The potential of plant systems to break the HIV‐TB link

Tuberculosis (TB) and human immunodeficiency virus (HIV) can place a major burden on healthcare systems and constitute the main challenges of diagnostic and therapeutic programmes. Infection with HIV is the most common cause of Mycobacterium tuberculosis (Mtb), which can accelerate the risk of latent TB reactivation by 20‐fold. Similarly, TB is considered the most relevant factor predisposing individuals to HIV infection. Thus, both pathogens can augment one another in a synergetic manner, accelerating the failure of immunological functions and resulting in subsequent death in the absence of treatment. Synergistic approaches involving the treatment of HIV as a tool to combat TB and vice versa are thus required in regions with a high burden of HIV and TB infection. In this context, plant systems are considered a promising approach for combatting HIV and TB in a resource‐limited setting because plant‐made drugs can be produced efficiently and inexpensively in developing countries and could be shared by the available agricultural infrastructure without the expensive requirement needed for cold chain storage and transportation. Moreover, the use of natural products from medicinal plants can eliminate the concerns associated with antiretroviral therapy (ART) and anti‐TB therapy (ATT), including drug interactions, drug‐related toxicity and multidrug resistance. In this review, we highlight the potential of plant system as a promising approach for the production of relevant pharmaceuticals for HIV and TB treatment. However, in the cases of HIV and TB, none of the plant‐made pharmaceuticals have been approved for clinical use. Limitations in reaching these goals are discussed.     

Mycobacterial lipolytic enzymes: A gold mine for tuberculosis research

Tuberculosis (TB) is one of the deadliest infectious diseases worldwide with a strong impact in developing countries. Mycobacterium tuberculosis, the etiological agent of TB, has a high capacity to evade the host immune system and establish a chronic, asymptomatic and latent infection. In a latent TB infection, persistent bacilli are present in a non-replicating dormant state within host granulomas. During reactivation, bacilli start replicating again leading to an active TB infection that can be highly contagious. Mycobacterial lipids and lipolytic enzymes are thought to play important physiological roles during dormancy and reactivation. The role of lipolytic enzymes in the physiology of M. tuberculosis and physiopathology of the disease will be discussed in this review, with an emphasis on the secreted or cell wall-associated, surface exposed lipolytic enzymes characterized to date. Studies on the localization, enzymatic activity and immunological properties of these enzymes highlighted their possible usefulness as new diagnostic markers in the fight against TB.     

Diagnosis of latent tuberculosis infection is associated with reduced HIV viral load and lower risk for opportunistic infections in people living with HIV

Approximately 28% of the human population have been exposed to Mycobacterium tuberculosis (MTB), with the overwhelming majority of infected individuals not developing disease (latent TB infection (LTBI)). While it is known that uncontrolled HIV infection is a major risk factor for the development of TB, the effect of underlying LTBI on HIV disease progression is less well characterized, in part because longitudinal data are lacking. We sorted all participants of the Swiss HIV Cohort Study (SHCS) with at least 1 documented MTB test into one of the 3 groups: MTB uninfected, LTBI, or active TB. To detect differences in the HIV set point viral load (SPVL), linear regression was used; the frequency of the most common opportunistic infections (OIs) in the SHCS between MTB uninfected patients, patients with LTBI, and patients with active TB were compared using logistic regression and time-to-event analyses. In adjusted models, we corrected for baseline demographic characteristics, i.e., HIV transmission risk group and gender, geographic region, year of HIV diagnosis, and CD4 nadir. A total of 13,943 SHCS patients had at least 1 MTB test documented, of whom 840 (6.0%) had LTBI and 770 (5.5%) developed active TB. Compared to MTB uninfected patients, LTBI was associated with a 0.24 decreased log HIV SPVL in the adjusted model (p < 0.0001). Patients with LTBI had lower odds of having candida stomatitis (adjusted odds ratio (OR) = 0.68, p = 0.0035) and oral hairy leukoplakia (adjusted OR = 0.67, p = 0.033) when compared to MTB uninfected patients. The association of LTBI with a reduced HIV set point virus load and fewer unrelated infections in HIV/TB coinfected patients suggests a more complex interaction between LTBI and HIV than previously assumed.

