Assessment of three commercially available serologic assays for detection of antibodies to Mycobacterium tuberculosis and identification of active tuberculosis

Potential biomarkers for evaluating the BCG vaccination response based on humoral immunity

Background

The current prophylactic tuberculosis vaccine Bacille Calmette-Guérin (BCG), was derived in the 1920s, but the humoral immune responses induced by BCG vaccination have not been fully elucidated to date. In this study, our aim was to reveal the profiles of antibody responses induced by BCG vaccination in adults and identify the potential biomarkers for evaluating the BCG vaccination response.

Methods

Proteome microarrays were performed to reveal the serum profiles of antibody responses induced by BCG vaccination in adults. ELISA was used to validate the potential biomarkers in validation cohort (79 healthy controls and 58 BCG-vaccinated subjects). Then combined panel was established by logistic regression analysis based on OD values of potential biomarkers.

Results

Multiple antigens elicited stronger serum IgG or IgM antibody responses in BCG vaccinated subjects than healthy subjects at 12 weeks post BCG vaccination; among the antigens, Rv0060, Rv2026c and Rv3379c were further verified using 137 serum samples and presented the moderate performance in assessment of the BCG vaccination response by receiver operating characteristic analysis. Furthermore, a combined panel exhibited an improved AUC of 0.923, and the sensitivity and specificity were 77.59 % and 91.14 %, respectively. In addition, the antibody response against Rv0060, Rv2026c and Rv3379c was related to the clinical background to a certain extent.

Conclusions

The novel antigens identified in our study could offer better knowledge towards developing a more efficacious vaccine based on humoral immune responses, and they could be potential biomarkers in assessments of BCG vaccination responses.

Past and Present Approaches to Diagnosis of Active Pulmonary Tuberculosis

Tuberculosis disease continues to contribute to the mortality burden globally. Due to the several shortcomings of the available diagnostic methods, tuberculosis disease continues to spread. The difficulty to obtain sputum among the very ill patients and the children also affects the quick diagnosis of tuberculosis disease. These challenges warrant investigating different sample types that can provide results in a short time. Highlighted in this review are the approved pulmonary tuberculosis diagnostic methods and ongoing research to improve its diagnosis. We used the PRISMA guidelines for systematic reviews to search for studies that met the selection criteria for this review. In this review we found out that enormous biosignature research is ongoing to identify host biomarkers that can be used as predictors of active PTB disease. On top of this, more research was also being done to improve already existing diagnostic tests. Host markers required more optimization for use in different settings given their varying sensitivity and specificity in PTB endemic and non-endemic settings.

Anything You Can Do, I Can Do Better: Can Aptamers Replace Antibodies in Clinical Diagnostic Applications?

The mainstay of clinical diagnostics is the use of specialised ligands that can recognise specific biomarkers relating to pathological changes. While protein antibodies have been utilised in these assays for the last 40 years, they have proven to be unreliable due to a number of reasons. The search for the 'perfect' targeting ligand or molecular probe has been slow, though the description of chemical antibodies, also known as aptamers, nearly 30 years ago suggested a replacement reagent. However, uptake has been slow to progress into the clinical environment. In this review, we discuss the issues associated with antibodies and describe some of the applications of aptamers that have relevancy to the clinical diagnostic environment.

Evaluation of Mycobacterium tuberculosis-specific antibody responses for the discrimination of active and latent tuberculosis infection

OBJECTIVES

The serological antibody detection tests offer several advantages for the rapid diagnosis of tuberculosis (TB). The Mycobacterium tuberculosis-specific antibody responses associated with different stages of TB infection remain to be investigated.

METHODS

The Pathozyme-Myco IgG (Myco G), Pathozyme TB Complex Plus (TB Complex), IBL M. tuberculosis IgG ELISA (IBL), Anda Biologicals TB IgG (Anda-TB), and T-SPOT.TB (T-SPOT) tests were performed for 133 active TB patients (ATB group), 131 controls (CON group), and 95 subjects with latent TB infection (LTBI group).

RESULTS

The four serological tests all showed relatively low sensitivity in the ATB group but high specificity in the LTBI and CON groups. The antibody levels of the four serological tests were significantly higher in the ATB group than in the LTBI group. The same trend was observed between the LTBI and CON groups. The four serological tests demonstrated potential diagnostic value in discriminating ATB from LTBI. A combination of the Anda-TB and TB Complex tests exhibited the best diagnostic potential in discriminating ATB from LTBI, with a sensitivity of 89.4% and a specificity of 94.7%. Further, the diagnostic value of Anda-TB and TB Complex were validated in a prospective cohort including 106 patients with suspected ATB. Combined with the T-SPOT test, the tests showed a sensitivity of 87.2% and a specificity of 92.5% for discriminating ATB patients from all ATB suspected cases in the validation group.

