The two IGRAs that are available commercially include the T-Spot TB test (based on the ELISpot technology to directly count the number of IFN-γ-secreting T cells) and Quantiferon TB Gold In-Tube test (based on the ELISA technology, which measures the concentration of IFN-γ secretion; Cellestis Limited, Carnegie, Victoria, Australia). Here, IFNG is linked to tuberculosis.