Mice were infected with 37 ± 32 CFU of M.tb Erdman by aerosol and euthanized at day 21 of infection. Lung cells were cultured for 24 hours in the presence of M.tb Ag85. The frequency of IFN-γ SFU (A), absolute numbers of SFU (B), and SFU size (C) were quantified by ELISPOT. Antigen-specific IFN-γ was calculated by subtracting the numbers of IFN-γ SFU produced in the presence of ovalbumin (average 30.1 per 2 × 105 cells, no strain dependent variation). Results are the average and SEM from two independent experiments, each with 5 mice per strain: total per strain, n=10. 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, **p<0.01.