mmpl8::Tn mutant induces a stronger innate immune response. THP-1 cells were infected by the M. tuberculosis GC1237 wild-type or mmpL8::Tn mutant strains at the indicated MOI. After 16 h, NF-κB activation (A and D), IL-8 production in the culture supernatant (B) and CD40 expression (C) were measured. (A and D) NF-κB activation was determined by measuring alkaline phosphatase activity in the culture supernatant and reading OD at 630 nm. TLR2 dependence was investigated by preincubating cells for 30 min at 37 °C with 5 µg/mL of anti-TLR2 or IgG1 isotype control antibodies. (B) IL-8 release in the culture supernatant was determined by sandwich ELISA. (C) CD40 expression was monitored by flow cytometry. Data show mean ± SEM ***P < 0.001; iso ctrl, isotype control; n.i., not induced; n.s., not significant.