Sero-diagnosis of tuberculosis with A60 antigen enzyme-linked immunosorbent assay: failure in HIV-infected individuals in Ghana

A toolbox for tuberculosis (TB) diagnosis: an Indian multi-centric study (2006-2008); evaluation of serological assays based on PGL-Tb1 and ESAT-6/CFP10 antigens for TB diagnosis

BACKGROUND

The aim of this multi-centric prospective study in India was to assess the accuracy of a serological test as an additional tool for diagnosing active tuberculosis (ATB). In particular, an assay based on ELISA using a phenolic glycolipid (PGL-Tb1) or a fusion protein (ESAT-6/CFP10) was compared to the tuberculin skin test (TST) and the microbiological results according to HIV status.

METHODS

Individuals with and without ATB and HIV infection were enrolled. Serology and TST results were analyzed per se and in combination with the microbiological data.

RESULTS

Among the 778 ATB patients, 102 were HIV-infected, 316 HIV-uninfected and 360 had an HIV-unknown status. Of the 945 non-ATB subjects, 559 were at low risk (community adults) and 386 at high risk of M. tuberculosis exposure. Among those with ATB, the sensitivity of ELISA-PGL-Tb1 for ATB was higher than that of ELISA-ESAT-6/CFP10, both in HIV-infected (72.3% versus 63.7%, p = 0.29) and HIV-uninfected/HIV-unknown groups (40.5% versus 28.6%; p<0.0001), whereas the specificity was around 91% for both tests. Sensitivity for ATB increased when the results of the two ELISA were combined, reaching 75.5% in the HIV-infected and 50.9% in the group of HIV-uninfected/HIV-unknown ATB, with a significant decrease of the global specificity (83.9%). Analyzing the ELISA results with the microbiological results, we observed that the sensitivity of both serology tests was independent of the ATB patients' smear microscopy (SM) status and grade. Combining the results of SM with both ELISA, the detection of ATB patients significantly increased (p<0.0001), particularly in those with extrapulmonary TB (up to 45.1%) or HIV infection (up to 83.3%). No significant association was observed between TST and serology results.

CONCLUSIONS

In this prospective multi-centric study, the combination of two rapid tests, such as SM and serology, might be useful in detecting ATB, especially in HIV-infected patients.

Improved diagnosis of tuberculosis in HIV-positive patients using RD1-encoded antigen CFP-10

OBJECTIVE

The present study was aimed at determining the serodiagnostic potential of 38-kDa (Rv0934, Mycobacterium tuberculosis complex-specific antigen) and CFP-10 (Rv3874, RD1 antigen) antigens among HIV-positive and HIV-negative patients with pulmonary TB.

METHODS

The diagnostic potential of native 38-kDa (n38-kDa) and recombinant CFP-10 (rCFP-10) antigens was ascertained in terms of sensitivity and specificity using an indirect ELISA. The study included 508 HIV-seronegative TB patients (TB), 54 HIV-seropositive TB patients (HIV-TB), 30 HIV-positive patients without TB (HIV), and 256 controls.

RESULTS

In HIV-TB, the sensitivities for individual antigens ranged from 14.8% to 31.5% and the specificity was >98% for IgG. When IgA results were added to IgG, the sensitivity increased to 25.9% for 38-kDa and 57.4% for CFP-10; specificity changed to 97.5% for 38-kDa and 98.1% for CFP-10. The combined results of both the antigens gave 59.3% sensitivity and 95.6% specificity. In TB, the sensitivity was 82.8% when the antigen results were combined. None of the HIV-infected controls showed positivity for IgG to either of the two antigens.

CONCLUSION

Use of CFP-10 enhances the sensitivity of 38-kDa, and therefore the 38-kDa and CFP-10 antigen combination can be a diagnostic marker in HIV-TB.

