Diagnosis of active and latent tuberculosis (TB) remains a challenge; however, over the last few years, a new approach based on detecting Mycobacterium tuberculosis-specific T cells has shown much promise. In particular, there is substantial published evidence showing that the detection of ESAT-6- and CFP-10-specific T cells using the ex vivo enzyme-linked immunospot technique is a marked improvement over the existing tuberculin skin test. This technique, which detects gamma interferon-producing T cells, is now available as the commercial assay T SPOT-TB (Oxford Immunotec, Oxford, UK). In the present study, the usefulness of the T SPOT-TB test for diagnosis of TB in "real-world" clinical practice was investigated. Ninety patients of a southern German referral centre for TB with confirmed or suspected TB were randomly selected for this study. The results of the T SPOT-TB test were compared with the results of conventional diagnostic tools. The T SPOT-TB test detected 70 of 72 patients with pulmonary or extrapulmonary TB, indicating a sensitivity of 97.2% (95% confidence interval, 90.3-99.7). For 45 of these patients, tuberculin skin test (TST) results were also available. Only 40 (89%) of these 45 patients were positive in the TST compared to all 45 (100%) in the T SPOT-TB test (p=0.056). Among 12 of 90 patients for whom active TB disease was ruled out, the T SPOT-TB test was negative for 11 (92%), allowing the rapid exclusion of TB in patients suspected to have active TB disease. The T SPOT-TB test is a sensitive assay for detection of TB and represents a useful addition to the diagnostic algorithm available for detecting TB in low-incidence settings.

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T-cell responses towards tuberculin (purified protein derivative; PPD) or the Mycobacterium tuberculosis-specific antigens early secretory antigenic target (ESAT)-6 and culture filtrate protein-10 are indicative of prior contact with mycobacterial antigens. In this study, we investigated the exceptional case of a 75-yr-old patient who devoted more than one-third of his CD4 T-cells against PPD and ESAT-6.Antigen-specific T-cells were characterised using flow cytometric intracellular cytokine staining, ELISPOT assay, proliferation assays, and T-cell receptor spectratyping.T-cell frequencies were far above those found in age-matched controls (median 0.33%, range 0.05-6.32%) and remained at high levels for .2 yrs. The patient initially presented with haemoptysis, but active tuberculosis was ruled out by repeated analysis of sputum and bronchoalveolar lavage fluid. Skin testing was negative and haemoptyses did not have a M. tuberculosis-related aetiology. Phenotypical and functional properties of specific T-cells were consistent with a terminally differentiated effector-memory phenotype with capacity to produce interferon-c, interleukin-2 and tumour necrosis factor-a. Epitope mapping showed that the CD4 T-cells were directed against a single peptide from ESAT-6 (amino acid 5-20) that was presented in context of HLA-DR. T-cell receptor Vb-spectratyping and sequencing of specific CD4 T-cells revealed a prominent peak fraction of monoclonal origin.In conclusion, similar to monoclonal gammopathies of undetermined significance, this may represent the first T-cell counterpart with known specificity against M. tuberculosis.

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