Biomarkers for clinical and incipient tuberculosis: performance in a TB-endemic country

Antigen specificity shapes antibody functions in tuberculosis

Tuberculosis (TB) is the number one infectious disease cause of death worldwide due to an incomplete understanding of immunity. Emerging data highlight antibody functions mediated by the Fc domain as immune correlates. However, the mechanisms by which antibody functions impact the causative agent Mycobacterium tuberculosis (Mtb) are unclear. Here, we examine how antigen specificity determined by the Fab domain shapes Fc effector functions against Mtb. Using the critical structural and secreted virulence proteins Mtb cell wall and ESAT-6 & CFP-10, we observe that antigen specificity alters subclass, antibody post-translational glycosylation, and Fc effector functions in TB patients. Moreover, Mtb cell wall IgG3 enhances disease through opsonophagocytosis of extracellular Mtb . In contrast, polyclonal and a human monoclonal IgG1 we generated targeting ESAT-6 & CFP-10 inhibit intracellular Mtb . These data show that antibodies have multiple roles in TB and antigen specificity is a critical determinant of the protective and pathogenic capacity.

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.

Composition and Clinical Significance of Exosomes in Tuberculosis: A Systematic Literature Review

Tuberculosis (TB) remains a major health issue worldwide. In order to contain TB infections, improved vaccines as well as accurate and reliable diagnostic tools are desirable. Exosomes are employed for the diagnosis of various diseases. At present, research on exosomes in TB is still at the preliminary stage. Recent studies have described isolation and characterization of Mycobacterium tuberculosis (Mtb) derived exosomes in vivo and in vitro. Mtb-derived exosomes (Mtbexo) may be critical for TB pathogenesis by delivering mycobacterial-derived components to the recipient cells. Proteomic and transcriptomic analysis of Mtbexo have revealed a variety of proteins and miRNA, which are utilized by the TB bacteria for pathogenesis. Exosomes has been isolated in body fluids, are amenable for fast detection, and could contribute as diagnostic or prognostic biomarker to disease control. Extraction of exosomes from biological fluids is essential for the exosome research and requires careful standardization for TB. In this review, we summarized the different studies on Mtbexo molecules, including protein and miRNA and the method used to detect exosomes in biological fluids and cell culture supernatants. Thus, the detection of Mtbexo molecules in biological fluids may have a potential to expedite the diagnosis of TB infection. Moreover, the analysis of Mtbexo may generate new aspects in vaccine development.

Exosomes in tuberculosis: Still terra incognita?

Today, diagnosis, vaccination, and treatment of tuberculosis (TB) remain major clinical challenges. Therefore, an introduction of new diagnostic measures and biomarkers is necessary to improve infection control. The ideal biomarker for TB infection can be defined as a host or pathogen-derived biomolecule, which is potent for identifying infection and determining its clinical stage. Exosomes, defined as cell-derived nanovesicles released into biological fluids, are involved in cell-cell communication and immune modulation. These vesicles have emerged as a new platform for improving the clinical diagnosis and prognosis of different infectious diseases and cancers. The role of these nanovehicles, as alternative biomarkers for the improvement of TB diagnosis and treatment, has been demonstrated in a significant body of literature. In this review, we summarized recent progress in the clinical application of exosome-based biomarkers in TB infection.

Incipient and Subclinical Tuberculosis: a Clinical Review of Early Stages and Progression of Infection

Tuberculosis (TB) is the leading infectious cause of mortality worldwide, due in part to a limited understanding of its clinical pathogenic spectrum of infection and disease. Historically, scientific research, diagnostic testing, and drug treatment have focused on addressing one of two disease states: latent TB infection or active TB disease. Recent research has clearly demonstrated that human TB infection, from latent infection to active disease, exists within a continuous spectrum of metabolic bacterial activity and antagonistic immunological responses. This revised understanding leads us to propose two additional clinical states: incipient and subclinical TB. The recognition of incipient and subclinical TB, which helps divide latent and active TB along the clinical disease spectrum, provides opportunities for the development of diagnostic and therapeutic interventions to prevent progression to active TB disease and transmission of TB bacilli. In this report, we review the current understanding of the pathogenesis, immunology, clinical epidemiology, diagnosis, treatment, and prevention of both incipient and subclinical TB, two emerging clinical states of an ancient bacterium.

