Induction of the antigen 85 complex of Mycobacterium tuberculosis in sputum: a determinant of outcome in pulmonary tuberculosis treatment

Mycobacterium tuberculosis antigen 85B modifies BCG-induced antituberculosis immunity and favors pathogen survival

Tuberculosis is one of the deadliest infectious diseases worldwide. Mycobacterium tuberculosis has developed strategies not only to evade host immunity but also to manipulate it for its survival. We investigated whether Mycobacterium tuberculosis exploited the immunogenicity of Ag85B, one of its major secretory proteins, to redirect host antituberculosis immunity to its advantage. We found that administration of Ag85B protein to mice vaccinated with Bacillus Calmette-Guérin impaired the protection elicited by vaccination, causing a more severe infection when mice were challenged with Mycobacterium tuberculosis. Ag85B administration reduced Bacillus Calmette-Guérin-induced CD4 T-cell activation and IFN-γ, CCL-4, and IL-22 production in response to Mycobacterium tuberculosis-infected cells. On the other hand, it promoted robust Ag85B-responsive IFN-γ-producing CD4 T cells, expansion of a subset of IFN-γ/IL-10-producing CD4+FOXP3+Treg cells, differential activation of IL-17/IL-22 responses, and activation of regulatory and exhaustion pathways, including programmed death ligand 1 expression on macrophages. All this resulted in impaired intracellular Mycobacterium tuberculosis growth control by systemic immunity, both before and after the Mycobacterium tuberculosis challenge. Interestingly, Mycobacterium tuberculosis infection itself generated Ag85B-reactive inflammatory immune cells incapable of clearing Mycobacterium tuberculosis in both unvaccinated and Bacillus Calmette-Guérin-vaccinated mice. Our data suggest that Mycobacterium tuberculosis can exploit the strong immunogenicity of Ag85B to promote its own survival and spread. Since Ag85B is normally secreted by replicating bacteria and is commonly found in the lungs of the Mycobacterium tuberculosis-infected host, our findings may advance the understanding on the mechanisms of Mycobacterium tuberculosis pathogenesis and immune evasion.

Exploring the Potential of Exosomes as Biomarkers in Tuberculosis and Other Diseases

Tuberculosis (TB) is a major cause of morbidity and mortality and remains an important public health issue in developing countries worldwide. The existing methods and techniques available for the diagnosis of TB are based on combinations of laboratory (chemical and biological), radiological, and clinical tests. These methods are sophisticated and laborious and have limitations in terms of sensitivity, specificity, and accuracy. Clinical settings need improved diagnostic biomarkers to accurately detect biological changes due to pathogen invasion and pharmacological responses. Exosomes are membrane-bound vesicles and mediators of intercellular signaling processes that play a significant role in the pathogenesis of various diseases, such as tuberculosis, and can act as promising biomarkers for the monitoring of TB infection. Compared to conventional biomarkers, exosome-derived biomarkers are advantageous because they are easier to detect in different biofluids, are more sensitive and specific, and may be useful in tracking patients' reactions to therapy. This review provides insights into the types of biomarkers, methods of exosome isolation, and roles of the cargo (proteins) present in exosomes isolated from patients through omics studies, such as proteomics. These findings will aid in developing new prognostic and diagnostic biomarkers and could lead to the identification of new therapeutic targets in the clinical setting.

New Insights into Biomarkers for Evaluating Therapy Efficacy in Pulmonary Tuberculosis: A Narrative Review

Evaluating therapy efficacy is crucial for patients with tuberculosis (TB), especially those with drug-resistant tuberculosis (DR-TB). The World Health Organization currently recommends sputum smear and culture as the standard methods for evaluating pulmonary tuberculosis (PTB) therapy efficacy. However, these approaches have limitations including low sensitivity, lengthy culture periods, and susceptibility to contamination. There is an urgent need for dependable biomarkers to evaluate therapy efficacy in patients with PTB. Numerous new biomarkers of Mycobacterium tuberculosis (MTB) and the host have been used in recent studies to evaluate PTB therapy efficacy. A systematic review and update of these biomarkers can facilitate the discovery of novel biomarkers and assessment models, as well as provide a solid scientific basis for alternative indicators of evaluating therapy efficacy. In this review we summarize the recent advancements and limitations of biomarkers used to monitor therapy efficacy, highlighting the importance of utilizing a combination of biomarkers. Although some biomarkers have potential in evaluating the efficacy of therapy in patients with PTB, they also have some limitations. Further research, validation, and optimization are required to identify the most reliable and effective alternative biomarkers and apply them to clinical practice.

Adhesion molecules facilitate host-pathogen interaction & mediate Mycobacterium tuberculosis pathogenesis

Most of the microorganisms display adhesion molecules on their surface which help them to bind and interact with the host cell during infection. Adhesion molecules help mycobacteria to colonize and invade immune system of the host, and also trigger immune response explicated by the host against the infection. Hence, understanding the signalling pathways illustrated by these molecules to enhance our knowledge on mycobacterial survival and persistence inside the host cell is required. Hence, this review was focussed on the role of adhesion molecules and their receptor molecules. The various mechanisms adopted by adhesion molecules to bind with the specific receptors on the host cell and their role in invasion and persistence of mycobacterium inside the host cell are explained.

Immuno-PCR, a new technique for the serodiagnosis of tuberculosis

Rapid and accurate diagnosis of tuberculosis (TB) is essential to control the disease. The conventional microbiological tests have limitations and there is an urgent need to devise a simple, rapid and reliable point-of-care (POC) test. The failure of TB diagnostic tests based on antibody detection due to inconsistent and imprecise results has stimulated renewed interest in the development of rapid antigen detection methods. However, the World Health Organization (WHO) has emphasized to continue research for designing new antibody-based detection tests with improved accuracy. Immuno-polymerase chain reaction (I-PCR) combines the simplicity and versatility of enzyme-linked immunosorbent assay (ELISA) with the exponential amplification capacity and sensitivity of PCR thus leading to several-fold increase in sensitivity in comparison to analogous ELISA. In this review, we have described the serodiagnostic potential of I-PCR assays for an early diagnosis of TB based on the detection of potential mycobacterial antigens and circulating antibodies in body fluids of TB patients.

