ER Stress-Mediated Apoptosis in Mtb Infections Figure 3. Mtb H37Rv infection induces ER stress sensor proteins in macrophage cells and CHOP is activated in BMDMs or A549 cells. Cells were infected with Mtb H37Rv (MOI = 1) for 3 h, and then incubated for 0–48 h. Immunoblot analysis was performed as described in Materials and Methods. The statistical significance (*P,0.05, **P,0.01 and ***P,0.001) of observed differences between Mtb H37Rv infected and uninfected groups were verified by two-tailed t-test. (A) Raw264.7 cells, (B) BMDMs or A549 cells. Representative data from three independent experiments are shown. STS: staurosporine. doi:10.1371/journal.pone.0028531.g003 increased in Raw264.7 cells infected with heat-killed Mtb compared with live Mtb. A similar pattern of ER stress sensors at a higher multiplicity of infection (MOI) was also observed with Mtb infection. These results suggest that ER stress induced CHOP expression may play an important role in anti- mycobacterial immunity. PLoS ONE | www.plosone.org 5 December 2011 | Volume 6 | Issue 12 | e28531