Elevated serum β2-microglobulin in individuals coinfected with hepatitis B and hepatitis D virus in a rural settings in Southwest Nigeria

OBJECTIVE

Coinfection of hepatitis B virus (HBV) with hepatitis D virus (HDV) has being reported to increase severity of progression to hepatocellular carcinoma (HCC) and liver cirrhosis (LC). Beta microglobulin (2βM) which is present on the surfaces of blood cells in acceptable levels is a tumor marker which may become elevated in disease conditions. This study hence observed the prevalence of HBV and HDV coinfection in a rural population and their 2βM concentration.

RESULTS

Of the 368 samples, 66 (17.9%) were positive to hepatitis B surface antigen (HBsAg) and 33 (50%) were coinfected with HDV, 8 (2.1%) were monoinfected with HDV. 2βM concentration increased beyond the normal level in individuals coinfected with HBV and HDV as compared with the monoinfected individuals. Coinfection resulted in the increased concentration of 2βM in HBV and HDV coinfection and the likelihood of progression to HCC and LC may not be ruled out. Monoinfection with HDV also had high 2βM concentration but this is due to having being infected with a non-detected HBV or chronic infection in which HBV is clearing.

Assessing humoral immune response of 4 recombinant antigens for serodiagnosis of tuberculosis

Serodiagnostic potential of four recombinant proteins (38 kDa[Rv0934], MPT64[Rv1980c], Adk[Rv0733], and BfrB[Rv3874]) was evaluated in Healthy control subjects (HCS), Healthy household contacts (HHC), Pulmonary tuberculosis patients (PTB), and Human immuno deficiency virus & Tuberculosis co-infected patients (HIV-TB). All the antigens tested individually for the detection of serum IgG by indirect ELISA. All the four antigens have a significantly higher antibody response in PTB compared to healthy controls (P < 0.05). The sensitivity of individual antigens ranged from 20% to 52.5% for the prefixed specificity of 95%. When results of all 4 antigens were combined the sensitivity was increased to 75% and specificity was reduced 89% in HCS. In smear- and culture-positive (S+C+) PTB, four antigen combination gives maximum sensitivity (89.6%) with 89% specificity. In smear negative culture negative (S-C+) PTB, three antigen combination (38 kDa with MPT64 and BfrB) gives maximum sensitivity (69.5%) and specificity (91.6%). In HIV-TB, 4 antigen combinations give the maximum sensitivity of 51.2% with 89% specificity. Combining serology (Four antigen combination) with smear was able to increase the sensitivity from 70% to 92.5% in culture positive PTB. So, we propose that this serology test can be used as adjunct test along with smear for rapid diagnosis of PTB.

Development of a POC test for TB based on multiple immunodominant epitopes of M. tuberculosis specific cell-wall proteins