Surprisingly little is known about how latent tuberculosis infection alters human physiology and immune function. Extensive statistical analyses of the large Swiss HIV Cohort Study suggests that latent tuberculosis infection can be protective in individuals with HIV.     

Is HIV Infection a Risk Factor for Multi-Drug Resistant Tuberculosis? A Systematic Review

Background

Tuberculosis (TB) is an important cause of human suffering and death. Human immunodeficiency virus (HIV), multi-drug resistant TB (MDR-TB), and extensive drug resistant tuberculosis (XDR-TB) have emerged as threats to TB control. The association between MDR-TB and HIV infection has not yet been fully investigated. We conducted a systematic review and meta-analysis to summarize the evidence on the association between HIV infection and MDR-TB.

Methods and Results

Original studies providing Mycobacterium tuberculosis resistance data stratified by HIV status were identified using MEDLINE and ISI Web of Science. Crude MDR-TB prevalence ratios were calculated and analyzed by type of TB (primary or acquired), region and study period. Heterogeneity across studies was assessed, and pooled prevalence ratios were generated if appropriate. No clear association was found between MDR-TB and HIV infection across time and geographic locations. MDR-TB prevalence ratios in the 32 eligible studies, comparing MDR-TB prevalence by HIV status, ranged from 0.21 to 41.45. Assessment by geographical region or study period did not reveal noticeable patterns. The summary prevalence ratios for acquired and primary MDR-TB were 1.17 (95% CI 0.86, 1.6) and 2.72 (95% CI 2.03, 3.66), respectively. Studies eligible for review were few considering the size of the epidemics. Most studies were not adjusted for confounders and the heterogeneity across studies precluded the calculation of a meaningful overall summary measure.

Conclusions

We could not demonstrate an overall association between MDR-TB and HIV or acquired MDR-TB and HIV, but our results suggest that HIV infection is associated with primary MDR-TB. Future well-designed studies and surveillance in all regions of the world are needed to better clarify the relationship between HIV infection and MDR-TB.     

Tuberculosis as a complex trait: impact of genetic epidemiological study design

Several studies have suggested a role for human genetic risk factors in the susceptibility to developing tuberculosis (TB). However, results of these studies have been inconsistent, and one potential reason for these inconsistencies is variation in aspects of study design. Specifically, phenotype definitions and population genetic factors have varied dramatically. Since TB is a complex trait, there are many challenges in designing studies to assess appropriately human genetic risk factors for the development of TB as opposed to the acquisition of latent M. tuberculosis infection. In this review we summarize these important study design differences, with illustrations from the TB genetics literature. We cite specific examples of studies of the NRAMP1 (SLC11A1) gene and present Fisher??s combined p values for different stratifications of these studies to further illustrate the impact of study design differences. Finally, we provide suggestions for the design of future genetic epidemiological studies of TB.     

Microbiome-immune interactions in tuberculosis

Tuberculosis (TB) remains an infectious disease of global significance and a leading cause of death in low- and middle-income countries. Significant effort has been directed towards understanding Mycobacterium tuberculosis genomics, virulence, and pathophysiology within the framework of Koch postulates. More recently, the advent of “-omics” approaches has broadened our appreciation of how “commensal” microbes have coevolved with their host and have a central role in shaping health and susceptibility to disease. It is now clear that there is a diverse repertoire of interactions between the microbiota and host immune responses that can either sustain or disrupt homeostasis. In the context of the global efforts to combatting TB, such findings and knowledge have raised important questions: Does microbiome composition indicate or determine susceptibility or resistance to M. tuberculosis infection? Is the development of active disease or latent infection upon M. tuberculosis exposure influenced by the microbiome? Does microbiome composition influence TB therapy outcome and risk of reinfection with M. tuberculosis? Can the microbiome be actively managed to reduce risk of M. tuberculosis infection or recurrence of TB? Here, we explore these questions with a particular focus on microbiome-immune interactions that may affect TB susceptibility, manifestation and progression, the long-term implications of anti-TB therapy, as well as the potential of the host microbiome as target for clinical manipulation.     