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

Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a major world disease, with approximately 9 million new cases each year. Identification and treatment of active disease are essential for TB control. Serology may offer increased detection of active disease in patients with a positive tuberculin skin test (TST) or QuantiFERON-TB (QFT-G). The InBios Active TbDetect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA), IBL M. tuberculosis IgG ELISA, and Anda Biologics TB ELISAs were evaluated for the ability to detect M. tuberculosis antibodies in patients with active disease. Agreement, sensitivity, and specificity for each ELISA were determined and compared to those for culture or amplified direct detection and M. tuberculosis low-risk control patients. The InBios Active TbDetect ELISA had an agreement of 96.2%, a sensitivity of 83.3%, and a specificity of 98.9%. The IBL M. tuberculosis ELISA had an agreement of 84.0%, a sensitivity of 5.6%, and a specificity of 100.0%. The agreement, sensitivity, and specificity of the Anda Biologics TB ELISA were 74.2%, 83.3%, and 72.0%, respectively. The sensitivity for detecting M. tuberculosis antibodies in human immunodeficiency virus-associated TB was 50% for both the InBios Active TbDetect ELISA and the Anda Biologics TB ELISA and 0% for the IBL M. tuberculosis ELISA. The positivity rates for InBios Active TbDetect ELISA, IBL M. tuberculosis ELISA, and Anda Biologics TB ELISA in latently infected individuals positive by TST and/or QFT-G were 5.1%, 0.0%, and 30.8%, respectively. It can be concluded that the InBios Active TbDetect IgG ELISA is superior to the other ELISAs in accurately detecting active TB.

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

Background

Simple biomarkers are required to identify TB in both HIV⁻TB⁺ and HIV⁺TB⁺ patients. Earlier studies have identified the M. tuberculosis Malate Synthase (MS) and MPT51 as immunodominant antigens in TB patients. One goal of these investigations was to evaluate the sensitivity and specificity of anti-MS and –MPT51 antibodies as biomarkers for TB in HIV⁻TB⁺ and HIV⁺TB⁺ patients from a TB-endemic setting. Earlier studies also demonstrated the presence of these biomarkers during incipient subclinical TB. If these biomarkers correlate with incipient TB, their prevalence should be higher in asymptomatic HIV⁺ subjects who are at a high-risk for TB. The second goal was to compare the prevalence of these biomarkers in asymptomatic, CD4⁺ T cell-matched HIV⁺TB⁻ subjects from India who are at high-risk for TB with similar subjects from US who are at low-risk for TB.

Methods and Results

Anti-MS and -MPT51 antibodies were assessed in sera from 480 subjects including PPD⁺ or PPD⁻ healthy subjects, healthy community members, and HIV⁻TB⁺ and HIV⁺TB⁺ patients from India. Results demonstrate high sensitivity (∼80%) of detection of smear-positive HIV⁻TB⁺ and HIV⁺TB⁺ patients, and high specificity (>97%) with PPD⁺ subjects and endemic controls. While ∼45% of the asymptomatic HIV⁺TB⁻ patients at high-risk for TB tested biomarker-positive, >97% of the HIV⁺TB⁻ subjects at low risk for TB tested negative. Although the current studies are hampered by lack of knowledge of the outcome, these results provide strong support for the potential of these biomarkers to detect incipient, subclinical TB in HIV⁺ subjects.

Conclusions

These biomarkers provide high sensitivity and specificity for TB diagnosis in a TB endemic setting. Their performance is not compromised by concurrent HIV infection, site of TB and absence of pulmonary manifestations in HIV⁺TB⁺ patients. Results also demonstrate the potential of these biomarkers for identifying incipient subclinical TB in HIV⁺TB⁻ subjects at high-risk for TB.

Commercial serological antibody detection tests for the diagnosis of pulmonary tuberculosis: a systematic review

BACKGROUND

The global tuberculosis epidemic results in nearly 2 million deaths and 9 million new cases of the disease a year. The vast majority of tuberculosis patients live in developing countries, where the diagnosis of tuberculosis relies on the identification of acid-fast bacilli on unprocessed sputum smears using conventional light microscopy. Microscopy has high specificity in tuberculosis-endemic countries, but modest sensitivity which varies among laboratories (range 20% to 80%). Moreover, the sensitivity is poor for paucibacillary disease (e.g., pediatric and HIV-associated tuberculosis). Thus, the development of rapid and accurate new diagnostic tools is imperative. Immune-based tests are potentially suitable for use in low-income countries as some test formats can be performed at the point of care without laboratory equipment. Currently, dozens of distinct commercial antibody detection tests are sold in developing countries. The question is "do they work?"

METHODS AND FINDINGS

We conducted a systematic review to assess the accuracy of commercial antibody detection tests for the diagnosis of pulmonary tuberculosis. Studies from all countries using culture and/or microscopy smear for confirmation of pulmonary tuberculosis were eligible. Studies with fewer than 50 participants (25 patients and 25 control participants) were excluded. In a comprehensive search, we identified 68 studies. The results demonstrate that (1) overall, commercial tests vary widely in performance; (2) sensitivity is higher in smear-positive than smear-negative samples; (3) in studies of smear-positive patients, Anda-TB IgG by enzyme-linked immunosorbent assay shows limited sensitivity (range 63% to 85%) and inconsistent specificity (range 73% to 100%); (4) specificity is higher in healthy volunteers than in patients in whom tuberculosis disease is initially suspected and subsequently ruled out; and (5) there are insufficient data to determine the accuracy of most commercial tests in smear microscopy-negative patients, as well as their performance in children or persons with HIV infection.

