Identification of Immunological Biomarkers Which May Differentiate Latent Tuberculosis from Exposure to Environmental Nontuberculous Mycobacteria in Children
ABSTRACTA positive gamma interferon (IFN-γ) response toMycobacterium 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 toM. tuberculosisESAT-6 and cross-reactive responses to ESAT-6 homologues ofMycobacterium aviumandMycobacterium kansasii. Archived culture supernatant samples from children at 3 years post-BCG vaccination were tested for cytokine/chemokine responses toM. tuberculosisantigens. Furthermore, the IFN-γ responses toM. tuberculosisantigens were followed up for 40 children at 8 years post-BCG vaccination, and 15 TB patients were recruited as a control group for theM. tuberculosisESAT-6 response in Malawi. IFN-γ enzyme-linked immunosorbent assays (ELISAs) on supernatants from diluted whole-blood assays, IFN-γ enzyme-linked immunosorbent spot (ELISpot) assays, QuantiFERON TB Gold-In Tube tests, and multiplex bead assays were performed. More than 45% of the responders toM. tuberculosisESAT-6 showed IFN-γ responses toM. aviumandM. kansasiiESAT-6. In response toM. tuberculosisESAT-6/CFP-10, interleukin 5 (IL-5), IL-9, IL-13, and IL-17 differentiated the stronger IFN-γ responders toM. tuberculosisESAT-6 from those who preferentially responded toM. kansasiiandM. 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 toM. aviumandM. kansasiiin Malawian children, indicating that this signature might be particularly informative in areas where both TB and exposure to environmental nontuberculous mycobacteria are endemic.