TPA-mediated differentiation of U937 cells delays etoposide-induced apoptosis.

Undifferentiated (▴) and TPA-differentiated (●) U937 cells were treated with 50 μM etoposide for indicated times. Percentages of apoptotic cells were determined by fluorescent microscopy after Hoechst staining. Each value is the mean ± SD of triplicate determinations.