Mycobacterial antigen 85 complex (Ag85) as a target for ficolins and mannose-binding lectin

The pattern recognition molecules (PRMs) able to activate complement via the lectin pathway are suspected to be involved in the interaction between pathogenic Mycobacteria and the host immune response. Recently, we have found strong interactions between 25 and 35kDa mycobacterial cell fractions and mannose-binding lectin (MBL) and ficolins. Here we demonstrate that two biologically important mycobacterial structures, mannosylated lipoarabinomannan (ManLAM) and the antigen 85 (Ag85) complex, induce activation of the lectin pathway of complement. The strong interaction of recombinant MBL with purified ManLAM was confirmed, but no binding of recombinant ficolins (ficolin-1, -2, -3) with this structure was observed. Interestingly, all PRMs tested reacted with the mycobacterial antigen 85 (Ag85) complex. Based on the use of specific inhibitors (mannan for MBL, acetylated bovine serum albumin for ficolin-1 and -2, Hafnia alvei PCM 1200 lipopolysaccharide for ficolin-3), we concluded that carbohydrate-recognition (MBL) and fibrinogen-like domains (ficolins) were involved in these interactions. Our results indicate that the mycobacterial antigen 85 complex is a target for ficolins and MBL. Furthermore, those PRMs also bound to fibronectin and therefore might influence the Ag85 complex-dependent interaction of Mycobacterium with the extracellular matrix.

Assessment of treatment response in tuberculosis

Antibiotic treatment of tuberculosis has a duration of several months. There is significant variability of the host immune response and the pharmacokinetic-pharmacodynamic properties of Mycobacterium tuberculosis sub-populations at the site of disease. A limitation of sputum-based measures of treatment response may be sub-optimal detection and monitoring of Mycobacterium tuberculosis sub-populations. Potential biomarkers and surrogate endpoints should be benchmarked against hard clinical outcomes (failure/relapse/death) and may need tailoring to specific patient populations. Here, we assess the evidence supporting currently utilized and future potential host and pathogen-based models and biomarkers for monitoring treatment response in active and latent tuberculosis. Biomarkers for monitoring treatment response in extrapulmonary, pediatric and drug resistant tuberculosis are research priorities.

Diagnosis of pulmonary and extrapulmonary tuberculosis based on detection of mycobacterial antigen 85B by immuno-PCR

We developed a novel indirect sandwich immuno-polymerase chain reaction (I-PCR) assay for the detection of mycobacterial antigen 85B (Ag85B, 30kDa, Rv1886c) in pulmonary tuberculosis (PTB) and extrapulmonary tuberculosis (EPTB) patients. The amino-modified reporter DNA was covalently attached with the antidetection antibody through a heterobifunctional cross-linking agent succinimidyl 4-[N-maleimidomethyl]-cyclohexane-1-carboxylate. The detection limit of Ag85B by I-PCR was found to be 1 femtogram (fg)/mL, which was 10(6)-fold lower than an analogous enzyme-linked immunosorbent assay (ELISA). The sensitivities of 85% and 77% with I-PCR and 77.6% and 62.5% with ELISA were observed in smear-positive and smear-negative PTB patients, respectively, with high specificity. On the other hand, sensitivities of 84% and 63.7% with I-PCR and 68% and 47.5% with ELISA were observed in confirmed and clinically suspected EPTB cases, respectively, with high specificity.

Urine lipoarabinomannan to monitor antituberculosis therapy response and predict mortality in an HIV-endemic region: a prospective cohort study

OBJECTIVE

To determine if urinary lipoarabinomannan (LAM) may serve as a biomarker to monitor antituberculosis (TB) therapy response, and whether LAM results before and after treatment are predictive of patient outcomes.

DESIGN

Prospective cohort.

SETTING

Outpatient referral clinic and tertiary hospital in South Africa.

PARTICIPANTS

Adults (≥18 years) with ≥2 TB-related symptoms (cough, fever, weight loss, night sweats) for ≥2 weeks being initiated on anti-TB therapy.

INTERVENTIONS

On enrolment, we obtained urine and nebulised sputum specimens, offered HIV testing and started participants on anti-TB therapy for ≥6 months. We collected urine samples after the 2-month intensive treatment phase and at the completion of anti-TB therapy. Positive LAM results were graded from 1 (low) to 5 (high). Participants were followed for >3 years.

OUTCOME MEASURES

The primary outcome was change in urine LAM results during anti-TB therapy. The secondary outcome was all-cause mortality.

RESULTS

Among 90 participants, 57 (63%) had culture-confirmed pulmonary TB. Among the 88 participants tested, 82 (93%) were HIV-infected with median CD4 168/mm(3) (IQR 89-256/mm(3)). During anti-TB therapy, the percentage of LAM-positive participants decreased from baseline to 2 months (32% to 16%), and from baseline to 6-months (32% to 10%) (p values <0.005). In multivariate longitudinal analyses, urine LAM positivity and grade decreased among those with culture-confirmed pulmonary TB (p<0.0001), and had no change in sputum culture-negative participants. At the 2-month visit, participants with positive laboratory-based LAM or rapid LAM with ≥2+ grade had a significantly greater risk of mortality. In analyses adjusted for age, sex, baseline Karnofsky score and HIV status, participants with a rapid LAM ≥2+ grade after 2 months of anti-TB therapy had a 5.6-fold (95% CI 1.2 to 25.2) greater risk of mortality.

