Interferon (IFN)–γ responses to bromohydrin pyrophosphate (BrHPP) in whole blood obtained from healthy tuberculin skin test (TST)–positive and TST-negative subjects living an area in which Mycobacterium tuberculosis infection is not endemic (Cleveland). A, IFN-γ responses of whole blood from TST-positive (n = 9) and TST-negative (n = 15) subjects stimulated with 0.4, 2, 10, and 50 μmol/L BrHPP and interleukin (IL)–2 (25 U/mL) for 7 days. IFN-γ was measured by ELISA. B, Comparison of whole-blood IFN-γ responses of TST-positive and TST-negative subjects to BrHPP. Peripheral blood was diluted and stimulated with BrHPP (50 μmol/L) plus IL-2 (25 U/mL) for 7 days, and IFN-γ was measured by ELISA. Results are shown as box plots containing median IFN-γ levels, with error bars showing the 25th and 75th percentiles and whiskers indicating the 5th and 95th percentiles. P, not significant, TST-positive vs. TST-negative subjects.