Fig. 2.

A. phagocytophilum induces apoptosis in HL-60 cells but inhibits in neutrophils. HL-60 cells were mock-infected or infected with A. phagocytophilum for 4 h and also treated with 1 μM STS and 100 μM ETO for 4 h, where indicated. Then, the cells were harvested and allowed to Annexin-V staining as described in Materials and methods. Results are represented in quadrants, the lower right quadrant being the apoptotic population (a). The percentage of apoptotic cells are shown in (b). Next, the cells were treated exactly as in (a) and caspase activity assays were performed with 50 μM of Ac-DEVD-AMC (c), Ac-IETD-AMC (d, white bars) or Ac-LEHD-AMC (d, black bars) for caspase-3, caspase-8 or caspase-9-like activity, respectively. The increase in the activity was calculated from the 1 h readings obtained from the spectrofluorometer. *significantly different from mock at P < 0.05, **significantly different from mock treated ETO at P < 0.05. Freshly isolated neutrophils were analyzed for spontaneous apoptosis with Annexin-V staining (e, f) and Caspase-3-like activity (g). The results are expressed as above for both assays. *significantly different from mock at P < 0.01. Error bars represent ± Standard deviation from Mean values in all cases