Detection of pulmonary and extrapulmonary tuberculosis patients with the 38-kilodalton antigen from Mycobacterium tuberculosis in a rapid membrane-based assay

Evaluation of the ICT Tuberculosis test for the routine diagnosis of tuberculosis

BACKGROUND

Rapid and accurate diagnosis of tuberculosis (TB) is crucial to facilitate early treatment of infectious cases and thus to reduce its spread. To improve the diagnosis of TB, more rapid diagnostic techniques such as antibody detection methods including enzyme-linked immunosorbent assay (ELISA)-based serological tests and immunochromatographic methods were developed. This study was designed to evaluate the validity of an immunochromatographic assay, ICT Tuberculosis test for the serologic diagnosis of TB in Antalya, Turkey.

METHODS

Sera from 72 patients with active pulmonary (53 smear-positive and 19 smear-negative cases) and eight extrapulmonary (6 smear-positive and 2 smear-negative cases) TB, and 54 controls from different outpatient clinics with similar demographic characteristics as patients were tested by ICT Tuberculosis test.

RESULTS

The sensitivity, specificity, and negative predictive value of the ICT Tuberculosis test for pulmonary TB were 33.3%, 100%, and 52.9%, respectively. Smear-positive pulmonary TB patients showed a higher positivity rate for antibodies than smear-negative patients, but the difference was not statistically significant. Of the eight patients with extrapulmonary TB, antibody was detected in four patients.

CONCLUSION

Our results suggest that ICT Tuberculosis test can be used to aid TB diagnosis in smear-positive patients until the culture results are available.

Immunoglobulin A (IgA) and IgG immune responses against P-90 antigen for diagnosis of pulmonary tuberculosis and screening for Mycobacterium tuberculosis infection

The purpose of the present study was to evaluate the usefulness of detection of serum immunoglobulin A (IgA) and IgG antibodies directed against the mycobacterial P-90 antigen for the diagnosis of active pulmonary tuberculosis (PTB) among symptomatic individuals and for the detection of Mycobacterium tuberculosis infections among close contacts of PTB patients. Two commercially available enzyme immunoassay (EIA) kits (IgA EIA-TB [EIA-IgA] and IgG EIA-TB [EIA-IgG]; Kreatech Diagnostics) were evaluated in a blinded fashion by using stored serum samples from 268 individuals, including 69 patients with PTB, 41 patients with diseases other than tuberculosis (TB), 12 subjects with healed PTB, 39 close contacts of PTB patients, and 107 healthy volunteers. For the EIA-IgA, the sensitivity was 74% and the specificity was 68% when a cutoff determined by a receiver operator characteristic curve was used. For the EIA-IgG, the sensitivity was 69% and the specificity was 64%. The EIA-IgA was positive for 54% of healthy close contacts of PTB patients but only 8% of healthy controls without contact with a PTB patient or a prior personal history of TB (P < 0.001). The relatively low sensitivities and specificities of these serologic tests make them poor tools for the diagnosis of PTB among patients with suspected PTB. However, the relatively high prevalence of positive EIA-IgA results among healthy close contacts of PTB patients warrants further evaluation of this test with close contacts and other populations at risk for recent M. tuberculosis exposure and development of disease.

Evaluation of a rapid immunochromatographic test for the serologic diagnosis of tuberculosis in Italy

OBJECTIVE

To determine specificity, sensitivity and predictive values of a rapid immunochromatographic assay (ICT tuberculosis) for the diagnosis of tuberculosis (TB) in an Italian clinical setting, and to identify tentative new guidance for the interpretation of test results.

METHODS

The ICT tuberculosis test is an immunochromatographic test based on the detection of IgG antibodies directed against five highly purified antigens secreted by Mycobacterium tuberculosis during active growth. Sera from 60 patients with active pulmonary (48 sputum smear-positive and six sputum smear-negative cases) and extrapulmonary (six cases) TB were obtained. Personal, anamnestic and clinical data were investigated and recorded for each patient. The control groups comprised 156 subjects: 40 healthy individuals, half of them Mycobacterium bovis BCG-vaccinated, and 116 patients with mycobacterial diseases other than TB (five cases), with nonmycobacterial lung diseases (30 cases), with nonmycobacterial nonlung diseases (30 cases), with nonmycobacterial diseases and rheumatoid factors positivity (30 cases), and with asymptomatic HIV infection (21 cases). For 21 individuals the test was simultaneously performed with both serum and whole blood sample. Each positive result of the ICT test was reported with regard to the number (1-4), position (A, B, C, D) and color intensity (+ to ++++) of the evidenced lines in order to assess the quality of the antibody response.