CONCLUSIONS

The antibody responses of the serological tests all showed significant differences between the ATB and LTBI groups. A combination of Anda-TB and the TB Complex test demonstrated high diagnostic potential in discriminating ATB from LTBI and may be an additional diagnostic tool in the diagnosis of M. tuberculosis infection.

Dynamic IgG antibody response to immunodominant antigens of M. tuberculosis for active TB diagnosis in high endemic settings

BACKGROUND

Even though various techniques have been developed for rapid diagnosis of tuberculosis (TB), still there is an immense need for a simple, cost effective, highly sensitive and specific test. Hence, one of the possibilities is identification of Mycobacterium tuberculosis specific antibodies in infected serum by using specific antigens.

METHODS

We tested 10 recombinant M. tuberculosis antigens to evaluate IgG levels among Healthy control subjects (HCS), Healthy household contacts (HHC) and pulmonary TB patients (PTB) by ELISA.

RESULTS

The median IgG levels specific to all the antigens are higher in PTB than HHC and HCS. Amongst single antigens, 38-kDa antigen has showed maximum sensitivity of 50% than any other antigens at 95.5% specificity. Among the two antigen combination, 38-kDa+Rv1860 has showed maximum sensitivity of 66.6% with specificity of 92.2%. The same antigen combination (38-kDa and Rv1860) predominantly identifies smear negative and culture positive TB patients with 68% sensitivity and 92.2% specificity. Most of the antigens have exhibited higher antibody titre in cavitary TB than non cavitary. With regard to latent TB infection (LTBI) identification, Rv1860 has exhibited maximum sensitivity of 53.3% with 95% specificity.

CONCLUSIONS

IgG response to combination of recombinant mycobacterial antigens (38-kDa, Rv1860, Rv2204c and Rv0753c) presents good specificity with acceptable level of sensitivity for TB diagnosis.

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.

Performance of a Tuberculosis Serologic Assay in Various Patient Populations

OBJECTIVES

Detection of the humoral response to diagnose active tuberculosis has had varied success. We sought to further characterize the performance of a commercial serologic assay (Active TBDetect IgG ELISA; InBios International, Seattle, WA), which had demonstrated promising results in prior studies.

METHODS

Blood specimens from patients with mycobacterial infections, autoimmune disorders, and documented nonmycobacterial infections were prospectively collected for testing by the Active TBDetect IgG ELISA. Pertinent medical records were reviewed.

RESULTS

The sensitivity of the InBios IgG ELISA for active tuberculosis cases was 54.1% (20/37). Reactivity occurred in 24.1% (14/58) of nontuberculous mycobacterium cases, 10.4% (7/67) of nonmycobacterial infections, 10.5% (11/105) of autoimmune disorder cases, 8.7% (8/92) of noninfected patients, 14.3% (1/7) of patients with latent tuberculosis, and 10.7% (3/28) of control pediatric cases. Overall specificity was 87.5% (288/329). Receiver operator curve analysis demonstrated an area under the curve of 0.74. Reactivity with nontuberculous mycobacterium infection occurred with Mycobacterium avium-intracellulare complex, Mycobacterium chelonae/abscessus complex, Mycobacterium simiae, and Mycobacterium gordonae and was positively associated with having a positive acid-fast bacilli smear.

CONCLUSIONS

This study confirmed the limitations of serodiagnosis for active tuberculosis, including poor sensitivity and increased reactivity with nontuberculous mycobacterium-positive patients.

Point-of-care diagnostics, a major opportunity for change in traditional diagnostic approaches: potential and limitations

'Point-of-care' (POC) diagnostics are a powerful emerging healthcare approach. They can rapidly provide statistically significant results, are simple to use, do not require specialized equipment and are cost-effective. For these reasons, they have the potential to play a major role in revolutionizing the diagnosis, initiation and monitoring of treatment of major global diseases. This review focuses on antibody-based POC devices that target four major global diseases: cardiovascular diseases, prostate cancer, HIV infection and tuberculosis. The key statistics and pathology of each disease is described in detail, followed by an in-depth discussion on emerging POC devices that target each disease, highlighting their potential and limitations.

