FIG. 1.

CD8 T cells isolated from the lungs of old mice are a major source of IFN-γ following M. tuberculosis infection. Young and old mice were infected aerogenically with M. tuberculosis Erdman, and lungs were harvested at 0, 8, and 12 days postinfection (n = 3 to 5). CD8 cells (A) and NK cells (B) were purified from the lungs of young and old mice using magnetic beads. Purified cells were homogenized in Trizol and frozen at −80°C. RNA was isolated and reverse transcribed, and cDNA was amplified for IFN-γ by RT-PCR. The relative expression levels of IFN-γ mRNA are shown as means ± standard errors of the means (SEM) and are representative of data from at least two individual experiments. Statistical significance was determined using a one-way ANOVA with Tukey's posttest (**, P value of <0.01; ***, P value of <0.001 [significance between young and old mice]; +, P value of <0.05; ++, P value of <0.01; +++, P value of <0.001 [significance between time points for old mice, as there were no statistically significant increases for young mice]). RU, relative units.