The need for an accurate, rapid, simple and affordable point-of-care (POC) test for Tuberculosis (TB) that can be implemented in microscopy centers and other peripheral health-care settings in the TB-endemic countries remains unmet. This manuscript describes preliminary results of a new prototype rapid lateral flow TB test based on detection of antibodies to immunodominant epitopes (peptides) derived from carefully selected, highly immunogenic M. tuberculosis cell-wall proteins. Peptide selection was initially based on recognition by antibodies in sera from TB patients but not in PPD-/PPD+/BCG-vaccinated individuals from TB-endemic settings. The peptides were conjugated to BSA; the purified peptide-BSA conjugates striped onto nitrocellulose membrane and adsorbed onto colloidal gold particles to devise the prototype test, and evaluated for reactivity with sera from 3 PPD-, 29 PPD+, 15 PPD-unknown healthy subjects, 10 patients with non-TB lung disease and 124 smear-positive TB patients. The assay parameters were adjusted to determine positive/negative status within 15 minutes via visual or instrumented assessment. There was minimal or no reactivity of sera from non-TB subjects with the striped BSA-peptides demonstrating the lack of anti-peptide antibodies in subjects with latent TB and/or BCG vaccination. Sera from most TB patients demonstrated reactivity with one or more peptides. The sensitivity of antibody detection ranged from 28–85% with the 9 BSA-peptides. Three peptides were further evaluated with sera from 400 subjects, including additional PPD-/PPD+/PPD-unknown healthy contacts, close hospital contacts and household contacts of untreated TB patients, patients with non-TB lung disease, and HIV+TB- patients. Combination of the 3 peptides provided sensitivity and specificity>90%. While the final fully optimized lateral flow POC test for TB is under development, these preliminary results demonstrate that an antibody-detection based rapid POC lateral flow test based on select combinations of immunodominant M. tb-specific epitopes may potentially replace microscopy for TB diagnosis in TB-endemic settings.

Serological diagnostic assays for HIV-associated tuberculosis in sub-Saharan Africa?

In this issue of Clinical and Vaccine Immunology, Siev and colleagues present an evaluation of antibody responses to four immunodominant proteins of Mycobacterium tuberculosis in patients with HIV-associated pulmonary tuberculosis (TB) in South Africa (M. Siev, D. Wilson, S. Kainth, V. O. Kasprowicz, C. M. Feintuch, E. Jenny-Avital, and J. J. Achkar, 21:791-798, 2014, doi:http://dx.doi.org/10.1128/CVI.00805-13). This commentary discusses the enormous need for simple point-of-care assays for tuberculosis (TB) diagnosis in patients with and without HIV coinfection in high-burden settings and considers the potential role of serological assays and the huge challenges inherent in developing and validating such assays.

Antibodies against Mycobacterial proteins as biomarkers for HIV-associated smear-negative tuberculosis

Serology data are limited for patients with sputum smear-negative HIV-associated active tuberculosis (TB). We evaluated the serum antibody responses against the mycobacterial proteins MPT51, MS, and echA1 and the 38-kDa protein via enzyme-linked immunosorbent assay (ELISA) in South African (S.A.) HIV-positive (HIV(+)) smear-negative TB patients (n = 56), U.S. HIV(+) controls with a positive tuberculin skin test (TST(+); n = 21), and S.A. HIV-negative (HIV(-)) (n = 18) and HIV(+) (n = 24) controls. TB patients had positive antibody reactivity against MPT51 (73%), echA1 (59%), MS (36%), and the 38-kDa protein (11%). Little reactivity against MPT51 and echA1 was observed in control groups at low risk for TB, i.e., S.A. HIV(-) (0% and 6%, respectively), and at moderate risk for TB development, i.e., U.S. HIV(+) TST(+) controls (14% and 10%, respectively). By contrast, more reactivity was detected in the S.A. HIV(+) control group at higher risk for TB (25% and 45%, respectively). Our data hold promise that antibody detection against MPT51 and echA1 might have adjunctive value in the detection of HIV(+) smear-negative TB and might reflect increasing Mycobacterium tuberculosis infection activity in asymptomatic HIV(+) individuals.

