Studies comparing the two methods showed equivalent results on recall response to TB [38], the PDD-specific [31] and the Mtb-specific IFN-γ response [35], and the frequencies of PDD-specific dual IFN-γ/IL-2-secreting CD4+ T-cells [12] as measured by the two methods in various populations and stages of mycobacterial infection. This evidence concerns the gene IFNG and tuberculosis.