CONCLUSIONS

None of the commercial tests evaluated perform well enough to replace sputum smear microscopy. Thus, these tests have little or no role in the diagnosis of pulmonary tuberculosis. Lack of methodological rigor in these studies was identified as a concern. It will be important to review the basic science literature evaluating serological tests for the diagnosis of pulmonary tuberculosis to determine whether useful antigens have been described but their potential has not been fully exploited. Activities leading to the discovery of new antigens with immunodiagnostic potential need to be intensified.

B-cell immune responses in HIV positive and HIV negative patients with tuberculosis evaluated with an ELISA using a glycolipid antigen

The diagnostic value of the PGL-Tb1 enzyme-linked immunosorbent assays (ELISA) was established following a survey study using sera from 220 Tuberculosis patients (including 69 HIV coinfected) and 324 controls. A higher percentage (76.8%) of the HIV-seropositive compared to the HIV-seronegative (58.9%) TB patients were ELISA positive (p=0.02) with a specificity of 94%. In HIV-positive TB patients, ELISA sensitivity was identical for all sites of disease and antibody levels were not affected by the CD4+ counts, PPD results, age or bacterial yield. Combining data for both the smear microscopy and ELISA maximized sensitivity. The kinetics of anti-PGL-Tb1 antibody was evaluated in cohort studies using sera collected before, during and after treatment for clinical TB for 79 TB patients (including 39 HIV coinfected). Statistically significant ELISA signals were observed in 51.3% of HIV-seropositive TB patients prior to the diagnosis of clinical TB and elevated antibody levels persisting 18 months after the end of antituberculous chemotherapy. Asymptomatic development of antibody also occurred in 22.7% of a cohort of 44 HIV-positive patients with a high risk of tuberculosis, but no correlation was found between persisting elevated antibody levels and progression to active disease. This antibody response in absence of disease, might reflect the control of an incipient tuberculosis infection by antituberculous prophylaxis or through an improved protective immune response associated with antiretroviral therapy.

Can we control tuberculosis in high HIV prevalence settings?

The overlap between the epidemiology of HIV and tuberculosis and consequent rapid rise in numbers of patients with tuberculosis in many African countries has put a huge burden on health systems. The stigma of HIV has increased the existing stigma surrounding tuberculosis. There are three mechanisms by which we may reduce the number of cases of tuberculosis in a community: reducing transmission of tuberculosis, reducing reactivation of latent tuberculosis infection and reducing HIV transmission. Reinforcing the existing health service to find more cases, active case-finding in communities or enhanced case-finding in specific groups will reduce transmission of tuberculosis. However, health services that find it difficult to find cases efficiently will also find it difficult to support patients throughout treatment to achieve a cure. Partnership with traditional healers, community-based organizations and private practitioners could reduce this burden. Reactivation of tuberculosis among people living with HIV can be reduced by tuberculosis preventive therapy or by antiretroviral therapy. Programmes that identify people living with HIV can also implement enhanced tuberculosis case-finding increasing the benefits of the programme. However, the impact of widespread use of antiretroviral therapy may be to increase the number of people in a community who are mildly immunocompromised and the incidence of tuberculosis at a community level might rise. Any strategy that successfully reduces HIV transmission will benefit tuberculosis control, since around a third of all HIV-positive individuals will develop tuberculosis before they die. To control tuberculosis in high HIV prevalence settings, we must strengthen health systems to include not only expansion of the DOTS strategy but also full-blooded implementation of voluntary counselling and testing, enhanced and active tuberculosis case-finding, preventive therapy and better care for people living with HIV including antiretroviral therapy. The approach needed to control tuberculosis needs also to be integrated into broader development and poverty reduction goals.