Mycobacterium tuberculosis pili (MTP), a putative biomarker for a tuberculosis diagnostic test

Novel biomarkers are urgently needed for point of care TB diagnostics. In this study, we investigated the potential of the pilin subunit protein encoded by the mtp gene as a diagnostic biomarker. BLAST analysis of the mtp gene on published genome databases, and amplicon sequencing were performed in Mycobacterium tuberculosis Complex (MTBC) strains and other organisms. The protein secondary structure of the amino acid sequences of non-tuberculous Mycobacteria that partially aligned with the mtp sequence was analysed with PredictProtein software. The mtp gene and corresponding amino acid sequence of MTBC were 100% homologous with H37Rv, in contrast to the partial alignment of the non-tuberculous Mycobacteria. The mtp gene was present in all 91 clinical isolates of MTBC. Except for 2 strains with point mutations, the sequence was 100% conserved among the clinical strains. The mtp gene could not be amplified in all non-tuberculous Mycobacteria and respiratory organisms. The predicted MTP protein structure of Mycobacterium avium, Mycobacterium ulcerans and Mycobacterium abscessus differed significantly from that of the M. tuberculosis, which was similar to Mycobacterium marinum. The absence of the mtp gene in non-tuberculous Mycobacteria and other respiratory bacteria suggests that its encoded product, the pilin subunit protein of M. tuberculosis may be a suitable marker for a point of care TB test.

Detection of Mycobacterium tuberculosis GlcB or HspX Antigens or devR DNA impacts the rapid diagnosis of tuberculous meningitis in children

Background

Tuberculous meningitis (TBM) is the most common form of neurotuberculosis and the fifth most common form of extrapulmonary TB. Early diagnosis and prompt treatment are the cornerstones of effective disease management. The accurate diagnosis of TBM poses a challenge due to an extensive differential diagnosis, low bacterial load and paucity of cerebrospinal fluid (CSF) especially in children.

Methodology/Principal Findings

We describe the utility of ELISA and qPCR for the detection of Mycobacterium tuberculosis (M. tb) proteins (GlcB, HspX, MPT51, Ag85B and PstS1) and DNA for the rapid diagnosis of TBM. CSF filtrates (n = 532) derived from children were classified as ‘Definite’ TBM (M. tb culture positive, n = 29), ‘Probable and Possible’ TBM (n = 165) and ‘Not-TBM’ including other cases of meningitis or neurological disorders (n = 338). ROC curves were generated from ELISA and qPCR data of ‘Definite’ TBM and Non-Tuberculous infectious meningitis (NTIM) samples and cut-off values were derived to provide ≥95% specificity. devR qPCR, GlcB, HspX and PstS1 ELISAs showed 100% (88;100) sensitivity and 96–97% specificity in ‘Definite’ TBM samples. The application of these cut-offs to ‘Probable and Possible’ TBM groups yielded excellent sensitivity (98%, 94;99) and specificity (98%, 96;99) for qPCR and for GlcB, HspX and MPT51 antigen ELISAs (sensitivity 92–95% and specificity 93–96%). A test combination of qPCR with GlcB and HspX ELISAs accurately detected all TBM samples at a specificity of ∼90%. Logistic regression analysis indicated that these tests significantly added value to the currently used algorithms for TBM diagnosis.

Conclusions

The detection of M. tb GlcB/HspX antigens/devR DNA in CSF is likely to improve the utility of existing algorithms for TBM diagnosis and also hasten the speed of diagnosis.

Opportunities for improved serodiagnosis of human tuberculosis, bovine tuberculosis, and paratuberculosis

Mycobacterial infections—tuberculosis (TB), bovine tuberculosis (bTB), and Johne's disease (JD)—are major infectious diseases of both human and animals. Methods presently in use for diagnosis of mycobacterial infections include bacterial culture, nucleic acid amplification, tuberculin skin test, interferon-γ assay, and serology. Serological tests have several advantages over other methods, including short turn-around time, relatively simple procedures, and low cost. However, current serodiagnostic methods for TB, bTB and JD exhibit low sensitivity and/or specificity. Recent studies that have aimed to develop improved serodiagnostic tests have mostly focused on identifying useful species-specific protein antigens. A review of recent attempts to improve diagnostic test performance indicates that the use of multiple antigens can improve the accuracy of serodiagnosis of these mycobacterial diseases. Mycobacteria also produce a variety of species-specific nonprotein molecules; however, only a few such molecules (e.g., cord factor and lipoarabinomannan) have so far been evaluated for their effectiveness as diagnostic antigens. For TB and bTB, there has been recent progress in developing laboratory-free diagnostic methods. New technologies such as microfluidics and “Lab-on-Chip” are examples of promising new technologies that can underpin development of laboratory-free diagnostic devices for these mycobacterial infections.

