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Cytok1ne responses to esat-6 as an aid to diagnosis of tuberculosis

journal contribution
posted on 2001-12-01, 00:00 authored by Andrew HughesAndrew Hughes, P E Hutchinson, T Gooding, D Olden, N J Freezer, S R Holdsworth, P Johnson
BACKGROUND: The diagnosis of tuberculosis is hampered by the lack of a serological marker capable of confirming infection with Mycobacterium tuberculosis (MTB).Tuberculin Sensitivity Testing (TST) relies on the detection of delayed-type hypersensitivity to purified protein derivative (PPD) of MTB. However, TST lacks specificity in individuals vaccinated with BCG. Recently, several MTB-specific proteins have been identified that are not produced by M. bovisBCG. Such proteins have the potential to offer improved specificity compared with PPD when used as diagnostic antigens. ESAT-6 is one such antigen. METHODS: A pilot study of the in vitro immune responses to ESAT-6 of patients with newly diagnosed tuberculosis and matched controls (patients with non-tuberculous pneumonia). Cytokine assays were performed on 10ml whole blood samples by flow cytometry. Antigen specific CD4 T-cells were defined by CD69 positivity and cytokine and/or CD40L positivity. Cytokines measured included IL2,IL4,IL10, and ginterferon. RESULTS: 14 cases and 8 controls were évaluable. Controls were generally negative for all cytokine responses. Results of cases were considered positive if they exceeded three standard deviations above the mean of the control results. Cases showed clear gamma interferon(12), CD40L(8), IL10(2) IL2(4) and IL4(3)responses. Different cases produced different cytokine responses and no single cytokine was universally diagnostic. However, when results were summed and expressed in terms of percentage of CD4 positive T cells responding to ESAT-6 with any cytokine response, cases and controls clearly separated with no overlap of the groups. This result was highly statistically significant (p=0.0002). CONCLUSION: Measurement of a range of cytokine responses to ESAT-6 may be a sensitive and specific test for tuberculosis infection.










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