Mtb-specific Antigens Research Articles

Clinical Usefulness of QuantiFERON TB-2G Test for the Early Diagnosis of Pulmonary <i>Mycobacterium kansasii</i> Disease

We encountered five cases of pulmonary Mycobacterium kansasii (MK) disease for which the QuantiFERON-TB Gold (QFT-2G) test was useful as a supportive diagnostic method. Because none of these patients could expectorate sputum, we ultimately confirmed the clinical diagnosis of pulmonary MK disease using 6- to 8-week cultures of bronchoscopic specimens (bronchoalveolar lavage fluid) according to the guidelines for nontuberculous mycobacterial disease due to American Thoracic Society/Infectious Diseases Society of America. The tuberculin skin test showed positive responses in all cases, and the QFT-2G test showed positive response for ESAT-6 only or CFP-10 only antigens. After it was proved that the result of Mycobacterium tuberculosis (MTB)-nucleic acid amplification was negative and the result of the QFT-2G test was positive, we started treatment (isoniazid, rifampicin and ethambutol) for suspected pulmonary MK disease based on clinical findings in all cases. The clinical effect was good and the interferon-γ response to MTB-specific antigen decreased with treatment for pulmonary MK disease. The QFT-2G test may be useful as a rapid supportive diagnostic method for pulmonary infection due to MK possessing the same MTB-specific antigen.

Evaluation of the Contribution of Major T Cell Subsets to IFN-γ Production in TB Infection by ELISPOT

Interferon gamma remains a key effector molecule that is still widely used as the most informative biomarker for screening human immune responses against tuberculosis, particularly in ELISPOT assays. We investigated the participation of CD4+ and CD8+ T lymphocytes in the PBMC responses to Mycobacterium tuberculosis (Mtb) specific antigens in 33 TB cases and 49 contacts. Responses to ESAT-6 were higher than CFP-10. There was no significant difference in responses to both Mtb antigens between cases and contacts. PBMCs response to ESAT-6 but not CFP-10 in cases was significantly reduced by depletion of CD4+ cells whereas CD8+ cell depletion had no impact. In conclusion, ESAT-6 is a more recognized antigen in this population, and CD4+ lymphocytes are the main participants in IFN-γ response by ELISPOT. Thus, a decline of CD4+ T lymphocytes below a critical level might affect the sensitivity of IFN-γ release assays for detecting Mtb infection.

IL-24 modulates IFN-γ expression in patients with tuberculosis

IL-24 is a newly described member of the IL-10 family. We previously demonstrated that PBMC from TB patients exhibited low levels of IL-24 and IFN-γ compared to subjects with latent tuberculosis infection (LTBI). In order to investigate the role of IL-24 in IFN-γ expression in TB patients, we stimulated PBMC from individuals with LTBI or TB patients with the Mtb-specific antigen, early secretory antigenic target-6 (ESAT-6) and measured cytokine expression using quantitative real-time PCR (qPCR). Exogenous IL-24 increased IFN-γ expression in PBMC obtained from TB patients while neutralization of IL-24 reduced IFN-γ expression in PBMC from subjects with LTBI. Exogenous IL-24 enhanced IFN-γ expression by increasing expression of IL-12 family cytokines, including IL-12α, IL-12β, IL-23α and IL-27, and by reducing FOXP3 expression in PBMC from TB patients. This is the first demonstration that IL-24 may play an important role in IFN-γ expression following infection with Mtb.

IL-9 is associated with an impaired Th1 immune response in patients with tuberculosis

Although a defective Th1 response has been demonstrated in patients infected with Mycobacterium tuberculosis ( Mtb), the mechanisms leading to this defect are not well understood. To study the immune response to Mtb infection, we stimulated PBMC from individuals with latent tuberculosis infection (LTBI) or patients with tuberculosis (TB) with the Mtb specific antigen early secretory antigenic target-6 (ESAT-6). mRNAs for a panel of cytokines were measured using quantitative real-time PCR (qPCR). PBMC from TB patients exhibited low levels of IFN-γ, IL-12α, IL-12β, and IL-23 mRNA but high levels of IL-9 mRNA. Sera from TB patients blocked the differentiation and function of dendritic cells from TST negative (TST−) donors. Exogenous IL-9 reduced IFN-γ mRNA expression in PBMC from LTBI by 30% ( n = 4) and neutralization of IL-9 restored the IFN-γ mRNA expression in PBMC from TB patients by 66% ( n = 8). Thus, increased expression of IL-9 may contribute to the development of TB.

Diagnosis of Mycobacterium tuberculosis Infection using Ex-vivo interferon-gamma Assay

Until recently, the tuberculin skin test (TST) has been the only tool available for diagnosing a latent TB infection. However, the development of new diagnostic tools, using the Mycobacterium tuberculosis(MTB)-specific early secreted antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) antigens, should improve the control of tuberculosis (TB) by allowing a more accurate identification of a latent TB infection (LTBI). Antigen-specific interferon-gamma (IFN-γ) assays have greater specificity in BCG-vaccinated individuals, and as less biased by nontuberculous mycobacterial infections. Many comparative studies have suggested that those assays have a higher specificity than the TST, and the sensitivity of these assays are expected to remarkably improved if more MTB-specific antigens can become available. Nevertheless, the major obstacle to the widespread use of these tests is the limited financial resources. Similar to other diagnostic tests, the predictive value of IFN-γ assays depends on the prevalence of a MTB infection in the population being tested. Therefore, prospective studies will be meeded to establish the applicability of these new assays at multiple geographic locations among patients of different ethnicities, and to determine if the IFN-γ responses can indicate those with a high risk of progressing to active TB. (Tuberc Respir Dis 2006; 60: 497-509)