Comparative evaluation of profiles of antibodies to mycobacterial capsular polysaccharides in tuberculosis patients and controls stratified by HIV status

Despite the complexity of tuberculosis (TB) serology, antibodies (Abs) remain attractive biomarkers for TB. Recent evidence of a mycobacterial capsule that consists mainly of the polysaccharides arabinomannan (AM) and glucan provides new options for serologic targets. For this study, Ab responses to AM and glucan for 47 U.S. TB patients (33 HIV negative [HIV(-)], 14 HIV positive [HIV(+)]), 42 healthy controls, and 38 asymptomatic HIV(+) controls were evaluated by enzyme-linked immunosorbent assays (ELISAs). The results were compared with Ab responses to the mycobacterial glycolipid cell wall antigen lipoarabinomannan (LAM) and to the proteins malate synthase (MS) and MPT51. We found that the main immunoglobulin (Ig) isotype response to polysaccharides was IgG, predominantly of subclass IgG2. IgG responses to AM were significantly higher for HIV(-) and HIV(+) TB cases than for controls (P, <0.0001 and <0.01, respectively); significantly higher for HIV(-) than for HIV(+) TB cases (P, <0.01); and significantly higher in sputum smear-positive than smear-negative patients in both HIV(-) and HIV(+) cases (P, 0.01 and 0.02, respectively). In both TB groups, titers of Ab to glucan were significantly lower than titers of Ab to AM (P, <0.0001). IgG responses to AM and MS or to AM and MPT51 did not correlate with each other in HIV(-) TB patients, while they correlated significantly in HIV(+) TB patients (P, 0.01 and 0.05, respectively). We conclude that Ab responses to AM could contribute to the serodiagnosis of TB, especially for HIV(-) TB patients. This study also provides new and important insights into the differences in the profiles of Abs to mycobacterial antigens between HIV(-) and HIV(+) TB patients.

Adjunctive tests for diagnosis of tuberculosis: serology, ELISPOT for site-specific lymphocytes, urinary lipoarabinomannan, string test, and fine needle aspiration

The diagnostic gold standard for active tuberculosis (TB) is the detection of Mycobacterium tuberculosis (MTB) by culture or molecular methods. However, despite its limited sensitivity, sputum smear microscopy is still the mainstay of TB diagnosis in resource-limited settings. Consequently, diagnosis of smear-negative pulmonary and extrapulmonary TB remains challenging in such settings. A number of novel or alternative techniques could provide adjunctive diagnostic use in the context of difficult-to-diagnose TB. These may be especially useful in certain patient groups such as persons infected with human immunodeficiency virus (HIV) and children, who are disproportionably affected by smear-negative and extrapulmonary disease and who are also most adversely affected by delays in TB diagnosis and treatment. We review a selection of these methods that are independent of nucleic acid amplification techniques and could largely be implemented in resource-limited settings in current or adapted versions. Specifically, we discuss the diagnostic use and potential of serologic tests based on detection of antibodies to MTB antigens; interferon gamma release assays using site-specific lymphocytes; detection of lipoarabinomannan, a glycolipid of MTB, in urine; the string test, a novel technique to retrieve lower respiratory tract samples; and fine needle aspiration biopsy of lymph nodes.

