Clinical application of a rapid lung-orientated immunoassay in individuals with possible tuberculosis

Clinical Aspects of Adult Tuberculosis

Tuberculosis (TB) in adults can present in a large number of ways. The lung is the predominant site of TB. Primary pulmonary TB should be distinguished from postprimary pulmonary TB, which is the most frequent TB manifestation in adults (70%-80% cases). Cough is common, although the chest radiograph often raises suspicion of disease. Sputum sampling is a key step in the diagnosis of TB, and invasive procedures such as bronchoscopy may be necessary to achieve adequate samples for diagnosis. Extrapulmonary involvement, which may present many years after exposure, occurs in a variable proportion of cases (20%-45%). This reflects the country of origin of patients and also the frequency of associated human immunodeficiency virus (HIV) coinfection. In the latter case, the presentation of TB is often nonspecific, and care needs to be taken to not miss the diagnosis. Anti-TB therapy should be given in line with proven (or assumed) drug resistance. In extrapulmonary TB, adjunctive therapeutic measures may be indicated; although in all cases, support is often required to ensure that people are able to complete treatment with minimal adverse events and maximal adherence to the prescribed regimen, and so reduce risk of future disease for themselves and others.

HIV-1 infection of macrophages dysregulates innate immune responses to Mycobacterium tuberculosis by inhibition of interleukin-10

Human immunodeficiency virus (HIV)-1 and Mycobacterium tuberculosis (M. tuberculosis) both target macrophages, which are key cells in inflammatory responses and their resolution. Therefore, we tested the hypothesis that HIV-1 may modulate macrophage responses to coinfection with M. tuberculosis. HIV-1 caused exaggerated proinflammatory responses to M. tuberculosis that supported enhanced virus replication, and were associated with deficient stimulus-specific induction of anti-inflammatory interleukin (IL)-10 and attenuation of mitogen-activated kinase signaling downstream of Toll-like receptor 2 and dectin-1 stimulation. Our in vitro data were mirrored by lower IL-10 and higher proinflammatory IL-1β in airway samples from HIV-1-infected patients with pulmonary tuberculosis compared with those with non-tuberculous respiratory tract infections. Single-round infection of macrophages with HIV-1 was sufficient to attenuate IL-10 responses, and antiretroviral treatment of replicative virus did not affect this phenotype. We propose that deficient homeostatic IL-10 responses may contribute to the immunopathogenesis of active tuberculosis and propagation of virus infection in HIV-1/M. tuberculosis coinfection.

[Bacteriological tests for tuberculosis]

This review describes current developments for the bacteriological diagnosis of active tuberculosis. It deals mainly with molecular methods, describing their performance and how they can be integrated into more traditional diagnostic approaches. At present, microscopic examination and culture are still essential for the diagnosis of TB and to guide therapeutic decisions. Nucleic acid amplification and line probe assays speed up the identification and susceptibility testing of mycobacteria in AFB smear positive specimens or in culture. They are also efficient for comparison of M. tuberculosis strains with each other (genotyping). On the other hand, at present, molecular tests are not applicable for diagnosis in smear negative specimens and even less so for diagnosis of culture-negative tuberculosis. The use of serology for antibody/antigen detection is not useful and it is not appropriate to assays based on the release of interferon-γ release as they are currently available. Notable progress has been made but more sensitive diagnostic tests for TB are still urgently needed.

Flow cytometric measurements of TB-specific T cells comparing with QuantiFERON-TB gold

BACKGROUND

Interferon-gamma (IFN-gamma) release assays and the detection of IFN-gamma synthesis in the cytoplasm of activated CD4+ T cells by flow cytometry have recently been used for tuberculosis (TB) diagnosis. The aim of this study was to compare the performance of IFN-gamma assay between ELISA (QuantiFERON-TB Gold, QFT) and intracellular cytokine flow cytometry (ICCFC), and to investigate the significance of an optimal gating strategy in ICCFC.

METHODS

The CD4+ T cell response to TB antigens was measured using the intracellular cytokine staining technique and four color FC (CD3, CD4, IFN-gamma, and tumor necrosis factor-alpha (TNF-alpha)) on whole blood samples. The results were compared with those of QFT.