Antituberculosis IgG antibodies as a marker of active Mycobacterium tuberculosis disease

Anti-Mycobacterium tuberculosis IgG antibodies may aid in the diagnosis of active M. tuberculosis disease. We studied whether anti-M. tuberculosis IgG antibodies are elevated in active M. tuberculosis disease and assessed factors contributing to false-positive and -negative results. A retrospective study of 2,150 individuals tested by the QuantiFERON-TB Gold In-Tube (QFT-GIT) assay was conducted at the University of Utah, ARUP Laboratories, November 2008 to December 2010. All samples were tested with the InBios Active TbDetect antituberculosis (anti-TB) IgG antibody assay. Of 1,044 patients with a positive QFT-GIT, 59 (5.7%) were positive for M. tuberculosis antibodies. Fourteen of 1,106 (1.3%) with a negative or indeterminate QFT-GIT were positive for M. tuberculosis antibodies. M. tuberculosis antibody tests were positive in 61.5% with confirmed active M. tuberculosis disease and other mycobacterial infections. Over half of the false-negative M. tuberculosis antibody tests occurred in patients ≥ 90 years of age. False positives were seen in 12.9% of autoimmune patients. The odds ratio of being positive by the QFT-GIT and the InBios TB IgG assay increased with confirmed M. tuberculosis disease or highly suspected M. tuberculosis disease and was 86.7 (95% confidence interval [CI], 34.4 to 218.5) in these two groups compared to patients negative by both tests. Although anti-M. tuberculosis antibodies can be detected in patients with active M. tuberculosis disease, caution should be used with patients where immunoglobulin levels may be decreased or patients with autoantibodies.

Commercial serological tests for the diagnosis of active pulmonary and extrapulmonary tuberculosis: an updated systematic review and meta-analysis

BACKGROUND

Serological (antibody detection) tests for tuberculosis (TB) are widely used in developing countries. As part of a World Health Organization policy process, we performed an updated systematic review to assess the diagnostic accuracy of commercial serological tests for pulmonary and extrapulmonary TB with a focus on the relevance of these tests in low- and middle-income countries.

METHODS AND FINDINGS

We used methods recommended by the Cochrane Collaboration and GRADE approach for rating quality of evidence. In a previous review, we searched multiple databases for papers published from 1 January 1990 to 30 May 2006, and in this update, we add additional papers published from that period until 29 June 2010. We prespecified subgroups to address heterogeneity and summarized test performance using bivariate random effects meta-analysis. For pulmonary TB, we included 67 studies (48% from low- and middle-income countries) with 5,147 participants. For all tests, estimates were variable for sensitivity (0% to 100%) and specificity (31% to 100%). For anda-TB IgG, the only test with enough studies for meta-analysis, pooled sensitivity was 76% (95% CI 63%-87%) in smear-positive (seven studies) and 59% (95% CI 10%-96%) in smear-negative (four studies) patients; pooled specificities were 92% (95% CI 74%-98%) and 91% (95% CI 79%-96%), respectively. Compared with ELISA (pooled sensitivity 60% [95% CI 6%-65%]; pooled specificity 98% [95% CI 96%-99%]), immunochromatographic tests yielded lower pooled sensitivity (53%, 95% CI 42%-64%) and comparable pooled specificity (98%, 95% CI 94%-99%). For extrapulmonary TB, we included 25 studies (40% from low- and middle-income countries) with 1,809 participants. For all tests, estimates were variable for sensitivity (0% to 100%) and specificity (59% to 100%). Overall, quality of evidence was graded very low for studies of pulmonary and extrapulmonary TB.

CONCLUSIONS

Despite expansion of the literature since 2006, commercial serological tests continue to produce inconsistent and imprecise estimates of sensitivity and specificity. Quality of evidence remains very low. These data informed a recently published World Health Organization policy statement against serological tests. Please see later in the article for the Editors' Summary.