CONCLUSIONS

Rapid urine LAM testing may be a valuable tool to monitor anti-TB therapy response and to assess prognosis of patients being treated for pulmonary TB in HIV-endemic regions.

Pathogen-derived biomarkers for active tuberculosis diagnosis

Tuberculosis (TB) is an infectious disease caused by members of Mycobacterium tuberculosis complex. Despite the availability of effective treatments, TB remains a major public health concern in most low and middle-income countries, representing worldwide the second leading cause of death from an infectious disease. Inadequate case detection and failures to classify the disease status hamper proper TB control. The limitations of the conventional diagnostic methods have encouraged much research activities in this field, but there is still an urgent need for an accurate point of care test for active TB diagnosis. A rapid, precise, and inexpensive TB diagnostic test would allow an earlier implementation of an appropriate treatment and the reduction of disease transmission. Pathogen-derived molecules present in clinical specimens of affected patients are being validated for that purpose. This short review aims to summarize the available data regarding biomarkers derived from M. tuberculosis, and their current usage in active TB diagnosis.

Novel human recombinant antibodies against Mycobacterium tuberculosis antigen 85B

Background

Tuberculosis is the leading cause of death due to bacterial infections worldwide, mainly caused by Mycobacterium tuberculosis. The antigen 85 complex comprises a set of major secreted proteins of M. tuberculosis, which are potential biomarkers for diagnostic.

Results

In this work, the first human single chain fragment variable (scFv) antibodies specific for the tuberculosis biomarker 85 B were selected by phage display from naïve antibody gene libraries (HAL7/8). Produced as scFv-Fc in mammalian cells, these antibodies were further characterized and analysed for specificity and applicability in different tuberculosis antigen detection assays. Sandwich detection of recombinant 85 B was successful in enzyme linked immunosorbent assay (ELISA), lateral flow immunoassay and immunoblot. Whereas detection of M. tuberculosis cell extracts and culture filtrates was only possible in direct ELISA and immunoblot assays. It was found that the conformation of 85 B, depending on sample treatment, influenced antigen detection.

Conclusions

Recombinant antibodies, selected by phage display, may be applicable for 85 B detection in various assays. These antibodies are candidates for the development of future point of care tuberculosis diagnostic kits. Using 85 B as a biomarker, the antigen conformation influenced by sample treatment is important.

Immunologic evaluation and validation of methods using synthetic peptides derived from Mycobacterium tuberculosis for the diagnosis of tuberculosis infection

The goal of this study was to demonstrate the usefulness of an enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of pulmonary tuberculosis (PTB) and extrapulmonary TB (EPTB). This assay used 20 amino acid-long, non-overlapped synthetic peptides that spanned the complete Mycobacterium tuberculosis ESAT-6 and Ag85A sequences. The validation cohort consisted of 1,102 individuals who were grouped into the following five diagnostic groups: 455 patients with PTB, 60 patients with EPTB, 40 individuals with non-EPTB, 33 individuals with leprosy and 514 healthy controls. For the PTB group, two ESAT-6 peptides (12033 and 12034) had the highest sensitivity levels of 96.9% and 96.2%, respectively, and an Ag85A-peptide (29878) was the most specific (97.4%) in the PTB groups. For the EPTB group, two Ag85A peptides (11005 and 11006) were observed to have a sensitivity of 98.3% and an Ag85A-peptide (29878) was also the most specific (96.4%). When combinations of peptides were used, such as 12033 and 12034 or 11005 and 11006, 99.5% and 100% sensitivities in the PTB and EPTB groups were observed, respectively. In conclusion, for a cohort that consists entirely of individuals from Venezuela, a multi-antigen immunoassay using highly sensitive ESAT-6 and Ag85A peptides alone and in combination could be used to more rapidly diagnose PTB and EPTB infection.

Laboratory investigations on the diagnosis of tuberculosis in the malnourished tribal population of melghat, India

BACKGROUND

Malnutrition is a major risk factor for the development of tuberculosis (TB). In India, Melghat is among the tribal regions which consist of highest number of malnutrition cases. Because of the paucity of TB data from these malnourished areas there is an urgent need for the development and evaluation of improved TB diagnostic tests. In the present study, three in house developed diagnostic tests namely TB-Ag(antigen) ELISA, Adenosine deaminase (ADA) estimation and IS6110 polymerase chain reaction (PCR) assay were investigated for the detection of Mycobacterium tuberculosis (M. tb.) infection.

METHODS

For investigation, blood samples were collected from 128 study subjects from six villages of Melghat tribal area and evaluated using three in house developed assays, namely TB-Ag ELISA, ADA estimation and IS6110 PCR.

RESULTS

The TB-Ag ELISA method yielded 83% sensitivity and 94% specificity. The ADA and PCR assay gave a sensitivity of 61% and 49% and specificity of 62% and 98% respectively. A considerable good agreement of 82.81% (k=0.472) between TB-Ag ELISA and PCR was observed. The overall sensitivity of TB-Ag ELISA was significantly higher (p<0.05) than the ADA and PCR while PCR yielded highest specificity among all the three evaluated tests.

CONCLUSIONS

We concluded that the routine use of TB-Ag ELISA can be useful for screening of suspected TB patients in the malnourished population where sophisticated laboratory set up is difficult.

Diagnostic markers for tuberculosis ascites: a preliminary study

Objective:

The diagnosis of tuberculosis (TB) ascites is problematic. Delay in the diagnosis and treatment of TB ascites are considered to be major factors that contribute to the high mortality of TB. This study identifies specific protein markers in ascitic fluid which will be useful in diagnosis of TB ascites.

