Memory T-cells, detected by a tuberculin skin test (TST) and current M. tuberculosis interferon-gamma release assays (IGRAs) measure lasting TB immune responses and can represent any of the following: active TB disease, previous TB disease, latent TB infection, recent or remote TB exposure, or exposure to environmental nontuberculous mycobacteria (NTM; e.g. M. kansasii, M. szulgai, M. marinum) that may have cross-reactivity. Here, IFNG is linked to tuberculosis.