RESULTS

The overall sensitivity and specificity were 56.7% and 90.4%, respectively. The sensitivity for pulmonary TB patients was 61.1% (66.7% for smear-positive and 16.7% for smear-negative cases) and 16.7% for extrapulmonary TB patients. The difference between ICT results in pulmonary TB patients and control subjects was statistically significant (P < 0.0001). The analysis of the positive ICT tests revealed that samples with strong color intensity (>/=++) and specific antibodies bound to antigens immobilized on line D were significantly more frequent in TB patients than in controls (P = 0.001 and P= 0.027, respectively). ICT test results with the presence of at least three visible lines were more often observed in the TB patients than in controls, although not reaching statistical significance (P = 0.052). No difference was observed between the results of the ICT test performed both on serum and whole blood sample.

CONCLUSIONS

The ICT tuberculosis test was confirmed to be rapid and easy to perform without requiring special equipment, both on serum and whole blood sample. Our data, in accordance with those obtained in a previous study conducted in extra-European countries, confirmed higher sensitivities for the smear-positive TB patients than for the smear-negative TB patients, and for pulmonary TB patients than for the extrapulmonary TB patients. Data obtained on the quality of antibody response in the ICT positive samples, might be used to improve the performance of the test.

Gamma interferon responses induced by a panel of recombinant and purified mycobacterial antigens in healthy, non-mycobacterium bovis BCG-vaccinated Malawian young adults

We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-gamma) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis (MPB70), M. bovis BCG (Ag85), and M. leprae (65 kDa, 35 kDa, and 18 kDa) in >600 non-M. bovis BCG-vaccinated young adults in the Karonga District of northern Malawi. IFN-gamma was measured by enzyme-linked immunosorbent assay (ELISA) in day 6 supernatants of diluted whole-blood cultures. The recombinant M. leprae 35-kDa and 18-kDa and purified native M. bovis BCG Ag85 antigens induced the highest percentages of responders, though both leprosy and bovine tuberculosis are now rare in this population. The M. tuberculosis antigens ESAT-6 and MPT64 and the M. bovis antigen MPB70 induced the lowest percentages of responders. One of the subjects subsequently developed extrapulmonary tuberculosis; this individual had a 15-mm-diameter reaction to the Mantoux test and responded to M. tuberculosis PPD, Ag85, MPT64, and ESAT-6 but not to any of the leprosy antigens. We conclude that in this rural African population, exposure to M. tuberculosis or M. bovis is much less frequent than exposure to environmental mycobacteria such as M. avium, which have antigens homologous to the M. leprae 35-kDa and 18-kDa antigens. M. tuberculosis ESAT-6 showed the strongest association with the size of the Mantoux skin test induration, suggesting that among the three M. tuberculosis antigens tested it provided the best indication of exposure to, or infection with, M. tuberculosis.

Serologic diagnosis of tuberculosis using a simple commercial multiantigen assay

SETTING

Seven primary health clinics and a pulmonary disease specialty clinic in Rio de Janeiro City, Brazil.

OBJECTIVE

To evaluate a commercial immunochromatographic test kit (ICT Tuberculosis; AMRAD-ICT; Sidney, Australia) employing five recombinant Mycobacterium tuberculosis proteins for the detection of pulmonary tuberculosis (TB).

DESIGN

Serology test results were compared with duplicate sputum microscopy and culture in 277 patients with symptomatic pulmonary disease (243 with pulmonary TB and 34 with nontuberculous disease). An additional 110 healthy control subjects were also tested.

RESULTS

The serology test was simple and rapid to perform and detected 64.2% of smear-positive and 46.3% of smear-negative TB patients overall. HIV co-infection was present in 15.3% of TB patients, and serology was much less sensitive (overall 27.6%) in this small group, as was microscopy (13.8%). Specificity of the serology test was 100% in healthy control subjects and 85.2% in the small number of control patients with pulmonary disease, including those with prior TB. Combined with microscopy, serology detected 72.8% of TB patients.

