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A J Hughes, P Hutchinson, T Gooding, N J Freezer, S R Holdsworth, P D R Johnson, Diagnosis of Mycobacterium tuberculosis infection using ESAT-6 and intracellular cytokine cytometry, Clinical and Experimental Immunology, Volume 142, Issue 1, October 2005, Pages 132–139, https://doi.org/10.1111/j.1365-2249.2005.02884.x
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Summary
Diagnosis of infection with Mycobacterium tuberculosis (MTB) using tuberculin skin testing (TST) is often hampered by prior Bacille Calmette–Guérin (BCG) vaccination. ESAT-6 is a protein that is expressed by MTB but absent in BCG. It has been postulated that it might be useful in distinguishing MTB-specific immune responses. This study measured CD4 T cell responder frequencies specific for ESAT-6 and the TST reagent purified protein derivative (PPD) in patients with tuberculosis (n = 16), controls with non-tuberculous pneumonia (n = 8) and normal subjects (n = 7). Responses were identified using the intracellular cytokine staining technique and flow cytometry on whole blood samples, and performed blinded to the patient condition. Antigen-specific CD4 cells were defined by CD69 positivity and one or more cytokine [interleukin (IL)-2, IL-4, IL-10, interferon (IFN)-γ] and/or CD40L positivity. With ESAT-6 stimulation it was found that TB patients had significantly higher frequencies of IFN-γ and CD40L-positive CD4 T cells compared to the normal group, while no significant differences were measured with PPD stimulation. A responder frequency of 0·01% or higher for at least one of the measured cytokines/CD40L was defined as a positive response. Using this criterion to compare the two patient groups, PPD had 100% sensitivity but 0% specificity while ESAT-6 had 100% sensitivity and 88% specificity. Use of MTB-specific proteins such as ESAT-6 in combination with intracellular cytokine staining and flow cytometry has the potential to identify individuals with MTB infection.
