However, cohort studies have shown that a high PPD response, or high IFN-γ response to ESAT-6 or CFP-10, associates with the subsequent development of TB (Comstock et al., 1974; Higuchi et al., 2008; del Corral et al., 2009), suggesting that an excessive IFN-γ response may be deleterious. The gene discussed is IFNG; the disease is tuberculosis.