Early Secretory Antigenic Target-6 (ESAT-6) is a component of the H56 fusion protein used in the H56: IC31 vaccine [20], a novel TB subunit vaccine, but ESAT-6 is also one of the antigens used to stimulate IFN-γ production in the QuantiFERON-TB Gold In-Tube (QFT-GIT) IGRA assay [21]. Here, IFNG is linked to tuberculosis.