Identification of Early Secretory Antigen Target-6 Epitopes for the Immunodiagnosis of Active Tuberculosis
The early secretory antigenic target (ESAT)-6 purified protein and peptides from Mycobacterium tuberculosis were evaluated as antigens for the immunodiagnosis of tuberculosis (TB). Because the control of TB requires improved diagnostic procedures, efforts have increased to identify Mycobacterium tuberculosis-specific epitopes for the immunodiagnosis of active TB and to discriminate between active and latent states of infection. Two multiepitopic peptides from ESAT-6 protein were selected by computational analysis. Patients with active TB (7 HIV+ and 20 HIV−) and control patients (17 HIV+ and 28 HIV−) were enrolled. Enzyme-linked immunospot assay analysis for interferon-γ expression by peripheral blood mononuclear cells was quantified after stimulation with selected ESAT-6 peptides, purified protein derivative, or the intact ESAT-6 protein. During active TB, 20 of 27 patients responded in vitro to ESAT-6 peptides and 23 of 27 patients to purified protein derivative. None of the controls without active TB, including individuals with latent TB infection, recognized ESAT-6 peptides. By contrast, latently infected individuals did respond in vitro to both intact ESAT-6 protein and purified protein derivative. Thus, high T-cell response frequencies to ESAT-6 peptides are present only during active TB and can be used to discriminate between active and latent forms of infection.
The authors are grateful to all patients and the nursing staff who took part in this study. We thank V Colizzi and F Poccia for the helpful discussions, M Brescia for technical assistance, R Urso, M De Marco, R Maddaluno, and A Govoni for helping in the recruitment of patients, Jim Arthos, Zana Mariano, and Carla Nisii for editing the manuscript, and Massimo Carrara for helping with the graphics. This work was supported by Current Research Project of the Italian Ministry of Health grants.
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