Mycobacterium tuberculosis Promotes HIV trans-Infection and Suppresses Major Histocompatibility Complex Class II Antigen Processing by Dendritic Cells

Mycobacterium tuberculosis is a leading killer of HIV-infected individuals worldwide, particularly in sub-Saharan Africa, where it is responsible for up to 50% of HIV-related deaths. Infection by HIV predisposes individuals to M. tuberculosis infection, and coinfection accelerates the progression of both diseases. In contrast to most other opportunistic infections associated with HIV, an increased risk of M. tuberculosis infection occurs during early-stage HIV disease, long before CD4 T cell counts fall below critical levels. We hypothesized that M. tuberculosis infection contributes to HIV pathogenesis by interfering with dendritic cell (DC)-mediated immune control. DCs carry pathogens like M. tuberculosis and HIV from sites of infection into lymphoid tissues, where they process and present antigenic peptides to CD4 T cells. Paradoxically, DCs can also deliver infectious HIV to T cells without first becoming infected, a process known as trans-infection. Lipopolysaccharide (LPS)-activated DCs sequester HIV in pocketlike membrane invaginations that remain open to the cell surface, and individual virions are delivered from the pocket into T cells at the site of contact during trans-infection. Here we report that M. tuberculosis exposure increases HIV trans-infection and induces viral sequestration within surface-accessible compartments identical to those seen in LPS-stimulated DCs. At the same time, M. tuberculosis dramatically decreases the degradative processing and major histocompatibility complex class II (MHC-II) presentation of HIV antigens to CD4 T cells. Our data suggest that M. tuberculosis infection promotes a shift in the dynamic balance between antigen processing and intact virion presentation, favoring DC-mediated amplification of HIV infections.Dendritic cells (DCs) comprise a diverse family of cell types whose primary function is to initiate and drive immune responses. Myeloid DCs (myDCs) are essential antigen-presenting cells that monitor peripheral tissues for invading pathogens. myDCs bind and internalize bacteria and viruses using a variety of surface receptors. When stimulated by pathogenic or inflammatory signals, peripheral-tissue DCs migrate to lymphoid tissues and undergo maturation, degrading stored antigens into peptides that are loaded onto major histocompatibility complex class II (MHC-II) molecules and expressed on the cell surface for presentation to CD4 T cells (reviewed in reference 4). In addition to presentation of processed peptide antigens, DCs carry intact, unprocessed proteins and pathogens from peripheral tissues to lymph nodes, where they can be passed to other antigen-presenting cells to increase the breadth of the immune response (reviewed in reference 10).HIV can exploit the natural trafficking of DCs to establish and amplify infection of CD4 T cells. DCs efficiently transfer intact, infectious HIV to T cells during immune interactions through a process known as trans-infection (14). DCs trans-infect HIV by binding and concentrating the intact virus at the cellular interface, forming an “infectious synapse” that concentrates HIV receptors on the T cell to the same site (24). Importantly, trans-infection does not require productive infection of the DCs, which are not infected efficiently by HIV in vitro or in vivo (14). Immature DCs significantly enhance infection of T cells through trans-infection, and prior activation by cytokine or bacterial stimuli markedly increases infectious synapse formation and concomitant trans-infection (2, 24, 33).Worldwide, nearly one-third of HIV-infected people are coinfected with Mycobacterium tuberculosis, and active tuberculosis disease (TB) is the number one cause of death in HIV-infected people. Coinfected individuals are 30 times more likely to progress to active TB, which can in turn increase HIV replication and accelerate the progression to AIDS (35). The mechanisms by which coinfection with M. tuberculosis and HIV accelerates the progression of both diseases are poorly understood.Lung macrophages are the primary target of M. tuberculosis infection, and active disease is characterized by unconstrained replication in these cells. Dendritic cells can also be infected by M. tuberculosis, but M. tuberculosis growth is restricted due to a lack of nutrient access in the DC phagolysosomal structure in which it resides (20). Importantly, M. tuberculosis-infected DCs traffic between the infected lung and draining lymph nodes, bringing bacterial antigens into lymphoid tissues to initiate CD4 T cell responses essential for disease control (39).Others have established that M. tuberculosis binds to and is internalized by DCs via an interaction between the mycobacterial cell wall component mannosylated lipoarabinomannan (ManLAM) and the cell surface receptor DC-SIGN on dendritic cells (15). After ManLAM stimulation, DCs begin to secrete interleukin-10 (IL-10) and show defects in immunostimulatory functions (15). However, a more recent study suggests that ManLAM may not be solely responsible for these outcomes (1).Previously, it has been shown that lipopolysaccharide (LPS) potently stimulates HIV trans-infection of CD4 T cells by DCs (24, 33). Therefore, we reasoned that M. tuberculosis and its products might similarly stimulate DC trans-infection during active M. tuberculosis infections. Further, we hypothesized that DC activation by M. tuberculosis would result in downmodulation of processing and MHC-II presentation of newly bound HIV particles, shifting the balance away from immune control in favor of viral dissemination and pathogenesis.Here, we demonstrate that M. tuberculosis infection of DCs enhances HIV trans-infection mediated through surface-accessible, pocketlike invaginations of the plasma membrane. Increased HIV trans-infection is accompanied by decreased MHC-II processing and presentation of HIV antigens to CD4 T cells. Our results suggest one mechanism whereby M. tuberculosis infection can fuel HIV dissemination in coinfected individuals and at the same time decrease immune control of both HIV and M. tuberculosis infections.     

