GT preferentially induces apoptosis in monocytes. PBMCs from 7 healthy donors were analyzed by flow cytometry for caspase-3 activation at 30 minutes, 1, 2, 3, 4, and 6 hours after addition of GT (35 ng/mL). Panel A shows a typical histogram plot of caspase-3 expression in monocytes. Cells incubated without GT (top row) showed only low levels of caspase-3 expression, while incubation with GT (bottom row) substantially increased caspase-3 induction in a time-dependent fashion. By 2 and 3 hours, respectively, 6.1% and 27.4% of monocytes expressed active caspase-3. Panel B illustrates caspase-3 expression within monocyte and lymphocyte subsets. After 2 hours of incubation with 35 ng/mL GT (bottom row), monocytes (CD4^+dimCD14⁺) a mean of 11.4% of cells expressed active caspase-3. CD4⁺ T cells, CD8⁺ T cells, and CD19⁺ B lymphocytes showed lower frequencies at the same time point (0.64%, 1.13%, and 2.0%, respectively). The frequency of active caspase-3–positive cells increased progressively. By 6 hours, 59.2% of monocytes, 7.1% of CD4⁺, 25.4% of CD8⁺, and 18.7% of CD19⁺ lymphocytes expressed caspase-3. In the absence of GT (top row), caspase-3 activity was detectable only after 4 hours, with relative fractions always below 5%. Error bars indicate SEM.