Identification of Immunological Biomarkers Which May Differentiate Latent Tuberculosis from Exposure to Environmental Nontuberculous Mycobacteria in Children

ABSTRACTA positive gamma interferon (IFN-?) response to Mycobacterium tuberculosisearly secretory antigenic target-6 (ESAT-6)/culture filtrate protein-10 (CFP-10) has been taken to indicate latent tuberculosis (TB) infection, but it may also be due to exposure to environmental nontuberculous mycobacteria in which ESAT-6 homologues are present. We assessed the immune responses to M. tuberculosisESAT-6 and cross-reactive responses to ESAT-6 homologues of Mycobacterium aviumand Mycobacterium kansasii. Archived culture supernatant samples from children at 3 years post-BCG vaccination were tested for cytokine/chemokine responses to M. tuberculosisantigens. Furthermore, the IFN-? responses to M. tuberculosisantigens were followed up for 40 children at 8 years post-BCG vaccination, and 15 TB patients were recruited as a control group for the M. tuberculosisESAT-6 response in Malawi. IFN-? enzyme-linked immunosorbent assays (ELISAs) on supernatants from diluted whole-blood assays, IFN-? enzyme-linked immunosorbent spot (ELISpot) assays, QuantiFERON TB Gold-In Tube tests, and multiplex bead assays were performed. More than 45% of the responders to M. tuberculosisESAT-6 showed IFN-? responses to M. aviumand M. kansasiiESAT-6. In response to M. tuberculosisESAT-6/CFP-10, interleukin 5 (IL-5), IL-9, IL-13, and IL-17 differentiated the stronger IFN-? responders to M. tuberculosisESAT-6 from those who preferentially responded to M. kansasiiand M. aviumESAT-6. A cytokine/chemokine signature of IL-5, IL-9, IL-13, and IL-17 was identified as a putative immunological biosignature to differentiate latent TB infection from exposure to M. aviumand M. kansasiiin Malawian children, indicating that this signature might be particularly informative in areas where both TB and exposure to environmental nontuberculous mycobacteria are endemic.