Isotype-specific anti-38 and 27 kDa (mpt 51) response in pulmonary tuberculosis with human immunodeficiency virus coinfection

There is a need for rapid diagnostic methods to identify tuberculosis among human immunodeficiency virus-positive cases (HIV-TB). This study evaluated the serodiagnostic potential of the native 38 kDa and recombinant 27 kDa (mpt 51) antigens of Mycobacterium tuberculosis purified in the laboratory, when applied to HIV-TB patients. The antibody response was studied using enzyme-linked immunosorbent assays (ELISA). In the HIV-TB group, anti-38 kDa antibody of the immunoglobulin G (IgG), IgA and IgM isotypes was found in 38%, 43% and 7%, of patients, respectively. Antibodies to the 27 kDa antigen occurred in 50%, 31%, and 1%, for IgG, IgA and IgM, respectively. The sensitivity increased upon combination of the results of IgG and IgA isotypes for each of the antigens, without compromising specificity. When the results were analysed based on the smear positivity, 71-78% and 54-69% were positive among smear-positive and smear-negative HIV-TB cases, respectively. A higher sensitivity (71% and 69%) was obtained using the 27 kDa antigen. The use of both antigens offered a sensitivity of 82% in smear-positive and 69% in smear-negative cases. There was no difference in antibody response among the HIV-TB cases, related to CD4 counts. Thus, the combination of the 38 and 27 kDa (mpt 51) antigens proved to be of diagnostic utility in HIV-TB, irrespective of the severity of immunosuppression, in smear-positive and smear-negative TB.

Comparison of A60 and three glycolipid antigens in an ELISA test for tuberculosis

OBJECTIVES: To compare the diagnostic usefulness in tuberculosis of the serodiagnostic enzyme-linked immunosorbent assay (ELISA) kit A60 (Anda Biologicals, Strasbourg, France) and of our domestic ELISA based on three purified cell wall glycolipid antigens. METHODS: The presence and concentrations of IgG and IgM anti-A60 antibodies and anti-LOS, anti-DAT and anti-PGLTb1 antibodies against the glycolipid antigens were determined by ELISA in 50 HIV-seronegative and 46 HIV-seropositive patients, with documented active tuberculosis. The specificity of these ELISAs was determined with use of sera from 50 healthy blood donors, 29 patients with non-mycobacterial pulmonary diseases and 24 HIV-positive patients with disseminated Mycobacterium avium infection. RESULTS: With a calculated cut-off for each antigen and immunoglobulin that gave a specificity higher than or equal to 98%, the cumulative ELISA results showed that only 36.5% of the patients with tuberculosis had a positive response in the A60 test, as compared with 84.4% who showed a response to the three glycolipid antigens (p<0.001). This striking difference persisted when the cumulative sensitivities were calculated according to the HIV status of the patients and the localization of tuberculosis. The anti-A60 antibody (IgG and IgM) levels and the degree of sensitivity of the ELISA for detection of A60 antigen were always lower in HIV-positive patients with pulmonary and extrapulmonary tuberculosis than in HIV-negative patients with tuberculosis. The sensitivity of A60 ELISA was further decreased in HIV-positive patients with low CD4+ lymphocytes counts, in contrast to the results with the three glycolipid antigens. CONCLUSIONS: These results show the limitations of the A60 ELISA, and confirm the potencies of the glycolipid antigens in serodiagnosis of tuberculosis in HIV-positive and HIV-negative patients.

Analysis of the immunological humoral response to Mycobacterium tuberculosis glycolipid antigens (DAT, PGLTb1) for diagnosis of tuberculosis in HIV-seropositive and -seronegative patients

Using an enzyme immunoassay (EIA) test, the concentrations of IgG antibodies against 2,3 diacyl trehalose (DAT) and phenolic glycolipid Tb1 (PGLTb1) were measured in the sera of 153 patients with active tuberculosis, 50 of whom were coinfected with HIV, and in the sera of 152 healthy blood donors, 149 asymptomatic HIV-seropositive patients, 12 HIV-seronegative patients with conditions simulating tuberculosis, 23 HIV-seropositive patients with disseminated infection caused by mycobacteria other than tuberculosis and 24 HIV-seropositive patients with pulmonary disease from whom mycobacteria was not isolated in culture. A slightly lower percentage (74%) of the HIV-seropositive than the HIV-seronegative (77%) tuberculosis patients were positive for anti-DAT and anti-PGLTb1 IgG antibodies, with a specificity ranging from 91 to 95%. There was no significant difference between EIA sensitivity in smear-positive and smear-negative patients with pulmonary tuberculosis for all HIV immune statuses and sites of disease (pulmonary vs. extrapulmonary). In HIV-seropositive patients, however, sensitivity was always lower for disseminated tuberculosis than for localized tuberculosis. Combining data for both the smear test and the EIA maximized sensitivity. The main value of the EIA test could be to provide early complementary information by antibody detection in patients with tuberculosis, particularly those with a negative smear test.