LipC (Rv0220) is an immunogenic cell surface esterase of Mycobacterium tuberculosis

We have reported previously the identification of novel proteins of Mycobacterium tuberculosis by the immunoscreening of an expression library of M. tuberculosis genomic DNA with sera obtained from M. tuberculosis-infected rabbits at 5 weeks postinfection. In this study, we report the further characterization of one of these antigens, LipC (Rv0220). LipC is annotated as a member of the Lip family based on the presence of the consensus motif "GXSXG" characteristic of esterases. Although predicted to be a cytoplasmic enzyme, we provide evidence that LipC is a cell surface protein that is present in both the cell wall and the capsule of M. tuberculosis. Consistent with this localization, LipC elicits strong humoral immune responses in both HIV-negative (HIV-) and HIV-positive (HIV+) tuberculosis (TB) patients. The absence of anti-LipC antibodies in sera from purified protein derivative-positive (PPD+) healthy subjects confirms its expression only during active M. tuberculosis infection. Epitope mapping of LipC identified 6 immunodominant epitopes, 5 of which map to the exposed surface of the modeled LipC protein. The recombinant LipC (rLipC) protein also elicits proinflammatory cytokine and chemokine responses from macrophages and pulmonary epithelial cells. rLipC can hydrolyze short-chain esters with the carbon chain containing 2 to 10 carbon atoms. Together, these studies demonstrate that LipC is a novel cell surface-associated esterase of M. tuberculosis that is highly immunogenic and elicits both antibodies and cytokines/chemokines.

Serodiagnosis of tuberculosis: due to shift track

Development of novel diagnostics for tuberculosis has so far been governed by the clinical requirement of improving the detection of patients with paucibacillary forms of the disease. For this aim, serological assays have been evaluated using several antigens, but were found insufficiently sensitive, because antibody production associates with the bacterial load of the disease. Consequently, detection of antibodies against a relatively small number of selected well-defined antigens has a much higher sensitivity for sputum smear-positive pulmonary disease in adult HIV-negative patients. They are the most active in generating and spreading aerosols containing live tubercle bacilli, but their detection is often delayed, thus perpetuating the transmission of the infection and disease in the population. High volume throughput serological screening of clinical suspects with mild clinical symptoms may help to achieve diagnosis earlier, than currently used procedures. Such expanded testing could be done more efficiently in laboratories, than at 'points-of-care' and at a lower cost than other tests. The feasibility of this approach towards reducing the delayed diagnosis of the most infectious cases of pulmonary tuberculosis needs to be ascertained in prospective diagnostic trials, in populations at a high risk. Reducing the transmission of tuberculosis is of key importance for achieving its continued decline and therefore it is proposed, that the aims of serological screening should shift from clinical to public health priorities.

Correlation between serum and plasma antibody titers to mycobacterial antigens

The ability to utilize serum or plasma samples interchangeably is useful for tuberculosis (TB) serology. We demonstrate a strong correlation between antibody titers to several mycobacterial antigens in serum versus plasma from HIV-infected and non-HIV-infected TB and non-TB patients (r = 0.99 to 0.89; P < 0.0001). Plasma and serum can be used interchangeably in the same antibody detection assays.

Changing concepts of "latent tuberculosis infection" in patients living with HIV infection

One third of the world's population is estimated to be infected with Mycobacterium tuberculosis, representing a huge reservoir of potential tuberculosis (TB) disease. Risk of progression to active TB is highest in those with HIV coinfection. However, the nature of the host-pathogen relationship in those with “latent TB infection” and how this is affected by HIV coinfection are poorly understood. The traditional paradigm that distinguishes latent infection from active TB as distinct compartmentalised states is overly simplistic. Instead the host-pathogen relationship in “latent TB infection” is likely to represent a spectrum of immune responses, mycobacterial metabolic activity, and bacillary numbers. We propose that the impact of HIV infection might better be conceptualised as a shift of the spectrum towards poor immune control, higher mycobacterial metabolic activity, and greater organism load, with subsequent increased risk of progression to active disease. Here we discuss the evidence for such a model and the implications for interventions to control the HIV-associated TB epidemic.

