As shown in Fig. 1A, LTBI subjects and TB patients secreted significantly more IFN-γ in response to PPD than CTRL (medians 15.83 ng/ml and 6.84 ng/ml, respectively, versus 0.23 ng/ml; P<0.001), whereas the median level of IFN-γ produced was not significantly different between the LTBI and TB groups. The gene discussed is IFNG; the disease is tuberculosis.