Differences in Primary Sites of Infection between Zoonotic and Human Tuberculosis: Results from a Worldwide Systematic Review

Tuberculosis (TB) is one of the most devastating infectious diseases worldwide. Whilst global burden estimates for M. tuberculosis infection (MtTB) are well established, accurate data on the contribution of zoonotic TB (zTB) caused by M. bovis or M. caprae to human TB are scarce. The association of M. bovis infection with extrapulmonary tuberculosis has been suggested repeatedly, though there is little scientific evidence available to support this relationship. The present study aimed to determine globally the occurrence of extrapulmonary TB and the primary site (i.e. primary body location affected) of zTB in comparison with MtTB, based on previously published reports. A systematic literature review was conducted in 32 different bibliographic databases, selecting reports on zTB written in English, French, German, Spanish or Portuguese. Data from 27 reports from Africa, America, Europe and the Western Pacific Region were extracted for analyses. Low income countries, in Africa and South-East Asia, were highly underrepresented in the dataset. The median proportion of extrapulmonary TB cases was significantly increased among zTB in comparison with data from registries of Europe and USA, reporting mainly MtTB cases (47% versus 22% in Europe, 73% versus 30% in the USA). These findings were confirmed by analyses of eight studies reporting on the proportions of extrapulmonary TB in comparable populations of zTB and MtTB cases (median 63% versus 22%). Also, disparities of primary sites of extrapulmonary TB between zTB and MtTB were detected. Our findings, based on global data, confirm the widely suggested association between zTB and extrapulmonary disease. Different disability weights for zTB and MtTB should be considered and we recommend separate burden estimates for the two diseases.     

Marked Microevolution of a Unique Mycobacterium tuberculosis Strain in 17 Years of Ongoing Transmission in a High Risk Population

The transmission and persistence of Mycobacterium tuberculosis within high risk populations is a threat to tuberculosis (TB) control. In the current study, we used whole genome sequencing (WGS) to decipher the transmission dynamics and microevolution of M. tuberculosis ON-A, an endemic strain responsible for an ongoing outbreak of TB in an urban homeless/under-housed population. Sixty-one M. tuberculosis isolates representing 57 TB cases from 1997 to 2013 were subjected to WGS. Sequencing data was integrated with available epidemiological information and analyzed to determine how the M. tuberculosis ON-A strain has evolved during almost two decades of active transmission. WGS offers higher discriminatory power than traditional genotyping techniques, dividing the M. tuberculosis ON-A strain into 6 sub-clusters, each defined by unique single nucleotide polymorphism profiles. One sub-cluster, designated ON-A^NM (Natural Mutant; 26 isolates from 24 cases) was also defined by a large, 15 kb genomic deletion. WGS analysis reveals the existence of multiple transmission chains within the same population/setting. Our results help validate the utility of WGS as a powerful tool for identifying genomic changes and adaptation of M. tuberculosis.     