Methods:

We used Two-Dimensional Electrophoresis, liquid chromatography-mass spectrometry/mass spectrometry, immunoblot analysis and Enzyme Linked Immunosorbent assay (ELISA) as a comprehensive quantitative proteomic screening system for the diagnosis of TB ascites.

Results:

The screen identified several antigens of interest: a 30-kilodalton (kDa) protein that demonstrated significant homology to the antigen 85B and 85C (Ag 85) complex; a 65-kDa protein that corresponded to Mycobacterium tuberculosis (MTB) heat shock protein 65 (65-kDa HSP), Rv0440; a 14-kDa protein and 71-kDa protein that exhibits an amino acid sequence identical to that of MTB heat shock protein 14 (14-kDa HSP), GroES; and MTB heat shock protein 71 (71-kDa HSP), Rv0350 respectively. ELISA confirmed that TB ascites patients were consistently positive for these antigens at higher rates than non-TB ascites patients.

Conclusion:

The 65-kDa HSP, 71-kDa HSP, 14-kDa HSP and Ag 85 complex proteins may serve as very useful diagnostic markers for TB ascites.

Biomarkers and diagnostics for tuberculosis: progress, needs, and translation into practice

Human infection with Mycobacterium tuberculosis can progress to active disease, be contained as latent infection, or be eradicated by the host response. Tuberculosis diagnostics classify a patient into one of these categories. These are not fixed distinct states, but rather are continua along which patients can move, and are affected by HIV infection, immunosuppressive therapies, antituberculosis treatments, and other poorly understood factors. Tuberculosis biomarkers-host or pathogen-specific-provide prognostic information, either for individual patients or study cohorts, about these outcomes. Tuberculosis case detection remains difficult, partly because of inaccurate diagnostic methods. Investments have yielded some progress in development of new diagnostics, although the existing pipeline is limited for tests for sputum-smear-negative cases, childhood tuberculosis, and accurate prediction of reactivation of latent tuberculosis. Despite new, sensitive, automated molecular platforms for detection of tuberculosis and drug resistance, a simple, inexpensive point-of-care test is still not available. The effect of any new tests will depend on the method and extent of their introduction, the strength of the laboratories, and the degree to which access to appropriate therapy follows access to diagnosis. Translation of scientific progress in biomarkers and diagnostics into clinical and public health programmes is possible-with political commitment, increased funding, and engagement of all stakeholders.

Confronting the scientific obstacles to global control of tuberculosis

Tuberculosis (TB) is a major threat to global health, recently exacerbated by the emergence of highly drug-resistant forms of the disease-causing pathogen and synergy with HIV/AIDS. In 2006, the Stop TB Partnership published "The global plan to stop TB: 2006--2015," which set out a vision of halving the prevalence of and mortality caused by the disease by 2015, followed by eliminating the disease as a public health problem by 2050. This vision depends on the development of improved diagnostics, simpler treatment, and more effective vaccination. Recently, active translational research pipelines directed toward each of these goals have been established, but improved understanding of the fundamental biology of this complex disease will prove to be the key to radical advances in TB control.

Immune parameters as markers of tuberculosis extent of disease and early prediction of anti-tuberculosis chemotherapy response

This study investigates how the extent of pre-treatment radiological disease and early anti-tuberculous treatment response affect levels of selected circulating host immune markers. Twenty HIV-uninfected tuberculosis patients with BACTEC culture positivity for Mycobacterium tuberculosis at diagnosis and treated with directly observed short course anti-tuberculosis chemotherapy and 13 healthy community controls were enrolled. Serum samples were collected throughout treatment. After the intensive phase of treatment, 12 patients remained sputum culture-positive (slow responders) and eight patients were culture negative (fast responders). C-reactive protein (CRP), soluble intercellular adhesion molecule-1 (sICAM-1), soluble urokinase plasminogen activator receptor (suPAR), soluble lymphocyte activation gene-3 (sLAG-3), granzyme B, soluble tumour necrosis factor receptor one and two (sTNFR I and sTNFR II) and soluble death receptor 5 (sDR5) concentrations were measured. High levels of CRP at diagnosis were found to be associated (p</=0.05) with the presence of multiple cavities on chest x-rays and high levels of suPAR and sICAM-1 at diagnosis were associated (p</=0.05) with the extent of alveolar disease. Also significant were the associations between the level of granzyme B (p</=0.01) and LAG-3 (p</=0.05) at diagnosis, and the size of the cavities. The combination of diagnosis and week one measurements of selected serological markers in mathematical models was able to identify the fast responders with up to 87.5% accuracy and the slow responders with up to 83.3% accuracy These preliminary results suggest that predictive models for differential early treatment responses using combinations of host markers hold promise.

Facing the crisis: improving the diagnosis of tuberculosis in the HIV era

Although the human immunodeficiency virus (HIV) infection pandemic has had a catastrophic impact on tuberculosis (TB) control efforts, especially in sub-Saharan Africa, most of the fundamental concepts reflected in the directly observed treatment, short course (DOTS) strategy still hold true in the HIV era. What has changed, and dramatically, is the importance of speedy and accurate TB diagnosis and the difficulty of achieving this. The disproportionate amount of smear-negative disease in sub-Saharan Africa, which shoulders two-thirds of the global burden of HIV infection and acquired immunodeficiency syndrome, has greatly complicated TB case detection and disease control. Now, 15 years after TB rates began to soar in countries where HIV infection is prevalent, we have learned that the conventional approach -- passively waiting for patients with advanced symptomatic disease to make their way to microscopy centers for diagnosis -- has disastrous consequences. Without better diagnostic tools for TB and effective strategies for their implementation, transmission will not be interrupted, mortality will not be checked, and TB will not be controlled in areas where HIV infection is prevalent. Fortunately, a number of technical opportunities exist for the creation of improved diagnostic tests. Developing and exploiting such tests to support TB control in HIV-infected populations is an urgent priority. A substantial public sector effort is under way to work in partnership with the biotechnology industry to accelerate progress toward that goal. In this article, we will define the need for better TB tests and describe technologies being developed to meet that need.

