Assessment of the serodiagnostic potential of nine novel proteins from Mycobacterium tuberculosis

Identification of New Mycobacterium bovis antigens and development of a multiplexed serological bead-immunoassay for the diagnosis of bovine tuberculosis in cattle

Serological assays for bovine tuberculosis diagnosis require the use of multiple Mycobacterium bovis specific antigens to ensure the detection of infected animals. In the present study, identification and selection process of antigens, based on data from published proteomic studies and involving the use of bioinformatics tools and an immuno-screening step, was firstly performed for identifying novel antigens that elicit an antibody response in M. bovis infection. Based on this approach, a panel of 10 M. bovis antigens [with known relevance (MPB70, MPB83, MPB70/83, and ESAT6/CFP10) and novel (Mb1961c, Mb1301c, Mb3871, Mb1403, Mb0592, and PE25/PPE41)] were constructed and thenused to develop a new multiplexed serological assay based on Luminex technology. The performance of the Luminex-bTB immunoassay was evaluated using sera from cattle with known tuberculosis status. Among the proteins whose ability to detect bovine tuberculosis was evaluated for the first time, PE25/PPE41 and Mb1403, but not Mb3871, showed good detection capacity. Following multiple antigen combination, the final Luminex-bTB immunoassay included seven antigens (MPB70, MPB83, MPB70/83, ESAT6/CFP10, PE25/PPE41, Mb1403, and Mb0592) and showed better global performance than the immunoassay using the four usual antigens (MPB70, MPB70/83, MPB83 and ESAT6/CFP10). The specificity and sensitivity values were, respectively, of 97.6% and 42.8% when the cut-off of two-positive antigens was used to classify samples as positive. With the use of the more-restrictive criterion of three-positive antigens, the specificity increased to 99.2% but the sensitivity decreased to 23.9%. The analysis of antigen profiles generated with the Luminex-bTB immunoassay showed that mainly serodominant proteins were recognized in samples from infected cattle. The detection of Mb1961c and Mb1301c appeared to be associated with presumed false-positive results. Moreover, sera from cattle originating from bTB-outbreaks but having inconclusive or negative skin test results were identified as positive by the Luminex-bTB immunoassay and showed an antigen pattern associated with M. bovis infection. The Luminex-bTB immunoassay including seven antigens may be useful as adjunct test for the detection of M. bovis-infected herds, and different cut-offs could be applied according to the bovine tuberculosis epidemiological context.

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.

IgG, IgM and IgA antibodies against the novel polyprotein in active tuberculosis

BACKGROUND

The present study was aimed to evaluate whether IgG, IgM and IgA antibodies levels detected against a novel Mycobacterium tuberculosis polyprotein 38 F-64 F (with 38 F being the abbreviation for 38kD-ESAT6-CFP10 and 64 F for Mtb8.4-MPT64-TB16.3-Mtb8) are suitable for diagnosing active tuberculosis, and for monitoring the efficacy of chemotherapy on TB patients.

METHODS

In this study, a total of 371 active TB patients without treatment were selected and categorized into S+/C+group (n=143), S-/C+group (n=106) or S-/C- group (n=122). A series of serum samples were collected from 82 active TB patients who had undergone anti-TB chemotherapy for 0-6 months at one month interval. Humoral responses (IgG, IgM and IgA) were determined for the novel Mycobacterium tuberculosis polyprotein using indirect ELISA methods in all of serum samples.

RESULTS

For S+/C+, S-/C+and S-/C- active tuberculosis patients before anti-TB chemotherapy, the sensitivities of tests based on IgG were 65.7%, 46.2% and 52.5% respectively; the sensitivities based on IgM were 21.7%, 24.5% and 18.9%; and the sensitivities based on IgA were 25.2%, 17.9% and 23.8%. By combination of three isotypes, for all active tuberculosis patients, the test sensitivity increased to 70.4% with the specificity being 91.5%. After anti-TB chemotherapy, there were no significant differences between groups with different courses of anti-TB chemotherapy.

CONCLUSIONS

The novel Mycobacterium tuberculosis polyprotein 38 F-64 F represents potential antigen suitable for measuring IgG, IgM and IgA antibodies. However, the serodiagnostic test based on the 38 F-64 F polyprotein appears unsuitable for monitoring the efficacy of chemotherapy.