RESULTS

Regarding sensitivity in the TB group, patients in the QFT positive TB group (N = 22) were all ICCFC positive and 9 patients (64%) in the QFT negative TB group (N = 14) were ICCFC positive. In all test tubes (N = 72), sensitivity of "targeted" gating for TNF-alpha+ IFN-gamma+ CD4+ T cells was significantly higher than customary gating (72%, 54%, respectively, P = 0.001).

CONCLUSIONS

The diagnostic sensitivity of ICCFC was further confirmed to be much higher than that of QFT. In the ICCFC analysis, TNF-alpha+ IFN-gamma+ CD4+ T cells should be sequentially gated through appropriately defined regions, minimizing interferents and reflecting characteristics of light scatter and marker expressions of CD4+ T cells activated by TB antigens.

Exploring the immune response against Mycobacterium tuberculosis for a better diagnosis of the infection

Tuberculosis (TB) still represents a monumental problem, with more than two million deaths every year worldwide. The current diagnostics for TB offer sub-optimal accuracy both for the active and the latent form of infection and are often based on technologies unaffordable in low-income settings. The tuberculin skin test was the first diagnostic based on an acquired immune response towards Mycobacterium tuberculosis (MTB). Advances in molecular and cellular biology and the elucidation of the mechanisms governing the relation between MTB and the human immune system form the basis for new and more accurate assays, potentially able to fill the gaps and limits of classical diagnostics. However, the process of validating new tests is still complex and hampered by specific questions regarding TB immunology and natural history. We present here a summary of the current approaches to validate new diagnostics based on the detection of immunological biomarkers of TB infection.

Diagnosis of abdominal tuberculosis by T-cell-based assays on peripheral blood and peritoneal fluid mononuclear cells

OBJECTIVES

Diagnosing abdominal tuberculosis (TB) remains a challenge. A recently developed RD-1 gene-based assay for diagnosing tuberculosis infection shows promising results. We evaluated the diagnostic usefulness of this assay compared with conventional tests in patients with suspected abdominal TB in clinical practice.

METHODS

All patients with suspected abdominal TB were prospectively enrolled in a tertiary hospital during a 1-year period. In addition to the conventional tests for diagnosing TB, the IFN-gamma-producing T-cell response to ESAT-6 and CFP-10 by ELISPOT assay using peripheral blood mononuclear cells (PBMC) and peritoneal fluid mononuclear cells (PF-MC) were performed.

RESULTS

Forty eight patients with suspected abdominal TB were enrolled. Of these patients, 30 (63%) were classified as abdominal TB including 14 TB peritonitis (12 confirmed + 1 probable + 1 possible), 6 abdominal TB lymphadenitis (3 confirmed + 3 probable), 4 hepatic TB (3 confirmed + 1 possible), 2 intestinal TB (1 confirmed + 1 probable), 3 renal TB (1 confirmed + 2 probable), and 1 pancreatic TB (1 confirmed). Eighteen (38%) were classified as not TB. ELISPOT assay using PBMC was performed on samples from all 48 subjects. The sensitivity and specificity of the PBMC ELISPOT assay were 89% (95% CI, 71-98%) and 78% (95% CI, 52-94%), respectively. In the 11 patients in whom PF-MC ELISPOT assay was performed, it was positive in 5 of 6 patients with TB peritonitis, and negative in all 5 patients with not TB.

CONCLUSIONS

The ELISPOT assay using PBMC and PF-MC is a useful adjunct to the current tests for diagnosing abdominal TB.

Bronchoalveolar lavage enzyme-linked immunospot for a rapid diagnosis of tuberculosis: a Tuberculosis Network European Trialsgroup study

RATIONALE

The rapid diagnosis of pulmonary tuberculosis (TB) is difficult when acid fast bacilli (AFB) cannot be detected in sputum smears.