Diagnosis of tuberculosis in an Indian population by an indirect ELISA protocol based on detection of Antigen 85 complex: a prospective cohort study

BACKGROUND

Diagnosis of tuberculosis (TB) remains problematic despite many new advanced diagnostic methods. A reliable and rapid diagnostic test, which could be performed in any standard pathology laboratory, would help to obtain definitive early diagnoses of TB. In the present study we describe a prospective evaluation for demonstrating Antigen (Ag) 85 complex in the sera from TB patients.

METHODS

Indirect ELISA, employing monoclonal antibodies (mAb) against the purified Ag 85 complex, was used to demonstrate Ag 85 complex in sera from TB patients. Serum samples were obtained from 197 different groups of patients: confirmed TB {n = 24}, clinically diagnosed TB {n = 104}, disease controls {n = 49} and healthy controls {n = 20}. Receiver operating curve (ROC) was used to calculate the cut off value and comparison between TB and non-TB groups were done by the chi-square test.

RESULTS

The indirect ELISA method, using an mAb against Ag 85 complex, yielded 82% sensitivity (95% confidence interval [CI] 67 to 93%) and 86% specificity (95% CI, 57 to 98%) for the diagnosis of TB. The serum positivities for Ag 85 complex in cases of confirmed and clinically diagnosed TB patients were 96% (23/24) and 79% (82/104) respectively, while the positivity for patients in the non-tuberculosis group was 14% (10/69).

CONCLUSION

The detection of Ag 85 complex in sera from TB patients by indirect ELISA using mAb against purified Ag 85 complex gives a reliable diagnosis and can be used to develop an immunodiagnostic assay with increased sensitivity and specificity.

Biomarkers of treatment response in clinical trials of novel antituberculosis agents

Global initiatives have been launched to develop improved tuberculosis chemotherapy. New drugs and potential treatment-shortening regimens require careful assessment in clinical trials, but existing markers of treatment outcome-clinical cure and relapse-require prolonged follow-up of patients. There is, therefore, a need to find alternative biomarkers or surrogate endpoints predictive of response. Effective treatment requires drugs with sterilising activity to produce clinical cure without relapse, and thus a useful biomarker for a drug under trial must predict the likelihood of relapse. We explore the strengths and weaknesses of existing biomarkers, which assess either host response or mycobacterial load. Change in mycobacterial burden is likely to be the best indicator of treatment outcome, but the optimum study techniques remain undefined. Finally, we propose methods to assess candidate markers, and how these candidate markers could be implemented in future clinical trials.

The prognosis of latent tuberculosis: can disease be predicted?

In humans, Mycobacterium tuberculosis persists for long periods in a clinically latent state, creating a huge reservoir of 'silent' tuberculosis (TB) (roughly one-third of the global population) from which new cases continually arise. A prognostic marker for active TB would enable targeted treatment of the small fraction of infected individuals who are most at risk of developing contagious TB, contributing greatly to TB control efforts. Here, we propose that TB-specific interferon-gamma release assays might be useful for identifying individuals with progressive infections who are likely to develop the disease. This might provide an unprecedented advantage for TB control, namely targeted preventive therapy for individuals who are most at risk of developing active contagious TB.

Allicin-induced suppression of Mycobacterium tuberculosis 85B mRNA in human monocytes

Despite of encountering a robust immune response, Mycobacterium tuberculosis (MTB) successfully survives and persists in the human host. We investigated the early regulation of MTB 85B gene by allicin in MTB-infected human monocytes. During the first 24h of infection, levels of both MTB 85B intracellular mRNA and secreted protein were significantly down-regulated by allicin in a dose-dependent manner, which was mediated by inhibition of glutathione and NF-kappaB pathway. Allicin-induced MTB 85B suppression correlated with suppression of TNF-alpha released from infected monocytes. The allicin-induced up-regulation of glutathione and IFN-gamma with simultaneous decrease in TNF-alpha supports the anti-inflammatory property of allicin by elicitation of protective immune response. Thus, allicin may prove to be valuable in the containment of MTB and therefore be useful as an adjunct in treatment of tuberculosis.

Survival and replication of clinical Mycobacterium tuberculosis isolates in the context of human innate immunity

The initial host response to Mycobacterium tuberculosis is driven by innate immunity. For this study, we examined the ability of 18 recent clinical isolates and 5 reference strains to survive and replicate in the context of host innate immunity by using whole blood culture. Six healthy tuberculin-negative volunteers served as subjects. H(37)Ra showed the least capacity to replicate of any of the strains tested, decreasing in viability 1.3 log CFU during 72 h of whole blood culture, whereas H(37)Rv increased 0.32 log. Clinical isolates varied greatly in their ability to replicate in blood cells, ranging from -0.4 to +0.8 log (P < 0.001). Four showed significantly more growth than H(37)Rv, and one showed significantly reduced growth. Host mechanisms for restricting intracellular mycobacterial growth were more effective during the first 24 h of whole blood culture than during the 24- to 72-h period. Certain mycobacterial isolates appeared preferentially able to withstand host defenses during each of these intervals. Although there was relatively more homogeneity among subjects than among strains, one of the six subjects showed a reduced capacity to restrict intracellular mycobacterial growth due to a defect expressed during the first 24 h of culture. Our findings indicate substantial variability in the capacity of clinical tuberculosis isolates to replicate in host cells in the face of innate host immunity.

