IFNG and tuberculosis: Two imperfect but widely used tests for LTBI that measure the host's cell-mediated immune response to Mycobacterium tuberculosis antigens are the tuberculin skin test (TST) and interferon-gamma (IFN-γ) release assays (IGRAs) (QuantiFERON®-TB Gold In-Tube [QGIT], QIAGEN, Hilden, Germany; and the T-SPOT®.