Potent anti-mycobacterial and immunomodulatory activity of some bioactive molecules of Indian ethnomedicinal plants that have the potential to enter in TB management

Tuberculosis (TB) is one of the deadliest infectious diseases of human civilization. Approximately one-third of global population is latently infected with the TB pathogen Mycobacterium tuberculosis (M.tb). The discovery of anti-TB antibiotics leads to decline in death rate of TB. However, the evolution of antibiotic-resistant M.tb-strain and the resurgence of different immune-compromised diseases re-escalated the death rate of TB. WHO has already cautioned about the chances of pandemic situation in TB endemic countries until the discovery of new anti-tubercular drugs, that is, the need of the hour. Analysing the pathogenesis of TB, it was found that M.tb evades the host by altering the balance of immune response and affects either by killing the cells or by creating inflammation. In the pre-antibiotic era, traditional medicines were only therapeutic measures for different infectious diseases including tuberculosis. The ancient literatures of India or ample Indian traditional knowledge and ethnomedicinal practices are evidence for the treatment of TB using different indigenous plants. However, in the light of modern scientific approach, anti-TB effects of those plants and their bioactive molecules were not established thoroughly. In this review, focus has been given on five bioactive molecules of different traditionally used Indian ethnomedicinal plants for treatment of TB or TB-like symptom. These compounds are also validated with proper identification and their mode of action with modern scientific approaches. The effectiveness of these molecules for sensitive or drug-resistant TB pathogen in clinical or preclinical studies was also evaluated. Thus, our specific aim is to highlight such scientifically validated bioactive compounds having anti-mycobacterial and immunomodulatory activity for future use as medicine or adjunct-therapeutic molecule for TB management.     

Drug resistance mechanisms and novel drug targets for tuberculosis therapy

Drug-resistant tuberculosis (TB) poses a significant challenge to the successful treatment and control of TB worldwide. Resistance to anti-TB drugs has existed since the beginning of the chemotherapy era. New insights into the resistant mechanisms of anti-TB drugs have been provided. Better understanding of drug resistance mechanisms helps in the development of new tools for the rapid diagnosis of drug-resistant TB. There is also a pressing need in the development of new drugs with novel targets to improve the current treatment of TB and to prevent the emergence of drug resistance in Mycobacterium tuberculosis. This review summarizes the anti-TB drug resistance mechanisms, furnishes some possible novel drug targets in the development of new agents for TB therapy and discusses the usefulness using known targets to develop new anti-TB drugs. Whole genome sequencing is currently an advanced technology to uncover drug resistance mechanisms in M. tuberculosis. However, further research is required to unravel the significance of some newly discovered gene mutations in their contribution to drug resistance.     

HIV Infection Disrupts the Sympatric Host–Pathogen Relationship in Human Tuberculosis

The phylogeographic population structure of Mycobacterium tuberculosis suggests local adaptation to sympatric human populations. We hypothesized that HIV infection, which induces immunodeficiency, will alter the sympatric relationship between M. tuberculosis and its human host. To test this hypothesis, we performed a nine-year nation-wide molecular-epidemiological study of HIV–infected and HIV–negative patients with tuberculosis (TB) between 2000 and 2008 in Switzerland. We analyzed 518 TB patients of whom 112 (21.6%) were HIV–infected and 233 (45.0%) were born in Europe. We found that among European-born TB patients, recent transmission was more likely to occur in sympatric compared to allopatric host–pathogen combinations (adjusted odds ratio [OR] 7.5, 95% confidence interval [95% CI] 1.21–infinity, p = 0.03). HIV infection was significantly associated with TB caused by an allopatric (as opposed to sympatric) M. tuberculosis lineage (OR 7.0, 95% CI 2.5–19.1, p<0.0001). This association remained when adjusting for frequent travelling, contact with foreigners, age, sex, and country of birth (adjusted OR 5.6, 95% CI 1.5–20.8, p = 0.01). Moreover, it became stronger with greater immunosuppression as defined by CD4 T-cell depletion and was not the result of increased social mixing in HIV–infected patients. Our observation was replicated in a second independent panel of 440 M. tuberculosis strains collected during a population-based study in the Canton of Bern between 1991 and 2011. In summary, these findings support a model for TB in which the stable relationship between the human host and its locally adapted M. tuberculosis is disrupted by HIV infection.     