Antibodies against immunodominant antigens of Mycobacterium tuberculosis in subjects with suspected tuberculosis in the United States compared by HIV status

The immunodominance of Mycobacterium tuberculosis proteins malate synthase (MS) and MPT51 has been demonstrated in case-control studies with patients from countries in which tuberculosis (TB) is endemic. The value of these antigens for the serodiagnosis of TB now is evaluated in a cross-sectional study of pulmonary TB suspects in the United States diagnosed to have TB, HIV-associated TB, or other respiratory diseases (ORD). Serum antibody reactivity to recombinant purified MS and MPT51 was determined by enzyme-linked immunosorbent assays (ELISAs) of samples from TB suspects and well-characterized control groups. TB suspects were diagnosed with TB (n = 87; 49% sputum microscopy negative, 20% HIV(+)) or ORD (n = 63; 58% HIV(+)). Antibody reactivity to MS and MPT51 was significantly higher in U.S. HIV(+)/TB samples than in HIV(-)/TB samples (P < 0.001), and it was significantly higher in both TB groups than in control groups with latent TB infection (P < 0.001). Antibody reactivity to both antigens was higher in U.S. HIV(+)/TB samples than in HIV(+)/ORD samples (P = 0.052 for MS, P = 0.001 for MPT51) but not significantly different between HIV(-)/TB and HIV(-)/ORD. Among U.S. HIV(+) TB suspects, a positive anti-MPT51 antibody response was strongly and significantly associated with TB (odds ratio, 11.0; 95% confidence interval, 2.3 to 51.2; P = 0.002). These findings have implications for the adjunctive use of TB serodiagnosis with these antigens in HIV(+) subjects.

Utility of a combination of RD1 and RD2 antigens as a diagnostic marker for tuberculosis

We evaluated the diagnostic potential of a cocktail of 4 antigens encoded by regions of difference (RD) 1 and 2 of Mycobacterium tuberculosis, that is, early secretory antigenic target-6, culture filtrate protein-10 (CFP-10), CFP-21, and mycobacterial protein from species tuberculosis-64 (MPT-64) on the basis of antigen and antibody detection by enzyme-linked immunosorbent assay. Parallel detection of antigens and antibodies in the serum samples of pulmonary tuberculosis (PTB) patients resulted in higher sensitivity as compared to either of the single tests in both smear-positive (90%) and smear-negative (60%) PTB patients. In addition, combined detection of antigens and antibodies in the fluids of extrapulmonary tuberculosis (EPTB) patients could detect >90% of the patients with high specificity. These results demonstrate the ability of the combination of antigen and antibody detection assays based on the cocktail of RD antigens to diagnose a substantial number of PTB and EPTB cases with high specificity.

Major roles of isocitrate lyase and malate synthase in bacterial and fungal pathogenesis

The glyoxylate cycle is an anaplerotic pathway of the tricarboxylic acid (TCA) cycle that allows growth on C(2) compounds by bypassing the CO(2)-generating steps of the TCA cycle. The unique enzymes of this route are isocitrate lyase (ICL) and malate synthase (MS). ICL cleaves isocitrate to glyoxylate and succinate, and MS converts glyoxylate and acetyl-CoA to malate. The end products of the bypass can be used for gluconeogenesis and other biosynthetic processes. The glyoxylate cycle occurs in Eukarya, Bacteria and Archaea. Recent studies of ICL- and MS-deficient strains as well as proteomic and transcriptional analyses show that these enzymes are often important in human, animal and plant pathogenesis. These studies have extended our understanding of the metabolic pathways essential for the survival of pathogens inside the host and provide a more complete picture of the physiology of pathogenic micro-organisms. Hopefully, the recent knowledge generated about the role of the glyoxylate cycle in virulence can be used for the development of new vaccines, or specific inhibitors to combat bacterial and fungal diseases.

New diagnostic methods for tuberculosis

PURPOSE OF REVIEW

During the last decade, laboratory tests for the detection of Mycobacterium tuberculosis (Mtb) have improved dramatically. Improvements in the ability to detect latent infection with Mtb, disease associated with Mtb, and strains resistant to commonly used antibiotics are reviewed.