Assessment of five antigens from Mycobacterium tuberculosis for serodiagnosis of tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis, is a major public health issue, particularly in developing countries, and thus effective diagnostic methods for TB remain a central theme in basic and clinical research. To evaluate five antigens (38-kDa protein [38kDa], Rv3621c, Rv3618, 38kDa-ESAT-6 [38E6], and Ag85B-HBHA [AH]) in serological tests for TB patients, we recruited 288 patients and 201 healthy controls. The median IgG reactivity to 38kDa, 38E6, and AH was higher than that to Rv3618 and Rv3621c in pulmonary TB. 38kDa and 38E6 provided high sensitivities in pulmonary TB but low sensitivities in extrapulmonary TB (EPTB). The specificities achieved by 38kDa and 38E6 ranged from 82.0% to 93.9% in patients with non-TB respiratory disease (PD) and in controls. 38kDa and 38E6 exhibited lower sensitivities and higher specificities than their combinations with Rv3618. These findings provide useful information on the relative importance of the above five antigens and suggest that combinations of Rv3618 with 38kDa and 38E6 can increase their sensitivities, but their specificities need to be further increased.

Serological evaluation of Mycobacterium ulcerans antigens identified by comparative genomics

A specific and sensitive serodiagnostic test for Mycobacterium ulcerans infection would greatly assist the diagnosis of Buruli ulcer and would also facilitate seroepidemiological surveys. By comparative genomics, we identified 45 potential M. ulcerans specific proteins, of which we were able to express and purify 33 in E. coli. Sera from 30 confirmed Buruli ulcer patients, 24 healthy controls from the same endemic region and 30 healthy controls from a non-endemic region in Benin were screened for antibody responses to these specific proteins by ELISA. Serum IgG responses of Buruli ulcer patients were highly variable, however, seven proteins (MUP045, MUP057, MUL_0513, Hsp65, and the polyketide synthase domains ER, AT propionate, and KR A) showed a significant difference between patient and non-endemic control antibody responses. However, when sera from the healthy control subjects living in the same Buruli ulcer endemic area as the patients were examined, none of the proteins were able to discriminate between these two groups. Nevertheless, six of the seven proteins showed an ability to distinguish people living in an endemic area from those in a non-endemic area with an average sensitivity of 69% and specificity of 88%, suggesting exposure to M. ulcerans. Further validation of these six proteins is now underway to assess their suitability for use in Buruli ulcer seroepidemiological studies. Such studies are urgently needed to assist efforts to uncover environmental reservoirs and understand transmission pathways of the M. ulcerans.

Buruli ulcer is a slowly progressive but potentially devastating disease of skin and subcutaneous tissue caused by the bacterium Mycobacterium ulcerans. The disease is widespread throughout West and Central Africa, and some countries in the region have established Buruli ulcer control programs. Buruli ulcer is difficult to distinguish from other chronic skin conditions that require different treatments, and there is an urgent need for an accurate point-of-care diagnostic test. In this study, we have used genomic techniques to identify 45 potential M. ulcerans–specific antigens, 33 of which we have been able to produce and purify. We tested these proteins against sera from patients, healthy people living in the same region as the patients and from individuals living in a region with no cases of Buruli ulcer. We found that seven proteins were able to elicit antibody responses that were significantly different between patients and the control subjects from the non-endemic region but not from the healthy individuals in the same Buruli ulcer endemic region. Further analysis showed that six of these M. ulcerans proteins might be useful as markers of exposure to M. ulcerans and could be developed into tools to uncover environmental reservoirs and understand transmission pathways of the bacterium.

PCR and Elisa methods (IgG and IgM): their comparison with conventional techniques for diagnosis of Mycobacterium tuberculosis

In order to establish a rapid and stable method for diagnosis of Mycobacterium tuberculosis infection and minimize the side effects of delayed diagnosis on patients and health system, a cross sectional study was carried out. Since, the infection rate with this bacteria increasing and one of the reasons for this increase is long process of laboratory identification, therefore establishing new diagnosis methods could decrease disease rate. To achieve this aim, collected sputum and blood specimens from 50 patients with clinical suspicion of pulmonary tuberculosis were studied with both traditional, acid-fast stain (AFB) and culture method compare to Enzyme-linked immunosorbent assay (Elisa) (IgG and IgM) and Polymerase Chain Reaction (PCR) methods. The sensitivity and specificity of all methods were determined by using the PCR results as the gold standard. The overall sensitivity, specificity, positive predictive value and negative predictive value of AFB were 17.64, 100, 100 and 70.12%. These values for culture method was 29.41, 100, 100 and 73.33% and for IgG antibody were 66.7, 81.81, 64.7 and 81.81% and IgM antibody were 70.58, 90.9, 80 and 85.71%, respectively. It was concluded that maximum sensitivity and specificity can be achieved by PCR method.