CONCLUSION

Depending on the population studied, multiantigen serologic tests for TB may be as sensitive as microscopy, but detect a different and overlapping subset of patients. The use of multiple antigens in this kit increased test sensitivity without significant loss of specificity. Bacille Calmette-Guérin vaccination and tuberculin sensitivity did not affect serology results. Estimating specificity in clinical use will require testing a much larger cohort of symptomatic patients with nontuberculous disease. The TB diagnostic performance of this group of antigens in HIV co-infected individuals was poor.

Evaluation of an in-house-developed radioassay kit for antibody detection in cases of pulmonary tuberculosis and tuberculous meningitis

A radioassay for the detection of antitubercular antibody has been developed. The technique involves the addition of (125)I-labeled Mycobacterium tuberculosis antigen as a tracer, diluted clinical sample (serum or cerebrospinal fluid [CSF]), and heat-inactivated Staphylococcus aureus to capture the antibody, incubation for 4 h, and quantitation of the amount of antibody present in the sample. A total of 330 serum samples from patients with pulmonary tuberculosis and 138 control serum samples from individuals who were vaccinated with M. bovis BCG and from patients with pulmonary disorders of nontubercular origin were analyzed. Also, 26 CSF samples from patients with tuberculous meningitis and 24 CSF samples as controls from patients with central nervous system disorders of nontuberculous origin were analyzed. Sensitivities of 80 and 73% were observed for patients with pulmonary tuberculosis and tuberculous meningitis, respectively, and specificities of 90 and 88% were seen for the two groups of patients, respectively. The sensitivity was lower, however, for human immunodeficiency virus-infected patients coinfected with M. tuberculosis. The control population could be differentiated from the patient population. This assay is rapid and user friendly and, with its good sensitivity and specificity, should benefit the population by providing diagnoses early in the course of disease and, hence, permit the early administration of appropriate chemotherapy.

Identification, molecular cloning, and evaluation of potential use of isocitrate dehydrogenase II of Mycobacterium bovis BCG in serodiagnosis of tuberculosis

Diagnosis of tuberculosis is time-consuming and requires infrastructures which are often not available in countries with high incidences of the disease. In the present study, an 82-kDa protein antigen was isolated by affinity chromatography and was identified by peptide mass fingerprinting as isocitrate dehydrogenase II, which is encoded by the icd2 gene of Mycobacterium bovis BCG. The icd2 gene of BCG was cloned by PCR, and the product of recombinant gene expression was purified and analyzed by two-dimensional polyacrylamide gel electrophoresis. The recombinant protein, named rICD2, was tested for its recognition by immunoglobulin G (IgG) antibodies from the sera of 16 patients with tuberculosis (TB) and 23 healthy individuals by Western blotting. The results showed that rICD2 is recognized by IgG antibodies from the sera of all TB patients tested at serum dilutions of > or = 1:640. At a serum dilution of 1:1,280, the sensitivity was 50% and the specificity was 86.9%. These results indicate that rICD2 might represent a candidate for use in a new assay for the serodiagnosis of TB.

A multi-antigen print immunoassay for the development of serological diagnosis of infectious diseases

Serological diagnosis of infectious diseases that generate a highly heterogeneous antibody repertoire, such as tuberculosis, requires tests based on cocktails of antigens. We describe a new method called multi-antigen print immunoassay (MAPIA) for cocktail-based serological diagnosis. The assay entails the application of antigen to nitrocellulose membranes by micro-aerosolization (printing), followed by antibody detection using standard chromogenic immunodevelopment. Cocktails of protein antigens of Mycobacterium tuberculosis tested by MAPIA were found to maintain the serological activity of each of their components. In contrast, the same cocktails tested by enzyme-linked immunosorbent assay (ELISA) had a serological activity that was lower than the sum of the activities of their components. Consequently, cocktail-based MAPIA attained the diagnostic sensitivity expected on the basis of single antigen results, while a significant loss of diagnostic sensitivity was observed with cocktail-based ELISA. Thus, the MAPIA format is superior to conventional ELISA for the serological diagnosis of infectious diseases characterized by heterogeneous antibody responses.