RECENT FINDINGS

Advances in the detection of Mtb include light-emitting diode fluorescence microscopy, nucleic acid amplification of Mtb and drug-resistant strains, and more rapid liquid culture with adjunct drug susceptibility testing. In the detection of latent tuberculosis infection, interferon [gamma] release assays offer improved accuracy over the tuberculin skin test.

SUMMARY

The past 10 years have seen the most rapid growth in new diagnostics for Mtb in over a century. Although these tests offer improvements in the ability to detect Mtb, drug-resistant isolates, and those with latent tuberculosis infection, these improvements are counter-balanced by the need to deploy these tests in areas where Mtb burden is highest.

Performance of purified antigens for serodiagnosis of pulmonary tuberculosis: a meta-analysis

Serological antibody detection tests for tuberculosis may offer the potential to improve diagnosis. Recent meta-analyses have shown that commercially available tests have variable accuracies and a limited clinical role. We reviewed the immunodiagnostic potential of antigens evaluated in research laboratories (in-house) for the serodiagnosis of pulmonary tuberculosis and conducted a meta-analysis to evaluate the performance of comparable antigens. Selection criteria included the participation of at least 25 pulmonary tuberculosis patients and the use of purified antigens. Studies evaluating 38 kDa, MPT51, malate synthase, culture filtrate protein 10, TbF6, antigen 85B, alpha-crystallin, 2,3-diacyltrehalose, 2,3,6-triacyltrehalose, 2,3,6,6'-tetraacyltrehalose 2'-sulfate, cord factor, and TbF6 plus DPEP (multiple antigen) were included in the meta-analysis. The results demonstrated that (i) in sputum smear-positive patients, sensitivities significantly >or=50% were provided for recombinant malate synthase (73%; 95% confidence interval [CI], 58 to 85) and TbF6 plus DPEP (75%; 95% CI, 50 to 91); (ii) protein antigens achieved high specificities; (iii) among the lipid antigens, cord factor had the best overall performance (sensitivity, 69% [95% CI, 28 to 94]; specificity, 91% [95% CI, 78 to 97]); (iv) compared with the sensitivities achieved with single antigens (median sensitivity, 53%; range, 2% to 100%), multiple antigens yielded higher sensitivities (median sensitivity, 76%; range, 16% to 96%); (v) in human immunodeficiency virus (HIV)-infected patients who are sputum smear positive, antibodies to several single and multiple antigens were detected; and (vi) data on seroreactivity to antigens in sputum smear-negative or pediatric patients were insufficient. Potential candidate antigens for an antibody detection test for pulmonary tuberculosis in HIV-infected and -uninfected patients have been identified, although no antigen achieves sufficient sensitivity to replace sputum smear microscopy. Combinations of select antigens provide higher sensitivities than single antigens. The use of a case-control design with healthy controls for the majority of studies was a limitation of the review. Efforts are needed to improve the methodological quality of tuberculosis diagnostic studies.

Peptide-based antibody detection for tuberculosis diagnosis

Tuberculosis (TB) is a major cause of morbidity and mortality, especially in developing countries. Despite significant limitations, microscopy remains the cornerstone of the global TB control strategy. As the TB epidemic escalates, new diagnostic methods that are accurate and also economical and simple to manufacture and deploy are urgently needed. Although several promising antigens have been identified and evaluated in recent years, the reproducible production of high-quality recombinant mycobacterial proteins with minimal batch-to-batch variation is difficult, laborious, and expensive. To determine the feasibility of devising a synthetic peptide-based diagnostic test for TB, we have delineated the immunodominant epitopes of three candidate antigens, Ag85B, BfrB, and TrxC, that were previously identified to be immunogenic in TB patients. The results demonstrate that combinations of carefully selected synthetic peptides derived from highly immunogenic proteins can be the basis for devising an immunodiagnostic test for TB.