OBJECTIVES

Following a proof of principle study, we examined in routine clinical practice whether individuals with sputum AFB smear-negative TB can be discriminated from those with latent TB infection by local immunodiagnosis with a Mycobacterium tuberculosis-specific enzyme-linked immunospot (ELISpot) assay.

METHODS

Subjects suspected of having active TB who were unable to produce sputum or with AFB-negative sputum smears were prospectively enrolled at Tuberculosis Network European Trialsgroup centers in Europe. ELISpot with early-secretory-antigenic-target-6 and culture-filtrate-protein-10 peptides was performed on peripheral blood mononuclear cells (PBMCs) and bronchoalveolar lavage mononuclear cells (BALMCs). M. tuberculosis-specific nucleic acid amplification (NAAT) was performed on bronchoalveolar lavage fluid.

MEASUREMENTS AND MAIN RESULTS

Seventy-one of 347 (20.4%) patients had active TB. Out of 276 patients who had an alternative diagnosis, 127 (46.0%) were considered to be latently infected with M. tuberculosis by a positive PBMC ELISpot result. The sensitivity and specificity of BALMC ELISpot for the diagnosis of active pulmonary TB were 91 and 80%, respectively. The BALMC ELISpot (diagnostic odds ratio [OR], 40.4) was superior to PBMC ELISpot (OR, 10.0), tuberculin skin test (OR, 7.8), and M. tuberculosis specific NAAT (OR, 12.4) to diagnose sputum AFB smear-negative TB. In contrast to PBMC ELISpot and tuberculin skin test, the BALMC ELISpot was not influenced by previous history of TB.

CONCLUSIONS

Bronchoalveolar lavage ELISpot is an important advancement to rapidly distinguish sputum AFB smear-negative TB from latent TB infection in routine clinical practice.

How flow cytometry is changing the study of TB immunology and clinical diagnosis

The application of flow cytometry has hugely advanced the field of tuberculosis (TB) across all areas of research ranging from diagnostic tests to understanding the underlying immunology. As cellular responses are understood to be the mainstay of the immune response in the control of TB it is very likely that polychromatic flow will become the tool of choice for assessing the effects of vaccination. Results are particularly encouraging in this area. The development of a new type of diagnostic test, a prototype of which has been reported, may be the spin-off of a broad and systematic approach to understanding and profiling the T-cell response to TB. It is obvious that flow cytometry will not be able to address all research questions in the field of TB. However, its enormous flexibility as a technology will make it the tool of choice in many situations. An ever increasing availability of flow cytometers, even in resource-poor countries, will rapidly change the face of TB research and management in the years ahead.

Impaired antigen-specific CD4(+) T lymphocyte responses in cavitary tuberculosis

The clinical outcome in tuberculosis is determined by the host-pathogen interaction. Successful immune responses result in granulomas and curtailment of disease, whilst cavitation indicates a failing immune response. We sought to investigate the mechanisms involved in these processes. Fourteen patients with confirmed pulmonary tuberculosis underwent bronchoalveolar lavage with washings from areas of cavitation, or pulmonary infiltrates and also from the contra-lateral radiologically normal lung. Flow cytometry was utilised to determine both the leukocyte populations and the Mycobacterium antigen-specific T cell component of the response. Cavitation was associated with local neutrophilia and relative lymphopenia, whereas lymphocytosis and lower levels of granulocytes were detected from areas of pulmonary infiltrates and also from radiologically unaffected lobes. The Mycobacterium-specific T cell response from cavitary sites was significantly lower when compared to the radiologically normal lobes in the same individuals (p=0.003). By contrast, the Mycobacterium-specific T cell responses from areas of infiltrates were remarkably similar to paired responses from the radiologically unaffected lung (p=0.45). These results confirm the selective accumulation of Mycobacterium-specific lymphocytes in the lung in general though they also demonstrate that this is diminished in cavities. It remains unclear whether neutrophilia is a cause, or a result of cavitation in pulmonary tuberculosis.