Cloning and expression of immunoreactive antigens from Mycobacterium tuberculosis

Four immunoreactive proteins, B.4, B.6, B.10, and B.M, with molecular weights ranging from 16,000 to 58,000, were observed from immunoblots of Mycobacterium tuberculosis total lysates screened with sera from individuals with active tuberculosis. These proteins were identified from microsequence analyses, and genes of proteins with the highest homology were PCR amplified and cloned into the pQE30 vector for expression studies. In addition, a 37.5-kDa protein, designated C17, was identified from a phage expression library of M. tuberculosis genomic DNA. Preliminary immunoblot assays indicated that these five resultant recombinant proteins could detect antibodies in individuals with active pulmonary and extrapulmonary tuberculosis. The overall ranges of sensitivities, specificities, positive predictive values, and negative predictive values for the recombinant antigens were 20 to 58, 88 to 100, 69 to 100, and 56 to 71%, respectively. The B.6 antigen showed preferential reactivity to antibodies in pulmonary compared to nonpulmonary tuberculosis serum specimens. All of these recombinant antigens demonstrated potential for serodiagnosis of tuberculosis.

Mass spectrometric identification of mtb81, a novel serological marker for tuberculosis

We have used serological proteome analysis in conjunction with tandem mass spectrometry to identify and sequence a novel protein, Mtb81, which may be useful for the diagnosis of tuberculosis (TB), especially for patients coinfected with human immunodeficiency virus (HIV). Recombinant Mtb81 was tested by an enzyme-linked immunosorbent assay to detect antibodies in 25 of 27 TB patients (92%) seropositive for HIV as well as in 38 of 67 individuals (57%) who were TB positive alone. No reactivity was observed in 11 of 11 individuals (100%) who were HIV seropositive alone. In addition, neither sera from purified protein derivative (PPD)-negative (0 of 29) nor sera from healthy (0 of 45) blood donors tested positive with Mtb81. Only 2 of 57 of PPD-positive individuals tested positive with Mtb81. Sera from individuals with smear-positive TB and seropositive for HIV but who had tested negative for TB in the 38-kDa antigen immunodiagnostic assay were also tested for reactivity against Mtb81, as were sera from individuals with lung cancer and pneumonia. Mtb81 reacted with 26 of 37 HIV(+) TB(+) sera (70%) in this group, compared to 2 of 37 (5%) that reacted with the 38-kDa antigen. Together, these results demonstrate that Mtb81 may be a promising complementary antigen for the serodiagnosis of TB.

A comparison of seven tests for serological diagnosis of tuberculosis

Seven serological tests, two immunochromatographic tests, ICT Tuberculosis and RAPID TEST TB, and five enzyme-linked immunosorbent assays, TUBERCULOSIS IgA EIA, PATHOZYME-TB complex, PATHOZYME-MYCO IgG, PATHOZYME-MYCO IgA, and PATHOZYME-MYCO IgM, were evaluated simultaneously with 298 serum samples from three groups of individuals: 44 patients with active tuberculosis, 204 controls who had undergone the Mantoux test (89 Mantoux test-positive and 115 Mantoux test-negative controls), and 50 anonymous controls. The sensitivities of the tests with sera from patients with active tuberculosis were poor to modest, ranging from 16 to 57%. All the tests performed equally with sera from subgroups of those with active tuberculosis, those with pulmonary (33 patients) versus extrapulmonary (11 patients) disease, and those who were smear positive (24 patients) versus smear negative (12 patients) (P > 0.05). The specificities of the tests ranged from 80 to 97% with sera from the Mantoux test controls and 62 to 100% with sera from the anonymous controls. The TUBERCULOSIS IgA EIA had the highest sensitivity (57%) with sera from patients with active tuberculosis, with a high specificity of 93% with sera from the Mantoux test controls, but a very poor specificity of 62% with sera from the anonymous controls. Overall, ICT Tuberculosis followed by PATHOZYME-MYCO IgG had the best performance characteristics, with sensitivities of 41 and 55%, respectively, with sera from patients with active tuberculosis and specificities of 96 and 89%, respectively, with sera from the Mantoux test controls and 88 and 90%, respectively, with sera from the anonymous controls. By combining all the test results, a maximum sensitivity of 84% was obtained, with reciprocal drops in specificities to 55 and 42% for the Mantoux test controls and anonymous controls, respectively. The best combination was that of ICT Tuberculosis and PATHOZYME-MYCO IgG, with a sensitivity of 66% and a specificity of 86% for the Mantoux test controls and a sensitivity and specificity of 78% for the anonymous controls. While a negative result by any one of these tests would be useful in helping to exclude disease in a population with a low prevalence of tuberculosis, a positive result may aid in clinical decision making when applied to symptomatic patients being evaluated for active tuberculosis.