Demonstration of components of antigen 85 complex in cerebrospinal fluid of tuberculous meningitis patients

Tuberculous meningitis (TBM) is the most common form of chronic infection of the central nervous system. Despite the magnitude of the problem, the general diagnostic outlook is discouraging. Specifically, there is no generally accepted early confirmative diagnosis protocol available for TBM. Various Mycobacterium tuberculosis antigens are now recognized as potential markers for diagnosis of TBM. However, their presence remains questionable, and many of these antigens are reported in the blood but not in the cerebrospinal fluid (CSF). This study identifies a specific protein marker in CSF which will be useful in early diagnosis of TBM. We have demonstrated the presence of a 30-kDa protein band in CSF of 100% (n = 5) of confirmed and 90% (n = 138) of suspected TBM patients out of 153 TBM patients. The 30-kDa band was excised from the gel, destained extensively, and digested with trypsin. The resulting peptides were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Partially purified proteins from CSF samples of TBM were analyzed by two-dimensional polyacrylamide gel electrophoresis and Western blotting. Immunoblotting and enzyme-linked immunosorbent assay (ELISA) were performed to confirm the presence of proteins in the 30-kDa protein band. The antigen 85 (Ag 85) complex was detected in CSF of TBM patients by indirect ELISA using antibodies against Ag 85 complex. The results of this study showed the 30-kDa protein band contained MTB proteins Rv3804c (Ag85A) and Rv1886c (Ag 85B), both members of the Ag85 complex. This was also confirmed by using immunotechniques such as indirect ELISA and the dot immunobinding assay. Detection of Ag85 complex was observed in CSF of 89% (71 out of 80) of suspected TBM patients that were 30-kDa protein positive. The observed 30-kDa protein in the CSF is comprised of the MTB Ag85 complex. This protein was earlier reported to be present in the blood of patients with extra-central nervous system tuberculosis. Therefore, this finding suggests that this protein can be used as a molecular marker for any type of tuberculous infection. It also provides a more sensitive immunoassay option for the early and confirmatory diagnosis of TBM.

Protein expression by a Beijing strain differs from that of another clinical isolate and Mycobacterium tuberculosis H37Rv

The Beijing strain family has often been associated with tuberculosis (TB) outbreaks and drug resistance worldwide. In this study the authors have compared the protein expression and antigen recognition profiles of a local Beijing strain with a less prevalent clinical isolate belonging to the family 23 strain lineage, and the laboratory strain Mycobacterium tuberculosis H37Rv. Using two-dimensional electrophoresis, liquid chromatography tandem mass spectrometry and Western blot analysis several proteins were identified as quantitatively increased or decreased in both clinical strains compared to H37Rv. Remarkably, the Beijing strain showed increased expression of alpha-crystallin and decreased expression of Hsp65, PstS1, and the 47 kDa protein compared to the other clinical strain and H37Rv. One- and two-dimensional Western blot analysis of antigens expressed by the three strains, using plasma from TB patients, confirmed differential antigen expression by strains and patient-to-patient variation in humoral immunity. These observed protein differences could aid the elucidation of mechanisms underlying the success of the Beijing strain family, measured by global dissemination, compared to other M. tuberculosis strains.

Early bactericidal activity of antituberculosis agents

The early bactericidal activity (EBA) of an antituberculosis agent is arbitrarily defined as the fall in log(10) colony forming units (cfu) of Mycobacterium tuberculosis per ml sputum per day during the first 2 days of treatment. Determining the EBA is an important preliminary step in the clinical evaluation of an antituberculosis agent. We review the results of eight published studies of the EBA of different antituberculosis agents, the impact of these results on our understanding of the actions of the respective agents, the clinical characteristics and sputum findings of patients included in these studies, and explore sources of variation in the EBA results. Patients in these studies had a mean age of 31-36 years, a mean weight of 50-57 kg, 67% were male and 56% had lung involvement covering an area of more than one lung, and 90% had multicavitary disease. None of these findings were related to EBA in any study. The mean log(10) cfu per ml sputum in the first specimen was 6.474. This was related to radiological extent of disease and cavity size in one study (p < 0.001) and, in the case of isoniazid to EBA with a rise in EBA of 0.094 (95% CL 0.029-0.158) for each tenfold rise in cfu counts/ml sputum. The overall variation in EBA in these studies was 0.0303, that due to laboratory processing of specimens was 0.0011, and due to patient characteristics and sputum sampling 0.0212. The EBA is a reproducible investigation that has contributed significantly to our knowledge of the actions and characteristics of both established and new antituberculosis agents. The greatest source of variation in EBA results appears to be that due to interpatient variation in disease characteristics and sputum sampling.

A study of the safety, immunology, virology, and microbiology of adjunctive etanercept in HIV-1-associated tuberculosis

OBJECTIVE

Tumor necrosis factor (TNF), an important inflammatory mediator in tuberculosis, has been implicated in causing accelerated HIV disease progression in HIV-associated tuberculosis. However, TNF blockade, particularly by monoclonal antibody, has been associated with the reactivation of latent Mycobacterium tuberculosis infection by the impairment of mycobacterial immunity. This phase 1 study examined the safety, microbiology, immunology, and virology of TNF blockade using etanercept (soluble TNF receptor, Enbrel) during the initial treatment of HIV-associated tuberculosis.

DESIGN

A single-arm trial, with key endpoints compared with historical controls, conducted in Mulago Hospital, Kampala, Uganda.

SUBJECTS

: Sixteen HIV-1-infected patients and 42 CD4-frequency-matched controls with sputum smear-positive tuberculosis and CD4 cell counts > 200 cells/microl.

INTERVENTION

Etanercept 25 mg, eight doses administered subcutaneously twice weekly beginning on day 4 of tuberculosis therapy.

MAIN OUTCOME MEASURES

Serial examination, radiography, sputum culture, CD4 T-cell counts, plasma log10 HIV-RNA copy numbers.

