Detection of IgG and IgA against the mycobacterial antigen A60 in patients with extrapulmonary tuberculosis

Discovery of Novel Transketolase Epitopes and the Development of IgG-Based Tuberculosis Serodiagnostics

Despite advances in rapid molecular techniques for tuberculosis (TB) diagnostics, there is an unmet need for a point-of-care, nonsputum-based test. Previously, through a T7 phage antigen display platform and immunoscreening, we identified that the serum IgGs of active TB patients differentially bind to several antigen-clones and that this immunoreactivity discriminates TB from other respiratory diseases. One of these high-performance clones has some homology to the transketolase of Mycobacterium tuberculosis (M.tb TKT). In this study, we developed a direct enzyme-linked immunosorbent assay (ELISA) detecting IgG against the TKT antigen-clone (TKTμ). Through sequence alignment and in silico analysis, we designed two more peptides with potential antigenicity that correspond to M.tb-specific transketolase (M.tb TKT1 and M.tb TKT3) epitopes. After the development and standardization of a direct peptide ELISA for three peptides, we tested 292 subjects, including TB (n = 101), latent tuberculosis infection (LTBI) (n = 49), healthy controls (n = 66), and sarcoidosis (n = 76). We randomly assigned 60% of the subjects to a training set to create optimal models to distinguish positive TB samples, and the remaining 40% were used to validate the diagnostic power of the IgG-based assays that were developed in the training set. Antibodies against M.tb TKT3 yielded the highest sensitivity (0.845), and these were followed by TKTμ (0.817) and M.tb TKT1 (0.732). The specificities obtained by TKTμ, M.tb TKT3, and M.tb TKT1 on the test sets were 1, 0.95, and 0.875, respectively. The model using TKTμ obtained a perfect positive predictive value (PPV) of 1, and this was followed by M.tb TKT3 (0.968) and M.tb TKT1 (0.912). These results show that IgG antibodies against transketolase can discriminate active TB against LTBI, sarcoidosis, and controls. IMPORTANCE There is an unmet need for a point-of-care, nonsputum-based TB test. Through the immunoscreening of a novel T7 phage library, we identified classifiers that specifically bind to IgGs in active TB sera. We discovered that one of these clones is aligned with Mycobacterium tuberculosis transketolase (TKT). TKT is an essential enzyme for Mycobacterium tuberculosis growth. We designed three TKT epitopes (TKTμ, TKT1, and TKT3) to detect TKT-specific IgGs. After the development and standardization of three different ELISA-utilizing TKT peptides, we tested 292 subjects, including active TB, LTBI, healthy controls, and sarcoidosis. Rigorous statistical analyses using training and validation sets showed that ELISA-based detections of specific IgGs against TKT3 and TKTμ have the greatest sensitivity, specificity, and accuracy to distinguish active TB subjects from others, even LTBI. Our work provides a novel scientific platform from which to further develop a point-of-care test, thereby aiding in faster TB diagnoses.

Diagnostic Potential of IgG and IgA Responses to Mycobacterium tuberculosis Antigens for Discrimination among Active Tuberculosis, Latent Tuberculosis Infection, and Non-Infected Individuals

Tuberculosis remains a major public health problem. Conventional tests are inadequate to distinguish between active tuberculosis (ATB) and latent tuberculosis infection (LTBI). We measured antibody responses to Mycobacterium tuberculosis antigens (Mycobacterium tuberculosis chorismate mutase (TBCM), antigen 85B (Ag85B), early secreted antigen-6 (ESAT-6), and culture filtrate protein-10 (CFP-10) in ATB, LTBI, and non-infected (NI) individuals. Serum immunoglobulin G (IgG) and immunoglobulin A (IgA) levels were measured and the QuantiFERON-TB Gold In-Tube assay was used to diagnose LTBI. IgG levels against TBCM were significantly higher in LTBI than NI subjects. IgG and IgA levels against Ag85B and IgG levels against CFP-10 were significantly higher in ATB, followed by LTBI, and then NI. When the ATB group was subdivided, IgG levels against Ag85B and CFP-10 were significantly higher in each subgroup compared with those in LTBI and NI groups. Positive correlation trends between interferon-gamma and IgG levels against Ag85B, TBCM, and CFP-10 and IgA levels against Ag85B in LTBI and NI subjects were observed. Age- and sex-adjusted models showed that IgG against TBCM and CFP-10 was independently related to LTBI diagnosis, and IgG against Ag85B was independently related to the diagnosis of ATB and could distinguish between LTBI and ATB. Overall, IgG antibody responses to TBCM, Ag85B, and CFP-10 can discriminate among ATB, LTBI, and NI groups.

