When the IFN-γ responses to PPD and ESAT-6 were compared pair-wise to the HBHA-specific responses, a moderate correlation was found for HBHA to PPD both in LTBI subjects (r = 0.55, P<0.0001) (Fig. 3A) and in TB patients (r = 0.71, P<0.0001) (Fig. 3B). This evidence concerns the gene IFNG and tuberculosis.