Target Prediction for an Open Access Set of Compounds Active against Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects an estimated two billion people worldwide and is the leading cause of mortality due to infectious disease. The development of new anti-TB therapeutics is required, because of the emergence of multi-drug resistance strains as well as co-infection with other pathogens, especially HIV. Recently, the pharmaceutical company GlaxoSmithKline published the results of a high-throughput screen (HTS) of their two million compound library for anti-mycobacterial phenotypes. The screen revealed 776 compounds with significant activity against the M. tuberculosis H37Rv strain, including a subset of 177 prioritized compounds with high potency and low in vitro cytotoxicity. The next major challenge is the identification of the target proteins. Here, we use a computational approach that integrates historical bioassay data, chemical properties and structural comparisons of selected compounds to propose their potential targets in M. tuberculosis. We predicted 139 target - compound links, providing a necessary basis for further studies to characterize the mode of action of these compounds. The results from our analysis, including the predicted structural models, are available to the wider scientific community in the open source mode, to encourage further development of novel TB therapeutics.     

Research questions and priorities for tuberculosis: a survey of published systematic reviews and meta-analyses

Background

Systematic reviews are increasingly informing policies in tuberculosis (TB) care and control. They may also be a source of questions for future research. As part of the process of developing the International Roadmap for TB Research, we did a systematic review of published systematic reviews on TB, to identify research priorities that are most frequently suggested in reviews.

Methodology/Principal Findings

We searched EMBASE, MEDLINE, Web of Science, and the Cochrane Library for systematic reviews and meta-analyses on any aspect of TB published between 2005 and 2010. One reviewer extracted data and a second reviewer independently extracted data from a random subset of included studies. In total, 137 systematic reviews, with 141 research questions, were included in this review. We used the UK Health Research Classification System (HRCS) to help us classify the research questions and priorities. The three most common research topics were in the area of detection, screening and diagnosis of TB (32.6%), development and evaluation of treatments and therapeutic interventions (23.4%), and TB aetiology and risk factors (19.9%). The research priorities determined were mainly focused on the discovery and evaluation of bacteriological TB tests and drug-resistant TB tests and immunological tests. Other important topics of future research were genetic susceptibility linked to TB and disease determinants attributed to HIV/TB. Evaluation of drug treatments for TB, drug-resistant TB and HIV/TB were also frequently proposed research topics.

Conclusions

Systematic reviews are a good source of key research priorities. Findings from our survey have informed the development of the International Roadmap for TB Research by the TB Research Movement.     

The Isoniazid Paradigm of Killing,Resistance, and Persistence in Mycobacterium tuberculosis

Isoniazid (INH) was the first synthesized drug that mediated bactericidal killing of the bacterium Mycobacterium tuberculosis, a major clinical breakthrough. To this day, INH remains a cornerstone of modern tuberculosis (TB) chemotherapy. This review describes the serendipitous discovery of INH, its effectiveness on TB patients, and early studies to discover its mechanisms of bacteriocidal activity. Forty years after its introduction as a TB drug, the development of gene transfer in mycobacteria enabled the discovery of the genes encoding INH resistance, namely, the activator (katG) and the target (inhA) of INH. Further biochemical and x-ray crystallography studies on KatG and InhA proteins and mutants provided comprehensive understanding of INH mode of action and resistance mechanisms. Bacterial cultures can harbor subpopulations that are genetically or phenotypically resistant cells, the latter known as persisters. Treatment of exponentially growing cultures of M. tuberculosis with INH reproducibly kills 99% to 99.9% of cells in 3 days. Importantly, the surviving cells are slowly replicating or non-replicating cells expressing a unique stress response signature: these are the persisters. These persisters can be visualized using dual-reporter mycobacteriophages and their formation prevented using reducing compounds, such as N-acetylcysteine or vitamin C, that enhance M. tuberculosis' respiration. Altogether, this review portrays a detailed molecular analysis of INH killing and resistance mechanisms including persistence. The phenomenon of persistence is clearly the single greatest impediment to TB control, and research aimed at understanding persistence will provide new strategies to improve TB chemotherapy.     