RESULTS

Trends towards superior responses to tuberculosis treatment were evident in etanercept-treated subjects in body mass, performance score, number of involved lung zones, cavitary closure, and time to sputum culture conversion. Etanercept treatment resulted in a 25% increase in CD4 cells by week 4 (P = 0.1 compared with controls). The change in CD4 cell count was inversely related to the change in serum neopterin, a marker of macrophage activation. There was no effect on plasma HIV RNA.

CONCLUSION

Etanercept can be safely administered during the initial treatment of pulmonary tuberculosis. Further studies are warranted to examine the effects of etanercept on T-cell numbers, activation and apoptosis in AIDS and tuberculosis.

Safety and bactericidal activity of rifalazil in patients with pulmonary tuberculosis

Rifalazil, also known as KRM-1648 or benzoxazinorifamycin, is a new semisynthetic rifamycin with a long half-life of approximately 60 h. Rifalazil has potent bactericidal activity against Mycobacterium tuberculosis in vitro and in animal models of tuberculosis (TB). Prior studies in healthy volunteers showed that once-weekly doses of 25 to 50 mg of rifalazil were well tolerated. In this randomized, open-label, active-controlled phase II clinical trial, 65 subjects with sputum smear-positive pulmonary TB received one of the following regimens for the first 2 weeks of therapy: 16 subjects received isoniazid (INH) (5 mg/kg of body weight) daily; 16 received INH (5 mg/kg) and rifampin (10 mg/kg) daily; 17 received INH (5 mg/kg) daily plus 10 mg of rifalazil once weekly; and 16 received INH (5 mg/kg) daily and 25 mg of rifalazil once weekly. All subjects were then put on 6 months of standard TB therapy. Pretreatment and day 15 sputum CFU of M. tuberculosis were measured to assess the bactericidal activity of each regimen. The number of drug-related adverse experiences was low and not significantly different among treatment arms. A transient decrease in absolute neutrophil count to less than 2,000 cells/mm(3) was detected in 10 to 20% of patients in the rifalazil- and rifampin-containing treatment arms without clinical consequences. Decreases in CFU counts were comparable among the four treatment arms; however, the CFU results were statistically inconclusive due to the variability in the control arms. Acquired drug resistance did not occur in any patient. Studies focused on determining a maximum tolerated dose will help elucidate the full anti-TB effect of rifalazil.

Combinatorial use of antibodies to secreted mycobacterial proteins in a host immune system-independent test for tuberculosis

Laboratory diagnosis of tuberculosis is often difficult. Immunodetection of circulating Mycobacterium tuberculosis proteins shed during active infection would not depend on an intact host immune response and could take advantage of the speed and low costs afforded by antibody-based assays. We previously showed that patients with active tuberculosis had increased levels of circulating antigen 85 (Ag85) proteins independent of their tuberculin skin test status (S. I. Bentley-Hibbert, X. Quan, T. Newman, K. Huygen, and H. P. Godfrey, Infect. Immun. 67:581-588, 1999). To extend these observations to a Mycobacterium bovis BCG-vaccinated population and to another secreted mycobacterial protein, Ag85 and PstS-1 (protein antigen B, p38 antigen) were quantified in sera from 97 Chilean tuberculosis patients and healthy controls (many of whom had received BCG as children) using dot immunobinding, mouse monoclonal anti-BCG Ag85 complex antibody, and chicken antipeptide antibodies reactive with M. tuberculosis Ag85B and PstS-1. The latter antibodies had been raised to peptide-derived immunogens expressed on a novel proprietary protein carrier in Escherichia coli. Median serum Ag85 levels measured by using either anti-Ag85 antibody were significantly higher in patients with active tuberculosis than in healthy controls (P, <0.001 to 0.01); the median serum PstS-1 levels were similar in patients and controls. The sensitivity of significantly elevated circulating Ag85 levels in patients with pulmonary tuberculosis measured by anti-Ag85 complex or anti-Ag85B antibodies was 60 and 55%, respectively, but increased to 77% when results obtained with both anti-Ag85 antibodies were considered jointly (P < 0.02). The corresponding specificities for individual and joint consideration were 95, 85, and 80%, respectively. These results indicate that elevated Ag85 levels can be detected in patients with active tuberculosis even after BCG vaccination and suggest that combinatorial use of antibodies directed at different epitopes of this protein could provide a viable strategy for developing new host immune response-independent diagnostic tests for tuberculosis.

Adult tuberculosis in the 21st century: pathogenesis, clinical features, and management

This article reviews the significant advances in the past year in the basic and clinical aspects of adult tuberculosis (TB). Further research has deepened our understanding of host susceptibility and resistance mechanisms, including cytotoxicity, apoptosis, and antimicrobial polypeptides such as granulysin. Studies have confirmed the effects of HIV infection on risk of disease and disease manifestations, and have defined the effects of HIV on TB transmission. Recent studies also indicate a possible role for extended treatment of active disease and latent infection in HIV-1 infected individuals. Multidrug-resistant disease has been reported on every continent; rapid molecular approaches to the simultaneous diagnosis of TB and detection of rifampin resistance may facilitate prompt initiation of treatment. TB remains one of the major problems in global health.

Inhibition of isoniazid-induced expression of Mycobacterium tuberculosis antigen 85 in sputum: potential surrogate marker in tuberculosis chemotherapy trials

Mycobacterium tuberculosis antigen 85 is induced in vitro by isoniazid (INH); its sustained induction in sputum during tuberculosis (TB) therapy predicts relapse. In this trial, rifampin or rifalazil inhibited the induction of sputum antigen 85 by INH in a dose-dependent fashion. This approach may facilitate the evaluation of new TB drugs.