Diagnosis and treatment of paediatric tuberculosis: An insight review

Tuberculosis (TB) is a major public health problem, invading all age groups world-wide. It is an opportunistic infection affecting the individuals alone or with co-infections. Childhood TB is a neglected aspect and a significant health problem in epidemic areas. It constitutes more than 20% of TB incidence. Pediatric TB exists in the shadow of adult TB. The clinicians concentrate on pulmonary manifestation of TB, whereas it is a major problem in both pulmonary and extra-pulmonary infections. The rate of infection with this disease is mostly associated with poverty, social disruption and human immunodeficiency virus (HIV) infection. The diagnosis of extra-pulmonary TB (EPTB) is more difficult than pulmonary TB (PTB). Delayed diagnosis and executive treatment contribute to increase in the mortality rate in endemic areas. This article provides the evidence-based simple and safe screening method, indicating rapid, highly sensitive and specific diagnostic tests for pulmonary and EPTB in children. The most important aspect of treatment is the correct course of anti-tubercular drugs. This review serves the purpose of quick reference for microbiologists, epidemiologists, academicians, students and researchers. It provides guidance regarding early diagnosis and treatment accuracy of pediatric TB.

Differential in vivo expression of mycobacterial antigens in Mycobacterium tuberculosis infected lungs and lymph node tissues

Background

The clinical course of tuberculosis (TB) infection, bacterial load and the morphology of lesions vary between pulmonary and extrapulmonary TB. Antigens expressed in abundance during infection could represent relevant antigens in the development of diagnostic tools, but little is known about the in vivo expression of various M. tuberculosis antigens in different clinical manifestations. The aim of this study was to study the differences in the presence of major secreted as well as somatic mycobacterial antigens in host tissues during advanced rapidly progressing and fatal pulmonary disease with mainly pneumonic infiltrates and high bacterial load, and to compare this to the presence of the same antigens in TB lymphadenitis cases, which is mainly chronic and self-limiting disease with organised granulomas and lower bacterial load.

Methods

Human pulmonary (n = 3) and lymph node (n = 17) TB biopsies, and non-TB controls (n = 12) were studied. Ziehl-Neelsen stain, nested PCR 1S6110 and immunohistochemistry were performed. Major secreted (MPT32, MPT44, MPT46, MPT51, MPT53, MPT59, MPT63, and MPT64) and somatic mycobacterial antigens (Mce1A, Hsp65, and MPT57) were detected by using rabbit polyclonal antibodies.

Results

Plenty of bacilli were detectable with Ziehl-Neelsen stain in the lung biopsies while no bacilli were detected in the lymph node biopsies. All the cases were shown to be positive by PCR. Both secretory and somatic antigens were expressed in abundance in pulmonary infiltrates, while primarily somatic antigens were detected in the lymphadenitis cases. Of the secreted antigens, only MPT64 was consistently detected in both cases, indicating a preferential accumulation of this antigen within the inflammatory cells, even if the cells of the granuloma can efficiently restrict bacterial growth and clear away the secreted antigens.

Conclusions

This study shows that major secreted mycobacterial antigens were found in high amounts in advanced pulmonary lesions without proper granuloma formation, while their level of staining was very low, or absent, in the lymph node TB lesions with organised granulomas and very low bacillary load, with one exception of MPT64, suggesting its role in the persistence of chronic infection. These findings have implication for development of new diagnostic tools.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-535) contains supplementary material, which is available to authorized users.

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.

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.

Detection of Antibodies Against 6, 16 and 38 kDa Antigens of Mycobacterium tuberculosis as a Rapid Test for Diagnosis of Tuberculosis

BACKGROUND

Serological assays for diagnosis of tuberculosis (TB) are very attractive because they are inexpensive, non invasive and simple. Present study was conducted to evaluate the tuberculosis rapid test device in Iran.