Mycobacterium Tuberculosis Infection in Rhesus Monkeys (Macaca mulatta) and Evaluation of ESAT-6 and CFP10 as Immunodiagnostic Antigens#

Tuberculosis (TB) in nonhuman primates is a serious menace to the welfare of the animals and human who come into contact with them, while the rapid, accurate, and robust diagnosis is challenging. In this study, we first sought to establish an appropriate primate TB model resembling natural TB in nonhuman primates. Four rhesus monkeys (Macaca mulatta) of Chinese origin were infected intratracheally with two low doses of M. tuberculosis H37Rv. Regardless of the infectious doses, all monkeys were demonstrated to be successfully infected by clinical assessments, tuberculin skin test conversions, peripheral immune responses, gross observations, histopathology analysis, and M. tuberculosis burdens. Furthermore, we extended the usefulness of this model for assessing the following immunodiagnostic antigens: CFP10, ESAT-6, CFP10-ESAT-6, and an antigen cocktail of CFP10 and ESAT-6. The data showed that CFP10 was an M. tuberculosis-specific, “early” antigen used for serodiagnosis of TB in nonhuman primates. In conclusion, we established a useful primate TB model depending on low doses of M .tuberculosis and affording new opportunities for studies of M. tuberculosis disease and diagnostics.     

A Locus at 5q33.3 Confers Resistance to Tuberculosis in Highly Susceptible Individuals

Immunosuppression resulting from HIV infection increases the risk of progression to active tuberculosis (TB) both in individuals newly exposed to Mycobacterium tuberculosis (MTB) and in those with latent infections. We hypothesized that HIV-positive individuals who do not develop TB, despite living in areas where it is hyperendemic, provide a model of natural resistance. We performed a genome-wide association study of TB resistance by using 581 HIV-positive Ugandans and Tanzanians enrolled in prospective cohort studies of TB; 267 of these individuals developed active TB, and 314 did not. A common variant, rs4921437 at 5q33.3, was significantly associated with TB (odds ratio = 0.37, p = 2.11 × 10⁻⁸). This variant lies within a genomic region that includes IL12B and is embedded in an H3K27Ac histone mark. The locus also displays consistent patterns of linkage disequilibrium across African populations and has signals of strong selection in populations from equatorial Africa. Along with prior studies demonstrating that therapy with IL-12 (the cytokine encoded in part by IL12B, associated with longer survival following MTB infection in mice deficient in CD4 T cells), our results suggest that this pathway might be an excellent target for the development of new modalities for treating TB, especially for HIV-positive individuals. Our results also indicate that studying extreme disease resistance in the face of extensive exposure can increase the power to detect associations in complex infectious disease.     

Evaluation of Giant African Pouched Rats for Detection of Pulmonary Tuberculosis in Patients from a High-Endemic Setting

BackgroundThis study established evidence about the diagnostic performance of trained giant African pouched rats for detecting Mycobacterium tuberculosis in sputum of well-characterised patients with presumptive tuberculosis (TB) in a high-burden setting.MethodsThe TB detection rats were evaluated using sputum samples of patients with presumptive TB enrolled in two prospective cohort studies in Bagamoyo, Tanzania. The patients were characterised by sputum smear microscopy and culture, including subsequent antigen or molecular confirmation of Mycobacterium tuberculosis, and by clinical data at enrolment and for at least 5-months of follow-up to determine the reference standard. Seven trained giant African pouched rats were used for the detection of TB in the sputum samples after shipment to the APOPO project in Morogoro, Tanzania.ResultsOf 469 eligible patients, 109 (23.2%) were culture-positive for Mycobacterium tuberculosis and 128 (27.3%) were non-TB controls with sustained recovery after 5 months without anti-TB treatment. The HIV prevalence was 46%. The area under the receiver operating characteristic curve of the seven rats for the detection of culture-positive pulmonary tuberculosis was 0.72 (95% CI 0.66–0.78). An optimal threshold could be defined at ≥2 indications by rats in either sample with a corresponding sensitivity of 56.9% (95% CI 47.0–66.3), specificity of 80.5% (95% CI 72.5–86.9), positive and negative predictive value of 71.3% (95% CI 60.6–80.5) and 68.7% (95% CI 60.6–76.0), and an accuracy for TB diagnosis of 69.6%. The diagnostic performance was negatively influenced by low burden of bacilli, and independent of the HIV status.ConclusionGiant African pouched rats have potential for detection of tuberculosis in sputum samples. However, the diagnostic performance characteristics of TB detection rats do not currently meet the requirements for high-priority, rapid sputum-based TB diagnostics as defined by the World Health Organization.