Kinetics of circulating antibodies, immune complex and specific antibody-secreting cells in tuberculosis patients during 6 months of antimicrobial therapy

OBJECTIVE

During the follow-up of a group of patients with active tuberculosis, the predictive potential of several antibody-based assays was evaluated in monitoring treatment efficacy.

DESIGN

Eleven patients with bacteriologically documented pulmonary tuberculosis and two patients with tuberculosis pleurisy were studied over a period of 6 months, from the day before treatment to its completion. The kinetics of the humoral response to Mycobacterium tuberculosis was determined by the number of specific circulating antibody secreting cells (ASC) (ELISPOT assay), as well as the titres of specific circulating antibody and specific antibody present in circulating immune complexes (quantitative ELISA).

RESULTS

Follow-up ELISPOT assays, performed after initiation of tuberculosis therapy showed a rapid increase of ASC, during the first week, followed by rapid 3-10 fold decline of ASC in 12 of 13 patients tested. This decline occurred more rapidly than the mycobacterial culture conversion. In contrast, follow-up of ELISA assays did not give relevant information in assessing the outcome of treatment.

CONCLUSION

In comparison with direct detection of tubercle bacilli in sputum samples, the rapid clearance of specific circulating ASC occurring early on after the onset of therapy could suggest a potential usefulness of ELISPOT in monitoring therapeutic response.

Predicting the outcome of therapy for pulmonary tuberculosis

Patients vary considerably in their response to treatment of pulmonary tuberculosis. Although several studies have indicated that adverse outcomes are more likely in those patients with delayed sputum sterilization, few tools are available to identify those patients prospectively. In this study, multivariate models were developed to predict the response to therapy in a prospectively recruited cohort of 42 HIV-uninfected subjects with drug-sensitive tuberculosis. The cohort included 2 subjects whose initial response was followed by drug-sensitive relapse. The total duration of culture positivity was best predicted by a model that included sputum M. tuberculosis antigen 85 concentration on Day 14 of therapy, days-to-positive in BACTEC on Day 30, and the baseline radiographic extent of disease (R = 0.63). A model in which quantitative AFB microscopy replaced BACTEC also performed adequately (R = 0.58). Both models predicted delayed clearance of bacilli in both relapses (> 85th percentile of all subjects) using information collected during the first month of therapy. Stratification of patients according to anticipated response to therapy may allow TB treatment to be individualized, potentially offering superior outcomes and greater efficiency in resource utilization, and aiding in the conduct of clinical trials.

Drug tolerance in Mycobacterium tuberculosis

Although Mycobacterium tuberculosis is eradicated rapidly during therapy in some patients with pulmonary tuberculosis, it can persist for many months in others. This study examined the relationship between mycobacterial drug tolerance (delayed killing in vitro), persistence, and relapse. It was performed with 39 fully drug-susceptible isolates from a prospective trial of standard short-course antituberculous therapy with sputum smear-positive, human immunodeficiency virus-uninfected subjects with pulmonary tuberculosis in Brazil and Uganda. The rate of killing in vitro was determined by monitoring the growth index (GI) in BACTEC 12B medium after addition of drug to established cultures and was measured as the number of days required for 99% sterilization. Drugs differed significantly in bactericidal activity, in the following order from greatest to least, rifampin > isoniazid-ethambutol > ethambutol (P < 0.001). Isolates from subjects who had relapses (n = 2) or in whom persistence was prolonged (n = 1) were significantly more tolerant of isoniazid-ethambutol and rifampin than isolates from other subjects (P < 0.01). More generally, the duration of persistence during therapy was predicted by strain tolerance to isoniazid and rifampin (P = 0.012 and 0.026, respectively). Tolerance to isoniazid-ethambutol and tolerance to rifampin were highly correlated (P < 0.001). Tolerant isolates did not differ from others with respect to the MIC of isoniazid; the rate of killing of a tolerant isolate by isoniazid-ethambutol was not increased at higher drug concentrations. These observations suggest that tolerance may not be due to drug-specific mechanisms. Tolerance was of the phenotypic type, although increased tolerance appeared to emerge after prolonged drug exposure in vivo. This study suggests that drug tolerance may be an important determinant of the outcome of therapy for tuberculosis.

Molecular techniques for the diagnosis of respiratory bacterial infection

DNA amplification techniques are now available for all of the major respiratory bacterial pathogens. The most important recent developments have been in the application of these techniques to routine clinical practice. A major problem for rapid techniques is the need to provide susceptibility results. Effective susceptibility techniques have now been described for Streptococcus pneumoniae and Mycobacterium tuberculosis. It has also been possible to use amplification techniques to monitor the response to antituberculosis chemotherapy by monitoring mRNA in sputum samples. The added sensitivity the amplification-based techniques give over conventional culture techniques is valuable not only in enhancing diagnosis, which allows the use of less invasive specimens, but also in opening new investigative areas in the pathogenesis of respiratory conditions.

Pulmonary tuberculosis

Pulmonary tuberculosis is a major cause of morbidity and mortality worldwide, resulting in the greatest number of deaths due to any one single infectious agent. This trend is due, at least in part, to increasing numbers of individuals co-infected with HIV and Mycobacterium tuberculosis (MTB). Concerted efforts between the World Health Organization and other agencies, therefore, are underway to improve tuberculosis control worldwide. These include basic research in tuberculosis diagnostics and vaccine development, institution of preventive therapy in individuals dually infected with HIV and MTB, and directly observed short-course antituberculous therapy in developing countries with a high prevalence of MTB infection. Further, newer, longer-acting antituberculous therapeutic agents such as rifapentine, which allow twice-weekly dosing in the continuation phase of anti-MTB therapy, have recently been released and are undergoing clinical trials. This review provides a synopsis of recent developments in these areas and serves as a reference source for interested readers.