MATERIALS AND METHODS

The tuberculosis rapid test device based on detection of IgM, IgA and IgG antibodies against 6, 16 and 38-kDa antigens of Mycobacterium tuberculosis via chromatography was used in 96 cases of pulmonary and extra pulmonary TB. Fifty four patients with conditions other than TB were selected as the control group. Tuberculin skin test (TST) was performed in two groups. None of the patients were immunodeficient. All of them were evaluated in terms of presence of BCG scar.

RESULTS

Tuberculosis rapid test was positive in 75 cases (78.1%) and 15 controls (27.8%). This difference was statistically significant (P-value < 0.001). TST was positive in 66 patients (68.8%) with tuberculosis and 10 (18.5%) controls with no statistically significant difference (P-value = 0.065). Sensitivity, specificity, positive and negative predictive values of the tuberculosis rapid test for diagnosis of tuberculosis were 78.1%, 72.2%, 83.3% and 65%, respectively. These parameters for TST were 31.3%, 81.5%, 75%, and 40%, respectively.

CONCLUSION

Tuberculosis rapid test has better sensitivity than TST and may be helpful in diagnosis of tuberculosis as a complementary test or in epidemiological investigations.

Progress in serodiagnosis of Mycobacterium tuberculosis infection

One-third of the world population is estimated to have Mycobacterium tuberculosis infection. Accurate and timely identification of infected individuals is critical for treatment and control. The current diagnostic methods lack the desired sensitivity and specificity, require sophisticated equipment and skilled workforce or take weeks to yield results. Diagnosis of extrapulmonary TB, TB-HIV co-infection, childhood TB and sputum smear-negative pulmonary TB pose serious challenges. Interest in developing serodiagnostic methods is increasing because detection of antibody is rapid, simple and relatively inexpensive, and does not require a living cell for detection. Three types of tests, namely screening tests to overcome diagnostic delay, specific tests for diagnosis of extrapulmonary TB and other bacteriologically negative cases, and tests for vaccine-induced immunity need critical consideration. Several factors must be considered to develop serodiagnostic methods for TB. Antigen recognition by infected individuals is highly heterogeneous due to stage of disease, differences in HLA types, strain of the bacilli, health of the patient and bacillary load. With advances in molecular biological techniques, a number of novel antigens have been identified. Some of these antigens have proven valuable in detecting specific antibodies in some of the most challenging TB patients. The best example is a fusion protein containing several M. tuberculosis proteins (e.g. CFP-10, MTB8, MTB48, MTB81 and the 38-kDa protein) which showed encouraging results in detecting antibodies in sera of patients, including TB-HIV co-infection. This review presents progress made in the serodiagnosis of TB during the last decade.

A systematic review of commercial serological antibody detection tests for the diagnosis of extrapulmonary tuberculosis

Conventional diagnostic tests for tuberculosis have several limitations and are often unhelpful in establishing the diagnosis of extrapulmonary tuberculosis. Although commercial serological antibody based tests are available, their usefulness in the diagnosis of extrapulmonary tuberculosis is unknown. A systematic review was conducted to assess the accuracy of commercial serological antibody detection tests for the diagnosis of extrapulmonary tuberculosis. In a comprehensive search, 21 studies that reported data on sensitivity and specificity for extrapulmonary tuberculosis were identified. These studies evaluated seven different commercial tests, with Anda-TB IgG accounting for 48% of the studies. The results showed that (1) all commercial tests provided highly variable estimates of sensitivity (range 0.00-1.00) and specificity (range 0.59-1.00) for all extrapulmonary sites combined; (2) the Anda-TB IgG kit showed highly variable sensitivity (range 0.26-1.00) and specificity (range 0.59-1.00) for all extrapulmonary sites combined; (3) for all tests combined, sensitivity estimates for both lymph node tuberculosis (range 0.23-1.00) and pleural tuberculosis (range 0.26-0.59) were poor and inconsistent; and (4) there were no data to determine the accuracy of the tests in children or in patients with HIV infection, the two groups for which the test would be most useful. At present, commercial antibody detection tests for extrapulmonary tuberculosis have no role in clinical care or case detection.