Diagnosis of central nervous system tuberculosis by T-cell-based assays on peripheral blood and cerebrospinal fluid mononuclear cells

In active tuberculosis (TB), Mycobacterium tuberculosis-specific T cells are compartmentalized more to the site of infection than to the circulating blood. Therefore, an M. tuberculosis-specific enzyme-linked immunospot (ELISPOT) assay with samples from the site of infection may permit a more sensitive or specific diagnosis of active central nervous system (CNS) TB than that achieved by the assay with blood alone. Therefore, we prospectively evaluated the usefulness of circulating and compartmentalized mononuclear cell (MC; i.e., peripheral blood mononuclear cell [PBMC] and cerebrospinal fluid [CSF] MC)-based ELISPOT assays (i.e., the T-SPOT.TB test) for the diagnosis of active TB in patients with suspected CNS TB. The clinical categories of CNS TB were classified as described previously (G. E. Thwaites, T. T. Chau, K. Stepniewska, N. H. Phu, L. V. Chuong, D. X. Sinh, N. J. White, C. M. Parry, and J. J. Farrar, Lancet 360:1287-1292, 2002). Thirty-seven patients with suspected CNS TB were enrolled over a 12-month period. Of these, 31 (84%) showed clinical manifestations of suspected TB meningitis and 6 (16%) gave indications of intracranial tuberculoma with disseminated TB. The final clinical categories of the 37 patients with suspected CNS TB were as follows: 12 (32%) were classified as having CNS TB (7 with confirmed TB, 3 with probable TB, and 2 with possible TB) and 25 (68%) were classified as not having active TB. The sensitivity and specificity of the PBMC ELISPOT assay were 91% (95% confidence interval [CI], 59% to 100%) and 63% (95% CI, 41% to 81%), respectively. By comparison, the sensitivity and specificity of the CSF MC ELISPOT assay were 75% (95% CI, 19% to 99%) and 75% (95% CI, 43% to 95%), respectively. When the ratio of the CSF MC ELISPOT assay results to the PBMC ELISPOT results was 2 or more, the sensitivity and specificity were 50% (95% CI, 7% to 93%) and 100% (95% CI, 74% to 100%), respectively. The ELISPOT assay with PBMCs and CSF MCs is a useful adjunct to the current tests for the diagnosis of CNS TB.

Rapid diagnosis of smear-negative tuberculosis using immunology and microbiology with induced sputum in HIV-infected and uninfected individuals

Rationale and Objectives

Blood-based studies have demonstrated the potential of immunological assays to detect tuberculosis. However lung fluid sampling may prove superior as it enables simultaneous microbiological detection of mycobacteria to be performed. Until now this has only been possible using the expensive and invasive technique of broncho-alveolar lavage. We sought to evaluate an immunoassay using non-invasive induced-sputum to diagnose active tuberculosis.

Methods and Results

Prospective cohort study of forty-two spontaneous sputum smear-negative or sputum non-producing adults under investigation for tuberculosis. CD4 lymphocytes specific to purified-protein-derivative of Mycobacterium tuberculosis actively synthesising interferon-gamma were measured by flow cytometry and final diagnosis compared to immunoassay using a cut-off of 0.5%. Sixteen subjects (38%) were HIV-infected (median CD4 count [range] = 332 cells/µl [103–748]). Thirty-eight (90%) were BCG-vaccinated. In 27 subjects diagnosed with active tuberculosis, the median [range] percentage of interferon-gamma synthetic CD4+ lymphocytes was 2.77% [0–23.93%] versus 0% [0–2.10%] in 15 negative for active infection (p<0.0001). Sensitivity and specificity of the immunoassay versus final diagnosis of active tuberculosis were 89% (24 of 27) and 80% (12 of 15) respectively. The 3 positive assays in the latter group occurred in subjects diagnosed with quiescent/latent tuberculosis. Assay performance was unaffected by HIV-status, BCG-vaccination or disease site. Combining this approach with traditional microbiological methods increased the diagnostic yield to 93% (25 of 27) alongside acid-fast bacilli smear and 96% (26 of 27) alongside tuberculosis culture.

Conclusions

These data demonstrate for the first time that a rapid immunological assay to diagnose active tuberculosis can be performed successfully in combination with microbiological methods on a single induced-sputum sample.