Rapid identification of Mycobacterium tuberculosis infection by a new array format-based surface plasmon resonance method

Tubercle bacillus [TB] is one of the most important chronic infectious diseases that cause millions of deaths annually. While conventional smear microscopy and culture methods are widely used for diagnosis of TB, the former is insensitive, and the latter takes up to 6 to 8 weeks to provide a result, limiting the value of these methods in aiding diagnosis and intermediate decisions on treatment. Therefore, a rapid detection method is essential for the diagnosis, prognosis assessment, and recurrence monitoring. A new surface plasmon resonance [SPR] biosensor based on an array format, which allowed immobilizing nine TB antigens onto the sensor chip, was constructed. Simultaneous determination of multiple TB antibodies in serum had been accomplished with this array-based SPR system. The results were compared with enzyme-linked immunosorbent assay, a conventional immunological method. Array-based SPR showed more advantages in providing label-free and real-time detection. Additionally, the high sensitivity and specificity for the detection of TB infection showed its potential for future development of biosensor arrays for TB diagnosis.

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.

Humoural Immune Responses to a Recombinant 16-kDa–38-kDa—ESAT-6 Mycobacterial Antigen in Tuberculosis

The present study investigated the diagnostic value of a recombinant 38-kDa–16-kDa—early secreted antigenic target of 6 kDa (ESAT-6) Mycobacterium tuberculosis (MTB) fusion antigen in 105 patients with tuberculosis (TB), 25 non-TB pulmonary disease patients and 20 healthy individuals. Its diagnostic value was compared with the commercially available enzyme-linked immunosorbent assay kit, the TB-directly observed therapy (DOT) kit. In the controls, the rate of positive antibody response to the TB-DOT kit was significantly higher than that of the recombinant antigen. The area under the receiver operating characteristic curve was 0.751, and the optimum sensitivity and specificity for detecting antibody responses to the recombinant antigen were 65.4% and 84.8%, respectively. The recombinant 38-kDa–16-kDa—ESAT-6 MTB antigen was more effective than the TB-DOT kit in distinguishing between TB patients and controls, and may be an optimal combination of antigens to provide a useful tool for the sensitive and specific diagnosis of patients with TB.

Comparison of antibody responses to seventeen antigens from Mycobacterium tuberculosis

BACKGROUND

The detection of Mycobacteriumtuberculosis (MTB)-specific human antibodies has been an important diagnostic aid in the diagnosis of TB, especially for the bacterium-negative TB. The humoral antibody responses to different antigens of M.tuberculosis (MTB) are heterogeneous in active TB patients. Hence, detection of antibody responses to several MTB antigens may improve the sensitivity and specificity of serological diagnosis of active TB.

METHODS

Seventeen MTB antigens (38kD, 16kD, Ag85A, Ag85B, MPT32, MPT63, MPT64, Mtb39, MTB48, Mtb81, MTC28, Rv1009, ESAT6, CFP10, CFP10-ESAT6, katG, and LAM) were prepared by cloning, expression, and purification from E. coli, and their antigenicities were evaluated in the antibody responses of 210 active TB patients (103 sera from smear- or culture-positive patients, and 107 from smear- or culture-negative patients) and 192 healthy control (95 sera from purified protein derivative-negative healthy donors, and 97 sera from BCG-vaccinated individuals) by an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The levels of antibodies against these antigens in bacterium-negative TB patients were significantly higher than that in healthy controls (p<0.001). The sensitivity with individual antigens to detect antibody responses ranged from 55.7 to 82.9%, with the specificity from 62.0 to 92.2%. Importantly, the sensitivity with five antigens (LAM, 38kD, katG, 16kD, and MPT63 or Mtb39) to detect antibody responses reached 69.5% (146/210), with a specificity of 91.1% (17/192), and the sensitivity with another five antigens (LAM, katG, 16kD, Mtb39 and Mtb81) to detect antibody responses reached 67.1% (141/210), with a specificity of 92.7% (14/192).

CONCLUSIONS

The combination of optimal multiple antigens to detect anti-MTB antibody responses increased the sensitivity and specificity. Therefore, detection of anti-MTB antibody responses with multiple antigens may be valuable in the clinical diagnosis of TB patients.

A novel application of affinity biosensor technology to detect antibodies to mycolic acid in tuberculosis patients