Osteoarticular tuberculosis in a developed country

OBJECTIVES

To evaluate the clinical and diagnostic features of osteoarticular tuberculosis (OT) from a series of cases seen over 30 years in a large university hospital in Naples, Italy.

METHODS

We reviewed the files of all patients admitted to our department from 1975 to 2004 with a diagnosis of osteoarticular tuberculosis.

RESULTS

We identified 136 patients with 140 osteoarticular tuberculosis lesions. Fifty-three cases were diagnosed from 1975 to 1984, 36 cases from 1985 to 1994, and 47 cases from 1995 to 2004. Eleven patients (8%) were from high-incidence areas outside of Italy. The mean delay until diagnosis was 216.6 days. Pain, low-grade fever, and loss of weight were the most common presenting symptoms. Neurological involvement was present in 11 cases out of 79 spinal lesions (13.9%). Serological methods were used to study antimycobacterial antibodies using enzyme-linked immunosorbent assays (ELISA-TB test) in 59 patients (42.1%). Positive results on this test were obtained in 43 patients (72.9%). ELISA-TB test was the only diagnostic test associated with a shorter diagnostic delay in a model of multivariate regression analysis (p=0.001). Tc-99m MDP bone scans were obtained from 83 patients with 84 lesions and increased uptake in the affected area was noted in 72 lesions (85.7%). Histological and microbiological examinations were positive in 97 (69.3%) and 57 (40.7%) lesions, respectively. In 43 (30.7%) lesions, we could not definitively confirm the diagnosis. In these cases chemotherapy was nevertheless initiated.

CONCLUSIONS

Thorough and even invasive diagnostic work-up is mandatory for the proper and timely management of patients with OT. Tc-99m MDP bone scanning and ELISA-TB test are useful diagnostic tools. We always used microbiological testing and histological examination to confirm the diagnosis of OT, but empirical antituberculosis treatment was nevertheless initiated in the patients with high clinical suspicion in order to limit the potentially permanent destruction of affected skeletal segments.

Prognostic variables for high titres in a fluorescent antibody test to diagnose tuberculosis

SETTING

The four hospitals and a tuberculosis clinic in the province of Zeeland, The Netherlands.

OBJECTIVE

To assess the usefulness of PPD antibody measurement in the diagnosis of tuberculosis in patients admitted to hospital.

PATIENTS AND METHODS

Sixty-one patients presenting with active tuberculosis, and 215 control patients were included in the study. Initial serum PPD antibody titres were determined with a macrophage uptake Fluorescent antibody test (MuFat) to construct a discrimination model between Tuberculosis (TB) and non-TB. We also retrospectively collected clinical parameters of the TB patients at presentation. Univariate and multivariate logistic regression are used to identify variables predicting high antibody titres.

RESULTS

In TB patients, the presence of clinical symptoms (OR=10.63) and the presence of at least two concurrent non-lymph node disease localizations outside thorax and abdomen (OR=13.94) are necessary and sufficient to predict high titres. The logistic model shows a significant contribution of the 2log (titre) to the discrimination between TB and non-TB patients. At a cut-off value of 128, a specificity, sensitivity, and positive predictive and negative predictive values of 97%, 39%, 80% and 85%, respectively, are calculated in the study cohort.

CONCLUSION

Our data suggest an application of the test at high cut-off values for timely diagnosis of difficult-to-diagnose TB patients. The results of this retrospective study will have to be confirmed in further prospective studies.

Measurement of Immunoglobulin G against Mycobacterial Antigen A60 in Patients with Cystic Fibrosis and Lung Infection Due to Mycobacterium abscessus

BACKGROUND

The diagnosis and prognosis of lung infections due to the emerging nontuberculous mycobacterium (NTM) Mycobacterium abscessus are difficult to establish in children with cystic fibrosis.

METHODS

We evaluated the usefulness of an enzyme-linked immunosorbent assay for detecting serum IgG antibodies against the ubiquitous mycobacterial antigen A60.

