Despite the fact that negative IGRA results fell below the assay cut-off level, the median IFN-γ level differed only slightly between TB patients with negative IGRAs and healthy controls; this result indicated that TB-specific memory T cell populations were present in IGRA-negative TB patient blood that did not effectively control MTB infection, as reflected by decreased IFN-γ secretion by T cells of these patients. Here, IFNG is linked to tuberculosis.