IFNG and tuberculosis: IGRA is available in two commercial formats: (i) Quantiferon TB Gold (QFT-G) (Cellestis Ltd, Victoria, Australia), which measures the quantity of IFN-γ secreted by T cells and (ii) T-Spot.TB assay (Oxford Immunotech, Oxford, UK) which enumerates the number of IFN-γ secreting T cells after in vitro stimulation with TB-specific antigens.