OBJECTIVETo investigate the effects of Mycobacterium tuberculosis on apoptosis of mouse dendritic cells (DC 2. 4) and the activation of caspase-3, caspase-8.

METHODSMycobacterium tuberculosis H37Rv strain was co-cultured with DC 2. 4 cells. The morphological changes of DC 2. 4 cells were observed with fluorescence microscope after DAPI staining and transmission electron microscope. The apoptosis of DC 2. 4 cells were examined by DNA agarose gel electrophoresis. The activities of caspase-3 and caspase-8 were detected by colorimetric assay.

RESULTSBacterial invasion was observed while DC 2. 4 cells and H37Rv were co-cultured for 2 h; and the rates of invasion were (16.1 ± 4.3)%, (35.8 ± 5.1)%, (50.2 ± 5.7)%, (58.3 ± 6.2)% and(65.9 ± 6.9)% at 4, 6, 8,10, 12 h, respectively. The phenomenon of nuclear condensation and marginalization were shown by DAPI staining and transmission electron microscope in DC 2. 4 cells at 6 h of co-cultivation with H37Rv. The characteristic bands of apoptosis by DNA electrophoresis were detected. The activities of caspase-3 and caspase-8 were increased in a time-dependent manner. The rates of DC 2. 4 cell apoptosis were (6.4 ± 2.5)%, (11.8 ± 5.3)% and (31.1 ± 8.7)% at 6 h,12 h and 24 h after co-cultivation with H37Rv, respectively. The maximal activities of intracellular caspase-3 and caspase-8 at 10 h and 6 h were (2.01 ± 0.09) U/μg and (2.40 ± 0.07)U/μg, respectively, which was significantly different compared with the control groups(P<0.05). The activation of caspase-8 was earlier than that of caspase-3.

CONCLUSIONMycobacterium tuberculosis can induce the apoptosis of DC 2. 4 cells, which is associated with the activation of intracellular caspase-3 and caspase-8.