Fig. 2
Caspase-3 activity in cells of the Rhipicephalus microplus (Canestrini) BME26 and Amblyomma sculptum (Berlese) embyronic cell lines (BME26 and IBU/ASE-16, respectively) exposed to either viable or thermo-inactivated R. rickettsii. The activity of caspase-3, induced or not by staurosporine, was evaluated in BME26 (a) and IBU/ASE-16 (b) cells exposed to viable (red bars) or thermo-inactivated (green bars) R. rickettsii. As a control, caspase-3 activity was determined in noninfected cells (blue bars). Forty-eight hours after exposure, the enzymatic activity was determined by measuring the release of the AMC fluorescent cleavage product from the synthetic fluorogenic substrate Ac-DEVD-AMC (emission excitation: 380–460 nm). The relative activity of caspase-3 (in units of arbitrary fluorescence [UAF]) represents the ratio of ΔUAF (UAF60 min − UAF0 min) of each condition to the ΔUAF of noninfected cells treated with 400 nM staurosporine. Error bars: ± standard deviation of six measurements (n = 6). Asterisks indicate significant difference at *P < 0.05 and **p < 0.001 (Student’s t-test)