these bacilli.

Human macrophage responses to clinical isolates from the Mycobacterium tuberculosis complex discriminate between ancient and modern lineages

The aim of the present study was to determine whether there is a correlation between phylogenetic relationship and inflammatory response amongst a panel of clinical isolates representative of the global diversity of the human Mycobacterium tuberculosis Complex (MTBC). Measurement of cytokines from infected human peripheral blood monocyte-derived macrophages revealed a wide variation in the response to different strains. The same pattern of high or low response to individual strains was observed for different pro-inflammatory cytokines and chemokines, and was conserved across multiple human donors. Although each major phylogenetic lineage of MTBC included strains inducing a range of cytokine responses, we found that overall inflammatory phenotypes differed significantly across lineages. In particular, comparison of evolutionarily modern lineages demonstrated a significant skewing towards lower early inflammatory response. The differential response to ancient and modern lineages observed using GM-CSF derived macrophages was also observed in autologous monocyte-derived dendritic cells and murine bone marrow-derived macrophages, but not in human unfractionated peripheral blood mononuclear cells. We hypothesize that the reduced immune responses to modern lineages contribute to more rapid disease progression and transmission, which might be a selective advantage in the context of expanding human populations. In addition to the lineage effects, the large strain-to-strain variation in innate immune responses elicited by MTBC will need to be considered in tuberculosis vaccine development.

Genomic stability over 9 years of an isoniazid resistant Mycobacterium tuberculosis outbreak strain in Sweden

In molecular epidemiological studies of drug resistant Mycobacterium tuberculosis (TB) in Sweden a large outbreak of an isoniazid resistant strain was identified, involving 115 patients, mainly from the Horn of Africa. During the outbreak period, the genomic pattern of the outbreak strain has stayed virtually unchanged with regard to drug resistance, IS6110 restriction fragment length polymorphism and spoligotyping patterns. Here we present the complete genome sequence analyses of the index isolate and two isolates sampled nine years after the index case as well as experimental data on the virulence of this outbreak strain. Even though the strain has been present in the community for nine years and passaged between patients at least five times in-between the isolates, we only found four single nucleotide polymorphisms in one of the later isolates and a small (4 amino acids) deletion in the other compared to the index isolate. In contrast to many other evolutionarily successful outbreak lineages (e.g. the Beijing lineage) this outbreak strain appears to be genetically very stable yet evolutionarily successful in a low endemic country such as Sweden. These findings further illustrate that the rate of genomic variation in TB can be highly strain dependent, something that can have important implications for epidemiological studies as well as development of resistance.