Figure 2.

Flow sorting of activated and resting Mtb-infected host cells demonstrates that the drug sensitivity of Mtb recovered from in vivo infection correlates inversely with the immune status of the host phagocyte. Mtb recovered from activated host cells in vivo were more tolerant to both INH and RIF than those recovered from resting host cells. C57BL/6J mice were infected with mCherry-expressing Erdman Mtb for 21 d, and Mtb-containing myeloid cells with different immune activation status were isolated from lung tissue using flow cytometry. (A) CD11b⁺ mCherry⁺ CD80^high cells (activated population) and CD11b⁺ mCherry⁺ CD80^low cells (resting population) were sorted according to the depicted gating strategies. FSC, forward scatter. (B) Flow cytometry analysis of the expression levels of MHCII, CD40, CD86, and iNOS revealed the increased expression of classical activation markers in the CD11b⁺ mCherry⁺ CD80^high cells (activated population) in comparison with the CD11b⁺ mCherry⁺ CD80^low cells (resting population). (C and D) Isolated cells were established in culture and subjected to treatment with 1 µg/ml INH or RIF or an equivalent volume of DMSO. After 24 h of drug treatment, bacterial survival was determined by CFU enumeration (C), and the percentage of Mtb surviving drug treatment was quantified by normalizing the bacterial load in drug-treated samples against that in DMSO-treated samples (D). Data represent the mean ± SD of duplicates from an individual experiment representative of two independent experiments. MFI, mean fluorescence intensity. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001, by two-tailed Student’s t test.