RESULTS

A total of 186 patients with cystic fibrosis (mean age+/-SD, 12.0+/-5.0 years) were studied, including 15 M. abscessus-positive patients who fulfilled American Thoracic Society (ATS) criteria for NTM infection (M. abscessus-infected patients), 7 M. abscessus-positive patients who did not fulfill ATS criteria, 20 patients positive for various other NTM who did not fulfill ATS criteria, and 144 NTM-negative control patients; mean IgG titers (+/-SD) for these 4 groups were 718+/-342 U, 193+/-113 U, 129+/-49 U, and 121+/-53 U, respectively (M. abscessus-infected patients vs. each of the other groups, P<.005). The A60 IgG test was both sensitive (approximately 87%) and specific (approximately 95%) if adapted cutoff values were used (150 U and 250 U for patients aged <or=10 years and patients aged >10 years, respectively) and correlated well with results of acid-fast bacilli smears.

CONCLUSION

Measurement of anti-A60 IgG may be useful for both the diagnosis and assessment of activity of M. abscessus lung infection in persons with cystic fibrosis.

Serodiagnosis of tuberculosis using two ELISA systems

Serodiagnosis by ELISA has been widely explored over the years, in the diagnosis of tuberculosis. Two ELISA systems were evaluated for detection of mycobacterial antibodies in pulmonary and extra pulmonary tuberculosis. The two test assays explored were ERBA LISA (TB IgG) test (Anda Biologicals) which uses A60 antigen complex found in the cytosol of typical and atypical mycobacteria, and SEVA TB (IgG) ELISA, which uses a 31 kDa, glycoprotein antigen purified fromM. tb H(37)Ra culture filtrate. Sera from 98 proven tuberculosis [pulmonary TB (48), tuberculous lymphadenopathy (30), tuberculous meningitis (15) & genitourinary TB (5)] were studied along with 32 healthy controls. The overall positivity obtained using ERBA LISA (TB IgG) test and SEVA TB (IgG) ELISA test was 72.9% and 91.6% in pulmonary tuberculosis, 43.3% and 76.6% in tuberculous lymphadenopathy respectively. The sensitivity of ERBA LISA test in tuberculous meningitis and genito-urinary TB was significantly low (26.6% & 40% respectively) compared to sensitivity obtained using SEVA TB ELISA (86.6% & 60% respectively) with overall specificity of 60% and 87.5%. Thus SEVA TB IgG ELISA test was found to be more sensitive than ERBA LISA in detecting IgG antibodies in tuberculous sera, in particular in extra pulmonary tuberculosis cases.

The value of pleural fluid anti-A60 IgM in BCG-vaccinated tuberculous pleurisy patients

OBJECTIVES

To determine if detection of IgM and IgG antibodies against mycobacterial antigen A60, together with the Mantoux tuberculin skin test (TST), could be used in the diagnosis of tuberculous pleurisy (TP) in BCG-vaccinated cases.

METHODS

We investigated 125 BCG-vaccinated patients with pleural effusion. Of these, 88 had TP and 37 had non-tuberculous pleurisy (NTP). TST and anti-A60 IgM and IgG measurements by ELISA were performed in the sera and pleural effusions of both groups.

RESULTS

Cut-off values, in optical density, for serum anti-A60 IgM, pleural fluid anti-A60 IgM, serum anti-A60 IgG and pleural fluid anti-A60 IgG were defined as 0.624, 0.614, 0.464, and 0.613, respectively. TP patients had higher IgG and IgM levels in the serum (P < 0.001 and P < 0.05, respectively) and pleural effusion (P < 0.001 and P < 0.001, respectively). Regardless of the diagnosis, IgG and IgM levels were higher in the sera (P < 0.001 and P < 0.05, respectively) and pleural effusions (P < 0.001 and P < 0.001, respectively) of TST-positive cases, and serum and pleural fluid IgM levels were higher (P < 0.001 and P < 0.001, respectively) in the TST-positive TP cases. Sensitivity and specificity of TST were 65% and 68%, respectively. As a single parameter, pleural fluid anti-A60 IgM had the highest sensitivity (77%) and specificity (94%) in patients with negative TST.

CONCLUSION

We suggest that in populations where tuberculosis prevalence is high and BCG vaccination is common, pleural fluid anti-A60 IgM can facilitate the diagnosis of TP.