Tuberculosis has re-emerged as a global health problem due to co-infection with HIV and the emergence of drug-resistant strains of Mycobacterium tuberculosis. HIV co-infection introduced a 30% underestimation in TB diagnosis based on sputum analysis, calling for a reliable and fast serodiagnostic assay to assist in the management of TB in HIV-burdened populations. Serodiagnosis with mycobacterial lipid cell wall antigens gave promising results, in particular with LAM and cord factor. Free mycolic acids have also been considered because they are unique in structure to each species of Mycobacterium and can be economically extracted and purified. In a standard immunoassay such as ELISA, however, an unacceptable number of false positive and false negative test results were obtained. Here we report a much improved biosensor method to detect antibodies to mycolic acids in patient serum as surrogate markers of active tuberculosis. Mycolic acid (MA) liposomes were immobilized on a non-derivatized twin-celled biosensor cuvette and blocked with saponin. A high dilution of serum was used to calibrate the binding signal of the two cells, followed by contact with patient serum at a lesser dilution, but pre-incubated with either antigen-carrying, or empty liposomes. The serum, or the protein A purified IgG thereof, from sputum-positive tuberculosis patients could be inhibited from binding to the MA in the biosensor by prior incubation with MA-containing liposomes. The accuracy of the inhibition test was 84% if HIV-positive patients for whom a negative TB sputum analyses could not be relied upon to serve as a reference standard were excluded. If biosensor technology could be made suitable for high throughput screening, then it may provide the solution to the serodiagnosis of tuberculosis against a background of HIV.

Rapid and simple detection of a mycobacterium circulating antigen in serum of pulmonary tuberculosis patients by using a monoclonal antibody and Fast-Dot-ELISA

OBJECTIVES

Several immunoassays have been established for detection of Mycobacterium tuberculosis (MTB) antigens in serum, sputum and cerebrospinal fluid of tuberculous patients using polyclonal or monoclonal antibodies raised against different mycobacterium antigens. Some of these assays display both high sensitivity and specificity for the detection of these antigens. However, these assays require special and highly expensive equipment and the procedures require long periods for their completion. Thus, the rationale of this study was to establish and evaluate Fast-Dot-Enzyme-Linked Immunosorbent Assay (FD-ELISA) as a fast, cheap and field applicable assay for detection of mycobacterium antigen in serum of patients with pulmonary TB.

DESIGNS AND METHODS

This study included three groups: group I: 175 tuberculous patients with pulmonary TB proves with sputum Ziehl-Neelsen (ZN) for acid-fast bacilli and sputum culture (all cases were culture positive for MTB); Group II: 65 patients with diseases other than pulmonary TB as bronchial carcinoma (17 patients), bronchial asthma (29 patients) and chronic obstructive pulmonary disease (19 patients); group III: 50 healthy individuals. Groups II and III served as negative control groups. The target mycobacterium antigen was identified in both crude mycobacterium antigens extract and serum of patients with pulmonary TB, using western blotting technique and anti-TB monoclonal antibody (TB20-mAb) and then it was estimated in the serum samples of all studied groups as an index of tuberculosis, using a newly developed FD-ELISA.

RESULTS

The target mycobacterium antigen was identified at 20 kDa molecular mass in crude mycobacterium antigens extract as well as in serum of patients with pulmonary TB. The developed FD-ELISA detected the mycobacterium antigen in the sera of 159 out of 175 pulmonary TB patients with a sensitivity of 90.8% and 93.0% positive predictive value (PPV). In addition, it identified 12 false weakly positive cases out of 115 samples of negative control groups (7 out of 65 non-TB patients and 5 out of 50 healthy individuals) with a specificity of 89.6% and 86.6% negative predictive value (NPV). Standardization of the FD-ELISA using a serial dilution of the purified mycobacterium antigen indicated that the assay was able to detect 1.8 microg/ml as a lowest detectable antigen concentration.

CONCLUSIONS

The newly developed FD-ELISA is a simple, rapid and highly sensitive assay for detection of mycobacterium antigen in patients with pulmonary TB. Moreover, all steps were performed at room temperature and without the need to use expensive equipment, and this may enhance the application of this assay in tuberculosis screening programs. Further study is needed for confirmation of FD-ELISA reproducibility in light infected pulmonary TB patients and in a large population.

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.

PPE protein (Rv3425) from DNA segment RD11 of Mycobacterium tuberculosis: a potential B-cell antigen used for serological diagnosis to distinguish vaccinated controls from tuberculosis patients

Proteins encoded by a 9.5-kb DNA segment, termed the region of difference (RD), of Mycobacterium tuberculosis have been demonstrated to be important in bacterial virulence, vaccine development and the design of diagnostic reagents. This study evaluated the immunogenic properties of Rv3425, a member of the PPE family of proteins, encoded by an open reading frame found in RD11 of M. tuberculosis, in comparison with two other well-known antigens, the early secreted antigen target 6 (ESAT-6) and the 10-kDa culture filtrate protein (CFP-10). RT-PCR demonstrated that Rv3425 mRNA is expressed in liquid culture by M. tuberculosis H37Rv. When tested in a conventional ELISA in the form of a His-tagged recombinant protein, Rv3425 revealed a statistically significant antigenic distinction between healthy bacille Calmette-Guérin (BCG)-vaccinated controls and tuberculosis (TB) patients (p <0.0001). The anti-IgG response to recombinant Rv3425 was almost equal to that for CFP-10, and was higher than that for ESAT-6. The results highlight the immunosensitive and immunospecific nature of Rv3425, which shows promise for use in the serodiagnosis of TB.

