IGRAs are whole-blood tests which detect secretion of IFNγ in response to two or three synthetic, Mtb-specific peptides depending on the manufacturer (QuantiFERON-TB Gold In-Tube test: ESAT-6, CFP-10 & TB7.7; T-SPOT TB test: ESAT-6 & CFP-10), relative to a negative control antigen (nil) and a positive control antigen (the polyclonal mitogen phytohemagglutinin, PHA). Here, IFNG is linked to tuberculosis.