Mice were infected with 37 ± 32 CFU of M.tb Erdman by aerosol and euthanized at day 21 of infection. Lung cells (A, B) and 1:10 diluted whole blood (C, D) were cultured for 72 hours with M.tb CFP (A, C) or M.tb Ag85 (B, D). Antigen-specific IFN-γ was calculated by subtracting the amount of IFN-γ produced in the presence of ovalbumin (lung averages ng/ml: C57BL/6 = 7.6; C57BL/6 H-2k = 2.3; CBA/J = 1.0; C3H/HeJ = 0.25; blood average ng/ml = 0.42, no strain dependent variation). Data shown are the average plus SEM from one experiment with 5–10 mice per group and are representative of three independent experiments. Statistical significance was calculated by the Student’s t-test (C57BL/6 vs C57BL/6 H-2k) and one-way ANOVA with Tukey’s post test (C57BL/6 H-2k, CBA/J, C3H/HeJ), *p<0.05, NS not significant.