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.

Comparison of antibody responses to a potential combination of specific glycolipids and proteins for test sensitivity improvement in tuberculosis serodiagnosis

The humoral response to different proteinaceous antigens of Mycobacterium tuberculosis is heterogeneous among patients with active disease, and this has originated in the proposal to use a combination of several specific antigens to find an efficient serodiagnostic test for tuberculosis (TB). However, to date, comparisons of antibody responses to several antigens in the same population have been carried out without consideration of antigenic cell wall glycolipids. In the present study the presence of immunoglobulin G (IgG), IgM, and IgA antibodies to M. tuberculosis glycolipids (sulfolipid I, diacyltrehaloses, triacyltrehaloses, and cord factor) was compared with the response to four commercially available tests based on the 38-kDa protein mixed with the 16-kDa protein or lipoarabinomannan. Fifty-two serum samples from TB patients and 83 serum samples from control individuals (48 healthy individuals and 35 non-TB pneumonia patients) were studied. Three relevant results were obtained. (i) Smear-negative TB patients presented low humoral responses, but the sera which did react principally showed IgA antibodies to some glycolipidic antigens. (ii) TB patients exhibit heterogeneous humoral responses against glycolipidic antigens. (iii) Finally, test sensitivity is improved (from 23 to 62%) when IgG and IgA antibodies are detected together in tests based on different antigens (proteins and glycolipids). We conclude that it is possible to include glycolipidic antigens in a cocktail of specific antigens from M. tuberculosis to develop a serodiagnostic test.

Potential serological use of a recombinant protein that is a replica of a Mycobacterium tuberculosis protein found in the urine of infected mice

The recent availability of numerous well-characterized Mycobacterium tuberculosis recombinant proteins has revived interest in the serological diagnosis of tuberculosis. Several promising results have been reported, particularly when more than one antigen is used in the test. However, thus far these antigens have not been used in routine diagnostic tests because they lack sufficient sensitivity. In addition, with the exception of one antigen, most recombinant M. tuberculosis proteins do not identify the majority of tuberculosis patients coinfected with human immunodeficiency virus (HIV). Here, we report a newer M. tuberculosis protein that is a promising candidate for increasing the sensitivity of the serological tests, in particular for patients coinfected with HIV. The protein was found in the urine of mice during the early stages of infection with M. tuberculosis (10 to 14 days), thus suggesting that the antigen is abundantly released during the in vivo growth of the mycobacterium. Reverse genetics was used to produce the recombinant protein, which we named U1 (for urine protein 1). Using a conventional enzyme-linked immunosorbent assay (ELISA), antibody to U1 could be detected in 60% of patients with pulmonary tuberculosis with no signs of coinfection with HIV (n = 83). Conversely, anti-U1 antibody was detected in 87% of the sera from tuberculosis patients coinfected with HIV (n = 47). Out of 12 HIV-infected nontuberculosis patients' sera, 9 did not react with U1 and three sera gave borderline ELISA signals (signal/cutoff of < or =1.75). These results suggest that the high efficiency of U1 in identifying tuberculosis patients coinfected with HIV may be related to abundant release of this protein during the initial phase of the HIV coinfection. The immediate availability of the antigen at a time point in which the patient's immune system is still competent would lead to a secondary immune response to U1 that persists for months in the patient's serum.

Comprehensive Proteomic Profiling of the Membrane Constituents of a Mycobacterium tuberculosis Strain

Mycobacterium tuberculosis is an infectious microorganism that causes human tuberculosis. The cell membranes of pathogens are known to be rich in possible diagnostic and therapeutic protein targets. To compliment the M. tuberculosis genome, we have profiled the membrane protein fraction of the M. tuberculosis H37Rv strain using an analytical platform that couples one-dimensional SDS gels to a microcapillary liquid chromatography-nanospray-tandem mass spectrometer. As a result, 739 proteins have been identified by two or more distinct peptide sequences and have been characterized. Interestingly, approximately 450 proteins represent novel identifications, 79 of which are membrane proteins and more than 100 of which are membrane-associated proteins. The physicochemical properties of the identified proteins were studied in detail, and then biological functions were obtained by sorting them according to Sanger Institute gene function category. Many membrane proteins were found to be involved in the cell envelope, and those proteins with energy metabolic functions were also identified in this study.